An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
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.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
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.
Supermassive black holes in galaxy centres can grow by the accretion
of gas, liberating enormous amounts of energy that might
regulate star formation on galaxy-wide scales1–3
. The nature of
gaseous fuel reservoirs that power black hole growth is nevertheless
largely unconstrained by observations, and is instead routinely
simplified as a smooth, spherical inflow of very hot gas
in accordance with the Bondi solution4
. Recent theory5–7 and
simulations8–10 instead predict that accretion can be dominated by
a stochastic, clumpy distribution of very cold molecular clouds,
though unambiguous observational support for this prediction remains
elusive. Here we show observational evidence for a cold,
clumpy accretion flow toward a supermassive black hole fuel reservoir
in the nucleus of the Abell 2597 Brightest Cluster Galaxy
(BCG), a nearby (z = 0.0821) giant elliptical galaxy surrounded
by a dense halo of hot plasma11–13. Under the right conditions,
thermal instabilities can precipitate from this hot gas, producing a
rain of cold clouds that fall toward the galaxy’s centre14, sustaining
star formation amid a kiloparsec-scale molecular nebula that inhabits
its core15. New interferometric sub-millimetre observations
show that these cold clouds also fuel black hole accretion, revealing
“shadows” cast by molecular clouds as they move inward at ∼ 300
km s−1
toward the active supermassive black hole in the galaxy
centre, which serves as a bright backlight. Corroborating evidence
from prior observations16 of warmer atomic gas at extremely high
spatial resolution17, along with simple arguments based on geometry
and probability, indicates that these clouds are within the innermost
hundred parsecs of the black hole, and falling closer toward
it
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
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)
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
A giant galaxy in the young Universe with a massive ringSérgio Sacani
In the local (redshift z ≈ 0) Universe, collisional ring galaxies make up only ~0.01% of galaxies1 and are formed by head-on galactic collisions that trigger radially propagating density waves2–4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe5–9. However, not much is known about distant (z > 0.1) collisional rings10–14. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z = 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5–2.2 times larger and is forming stars 50 times faster. The extended, dif- fuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved15,16, the implied large bar in a giant disk would be inconsistent with the current understand- ing of the earliest formation of barred spirals17–21. Contrary to previous predictions10–12, this work suggests that massive col- lisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
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)
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
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values
in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to
provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to
cluster members themselves.
Methods.We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC,
which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband
information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or
from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six dierent approaches
to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing
models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts.
Results. We show that photometric redshifts reach a remarkable 3–5% accuracy. After accounting for magnification, the H-band
number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending
the presently available samples to galaxies that, intrinsically, are as faint as H 32 33, thanks to strong gravitational lensing. The
Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with
respect to extragalactic wide fields, including sources at Mstar 107–108 M at z > 5. Similarly, they allow the detection of objects
with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M=yr at z 6–10.
It has been proposed that ~3.4 billion years ago an ocean fed by enormous catastrophic floods covered
most of the Martian northern lowlands. However, a persistent problem with this hypothesis is the
lack of definitive paleoshoreline features. Here, based on geomorphic and thermal image mapping in
the circum-Chryse and northwestern Arabia Terra regions of the northern plains, in combination with
numerical analyses, we show evidence for two enormous tsunami events possibly triggered by bolide
impacts, resulting in craters ~30km in diameter and occurring perhaps a few million years apart. The
tsunamis produced widespread littoral landforms, including run-up water-ice-rich and bouldery lobes,
which extended tens to hundreds of kilometers over gently sloping plains and boundary cratered
highlands, as well as backwash channels where wave retreat occurred on highland-boundary surfaces.
The ice-rich lobes formed in association with the younger tsunami, showing that their emplacement
took place following a transition into a colder global climatic regime that occurred after the older
tsunami event. We conclude that, on early Mars, tsunamis played a major role in generating and
resurfacing coastal terrains.
A statistical analysis_of_the_accuracy_of_the_digitized_magnitudes_of_photome...Sérgio Sacani
We present a statistical analysis of the accuracy of the digitized magnitudes of photometric plates on
the time scale of decades. In our examination of archival Johnson B photometry from the Harvard
DASCH archive, we nd a median RMS scatter of lightcurves of order 0.15mag over the range B
9 17 for all calibrations. Slight underlying systematics (trends or
ux discontinuities) are on a level
of . 0:2mag per century (1889{1990) for the majority of constant stars. These historic data can
be unambiguously used for processes that happen on scales of magnitudes, and need to be carefully
examined in cases approaching the noise
oor. The characterization of these limits in photometric
stability may guide future studies in their use of plate archives. We explain these limitations for the
example case of KIC8462852, which has been claimed to dim by 0:16mag per century, and show that
this trend cannot be considered as signicant.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
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)
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
A giant galaxy in the young Universe with a massive ringSérgio Sacani
In the local (redshift z ≈ 0) Universe, collisional ring galaxies make up only ~0.01% of galaxies1 and are formed by head-on galactic collisions that trigger radially propagating density waves2–4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe5–9. However, not much is known about distant (z > 0.1) collisional rings10–14. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z = 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5–2.2 times larger and is forming stars 50 times faster. The extended, dif- fuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved15,16, the implied large bar in a giant disk would be inconsistent with the current understand- ing of the earliest formation of barred spirals17–21. Contrary to previous predictions10–12, this work suggests that massive col- lisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
Past studies have identified a spatially extended excess of ∼1-3 GeV gamma rays from the region
surrounding the Galactic Center, consistent with the emission expected from annihilating dark
matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics
and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails
of the point spread function and generate high resolution gamma-ray maps, enabling us to more
easily separate the various gamma-ray components. Within these maps, we find the GeV excess
to be robust and highly statistically significant, with a spectrum, angular distribution, and overall
normalization that is in good agreement with that predicted by simple annihilating dark matter
models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to
b
¯b with an annihilation cross section of σv = (1−3)×10−26 cm3
/s (normalized to a local dark matter
density of 0.4 GeV/cm3
). Furthermore, we confirm that the angular distribution of the excess is
approximately spherically symmetric and centered around the dynamical center of the Milky Way
(within ∼0.05◦
of Sgr A∗
), showing no sign of elongation along the Galactic Plane. The signal is
observed to extend to at least ' 10◦
from the Galactic Center, disfavoring the possibility that this
emission originates from millisecond pulsars.
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
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)
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
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values
in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to
provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to
cluster members themselves.
Methods.We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC,
which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband
information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or
from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six dierent approaches
to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing
models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts.
Results. We show that photometric redshifts reach a remarkable 3–5% accuracy. After accounting for magnification, the H-band
number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending
the presently available samples to galaxies that, intrinsically, are as faint as H 32 33, thanks to strong gravitational lensing. The
Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with
respect to extragalactic wide fields, including sources at Mstar 107–108 M at z > 5. Similarly, they allow the detection of objects
with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M=yr at z 6–10.
It has been proposed that ~3.4 billion years ago an ocean fed by enormous catastrophic floods covered
most of the Martian northern lowlands. However, a persistent problem with this hypothesis is the
lack of definitive paleoshoreline features. Here, based on geomorphic and thermal image mapping in
the circum-Chryse and northwestern Arabia Terra regions of the northern plains, in combination with
numerical analyses, we show evidence for two enormous tsunami events possibly triggered by bolide
impacts, resulting in craters ~30km in diameter and occurring perhaps a few million years apart. The
tsunamis produced widespread littoral landforms, including run-up water-ice-rich and bouldery lobes,
which extended tens to hundreds of kilometers over gently sloping plains and boundary cratered
highlands, as well as backwash channels where wave retreat occurred on highland-boundary surfaces.
The ice-rich lobes formed in association with the younger tsunami, showing that their emplacement
took place following a transition into a colder global climatic regime that occurred after the older
tsunami event. We conclude that, on early Mars, tsunamis played a major role in generating and
resurfacing coastal terrains.
A statistical analysis_of_the_accuracy_of_the_digitized_magnitudes_of_photome...Sérgio Sacani
We present a statistical analysis of the accuracy of the digitized magnitudes of photometric plates on
the time scale of decades. In our examination of archival Johnson B photometry from the Harvard
DASCH archive, we nd a median RMS scatter of lightcurves of order 0.15mag over the range B
9 17 for all calibrations. Slight underlying systematics (trends or
ux discontinuities) are on a level
of . 0:2mag per century (1889{1990) for the majority of constant stars. These historic data can
be unambiguously used for processes that happen on scales of magnitudes, and need to be carefully
examined in cases approaching the noise
oor. The characterization of these limits in photometric
stability may guide future studies in their use of plate archives. We explain these limitations for the
example case of KIC8462852, which has been claimed to dim by 0:16mag per century, and show that
this trend cannot be considered as signicant.
