This document summarizes a study that uses distance measurements in the nearby universe to test theories of modified gravity. The study compares distance measurements from cepheid variable stars, tip of the red giant branch stars, and water masers in different galaxies. These distance indicators operate in gravitational fields of different strengths, enabling tests of scalar-tensor gravity theories where fifth forces are screened to different extents depending on the local gravitational potential. The study finds no evidence for the enhanced gravitational forces predicted by chameleon and symmetron screening scenarios, constraining the parameter space of these theories.
Toward a new_distance_to_the_active_galaxy_ngc4258Sérgio Sacani
This document reports on measurements of centripetal accelerations of maser spectral components in the active galaxy NGC 4258 using data from 51 epochs spanning 1994 to 2004. Accelerations of high-velocity maser emission indicate an origin within 13 degrees of the disk midline. Accelerations do not support a model of trailing shocks from spiral arms but find evidence of spiral structure with a wavelength of 0.75 mas. Accelerations of low-velocity emission are consistent with originating from a concave region where the thin disk is tangent to the line of sight.
End point of_black_ring_instabilities_and_the_weak_cosmic_censorship_conjectureSérgio Sacani
We produce the first concrete evidence that violation of the weak cosmic censorship conjecture can occur
in asymptotically flat spaces of five dimensions by numerically evolving perturbed black rings. For certain
thin rings, we identify a new, elastic-type instability dominating the evolution, causing the system to settle to
a spherical black hole. However, for sufficiently thin rings the Gregory-Laflamme mode is dominant, and the
instability unfolds similarly to that of black strings, where the horizon develops a structure of bulges connected
by necks which become ever thinner over time.
1) High-resolution N-body simulations were conducted of isolated disk galaxies to explore the origin of spiral arms. Mass concentrations similar to giant molecular clouds were included to perturb the disks.
2) The simulations demonstrated that the disks developed long-lived, multi-armed spiral structures in response to the perturbations. This challenges the expectation that spiral arms should fade quickly once perturbations are removed.
3) Contrary to linear theories of spiral structure formation, the response of the disks to local perturbations was found to be highly non-linear and time-variable, significantly modifying the formation and longevity of spiral patterns.
The document describes measurements of the proper motion of the Andromeda Galaxy (M31) using Hubble Space Telescope imaging data from multiple fields observed at two epochs separated by 5-7 years. Background galaxies in the images are used as stationary reference objects to measure the displacement of thousands of M31 stars between epochs. This allows determining M31's absolute proper motion with an accuracy of 12 microarcseconds per year, providing crucial information about M31 and the Local Group's dynamics and future evolution.
Small scatter and_nearly_isothermal_mass_profiles_to_four_half_light_radii_fr...Sérgio Sacani
This document summarizes the results of a study analyzing the total mass density profiles of 14 early-type galaxies using two-dimensional stellar kinematic data out to large radii of 2-6 half-light radii. The study finds that the total density profiles are well described by a nearly-isothermal power law with density proportional to radius from 0.1 to at least 4 half-light radii. The average logarithmic slope is -2.19 with a small scatter of only 0.11. This places tight constraints on galaxy formation models and illustrates the power of extended two-dimensional stellar kinematic observations.
The colision between_the_milky_way_and_andromedaSérgio Sacani
The document summarizes a simulation of the future collision between the Milky Way and Andromeda galaxies. It finds that given current observational constraints on their distance, velocity, and masses:
1) The Milky Way and Andromeda are likely to collide in a few billion years, within the lifetime of the Sun.
2) During the interaction, there is a chance the Sun could be pulled into an extended tidal tail between the galaxies.
3) Eventually, after the merger is complete, the Sun would most likely be scattered to the outer halo of the merged galaxy at a distance over 30 kpc.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
Toward a new_distance_to_the_active_galaxy_ngc4258Sérgio Sacani
This document reports on measurements of centripetal accelerations of maser spectral components in the active galaxy NGC 4258 using data from 51 epochs spanning 1994 to 2004. Accelerations of high-velocity maser emission indicate an origin within 13 degrees of the disk midline. Accelerations do not support a model of trailing shocks from spiral arms but find evidence of spiral structure with a wavelength of 0.75 mas. Accelerations of low-velocity emission are consistent with originating from a concave region where the thin disk is tangent to the line of sight.
End point of_black_ring_instabilities_and_the_weak_cosmic_censorship_conjectureSérgio Sacani
We produce the first concrete evidence that violation of the weak cosmic censorship conjecture can occur
in asymptotically flat spaces of five dimensions by numerically evolving perturbed black rings. For certain
thin rings, we identify a new, elastic-type instability dominating the evolution, causing the system to settle to
a spherical black hole. However, for sufficiently thin rings the Gregory-Laflamme mode is dominant, and the
instability unfolds similarly to that of black strings, where the horizon develops a structure of bulges connected
by necks which become ever thinner over time.
1) High-resolution N-body simulations were conducted of isolated disk galaxies to explore the origin of spiral arms. Mass concentrations similar to giant molecular clouds were included to perturb the disks.
2) The simulations demonstrated that the disks developed long-lived, multi-armed spiral structures in response to the perturbations. This challenges the expectation that spiral arms should fade quickly once perturbations are removed.
3) Contrary to linear theories of spiral structure formation, the response of the disks to local perturbations was found to be highly non-linear and time-variable, significantly modifying the formation and longevity of spiral patterns.
The document describes measurements of the proper motion of the Andromeda Galaxy (M31) using Hubble Space Telescope imaging data from multiple fields observed at two epochs separated by 5-7 years. Background galaxies in the images are used as stationary reference objects to measure the displacement of thousands of M31 stars between epochs. This allows determining M31's absolute proper motion with an accuracy of 12 microarcseconds per year, providing crucial information about M31 and the Local Group's dynamics and future evolution.
Small scatter and_nearly_isothermal_mass_profiles_to_four_half_light_radii_fr...Sérgio Sacani
This document summarizes the results of a study analyzing the total mass density profiles of 14 early-type galaxies using two-dimensional stellar kinematic data out to large radii of 2-6 half-light radii. The study finds that the total density profiles are well described by a nearly-isothermal power law with density proportional to radius from 0.1 to at least 4 half-light radii. The average logarithmic slope is -2.19 with a small scatter of only 0.11. This places tight constraints on galaxy formation models and illustrates the power of extended two-dimensional stellar kinematic observations.
The colision between_the_milky_way_and_andromedaSérgio Sacani
The document summarizes a simulation of the future collision between the Milky Way and Andromeda galaxies. It finds that given current observational constraints on their distance, velocity, and masses:
1) The Milky Way and Andromeda are likely to collide in a few billion years, within the lifetime of the Sun.
2) During the interaction, there is a chance the Sun could be pulled into an extended tidal tail between the galaxies.
3) Eventually, after the merger is complete, the Sun would most likely be scattered to the outer halo of the merged galaxy at a distance over 30 kpc.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
This document summarizes research determining the velocity vector of the Andromeda Galaxy (M31) relative to the Milky Way using Hubble Space Telescope measurements of M31's proper motion. N-body models of M31 are used to correct for internal stellar motions within M31. The results imply M31 is on a radial orbit towards the Milky Way. The velocity vector is then used to estimate the mass of the Local Group, obtaining a value of (3.17 ± 0.57) × 1012 M☉. It is also implied M33 is likely bound to M31.
To the Issue of Reconciling Quantum Mechanics and General RelativityIOSRJAP
The notion of gravitational radiation as a radiation of the same level as the electromagnetic radiation is based on theoretically proved and experimentally confirmed fact of existence of stationary states of an electron in its gravitational field characterized by the gravitational constant K = 1042G (G is the Newtonian gravitational constant) and unrecoverable space-time curvature Λ. If the numerical values of K 5.11031 Nm2 kg-2 and =4.41029 m -2 , there is a spectrum of stationary states of the electron in its own gravitational field (0.511 MeV ... 0.681 MeV).Adjusting according to the known mechanisms of broadening does not disclose the broadening of the registered portion of the emission spectrum of the micropinch. It indicates the presence of an additional mechanism of broadening the registered portion of the spectrum of the characteristic radiation due to the contribution of the excited states of electrons in their own gravitational field. The energy spectrum of the electron in its own gravitational field and the energy spectra of multielectron atoms are such that there is a resonance of these spectra. As obvious, the consequence of such resonant interaction is appearance, including new lines, of electromagnetic transitions not associated with atomic transitions. The manuscript is the review of previously published papers cited in the references.
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
Structure and transport coefficients of liquid Argon and neon using molecular...IOSR Journals
Molecular dynamics simulation was employed to deduce the dynamics property distribution function of Argon
and Neon liquid. With the use of a Lennnard-Jones pair potential model, an inter-atomic interaction function was observed
between pair of particles in a system of many particles, which indicates that the pair distribution function determines the
structures of liquid Argon. This distribution effect regarding the liquid structure of Lennard-Jones potential was strongly
affected such that its viscosity depends on density distribution of the model. The radial distribution function, g(r) agrees well
with the experimental data used. Our results regarding Argon and Neon show that their signatures are quite different at
each temperature, such that their corresponding viscosity is not consistent. Two sharps turning points are more
prominent in Argon, one at temperature of 83.88 Kelvin (K) with viscosity of -0.548 Pascal second (Pa-s) and the
other at temperature of 215.64 K with viscosity of -0.228 Pa-s.
In Argon and Neon liquid, temperature and density are inversely and directly proportional to diffusion
coefficient, in that order. This characteristic suggests that the observed non linearity could result from the non
uniform thermal expansion in liquid Argon and Neon, which are between the temperature range of 21.98 K and
239.52 K.
- The document investigates the implications of a proposed metallicity-dependent initial mass function (IMF), which suggests the IMF varies based on the metallicity of a star formation environment.
- Using observations of globular cluster Palomar 14 and open cluster M42, the author constrains an upper bound for metallicity dependence, resulting in a two-part power law IMF function that depends on metallicity.
- However, the document concludes that current evidence is inadequate to prove a metallicity-dependent IMF, as measurements of cluster IMFs are complicated by issues like dynamics, binaries, and evolution over time.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
This document summarizes the identification of two young objects, TYC 9486-927-1 and 2MASS J21265040−8140293, as a likely very wide binary system. It presents revised astrometry showing they have common proper motion. Spectroscopy of the secondary yields a radial velocity consistent with the primary. Analysis of lithium absorption and kinematics suggests an age range of 10-45 Myr, with the secondary having an estimated mass in the planetary mass regime. If confirmed, this would be the widest known exoplanet system at over 4500 AU separation.
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
This document summarizes results from simulations of galaxy formation and evolution using hydrodynamical simulations. Higher resolution simulations that include feedback produce galaxies with larger disk scale lengths and smaller bulge-to-disk ratios, in better agreement with observations. Feedback and resolution are necessary to form galaxies with flatter rotation curves and properties matching observed galaxies, like the Tully-Fisher relation. One simulated galaxy has a large disk scale length of 9.2 kpc and small bulge-to-disk ratio of 0.64.
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster
galaxies, with r-band monochromatic luminosity Lr = 8 14L (4:3 7:5 1044 erg s 1). These
super spiral galaxies are also giant and massive, with diameter D = 57 134 kpc and stellar mass
Mstars = 0:3 3:4 1011M. We nd 53 super spirals out of a complete sample of 1616 SDSS
galaxies with redshift z < 0:3 and Lr > 8L. The closest example is found at z = 0:089. We use
existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS
and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the
extreme masses and rapid SFRs of 5 65M yr 1 place super spirals in a sparsely populated region
of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a
diverse range of environments, from isolation to cluster centers. We nd four super spiral galaxy
systems that are late-stage major mergers{a possible clue to their formation. We suggest that super
spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become
massive lenticular galaxies after they are cut o from their gas supply and their disks fade.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Precise measurements of light from distant quasars suggest the value of the fine-structure constant may have changed over the history of the universe. If confirmed, this would have enormous significance for the foundations of physics. Measurements of light from quasars billions of years in the past can be used to determine the value of fundamental constants like the fine-structure constant at early times and test if they have remained constant.
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
The Gravity Probe B experiment tested two predictions of general relativity using gyroscopes in a satellite orbiting Earth. It measured the geodetic precession and frame-dragging precession predicted by Einstein to within 0.2% and 18.4% accuracy, respectively, confirming his theory of gravitation. Technical challenges arose from the gyroscopes not being perfectly spherical, leading to greater errors than anticipated. The experiment was a decades-long effort involving NASA, Stanford University, and collaboration with other institutions.
The document discusses Einstein's field equations and Heisenberg's uncertainty principle. It begins by providing background on Einstein's field equations, which relate the geometry of spacetime to the distribution of mass and energy within it. It then discusses some key mathematical aspects of the field equations, including their nonlinear partial differential form. Finally, it notes that the field equations can be consolidated with Heisenberg's uncertainty principle to provide a unified description of gravity and quantum mechanics.
This document presents a new preon model with three fundamental spin-1/2 preons (α, β, δ) that can combine to form nine leptons, nine quarks, and nine heavy vector bosons. The preons have charges of +e/3, -2e/3, and +e/3. Quarks and leptons are composed of combinations of one spin-1/2 preon and one spin-0 "dipreon" made of two spin-1/2 preons. This model aims to address shortcomings of the standard model such as the large number of fundamental particles and mixings between particles, through a more fundamental layer of preons with an underlying symmetry.
This document provides guidelines for news organizations on using social media effectively and appropriately. It summarizes 10 best practices for social media use based on a review of existing social media policies at various news outlets. The best practices are: 1) Traditional journalism ethics still apply online; 2) Assume anything written online could become public; 3) Engage readers professionally on social media; 4) Break news on your own website, not social media; 5) Be aware of perceptions; 6) Independently verify information found on social media; 7) Identify yourself as a journalist; 8) Treat social media as a tool, not just for personal use; 9) Be transparent and admit mistakes; 10) Keep internal deliberations confidential.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
This document summarizes research determining the velocity vector of the Andromeda Galaxy (M31) relative to the Milky Way using Hubble Space Telescope measurements of M31's proper motion. N-body models of M31 are used to correct for internal stellar motions within M31. The results imply M31 is on a radial orbit towards the Milky Way. The velocity vector is then used to estimate the mass of the Local Group, obtaining a value of (3.17 ± 0.57) × 1012 M☉. It is also implied M33 is likely bound to M31.
To the Issue of Reconciling Quantum Mechanics and General RelativityIOSRJAP
The notion of gravitational radiation as a radiation of the same level as the electromagnetic radiation is based on theoretically proved and experimentally confirmed fact of existence of stationary states of an electron in its gravitational field characterized by the gravitational constant K = 1042G (G is the Newtonian gravitational constant) and unrecoverable space-time curvature Λ. If the numerical values of K 5.11031 Nm2 kg-2 and =4.41029 m -2 , there is a spectrum of stationary states of the electron in its own gravitational field (0.511 MeV ... 0.681 MeV).Adjusting according to the known mechanisms of broadening does not disclose the broadening of the registered portion of the emission spectrum of the micropinch. It indicates the presence of an additional mechanism of broadening the registered portion of the spectrum of the characteristic radiation due to the contribution of the excited states of electrons in their own gravitational field. The energy spectrum of the electron in its own gravitational field and the energy spectra of multielectron atoms are such that there is a resonance of these spectra. As obvious, the consequence of such resonant interaction is appearance, including new lines, of electromagnetic transitions not associated with atomic transitions. The manuscript is the review of previously published papers cited in the references.
