This document describes measurements of the solar radius taken from images of the 2003 and 2006 transits of Mercury captured by the Michelson Doppler Imager aboard the Solar and Heliospheric Observatory. The authors measured contact times between Mercury and the solar limb to an accuracy of 0.09 arcseconds, finding a solar radius of 960”.12 ± 0”.09 or 696,342 ± 65km. This value is consistent between the two transits and after accounting for systematic effects between different instrument focus settings. The measurements represent some of the most accurate to date due to being taken from space above the Earth's atmosphere.
Solar limb darkening_function_from_baily_beads_observationsSérgio Sacani
This document presents a new method for measuring the solar limb darkening function using observations of Baily's beads during solar eclipses. The method involves analyzing the light curve profiles of emerging and disappearing Baily's beads to determine the surface brightness profile of the outer solar atmosphere with high resolution. The method is applied to eclipse videos from 2010, yielding constraints on the position of the limb darkening function inflection point between -0.190 and +0.050 arcseconds. The results suggest reconsidering evaluations of historical eclipses that assumed a step function profile for the limb darkening.
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.
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.
This study uses asteroseismology to reveal fast core rotation in red giant stars, finding that the cores rotate at least 10 times faster than the surface by analyzing rotational splitting of mixed modes. Mixed modes that probe the core show larger rotational splitting than modes dominated by the outer layers, indicating non-rigid rotation that increases towards the stellar interior. Models are able to reproduce the observations, confirming theoretical predictions of a steep rotational gradient within red giant cores.
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
This document discusses a study that used difference imaging techniques to search for variable stars and microlensing events in the elliptical galaxy Centaurus A. The study obtained deep photometric data over almost two months using the Wide Field Imager on the ESO/MPG 2.2 m telescope. It detected 271 variable stars in Centaurus A with a detection limit of magnitude 24.5. Based on a simple model of Centaurus A's halo, the study estimated it could detect around 4 microlensing events per year, but a higher sensitivity is needed for a meaningful microlensing survey. The spatial distribution of any microlensing events could help constrain the shape of Centaurus A's dark matter halo.
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
Discovery of a_probable_4_5_jupiter_mass_exoplanet_to_hd95086_by_direct_imagingSérgio Sacani
The document reports the discovery of a probable 4-5 Jupiter-mass exoplanet orbiting the young star HD 95086. Deep imaging observations using VLT/NaCo detected a faint source at a separation of 56 AU from the star. Follow-up observations over more than a year found the source to be co-moving with the star, suggesting it is bound. Its luminosity corresponds to a predicted mass of 4-5 Jupiter masses, making it the lowest mass exoplanet directly imaged around a star. If confirmed, this discovery could provide insights into giant planet formation and evolution.
Solar limb darkening_function_from_baily_beads_observationsSérgio Sacani
This document presents a new method for measuring the solar limb darkening function using observations of Baily's beads during solar eclipses. The method involves analyzing the light curve profiles of emerging and disappearing Baily's beads to determine the surface brightness profile of the outer solar atmosphere with high resolution. The method is applied to eclipse videos from 2010, yielding constraints on the position of the limb darkening function inflection point between -0.190 and +0.050 arcseconds. The results suggest reconsidering evaluations of historical eclipses that assumed a step function profile for the limb darkening.
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.
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.
This study uses asteroseismology to reveal fast core rotation in red giant stars, finding that the cores rotate at least 10 times faster than the surface by analyzing rotational splitting of mixed modes. Mixed modes that probe the core show larger rotational splitting than modes dominated by the outer layers, indicating non-rigid rotation that increases towards the stellar interior. Models are able to reproduce the observations, confirming theoretical predictions of a steep rotational gradient within red giant cores.
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
This document discusses a study that used difference imaging techniques to search for variable stars and microlensing events in the elliptical galaxy Centaurus A. The study obtained deep photometric data over almost two months using the Wide Field Imager on the ESO/MPG 2.2 m telescope. It detected 271 variable stars in Centaurus A with a detection limit of magnitude 24.5. Based on a simple model of Centaurus A's halo, the study estimated it could detect around 4 microlensing events per year, but a higher sensitivity is needed for a meaningful microlensing survey. The spatial distribution of any microlensing events could help constrain the shape of Centaurus A's dark matter halo.
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
Discovery of a_probable_4_5_jupiter_mass_exoplanet_to_hd95086_by_direct_imagingSérgio Sacani
The document reports the discovery of a probable 4-5 Jupiter-mass exoplanet orbiting the young star HD 95086. Deep imaging observations using VLT/NaCo detected a faint source at a separation of 56 AU from the star. Follow-up observations over more than a year found the source to be co-moving with the star, suggesting it is bound. Its luminosity corresponds to a predicted mass of 4-5 Jupiter masses, making it the lowest mass exoplanet directly imaged around a star. If confirmed, this discovery could provide insights into giant planet formation and evolution.
A young protoplanet_candidate_embedded_in_the_circumstellar_disk_of_hd100546Sérgio Sacani
This document summarizes observations of HD100546 using high-contrast imaging techniques. A faint emission source was detected near the star at a projected separation of about 47 AU. The position of the source coincides with a deficit in polarization observed from the circumstellar disk. This suggests a physical link between the source and the disk. Considering various scenarios, the authors favor interpreting the source as a young protoplanet currently forming within the disk. Follow-up observations could distinguish between different possible explanations for the observed features. If confirmed, it would be a unique opportunity to study giant planet formation within an optically thick disk.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
The ALMA observations of the Fomalhaut debris disk resolve the ring of parent bodies that produce the dust. The parent body ring has a sharp inner edge at 135 AU and outer edge at 151 AU, giving it a width of 16 AU. The ring has a vertical scale height corresponding to an opening angle of 1 degree. The observations are consistent with the ring being confined by shepherd planets. The dust in the ring has a total mass of 0.017 Earth masses, requiring the parent body population to be at least 1.7 Earth masses.
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.
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
Non xrays from_the_very_nearby_typeia_sn_2014j_constraints_on_its_environmentSérgio Sacani
Deep X-ray observations of SN 2014J reveal no X-ray emission down to a luminosity limit of Lx < 7 × 1036 ergs−1, constraining the mass-loss rate of the progenitor system to be < 10−9 M☉/yr. Alternatively, the SN shock could be expanding into a uniform medium with density < 3 cm−3. These results rule out single-degenerate systems with steady mass transfer until explosion and constrain unstable hydrogen burning systems to have recurrence times < 300 years. Allowed progenitors include double white dwarf systems or systems where mass transfer ceased before explosion.
Rapid formation of large dust grains in the luminous supernova SN 2010jlGOASA
This document summarizes observations of rapid dust formation in the luminous supernova SN 2010jl over multiple epochs from 26 to 868 days past peak brightness. Analysis of emission line profiles shows increasing extinction over time, indicating continuous dust formation. The extinction curve implies the presence of very large (>1 micron) dust grains. Thermal emission models suggest dust temperatures declining from 2300K to 1100K over time, requiring carbonaceous rather than silicate dust. Combined extinction and emission data indicate a dust mass of ~0.0025 solar masses at 868 days, growing rapidly and expected to reach ~0.5 solar masses by 8000 days if production continues. The results provide evidence for very efficient and rapid dust formation in the dense
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
This document presents an analysis of transit spectroscopy observations of three exoplanets - WASP-12 b, WASP-17 b, and WASP-19 b - using the Wide Field Camera 3 instrument on the Hubble Space Telescope. The observations achieved almost photon-limited precision but uncertainties in the transit depths were increased by the uneven sampling of the light curves. The final transit spectra for all three planets are consistent with the presence of a water absorption feature at 1.4 microns, though the amplitude is smaller than expected from previous Spitzer observations possibly due to hazes. Due to degeneracies between models, the data cannot unambiguously constrain the atmospheric compositions without additional observations.