A 17 billion_solar_mass_black_hole_in_a_group_galaxy_with_a_difuse_coreSérgio Sacani
Quasars are associated with and powered by the accretion of
material onto massive black holes; the detection of highly luminous
quasars with redshifts greater than z = 6 suggests that black holes of
up to ten billion solar masses already existed 13 billion years ago1.
Two possible present-day ‘dormant’ descendants of this population
of ‘active’ black holes have been found2 in the galaxies NGC 3842
and NGC 4889 at the centres of the Leo and Coma galaxy clusters,
which together form the central region of the Great Wall3—the
largest local structure of galaxies. The most luminous quasars,
however, are not confined to such high-density regions of the
early Universe4,5; yet dormant black holes of this high mass have
not yet been found outside of modern-day rich clusters. Here we
report observations of the stellar velocity distribution in the galaxy
NGC 1600—a relatively isolated elliptical galaxy near the centre
of a galaxy group at a distance of 64 megaparsecs from Earth. We
use orbit superposition models to determine that the black hole at
the centre of NGC 1600 has a mass of 17 billion solar masses. The
spatial distribution of stars near the centre of NGC 1600 is rather
diffuse. We find that the region of depleted stellar density in the
cores of massive elliptical galaxies extends over the same radius as
the gravitational sphere of influence of the central black holes, and
interpret this as the dynamical imprint of the black holes.
We describe the discovery of a satellite in orbit about the dwarf planet (136472) Makemake. This
satellite, provisionally designated S/2015 (136472) 1, was detected in imaging data collected with the
Hubble Space Telescope’s Wide Field Camera 3 on UTC April 27, 2015 at 7.80±0.04 magnitudes
fainter than Makemake. It likely evaded detection in previous satellite searches due to a nearly edgeon
orbital configuration, placing it deep within the glare of Makemake during a substantial fraction
of its orbital period. This configuration would place Makemake and its satellite near a mutual event
season. Insufficient orbital motion was detected to make a detailed characterization of its orbital
properties, prohibiting a measurement of the system mass with the discovery data alone. Preliminary
analysis indicates that if the orbit is circular, its orbital period must be longer than 12.4 days, and
must have a semi-major axis &21,000 km. We find that the properties of Makemake’s moon suggest
that the majority of the dark material detected in the system by thermal observations may not reside
on the surface of Makemake, but may instead be attributable to S/2015 (136472) 1 having a uniform
dark surface. This “dark moon hypothesis” can be directly tested with future JWST observations.
We discuss the implications of this discovery for the spin state, figure, and thermal properties of
Makemake and the apparent ubiquity of trans-Neptunian dwarf planet satellites.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
Stellar-like objects with effective temperatures of 2700K and below are referred to as
20 "ultracool dwarfs"1. This heterogeneous group includes both extremely low-mass stars
21 and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion),
22 and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on
23 the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for
24 ultracool dwarfs predicts a large, but heretofore undetected, population of close-in
25 terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable
26 volatile-rich Earth-sized planets7. Here we report the discovery of three short-period
27 Earth-sized planets transiting an ultracool dwarf star 12 parsecs away. The inner two
28 planets receive four and two times the irradiation of Earth, respectively, placing them
29 close to the inner edge of the habitable zone of the star8. Eleven orbits remain possible
30 for the third planet based on our data, the most likely resulting in an irradiation
31 significantly smaller than Earth's. The infrared brightness of the host star combined
32 with its Jupiter-like size offer the possibility of constraining the composition and
33 thoroughly characterizing the atmospheric properties of the components of this nearby
34 planetary system, notably to detect potential biosignatures.
Direct Measure of Radiative And Dynamical Properties Of An Exoplanet AtmosphereSérgio Sacani
Two decades after the discovery of 51Pegb, the formation processes and atmospheres of short-period gas giants
remain poorly understood. Observations of eccentric systems provide key insights on those topics as they can
illuminate how a planet’s atmosphere responds to changes in incident flux. We report here the analysis of multi-day
multi-channel photometry of the eccentric (e ~ 0.93) hot Jupiter HD80606b obtained with the Spitzer Space
Telescope. The planet’s extreme eccentricity combined with the long coverage and exquisite precision of new
periastron-passage observations allow us to break the degeneracy between the radiative and dynamical timescales
of HD80606b’s atmosphere and constrain its global thermal response. Our analysis reveals that the atmospheric
layers probed heat rapidly (∼4 hr radiative timescale) from<500 to 1400 K as they absorb ~20% of the incoming
stellar flux during the periastron passage, while the planet’s rotation period is 93 35
85
-
+ hr, which exceeds the predicted
pseudo-synchronous period (40 hr).
Key words: methods: numerical – planet–star interactions – planets and satellites: atmospheres – planets and
satellites: dynamical evolution and stability – planets and satellites: individual (HD 80606 b) – techniques:
photometric
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
Dust Enrichment and Grain Growth in a Smooth Disk around the DG Tau Protostar...Sérgio Sacani
Characterizing the physical properties of dust grains in a protoplanetary disk is critical to comprehending the planet
formation process. Our study presents Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution
observations of the young protoplanetary disk around DG Tau at a 1.3 mm dust continuum. The observations, with
a spatial resolution of ≈0 04, or ≈5 au, revealed a geometrically thin and smooth disk without substantial
substructures, suggesting that the disk retains the initial conditions of the planet formation. To further analyze the
distributions of dust surface density, temperature, and grain size, we conducted a multiband analysis with several
dust models, incorporating ALMA archival data of the 0.87 and 3.1 mm dust polarization. The results showed that
the Toomre Q parameter is 2 at a 20 au radius, assuming a dust-to-gas mass ratio of 0.01. This implies that a
higher dust-to-gas mass ratio is necessary to stabilize the disk. The grain sizes depend on the dust models, and for
the DSHARP compact dust, they were found to be smaller than ∼400 μm in the inner region (r 20 au) while
exceeding larger than 3 mm in the outer part. Radiative transfer calculations show that the dust scale height is lower
than at least one-third of the gas scale height. These distributions of dust enrichment, grain sizes, and weak
turbulence strength may have significant implications for the formation of planetesimals through mechanisms such
as streaming instability. We also discuss the CO snowline effect and collisional fragmentation in dust coagulation
for the origin of the dust size distribution.
The xmm newton-view_of_the_central_degrees_of_the_milk_waySérgio Sacani
Novas imagens do Observatório de Raios-X XMM-Newton da ESA revelaram alguns dos processos mais intensos que acontecem no coração da nossa Via Láctea.
As fontes brilhantes e pontuais que se destacam por toda imagem indicam os sistemas estelares binários onde uma das estrelas atingiu o final de sua vida, desenvolvendo para um objeto compacto e denso – uma estrela de nêutrons ou um buraco negro.
A região central da Via Láctea também contém jovens estrelas e aglomerados estelares e algumas dessas fontes são visíveis como pontos brancos e vermelhos brilhando na imagem, que se espalha por 1000 anos-luz.
A maior parte da ação ocorre no centro, onde nuvens difusas de gás estão sendo cavadas por ventos poderosos soprados por estrelas jovens, bem como por supernovas.
ALMA Observations of the Extraordinary Carina Pillars: A Complementary SampleSérgio Sacani
We present a study of six dusty and gaseous pillars (containing the HH 1004 and HH 1010 objects)
and globules (that contain the HH 666, HH 900, HH 1006, and HH 1066 objects) localized in the Carina
nebula using sensitive and high angular resolution (∼0.3′′) Atacama Large Millimeter/Sub-millimeter
Array (ALMA) observations. This is a more extensive study that the one presented in Cortes-Rangel
et al. (2020). As in this former study, we also analyzed the 1.3 mm continuum emission and C18O(2−1),
N2D+(3−2) and 12CO(2−1) spectral lines. These new observations revealed the molecular outflows
emanating from the pillars, the dusty envelopes+disks that are exciting them, and the extended HH
objects far from their respective pillars. We reveal that the masses of the disks+envelopes are in a
range of 0.02 to 0.38 M⊙, and those for the molecular outflows are of the order of 10−3 M⊙, which
suggests that their exciting sources might be low- or intermediate-mass protostars as already revealed
in recent studies at infrared and submillimeter bands. In the regions associated with the objects HH
900 and HH 1004, we report multiple millimeter continuum sources, from where several molecular
outflows emanate.
Galaxy growth in a massive halo in the first billion years of cosmic historySérgio Sacani
According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field1–3. Observing these structures during their period of active growth and assembly—the first few hundred million years of the Universe—is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far4,5. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey6. High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe7. These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.