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
Structure and transport coefficients of liquid Argon and neon using molecular...IOSR Journals
Molecular dynamics simulation was employed to deduce the dynamics property distribution function of Argon
and Neon liquid. With the use of a Lennnard-Jones pair potential model, an inter-atomic interaction function was observed
between pair of particles in a system of many particles, which indicates that the pair distribution function determines the
structures of liquid Argon. This distribution effect regarding the liquid structure of Lennard-Jones potential was strongly
affected such that its viscosity depends on density distribution of the model. The radial distribution function, g(r) agrees well
with the experimental data used. Our results regarding Argon and Neon show that their signatures are quite different at
each temperature, such that their corresponding viscosity is not consistent. Two sharps turning points are more
prominent in Argon, one at temperature of 83.88 Kelvin (K) with viscosity of -0.548 Pascal second (Pa-s) and the
other at temperature of 215.64 K with viscosity of -0.228 Pa-s.
In Argon and Neon liquid, temperature and density are inversely and directly proportional to diffusion
coefficient, in that order. This characteristic suggests that the observed non linearity could result from the non
uniform thermal expansion in liquid Argon and Neon, which are between the temperature range of 21.98 K and
239.52 K.
- The document investigates the implications of a proposed metallicity-dependent initial mass function (IMF), which suggests the IMF varies based on the metallicity of a star formation environment.
- Using observations of globular cluster Palomar 14 and open cluster M42, the author constrains an upper bound for metallicity dependence, resulting in a two-part power law IMF function that depends on metallicity.
- However, the document concludes that current evidence is inadequate to prove a metallicity-dependent IMF, as measurements of cluster IMFs are complicated by issues like dynamics, binaries, and evolution over time.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
This document summarizes the identification of two young objects, TYC 9486-927-1 and 2MASS J21265040−8140293, as a likely very wide binary system. It presents revised astrometry showing they have common proper motion. Spectroscopy of the secondary yields a radial velocity consistent with the primary. Analysis of lithium absorption and kinematics suggests an age range of 10-45 Myr, with the secondary having an estimated mass in the planetary mass regime. If confirmed, this would be the widest known exoplanet system at over 4500 AU separation.
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
This document summarizes results from simulations of galaxy formation and evolution using hydrodynamical simulations. Higher resolution simulations that include feedback produce galaxies with larger disk scale lengths and smaller bulge-to-disk ratios, in better agreement with observations. Feedback and resolution are necessary to form galaxies with flatter rotation curves and properties matching observed galaxies, like the Tully-Fisher relation. One simulated galaxy has a large disk scale length of 9.2 kpc and small bulge-to-disk ratio of 0.64.
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster
galaxies, with r-band monochromatic luminosity Lr = 8 14L (4:3 7:5 1044 erg s 1). These
super spiral galaxies are also giant and massive, with diameter D = 57 134 kpc and stellar mass
Mstars = 0:3 3:4 1011M. We nd 53 super spirals out of a complete sample of 1616 SDSS
galaxies with redshift z < 0:3 and Lr > 8L. The closest example is found at z = 0:089. We use
existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS
and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the
extreme masses and rapid SFRs of 5 65M yr 1 place super spirals in a sparsely populated region
of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a
diverse range of environments, from isolation to cluster centers. We nd four super spiral galaxy
systems that are late-stage major mergers{a possible clue to their formation. We suggest that super
spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become
massive lenticular galaxies after they are cut o from their gas supply and their disks fade.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Precise measurements of light from distant quasars suggest the value of the fine-structure constant may have changed over the history of the universe. If confirmed, this would have enormous significance for the foundations of physics. Measurements of light from quasars billions of years in the past can be used to determine the value of fundamental constants like the fine-structure constant at early times and test if they have remained constant.
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
The Gravity Probe B experiment tested two predictions of general relativity using gyroscopes in a satellite orbiting Earth. It measured the geodetic precession and frame-dragging precession predicted by Einstein to within 0.2% and 18.4% accuracy, respectively, confirming his theory of gravitation. Technical challenges arose from the gyroscopes not being perfectly spherical, leading to greater errors than anticipated. The experiment was a decades-long effort involving NASA, Stanford University, and collaboration with other institutions.
The document discusses Einstein's field equations and Heisenberg's uncertainty principle. It begins by providing background on Einstein's field equations, which relate the geometry of spacetime to the distribution of mass and energy within it. It then discusses some key mathematical aspects of the field equations, including their nonlinear partial differential form. Finally, it notes that the field equations can be consolidated with Heisenberg's uncertainty principle to provide a unified description of gravity and quantum mechanics.
This document presents a new preon model with three fundamental spin-1/2 preons (α, β, δ) that can combine to form nine leptons, nine quarks, and nine heavy vector bosons. The preons have charges of +e/3, -2e/3, and +e/3. Quarks and leptons are composed of combinations of one spin-1/2 preon and one spin-0 "dipreon" made of two spin-1/2 preons. This model aims to address shortcomings of the standard model such as the large number of fundamental particles and mixings between particles, through a more fundamental layer of preons with an underlying symmetry.
This document provides guidelines for news organizations on using social media effectively and appropriately. It summarizes 10 best practices for social media use based on a review of existing social media policies at various news outlets. The best practices are: 1) Traditional journalism ethics still apply online; 2) Assume anything written online could become public; 3) Engage readers professionally on social media; 4) Break news on your own website, not social media; 5) Be aware of perceptions; 6) Independently verify information found on social media; 7) Identify yourself as a journalist; 8) Treat social media as a tool, not just for personal use; 9) Be transparent and admit mistakes; 10) Keep internal deliberations confidential.
This study presents a comprehensive digital mosaic of ice motion across Antarctica assembled from satellite radar data. The data reveal widespread, patterned, enhanced flow of tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent. This emphasizes the importance of basal-slip dominated tributary flow over deformation-dominated ice sheet flow, redefining our understanding of ice sheet dynamics. The extensive network of fast-flowing tributaries challenges prior views of ice sheet flow and implies a tighter connection between coastal and interior ice flow than previously thought.
Direct detection of the enceladus water torus with herschelSérgio Sacani
The Herschel Space Observatory directly detected the water vapor torus around Saturn's moon Enceladus by observing absorption lines of water vapor against Saturn. Spectroscopic observations with Herschel's HIFI instrument detected water vapor lines at 557, 987, 1113, and 1670 GHz. Modeling of the spectra determined the water vapor has a column density of ~4 × 1013 cm-2 near the equatorial plane and a vertical scale height of ~50,000 km. The water torus appears rotationally cold at 16 K but is dynamically excited with non-Keplerian velocities of ~2 km/s, shaped largely by molecular collisions. Estimates of the influx of torus material into
Observational evidence from supernovae for an accelerating universe and a cos...Sérgio Sacani
The document presents observations of 10 type Ia supernovae (SNe Ia) with redshifts between 0.16 and 0.62. Combined with previous data from the team and others, the distances to the 16 high-redshift SNe Ia are on average 10-15% farther than expected in a low-mass density universe without a cosmological constant. Different analysis methods find evidence favoring an expanding universe with a positive cosmological constant and acceleration of the expansion. The data are consistent with an accelerating universe and cosmological constant at a statistical significance of 2.8-9 sigma depending on the method and assumptions.
Teachable moment the japan earthquake and tsunamiSérgio Sacani
On March 11, 2011, a 9.0 magnitude earthquake struck off the coast of Honshu, Japan, generating a powerful tsunami. This was one of the largest earthquakes in Japanese history and caused widespread damage. The earthquake and tsunami highlighted Japan's vulnerability to natural disasters due to its location at the boundary of four tectonic plates.
1. INTEGRAL observations of the SNR IC443 region detected several sources, including the pulsar wind nebula (Src #5) and the enigmatic hard X-ray source Src #11.
2. JEM-X images in the 6-10 and 10-20 keV bands tentatively identified counterparts for Src #5 and Src #11. Measured fluxes from JEM-X were consistent with XMM spectra but did not provide strong constraints.
3. Optical and infrared images showed possible counterparts for Src #11, including point sources and diffuse 2MASS-Ks emission thought to originate from shocked molecular hydrogen, suggesting a correlation between X-ray and infrared emission.
The OPERA experiment measures the velocity of neutrinos produced at CERN and detected 730 km away at the Gran Sasso laboratory to high precision. To do so it must accurately measure the time of flight of neutrinos between the two sites by precisely synchronizing clocks at CERN and Gran Sasso, determining the baseline distance through geodesy, and calibrating the timing of the proton beam and neutrino detection. This allows OPERA to search for small deviations from the speed of light in the measurement of the neutrino velocity.
1. This paper presents results from a 600 ks XMM-Newton observation of Mrk 509 as part of a large multiwavelength campaign.
2. The high quality spectrum allows an unprecedented investigation of the ionized outflow through the detection of multiple absorption lines.
3. The outflow is found to consist of at least two velocity components that have been observed previously, as well as a tentative high velocity component. Discrete ionization components are detected spanning four orders of magnitude in ionization parameter.
The document summarizes research on the concentric crater located in Humboldt on the Moon. It finds that the concentric crater is typical in size and ratio of inner to outer ring diameters compared to other known concentric craters. Spectral analysis indicates the interior of the concentric crater is composed of highland material, supporting the hypothesis that it formed through igneous intrusion rather than volcanic extrusion. The proximity of two younger, non-concentric craters of similar size suggests conditions for concentric crater formation no longer existed at the time of their impacts. Together, this provides evidence that the concentric crater in Humboldt formed through igneous intrusion rather than volcanic activity.
1) The Fermi bubbles are giant gamma-ray emitting structures extending above and below the galactic center.
2) The bubbles may have been formed by periodic capture of stars by the supermassive black hole at the galactic center, releasing energy of around 3x10^52 ergs per capture.
3) This energy injection could produce very hot plasma, accelerating electrons that produce radio and gamma-ray emission through synchrotron radiation and inverse Compton scattering.
Vegetti et al. discovered a satellite galaxy located around a more distant elliptical galaxy acting as a gravitational lens. They were able to detect the satellite galaxy through its effect on distorting light from a background source, causing detectable "dents and blobs" in the ring of light formed by the main lens galaxy. This satellite galaxy has a mass of about 113 million solar masses, making it one of the lowest-mass satellite galaxies detected so far. The discovery provides evidence that gravitational lensing techniques can be used to find satellite galaxies beyond the Local Group and help test theories of galaxy formation and evolution.
The Voyager flights to Jupiter and Saturn were NASA missions launched in 1977 that took advantage of a rare planetary alignment to visit multiple outer planets using gravitational assists. Voyager 1 and 2 were each complex, long-lived spacecraft carrying instruments to study the planets, rings, moons, and environments. Voyager 1's encounter with Jupiter in 1979 revealed active volcanoes on Io and details of Jupiter's atmosphere, while both probes provided the first close images of Jupiter's moons."
Stefano Sposetti and Marco Iten detected a probable lunar impact event on February 11, 2011 while monitoring the moon from two separate observatories in Switzerland. Their videos showed a flash of light on the lunar surface at 20:36:58 UTC. Analysis of the light curves and location of the flash place the impact in a region of craters near 86°W, 16°N. The editorial board of Selenology Today notes that images from the Lunar Reconnaissance Orbiter before and after the reported event can be searched to look for an impact crater at the reported coordinates.
This document reports the detection of a compact CO outflow from L1148-IRS, confirming that this Spitzer source is physically associated with the nearby L1148 dense core. Radiative transfer modeling suggests the internal luminosity of L1148-IRS is between 0.08 and 0.13 solar luminosities, validating it as a Very Low Luminosity Object (VeLLO). The L1148 dense core has unusually low densities and column densities for a star-forming core, making it difficult to understand how L1148-IRS might have formed under these conditions.
This document describes a model of crater formation on the Moon and terrestrial planets based on the current understanding of the impactor population in the inner Solar System. The model calculates impact rates spatially across planetary surfaces to account for nonuniform cratering. It finds that the lunar cratering rate varies with latitude and longitude, being about 25% lower in some regions and higher in others. The model reconciles measured lunar crater size-frequency distributions with observations of near-Earth objects, assuming the presence of a porous lunar megaregolith affects the size of small craters. It provides revised estimates of the ages of some lunar and planetary geological features based on crater counts and the derived crater chronology.
1) The document describes small-scale graben (extensional faults) discovered on the Moon using images from the Lunar Reconnaissance Orbiter Camera.
2) Some graben are located near lobate scarps (contractional faults), while others are found in mare basalts and in the highlands.
3) The graben crosscut small impact craters, suggesting they formed recently, within the last 50 million years. This indicates the Moon has experienced recent extensional tectonic activity.
Direct detection of ultralight dark matter bound to the Sun with space quantu...Sérgio Sacani
Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock and the Parker Solar Probe, we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxion targets motivated by naturalness and Higgs mixing. If a two-clock system were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter, which couples to electron, photon and gluon fields, based on current and future atomic, molecular and nuclear clocks
This document summarizes an article that proposes an alternative explanation for dark energy and dark matter based on a modified theory of gravity. It begins by providing background on dark matter and dark energy in standard cosmology and the evidence that supports their existence. It then outlines the proposed alternative theory, which modifies Einstein's field equations by adding a function of the Ricci scalar. This introduces new curvature terms that could potentially drive accelerated expansion, providing an alternative to dark energy. The theory aims to match observations without requiring dark matter or energy, but reduces to general relativity in the solar system scale where it has been tightly tested.
This document summarizes cosmological parameters measured from galaxy surveys. It discusses:
1) Direct measurements of the Hubble constant from the Hubble Space Telescope and Planck, finding values of 72-74 km/s/Mpc and 67.3 km/s/Mpc respectively.
2) Supernova surveys finding evidence for an accelerating universe with matter density of ~30% and dark energy density of ~70%.
3) Measurements of cosmic microwave background from COBE, WMAP and Planck, determining ages and densities of the universe.
4) Galaxy clustering surveys like SDSS detecting baryon acoustic oscillations to measure dark energy properties.
A rapidly spinning_supermassive_black_hole_at_the_centre_of_ngc1365Sérgio Sacani
1) XMM-Newton and NuSTAR observed the galaxy NGC 1365 simultaneously over 130 ks, detecting broadband X-ray emission from 3-79 keV.
2) The observations revealed variable absorption below 10 keV and prominent broad emission features between 5-7 keV and 10-30 keV, indicative of relativistic reflection from an accretion disk near a spinning supermassive black hole.
3) Time-resolved spectral analysis was able to disentangle the variable absorption component from the relativistic reflection component. Absorption-dominated models without reflection could be ruled out statistically and on physical grounds.
This study measures the spatial clustering of submillimeter galaxies (SMGs) at redshifts of 1-3 using data from a submillimeter survey of galaxies in the Extended Chandra Deep Field South. The authors detect clustering between SMGs and galaxies at over 4 sigma significance. They estimate an autocorrelation length of 7.7-2.3 h-1 Mpc for SMGs, corresponding to dark matter halo masses of log(Mhalo[h-1 M⊙]) = 12.8-0.5. Based on simulations, the descendants of z=2 SMGs are expected to be massive elliptical galaxies in moderate- to high-mass groups today.