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
The long period_galactic_cepheid_rs_puppisSérgio Sacani
This document summarizes an observational study that uses light echoes to determine the geometric distance to the Cepheid variable star RS Puppis. Images of RS Puppis and its surrounding nebula were taken over multiple epochs with the ESO NTT telescope to track the progression of light variations within the nebula. Photometric measurements of the phase lag in several nebula regions were used to derive a geometric distance of 1,992 ± 28 parsecs to RS Puppis, one of the most accurate distances yet measured to a Cepheid variable star.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
This document summarizes VLBI observations of supernova SN 2011dh made 14 days after its discovery, providing the earliest radio image of a supernova. The observations detected SN 2011dh at 22 GHz using a subset of the EVN array. The recovered flux density was approximately half the value measured by the EVLA at the same frequency and epoch, possibly due to extended emission or calibration issues. Precise coordinates for SN 2011dh were determined, linked to the ICRF, which may help improve future VLBI observations of the supernova.
1. Conformal cyclic cosmology (CCC) predicts the existence of concentric circles of anomalously low temperature variance in the cosmic microwave background (CMB) that would provide evidence of violent events prior to the Big Bang.
2. Analysis of WMAP and BOOMERANG CMB data reveals families of concentric circles up to 6 standard deviations below the mean temperature variance, consistent with CCC predictions.
3. These circles are not easily explained by standard inflationary cosmology, as the events that could cause some of the largest circles observed would need to occur before the end of inflation in the previous aeon.
A young protoplanet_candidate_embedded_in_the_circumstellar_disk_of_hd100546Sérgio Sacani
This document summarizes observations of HD100546 using high-contrast imaging techniques. A faint emission source was detected near the star at a projected separation of about 47 AU. The position of the source coincides with a deficit in polarization observed from the circumstellar disk. This suggests a physical link between the source and the disk. Considering various scenarios, the authors favor interpreting the source as a young protoplanet currently forming within the disk. Follow-up observations could distinguish between different possible explanations for the observed features. If confirmed, it would be a unique opportunity to study giant planet formation within an optically thick disk.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
The ALMA observations of the Fomalhaut debris disk resolve the ring of parent bodies that produce the dust. The parent body ring has a sharp inner edge at 135 AU and outer edge at 151 AU, giving it a width of 16 AU. The ring has a vertical scale height corresponding to an opening angle of 1 degree. The observations are consistent with the ring being confined by shepherd planets. The dust in the ring has a total mass of 0.017 Earth masses, requiring the parent body population to be at least 1.7 Earth masses.
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.
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
Non xrays from_the_very_nearby_typeia_sn_2014j_constraints_on_its_environmentSérgio Sacani
Deep X-ray observations of SN 2014J reveal no X-ray emission down to a luminosity limit of Lx < 7 × 1036 ergs−1, constraining the mass-loss rate of the progenitor system to be < 10−9 M☉/yr. Alternatively, the SN shock could be expanding into a uniform medium with density < 3 cm−3. These results rule out single-degenerate systems with steady mass transfer until explosion and constrain unstable hydrogen burning systems to have recurrence times < 300 years. Allowed progenitors include double white dwarf systems or systems where mass transfer ceased before explosion.
Rapid formation of large dust grains in the luminous supernova SN 2010jlGOASA
This document summarizes observations of rapid dust formation in the luminous supernova SN 2010jl over multiple epochs from 26 to 868 days past peak brightness. Analysis of emission line profiles shows increasing extinction over time, indicating continuous dust formation. The extinction curve implies the presence of very large (>1 micron) dust grains. Thermal emission models suggest dust temperatures declining from 2300K to 1100K over time, requiring carbonaceous rather than silicate dust. Combined extinction and emission data indicate a dust mass of ~0.0025 solar masses at 868 days, growing rapidly and expected to reach ~0.5 solar masses by 8000 days if production continues. The results provide evidence for very efficient and rapid dust formation in the dense
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
This document reports the discovery of a newly discovered optical Einstein ring (ER) called the "Canarias Einstein Ring". It was discovered serendipitously in imaging data from the Dark Energy Camera. Follow-up spectroscopy with the Gran Telescopio CANARIAS confirmed the nature of the system, with the lens being an early-type galaxy at a redshift of z=0.581 and the source being a starburst galaxy at z=1.165. Analysis of the system determined the Einstein radius to be 2.16 arcseconds and the total enclosed mass producing the lensing effect to be 1.86 ± 0.23 × 1012 solar masses.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
This document presents an analysis of transit spectroscopy observations of three exoplanets - WASP-12 b, WASP-17 b, and WASP-19 b - using the Wide Field Camera 3 instrument on the Hubble Space Telescope. The observations achieved almost photon-limited precision but uncertainties in the transit depths were increased by the uneven sampling of the light curves. The final transit spectra for all three planets are consistent with the presence of a water absorption feature at 1.4 microns, though the amplitude is smaller than expected from previous Spitzer observations possibly due to hazes. Due to degeneracies between models, the data cannot unambiguously constrain the atmospheric compositions without additional observations.
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
The long period_galactic_cepheid_rs_puppisSérgio Sacani
This document summarizes an observational study that uses light echoes to determine the geometric distance to the Cepheid variable star RS Puppis. Images of RS Puppis and its surrounding nebula were taken over multiple epochs with the ESO NTT telescope to track the progression of light variations within the nebula. Photometric measurements of the phase lag in several nebula regions were used to derive a geometric distance of 1,992 ± 28 parsecs to RS Puppis, one of the most accurate distances yet measured to a Cepheid variable star.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
This document summarizes VLBI observations of supernova SN 2011dh made 14 days after its discovery, providing the earliest radio image of a supernova. The observations detected SN 2011dh at 22 GHz using a subset of the EVN array. The recovered flux density was approximately half the value measured by the EVLA at the same frequency and epoch, possibly due to extended emission or calibration issues. Precise coordinates for SN 2011dh were determined, linked to the ICRF, which may help improve future VLBI observations of the supernova.
1. Conformal cyclic cosmology (CCC) predicts the existence of concentric circles of anomalously low temperature variance in the cosmic microwave background (CMB) that would provide evidence of violent events prior to the Big Bang.
2. Analysis of WMAP and BOOMERANG CMB data reveals families of concentric circles up to 6 standard deviations below the mean temperature variance, consistent with CCC predictions.
3. These circles are not easily explained by standard inflationary cosmology, as the events that could cause some of the largest circles observed would need to occur before the end of inflation in the previous aeon.
The article provides a plausible explanation for reports of red glows seen in the Aristarchus crater on the moon. It details observations from 1963 of reddish spots near Aristarchus seen through a telescope. The authors recreate the illumination conditions and take their own image of the area. Their image shows chromatic dispersion that causes a reddish tint on the western rim of Aristarchus. When the color channels are properly aligned, no color is actually present. They conclude that atmospheric or chromatic dispersion is a logical explanation for the reported red color sightings in Aristarchus described in the 1963 observations.
This document summarizes a study that uses ab initio calculations to examine the solubility of magnesium oxide (MgO) in fluid hydrogen at conditions relevant to giant planet cores like Jupiter. The study finds that MgO is highly soluble in hydrogen for temperatures exceeding around 10,000 K, indicating rocky core materials would significantly redistribute within Jupiter and larger exoplanets. Free energy calculations based on density functional theory molecular dynamics and coupling constant integration techniques were used to determine the Gibbs free energy of solubilizing MgO in hydrogen at pressures from 10 to 40 megabars and temperatures from 10,000 to 20,000 K.
This document appears to be a citation to a 1996 Astrophysical Journal paper with the volume number 458 and page number 600, but it provides no other contextual information about the content or findings of the cited paper. The summary is limited due to the lack of substantive information in the given document.
The document summarizes the first results from an ambitious HARPS program to detect Earth-like planets around nearby solar-type stars using high-precision radial velocity measurements. It reports the discovery of five new low-mass planets around the stars HD 20794, HD 85512, and HD 192310, including a system of three super-Earths and a planet with a mass of 3.6 Earth masses located at the inner edge of the habitable zone. This confirms previous indications that low-mass planets seem to be very frequent around solar-type stars, with an occurrence rate that may be higher than 30%.