SO and SiS Emission Tracing an Embedded Planet and Compact 12CO and 13CO Coun...Sérgio Sacani
Planets form in dusty, gas-rich disks around young stars, while at the same time, the planet formation
process alters the physical and chemical structure of the disk itself. Embedded planets will locally heat
the disk and sublimate volatile-rich ices, or in extreme cases, result in shocks that sputter heavy atoms
such as Si from dust grains. This should cause chemical asymmetries detectable in molecular gas
observations. Using high-angular-resolution ALMA archival data of the HD 169142 disk, we identify
compact SO J=88–77 and SiS J=19–18 emission coincident with the position of a ∼2 MJup planet seen
as a localized, Keplerian NIR feature within a gas-depleted, annular dust gap at ≈38 au. The SiS
emission is located along an azimuthal arc and has a similar morphology as a known 12CO kinematic
excess. This is the first tentative detection of SiS emission in a protoplanetary disk and suggests that
the planet is driving sufficiently strong shocks to produce gas-phase SiS. We also report the discovery of
compact 12CO and 13CO J=3–2 emission coincident with the planet location. Taken together, a planetdriven outflow provides the best explanation for the properties of the observed chemical asymmetries.
We also resolve a bright, azimuthally-asymmetric SO ring at ≈24 au. While most of this SO emission
originates from ice sublimation, its asymmetric distribution implies azimuthal temperature variations
driven by a misaligned inner disk or planet-disk interactions. Overall, the HD 169142 disk shows
several distinct chemical signatures related to giant planet formation and presents a powerful template
for future searches of planet-related chemical asymmetries in protoplanetary disks.
An almost dark galaxy with the mass of the Small Magellanic CloudSérgio Sacani
Almost Dark Galaxies are objects that have eluded detection by traditional surveys such as the Sloan Digital Sky Survey (SDSS). The
low surface brightness of these galaxies (µr(0)> 26 mag/arcsec2
), and hence their low surface stellar mass density (a few solar masses
per pc2 or less), suggests that the energy density released by baryonic feedback mechanisms is inefficient in modifying the distribution
of the dark matter halos they inhabit. For this reason, almost dark galaxies are particularly promising for probing the microphysical
nature of dark matter. In this paper, we present the serendipitous discovery of Nube, an almost dark galaxy with < µV >e∼ 26.7
mag/arcsec2
. The galaxy was identified using deep optical imaging from the IAC Stripe82 Legacy Project. Follow-up observations
with the 100m Green Bank Telescope strongly suggest that the galaxy is at a distance of 107 Mpc. Ultra-deep multi-band observations
with the 10.4m Gran Telescopio Canarias favour an age of ∼ 10 Gyr and a metallicity of [Fe/H]∼ −1.1. With a stellar mass of ∼ 4×108
M⊙ and a half-mass radius of Re = 6.9 kpc (corresponding to an effective surface density of < Σ >e∼ 0.9 M⊙/pc2
), Nube is the most
massive and extended object of its kind discovered so far. The galaxy is ten times fainter and has an effective radius three times larger
than typical ultra-diffuse galaxies with similar stellar masses. Galaxies with comparable effective surface brightness within the Local
Group have very low mass (tens of 105 M⊙) and compact structures (effective radius Re < 1 kpc). Current cosmological simulations
within the cold dark matter scenario, including baryonic feedback, do not reproduce the structural properties of Nube. However, its
highly extended and flattened structure is consistent with a scenario where the dark matter particles are ultra-light axions with a mass
of mB=(0.8
+0.4
−0.2
)×10−23 eV
Similar to Exocometary gas in_th_hd_181327_debris_ring (20)
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.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
2. 2 S. Marino et al.
Figure 1. ALMA dust continuum maps at 220 GHz (Band 6). a) panel: MEM non-parametric model (regularized with the maximum entropy method). b)
panel: restored image adding residuals and convolving with a synthetic beam corresponding to Briggs weighting (0. 47×0. 36). c) panel: restored image adding
residuals and convolving with a synthetic beam corresponding to natural weighting (0. 69 × 0. 58). The respective beams are represented by white ellipses.
The x- and y-axes indicate the offset from the stellar position in R.A. and decl. in arcsec, i.e. north is up and east is left. The stellar position is marked with a
white star.
Optical observations of discs can give insights about the dis-
tribution of µm-sized dust grains at the bottom of the collisional
cascade, where stellar radiation and stellar winds become signif-
icant for the dust dynamics (Thébault & Wu 2008). On the other
hand, dust thermal emission at millimetre wavelengths is domi-
nated by big grains (∼0.1-10 mm) for which radiation forces are
negligible (β ≡ Frad/Fg<<1.0), tracing the location of the parent
bodies. Therefore, millimetre observations are fundamental to study
the distribution of the more massive planetesimals at the top of the
collisional cascade.
Moreover, in some of these systems significant amounts of gas
has been detected, especially in young debris discs that recently
left the protoplanetary disc phase. This gas can potentially impact
the dust dynamics and density distribution, producing structures
that are usually attributed to perturbing planets (Lyra & Kuchner
2013). The origin of this gas is still under debate; however, recent
ALMA observations have allowed dynamical studies and thus a
more detailed picture. This has favoured a secondary origin scenario
in the case of β Pictoris (Dent et al. 2014) and 49 Ceti (Zuckerman
et al. 1995; Zuckerman & Song 2012) from destructive collisions
of icy-bodies. In other systems the gas seems to be primordial (e.g.
HD 21997, Kóspál et al. 2013). However, until now gas had only
been detected in seven debris discs, all of them around A stars. (see
Table 5 in Moór et al. 2015, for a complete list of debris discs with
gas detections).
In this work we study the debris disc around the F5/6 main
sequence star HD 181327 (Nordström et al. 2004; Torres et al. 2006),
member of the 23 ± 3 Myr old β Pic moving group (Mamajek &
Bell 2014) and located at a distance of 51.8 ± 1.7 pc (van Leeuwen
2007). The star has an IR excess with a fractional luminosity of
LIR/L ∼ 0.2% (Lebreton et al. 2012) that comes from dust thermal
emission that has been marginally resolved at different wavelengths:
at 18.3 µm by Chen et al. (2008) and at 70 µm, 100 µm and 3.2 mm
by Lebreton et al. (2012). HST scattered light observations resolved
a debris ring of µm-sized grains with a peak at ∼ 90 AU and 36
AU wide (Schneider et al. 2006; Stark et al. 2014). The latter study
identified a possible radial dust size segregation due to radiation
pressure, based on variations of the scattering phase function with
radius. Moreover, they found asymmetries that could be interpreted
as an increase in the optical depth in the west side of the ring,
potentially due to either a recent catastrophic disruption or warping
of the disk by the ISM.
We present the first ALMA observations to study the dust
continuum at 220 GHz and the CO gas distribution, constrain the
location of planetesimals, look for asymmetries that could give hints
on the origin of the asymmetric features observed by the HST, and
study the origin of the CO gas. In Sec. 2 we present the observations
and imaging of the dust continuum and CO line emission. In Sec.
3 we compare the observations with an axisymmetric disc model
for the dust continuum and CO (2-1), using a Markov chain Monte
Carlo (MCMC) method coupled with radiative transfer simulations
to sample the parameter space and estimate the debris spatial dis-
tribution, CO gas mass and the disc orientation in the sky. In Sec.
4 we discuss the implications of the dust continuum and CO ob-
servations, we compare them with the previous HST observations,
we derive a cometary composition based on the CO observations,
and we discuss scale height constrains from ALMA observations of
debris discs. Finally in Sec. 5 we summarise the main results and
conclusions.
2 ALMA OBSERVATIONS AND IMAGING
HD 181327 was observed by ALMA in band 6 on 10 March 2014
as part of the cycle 1 project 2012.1.00437.S. The total number of
antennas was 26 with minimum and maximum projected baselines
of 12 and 365 m, respectively. The total time on source excluding
overheads was 34 min. Three months later, on the 4 and 12 June,
three new observation runs using the same band were carried out
corresponding to the cycle 2 project 2013.1.00523.S. The total num-
MNRAS 000, 1–11 (2015)
3. HD 181327 debris ring 3
ber of antennas was 39 with a minimum and maximum projected
baselines of 15 and 650 m, respectively. The total time on source
excluding overheads was 129 min.
On the first run J1924-2914 was used as bandpass calibra-
tor, while Titan and J1819-6365 were used as primary flux and
phase calibrators, respectively. In the second project, J2056-4714
and J2056-472 were used as bandpass calibrators, with the latter
used as primary flux calibrator too. We used J2009-4849 as phase
calibrator. Calibrations were applied using the pipeline provided by
ALMA.
On both projects, the ALMA correlator provided 4 spectral
windows (spws), 3 exclusively dedicated to study the dust continuum
with 128 channels and a total bandwidth of 2 GHz centered at:
212.9, 214.9 and 228.1 GHz in the first project, and 214.6, 216.6
and 232.5 GHz in the second. The fourth spw was configured with
a higher spectral resolution of 244 KHz and total bandwidth of
937.5 MHz (3840 channels), centered at 230.5 GHz to target the
12CO (2-1) transition at 230.538 GHz in both projects. We combine
the two datasets from both projects to achieve the most complete
u − v coverage and the highest signal-to-noise ratio (S/N) on the
reconstructed continuum image and CO line emission.