The document summarizes a study that uses strong and weak gravitational lensing to analyze the mass distribution of 28 galaxy clusters. Key findings include:
- The concentration parameter cvir is found to steeply decrease with increasing mass, approximately following cvir ∝ Mvir-0.59±0.12, consistent with theoretical predictions for high-mass clusters but observationally inferred concentrations are higher for lower-mass clusters possibly due to baryon cooling effects.
- Stacking weak lensing shear profiles also supports a steep mass-concentration relation.
- Stacking weak lensing shear maps with position angle information from strong lensing indicates significant ellipticity of the mean mass distribution, with a best-fit ellipticity
Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
In this talk I explain (a) what observations speak
for the hypothesis of dark matter, (b) what observations speak for the hypothesis of modified gravity, and (c) why it is a mistake
to insist that either hypothesis on its own must explain all
the available data. The right explanation, I will argue,
is instead a suitable combination of dark matter and modified
gravity, which can be realized by the idea that dark matter
has a superfluid phase.
Conformal Anisotropic Mechanics And The HořAva Dispersion Relationvcuesta
This document summarizes a paper that implements scale anisotropic transformations between space and time in classical mechanics. This results in a system consistent with the dispersion relation proposed in Horava gravity. The paper constructs an action principle for a particle that is invariant under anisotropic scaling transformations between space and time. This action reduces to known systems like conformal mechanics in certain limits of the dynamical exponent z. The paper also analyzes the canonical formalism, equations of motion, symmetries and thermodynamic properties of this anisotropic mechanical system.
The document discusses string theory, extra dimensions, and cosmology. It notes that inflation and dark energy require new physics beyond general relativity and quantum field theory. Most string cosmology models invoke string theory, branes, or extra dimensions as approximations of string theory solutions. However, reliably anchoring cosmology in string theory has proven difficult, with success being rare. While cosmological observations can't determine the nature of dark energy, understanding fundamental physics through experiments like the LHC remains a key hope.
WHAT CAN WE DEDUCE FROM STUDIES OF NEARBY GALAXY POPULATIONS?CosmoAIMS Bassett
Studies of nearby galaxy populations using large optical surveys like SDSS have provided insights into galaxy formation and evolution. Key findings include identifying characteristic scales where baryon conversion peaks at halo masses of ~10^12 solar masses and galaxies transition from blue to red at stellar masses of ~10^10 solar masses. While surveys have constrained stellar populations and traced dark matter halos, they have not well constrained gas accretion onto galaxies, gas outflows, or the influence of black holes on galaxy evolution.
A weak lensing_mass_reconstruction_of _the_large_scale_filament_massive_galax...Sérgio Sacani
This study reports the first weak-lensing detection of a large-scale filament funneling matter onto the core of the massive galaxy cluster MACSJ0717.5+3745. The analysis is based on Hubble Space Telescope images covering an area of 10x20 arcmin^2 around the cluster. A weak-lensing mass reconstruction detects the filament within 3 sigma and measures its projected length as ~4.5 h^-1 Mpc and mean density as (2.92±0.66)×10^8 h74 M⊙ kpc^-2. Assuming constraints on the filament's geometry based on galaxy velocities, the three-dimensional length is estimated to be 18 h^-1 M
This document describes a study searching for supermassive black holes (SMBHs) with masses below 107 solar masses by looking for signs of low-level nuclear activity in nearby galaxies that are not known to be active galactic nuclei (AGNs). The study uses Chandra X-ray Observatory data to select for X-ray emission, a signature of AGNs, focusing on late-type spiral and dwarf galaxies most likely to host low-mass SMBHs. Preliminary results applying this technique to six nearby spiral galaxies find nuclear X-ray sources in all six, with NGC 3169 and NGC 4102 likely confirmed as AGNs and NGC 3184 and NGC 5457 possibly hosting AGNs.
Relatively and Quantum Mechanics assignment 5&7Brandy Wang
1. General relativity describes large astronomical scales while quantum mechanics describes microscopic scales. When applying the theories at small scales, general relativity's smooth geometric model of space conflicts with quantum mechanics' principle of uncertainty.
2. Quantum tunneling allows particles to temporarily "borrow" energy to pass through classically forbidden areas, but does not violate energy conservation as any additional energy is given back when measured.
3. Pauli's exclusion principle states that two fermions cannot be in the same quantum state. When compressing fermions, their wavelengths shrink and momenta/energy increase, requiring more energy to further reduce separation below their wavelengths. This creates degeneracy pressure resisting compression.
The electromagnetism and gravity are unified where, while the first originates from the electric charges in a
linear exposition, the second emerges in a quadratic manifestation of it, making the gravity always
attractive. This helps identify the inner structures of all the primary particles—quarks, leptons, and the
{Z,W} bosons as well as the 125 GeV state without the Higgs mechanism—to predict their masses by one
integer parameter formulas in close agreement with the observed values. This in turn enables
determination of the mechanism for building their ground and excited compound states. The consequences
are far-reaching and embracing, for examples, from identifying dark matter and energy that makes the
explanation of masses in the Universe 100 % inclusive, to solving the hackneyed yet equally elusive puzzle
of why the inertial mass is equal to the gravitational mass.
The electromagnetism and gravity are unified where, while the first originates from the electric charges in a
linear exposition, the second emerges in a quadratic manifestation of it, making the gravity always
attractive. This helps identify the inner structures of all the primary particles—quarks, leptons, and the
{Z,W} bosons as well as the 125 GeV state without the Higgs mechanism—to predict their masses by one
integer parameter formulas in close agreement with the observed values. This in turn enables
determination of the mechanism for building their ground and excited compound states. The consequences
are far-reaching and embracing, for examples, from identifying dark matter and energy that makes the
explanation of masses in the Universe 100 % inclusive, to solving the hackneyed yet equally elusive puzzle
of why the inertial mass is equal to the gravitational mass.
The electromagnetism and gravity are unified where, while the first originates from the electric charges in a
linear exposition, the second emerges in a quadratic manifestation of it, making the gravity always
attractive. This helps identify the inner structures of all the primary particles—quarks, leptons, and the
{Z,W} bosons as well as the 125 GeV state without the Higgs mechanism—to predict their masses by one
integer parameter formulas in close agreement with the observed values. This in turn enables
determination of the mechanism for building their ground and excited compound states. The consequences
are far-reaching and embracing, for examples, from identifying dark matter and energy that makes the
explanation of masses in the Universe 100 % inclusive, to solving the hackneyed yet equally elusive puzzle
of why the inertial mass is equal to the gravitational mass.
This document describes observations of Cepheid variables in the host galaxies of two Type Ia supernovae, SN 1995al in NGC 3021 and SN 2002fk in NGC 1309, using the Hubble Space Telescope. The observations aim to increase the sample of reliably calibrated supernovae to improve the measurement of the Hubble constant. New Cepheids were discovered, including many with periods over 60 days. Metallicity measurements of the galaxies' H II regions were also consistent with solar metallicity. The new data on the supernovae and Cepheids will help strengthen the distance ladder and reduce systematic uncertainties in the determination of the Hubble constant.
Quantization of photonic energy and photonic wave lengthEran Sinbar
The document proposes that if space is quantized at the Planck length, then photonic energy and wavelength must also be quantized. It suggests that future experiments could detect these quantization levels in cosmic radiation or particle collisions. It also puts forward a "grid dimensions" theory that proposes extra non-local dimensions between Planck length pieces of space that could explain quantum non-local effects like entanglement. Key equations presented quantify proposed quantized limits for momentum, mass, velocity of particles if space-time is quantized.
Similar to Astrophysical tests of_modified_gravity (20)
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
[OReilly Superstream] Occupy the Space: A grassroots guide to engineering (an...Jason Yip
The typical problem in product engineering is not bad strategy, so much as “no strategy”. This leads to confusion, lack of motivation, and incoherent action. The next time you look for a strategy and find an empty space, instead of waiting for it to be filled, I will show you how to fill it in yourself. If you’re wrong, it forces a correction. If you’re right, it helps create focus. I’ll share how I’ve approached this in the past, both what works and lessons for what didn’t work so well.
Freshworks Rethinks NoSQL for Rapid Scaling & Cost-EfficiencyScyllaDB
Freshworks creates AI-boosted business software that helps employees work more efficiently and effectively. Managing data across multiple RDBMS and NoSQL databases was already a challenge at their current scale. To prepare for 10X growth, they knew it was time to rethink their database strategy. Learn how they architected a solution that would simplify scaling while keeping costs under control.
5th LF Energy Power Grid Model Meet-up SlidesDanBrown980551
5th Power Grid Model Meet-up
It is with great pleasure that we extend to you an invitation to the 5th Power Grid Model Meet-up, scheduled for 6th June 2024. This event will adopt a hybrid format, allowing participants to join us either through an online Mircosoft Teams session or in person at TU/e located at Den Dolech 2, Eindhoven, Netherlands. The meet-up will be hosted by Eindhoven University of Technology (TU/e), a research university specializing in engineering science & technology.
Power Grid Model
The global energy transition is placing new and unprecedented demands on Distribution System Operators (DSOs). Alongside upgrades to grid capacity, processes such as digitization, capacity optimization, and congestion management are becoming vital for delivering reliable services.
Power Grid Model is an open source project from Linux Foundation Energy and provides a calculation engine that is increasingly essential for DSOs. It offers a standards-based foundation enabling real-time power systems analysis, simulations of electrical power grids, and sophisticated what-if analysis. In addition, it enables in-depth studies and analysis of the electrical power grid’s behavior and performance. This comprehensive model incorporates essential factors such as power generation capacity, electrical losses, voltage levels, power flows, and system stability.
Power Grid Model is currently being applied in a wide variety of use cases, including grid planning, expansion, reliability, and congestion studies. It can also help in analyzing the impact of renewable energy integration, assessing the effects of disturbances or faults, and developing strategies for grid control and optimization.
What to expect
For the upcoming meetup we are organizing, we have an exciting lineup of activities planned:
-Insightful presentations covering two practical applications of the Power Grid Model.
-An update on the latest advancements in Power Grid -Model technology during the first and second quarters of 2024.
-An interactive brainstorming session to discuss and propose new feature requests.
-An opportunity to connect with fellow Power Grid Model enthusiasts and users.
How to Interpret Trends in the Kalyan Rajdhani Mix Chart.pdfChart Kalyan
A Mix Chart displays historical data of numbers in a graphical or tabular form. The Kalyan Rajdhani Mix Chart specifically shows the results of a sequence of numbers over different periods.
Have you ever been confused by the myriad of choices offered by AWS for hosting a website or an API?
Lambda, Elastic Beanstalk, Lightsail, Amplify, S3 (and more!) can each host websites + APIs. But which one should we choose?
Which one is cheapest? Which one is fastest? Which one will scale to meet our needs?
Join me in this session as we dive into each AWS hosting service to determine which one is best for your scenario and explain why!
What is an RPA CoE? Session 1 – CoE VisionDianaGray10
In the first session, we will review the organization's vision and how this has an impact on the COE Structure.
Topics covered:
• The role of a steering committee
• How do the organization’s priorities determine CoE Structure?
Speaker:
Chris Bolin, Senior Intelligent Automation Architect Anika Systems
HCL Notes and Domino License Cost Reduction in the World of DLAUpanagenda
Webinar Recording: https://www.panagenda.com/webinars/hcl-notes-and-domino-license-cost-reduction-in-the-world-of-dlau/
The introduction of DLAU and the CCB & CCX licensing model caused quite a stir in the HCL community. As a Notes and Domino customer, you may have faced challenges with unexpected user counts and license costs. You probably have questions on how this new licensing approach works and how to benefit from it. Most importantly, you likely have budget constraints and want to save money where possible. Don’t worry, we can help with all of this!
We’ll show you how to fix common misconfigurations that cause higher-than-expected user counts, and how to identify accounts which you can deactivate to save money. There are also frequent patterns that can cause unnecessary cost, like using a person document instead of a mail-in for shared mailboxes. We’ll provide examples and solutions for those as well. And naturally we’ll explain the new licensing model.
Join HCL Ambassador Marc Thomas in this webinar with a special guest appearance from Franz Walder. It will give you the tools and know-how to stay on top of what is going on with Domino licensing. You will be able lower your cost through an optimized configuration and keep it low going forward.
These topics will be covered
- Reducing license cost by finding and fixing misconfigurations and superfluous accounts
- How do CCB and CCX licenses really work?
- Understanding the DLAU tool and how to best utilize it
- Tips for common problem areas, like team mailboxes, functional/test users, etc
- Practical examples and best practices to implement right away
Essentials of Automations: Exploring Attributes & Automation ParametersSafe Software
Building automations in FME Flow can save time, money, and help businesses scale by eliminating data silos and providing data to stakeholders in real-time. One essential component to orchestrating complex automations is the use of attributes & automation parameters (both formerly known as “keys”). In fact, it’s unlikely you’ll ever build an Automation without using these components, but what exactly are they?
Attributes & automation parameters enable the automation author to pass data values from one automation component to the next. During this webinar, our FME Flow Specialists will cover leveraging the three types of these output attributes & parameters in FME Flow: Event, Custom, and Automation. As a bonus, they’ll also be making use of the Split-Merge Block functionality.
You’ll leave this webinar with a better understanding of how to maximize the potential of automations by making use of attributes & automation parameters, with the ultimate goal of setting your enterprise integration workflows up on autopilot.
AppSec PNW: Android and iOS Application Security with MobSFAjin Abraham
Mobile Security Framework - MobSF is a free and open source automated mobile application security testing environment designed to help security engineers, researchers, developers, and penetration testers to identify security vulnerabilities, malicious behaviours and privacy concerns in mobile applications using static and dynamic analysis. It supports all the popular mobile application binaries and source code formats built for Android and iOS devices. In addition to automated security assessment, it also offers an interactive testing environment to build and execute scenario based test/fuzz cases against the application.
This talk covers:
Using MobSF for static analysis of mobile applications.
Interactive dynamic security assessment of Android and iOS applications.
Solving Mobile app CTF challenges.
Reverse engineering and runtime analysis of Mobile malware.
How to shift left and integrate MobSF/mobsfscan SAST and DAST in your build pipeline.
How information systems are built or acquired puts information, which is what they should be about, in a secondary place. Our language adapted accordingly, and we no longer talk about information systems but applications. Applications evolved in a way to break data into diverse fragments, tightly coupled with applications and expensive to integrate. The result is technical debt, which is re-paid by taking even bigger "loans", resulting in an ever-increasing technical debt. Software engineering and procurement practices work in sync with market forces to maintain this trend. This talk demonstrates how natural this situation is. The question is: can something be done to reverse the trend?
Taking AI to the Next Level in Manufacturing.pdfssuserfac0301
Read Taking AI to the Next Level in Manufacturing to gain insights on AI adoption in the manufacturing industry, such as:
1. How quickly AI is being implemented in manufacturing.
2. Which barriers stand in the way of AI adoption.
3. How data quality and governance form the backbone of AI.
4. Organizational processes and structures that may inhibit effective AI adoption.
6. Ideas and approaches to help build your organization's AI strategy.
Skybuffer SAM4U tool for SAP license adoptionTatiana Kojar
Manage and optimize your license adoption and consumption with SAM4U, an SAP free customer software asset management tool.
SAM4U, an SAP complimentary software asset management tool for customers, delivers a detailed and well-structured overview of license inventory and usage with a user-friendly interface. We offer a hosted, cost-effective, and performance-optimized SAM4U setup in the Skybuffer Cloud environment. You retain ownership of the system and data, while we manage the ABAP 7.58 infrastructure, ensuring fixed Total Cost of Ownership (TCO) and exceptional services through the SAP Fiori interface.