Characterizing interstellar filaments with herschel in ic5146Sérgio Sacani
This document summarizes early results from the Herschel Gould Belt survey of the IC5146 molecular cloud. It reveals a complex network of filaments identified in the cloud, which are shown to be the main sites of prestellar core formation. Analysis of 27 filaments finds that their radial column density profiles fall off with radii as r^-1.5 to r^-2.5. Remarkably, the filaments seem to have a narrow distribution of widths centered around 0.1 pc, in contrast to a broader distribution of central Jeans lengths. This characteristic width corresponds to the sonic scale below which turbulence becomes subsonic, supporting the argument that filaments may form from dissipating large-scale turbulence.
This document summarizes the discovery of a luminous quasar (ULAS J112001.481064124.3) with a redshift of z=7.085, located approximately 777 million years after the Big Bang. It has a luminosity of 6.3 x 10^13 solar luminosities and hosts a black hole with a mass of 2 x 10^9 solar masses. The radius of its ionized region is 1.9 megaparsecs, smaller than typical quasars from z=6.0 to z=6.4. Analysis of its spectrum is consistent with a high neutral fraction (>0.1) of the intergalactic medium in front of it. This makes it the most
This document reports on high-resolution images from the MESSENGER spacecraft that reveal unusual landforms on Mercury characterized by irregular, shallow depressions known as hollows. The hollows range in size and are commonly found in clusters associated with high-reflectance materials within impact craters. The most likely formation mechanisms involve recent loss of volatile materials through processes like sublimation or pyroclastic volcanism. These features suggest Mercury's interior contains more volatile materials than predicted, challenging models of the planet's formation.
The document summarizes a study of tungsten isotope ratios in lunar metals. The key findings are:
1) All lunar metal samples studied have identical tungsten isotope ratios within measurement error, indicating the lunar magma ocean did not crystallize within the first 60 million years as previously suggested.
2) Tungsten isotope ratios in lunar metals are identical to those in the Earth's mantle, suggesting the Moon and Earth mantles equilibrated after the giant impact that formed the Moon.
3) Together with previous samarium-neodymium dating of oldest lunar rocks, the results constrain the age of the Moon and Earth to 62 ± 10 million years after solar system formation.
1) Newly-born pulsars offer favorable conditions for accelerating heavy nuclei like iron to ultrahigh energies via unipolar induction. However, these nuclei must escape the surrounding dense supernova envelope.
2) The paper analytically and numerically examines the escape of ultrahigh energy cosmic rays (UHECRs) from supernova envelopes. It finds that at early times when protons could reach energies above 10^20 eV, the envelope prevents their escape. However, heavier iron nuclei can still reach the highest observed energies at later times when the envelope has thinned.
3) The authors conclude that a small fraction (0.01%) of extragalactic rapidly rotating young pulsars embedded in supernov
This article reports the detection of two gas clouds with no discernible elements heavier than hydrogen, representing the lowest heavy-element abundance observed in the early universe. One cloud at z=3.4 exhibits a deuterium abundance matching predictions from Big Bang nucleosynthesis, providing direct evidence for the standard cosmological model. The sparse metal enrichment of these clouds implies an inhomogeneous process for transporting heavy elements from galaxies into the surrounding intergalactic medium.
The document summarizes research on the South Pole-Aitken basin, the largest impact crater on the Moon. It is over 2,500 km in diameter and more than 12 km deep. Spacecraft data show the basin has a higher concentration of iron than surrounding lunar highlands, suggesting it may expose deeper mantle rocks. However, the exact composition is debated, with some researchers arguing mantle rocks are not present based on mineral analysis. Understanding the basin's composition could provide insights into the Moon's interior structure and composition from the impact that formed the giant crater.
The document discusses the training that Apollo astronauts received for making observations and taking photographs from lunar orbit. It summarizes that (1) astronauts were trained to add to scientific knowledge by describing lunar features from their unique viewpoint in orbit, and (2) photographs from orbit could provide regional context for detailed surface exploration findings. The training grew over missions from briefings to extensive classroom sessions. Outstanding results from astronaut observations and photos included realizing limitations of depicting lunar surface colors photographically and discovering previously unknown farside features.
This document reports the detection of a low-mass dark satellite galaxy in a gravitational lens system. Using pixelated lens modeling of adaptive optics images, the researchers detected a positive density correction indicating the presence of a mass substructure. They estimate the mass of the substructure to be 1.9 x 108 solar masses located 600 parsecs from the density peak. Combining this detection with a previous one, they constrain the logarithmic slope of the mass function for dark matter substructure in elliptical galaxies to be 1.1-0.4 with an average mass fraction of 3.3-1.8%. This is consistent with predictions from cold dark matter simulations.
The study examines a post-starburst galaxy outflow using ultraviolet spectroscopy of multiple ions including hydrogen. It finds the outflow extends at least 160,000 light-years from the galaxy and contains a hidden mass of at least 6x10^9 times the mass of our Sun. This challenges previous assumptions about the extent and mass of galaxy outflows, suggesting they may play a larger role in regulating galaxy evolution than thought.
1. Chandra observations of the galaxy NGC 3351 revealed X-ray emission from its circumnuclear star-forming ring that is composed of numerous point-like sources embedded in diffuse hot gas.
2. The morphology of the X-ray emission is similar to but not identical with UV and H-alpha hot spots in the ring, which can be understood if star formation occurs through intermittent starbursts around the ring with different emissions tracing later evolutionary stages.
3. X-ray emission also extends beyond the ring, which is interpreted as outflowing gas from the ring into the disk and halo of NGC 3351, providing evidence for confined outflow near the plane but less restricted outflow perpendicular to
Neowise observations of near earth objects- preliminary resultsSérgio Sacani
The NEOWISE survey observed near-Earth objects at infrared wavelengths, detecting over 130 new NEOs. Analysis of the 428 NEOs detected allows estimates of the total NEO population between 100m and 1km in size. The survey found an estimated 981±19 NEOs larger than 1km have been detected, meeting the Spaceguard goal of detecting 90% of objects this size. It also estimates 20,500±3000 NEOs larger than 100m. The cumulative size distribution is best represented by a broken power law.
Herschel space telescope observations reveal cold dust emitting from Supernova 1987A at a temperature of 17-23 K, indicating a dust mass of 0.4-0.7 solar masses. The dust must originate from the supernova ejecta, requiring efficient precipitation of refractory elements into dust. This implies that supernovae can produce the large dust masses seen in early galaxies.
1. The document analyzes the spatial distribution and size-frequency of rayed impact craters on the Moon using Clementine image data.
2. It finds that the size-frequency distribution of rayed craters indicates an average surface age of 750 million years, with compositional rays potentially persisting longer.
3. Small craters below 5 km in diameter show evidence of faster fading of ejecta rays, with an average retention time of only about 5 million years for craters 1-500m in size.
Detection of visible light from the darkest worldSérgio Sacani
This document reports the detection of visible light from the exoplanet TrES-2b using Kepler photometry data. The analysis finds a day-night contrast amplitude of 6.5 ± 1.9 parts per million, representing the lowest amplitude orbital phase variation discovered. This signal is detected at a confidence level of 99.98% and persists across different models of the data, appearing robust. If interpreted as scattering, it corresponds to a geometric albedo of 0.0253±0.0072 for TrES-2b, making it the darkest exoplanet detected so far. However, models indicate significant day-side emission, implying an even lower true albedo.