2.1 Dust continuum
The image synthesis of the dust continuum was carried out using
a non-parametric least-squared modeling technique that incorpo-
rates a regularization term called “entropy” from a family of Max-
imum Entropy Methods (MEMs). Examples of usage of MEM for
image synthesis in Astronomy can be found in Pantin & Starck
1996; Casassus et al. 2006; Levanda & Leshem 2010; Casassus
et al. 2013; Warmuth & Mann 2013; Coughlan & Gabuzda 2013;
Marino et al. 2015. These deconvolved images "superresolve" the
interferometric data, as the entropy prior allows an extrapolation
of spatial frequencies beyond those sampled by the interferometer.
We call the whole algorithm uvmem and the resulting images as
“MEM models”. The deconvolved image can then be “restored” by
convolving with a Clean beam corresponding to natural or Briggs
weighting and adding the dirty map of the residuals. The restored
maps are comparable to standard Clean images. While the resolu-
tion or point-spread-function on the deconvolved image can vary
at different locations, the resolution on the restored images is well
characterised by a synthetic beam of 0. 47×0. 36 and 0. 69×0. 58,
corresponding to Briggs and natural weighting respectively.
In Figure 1 we present the results of the image synthesis on
the continuum emission: (a) MEM model, (b) restored image with
Briggs weighting (Briggs map hereafter) and (c) restored image with
natural weights (natural map hereafter). To smooth the artefacts due
to thermal noise on the visibilities and characterize the noise level
in the image space, we perform a Monte Carlo simulation boot-
strapping the measured visibilities, i.e. adding a random Gaussian
noise according to the observed dispersion on each base-line and
repeating the image synthesis described above. The presented im-
ages are the median of 200 iterations. We observe a noise level of
0.022 mJy beam−1 on the Briggs map, while 0.015 mJy beam−1 on
the natural map, estimated from the median absolute deviation and
from the rms on the dirty map of the residuals. The total flux in the
Natural map inside a ellipse of semi-major axis 4 and oriented as
the best-fit model (see Sec. 3) is 7.9 ± 0.2 mJy. This is consistent
with the trend of the spectral energy distribution (SED) between
170 µm (Moór et al. 2006, ISO) and 3.2 mm (Lebreton et al. 2012,
ATCA), but too low compared to the 0.05 Jy at 870 µm observed
by LABOCA-APEX (Nilsson et al. 2009), possibly due to a back-
ground galaxy inside the primary beam. Inside the primary beam we
also detect two compact sources with peak intensities of 0.14 and
0.08 mJy beam−1, located at 8 with a PA=9.5◦ and 9 with a PA
of 210◦, respectively. These are probably background galaxies (see
Figure 8) as the position of the southern compact source is consis-
tent with an edge-on galaxy observed in the STIS/HST observations
in 2011 (Stark et al. 2014).
Similar to previous observations of scattered light, the disc
presents a ring-like morphology. The bulk of the emission is radi-
ally confined between ∼ 50 − 125 AU (∼ 1. 0 − 2. 4) with a peak
intensity at 85.8 ± 0.3 AU obtained by fitting an ellipse to the peak
intensities along the ring of the MEM model. When we compare
these results with the HST observations we find that the ring is
slightly narrower and shifted inwards in the millimetre, while the
inner edge in scattered light (82.3±1.1) is close to the peak radius in
the millimetre. This is consistent with what would be expected from
grain size segregation due to radiation pressure, previously sug-
gested in this disc by Stark et al. (2014). Radiation pressure causes
small dust grains to extend farther out in radius compared with
millimetre grains, shifting the density maximum of small grains to
larger radii (See discussion in Sec. 4.3).
The disc emission appears consistent with an axisymmetric
ring and most of the observed intensity variations along the ring
in the panels of Figure 1 and the small offset from the star can be
explained by the PA of the beam, the noise level and the ALMA
astrometric error (See Sec. 4.1). In Sec. 3.1 we compare with an
axisymmetric model.
In Figure 2 we present intensity profiles of the maps presented
in Figure 1a and 1b, along the ring’s major and minor axis, together
with the deprojected mean intensity at all azimuths extracted from
Figure 1c. In the top and middle panels the MEM model profile
is represented by a red line, while the Briggs map profile is repre-
sented in blue with blue shaded areas equivalent to 1 σ = 0.022/
√
2
mJy beam−1 (the factor 1/
√
2 is due to the mean between the oppo-
site sides of the disc). The projected Briggs Clean beam is presented
with dashed black lines. The radial extent of the emission both along
the major and minor axis is wider than the beam, demonstrating that
we can marginally resolve the width of the ring. The full width half
maximum (FWHM) of the ring is ∼ 0. 5, which at a distance of 51.8
pc translates to ∼ 25 AU. A more accurate estimation is presented
in Sec. 3.1. The bottom panel shows that the disc emission extends
out to ∼ 4 (200 AU) in either a second ring or a halo component.
The grey area in the bottom panel represents the 99.7% confidence
region equivalent to 3 σ = 0.015/
√
Nbeams mJy beam−1 (the factor
1/
√
Nbeams is due to the mean at all azimuth and the number of
independent points). In Figure 1c this emission is also just visible
as a broad ring around 4 . To test the significance of this detec-
tion and whether this could be a product of our image synthesis
method, we produce Clean images obtaining roughly the same re-
sults. Moreover, the second component is recovered in the dirty map
of the residuals when a best-fit ring model is subtracted to the data
(see Sec. 3 for a description of the ring model). A brief discussion
about the origin of this emission and the dirty map of the residuals
is presented in Sec. 4.
2.2 12CO (2-1)
To study the 12CO (2-1) transition line at 230.538 GHz (rest fre-
quency), we first subtract the continuum emission from the visibil-
ities fitting a polynomial of the first order at the frequencies where
no line emission is expected. The dirty map of the continuum sub-
tracted data does not show any significant emission above 3σ which
MNRAS 000, 1–11 (2015)
4. 4 S. Marino et al.
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Distance [arcsec]
0.0
0.5
1.0
1.5
2.0
Intensity[mJyarcsec−2]
Along major axisRestored with Briggs
Clean beam
MEM model
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Distance [arcsec]
0.0
0.5
1.0
1.5
2.0
Intensity[mJyarcsec−2]
Along minor axisRestored with Briggs
Clean beam
MEM model
0 1 2 3 4 5
Deprojected distance [arcsec]
10-2
10-1
100
Intensity[mJyarcsec−2]
Azimuthal averageRestored with natural
Figure 2. Intensity radial profiles of the dust continuum vs distance to the star
along the major (top panel) and minor axis of the disc (middle panel). In the
bottom panel we present the mean intensity at all azimuths vs the deprojected
distance to the star. The red, blue, black dashed and black continuous lines
represent the MEM model, Briggs map, projected Briggs Clean beam and
natural map, respectively. The blue and grey areas represent the 68% and
99.7% confidence regions, respectively.
could be attributed to CO. With natural weights we obtain a noise
level of 1.0 mJy beam−1 per channel. To search for any low CO level
emission we compute the total flux inside an elliptic mask and be-
tween a frequency or velocity range that we vary, both spatially and
in frequency, to maximise the S/N of the integrated flux. The S/N
is maximised inside an elliptic mask of minimum and maximum
semi-major axes of 1. 4 and 2. 1 (assuming the same orientation
and aspect ratio as the main ring) and a velocity range of -2.8 to
2.0 km s−1(Barycentric reference frame). These parameters match
the location of the main ring and the expected Doppler shift due to
Keplerian rotation, i.e. v0 = 0.1 ± 0.4 km s−1 (Gontcharov 2006)
and vmax = 1.9 km s−1 for M = 1.36 M (Lebreton et al. 2012).
The spectrum extracted from the data cube inside the elliptic mask
and smoothed with a Gaussian kernel is presented in Figure 3. The
horizontal lines represent ±1, 3, 4 and 5σ levels. The line peak is
∼ 5σ. The integrated flux where the S/N is maximised is 30.1 ± 5.4
mJy km s−1 (5.6σ). Moreover, we find that the CO emission in
150 100 50 0 50 100 150
Velocity BARY [km s−1 ]
4
2
0
2
4
6
8
Flux[mJy]
1σ
-1σ
3σ
4σ
5σ
Figure 3. Continuum subtracted integrated spectrum inside an elliptic mask
of minimum and maximum semi-major axis of 1. 4 and 2. 1, and oriented
as the dust continuum ring. The original spectrum was smoothed with a
Gaussian kernel with standard deviation of 4 channels. The horizontal lines
represent ±1, 3, 4 and 5σ levels. The grey region represents velocities be-
tween -2.8 km s−1and 2.0 km s−1where the S/N is maximised. The velocities
represent the Doppler shift with respect to 230.538 GHz in the Barycentric
reference frame.