Programming Foundation Models with DSPy - Meetup SlidesZilliz
Prompting language models is hard, while programming language models is easy. In this talk, I will discuss the state-of-the-art framework DSPy for programming foundation models with its powerful optimizers and runtime constraint system.
Fueling AI with Great Data with Airbyte WebinarZilliz
This talk will focus on how to collect data from a variety of sources, leveraging this data for RAG and other GenAI use cases, and finally charting your course to productionalization.
Monitoring and Managing Anomaly Detection on OpenShift.pdfTosin Akinosho
Monitoring and Managing Anomaly Detection on OpenShift
Overview
Dive into the world of anomaly detection on edge devices with our comprehensive hands-on tutorial. This SlideShare presentation will guide you through the entire process, from data collection and model training to edge deployment and real-time monitoring. Perfect for those looking to implement robust anomaly detection systems on resource-constrained IoT/edge devices.
Key Topics Covered
1. Introduction to Anomaly Detection
- Understand the fundamentals of anomaly detection and its importance in identifying unusual behavior or failures in systems.
2. Understanding Edge (IoT)
- Learn about edge computing and IoT, and how they enable real-time data processing and decision-making at the source.
3. What is ArgoCD?
- Discover ArgoCD, a declarative, GitOps continuous delivery tool for Kubernetes, and its role in deploying applications on edge devices.
4. Deployment Using ArgoCD for Edge Devices
- Step-by-step guide on deploying anomaly detection models on edge devices using ArgoCD.
5. Introduction to Apache Kafka and S3
- Explore Apache Kafka for real-time data streaming and Amazon S3 for scalable storage solutions.
6. Viewing Kafka Messages in the Data Lake
- Learn how to view and analyze Kafka messages stored in a data lake for better insights.
7. What is Prometheus?
- Get to know Prometheus, an open-source monitoring and alerting toolkit, and its application in monitoring edge devices.
8. Monitoring Application Metrics with Prometheus
- Detailed instructions on setting up Prometheus to monitor the performance and health of your anomaly detection system.
9. What is Camel K?
- Introduction to Camel K, a lightweight integration framework built on Apache Camel, designed for Kubernetes.
10. Configuring Camel K Integrations for Data Pipelines
- Learn how to configure Camel K for seamless data pipeline integrations in your anomaly detection workflow.
11. What is a Jupyter Notebook?
- Overview of Jupyter Notebooks, an open-source web application for creating and sharing documents with live code, equations, visualizations, and narrative text.
12. Jupyter Notebooks with Code Examples
- Hands-on examples and code snippets in Jupyter Notebooks to help you implement and test anomaly detection models.
Monitoring and Managing Anomaly Detection on OpenShift.pdf
Astrophysical tests of_modified_gravity
1. Astrophysical Tests of Modified Gravity: Constraints from Distance Indicators
in the Nearby Universe
Bhuvnesh Jain1 , Vinu Vikram1 , Jeremy Sakstein2
ABSTRACT
arXiv:1204.6044v2 [astro-ph.CO] 7 May 2012
We use distance measurements in the nearby universe to carry out new tests of grav-
ity, surpassing other astrophysical tests by over two orders of magnitude for chameleon
theories. The three nearby distance indicators – cepheids, tip of the red giant branch
(TRGB) stars, and water masers – operate in gravitational fields of widely different
strengths. This enables tests of scalar-tensor gravity theories because they are screened
from enhanced forces to different extents. Inferred distances from cepheids and TRGB
stars are altered (in opposite directions) over a range of chameleon gravity theory pa-
rameters well below the sensitivity of cosmological probes. Using published data we
have compared cepheid and TRGB distances in a sample of unscreened dwarf galaxies
within 10 Mpc. As a control sample we use a comparable set of screened galaxies. We
find no evidence for the order unity force enhancements expected in these theories. Us-
ing a two-parameter description of the models (the coupling strength and background
field value) we obtain constraints on both the chameleon and symmetron screening
scenarios. In particular we show that f (R) models with background field values fR0
above 5 × 10−7 are ruled out at the 95% confidence level. We also compare TRGB and
maser distances to the galaxy NGC 4258 as a second test for larger field values. While
there are several approximations and caveats in our study, our analysis demonstrates
the power of gravity tests in the local universe. We discuss the prospects for additional,
improved tests with future observations.
1. Introduction
1.1. Modified Gravity
Modified theories of gravity (MG) have received a lot of attention in recent years. Several
unexplained phenomena such as the observed accelerated expansion of the universe, spatio-temporal
variation of the fundamental constants (e.g. the fine-structure constant) and dark matter can in
principle be explained by modifying general relativity (GR) on large (astrophysical and greater)
scales. This study is motivated by recent work on MG to obtain cosmic acceleration without
1
Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
2
Department of Applied Mathematics and Theoretical Physics, Cambridge, CB3 0WA, UK
2. –2–
invoking quintessence-like dark energy. Even on theoretical grounds, GR is unlikely to be the
complete theory of gravity owing to singularities and its non-renormalizibility. Hence it is generally
considered to be the low energy effective action of some UV-complete theory (though our interest
is modifications in the long distance/low energy regime).
Any modification to GR generically introduces an additional degree of freedom (Weinberg
1965) and scalar-tensor theories, where a new scalar field couples non-minimally to gravity, are
ubiquitous in many attempts to find consistent theories. Theories of higher dimensional gravity
often appear as scalar-tensor theories to observers in four dimensions. Theories such as DGP (Dvali,
Gabadadze & Porrati 2000) invoke braneworld scenarios – the distance between two branes acts
as the scalar field. In Kaluza-Klein models, the parameters controlling the size of the compact
directions appear as a scalar coupled to gravity in four dimensions. The low energy effective action
of string theory contains a new scalar particle, the dilaton, coupled non-minimally to gravity and
any theory with N = 4 supergravity (or higher) contains at least two scalar fields in the gravity
multiplet. Even attempts to modify the geometrical properties of GR tend to lead to scalar-tensor
theories; for example the entire class of f (R) theories is equivalent to a single scalar field coupled
non-minimally to matter via a Weyl rescaling of the metric.
Thus a wide class of gravity theories contain a coupling of the scalar field to matter via a
universal fifth force which leads to enhancements of the gravitational force. Non-relativistic matter
– such as the stars, gas, and dust in galaxies – will feel this enhanced force and as a consequence, a
general feature of scalar-tensor theories is that dynamically inferred masses are larger than the true
masses. The discrepancy can be up to a factor of 1/3 in f (R) or DGP gravity (for recent reviews
see Silvestri & Trodden 2009 and Jain & Khoury 2010). Photons do not feel the enhanced force,
so that lensing probes the true mass distribution.
This enhanced gravitational force should be detectable through fifth force searches such as
the E¨t-Wash experiment (Kapner et al. 2007) and Casimir force experiments (e.g. Decca et al
o
2003) as well as tests of the equivalence principle1 (Mota & Shaw 2006) or through the orbits of
planets around the Sun (Will 2006). However, since all of these experiments have been performed
in our local vicinity, i.e. the solar system, they do not rule out any large-scale modifications where
fifth forces are active over large (cosmological) scales while matching the predictions of GR within
experimental bounds on small scales. Any theory where the fifth forces are suppressed on small
scales is said to possess a screening mechanism: regions where fifth forces are active are said to
be unscreened whereas those where they are suppressed are screened. Khoury & Weltman (2004)
proposed such a mechanism where non-linear screening of the scalar field, known as chameleon
screening, can suppress the fifth force in high density environments such as the Milky Way, so that
solar system and laboratory tests can be satisfied.
1
If the scalar coupling to matter is not constant then one generically expects violations of the weak equivalence
principle.
3. –3–
In this paper we will consider deviations from GR exhibited in theories that rely on chameleon
screening. Qualitatively similar behavior occurs in symmetron screening (Hinterbichler & Khoury
2010) and the environmentally dependent dilaton (Brax et al. 2010) and the tests we will present
here apply to these mechanisms as well We also note that chameleon screening was originally
suggested to hide the effects of a quintessence-like scalar that forms the dark energy and may
couple to matter (generically such a coupling is expected unless forbidden by a symmetry). Hence
there are reasons to expect such a screening effect to operate in either a dark energy or modified
gravity scenario, or even in scenarios that don’t relate to cosmic acceleration such as the scalar
fields invoked in string theories.
A different screening mechanism, Vainshtein screening (Vainshtein 1972), operates by including
non-canonical kinetic terms in the field equations whose non-linear nature acts to recover GR on
scales smaller than some Vainshtein radius. In theories that contain this mechanism (such as DGP,
massive gravity and Galileons) this radius must typically be taken to be of the order of the length
scale of typical galaxies, independent of their mass, and so does not produce the observable effects
considered here (see Appleby and Linder 2012 for recent cosmological constraints for a subclass of
Galileon theories). However recent studies have pointed out the possibility of enhanced forces even
within galaxies in Vainshtein theories, opening them up to astrophysical tests (Chan & Scoccimarro
2009; Hui & Nicolis 2012).
1.2. Observations of the Nearby Universe
The logic of screening of the fifth force in scalar-tensor gravity theories implies that signatures
of modified gravity will exist where gravity is weak. In particular, dwarf galaxies in low-density
environments may remain unscreened as the Newtonian potential ΦN , which determines the level
of screening, is at least an order of magnitude smaller than in the Milky Way. Hence dwarf galaxies
can exhibit manifestations of modified forces in both their infall motions and internal dynamics.
Hui, Nicolis & Stubbs (2009) and Jain & Vanderplas (2011) discuss various observational effects
while Vikram et al (2012, in preparation) present a set of tests from current observations.
Stars within unscreened galaxies may show the effects of modified gravity. Chang & Hui
(2010) and Davis et al. (2011a) describe the effects on giant and main sequence stars, respectively:
essentially the enhanced gravitational force makes stars of a given mass brighter and hotter than in
GR. They are also more ephemeral since they consume their fuel at a faster rate. For the Sun the
potential ΦN ≈ 2 × 10−6 (we set c = 1 and work with the amplitude of the potential throughout).
Coincidentally, the potential of the Milky Way is close to this value – and is believed to be sufficient
to screen the galaxy so that solar system tests of gravity are satisfied 2 . Thus main sequence stars
2
At least this is the straightforward interpretation; there may be loopholes to this logic where the galaxy is screened
by the Newtonian potential of the local group or structure on larger scales
4. –4–
whose masses are similar to that of the Sun are likely to be partially or completely screened. It
is worth noting that these screening conditions are found by considering static, non-dynamical
spherical objects sitting inside a fixed scalar field. Davis et al. (2011a) have shown that stars,
as dynamical objects which support themselves under the action of the enhanced gravity, can be
partially unscreened at Newtonian potentials where this simple model would predict them to be
completely screened, especially for higher mass objects.
Red giants are at least ten times larger in size than the main sequence star from which they
originated so they have ΦN ∼ 10−7 – thus their envelopes may be unscreened. The enhanced
forces lead to smaller radii, hotter surface temperatures and higher luminosities than their GR
doppelgangers. For f (R) theories (Capozziello et al 2003; Nojiri & Odintsov 2003; Carroll et al
2004; Starobinsky 2007; Hu & Sawicki 2007) with background field values (fR0 ) in the range 10−6 –
10−7 , Chang & Hui (henceforth CH) find that compared to GR a solar mass red giant has radius R
smaller by over 5%, luminosity L larger by over 50% at fixed effective temperature Te , while Te itself
is higher by about 5% at fixed L. They point out that the change in surface temperature of about
150 Kelvin may be detectable from data on the red giant branch in observed Hertzsprung-Russel
(HR) diagrams.
We focus on specific stages of the evolution of giants and supergiants to seek different obser-
vational signatures. The first feature, well known for its use in obtaining distances, is the nearly
universal luminosity of < 2M stars at the tip of the red giant branch. The second is the Period-
∼
Luminosity relation of cepheids, which are giant stars with ∼ 3 − 10M that pulsate when their
evolutionary tracks cross a near universal, narrow range in Te known as the instability strip. The
tight relation between luminosity and other observables is what makes these stars valuable distance
indicators – it also makes them useful for tests of gravity. For background field values in the range
10−6 –10−7 , the TRGB luminosity is largely robust to modified gravity while the cepheid P − L
relation is altered. Measurements of these properties within screened and unscreened galaxies then
provide tests of gravity: the two distance indicators should agree for screened galaxies but not for
unscreened galaxies.
This paper is organised as follows: In §2 we briefly describe chameleon gravity (a full discussion
for the interested reader is given in Appendix A) and explain the differences in stellar evolution
due to its influence. In §3 the properties of cepheids in GR and MG are presented, as well as a
summary of relevant observations; the corresponding details of TRGB distances are presented in
§4. §5 contains our main results based on a comparison of cepheid and TRGB distances. Water
masers in NGC 4258 are used for a second tests in §6, and other distance indicators are discussed.
We conclude in §7.
5. –5–
2. Modified Gravity and its Effect on Stellar Structure
2.1. Review of Chameleon Screening
Here we will briefly review the parameters that provide tests of gravity, motivated by the
chameleon-like screening mechanisms. We refer the interested reader to Appendix A for the full
details and examples of some of the more common models.
There are two parameters in these theories. The first, χc (see Appendix A and Davis et al.
2011a) determines how efficient the body is at screening itself. If the magnitude of the surface
Newtonian potential ΦN χc then the object will be completely unscreened whilst if the converse
is true then the body will be at least partially screened (see equation A9 in appendix A). Currently
there are two different constraints on χc in the literature. The Newtonian potential of the Sun is
around 2 × 10−6 and the Milky way has a similar value and so if one demands that these objects self
screen then χc > 10−6 is ruled out observationally. Independent constraints come from cosmological
∼
observables and cluster abundances and set an upper bound χc ≈ 10−4 for f (R) models (Schmidt,
Vikhlinin & Hu 2009; Lombriser et al 2010 and references therein). Our analysis here constitute
an independent constraint, so we examine several possible uses of TRGB, cepheid and water maser
distance indicators to test gravity.
The second parameter in these models is αc , which sets the strength of the fifth force in
unscreened regions. A completely unscreened object will feel a fifth force that is proportional to
the Newtonian force and the combined forces simply amount to a rescaling of G by
G → G(1 + αc ). (1)
For partially screened objects, the total force in the region exterior to the screening radius can be
described by a position dependent rescaling of G:
M (rs )
G(r) = G 1 + αc 1 − (2)
M (r)
where M (r) is the mass interior to a shell of radius r.
We will consider tests of chameleon theories that probe ranges of χc and αc well below current
astrophysical limits. For concreteness in evaluating screening conditions we work with f (R) models,
which are chameleon models with parameters:
αc = 1/3; χc = fR0 . (3)
where fR0 is a parameter commonly used in the literature to constrain the model (Hu & Sawicki
2007). αc = 1/3 is also the value found in the high density limit of the environmentally dependent
dilaton (see Appendix A). We will also consider other values of αc in comparisons with observations.