Mapping of the_extinction_in_giant_molecular_clouds_using_optical_star_countsSérgio Sacani
This document presents extinction maps of 14 Giant Molecular Clouds derived from a star count method using an adaptive grid and wavelet decomposition applied to optical data from the USNO-Precision Measuring Machine. The method involves fixing the number of counted stars per grid cell rather than the grid step size. Extinction maps are shown for Vela, Carina, Musca, Coalsack, Chamaeleon, Corona Australis, IC 5146, Lupus, ρ Ophiuchus, Orion, Taurus, Serpens clouds. Parameters like total mass and maximum extinction are estimated from the maps and compared between clouds. Individual clouds are also discussed.
This document summarizes a survey of the massive star forming region RCW 57 (NGC 3576) using JHKs and L-band (3.5 μm) infrared data. Over 50% of the sources detected showed infrared excess emission, indicating the presence of circumstellar disks. Comparison to other regions supported a very high initial disk fraction (>80%) around massive stars, though disks may dissipate faster around high-mass stars. 33 sources only detected at L-band indicated heavily embedded, massive Class I protostars. Diffuse polycyclic aromatic hydrocarbon emission was also detected throughout the region.
First Direct Imaging of a Kelvin–Helmholtz Instability by PSP/WISPRSérgio Sacani
We present a comprehensive analysis aimed at proving the hypothesis that a train of small-scale features observed by the Wide-field Imager (WISPR) onboard the Parker Solar Probe (PSP) are the signature of a Kelvin–Helmholtz instability (KHI). These features were seen near the flank of a Coronal Mass Ejection (CME) wake between 7.5 Re and 9.5Re, lasting for about 30 minutes. The CME was a slow event, associated with a streamer blowout. We analyzed the size of the eddies and found growth during their evolution while maintaining separation distances and alignment typical of Kelvin–Helmholtz vortexes. We then assessed the magnetic field conditions that would make the observation of such an instability plausible. Two methods were used to cross-check our findings. The measured thickness of the boundary layer supports KHI candidacy, and the estimated linear growth rate suggests nonlinear saturation within the expected timescale. We conclude that a KHI is a plausible explanation for the observed features, and therefore that such instabilities might exist in the low and middle solar corona (within ∼15 Re) and can be detected in white light observations. Their observation, however, might be rare due to stringent conditions like the observer’s proximity, suitable viewing circumstances, magnetic field topology, and flow properties. This study highlights the unique capability of PSP/WISPR in observing such phenomena, especially as PSP perihelia reach closer distances to the Sun.
Small dust particles escaping from Pluto's moons Nix and Hydra could temporarily form a ring around Pluto due to impacts, but the solar radiation pressure would remove about half of 1 micrometer particles within a year by causing collisions with Pluto and its moons. Numerical simulations found that a tenuous ring with an optical depth of 6×10^-11 could be maintained by dust released from Nix and Hydra.
Evidence for widespread hydrated minerals on asteroid (101955) BennuSérgio Sacani
Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRISREx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the
form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there
is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the
visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming
previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic
chemistry to Earth.
This document summarizes the results of a 180 ks Chandra-LETGS observation of Mrk 509 as part of a larger multi-wavelength campaign. The observation detected several absorption features in the X-ray spectrum originating from an ionized absorber, including ions with three distinct ionization degrees. The lowest ionized component is slightly redshifted and not in pressure equilibrium with the others, likely belonging to the host galaxy's interstellar medium. The other two components are outflowing at velocities of around -200 and -455 km/s. Simultaneous HST-COS observations detected 13 UV kinematic components, and at least three can be associated with the X-ray components, providing evidence that the UV and X-
The hazardous km-sized NEOs of the next thousands of yearsSérgio Sacani
This document discusses methods for assessing the long-term impact risk of km-sized near-Earth objects (NEOs) over thousands of years. It analyzes the evolution of the Minimum Orbit Intersection Distance (MOID) between NEOs and Earth to identify objects that remain in close proximity for extended periods. It then estimates the probability of a deep Earth encounter during these low-MOID periods based on the growth of orbital uncertainties over time. This allows the authors to rank km-sized NEOs by their long-term impact hazard and identify targets that warrant further observation and analysis.
Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U...Sérgio Sacani
During the formation and evolution of the Solar System, significant
numbers of cometary and asteroidal bodies were
ejected into interstellar space1,2. It is reasonable to expect that
the same happened for planetary systems other than our own.
Detection of such interstellar objects would allow us to probe
the planetesimal formation processes around other stars, possibly
together with the effects of long-term exposure to the
interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known
interstellar object, discovered by the Pan-STARRS1 telescope
in October 2017 (ref. 3). The discovery epoch photometry
implies a highly elongated body with radii of ~ 200 × 20 m
when a comet-like geometric albedo of 0.04 is assumed. The
observable interstellar object population is expected to be
dominated by comet-like bodies in agreement with our spectra,
yet the reported inactivity of 'Oumuamua implies a lack
of surface ice. Here, we report spectroscopic characterization
of ‘Oumuamua, finding it to be variable with time but similar
to organically rich surfaces found in the outer Solar System.
We show that this is consistent with predictions of an insulating
mantle produced by long-term cosmic ray exposure4.
An internal icy composition cannot therefore be ruled out by
the lack of activity, even though ‘Oumuamua passed within
0.25 au of the Sun.
Late accretion of Ceres-like asteroids and their implantation into the outer ...Sérgio Sacani
This document summarizes research measuring visible and infrared spectra of 10 large, dark asteroids in the mid-outer main asteroid belt that are spectrally similar to Ceres. Thermal evolution modeling shows these "Ceres-like" asteroids have highly porous interiors, accreted relatively late between 1.5-3.5 million years after calcium-aluminum inclusions formed, and experienced maximum interior temperatures under 900K. Dynamical modeling suggests these asteroids were likely implanted from more distant regions into their current orbits between 3.0-3.4 AU during dynamical instability of the giant planets.
Hydrogen Column Density Variability in a Sample of Local Compton-Thin AGNSérgio Sacani
We present the analysis of multiepoch observations of a set of 12 variable, Compton-thin, local (z<0.1) active galactic nuclei (AGN) selected from the 100-month BAT catalog. We analyze all available X-ray data from Chandra, XMMNewton, and NuSTAR, adding up to a total of 53 individual observations. This corresponds to between 3 and 7 observations per source, probing variability timescales between a few days and ∼ 20 yr. All sources have at least one NuSTAR observation, ensuring high-energy coverage, which allows us to disentangle the line-of-sight and reflection components in the X-ray spectra. For each source, we model all available spectra simultaneously, using the physical torus models MYTorus, borus02, and UXCLUMPY. The simultaneous fitting, along with the high-energy coverage, allows us to place tight constraints on torus parameters such as the torus covering factor, inclination angle, and torus average column density. We also estimate the line-of-sight column density (NH) for each individual observation. Within the 12 sources, we detect clear line-of-sight NH variability in 5, non-variability in 5, and for 2 of them it is not possible to fully disentangle intrinsic-luminosity and NH variability. We observe large differences between the average values of line-ofsight NH (or NH of the obscurer) and the average NH of the torus (or NH of the reflector), for each source, by a factor between ∼ 2 to > 100. This behavior, which suggests a physical disconnect between the absorber and the reflector, is more extreme in sources that present NH variability. NH-variable AGN also tend to present larger obscuration and broader cloud distributions than their non-variable counterparts. We observe that large changes in obscuration only occur at long timescales, and use this to place tentative lower limits on torus cloud sizes.
Studies of ngc_6720_with_calibrated_hst_wfc3_emission_line_filter_imagesSérgio Sacani
This study uses calibrated Hubble Space Telescope images of the Ring Nebula (NGC 6720) taken 12.925 years apart to measure tangential motions within the nebula. Individual features were measured in nitrogen emission line images as well as dark knots seen against oxygen emission. The results indicate that the nebula is expanding homologously, but at a faster rate along its major axis. Dark knots were found to expand more slowly than the nebular gas. The tangential motion measurements allow estimates of the nebula's distance and dynamic age to be about 720 pc and 4000 years, respectively.