0 1 2 3 4 5
Deprojected distance [arcsec]
0
2
4
6
8
10
Intensity[mJykms−1arcsec−2]
All azimuths
CO emission
Dust continuum
Figure 4. Mean intensity at all azimuths (black line) integrating from -2.8
km s−1and 2.0 km s−1with respect to 230.538 GHz, in the Barycentric
reference frame. The profile is extracted from the dirty map with natural
weights of the continuum subtracted visibilities. The grey area represents
the 99.7% confidence region. In blue we also present the mean intensity of
the dust continuum presented in Fig. 2 in an arbitrary scale.
the south east and north west side of the disc are consistent with
being blue and red shifted, respectively. As the disc north side is the
brightest in scattered light due to forward scattering, we can infer
that it is also the closest side. This implies that the disc is rotating
clockwise in the sky.
In Figure 4 we present the integrated intensity over the velocity
range specified above and averaging at all azimuths. The grey area
represents the 99.7% confidence region. The CO line peaks at 90±4
AU (error=0.5× beam semi-major axis × distance / (S/N)), close to
the ring radius in the continuum, suggesting that gas and dust are
co-located. This favours a secondary origin scenario, where the CO
is being released in destructive collisions of icy bodies. We study the
azimuthal profile of the emission along the ring and we find no ev-
idence for non-axisymmetry, similar to the dust continuum. In Sec.
3.2 we study the CO gas distribution by modeling the CO emission
in the non-LTE regime, with different excitation temperatures and
electron densities which act as the main collisional partner. Using
an MCMC technique we find constraints on the distribution of CO
gas in the disc to quantify its similarity to the dust distribution.
MNRAS 000, 1–11 (2015)
5. HD 181327 debris ring 5
Table 1. Best fit values. Median ± uncertainty based on the 16th and 84th
percentile of the marginalised distributions.
r0 [AU] ∆r2 [AU] H/r3 PA [◦] i [◦]
86.0 ± 0.4 23.2 ± 1.0 0.07 ± 0.03 98.8 ± 1.4 30.0 ± 0.7
3 DISC MODELLING
3.1 Dust continuum
To constrain the location of the millimetre-sized dust population, we
compare the observations with an axisymmetric debris disc model
in the Visibility space. The dust density distribution is parametrized
as a ring of radius r0, with a Gaussian radial profile of width ∆r
(FWHM) and a Gaussian vertical profile with a scale height H
(vertical standard deviation) or aspect ratio h = H/r:
ρ(r, z) = ρ0 exp −
(r − r0)2
2σ2
r
−
z2
2H2
, σr =
∆r
2 2 log 2
. (1)
For the dust optical properties we use a mass-weighted mean
opacity of astrosilicate grains with an internal density of 4.0 g cm−3.
We assume a Dohnanyi-like size distribution with a power law in-
dex of -3.5, and minimum and maximum grain size amin = 1.3µm
and amax = 1.0 cm. These values were roughly estimated com-
paring the model and observed SED in an iterative procedure. The
mass-weighted absorption opacity κabs = 1.0 cm2 g−1 at 1.3 mm,
computed using the “Mie Theory” code written by Bohren & Huff-
man (1983). While (amin, amax), κabs and the derived total dust
mass are highly dependent on our choice on the grain composition
and size distribution, these assumptions have very little effect on
the derived disc structure. A detailed study on the grain properties
of this disc can be found in Lebreton et al. (2012). Synthetic images
are computed using RADMC-3D1 (Dullemond et al. 2015), while
the corresponding visibilities were derived using our tool uvsim.
The free parameters in our model image and visibilities are R0, h,
∆r, Mdust, PA, inclination (i) and RA- and decl-offset. The last two
to account for astrometric uncertainty and disc eccentricity.
We use a Bayesian approach to constrain the different param-
eters of the ring model, sampling the parameter space to recover
the posterior distribution with the public python module emcee that
implements the Goodman & Weare’s Affine Invariant MCMC En-
semble sampler (Foreman-Mackey et al. 2013). The posterior dis-
tribution is defined as the product of the likelihood function and the
prior probability distribution functions for each parameter, which we
assume are uniform. The likelihood function is defined proportional
to exp[− χ2/2], where χ2 is the sum over the squared difference of
the model and measured visibilities, divided by the variance. In our
priors, we impose a lower limit to h equivalent to 0.03. This value
is consistent with the minimum aspect ratio expected in the absence
of perturbing planets (Thébault 2009), and similar to the minimum
h that can be derived from the fractional luminosity assuming an
radially optically thick disc, i.e. h∼ LIR/L ).
The posterior distribution of h, ∆r and r0 is presented in Fig-
ure 5, while in Table 1 we summarise the best fit values extracted
from the marginalised distribution. As we previously mentioned,
the ring is marginally resolved in the radial direction with an expec-
tation value ∆r = 23.2±1.0 AU, where the uncertainty represents
1 http://www.ita.uni-heidelberg.de/∼dullemond/software/radmc-3d/
0.06
0.09
0.12
0.15
0.18
h
20
22
24
26
∆r [AU]
84.8
85.6
86.4
87.2
r0[AU]
0.06
0.09
0.12
0.15
0.18
h
84.8
85.6
86.4
87.2
r0 [AU]
Figure 5. Posterior distribution of h = H/r, r0 and ∆r. The marginalised
distributions of ∆r, h = H/r and r0 are presented in the top, middle right and
bottom right panel, respectively. The vertical dashed lines represent the 2.5th,
50th and 97.5th percentiles. Left middle panel: marginalised distribution of
h and ∆r. Left bottom panel: marginalised distribution of r0 and ∆r. Middle
bottom panel: marginalised distribution of r0 and h. Contours correspond
to 68%, 95% and 99.7% confidence regions. This plot was generated using
the python module corner (Foreman-Mackey et al. 2014).
the standard deviation derived from the marginalised posterior dis-
tribution. The width of the ring can be well constrained with the
assumption of a gaussian radial profile, but as it is of the order of the
beam size a detailed analysis of the radial structure of the main ring
is impossible with the current angular resolution. The width of the
ring is significantly larger than in the Fomalhaut ring (Boley et al.
2012). This could be related to the age of the systems as well as any
possible planet- or star-disc interactions in the case of Fomalhaut
(Faramaz 2015; Shannon et al. 2014). In agreement with the ring
radius derived in Sec. 2, we find r0 = 86.0 ± 0.4 AU.
On the other hand the scale height is not fully constrained. In
principle, it should be possible to derive h from the ratio of the
ring’s width or surface brightness along the major and minor axis
of the projected ring, causing h and ∆r to be correlated. In addition
to this, in our case the estimation of h is limited as our observations
only marginally resolve the ring’s width. However, we can put a
99.7% confidence upper limit of 0.14 for h. Both upper limit and
best fit value (see Table 1) are consistent with the upper limit of
0.11 from Stark et al. (2014) and 0.09 from Schneider et al. (2006).
The same figure shows that h and ∆r are anticorrelated (see Sec.
4.9). The derived total dust mass in the main ring is 0.482 ± 0.006
M⊕. This value is highly dependant on our choice of dust internal
density (4.0 g cm−3) and for our assumed dust size distribution
scales as (amax/1 cm)0.5, noting that amax is unconstrained. In Sec.
4.9 we discuss about determining h in future observations and in
other discs.
Our best axisymmetric model has χ2
red ≡ χ2/(N − ν − 1) =
1.54, where N and ν are the number of independent measurements
(visibilities) and free parameters and equal to 74888 and 8, respec-
MNRAS 000, 1–11 (2015)
6. 6 S. Marino et al.
tively. When we compare the χ2 of our best axisymmetric model
with the MEM model we find a difference of 0.2%. Hence, we con-
clude the continuum emission is consistent with an axisymmetric
ring.
3.2 12CO (2-1)
To derive the CO gas distribution we follow a procedure similar to
the dust continuum modeling in the previous Section. We fit the
data with an axisymmetric disc of gas with a density distribution
parametrized similar to the dust density distribution, but with a
fixed vertical aspect ratio h of 0.07 and fixed disc orientation, that
corresponds to the best fit of the dust continuum (see Table 1). The
gas is in Keplerian circular orbits with a fixed systemic radial ve-
locity of 0.1 km s−1 in the Barycentric frame. Instead of simulating
visibilities as in the dust continuum analysis, we fit the data with
our gas models in the image space. The model images produced
with RADMC-3D at different frequencies (tracing different radial
velocities) are convolved with the dirty beam and then compared
directly with the dirty map of the CO data, both corresponding
to natural weights. This method is analogous to comparing model
visibilities with gridded visibility data. The likelihood function is
defined proportional to exp[− χ2/2], where χ2 is the sum over the
image and frequency space of the squared difference between the
model and observed dirty map, divided by the variance, and taking
into account the number of independent beams in the image and
the correlation between adjacent channels in ALMA data. The free
parameters in the MCMC are the CO gas mass (MCO), ring radius
(r0) and FWHM of the ring (∆r).