In f (R) theories, the parameter fR0 sets the screening condition for an isolated spherical halo
3
(Hu & Sawicki 2007): ΦN > 2 fR0 . The Navarro-Frenk-White (NFW) density profile is a good
6. –6–
approximation for halos of most galaxies both in GR and f (R) theories (Lombriser et al. 2012). It
is useful to express the Newtonian potential in terms of the scale radius rs of the NFW profile as:
GMg
ΦN F W =
N ln(1 + r/rs ) (4)
r
where we have followed Hu & Sawicki (2007) in using Mg to represent the mass contained within
5.3rs (see also Schmidt 2010). The screening condition can then be conveniently expressed in terms
of the observable maximum circular velocity vmax as:
2
vmax >
fR0
∼ . (5)
100 km/s 2 × 10−7
For the late-type dwarf galaxies of interest here, the peak circular velocity is likely to be reasonably
well estimated by the observed rotation curves. The effects of inclination and of limited radial
coverage typically lead to 10% level underestimates of vmax . For the range of circular velocities
used in our sample, we probe fR0 values in the range 10−6 − 10−7 .
2.2. Stellar Structure and Evolution
The structure of a spherically symmetric star is obtained by solving the equations of stellar
structure that at a given radius r relate M (r) to P (r), ρ(r) and T (r) – respectively the pressure,
density and temperature. The opacity κ and the energy generation rate are needed to close the
equations. We will denote the radius of the star as R, so that M = M (R) is the total mass and
L = L(R) the total luminosity. P , κ and are determined in terms of ρ and T by equations of
state which are independent of gravitational physics. As noted by CH and Davis et al. 2011a,
modifying gravity only alters the gravitational physics, which is entirely contained in the equation
of hydrostatic equilibrium:
dP G(r)ρ(r)M (r)
=− , (6)
dr r2
which represents the condition for the outward pressure to balance the (now enhanced) inward
gravitational pull and remain static. Note that the modification is expressed purely as a change
in G, which becomes dependent on r if the star is partially screened according to equation 2. The
other three equations – the continuity, radiative transfer and energy generation equations – are
all unaffected by this change in G. The result is that unscreened stars of a given mass are more
compact, brighter, and have a larger effective temperature than screened stars of identical mass
and chemical composition. They also have a shorter main sequence life-time due to their increased
burning rate and finite fuel supply.
We will assume that changes in the gravity theories occur on timescales longer than the evolu-
tionary timescales of stars. Since we are interested in massive post-main sequence stars, evolution-
ary timescales are shorter than a billion years, typically orders of magnitude smaller. Thus provided
7. –7–
the main sequence is the same as in GR (i.e. for fR0 < 10−6 ), the star’s post-main sequence evolu-
tion begins at the same point in the HR diagram as in GR, and subsequently responds to a static
(but possibly r-dependent) G. Our results do not require this assumption but it simplifies the story.
The complete system of stellar structure equations for main sequence stars can be solved
under certain simplifying assumptions (see Davis et al. 2011a). However, if one really wants to
look at the dynamical and nuclear properties, as well as the structure of post main sequence stars
then a numerical prescription is needed. In this work we shall use a modification of the publicly
available stellar evolution code MESA (Paxton et al. 2011) presented in (Davis et al. 2011a).
MESA can simulate individual stars of any given initial mass and metallicity and includes a fully
consistent implementation of nuclear reaction networks, mass loss, convection, radiative transfer,
opacity tables and metallicity effects. In brief, it is a one-dimensional (in that it assumes spherical
symmetry) code that divides the star into radial cells of unequal width, each with a set of properties
such as mass, temperature etc. The implementation of chameleon gravity into MESA uses a quasi-
static approximation where the structure of the star is solved first and then the value of G is
updated in every cell given this structure. This approximation is good provided that the time
between successive stellar models is smaller than the timescale over which the changes in G(r)
are significant and MESA provides a facility to ensure that this is always the case. This method
has been checked against that used by CH, who use a scalar-field ansatz and interpolation between
different cells, and the results have been found to be indistinguishable. Our method uses the general
screening properties set out in Appendix A and as such, applies to generic screening behavior, not
only chameleons.
The implicit relation for the screening radius is given in appendix A (equation A9) and is
completely equivalent to the condition
R
χc = 4πG rρ(r) dr. (7)
rs
Given an initial stellar model, the integral 7 is performed from the stellar surface, cell by cell until
the condition is satisfied. The cell where this is so is then designated as the screening radius and
the value of G is changed according to equation 2 in all cells exterior to this. The star is then
allowed to evolve under this new gravity until the next stellar model is reached and the process is
repeated.
3. Cepheid Variables
3.1. Cepheid Pulsations in GR
Cepheids are a class of massive, pulsating giant stars whose time period P is related to lu-
minosity L in a well understood way. After a giant reaches the tip of the red giant branch, its
luminosity falls and it moves into the core Helium burning stage. Stars that are sufficiently mas-
8. –8–
Fig. 1.— The post-main sequence HR diagram (L vs. Te ) is shown for stars with different masses as
indicated. The black vertical lines shows the blue edge (left) and red edge (right) of the instability
strip. At each crossing of the instability strip the star pulsates as a cepheid variable. The fits for
the instability strip are taken from Alibert et al 1999.
sive, M > 3M , actually follow trajectories called loops, which at three or more phases cross the
∼
instability strip – set by a narrow range in effective temperature Te . While in the instability strip,
their luminosity and radius oscillate with a time period of days-weeks in a very regular manner. We
are concerned here with a class of pulsating stars called (classical) cepheids. The radial oscillations
in a cepheid are the result of acoustic waves resonating within the star. For much of the lifetime
of a star, its envelope is stable to pulsations – the exception is the instability strip. Figure 1 shows
the post main sequence evolution of stars of different masses.
The instability strip arises due to the presence of a He+ ionisation zone in the stellar envelope
located where the temperature is around 4 × 104 K (corresponding to the ionisation potential of
He). The pulsation is driven by the κ-mechanism (and to a small extent the γ-mechanism3 ). The
opacity throughout the majority of the star is given by Kramer’s law, κ(R) ∝ ρT −3.5 . In the
ionisation zone however, the gradient d ln κ/ d ln T −3.5 and so a small compression, which
3
This is where the energy absorbed from the radiation is used to ionise the He and not to raise the temperature
and so small compressions raise the opacity by virtue of the increased density, the opposite of their usual effect.
9. –9–
increases the temperature slightly, causes a large increase in the opacity, absorbing radiation and
damming up energy. This further increases the opacity, resulting in an outward pressure which
drives the pulsations. This driving is only really effective when the thermal time-scale of the zone
is comparable to the pulsation period, which requires it to be located in the so called transition
region, where the stellar processes (which are adiabatic in the star’s interior) are becoming non-
adiabatic. The instability strip therefore corresponds to the region in the H-R diagram where the
ionisation zone coincides with this transition region.
Stars can cross the instability strip multiple times. The 1st crossing of the instability strip is
before the star goes up the red giant branch and is far too brief to be observationally irrelevant.
The 2nd crossing of the instability strip is the first crossing after the tip of the red giant branch
when the star is on the lower part of the blue loop. And the 3rd crossing is when it is on the
upper part of the blue loop. The 2nd and 3rd crossing of the strip, and in particular on the blue
edge, is probably where cepheid properties are best understood. There are nearly as many observed
cepheids on the 2nd and 3rd crossing. We will use the 3rd crossing of a 6 solar mass star as our
fiducial case (observed cepheids are typically 6-8 solar mass stars).
To estimate the pulsation period, one needs to go beyond hydrostatic equilibrium and consider
the full dynamical radial acceleration of a fluid element at radius r, which is described by the
momentum equation:
GM (r) 1 ∂P
r=−
¨ − (8)
r ρ ∂r
The time period of pulsations Π may be estimated through various approximations: 1. As the
√
sound crossing time for the diameter of the star, giving Π ∝ 1/ γGρ where γ is the ratio of specific
heats and ρ is the mean density of the star. This expression assumes that physical variables like
the density and temperature can be used. The dependence on G and ρ is essentially correct,
but the dependence on γ is not correct. 2. By perturbing equation 8 as well as the equations
of continuity, radiative transfer and energy generation one can derive a full non-adiabatic wave
equation for infinitesimal fluid elements in the Lagrangian picture (see Cox 1980). If one linearises
this equation in the adiabatic limit and searches for standing wave solutions then the resultant
eigenvalue equation for the radial wave, the linear adiabatic wave equation (LAWE), gives the
pulsation periods. The LAWE is highly non-trivial and depends on the zeroth order pressure and
first adiabatic index Γ1 and so the general case requires numerical matrix or shooting methods
applied to simulations involving envelope models. One simplifying assumption that can be made
however is that of a static sphere of fixed equilibrium radius and constant density composed of gas
with an adiabatic relation δP/P ∝ γ δρ/ρ. Under this assumption, the LAWE can be solved for
the period of small oscillations (note that the linear and adiabatic nature precludes a calculation
of the amplitude) to find:
2π
Π= . (9)
4/3πGρ(3γ − 4)
Using γ = 5/3 for an ideal monatomic gas yields Π = 3π/Gρ Π above is in the range of 1-100
days for a range of relevant red giant densities. This equation gives values of Π that are fairly close
10. – 10 –
to more detailed calculations as well as observations.
We note that detailed numerical models are able to predict not just the period but many
detailed properties of cepheids, including the variations of size and luminosity, the location of the
instability strip, and the dependence on mass and metallicity (e.g. Bono et al 1998). The primary
source of uncertainty is the treatment of convection, so to some extent input from observations is
used in theoretical models.
Fig. 2.— The profile of the effective gravitational constant G inside the star for cepheids (left panel)
and TRGB stars (right panel). Note that cepheid pulsations typically span 0.3 < R/RS < 0.9 while
the core physics that sets the TRGB luminosity occurs deep within the star. The core radius in the
right panel is shown by the arrow for χc = 10−5 . The plateau just below 1.1 on the y-axis shows
the enhanced gravity in the H-burning shell.
3.2. Cepheid Pulsations in Modified Gravity
The effect of MG theories on cepheid pulsations is well approximated by considering the de-
viation of G from its Newtonian value GN . We apply Eqn. 9 to estimate the change in period
for two choices of a constant G: in an idealized, completely unscreened star the first corresponds
to the coupling constant αc = 1, and the second to αc = 1/3, which applies to all f (R) models
(see above). The modified gravitational constant is denoted G1 and G2 for the two cases, and the
corresponding periods Π1 and Π2 are:
√
G1 = 2 GN =⇒ Π1 = ΠN / 2 (10)
G2 = 4/3 GN =⇒ Π2 = ΠN / 4/3 (11)
11. – 11 –
where the subscript N denotes values in the Newtonian gravity. The shorter period means that
in chameleon gravity, the inferred distance (based on incorrectly using the GR Period-Luminosity
relation) is smaller than the true distance.
A fully unscreened star is an idealization – it is important to take into account the spatial
profile of G and the fact it is not altered inside the screening radius. This will tend to lower the
deviation. We take this into account and estimate a more realistic value of ∆G in the unscreened
region by averaging G(r) according to
R
1
G = f (r)G(r) dr (12)
R 0
where G(r) is given by equation 2. The function f (r) is a weighting function that accounts for the
fact that different regions of the star are more important than others in driving the pulsations. The
simplest scenario is to simply take f (r) = 1, however Epstein (1950) has numerically solved the
pulsation equation and tabulated the weight function f (see figures 1 and 2 in his paper). Using
the numerical values given in the tables, we have reconstructed the normalised weight function. We
use the Epstein function in conjunction with G(r) profiles from MESA along the instability strip
to obtain G . Figure 2 shows the actual profiles G(r) for different choices of αc and χc .
To estimate the change in distance, we need the Period-Luminosity relation for a given obser-
vational band. If one uses ρ ∼ M/R3 in Equation 9, and L = 4πR2 σTe , then one gets a relation
4
between Π, L and Te that is nearly universal for all cepheids. The main residual dependence is
on metallicity. Using observational quantities, such as the V-band absolute magnitude MV (note
though that it is the bolometric magnitude MB that is directly related to L) and (intrinsic) color
B − V ∝ log Te gives
˜ ˜
MV = α log Π + β(B − V ) + γ ˜ (13)
˜
where α and β are universal in galaxies with similar metallicity, e.g. the Milky Way and other
˜
galaxies dominated by Pop II stars. For the observations discussed below a reasonable approxima-
tion is α ≈ −3. Using the P − L relation above and the fact that the flux goes as L/d2 , the change
˜
in inferred distance is
∆d ∆G ∆G G − GN
≈ −0.3 , where ≡ . (14)
d G G GN
Table 1 gives the effective values of ∆G/G obtained from MESA and the resulting change in
distance4 .
Note that we test for gravity using these predicted changes in distance using a sample of
galaxies each of which has dozens to hundreds of observed cepheids. While systematic errors in
4
The absolute value of α is significantly larger in the infrared, which would lead to larger changes in distance. It
˜
also provides an additional check on gravity: the inferred distance should vary with filter. We estimate a change in
distance of about 5% between the V and K band.
12. – 12 –
Table 1: Change in inferred distance due to the change in cepheid periods for different gravity
parameters. For a 6M cepheid, the change in effective G (using the Epstein weights as described
in the text) and inferred distance is shown for different values of the coupling constant αc and
background field value χc . All f (R) models correspond to αc = 1/3 with χc ≡ fR0 .
αc χc ∆G/G ∆d/d
1/3 4 × 10−7 0.11 -0.03
1/3 1 × 10−6 0.21 -0.06
1/2 4×10−7 0.17 -0.05
1/2 1×10−6 0.34 -0.09
1 2 × 10−7 0.21 -0.06
1 4 × 10−7 0.45 -0.12
absolute distances are a challenge, as is theoretical uncertainty, we use relative distances in our
tests, so some gain in accuracy is achieved via averaging over many cepheids and galaxies.
The above estimates are based on simple approximations for the theory of cepheid pulsa-
tions. We do not address the amplitude of the oscillations, which depends on luminosity and other
properties. Nor does our analysis deal with the location of the instability strip which involves the
Luminosity-Mass-effective Temperature relation; the instability strip itself is quite narrow, 200K.
The amplitude and shape of the pulsations, the precise value of the period, as well as location of
the instability strip are reasonably well understood and well measured. Changes in these proper-
ties are therefore additional possible tests of gravity. The computation involves the use of detailed
non-linear, non-adiabatic models that are well studied in the literature (though the treatment of
convection and metallicity dependence remain somewhat uncertain). For MG, this also requires
modeling the evolution up to the instability strip via MESA. These issues are beyond the scope of
this study and will be addressed elsewhere.
We use only the distances obtained from the P − L relation for our tests below: it is worth
noting that our analysis is robust to the effects of MG on the luminosity and radius of the star.
To see this note that in obtaining a distance estimate from the P − L relation of Eqn. 13, the
˜ ˜
observables are the flux f , Te and Π while the coefficients α and β follow from L = 4πσR2 Te . 4
So the entire dependence on MG is via G; the change in G may be regarded as contained in the
˜
coefficient γ. In practice α and β are set empirically since observations involve filters with finite
˜
wavelength coverage, so estimates of the flux and temperature are imperfect. We have used the
empirical value α ≈ −3 to check that the residual dependence on L is weak: ∆d/d ≈ −0.025∆L/L
˜
at constant Te – at least a factor of ten smaller than the signal from MG models we consider. An
additional effect is the mass dependence of MG effects (more massive stars have slightly larger force
enhancements). This leads to shallower predicted slopes of the P − L relation and other second
order effects that we do not consider here but merit further study.