The article discusses observations from multiple space-based observatories that tracked a sun-diving comet, C/2011 N3 (SOHO), as it passed through the Sun's corona and disintegrated. The observatories captured details of the comet's flight path, emissions, and disintegration over time. Studying how comets interact with and break apart in the corona can provide insights into comet composition and the early solar system.
Gravitational lensing characteristics of the transparent sunSérgio Sacani
The document models the Sun as a transparent gravitational lens and calculates its lensing characteristics using data from the 2005 Standard Solar Model. It finds that:
1) The Sun's minimum focal length for producing multiple images of distant sources is 23.5 ± 0.1 AU, just beyond the orbit of Uranus.
2) Regions exist where the Sun can produce three images of a distant source along with their associated magnifications.
3) Extremely high magnifications are possible for observers situated such that an unlensed source appears near a three-image caustic.
This document summarizes the results of a sub-mm survey of the Carina Nebula complex conducted with the LABOCA instrument on the APEX telescope. The survey mapped an area of 1.25° × 1.25° at 870 μm, revealing the morphology and distribution of cold dust clouds with masses down to a few solar masses. The total mass of clouds detected is estimated to be around 60,000 M☉. The cloud morphologies range from large clouds of several thousand solar masses to small diffuse clouds of only a few solar masses. The distribution of sub-mm emission generally agrees with Spitzer 8 μm maps, identifying clouds interacting with massive stars as well as infrared dark clouds. The survey provides crucial
Dust in the_polar_region_as_a_major_contributor_to_the_infrared_emission_of_a...Sérgio Sacani
The mid-infrared emission of the active galactic nucleus NGC 3783 was observed using interferometry over multiple epochs, providing dense coverage of position angles and baselines. The emission was found to be strongly elongated along a position angle of -52 degrees, closely aligned with the polar axis orientation of -45 degrees. The half-light radii were measured to be 20.0 mas by 6.7 mas, corresponding to an axis ratio of 3:1. This implies that 60-90% of the 8-13 micron emission is from the polar-elongated component. The observations support a scenario where the majority of mid-infrared emission in Seyfert galaxies originates from a dusty wind in the polar region,
Fleeting Small-scale Surface Magnetic Fields Build the Quiet-Sun CoronaSérgio Sacani
Arch-like loop structures filled with million Kelvin hot plasma form the building blocks of the quiet-Sun corona.
Both high-resolution observations and magnetoconvection simulations show the ubiquitous presence of magnetic
fields on the solar surface on small spatial scales of ∼100 km. However, the question of how exactly these quietSun coronal loops originate from the photosphere and how the magnetic energy from the surface is channeled to
heat the overlying atmosphere is a long-standing puzzle. Here we report high-resolution photospheric magnetic
field and coronal data acquired during the second science perihelion of Solar Orbiter that reveal a highly dynamic
magnetic landscape underlying the observed quiet-Sun corona. We found that coronal loops often connect to
surface regions that harbor fleeting weaker, mixed-polarity magnetic field patches structured on small spatial
scales, and that coronal disturbances could emerge from these areas. We suggest that weaker magnetic fields with
fluxes as low as 1015 Mx and/or those that evolve on timescales less than 5 minutes are crucial to understanding
the coronal structuring and dynamics.
This document summarizes an infrared survey of the massive star forming region RCW 57 (NGC 3576) using L-band (3.5 μm) data from SPIREX and JHKs data from 2MASS. Over 50% of the 209 sources detected showed infrared excess, indicating circumstellar disks. Comparison to other surveys supports a very high initial disk fraction (>80%) around massive stars, though disks may dissipate faster around high-mass stars. 33 sources only detected at L-band indicate heavily embedded, massive Class I protostars. Diffuse PAH emission was also detected throughout RCW 57.
This document discusses PyRISM, a Python program that models delays in pulsar timing observations caused by phenomena like dispersion in the interstellar medium (ISM) and gravitational waves. PyRISM was created to provide a more accessible alternative to an existing program called BRISM, which models ISM delays but is difficult for non-experts to understand. PyRISM reproduces BRISM's functionality using Python and is intended for use by undergraduate researchers. It models delays from dispersion, refraction in the ISM, and other effects to help astronomers correct for them and potentially detect gravitational waves through precise pulsar timing.
Similar to Measuring solar radius_from_space_during_the_2003_2006_mercury_transits (20)
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.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
For the full video of this presentation, please visit: https://www.edge-ai-vision.com/2024/06/building-and-scaling-ai-applications-with-the-nx-ai-manager-a-presentation-from-network-optix/
Robin van Emden, Senior Director of Data Science at Network Optix, presents the “Building and Scaling AI Applications with the Nx AI Manager,” tutorial at the May 2024 Embedded Vision Summit.
In this presentation, van Emden covers the basics of scaling edge AI solutions using the Nx tool kit. He emphasizes the process of developing AI models and deploying them globally. He also showcases the conversion of AI models and the creation of effective edge AI pipelines, with a focus on pre-processing, model conversion, selecting the appropriate inference engine for the target hardware and post-processing.
van Emden shows how Nx can simplify the developer’s life and facilitate a rapid transition from concept to production-ready applications.He provides valuable insights into developing scalable and efficient edge AI solutions, with a strong focus on practical implementation.
HCL Notes und Domino Lizenzkostenreduzierung in der Welt von DLAUpanagenda
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DLAU und die Lizenzen nach dem CCB- und CCX-Modell sind für viele in der HCL-Community seit letztem Jahr ein heißes Thema. Als Notes- oder Domino-Kunde haben Sie vielleicht mit unerwartet hohen Benutzerzahlen und Lizenzgebühren zu kämpfen. Sie fragen sich vielleicht, wie diese neue Art der Lizenzierung funktioniert und welchen Nutzen sie Ihnen bringt. Vor allem wollen Sie sicherlich Ihr Budget einhalten und Kosten sparen, wo immer möglich. Das verstehen wir und wir möchten Ihnen dabei helfen!
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Measuring solar radius_from_space_during_the_2003_2006_mercury_transits
1. To appear in Astrophysical Journal
Preprint typeset using L TEX style emulateapj v. 5/2/11
A
MEASURING THE SOLAR RADIUS FROM SPACE DURING THE 2003 AND 2006 MERCURY TRANSITS
M. Emilio1 , J. R. Kuhn2 , R. I. Bush3 , and I. F. Scholl2
(Dated: Received December 13, 2011; accepted March 5, 2012)
To appear in Astrophysical Journal
ABSTRACT
The Michelson Doppler Imager (MDI) aboard the Solar and Heliospheric Observatory observed the
arXiv:1203.4898v1 [astro-ph.SR] 22 Mar 2012
transits of Mercury on 2003 May 7 and 2006 November 8. Contact times between Mercury and the
solar limb have been used since the 17th century to derive the Sun’s size but this is the first time
that high-quality imagery from space, above the Earth’s atmosphere, has been available. Unlike other
measurements this technique is largely independent of optical distortion. The true solar radius is still
a matter of debate in the literature as measured differences of several tenths of an arcsecond (i.e.,
about 500 km) are apparent. This is due mainly to systematic errors from different instruments and
observers since the claimed uncertainties for a single instrument are typically an order of magnitude
smaller. From the MDI transit data we find the solar radius to be 960”.12 ± 0”.09 (696, 342 ± 65km).
This value is consistent between the transits and consistent between different MDI focus settings after
accounting for systematic effects.