However, the CO emission is not only constrained by the den-
sity distribution. Matrà et al. (2015) showed that local thermody-
namic equilibrium (LTE) does not necessarily apply in the low gas
density environments of debris discs. Depending on the gas kinetic
temperature and collisional partner densities, the derived gas mass
can vary by orders of magnitude. Thus, to model the 12CO (2-1)
emission it is necessary to include non-LTE effects, i.e to solve the
population levels including (de-)excitations through radiative pro-
cess, where the CMB photons and dust thermal emission dominate
the radiation field at 230 GHz, as well as through collisions. The
similarity between the dust and gas distribution showed in Sec. 2.2
suggest that the CO is of secondary origin, i.e. produced by colli-
sions between icy planetesimals that release volatile species such
as CO or H2O. This implies that the main collisional partner of CO
molecules are electrons produced by carbon ionization. However,
we stress that the derived CO gas distribution and total mass are
independent of this choice. In Sec. 4.6 we discuss about the origin
of the CO gas. We also use as input our best fit model of the dust
continuum to compute the dust contribution to the radiation field at
230 GHz.
We consider different kinetic temperatures ranging from half
to twice the dust temperature derived in the previous section
(50 K at the ring radius). The electron density is defined as
ne− (r)=n0
e− (r/86 AU)−1.1, where the power law index was assumed
equal to the one derived for β Pic (Matrà et al. prep). We vary
n0
e− between 10−2-107 cm−3 to cover from the radiation-dominated
regime to LTE. Scattered light images suggest that the north east
side of the disc is the closest as it is brighter in scattered light be-
cause of forwards scattering; thus, if the CO is in Keplerian rotation
we should be able to determine the direction at which the CO moves
in the sky. Hence, we consider models of the disc rotating clock-
wise as well as anticlockwise. We find a best fit with the gas rotating
clockwise on the sky. The best model is five times more likely than
10-2 10-1 100 101 102 103 104 105 106 107
ne− at 86 AU [cm−3]
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
MCO×106[M⊕]
TCO =0.5× Tdust
TCO =Tdust
TCO =2.0× Tdust
Figure 6. Best fit CO gas mass values obtained from our MCMC analy-
sis using different kinetic temperatures and electron densities (n0
e− , main
collisional partner). The blue, black and red lines correspond to kinetic
temperatures equal to 0.5, 1 and 2.0 times the dust temperature in the disc,
respectively. The grey area represents the 68% confidence region with gas
temperatures ranging between 0.5 − 2.0 times the dust temperature.
the best anticlockwise model and 300 times more likely than no CO
emission. In Sec. 4.1 we discuss about the implications to the ob-
served asymmetries in scattered light. Below, we concentrate only
on the clockwise case.
In Figure 6 we present the CO gas masses derived with our
MCMC-modeling technique for different kinetic temperatures and
electron densities. We find that our best fit value of MCO can vary
due to the uncertainty in the excitation temperature between 1.2 ±
0.4 × 10−6 - 2.9 ± 0.9 × 10−6 M⊕ in the worst case (LTE), while
it is very well constrained around 1.8 ± 0.6 × 10−6 M⊕ in the
radiation dominated regime (low ne− ). In the β Pic disc recent
ALMA observations suggest n0
e− ∼ 102 cm−3 (Matrà et al. prep).
In Figure 7 we present the posterior distributions, assuming n0
e− =
102 cm−3 and equal gas and dust temperatures. We find MCO =
1.8 ± 0.6 × 10−6 M⊕, r0 = 81+10
−9
AU and ∆r = 48+17
−21
AU. We also
find that the derived values of r0 and ∆r are independent of n0
e− and
the gas kinetic temperature. The radius of the CO ring matches with
the dust ring, confirming what we found averaging the data in Sec.
2.2, that gas and dust are co-located. Given the derived dust and CO
densities it is unlikely that the CO is self shielded enough to avoid
the photodissociation due to the ISM radiation field, which occurs
in a timescale of ∼ 120 yr (Visser et al. 2009) (see discussion in Sec.
4.6). This implies that the CO must be replenished and produced in
the main ring; therefore, we conclude that the CO is of secondary
origin and released in collisions between icy bodies. In Sec. 4.6
discuss about its origin. We also find that the CO ring could have a
radial width similar to the dust distribution, although it is not very
well constrained.
4 DISCUSSION
4.1 Axisymmetry
In Sec. 3 we analysed the observations assuming an axisymmetric
disc, however Stark et al. (2014) found large scale asymmetries
MNRAS 000, 1–11 (2015)
7. HD 181327 debris ring 7
4080
120
160
r0[AU]
1
2
3
4
MCO × 106 [M⊕]
20406080
∆r[AU]
40
80
120
160
r0 [AU]
20
40
60
80
∆r [AU]
Figure 7. Posterior distribution of MCO, r0 and ∆r of the CO disc. The
marginalised distributions of MCO, r0 and ∆r are presented in the top, mid-
dle right and bottom right panel, respectively. The vertical dashed lines rep-
resent the 16th, 50th and 84th percentiles. Left middle panel: marginalised
distribution of MCO and r0. Left bottom panel: marginalised distribution of
∆r and MCO. Middle bottom panel: marginalised distribution of r0 and ∆r.
Contours correspond to 68%, and 95% confidence regions. This plot was
generated using the python module corner (Foreman-Mackey et al. 2014).
consistent with either a recent catastrophic disruption of a large
body or disc warping due to interactions with the ISM. Figure 8
shows the best axisymmetric ring model image (a), the dirty map of
the residuals when the best model is subtracted from the observed
visibilities using natural weighting (b), and when the best double
ring model is subtracted (c, see Section below). The map of residuals
of a single ring is consistent with pure thermal noise without any
peak intensity greater than 3σ along the main ring or where scattered
light observations suggested an increase in the optical depth (black
contours). The same image shows the two compact emission at
∼ 8 N and 9 SW from the star described in Sec. 2.1. We can
put an upper limit on any fractional enhancement of emission in the
millimetre of ∼10%, which is lower than the asymmetries derived
in scattered light (10-42%). This can be translated to a mass upper
limit of any dust density enhancement of 6 × 10−3 M⊕ beam−1
(∼ 3 Pluto mass), assuming the dust composition and grain size
distribution (amax = 1.0 cm) described in Sec. 3. This mass upper
limit scales roughly as (amax/1 cm)1/2 with the Dohnanyi-like size
distribution, as noted in Sec. 3.1.
In a giant collision scenario, the small dust produced from the
collision would initially form a trailing outward-propagating spiral
structure due to radiation pressure that would orbit the star (Kral
et al. 2013). After one orbit the fragments would collide again in
the “pinch point” and would continually produce new debris in this
region where the density is higher. The small dust produced by col-
lisions would form a leading outward-propagating spiral structure
from the pitch point as it is affected by radiation pressure (Jackson
et al. 2014), and we would expect the millimetre-sized dust distri-
bution to be narrower at the collision point, increasing the surface
brightness. In addition, such a collision would produce a CO excess
that would extend from the collision point, along the ring in the
direction of motion as far as it can spread in ∼ 120 yr at which point
is photodissociated, as the disc is optically thin, similar to the case
of β Pictoris (Dent et al. 2014; Jackson et al. 2014).
Such features are not present in the millimetre continuum, nor
in the CO emission. In Sec. 2.2 and 3.2 we found that the CO and,
thus, all the debris rotates clockwise in the sky. This has strong
implications for the interpretation of the asymmetries in scattered
light that extend outwards in an anticlockwise direction, forming
a trailing spiral. The giant collision scenario could only explain
the asymmetry if the collision has occurred in the last 4 × 103 yr
or 5 orbits; thus, very unlikely. An alternative explanation of the
asymmetry in scattered light could be that the disc is being warped
by ISM interactions as suggested by Stark et al. (2014) or that the
excess is being produced by a large body releasing small dust (e.g
Rappaport et al. 2014), in which case the asymmetric structure
would form a trailing spiral of small grains that would orbit the star
in clockwise direction.
4.2 Extended emission
Even though we model the disc as a single ring, we detect emis-
sion that extends at least to 4 (see Sec. 2.1). This emission is
recovered both at the east and west side of the disc with no sig-
nificant differences, and using our image synthesis method as well
as using the Clean algorithm. Moreover, it appears in the residuals
presented in Figure 8b. Assuming the same dust composition and
grain size distribution as in the original ring, we model it with a
second component in the dust density distribution. We find that this
emission can be fitted by a power law surface density distribution,
that starts in the main ring with a surface density 25 times lower
and that decreases as r−1. An alternative is to add a second ring,
in which case we find that the observations are best fitted with a
second ring of radius ∼ 185 AU, FWHM∼ 76 AU and peak surface
density 25 times lower than the maximum of the main ring. In both
alternative models we obtain a total flux of 8.6 ± 0.4 mJy and a dust
mass of ∼ 0.65 ± 0.04 M⊕. Figure 8c shows the residuals when the
double ring model is subtracted, obtaining a map with pure thermal
noise. The origin of this emission could be dust in eccentric orbits
produced in the main ring, or even primordial dust from the pro-
toplanetary disc phase as this is a young system (∼ 23 Myr). This
extended component could be related with the change in slope of the
derived surface density near 150 AU in scattered light (see figure
9 in Stark et al. 2014). Deeper ALMA observations with a more
compact antenna configuration or even ACA observations coupled
with a detailed modeling are necessary to conclude about its origin.