13. – 13 –
Fig. 3.— The P − L relation for the galaxies in our sample. In the left panel, we show all the
cepheids observed along with the reported error bars. The right panel shows the mean period and
dispersion within bins in absolute magnitude of size 0.5. The red and black points show unscreened
and screened galaxies respectively. There is no evidence for a difference in the shape of the P − L
relation between the two samples.
3.3. Observations of Cepheids
Cepheid distances have been calibrated using parallaxes for 10 Milky Way cepheids in the
distance range ≈ 0.3 − 0.6 kpc, with periods ranging from ≈ 3 − 30 days. The error on the mean
distance is ±3% or 0.06 magnitude. The slope has in the past been obtained from the LMC since
the sample size is bigger, but at the cost of possible uncertainty due to metallicity effects. More
recently the maser distance to NGC 4258 has superseded the calibration with the LMC. Outside
the Local Group, cepheid distances have been measured to over 50 galaxies (see the review by
Freedman & Madore 2010 for more details). The final uncertainty in the distance modulus, which
includes zero point calibration, metallicity, reddening and other effects, is ±0.09 magnitude or 5%
in distance. 5 As discussed in Sasselov et al (1997) and subsequent work, the three basic ingredients
in the P − L relation (pulsation theory, stellar evolution and stellar atmospheres) are sensitive to
metallicity. A metal-poor cepheid is fainter for given period and temperature. The net dependence
on metallicity however is weak, in particular the slope of the relation between period and bolometric
luminosity is nearly unchanged.
The data for the P − L relation used in our analysis was compiled for individual cepheids in 19
galaxies – see Appendix C for details. Five galaxies were removed from the sample due to the large
5
The GAIA space telescope will improve cepheid calibration. An important recent development is the measurement
of the P − L − C relation in the IR. The slope is steeper and the scatter is significantly smaller in the IR, so Spitzer
and JWST should improve the calibration. A factor of two improvement is anticipated – see Table 2 in Freedman &
Madore (2010).
14. – 14 –
scatter in the relation. Of the remaining 14 galaxies used for Figure 3, seven galaxies have TRGB
based distances as well. The majority of the galaxies show late type morphology and include both
dwarf and normal galaxies with peak rotational velocities ranging from 40 to 240 km/s. The number
of cepheids in each galaxy varies between 5 and 117, and is in the range 10-50 for most galaxies. We
use only cepheids with good photometry in V-band. We use the phase-weighted cepheid luminosity
when possible (available for the majority of the cepheids) and intensity-weighted luminosity for the
remainder. Compiling this dataset requires a detailed compilation of data on hundreds of cepheids,
so we have used only a subset of existing data. The sample size can be significantly increased to
carry out additional tests, given more detailed theoretical predictions for MG as discussed below.
We classify these galaxies as screened or unscreened based on their mass (which determines
whether the self-screening condition is satisfied) and their environment. No rigorous criteria exist to
determine the screening effect of the neighboring galaxies, groups and clusters since the equations
are nonlinear. However, based on recent work (Zhao et al 2011; Cabre et al 2012) and on tests we
have performed, we use an estimate of the mean Newtonian potential over the galaxy due to its
neighbours within a (background) Compton wavelength. This is estimated from the SDSS, 2MASS
and other surveys, and used to determine the screening condition in combination with Eqn. 5 for
self-screening (details are presented in Cabre et al 2012).
Figure 3 shows the observed P −L relation in our sample. We use the normalization from Saha
et al (2006) to find the absolute magnitude. The left panel shows the individual data points with
error bars and the right panels shows the averaged P − L relation in bins of absolute magnitude.
The red points show cepheids in unscreened galaxies and black points in screened galaxies. The
slope of the P − L relation is consistent between the two samples. The unscreened sample has a
slightly steeper slope – we have checked that the expected signal from MG is the opposite, based
on changes in the period which is shorter for massive cepheids. We do not use this signature as a
test here since there are uncertainties in the model predictions. However, this is a potential future
test for MG.
4. TRGB: Tip of the Red Giant Branch Distances
The TRGB distance is obtained by comparing the measured flux to the universal peak lumi-
nosity expected for red giants with masses below 2 M . TRGB distances have been measured to
∼ 250 galaxies using the universality of the peak luminosity of red giants at the tip of the red giant
branch. These are applied to old, metal poor populations which enables distance estimates out to
about 20 Mpc, a bit closer than cepheid distances since cepheids are brighter. However since single
epoch photometry suffices, it is much easier to obtain the data for a TRGB distance. While it is
not an absolute distance method, and must in fact be calibrated using secondary indicators like
cepheids, a comparison of TRGB distances in screened and unscreened galaxies can still provide a
useful test.
15. – 15 –
Table 2: Change in inferred distance using the TRGB peak luminosity for different gravity parame-
ters. For a 1.5M red giant, the change in luminosity and the inferred distance is shown for different
values of the coupling constant αc and background field value χc . All f (R) models correspond to
αc = 1/3 with χc ≡ fR0 .
αc χc log L/L ∆d/d
0 0 3.34 0
1/3 1 × 10−6 3.32 0.02
1/3 2 × 10−6 3.30 0.04
1/3 4 × 10−6 3.25 0.12
1/3 8 × 10−6 <3 >0.20
The TRGB luminosity is set by the He flash during the post main sequence evolution. Low
mass stars develop a small He core region after the main sequence (which grows slower than that of
high mass stars). In the initial stage of post-main sequence evolution the core temperature is not
high enough to ignite the He and the core subsequently contracts due to the absence of outward
pressure. This catalyses the nuclear reaction in the outer hydrogen dominated region and the He
produced in the shell gets deposited on to the core. The increase in the mass of the core causes the
23/3 6
shell luminosity to grow – for stars of interest the luminosity of the star is roughly ∝ Mc /Rc ,
where Mc and Rc are the mass the radius of the core. When the core temperature becomes high
enough (Tc ∼ 108 K) to ignite He, the star moves to the left in the H-R diagram, settling onto the
horizontal branch. Nuclear physics within the core sets the TRGB luminosity, mostly independent
of composition or mass of the envelope.
The luminosity of the TRGB depends on the mass of the core which in turn depends weakly
on the metallicity of the star. In particular, for stars with low metallicities (−2.2 ≤ [Fe/H] ≤ −0.7)
the I band magnitude of the TRGB varies by only 0.1 magnitude within this metallicity range
(IT RGB = −4.0 ± 0.1), though it can vary a lot more in other bands. Figure 1 in Lee, Freeman &
Madore (1993) shows the variation of MV and MI over the above metallicity range. The remarkable
constancy of the TRGB magnitude leads to a discontinuity in the luminosity function of stars as
low mass stars continuously reach this phase. The distance to the TRGB can be measured if we
can filter out the magnitude at the discontinuity. Observationally, the TRGB is identified from
a semi-empirically calibrated color-magnitude diagram (Da Costa & Armandroff 1990) and the
metallicity corrected distance modulus is determined.
We have estimated the change in luminosity with modified gravity for the TRGB using MESA
(see Appendix B for a discussion and an analytic estimate). Figure 2 shows the profiles of G(r) at
the TRGB stage for a 1.5M star for different values of χc with αc = 1/3. There is a transition in
the enhancement of G in the shell as χc increases from 10−6 to 10−5 . We find that for α = 1/3,
the resulting change in luminosity is at the percent level for χc < 10−6 . However for χc between
16. – 16 –
5 × 10−6 − 10−5 , the shell becomes unscreened and the luminosity changes rapidly, falling by 20%
to over 50% in this range. The change in distance that would result is detectable – a fact used in
the comparison of TRGB and maser distances below. Table 2 gives the change in inferred distance
∆d/d for different values of χc .
The TRGB data used here is taken from the literature and involves many telescopes, including
WFPC2/ACS on board the Hubble Space Telescope, the 5m Hale telescope at Palomar Observatory,
Isaac Newton Telescope Wide Field Camera, Wisconsin Indiana Yale NOAO 3.5m telescope, VLT
etc. The photometry on these images was done using the DAOPHOT and/or ALLFRAME (Stetson
1987, 1994) packages. The observed magnitudes are corrected for foreground extinction. Methods
like Sobel edge-detection (Lee, Freeman & Madore 1993), maximum likelihood (M´ndez et al.
e
2002) etc. were used to estimate the TRGB magnitude. We classify the galaxies into screened and
unscreened samples as for the cepheids.
5. Results: Constraints on Gravity Theories with Cepheid and TRGB Distances
Fig. 4.— Left panel: A comparison of distances measured using the cepheid P − L relation and
TRGB luminosities. The black points are for screened galaxies and the red points for unscreened
galaxies. Middle panel: ∆d/d, the fractional difference between cepheid and TRGB distances, as
a function of TRGB distance. The shaded region in the middle panel shows the 68% confidence
region around our best fit to the unscreened sample (red line). The best fit to the screened sample is
shown by the dashed black line. The data are consistent with the GR expectation of zero deviation
in distance and there is no visible trend in the deviation with whether the galaxy is screened or
not. The dotted and dashed green lines show two possible predictions of chameleon theories with
αc = 1, χc = 4 × 10−7 and αc = 1/3, χc = 1 × 10−6 which corresponds to f (R) gravity. Right panel:
As checks on systematic errors and model uncertainties, the four lines show the best fits obtained
with other choices for the screening threshold or metallicity correction – see text for details. These
lines lie within the 68% confidence region shown in the middle panel.
We began with a sample of 27 galaxies with both TRGB and cepheid distances taken from
17. – 17 –
Table 3: Best fit values for ∆d/d and uncertainty σ in the fractional difference between cepheid and
TRGB distances, for screened and unscreened subsamples. Our estimated σ includes systematic
errors; the number of galaxies N and reduced χ2 is also given.
Sample N ∆d/d σ Reduced χ2
Unscreened 13 0.003 0.017 1.0
Screened 12 -0.005 0.022 1.3
the literature compiled by Madore & Steer using NED6 . This sample includes 12 galaxies from the
Hubble Space Telescope Key Project (Freedman et al. 2001). Other galaxies in their sample do not
have TRGB distance measurements. For many galaxies more than one measurement exists both
for TRGB and cepheid based distances. We use bootstrap resampling to obtain the average and
error bars on those measurements. We exclude one galaxy with TRGB distance beyond 10 Mpc
and another galaxy (DDO 187) which has only two confirmed cepheids. This leaves us with 25
viable galaxies.
We perform a likelihood analysis on the data to estimate the best fit value of ∆d/d. The best
values and 1-σ errors are given in Table 3 along with the reduced χ2 . We included empirically
estimated systematic errors in the estimate of the distance to each galaxy from multiple measure-
ments, as well as in the average deviation ∆d/d for each subsample of galaxies. For the latter we
made the ansatz that each galaxy has an additional unknown systematic error that can be added
in quadrature to the reported error. By further assuming that the systematic error was the same
for each galaxy, we could estimate σsys iteratively such that the reduced χ2 was unity. We found
that the systematic error thus estimated is subdominant for the majority of galaxies.
We have tested our estimate of statistical and systematic errors by using several different
methods of weighting the multiple distance measurements for each galaxy, of outlier rejection and
bootstrap resampling. The various estimates lie within the 1-σ interval shown and generally tend
to deviate towards positive values (i.e. further away from the MG predictions; see below). Note
that for higher values of χc the TRGB distances are also affected in a way that increases ∆d: the
inferred distance would be larger in modified gravity since the peak luminosity is lower. So the
predicted deviation from cepheid distances increases for χc > 10−6 .
∼
Figure 4 shows the cepheid distance vs. the TRGB distance for this sample of galaxies,
separated into screened (black points) and unscreened (red points) subsamples. The middle and
right panels show ∆d/d, the fractional difference between the cepheid and TRGB distances. The
shaded region in the middle panel shows the 68% confidence region around our best fit (red line) for
the unscreened sample. The dashed black line shows the best fit for the screened sample – it nearly
6
http://ned.ipac.caltech.edu/level5/NED1D/ned1d.html
18. – 18 –
overlaps the red line. Clearly the screened and unscreened samples are consistent. The two green
lines show the predictions for chameleon theories with coupling strength αc = 1/3, 1 and values of
χc as indicated. The two models shown are ruled out at over 95% confidence.
In the right panel of Figure 4 we show some alternate estimates of ∆d/d. Since our estimate
of the Newtonian potential due to neighbours is subject to uncertainties in the galaxy catalogue,
we show two other screening criteria, labelled A and B, with threshold ΦN = 2 × 10−7 and 1 × 10−6
(our fiducial choice is 4 × 10−7 ). We also show the result obtained using the full sample of galaxies
(labelled All). The three best fits are within the 68% confidence region of the middle panel, in
fact they deviate in the opposite direction from the MG model predictions. This indicates that
variations in the screening criterion, as required for other choices of chameleon theory parameters
or for symmetron screening, do not weaken our result. We also show the best fit obtained using
a simple average over the best 4 measurements per galaxy (B4). Finally the best fit value using
the metallicity correction of Sakai et al (2004) is also shown (Z-corr). The majority of the distance
estimates we used did not attempt such a correction. We have not used it in our fiducial best
fit since there is a slight correlation of metallicity with level of screening which may introduce
correlations with the signal; moreover the goodness of fit for our sample did not improve with the
Sakai et al metallicity correction. With a large enough sample of galaxies, one can attempt to
create screened and unscreened subsamples that have similar metallicity distributions and thus do
a controlled metallicity correction.
We note that cepheid and TRGB distances are calibrated using cepheids with parallaxes and
TRGB stars in globular clusters in the Milky Way. Thus we rely on the Milky Way being screened
in using them as tests of gravity in unscreened galaxies. This means that, as for other astrophysi-
cal/cosmological tests, the constraints we obtain for large values of χc (above about 10−6 ) require
an unconventional interpretation of screening to satisfy solar system tests of gravity, such as a
significant effect of the mass distribution of the Local Group. On the other hand, if somehow say
TRGB stars in the Milky Way were unscreened, thus implying that the TRGB distances in our
sample were calibrated with an unscreened luminosity relation, then there would be strong devia-
tions with stellar mass and host galaxy environment (large groups or clusters) that are likely ruled
out by current data.
5.1. Constraints on chameleon theories
Figure 5 summarizes our constraints on chameleon theories. In the αc -χc plane, we plot the
regions excluded at 68% and 95% confidence with the light and dark shaded regions. We have made
some approximations in obtaining this plot, especially in our criteria for screened and unscreened
galaxies: we use a fiducial choice αc = 1/3 and vary the subsamples as χc varies. The relatively
small number of galaxies available is responsible for the jaggedness in the contours. We assume
that the environmental screening criterion is not sensitive to the value of αc directly. While αc is
expected to change the thickness of the shell around screened objects, observable stars are located
19. – 19 –
well inside the galaxy halo. For our test, the best fit is very robust to the choice of the unscreened
sample, as evident from the right panel of Figure 4: essentially we cannot find any selection of
galaxy subsamples that correlates with screening and produces a statistically significant deviation
from GR.
We have also tested the results shown in Figure 5 with different screening criteria and several
methods of estimating systematic errors as described above: the 95% confidence contour is robust
to all our tests, while the 68% confidence contour can vary somewhat. A larger galaxy sample and
detailed theoretical calculations are required to obtain a more rigorous version of Figure 5.
We summarize our limits for two specific choices of αc :
• αc = 1/3: Upper limit at 95% confidence: χc ≈ 5 × 10−7
• αc = 1: Upper limit at 95% confidence: χc ≈ 1 × 10−7 .