Subject headings: astrometry, Sun: fundamental parameters, Sun: photosphere
1. INTRODUCTION analyzing 4500 archival contact-timings between 1631
Observations of the interval of time that the planet and 1973, found that the secular decrease did not exceed
Mercury takes to transit in front of the Sun provides, 0”.06 ± 0”.03.
in principle, one of the most accurate methods to mea- Modern values found in the literature for the solar ra-
sure the solar diameter and potentially its long-term dius range from 958”.54 ± 0”.12 (S´nchez et al. 1995) to
a
variation. Ground observations are limited by the spa- 960”.62 ± 0”.02 (Wittmann 2003). Figure 1 shows pub-
tial resolution with which one can determine the in- lished measurements of solar radius over the last 30 years
stant Mercury crosses the limb. Atmospheric seeing and (for a review see: Kuhn et al. (2004); Emilio & Leister
the intensity gradient near the limb (sometimes called (2005); Thuillier et al. (2005)). Evidently these uncer-
the “black drop effect”, see Schneider et al. (2004); tainties reflect the statistical errors from averaging many
Pasachoff et al. (2005)) contribute as error sources for measurements by single instruments and not the system-
the precise timing required to derive an accurate radius. atic errors between measurement techniques. For exam-
This is the first time accurate Mercury’s transit contact ple, our previous determination of the Sun’s radius with
times is measured by an instrument in space and im- MDI was based on an optical model of all instrumen-
proves at least 10 times the accuracy of classical obser- tal distortion sources (Kuhn et al. 2004). The method
vations (see Bessel (1832); Gambart (1832)). described here has only a second-order dependence on
About 2,400 observations of those contacts from 30 optical distortion (although it is sensitive to other sys-
transits of Mercury, distributed during the last 250 tematics) and may be more accurate for this reason.
years, were published by Morrison & Ward (1975), and
analyzed by Parkinson, Morrison & Stephenson (1980). 2. DATA ANALYSIS
Those measurements, collected mainly to determine the The data consist of 1024 × 1024 pixel MDI-SOHO im-
variations of rotation of the Earth and the relativis- ages from fixed wavelength filtergrams of Mercury cross-
tic movement of Mercury’s perihelion provided a time- ing in front of the Sun. Images were obtained with a one-
series of the Sun’s diameter. Analyzing this data set, minute cadence in both transits, cycling between four in-
Parkinson, Morrison & Stephenson (1980) marginally strument focus settings (focus blocks, FBs) in 2003 and
found a decrease in the solar semi-diameter of 0”.14 ± two in 2006. For each image obtained at a given focus
0”.08 from 1723 to 1973, consistent with the analysis block, we subtracted a previous image of the Sun without
of Shapiro (1980) which claimed a decrease of 0”.15 Mercury using the same focus setting. This minimized
per century. Those variations are consistent with our the effects of the limb darkening gradient and allowed
(Bush et al. 2010) null result and upper limit to secu- us to find the center of Mercury (Figure 2) more accu-
lar variations obtained from Michelson Doppler Imager rately. In a small portion of each image containing Mer-
(MDI) imagery of 0”.12 per century. Sveshnikov (2002), cury we fitted a negative Gaussian. We adopt the center
of the Gaussian as the center of Mercury. Images that
1 Observat´rio Astronˆmico-Departamento de Geociˆncias
o o e were too close to the solar limb were not fitted because
Universidade Estadual de Ponta Grossa, Paran´, Brazil,
a the black drop effect inflates our center-determination er-
memilio@uepg.br rors. The position of the center of the Sun and the limb
2 Institute for Astronomy, University of Hawaii, 2680
Woodlawn Dr. 96822, HI, USA, kuhn@ifa.hawaii.edu, if-
were calculated as described in Emilio et al. (2000). A
scholl@hawaii.edu polynomial was fit to the x − y pixel coordinates of Mer-
3 HEPL-Stanford University, Stanford, CA, 94305, USA,
cury’s center during the image time-series. This transit
rock@sun.stanford.edu trajectory was extrapolated to find the precise geometric
2. 2 Emilio et al.
Fig. 1.— Published measurements of solar radius in the last 32 years. Abscissa values are the mean observation dates. The plus signs
are drift scan measurements and they are from Wittmann (1980); Yoshizawa (1994); Neckel (1995); Brown & Christensen-Dalsgaard
(1998). The solar eclipses measurements are marked with an asterisk and are from Fiala et al. (1984); Kubo (1993); Akimov et al.
(1993); Kili¸ et al. (2009); Sigismondi (2009); Adassuriya et al. (2011). Helioseismology measurements (diamonds) have a different
c
definition of solar radius and can differ up to 300 km from the inflection point definition (Tripathy & Antia 1999). Helioseismology data
are from Schou et al. (1997); Antia (1998). SDS measurements are show in triangle and are from Sofia et al. (1983); Maier et al.
(1992); Egidi et al. (2006); Djafer et al. (2008). After applying systematic corrections to SDS measurement Djafer et al. (2008) found
the value of 959”.798 ± 0”.091 (showed in this figure as the upper triangle point in 1994). This value is inside the 2σ error bar of this work.
Published astrolabes measurements are show in square symbols and are from No¨l (1995); S´nchez et al. (1995); Leiter et al. (1996);
e a
Laclare et al. (1996); Kili¸ (1998); Jilinski et al. (1999); Laclare et al. (1999); Puliaev et al. (2000); Golbasi et al. (2001); Emilio
c
(2001); Andrei et al. (2004); No¨l (2004); Emilio & Leister (2005); Kili¸ et al. (2005). The astrolabe measurements showed here are not
e c
correct for the atmospheric and instrumental systematic effects. When those corrections are made the final value is bigger than the ones
displayed in this plot (see Chollet & Sinceac (1999)).
intersection with the limb by also iteratively accounting The total transit time was thus obtained with an ac-
for the time variable apparent change in the solar radius curacy of 4 s in 2003 and 1 s in 2006 from a comparison
(−0.221 ± 0.004 mas minute−1 in 2003 and 0.152 ± 0.003 of FB 4 and FB 5 data. The correction to the radius is
mas minute−1 in 2006) between images. found from the relation (Shapiro 1980).
The same procedure was performed independently for
ω2 O−C
each FB time-series. The contact times were found from ∆R = R⊙ T ∆T
a least-squares fit of Mercury’s center position trajectory
xF B (t) and y F B (t) to the intersection with the limb near where ω is the speed of Mercury relative to the Sun, T is
first/second and third/fourth contact. Here FB are the the total length of the transit, R⊙ is the apparent value of
FBs (3, 4, 5, 6). As a consequence we obtained eight dif- the solar radius at 1 AU from the ephemeris for each tran-
ferent contact times for 2003 and four for 2006, one for sit instant (where we adopt 959”.645 (696, 000 ± 40km)
each FB and two for each geometric contact. Figure 3 for the nominal solar radius) and ∆T O−C is the differ-
shows zoom images of the Sun containing Mercury close ence between the observed and ephemeris duration of
to the contact times for both 2003 and 2006 transits as the transit. Table 1 shows the ephemeris values used in
well as the Mercury trajectory and the limb fit. this analysis. We have used the NASA ephemeris cal-
FB 3 and 6 are far from an ideal focus, as Figure 4 culations 4 provided by NASA for the SOHO Mercury
(upper) and Figure 7 show, so that the shape of the limb transit observations. Ephemeris uncertainties for the ab-
darkening function (LDF) is different enough that it is solute contact times are not greater than 0.18 s based on
difficult to compare corresponding transit points with the the SOHO absolute position error. Using the above equa-
near-focus images. Those focus block were not utilized in tion we found the solar radius values to be 960”.03±0”.08
further analysis. We note also that FB 6 data contained (696, 277 ± 58km) and 960”.07 ± 0”.05 (696, 306 ± 36km)
a ghost image of Mercury which added new systematic
errors to the data. 4 see http://sohowww.nascom.nasa.gov/soc/mercury2003/
3. SOLAR RADIUS FROM THE 2003 AND 2006 MERCURY TRANSIT 3
TABLE 1
Mercury transit ephemerides
Year First Mercury Contact a Second Mercury Contact a Mercury Center Transit Duration Mercury Velocity
(minute) (arcsec minute−1 )
2003 50.433 b 374.342 b 323.909 4.102
2006 10.458 c 307.059 c 296.601 5.968
a Center contacts in (min).
b UTC-7 hr of 2003 May 7.
c UTC-20 hr of 2006 November 8.
to shift. The effect (corrected by the Fried parameter
to infinity) is at the order of 0”.123 for r0 = 5cm and
1”.21 r0 = 1cm (Djafer et al. 2008) and depends on
local atmospheric turbulence, the aperture of the instru-
ment and the wavelength resulting in an observed so-
lar radius smaller than the true one (Chollet & Sinceac
1999). Many of the published values were not corrected
for the Fried parameter which may explain most of the
low values seen in Figure 1.