If the dust surface density distribution has a local minimum between
2 and 4 , this could be evidence of a perturbing planet orbiting in
the gap or on a highly eccentric orbit (Pearce & Wyatt 2015).
4.3 Dust size segregation
From our MCMC analysis and the fit of an ellipse to the intensity
maxima along the ring, we find that its radius is 86.0 ± 0.4, sig-
nificantly smaller than at optical wavelengths (r0 = 90.5 ± 1.1).
On the other hand, the distribution of small and millimetre grains
overlaps. The main ring of millimetre grains extends roughly from
63 to 110 AU, while the small dust is found roughly from 70 AU
and beyond 200 AU. The difference in peak radius of 4.5 ± 1.2
AU reveals grain size segregation. Due to radiation pressure, small
MNRAS 000, 1–11 (2015)
8. 8 S. Marino et al.
Figure 8. a) panel: Synthetic model image of the best fit model with two rings at 220 GHz. b) panel: Dirty map of the residuals of the best fit model with a
singe ring corresponding to natural weighting. The black contours represent the optical depth deviations from a uniform disc derived from HST images (Stark
et al. 2014, left panel Figure 1). c) panel: Dirty map of the residuals of the best fit model with two rings corresponding to natural weighting. The white dashed
contours in panels b) and c) correspond to radius of the main and second ring of the best fit two rings model. The Clean beam is represented by a blue ellipse
(0. 67 × 0. 58) in the bottom left corner. The x- and y-axes indicate the offset from the stellar position in R.A. and decl. in arcsec, i.e. north is up and east is left.
dust grains released from larger bodies on circular orbits should
be put on eccentric orbits with larger semi-major axes that depend
on the grain sizes. The net effect is that the larger grains traced at
millimetre wavelengths should remain in almost circular orbits at
the radius of the parent planetesimal belt, while the spatial distribu-
tion of small grains shifts to larger radii (see Thébault & Wu 2008,
for detailed modelling). The same segregation has been proposed
for other debris discs, e.g. in AU Microscopii Strubbe & Chiang
(2006) suggested a parent planetesimal belt at a specific radius to
explain the surface brightness profile from scattered light images.
This was later corroborated by millimetre observations (MacGregor
et al. 2013).
4.4 Collisional timescales
Rough estimates of the time scale at which mass is being lost ( ˙M)
from planetesimals in the steady state collisional cascade can be
made under the following assumptions: (1) the particles in the disc
have small mean eccentricities and inclinations (e and I) equal
to 0.05; (2) the relative velocities between particles is equal to
vK(1.25e2 + I2)1/2 (valid for Rayleigh distributions of e and I,
Lissauer & Stewart 1993; Wetherill & Stewart 1993); (3) planetes-
imal strengths (QD) independent of size and equal to 230 J kg−1
(appropiate for km-sized weak ice bodies, Benz & Asphaug 1999;
Wyatt & Dent 2002). Constant QD leads to a universal particle size
distribution with a power law index of -3.5, consistent with our
assumptions in Sec. 3.1. Under these assumptions and using equa-
tions 15 and 16 from Wyatt (2008) we find ˙M ∼ 3 M⊕ Myr−1. By
equating the collisional lifetime of bodies of different size with the
age of the system (23 Myr), we also infer a maximum planetesimal
size in the collisional cascade (Dc) of at least 1.5 km. Larger plan-
etesimals may be present, but they would not yet have collided, thus
they do not contribute to the collisional cascade. The collisional
lifetime scales with the size of the body, Dc, roughly as (Dc/1.5
km)0.5. We can then extrapolate this to obtain a collisional lifetime
of mm-sized grains of 25 × 103 yr (∼ 40 orbits).
Note that this collision timescale is broadly consistent with
equation 16 in Wyatt et al. (1999) given the different assumptions
for these calculations. This emphasises that the collisional lifetime
of the mm-sized grains is set by the cross-sectional area in small
grains, which is relatively well constrained from the observations,
and is not dependent on the details of the collisional lifetimes of the
largest objects discussed above.
4.5 Eccentric ring?
In our analysis we also found that the ring center is offset by 96 ± 5
mas in RA and −42 ± 5 mas in decl with respect to the phase
center, which was centered at the expected stellar position at epoch.
However, the offset is within the astrometric rms of ALMA (∼ 0. 1;
private communication with ALMA helpdesk). Thus we cannot
conclude on a true eccentricity of the ring or compare with the
eccentricity measured by Stark et al. (2014).
4.6 CO origin
We found that the CO is co-located with the dust, with no evidence
for non-axisymmetry and with a radial extension consistent with
the width of the main ring, although not well constrained. Given
the CO derived mass and limits, we can estimate a vertical and
MNRAS 000, 1–11 (2015)
9. HD 181327 debris ring 9
radial column density of about 1013 and 1014 cm−2 depending on
the gas kinetic temperature and electron densities (see Sec. 3.2),
which implies a CO self shielding coefficient of ∼ 0.6 − 0.8 (Visser
et al. 2009) (low self-shielding) and a photodissociation timescale
of ∼ 150−200 yr due to the interstellar radiation field (see details in
Matrà et al. 2015). The CO must have been produced recently and is
probably continually replenished through destructive collisions of
icy planetesimals, i.e. it has a secondary origin. Furthermore, Given
that the CO cannot exist for an orbital period at these distances, the
majority of detected CO must be produced roughly axisymmetri-
cally throughout the disk ring.
If we compare the derived CO mass with other debris discs with
CO gas detected and of secondary origin (49 Ceti and β Pic, Dent
et al. 2005, 2014, , respectively), we find that for HD 181327 MCO
is at least an order of magnitude lower. Moreover, the CO/dust mass
ratio is about 3 orders of magnitude lower in HD 181327 compared
to β Pic. The difference could be in the host star as 49 Ceti and β Pic
are A stars, which could naturally favour the release of volatiles due
to stronger radiation environments.
4.7 Cometary composition
In Sec. 4.4 we derived the mass lost rate from planetesimals ( ˙M) and
in Sec. 4.6 we determined that the CO must be of secondary origin.
Assuming that the mass of CO present in gas phase is in steady state,
we can derive the CO ice to rock mass fraction fCO of planetesimals
as a function of ˙M and the photodissociation timescale of CO τco.
In steady state we expect fCO × ˙M = MCO × τ−1
co , thus
fCO = 4×10−3 MCO
1.8 × 10−6 M⊕
˙M
3 M⊕ Myr−1
−1
τco
175 yr
−1
.
(2)
This value could vary from 3×10−3 to 5×10−3 due to systematic
uncertainties in MCO and τco(MCO). Moreover, the value of ˙M is
highly dependant on QD which could vary between 200 and 104
J kg−1 for km-sized bodies, making fCO range between 3×10−3
to 0.12. The net effect is that fCO is probably between 0.3%-12%
which is consistent with the CO abundance in Solar system comets
(0.2-20 %, Mumma & Charnley 2011). If the planetesimals have an
ice to rock fraction similar to the Solar system of about unity, we
can extrapolate and obtain a CO/H2O ice ratio between 0.4-21%.
4.8 Dust-gas interactions
The origin of the ring-like morphology of the HD 181327 disk is
unclear. Lyra & Kuchner (2013) showed that dust-gas interactions
can be non-negligible in debris discs and produce instabilities that
shape the dust and gas distribution in narrow ring-like structures.
These instabilities arise if: the dust friction time τf is in the range
of 0.1-10 ×1/ΩK, with Ωk the Keplerian rotation frequency, and
dust to gas ratio ε 1. To ascertain if this could explain the dust
distribution in the HD 181327 debris disc we need to estimate τf
and ε. A reasonable value for the stopping time as a function of the
grain size can be obtained using the CO gas mass derived in our
modeling, i.e. MCO = 5 × 10−7 − 11 × 10−7 M⊕, and if we assume:
(1) the gas is dominated by CO, H2O and their photodissociaton
products; (2) the CO/H2O ice mass ratio in planetesimals derived
above (0.4-21%); (3) the C/CO abundance ratio is ∼ 100, the same
as in β Pic (Roberge et al. 2006). Under these assumptions we find
a total gas mass that could vary between 6 × 10−4 and 0.04 M⊕.