These limits correspond to a background Compton wavelength of ∼ 1 Mpc for the models discussed
in the literature (e.g. Schmidt, Vikhlinin and Hu 2009). The very short range of the scalar force
implies an extremely limited modification of gravity, i.e. a fine tuned model. The limits on both
parameters can be extended further in the near future with additional analysis and forthcoming
data on cepheids.
Limits from cosmological tests on the background field value are over two orders of magnitude
weaker than the limits obtained here. The cosmological analysis of f (R) gravity (including SN +
CMB + ISW + cluster data) done by Schmidt et al (2010) and Lombriser et al (2010) gives the upper
limit χc ≈ 10−4 for αc = 1/3. This limit is also indicated in Figure 5. The constraining power comes
mostly from galaxy cluster counts. The constraints on gravity by Reyes et al (2010) that use the test
proposed by Zhang et al (2007) do not constrain χc ∼ 10−4 even at 68% confidence. Cosmological
tests have not been used probe values of αc other than 1/3. While our local astrophysical tests
are more powerful for chameleon theories, it is worth noting that more generally any probe of
gravity in a distinct regime of length scale and redshift is valuable – in that sense the local tests
are complementary to cosmological tests.
5.2. Constraints on Symmetron Theories
The symmetron screening model has some qualitative similarities to chameleon screening (see
Appendix A). Hinterbichler and Khoury (2010) showed that solar system tests place constraints on
parameters of symmetron cosmology that are analogous to αc and χc . Clampitt, Jain & Khoury
(2011) computed the screening profile of galaxy halos of different masses. To translate our results
to symmetron models, we use the following relation of our parameters to those of Clampitt et
al: χc ≡ 1/2(Ms /MPlanck )2 and αc = 2g 2 . Solar system tests set the constraint χc < 10−6 or
∼
20. – 20 –
Ms < 10−3 MPlanck for g = 1 and a Compton wavelength of ∼ 1 Mpc (Hinterbichler & Khoury
∼
2010).
Our upper limit for the fiducial symmetron model described above is χc < 3 × 10−7 . We can
∼
extend our results for other values of αc to the symmetron parameters as well. We do not pursue a
more detailed analysis here as it would require the screening condition to be worked out carefully for
the symmetron case. We do use the mapping from chameleon to symmetron self-screening described
in Clampitt, Jain & Khoury (2012) but the environmental screening needs to be considered more
carefully (Joseph Clampitt, private communication).
5.3. Additional Tests of Gravity with Cepheids
We have not considered some additional gravity tests that are possible with distance indicators.
These include the following.
• The location of the instability strip and other properties of cepheids (size, luminosity and
pulsation amplitude) are affected by modified gravity. With more detailed theoretical predic-
tions, these provide additional tests (Sakstein et al., in preparation).
• Variation of the slope of the P − L relation and its dependence on filter. Since the periods
of massive cepheids are affected more strongly, the P − L relation should have a shallower
slope for unscreened galaxies. A second effect arises from the steeper slope of the P − L
relation in the IR – this means that the inferred distance would be smaller in the IR. We see
no hints of a signal with the limited available data, but a useful tests requires significantly
more observations with Spitzer and other IR instruments.
• The variation of estimated distance with cepheid mass and temperature and with the degree
of screening of the host galaxy. These would require detailed theoretical predictions, a high
resolution screening map for different galaxies and a far more detailed analysis of observations
than we have performed.
6. Masers and Other Distance Indicators
The comparison of distances from cepheids or TRGB with other methods that rely on self-
screened objects can provide useful tests. Distances obtained using Type Ia Supernovae (SN) are
likely unaffected by MG for χc < 10−4 , while maser distances use a purely geometric method so
∼
they are unaffected by MG. We do not attempt to create a screened vs. unscreened galaxy sample in
this section since maser and SN distances are not available for sufficient numbers of dwarf galaxies.
We rely on the calibration of cepheid or TRGB distances in the Milky Way (taken to be screened
either by its own potential or that of the Local Group) and work in the parameter range where
21. – 21 –
these distances are affected by modified gravity. As discussed above, along with other astrophysical
or cosmological tests, the logic of pursuing constraints at field values χc > 10−6 requires invoking
an unconventional source of screening for the solar system.
6.1. Water Masers and the Distance to NGC 4258
Maser distances are inferred by comparing the rotation velocity and proper motion (angular
velocity) of water masers in Keplerian motion around supermassive black holes in spiral galaxies.
Measurement of the centripetal acceleration provides a second distance estimate. NGC 4258 is a
Milky Way sized galaxy at a distance of 7 Mpc. The water masers in this galaxy provide a rotation
velocity of the accretion disk in excess of 1,000 km/s at distances on the order of 0.1-0.3 pc from
the inferred super-massive black hole of mass 4 × 107 M . The two distance estimates obtained
from the maser data are in excellent agreement – see Herrnstein et al (2005) and Humphreys et al
(2008) for recent studies.
A summary of the maser, cepheid and TRGB distance estimates to NGC 4258 following Freed-
man & Madore (2010) is:
NGC4258 Maser : d = 7.2 ± 0.2 Mpc (15)
NGC4258 Maser : d = 7.1 ± 0.2 Mpc (16)
NGC4258 Cepheid : d = 7.18 ± 0.07(statistical) Mpc (17)
NGC4258 TRGB : d = 7.18 ± 0.13 ± 0.40 Mpc (18)
There are several caveats to the above tabulation, especially for the cepheid distance which does
not include systematic errors, but a full discussion is beyond the scope of this paper (see Benedict
et al 2007; di Benedetto et al 2008 and Mager, Madore & Freedman 2008 for recent cepheid distance
estimates). We note that the distances agree within estimated errors that are at the few percent
level for the maser distances and (allowing for systematics) at the 5-10% level for cepheid and
TRGB distances.
The agreement of TRGB and water maser distances probe field values χc above 10−6 – the
precise range probed depends on the value of αc and the typical mass of the star. Specifically
for α = 1/3, χc > 4 × 10−6 and a typical star of mass 1.5M the TRGB luminosity is smaller
by over 20%, corresponding to an inferred distance that is larger by over 10%. Thus given the
measurements above, f (R) models with this parameter range are excluded. Note that the maser
distance is purely geometric: it is a ratio of velocities or a combination of velocity and accelerations
that is independent of the strength of gravity; it is immune to MG effects. Thus higher field values
up to the cosmological upper limit of 10−4 are also excluded since TRGB distances would change
drastically for these values.
The agreement with cepheid distances would probe lower field values but NGC 4258 is a Milky
Way sized galaxy, so for lower field values the galaxy would screen the cepheids. One must wait
22. – 22 –
for future observations of masers in smaller galaxies to probe field values below 10−6 though it is
unclear whether useful maser distances can be found for galaxies with much smaller Newtonian
potentials.
6.2. Other Distance Indicators
Type Ia SN are a valuable distance indicator at cosmological distances where cepheid and
TRGB methods cannot be applied. The energetics of a Type Ia SN is set by the thermonuclear
fusion of Carbon-Oxygen nuclei in the core of the progenitor white dwarf. The emission responsible
for the observed optical light curve comes from the expanding shell in which Nickel nuclei decay into
Iron and release high energy photons that subsequently thermalize. While the Newtonian potential
at the surface of the core is ∼ 10−4 , it is smaller at the distance of the expanding shell. We have
not attempted to use supernovae distances as a test here because SN distances are calibrated using
cepheid distances for a small number of galaxies with both distance indicators available. With a
much larger sample, using a subset of screened galaxies for calibration may make an unscreened
subsample available for tests.
Finally, other widely used distance indicators include Tully-Fisher, Fundamental Plane and
Surface Brightness Fluctuations. The first two methods rely on the dynamics of stars in disk and
elliptical galaxies. The scatter in these methods remains large and their use would require averaging
over large numbers of galaxies. We do not pursue these methods here.
7. Discussion
We have used low-redshift distance indicators to carry out tests of scalar-tensor gravity theories.
In particular, since different distance indicators operate in gravitational fields of different strengths,
their screening behavior varies. A comparison of distance estimates from cepheids, TRGB stars and
other distance indicators in nearby dwarf galaxies can provide powerful tests of gravity. The results
shown here are applicable to chameleon theories (including all f (R) models) and we have shown
rough constraints on symmetron screening as well. Indeed, with the notable exception of theories
that use Vainshtein screening, a generic scalar-tensor gravity theory is likely to be constrained by
our analysis. Our tests also constrain scalar field couplings to matter that may arise in dark energy,
string theory or other scenarios.
Cepheid variables are the least compact of the distance indicators considered here – the am-
plitude of the surface Newtonian potential is typically ΦN ∼ 10−7 (for TRGB stars the relevant
ΦN > 10−6 ). Thus in unscreened galaxies, cepheids may experience enhanced forces due to the
∼
scalar field – this will lower the inferred cepheid distance compared to screened distance indica-
tors. It turns out that the deviation of the inferred distance for cepheids and TRGB stars is in
opposite directions, so for field values in which both are unscreened they would show even larger
23. – 23 –
Fig. 5.— Upper limits on the two parameters of chameleon theories: the coupling parameter αc
and the background field value χc . The boundaries of the shaded regions show the upper limits at
68% and 95% confidence level. These are obtained using an interpolation of our tests for the two
gravity parameters as discussed in the text. The effects of discreteness are due to the small sample
of galaxies used. The upper end of the y-axis is extended to χc = 10−4 to show the upper limit
from cosmological+cluster constraints which was obtained for the f (R) model parameter fR0 ≡ χc
with αc = 1/3.
discrepancies.
We have shown that current data is consistent with GR and is inconsistent with chameleon
theories over a parameter range that is more than two orders of magnitude below previous astro-
physical tests. Figures 4 and 5 show our upper limits for the two parameters: the coupling αc and
the background field value χc . For chameleon theories with αc = 1/3 (all f (R) models) the upper
limit on χc is about 5 × 10−7 at 95% confidence. We show results for values of αc in the range
0.1 − 1. The upper limit on χc drops just below 10−7 for αc = 1. The comparison of maser and
TRGB distances to NGC 4258 provides an independent test of field values χc > 2 × 10−6 .
Cosmological observations so far have probed field values larger than 10−4 (Reyes et al 2010;
Schmidt, Vikhlinin & Hu 2009; Lombriser et al 2010 and references therein). Thus our limits
exceed the combined analysis of cosmological probes by over two orders of magnitude. Our upper
limits also exceed solar system and lab tests for some range of chameleon potentials (see e.g. the
discussion in Hu & Sawicki 2007 on the comparison of field values in galaxies vs. local tests). With
24. – 24 –
better data on distance indicators, lower values of αc and χc can be tested, though going much
below αc ≈ 0.1 or χc ≈ 10−7 will be difficult (due to systematic errors and the self-screening of
cepheids, respectively). Observations of nearby dwarf galaxies may probe lower field values, which
we explore in a separate study (Vikram et al, 2012). We note that theoretical considerations have
also been shown to limit acceptable chameleon theories by treating them as effective theories and
requiring small quantum corrections (Upadhey, Hu & Khoury 2012; see also Faulker et al 2007).
Thus the primary advantages of local astrophysical tests such as ours are as follows. 1. The
signal is stronger – it can be a large fraction of the maximum force modification due to the scalar
field. In contrast, the effect on the growth of cosmological fluctuations is typically much smaller.
2. Constraints are more general and translate directly to the two key parameters of the theories.
3. The availability of a control (screened) sample enables robustness to several systematics. 4.
There is almost no degeneracy with other cosmological parameters or assumptions. The primary
disadvantage is the presence of astrophysical uncertainties: metallicity, galaxy age and stellar
population, extinction and so on. However many of these systematics do not affect our tests
at lowest order since all our tests are relative, as discussed above (this allows us to carry out tighter
tests than say the distance ladder which requires an absolute calibration).
Nevertheless there are three significant sources of uncertainty in our analysis: an incomplete
modeling of the theory, systematic errors in the data, and approximations used in determining
the screening level of the host galaxies. We have used results reported in the literature on high
quality distance measurements, as summarized in Freedman & Madore (2010). We attempted
to use multiple weightings of the data as well as different estimates of systematic errors to test
for the robustness of our conclusions. Even so, we note that the data is inhomogeneous and our
understanding of the underlying systematics is limited. Ideally by starting with data on individual
cepheids a more careful and complete analysis can be performed.
There are a number of open questions for theoretical work that can sharpen the tests reported
here and enable new tests. Predictions for the screening level and effective G in symmetron/dilaton
screening scenarios would enable these theories to be tested in detail with the same datasets.
Non-adiabatic numerical models of cepheid pulsations are needed to improve on the approximate
predictions made here. We have recently learnt that the predicted deviations of the period that we
have used are close to estimates with such numerical models (which in fact appear to be slightly
higher – P. Chang and H. Saio, private communication). Several additional tests can be carried
out with complete theoretical models that incorporate MG, as discussed in §5.3.
These observational phenomena have been known for a long time – here we have demonstrated
a new use for them as tools for testing gravity. Future observations designed with this in mind
could obtain more powerful constraints on these theories. Cepheid and TRGB distances to dwarf
galaxies out to about 20 Mpc, in a variety of screening environments, are needed to check against
relative systematics and improve constraints on gravity. In this respect it would be prudent to carry
out new analyses that are designed to be immune to “confirmation bias”. Infrared observations of
25. – 25 –
the cepheid P − L relation can provide a strong new test through the variation of slope of the P − L
relation as discussed above. Currently, there is only one galaxy with simultaneous cepheid, TRGB
and maser measurements. Maser distances to additional galaxies, especially lower mass galaxies,
would strengthen the test described in §6.1. Tests that compare SN and cepheid distances are also
worth pursuing.
Acknowledgements: We are extremely grateful to Bill Paxton for developing and making public
the software package MESA and answering our numerous questions. We are very grateful to Anna
Cabre, Joseph Clampitt, Anne Davis, Lam Hui, Mike Jarvis, Eugene Lim, Hideyuki Saio and
especially Philip Chang for discussions and related collaborative studies. We acknowledge helpful
discussions with Gary Bernstein, Wayne Hu, Justin Khoury, Kazuya Koyama, Adam Lidz, Raquel
Ribeiro, Abhi Saha, Fabian Schmidt, Mark Trodden, Amol Upadhye, Jake VanderPlas and Gongbo
Zhao. BJ is partially supported by NSF grant AST-0908027. JS is supported by the STFC.
A. Scalar-Tensor Modifications of Gravity with Screening mechanisms
The density dependent screening mechanisms that we constrain in this work can arise through
the scalar-tensor action
2
√ mpl 1
S= d4 x g R− µφ
µ
φ − V (φ) + Sm [Ψi ; gµν ],
˜ (A1)
2 2
where Sm denotes the action for the matter fields and Ψi represent all matter species in the system.
This action looks a lot like the usual action for GR except that the matter fields are not coupled to
gravity via the metric but instead via the conformally scaled, Jordan Frame metric gµν = A2 (φ)gµν .