We analyzed some systematics regarding the numer-
ical calculation of the inflection point. The numerical
method to calculate the LDF derivative used is the five-
point rule of the Lagrange polynomial. The systematic
difference between the three-point rule that is used by
default in the interactive data language derivative rou-
tine, is 0.01 pixels for FB 5 up to 0.04 pixels for FB 6.
In this work we defined the inflection point as the maxi-
mum of the LDF derivative squared. From those points
we fit a Gaussian plus quadratic function and adopt the
maximum of this function as the inflection point. Adopt-
Fig. 2.— Composite image of two Mercury transits in 2003 May ing the maximum of the Gaussian part of the fit instead
(top, 4 minute cadence) and 2006 November (bottom, 2 minute differs 0.001 pixels for FB 3,4,5 and five times more for
cadence). Images were taken with one-minute cadence in both
transits, intercalating four different focus blocks in 2003 and two FB 6. The quadratic function part is important since the
focus blocks in 2006. Both images showed here are at focus settings LDF is not a symmetric function. Figure 5 compares the
4. gaussian plus quadratic fit to find the function maximum
for the 2003 and 2006 transits respectively. Uncertainties with only fitting a parabola using 3 points near the max-
were determined from the scatter in the two FB settings imum. They differ 0.01, -0.06, 0.04 and -.05 pixels for FB
from each epoch. We note that the observed absolute 3, 4, 5 and 6 respectively. The statistical error sampling
transit contact times are offset 8 s in 2003 and 5 s in for all the available data after accounting for changing
2006, both inside our 2σ error. the distance is 0.0002 pixels for FB 5 and 0.0003 pixels
Our accurate determination of the limb transit points, for FB 6. Figure 7 shows a close up of Mercury for each
compared with the ephemeris predictions, implies that focus block where we can visually see a spurious ghost
the orientation of the solar image is slightly rotated from image of FB 6 since this FB is far from the focus plane.
the solar north pole lying along the y axis. We find that That can explain why the numerical methods gave more
the true solar north orientation is rotated 7′ ± 1′ counter- difference for this FB. By fitting a parabola over the solar
clockwise in 2003 and 3′ .3 ± 0′.3 arcmin in 2006. Table 2 image center positions as a function of time, we also took
summarizes our results from this analysis. into account jitter movements of the SOHO spacecraft.
Solar limb coordinates and the Mercury trajectory were
3. SYSTEMATICS DEVIATIONS adjusted to the corrected solar center coordinate frame.
3.1. Numerical Limb Definition This procedure made a correction of order of 0.01 pixels
The solar radius in theoretical models is defined as in our definition of the solar limb. Smoothing the LDF
the photospheric region where optical depth is equal to derivative changes the inflection point up to .35 pixels
the unity. In practice, helioseismic inversions determine that is the major correction we applied in our previous
this point using f mode analysis, but most experiments published value in Kuhn et al. (2004). We describe all
which measure the solar radius optically use the inflec- corrections applied to this value at the end of this section.
tion point of the LDF as the definition of the solar radius.
Tripathy & Antia (1999) argue that the differences be- 3.2. Wavelength
tween the two definitions are between 200 and 300 km MDI made solar observations in five different posi-
(0”.276-0”.414). This explains why the two helioseismo- tions of a line center operating wavelength of 676.78
logic measurements in Figure 1 show a smaller value. nm. Conforming Figure 1. of Bush et al. (2010) at
The convolution of the LDF and Earth’s atmospheric line center, the apparent solar radius is 0.14 arcsec or
turbulence and transmission cause the inflection point approximately 100 km larger than the Sun observed in
4. 4 Emilio et al.
(a) 2003 Mercury Transit - 1st and 2nd contacts (b) 2003 Mercury Transit - 3rd and 4th contacts
(c) 2006 Mercury Transit - 1st and 2nd contacts (d) 2006 Mercury Transit - 3rd and 4th contacts
Fig. 3.— Images near the contact times for both 2003 and 2006 transits as well as the Mercury trajectory fit and the solar limb fit.
Mercury center geometric x and y contact positions with the solar limb where found from the interception of those fits.(a) 2003 Mercury
transit: first and second contacts, (b) 2003 Mercury transit: third and fourth contacts,(a) 2006 Mercury transit: first and second contacts,
(b) 2006 Mercury transit: third and fourth contacts
nearby continuum. We used a single filtergram nearby order of 0”.02 and was not applied since the dependence
the continuum in this work. Comparison with the com- of wavelength for the point-spread function (PSF) contri-
posite linear composition of filtergrams representing the bution goes to the opposite direction and the correction
continuum differs from 0.001 arcmin. Neckel (1995) is inside our error bars.
suggest the wavelength correction due to the (contin-
uum) increases with wavelength. Modern models confirm 3.3. Point-spread-Function (PSF)
this dependence with a smaller correction. Djafer et al. The MDI PSF is a complicated function since different
(2008) computed the contribution of wavelength using points of the image are in different focus positions (see
Hestroffer & Magnan (1998) model. According to this Kuhn et al. (2004) for description of MDI optical dis-
model and others cited by Djafer et al. (2008) the so- tortions). In our earlier work the non-circular low-order
lar radius also increases with wavelength (see Fig. 1 of optical aberrations are effectively eliminated by averag-
Djafer et al. (2008)). The correction at 550 nm is on the ing the radial limb position around the limb, over all
5. SOLAR RADIUS FROM THE 2003 AND 2006 MERCURY TRANSIT 5
Fig. 4.— Top: the best focus position fit when the two mercury transits happened. 2003 Mercury transit date is shown as a dotted line
and 2006 Mercury transit as a long dashed line. From the intersection of those lines with the best focus position fit (dashed line) we found
that the best focus positions are 4.94 and 5.35 for 2003 and 2006 Mercury transits respectively. Bottom: linear fit as a function of focus
block. Once again the 2003 Mercury transit best focus position is shown as a dotted line and 2006 Mercury transit as a long dashed line.
The mean value is shown as a dashed line. We looked for the intercept positions with the best estimate of the focus for 2003 and 2006
Mercury transits (solid line). The intercept values with the linear fit are the same for both 2003 and 2006 and represent our correction for
the changes in focus.
TABLE 2
Mercury transit observation
2003 2006
Focus Settings Transit Durationa Solar Radius Transit Durationa Solar Radius
(minute) (arcsec) (minute) (arcsec)
3 324.16 960.00 ··· ···
4 324.11 959.92 296.74 960.03
5 324.25 960.13 296.77 960.10
6 324.33 960.24 ··· ···
Averageb 324.18 960.03 296.75 960.07
p(O-C) 7′ ± 1′ 3′ .3 ± 0′ .3
a Transit duration for Mercury transit contact times
b Only FB 4 and FB 5 focus settings were used for the 2003 data (see the text for details).
angular bins. But in the case of the Mercury transit, scope dominated by diffraction. The authors made use
only two positions at the limb apply so that it is im- of the solar limb model of Hestroffer & Magnan (1998)
portant to recognize that the LDF (and the inflection to calculate the inflection point. They found that the
point) will systematically vary around the limb. The MDI instrumental LDF inflection point was displaced
overall contribution to the PSF of the solar image in- 0”.422 inward at ‘ideal focus’ from the undistorted LDF,
creases with increasing telescope aperture, and decreases but the authors used a MDI aperture of 15 cm instead
with increasing observing wavelength as noted in the last of actual aperture diameter of 12.5 cm. In addition,
section. Djafer et al. (2008) computed the contribution we do not find the pixelization effect cited by the au-
of the MDI instrument PSF at its center operating wave- thors. PSF and wavelength correction for SDS calcu-
length of 676.78 nm assuming a perfectly focused tele- lated by (Djafer et al. 2008) resulted in a diameter of
6. 6 Emilio et al.