The stopping time defined as τf = mvrel/Fdrag can be esti-
mated considering the Epstein drag force that gas exerts on dust
grains. We approximate the dust grain velocities with the same ex-
pression for the relative velocities presented in Sec. 4.4. The gas
drag force depends on the gas density, gas kinetic temperature (Tk )
and the grain size (ad). The first can be derived assuming a gas
density distribution proportional to the dust density distribution,
while the second is assumed to be close to the mm-dust dust grain
temperature in the ring (∼50 K). Finally we obtain
τfric 3 × 103 Mgas
0.04 M⊕
−1
ad
1 mm
Tk
50 K
−1/2
Ω−1
K . (3)
Thus, for mm-sized particles τfric 3 × 103Ω−1, much longer
than the necessary to trigger the instability. Moreover, the stopping
time is even longer than the collisional lifetime calculated in Sec.
4.4 (∼ 40 orbits). Only for grains at the bottom of the collisional
cascade, with sizes 10 µm, the stopping time is in the range
where the instability could be triggered. The dust-to-gas mass ratio
of grains smaller than 10 µm is of the order of unity. However,
given that this instability does not apply to the mm-sized grains,
and the distribution of micron-sized grains is consistent with being
derived from the mm-sized grains, with any differences in their
distribution attributable to radiation pressure without the need for
the photoelectric instability, we conclude that this instability does
not necessarily play a significant role in this disk. Furthermore,
the collisional lifetime of µm-sized grains can be obtained using
the fractional luminosity of the disk Wyatt et al. (1999), which
translates to ∼5 orbits, while the timescale for the instability to
occur is tens of orbital periods (Lyra & Kuchner 2013).
4.9 Scale height
We showed that ALMA observations can be useful to measure
or constrain the vertical mass distribution in discs, even for non
highly inclined discs. Moreover, the dust thermal emission is not
dependant on the scattering phase function, which hinders scale
height estimates from scattered light observations. In the case of
HD 181327, we found an upper limit for h = H/r consistent with
previous observations. As h is directly related to the mean orbital
inclination relative to the disk midplane, measurements of it at
(sub)millimetre wavelengths can be a powerful tool for identifying
perturbing massive bodies, e.g. planets on inclined orbits stirring
the disc vertically.
To illustrate why ALMA observations can constrain h in nar-
row discs, we study the brightness profile at a given radius of model
disc observations with different h, ∆r and i. For a given surface
density profile, different h’s result in different azimuthal intensity
profiles due to changes of the optical depth in the line of sight.
For a narrow ring, higher values of h make the disc brighter at the
ansae compared to the regions close to the disc minor-axis. This is
shown in Figure 9 where we plot intensity profiles, normalized at
the disc ansa (PA=90◦), versus position angle obtained from sim-
ulated ALMA cycle 3 observations. We used as input image our
best-fit ring model and we vary h and ∆r. The equivalent angular
resolution of the simulated observations is ∼ 0. 25. The upper panel
corresponds to a disc inclination similar to HD 181327 (30◦), while
the lower panel to a general disc inclined by 70◦. Based on the
curves of three reasonable values of h, we find that the S/N required
to determine the scale height is extremely dependent on the disc
inclination. For example, if we compare the profile of h=0.08 and
0.03, the largest difference in the normalized intensity profiles is
MNRAS 000, 1–11 (2015)
10. 10 S. Marino et al.
∼ 4% at PA=0◦ and ∼ 10% when comparing h=0.08 and 0.15. This
can give a rough estimate of the required S/N to recover the original
h in a real observation, i.e. S/N 1/0.04 = 25 to distinguish cases
with h between 0.03 and 0.08, and S/N 1/0.1 = 10 to exclude h
of 0.15 or higher. On the other hand, if the disc is inclined by 70◦
the S/N required to distinguished between the three cases would be
1/0.2 = 5. Hence, high S/N ALMA observations are fundamen-
tal to constrain the scale height of low inclined debris rings, and
thus, the level of stirring of the debris.
Interestingly, changing ∆r can produce a similar effect to the
intensity profile. In the bottom panel, the dashed yellow line cor-
responding to h = 0.08 and ∆r = 10 AU has a similar profile
compared with the case h = 0.15 and ∆r = 23 AU. However, ∆r
can be directly estimated measuring the width of the ring along the
major axis, breaking this degeneracy. The anticorrelation between
h and ∆r mentioned in Sec. 3.1 that appears in Figure 5 can be qual-
itatively understood as both h or ∆r have an impact on the width of
the ring projected in the sky.
Using the antenna configurations for cycle 3 provided in the
CASA software, we simulate ALMA observations to estimate the
necessary angular resolution to recover an aspect ratio H/r of
0.08 with an uncertainty less than 10% of our best-fit model for
HD 181327, using our RADMC3D-MCMC approach. We find that
provided with a maximum projected baseline of 1.3 km at 220 GHz,
i.e. an angular resolution of ∼ 0. 25, and a S/N of ∼ 50 along the
ring, it would be possible to constrain H/r = 0.083 ± 0.005.
5 SUMMARY
We resolved the HD 181327 debris ring in dust continuum for the
first time at millimetre-wavelengths with an angular resolution of
0. 47 × 0. 36 and we detected 12CO (2-1) emission for the first time
in a debris disc around a solar-type star. Assuming an axisymmetric
disc, we found that the dust continuum is best fitted with ring of
radius 86±0.4 AU and width 23.1±1.0 AU. At this angular resolu-
tion, the vertical mass distribution is hard to constrain, but we were
able to put an upper limit of 0.14 for the vertical aspect ratio H/r.
The ALMA observations are consistent with an axisymmetric
ring and no significant residuals along the main ring remain after
subtracting the best fit model to the continuum data. We also derived
an upper limit for any dust overdensity along the primary ring. When
we compared to previous HST observations at optical wavelengths
we found that the derived orientations of the disc on the sky are
consistent, but the ring radius derived from our data is significantly
smaller. This result is consistent with grain size segregation due to
radiation pressure.
Additionally, we detected low-level emission that extends be-
yond the primary ring, consistent with either an extended halo of
dust or a secondary ring. This result is robust against different im-
age synthesis methods and is also recovered in the residuals of our
best-fit ring model. Deeper ALMA or ACA observations could help
to study the origin of this emission.
We found that the CO is co-located with the dust, favouring
a secondary origin scenario. Assuming an axisymmetric model we
model the CO emission in the non-LTE regime with different kinetic
gas temperatures and collisional partner densities. With gas kinetic
temperatures of 50 K and electron densities similar to the ones
found in β Pic, the emission is best fitted with a total CO gas mass
of 6.4 ± 2.3 × 10−7M⊕. In addition, we derived CO ice abundances
in planetesimals and we found that they are consistent with the
composition observed in Solar system comets. Furthermore, it is
0◦
30◦
60◦
90◦
PA [deg]
0.90
0.95
1.00
1.05
Normalisedintensity
i=30.0◦
h=0.03, ∆r=23 AU
h=0.08, ∆r=23 AU
h=0.15, ∆r=23 AU
h=0.08, ∆r=10 AU
h=0.08, ∆r=30 AU
0◦
30◦
60◦
90◦
PA [deg]
0.2
0.4
0.6
0.8
1.0
Normalisedintensity
i=70.0◦
h=0.03, ∆r=23 AU
h=0.08, ∆r=23 AU
h=0.15, ∆r=23 AU
h=0.08, ∆r=10 AU
h=0.08, ∆r=30 AU
Figure 9. Intensity profiles along the ring projected ellipse on sky obtained
from simulated Clean images without noise and using our best fit ring
model. The values are normalised to the intensity at the ring semi-major
axis (PA=90◦). The upper panel corresponds to a disc inclined by 30◦, while
the lower to 70◦. In red, blue and green lines we present three different
profiles for disc aspect ratios of 0.03, 0.08 and 0.15 with ∆r fixed to 23 AU,
while in dashed lines we present profiles varying h and ∆r.
unlikely that the effect of hydrodynamics can affect the structure of
the disc.
Finally, we showed that ALMA observations can be very useful
to constrain the vertical distribution of discs. The S/N required is
strongly dependent on the disc inclination in the sky, making it
harder for discs close to a face on orientation as HD 181327.
ACKNOWLEDGEMENTS
We thank Pablo Roman for his help developing the tools uvmem
and uvsim used in this work. This paper makes use of the
following ALMA data: ADS/JAO.ALMA#2012.1.00437.S and
ADS/JAO.ALMA#2013.1.00523.S. ALMA is a partnership of ESO
(representing its member states), NSF (USA) and NINS (Japan), to-
getherwith NRC(Canada)and NSCand ASIAA(Taiwan)and KASI
(Republic of Korea), in cooperation with the Republic of Chile. The
Joint ALMA Observatory is operated by ESO, AUI/NRAO and
NAOJ. This work was supported by the European Union through
ERC grant number 279973. SM, SC, SP acknowledge financial
support from Millennium Nucleus RC130007 (Chilean Ministry of
Economy), and additionally by FONDECYT grants 1130949 and
MNRAS 000, 1–11 (2015)
11. HD 181327 debris ring 11
3140601. GMK is supported by the Royal Society as a Royal Society
University Research Fellow.
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