˜
Here A(φ) is an arbitrary function of a new scalar φ which is known as the coupling function. This
action is known as the Einstein frame action since the scalar field φ is coupled non-minimally to the
Ricci scalar. One could instead conformally transform to the Jordan frame where the fields couple
minimally to the metric but the scalar itself is non-minimally coupled to gravity via the Ricci scalar
A−2 (φ)R. In this work we shall work exclusively in the Einstein frame since this is where all of our
physical tests of GR lie. In this frame, matter fields follow geodesics of the gµν whilst observers in
˜
Einstein frame travel along geodesics of gµν and so these observers see an additional or fifth force
given (per unit mass) by (see Waterhouse 2006)
β(φ) d ln A
Fφ = φ where β(φ) ≡ mpl (A2)
mpl dφ
is known as the coupling. There are two methods by which the scalar-tensor screening mechanism
can act. Either the mass of the scalar is very large (the field gradient is small) so that the force
is Yukawa suppressed or the coupling β(φ) is very small and the force is negligible. The first
mechanism is utilised by the chameleon mechanism (Khoury & Weltman 2004), whereas the second
26. – 26 –
is utilised by the symmetron (Hinterbichler & Khoury 2010) and the environmentally dependent
dilaton (Brax et al. 2010)
In this section we shall first describe how these conditions can be achieved in general in the
neighbourhood of our solar system before elucidating this further with some common examples.
A.1. The General Mechanism
Varying the action with respect to the field φ results in the equation of motion
2φ = V,φ − Tm (ln A),φ (A3)
where T is the trace of the energy-momentum tensor in the Einstein frame. In standard GR we
have Tm = −ρ where ρ is the matter density, however, due to the non-minimal coupling to the
scalar field it is the Jordan frame and not the Einstein frame density that is covariantly conserved.
It can be shown (Waterhouse 2006) that the quantity A3 ρ satisfies the non-relativistic continuity
equation and so, taking this as our matter density from here on, equation A3 defines a density
dependent effective potential for φ
Veff (φ) = V (φ) + ρA(φ). (A4)
It is this density dependence of the effective potential that is responsible for the screening mech-
anism. Consider a body of high density (e.g. a star or galaxy) immersed inside a much larger
medium of smaller density (the universe) and suppose that the effective potential has a minimum.
The minimum of the effective potential will lie at different field values depending on the density
and so the field will try to minimise this potential inside both media. If the outer medium is much
larger than the high density one then the field will always reach its minimum at asymptotically large
distances. Theories with screening mechanisms have the property that either the coupling β at the
minimum becomes negligible at high densities or the mass of oscillations about said minimum is
very large. Hence, if the field can minimise its effective potential effectively inside the high density
body then the fifth force will be screened, if this is not possible then the body will be unscreened
and the Newtonian force law will receive order one corrections.
To see this more quantitatively, consider a spherically symmetric body of density ρb immersed
in a much larger medium with density ρc with ρb ρc . Inside the medium, far away from the
body, the field minimises its effective potential at field value φc and inside the body the field may
or may not reach its value which minimises the effective potential, φb . If the object is static i.e. on
changes occur on a time-scale much smaller than the time-scale for cosmological evolution of the
field then equation A3 becomes
2
φ = V (φ),φ + ρA(φ),φ . (A5)
Suppose that the field has reached φb at r = 0. In this case we have V (φ),φ ≈ −ρA(φ),φ so that
equation A5 has no source term and φ ≈ φb . In this case there is no field gradient and the fifth
27. – 27 –
force is not present. Of course the field must asymptote to φc away from the body and so there
must be some radius rs at which this approximation no longer holds and the source terms become
important. In this region the field will posses some gradient and approach its asymptotic values and
so we expect order one fifth forces. rs is hence known as the screening radius; the region interior
to this is screened whilst the exterior region is unscreened. In the unscreened region, the field is
a small perturbation about its cosmological value and so we can linearise equation A5 by setting
φ = φc + δφ to find
2 β(φc )
δφ ≈ m2 δφ +
c δρ (A6)
mpl
where δρ = ρb − ρc and m2 = d2 V (φ)/ dφ2 is the mass of the field in the cosmological vacuum.
c
On length scales R 1/mc i.e. on those far less than the range of the fifth force in vacuum, we
can neglect the first term and the second term can be related to the Newtonian potential via the
Poisson equation 2 ΦN = 4πGδρ. Integrating this twice gives the field in the unscreened region
1 1
2
δφ(r) ≈ −φc + 2βc mpl ΦN (r) − ΦN (rs ) + rs ΦN (rs ) − rs < r m−1 .
c (A7)
r rs
In the theories of interest to us we have φb φc , which sets the boundary condition δφ(rs ) ≈ −φc .
Using this in equation A2, we find the total force per unit mass (Newtonian plus fifth) in the
unscreened region is
G(r)M (r) M (rs )
F = Fφ + FN = where G(r) = G 1 + αc 1 − (A8)
r2 M (r)
2
where αc ≡ 2βc and M (r) is the mass contained inside a shell of radius r. Taking the limit
as r → ∞ in equation A7 gives us an implicit relation for the screening radius in terms of the
Newtonian potential
φc
χc ≡ = −Φ(rs ) − rs ΦN (rs ). (A9)
2mpl β(φc )
The quantity χc controls the ability of objects to self screen. Clearly if the surface Newtonian po-
tential ΦN (R) < χc then equation A9 can never be satisfied and the body is completely unscreened
(rs = 0) whilst if the converse is true then the body will be at least partially screened. If the body
is completely unscreened then equation A8 gives us an order one enhancement of the Newtonian
force by a factor (1 + αc ).
We can see that whereas βc and V (φc ) are the more fundamental of the parameters, it is
the combinations αc and χc which ultimately sets the overall force enhancement and degree of
screening and so it is these parameters which our tests of modified gravity constrain. Specific model
parameters map into these in straight forward manner and so by working with these combinations
we can place constraints in a model independent way. This is extremely useful when the fundamental
theories often have more than two parameters, which is often the case.
In this work we shall not be concerned with demanding that the field also acts as dark energy
however, for completeness, we note here that big band nucleosynthesis constraints (BBN) require
28. – 28 –
that the cosmological field remains at the minimum of the effective potential from BBN onwards
and so the expansion history is indistinguishable from that of ΛCDM (structure formation breaks
this degeneracy).
A.2. Some Common Examples
A.2.1. Chameleon Screening
Any theory where the coupling function A(φ) is a monotonically increasing function of φ falls
into the class of chameleon theories. The chameleon mechanism operates by exploiting the density
dependence of the mass of the scalar field; in high density environments the mass is large and the
force is very short ranged (Yukawa suppressed) whilst in low density (cosmological) environments
the force range can be very large. It is this mass blending in with its environment that gives rise
to its name. If the field can indeed reach its minimum at the centre then this large mass ensures
that it remains there and varies only in a thin shell near the surface. This has the effect that the
force exterior to the object receives contributions from flux lines within this thin shell only and not
the entire body and is hence suppressed by a small factor ∆R/R ≈ φc /6mpl βc ΦN (R); a phenomena
dubbed the thin shell effect.
In the original models (Khoury & Weltman 2004) β(φ) is a constant (A(φ) = Exp[βφ/mpl ]),
however many other models exist in the literature (Gubser & Khoury (2005); Brax et al. (2010a)
and Mota & Winther (2011)). Our most robust constraints apply to f (R) theories, which are
√
chameleon theories for certain choices of the function f (Brax et al. 2008) with constant β ≡ 1/ 6
so that αc ≡ 1/3 and χc arbitrary. Recently, a new unified parametrisation has been discovered
(Brax, Davis and Li 2011, Brax et al. 2012) where theories with screening mechanisms can be
reverse engineered by specifying a functional form of the cosmological mass and coupling in terms
of the scale factor. It would be interesting to repeat our analysis using this unified description and
this is left for future work.
There are a wide range of models and parameters that can act as dark energy (Brax et al.
2003; Gannouji et al. 2010; Mota et al. 2011), although some of these have be ruled out using
current laboratory searches for fifth forces (see Mota & Shaw 2006).
A.2.2. Symmetron Screening
Symmetron screening (Khoury & Hinterbichler 2010) relies on symmetry restoration in high
density environments to drive the coupling to zero and render the force negligible. The simplest
model (see Brax et al. 2012 for more general models) uses a Z2 symmetric potential and coupling
29. – 29 –
function given by
1 λ φ2
V (φ) = − µ2 φ2 + φ4 ; A(φ) = 1 + , (A10)
2 4! 2M 2
which results in the coefficient of the quadratic term in the effective potential being density depen-
dent:
1 ρ λ
Veff (φ) = − µ2 φ 2 + φ 4 . (A11)
2 M2 4!
In low density environments this coefficient is negative and the field vacuum expectation value
(VEV) at the minimum is non-zero-spontaneously breaking the symmetry-whilst in high density
environments the symmetry is restored and the VEV moves to zero. The coupling is given at
leading order by β ∝ φ and so the force enhancement is negligible in high density regions. The
requirement that the cosmic acceleration begins in our recent past constrains the parameter µ,
resulting in a force range of O(M pc) at most and so the symmetron cannot account for dark energy
without the inclusion of a cosmological constant (Hinterbichler et al. 2011; Davis et al 2011b).
B. TRGB Distances in Modified Gravity
In this section we briefly show how inferred TRGB distances can be greater than the true value
if the core of the star is unscreened. The luminosity of a star ascending the red giant branch is due
entirely to a very thin hydrogen burning shell just above the helium core. The triple alpha process
ignites in a process known as the helium flash at temperatures T ∼ 108 K and so for temperatures
below this the core has no source of outward pressure and contracts. As the star climbs further the
radius of the core decreases whilst the mass increases due to fresh helium being deposited by the
shell. This results in a gradual increase until the core temperature is high enough to begin helium
burning, at which point the star moves to the left in the H-R diagram. In GR, this sudden jump
to the left occurs at a fixed luminosity, however, as we shall see below, this luminosity at the tip is
lower in MG, provided that the core is unscreened.
Treating the core as a solid sphere of fixed temperature Tc , mass Mc and luminosity L, the
hydrogen burning shell is incredibly thin and can be treated as having constant mass and luminosity.
In this case, the shell pressure and temperature is given by the hydrostatic equilibrium and radiative
transfer equations,
dP GMc ρ(r) dT 4 3 κ(r)ρ(r)L
=− ; = (B1)
dr r2 dr 4a 4πr2
which can be used to find
GMc T 4
P ∝ , (B2)
L
where the opacity in the hydrogen shell is due mainly to electron scattering and so we have taken
it to be constant. The pressure in the shell is due mainly to the gas and so we ignore radiation
pressure and take the equation of state to be that of an ideal gas, P ∝ ρT . Using this and equation
30. – 30 –
B2 in the radiative transfer equation we find
GMc
T (r) ∝ , (B3)
r
where the integration constant is negligible near the base of the shell. Next, we can estimate the
luminosity given an energy generation rate per unit mass ∝ ρ(r)T (r)ν
L= 4πr2 ρ(r) (r) dr. (B4)
For temperatures above 107 K, which is the case in the shell, hydrogen burning proceeds mainly
via the CNO cycle and so ν = 15. Using the equation of state and the results above in equation
B4 one finds 8
G 3 Mc 7.7
L∝ 6
. (B5)
Rc
Now suppose that the core or shell becomes unscreened so that G(r) ≈ G(1 + αe ) where αe
is the effective value of αc given by equation A8. The He flash occurs at a fixed temperature,
independent of MG, and so if we set ξ = Mc /Rc at the point when Tc = 108 K then we have
ξMG /ξGR = (1 + αe )−1 < 1. The ratio of the core mass to the core radius at the He flash in MG
is then lower than that in GR. In general, this does not tell us anything about the core mass and
radius individually, however, in practice one finds that the core radius is the same in both cases
(this is borne out by MESA simulations) and so this is a relation between the core masses at fixed
temperature. Using equation B5 we then have
LMG 1
= (B6)
LGR (1 + αe )5
and hence the peak luminosity is lower in MG, contrary to what one would expect if the argument
that radii are generally smaller in MG is followed.
To infer distances using the TRGB method, one observes the flux (∝ L/d2 ) and uses the
(nearly) universal luminosity at the tip. If the star is indeed unscreened then its luminosity in MG
is lower than the universal value assumed, so one would over-estimate the distance.
31. – 31 –
C. Data
Table 4: The galaxies used in the P − L relation and their references. The second column labelled
N gives the number of cepheids observed for each galaxy. Names that end with * are galaxies with
unacceptably large dispersion in P-L relation.
Name N Reference
NGC300 117 Pietrzy´ski et al. (2002)
n
NGC5253 5 Saha et al (2006)
IC4182 13 Saha et al (2006)
NGC925 79 Silbermann et al (1996)
NGC2541 28 Ferrarese et al. (1998)
NGC3319 28 Sakai et al. (1999)
NGC1326A 17 Prosser et al. (1999)
NGC 2090 34 Phelpset al. (1998)
NGC 3031 25 Freedman et al. (1994)
NGC 3198 52 Kelson et al. (1999)
NGC 3351* 49 Graham et al. (1997)
NGC 3621* 69 Rawson et al. (1997)
NGC 4321* 52 Ferrarese et al. (1996)
NGC 4414* 9 Turner et al. (1998)
NGC 4535 50 Macri et al. (1999)
NGC 4548* 24 Graham et al. (1999)
NGC 4725 20 Gibson et al. (1999)
NGC 5457 29 Kelson et al. (1996)
NGC 7331 13 Hughes et al. (1998)
32. – 32 –
Table 5: Cepheid and TRGB based distances to the galaxies used in the paper. The final column
gives the screening for φ = 4 × 10−7 as follows: 0: Unscreened, 1: environmentally screened, 2:
self-screened.
Name Cepheid D(Mpc) TRGB D (Mpc) Screening
DDO 069 0.71 ± 0.01 0.78 ± 0.03 0
NGC 3109 1.15 ± 0.03 1.27 ± 0.02 0
DDO 216 1.27 ± 0.27 0.97 ± 0.03 0
Sextans A 1.31 ± 0.03 1.38 ± 0.03 0
Sextans B 1.49 ± 0.11 1.34 ± 0.02 0
GR8 1.80 ± 0.06 2.19 ± 0.15 0
NGC 0300 2.03 ± 0.05 1.95 ± 0.06 0
NGC 2403 3.20 ± 0.15 3.18 ± 0.35 0
NGC 2366 3.28 ± 0.30 3.19 ± 0.41 0
NGC 5253 3.43 ± 0.08 3.77 ± 0.19 0
NGC 4395 4.45 ± 0.37 4.61 ± 0.62 0
IC 4182 4.68 ± 0.04 4.47 ± 0.12 0
NGC 3621 7.17 ± 0.06 7.45 ± 0.38 0
SMC 0.06 ± 0.00 0.06 ± 0.00 1
NGC 6822 0.51 ± 0.03 0.48 ± 0.01 1
IC 1613 0.69 ± 0.01 0.72 ± 0.01 1
IC 0010 0.72 ± 0.05 0.50 ± 0.04 1
M33 0.90 ± 0.02 0.88 ± 0.02 1
WLM 0.95 ± 0.05 0.91 ± 0.02 1
M31 0.86 ± 0.02 0.78 ± 0.02 2
NGC 5128 3.44 ± 0.19 3.73 ± 0.24 2
M81 3.84 ± 0.06 4.04 ± 0.22 2
M83 5.01 ± 0.23 4.51 ± 0.31 2
M101 7.13 ± 0.14 7.66 ± 0.39 2
M106 8.41 ± 0.07 7.31 ± 0.30 2
33. – 33 –
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