Fig. 5.— Different MDI focus positions result in a different size of the Sun in pixels. Both Mercury and Sun are subject to the same
instrumental effects but since only the contact times are used to calculate the solar radius this effect is reduced. The linear trend of radius
with time in this plot is due to the change of distance of SOHO from the Sun. All measurements were used to interpolate the solar size in
pixels at the times of contacts (dashed lines). The triple-dot-dashed line indicates the middle of 2003 Mercury transit. The figure also shows
two different techniques to calculate the inflection points. The first one (dots) is a fit of a Gaussian plus quadratic to the squared radial
derivative of the LDF. The second (lines) is fitting a parabola on the same function. Those differences reflect the systematic uncertainty
in defining the solar radius.
959”.798 ± 0”.091 (Djafer et al. 2008). The original tenths of an arcsec for out-of-focus images. The Mercury
value found by Calern astrolabe (CCD observations) is image will also be subject to the same distortion, but
959”.44 ± 0”.02 (Chollet & Sinceac 1999). After ap- the inflection point moves from the first/second contact
plying a model taking into account atmospheric and to the third/forth contact. We see this systematic at dif-
instrumental effects (with Fried parameter, r → ∞) ferent FB since the total transit time grows for bigger
Chollet & Sinceac (1999) found 959”.64 ± 0”.02. From focus settings (see Table 2).
this value Djafer et al. (2008) applied PSF and wave- Figure 4 (top) shows the best focus setting over the
length correction and obtained 959”.811 ± 0.075. MDI history. From a polynomial fit we derived the best
focus position for the transit. For 2003, this value is 4.94
3.4. Focus variation FB units (solid line) and in 2006 it was 5.35 (long dashed
The overall focus of the instrument is adjusted by in- line). We made a first order correction to account for
serting BK7 and SF4 glass of different thickness into the the out-of-focus condition of the instrument during each
optical path after the secondary lens in order to vary transit. Figure 4 bottom shows the values found for the
the optical path length. The MDI focus changes oc- solar radius at different focus settings. The 2003 transit
cur in nine discrete increments using sets of three glass values are represented as ”diamonds” and 2006 transits
blocks in the two calibration focus mechanisms. Increas- as ”upper triangles”. As we have only two focus settings
ing the FB number by one unit moves the nominal fo- in 2006 we represent the function as a line. As the best
cus toward the primary lens by 0.4 mm. As described focus is not so far from FB 5, the systematic error for
by Kuhn et al. (2004) a change in the focus condition adopting a line is small. The vertical lines (for 2003 we
causes a net change in the image plate scale, but it also plot a short dashed line and 2006 the long dashed line)
changes the shape of the LDF which affects the inflection represent the best focus position for each year. With a
point. Figure 6 plots the mean LDF averaged around linear interpolation we found the effective solar radius at
the limb for the various limb focus conditions during the best focus for both transits. The 2003 and 2006 focus
two transits. The curves are shifted to account for the correction resulted in a value of 960”.12 for both years.
plate scale change by matching the half-intensity dis-
tance. The data here show how the defocused image
causes the inflection point to move to larger radii, thus 3.5. Systematics Effects from our previous 2004 MDI
implying a larger solar diameter by as much as a few Solar Radius Determination
7. SOLAR RADIUS FROM THE 2003 AND 2006 MERCURY TRANSIT 7
Fig. 6.— Top: mean LDfs at 2003 transit, one for each FB settings. Bottom: derivative squared of top Ldfs. The dashed lines indicate
the inflection point location calculated from a Gaussian plus quadratic fit from the derivative squared points.
The largest residual error comes from the variation in
focus condition across the image. Figure 6 shows four
typical LDF’s at the middle of the 2003 transit (one for
each FB). Each LDF in Figure 6 is evaluated as a mean
over the whole image. In contrast with Kuhn et al.
(2004), here we calculate mean LDFs around the solar
limb. This is accomplished by using the computed limb-
shift at each angle (which depends on the average LDF)
to obtain a distortion corrected mean LDF. We iterate
with this corrected LDF to obtain improved limb shift
data and an unsmeared LDF (see Emilio et al. (2007)).
We have also improved the LDF inflection point calcu-
lation from the local unsmeared LDF following the dis-
cussion in Section 3.1. Applying the above modifications
the solar radius in pixels at the 2003 transit for FB 4 is
484.192 pixels at the middle of the transit (it was 484.371
in Kuhn et al. (2004)).
Our 2004 result obtained the mean image platescale
by combining a detailed optical raytrace model and the
measured solar radius change with FB. We also derived
Fig. 7.— Close-up of Mercury observed by MDI. FB 6 is far from what we called the “symmetric pincushion image distor-
the instrument focal plane and has large systematics including a tion” from the apparent path of Mercury across the solar
spurious ghost image.
image. These two effects are contained in the empirical
The solar radius we determine from the transit data plate-scale measurement so that we should not have in-
is bigger than our published 2004 MDI results that were dependently applied the symmetric distortion correction
obtained from a detailed optical distortion model. In to the corrected plate-scale-data. After correcting the
the process of understanding the transit measurements plate-scale only a non-circularly symmetric correction (-
here we have found several systematic effects that affect 0.32 pixels) was needed. With this correction we obtain
these and our 2004 measurements. Observing from space 483.872 ± 0.05 pixels for the FB4 2003 Mercury transit
allows us to measure and correct for field-dependent PSF solar radius. With the FB 4 calibration of 1.9870±0.0002
errors that would normally be too small to separate from pixel−1 the corrected solar radius is 961”.45 ± 0”.15 (as
an atmospheric seeing-distorted solar image. seen from SOHO). During the middle of the 2003 tran-
8. 8 Emilio et al.
are 3 s in 2003 and 1 s in 2006. The value we found
for the solar radius as defined by the apparent inflec-
tion point of the continuum filtergram images of MDI is
960”.12±0”.09 (696, 342±65km). This is consistent with
earlier MDI absolute radius measurements after taking
into account systematic corrections and a calibration er-
ror in the 2004 optical distortion measurements. We also
obtain an MDI solar reference frame, counterclockwise,
p angle correction of 7′ ± 1′ in 2003 and 3′ .3 ± 0′ .3 in
2006. Figure 8 shows the residual variation of the solar
radius (Bush et al. 2010) and the residual values found
in this work for the Mercury transit after averaging the
focus blocks settings. As seen in Figure 8 no variation of
the solar radius was observed over 3 years between the
Fig. 8.— Residual variation of the solar radius (dots; Bush et al. two transits.
(2010)) and the residual values found in this work for the Mer-
cury transit after averaging the focus blocks settings (”diamonds”).
Solid line represents the moving average values and the dashed line We are grateful to Manuel Montoro from the Flight Dy-
a linear fit from all the residual variation of the solar radius.
namics Facility Goddard Space Flight Center to provide
sit, SOHO was 0.99876 AU from the Sun, so that the us with updated ephemeris. This research was supported
apparent solar radius at 1 AU is then 960”.26 ± 0”.15. by the NASA SOHO/GI program through a grant to
This value is consistent with the 1σ uncertainty in the the IfA, by the NASA Michelson Doppler Imager grant
Mercury timing radius derived here. NNX09AI90G to Stanford and the NASA Helioseismic
and Magnetic Imager contract NAS5-02139 to Stanford
4. CONCLUSION and subcontract to the IfA. This work was also partially
We now find a consistent value for the solar radius from supported by CNPq grant 303873/2010-8, the Instituto
Mercury transit timing, and satellite solar imagery using Nacional de Estudos do Espa¸o (CNPq) and CAPES
c
MDI. The averaged O-C transit duration uncertainties grant 0873/11-0.
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