Com o auxílio do Atacama Large Millimeter/submillimeter Array (ALMA), astrônomos obtiveram as mais claras indicações conseguidas até hoje de que planetas com várias vezes a massa de Júpiter se formaram recentemente nos discos de gás e poeira que rodeiam quatro estrelas jovens. Medições do gás em torno das estrelas forneceram também pistas adicionais relativas às propriedades destes planetas.
Existem planetas em órbita de quase todas as estrelas, no entanto os astrônomos ainda não compreendem bem como — e sob que condições — é que estes corpos se formam. Para responder a estas perguntas, foi feito um estudo dos discos em rotação de gás e poeira que se situam em torno de estrelas jovens e a partir dos quais se formam os planetas. Como estes discos são pequenos e encontram-se muito distantes da Terra, foi necessário utilizar o ALMA para revelar os seus segredos.
Uma classe especial destes discos, os discos transitórios, possui uma falta surpreendente de poeira nos seus centros, na região em torno da estrela. Duas ideias principais foram adiantadas para explicar estas estranhas cavidades na poeira dos discos. A primeira diz que ventos estelares fortes e radiação intensa poderiam ter soprado para longe ou mesmo destruído o material à sua volta [1]. Alternativamente, planetas jovens massivos em processo de formação poderão também ter limpo o material à medida que orbitam a estrela [2].
Imaging of the_co_snow_line_in_a_solar_nebula_analogSérgio Sacani
This document summarizes research on observing the location of the carbon monoxide (CO) snow line in protoplanetary disks. Key points:
1) N2H+ emission is expected to trace the CO snow line as N2H+ forms most abundantly in gas where CO is frozen onto dust grains.
2) Observations of the protoplanetary disk around the young star TW Hya using ALMA revealed a ring-shaped distribution of N2H+ emission with an inner radius of 21-32 AU, indicating the location of the CO snow line.
3) Disk models suggest the N2H+ emission inner edge corresponds to a midplane temperature of 16-20K,
Observations of gas_flows_inside_a_protoplanetary_gapSérgio Sacani
1) ALMA observations of the protoplanetary disk around HD 142527 reveal diffuse CO gas and denser HCO+ filaments inside the dust gap.
2) The HCO+ filaments extend from the outer disk towards the inner disk and star, indicating gas flowing across the gap.
3) Estimates of the gas flow rate through the filaments are sufficient to sustain the observed rate of accretion onto the star, supporting the interpretation that the filaments are planet-induced gap-crossing accretion streams.
This document presents an analysis of transit spectroscopy observations of three exoplanets - WASP-12 b, WASP-17 b, and WASP-19 b - using the Wide Field Camera 3 instrument on the Hubble Space Telescope. The observations achieved almost photon-limited precision but uncertainties in the transit depths were increased by the uneven sampling of the light curves. The final transit spectra for all three planets are consistent with the presence of a water absorption feature at 1.4 microns, though the amplitude is smaller than expected from previous Spitzer observations possibly due to hazes. Due to degeneracies between models, the data cannot unambiguously constrain the atmospheric compositions without additional observations.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
This document summarizes a study that estimates the dynamical surface mass density between 1.5 and 4 kpc from the Galactic plane using kinematics of thick disk stars. The authors derive an exact analytical expression for the surface density based on assumptions about the stellar population and Galactic potential. Their expression matches expectations of visible mass alone, with no evidence for additional dark matter required. They extrapolate a local dark matter density of 0±1 mM⊙ pc−3, excluding all current spherical dark matter halo models at over 4σ confidence. Only a highly prolate dark matter halo could potentially reconcile the observations with models, but this is unlikely according to ΛCDM.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
Olivine in an_unexpected_location_on_vesta_surfaceSérgio Sacani
The document reports on the discovery of olivine on the surface of the asteroid Vesta in unexpected locations, based on data from the Dawn spacecraft's VIR instrument. Specifically:
- Olivine was found in the northern hemisphere of Vesta, rather than the southern basins where mantle rocks were expected based on previous models.
- The olivine occurs in large patches hundreds of meters across mixed with howardite regolith, unlike in meteorites where it is a minor component of diogenites.
- The amount and distribution of olivine-rich material suggests a complex evolutionary history for Vesta and is not consistent with previous ideas of olivine occurrence being associated with diogenites
Imaging of the_co_snow_line_in_a_solar_nebula_analogSérgio Sacani
This document summarizes research on observing the location of the carbon monoxide (CO) snow line in protoplanetary disks. Key points:
1) N2H+ emission is expected to trace the CO snow line as N2H+ forms most abundantly in gas where CO is frozen onto dust grains.
2) Observations of the protoplanetary disk around the young star TW Hya using ALMA revealed a ring-shaped distribution of N2H+ emission with an inner radius of 21-32 AU, indicating the location of the CO snow line.
3) Disk models suggest the N2H+ emission inner edge corresponds to a midplane temperature of 16-20K,
Observations of gas_flows_inside_a_protoplanetary_gapSérgio Sacani
1) ALMA observations of the protoplanetary disk around HD 142527 reveal diffuse CO gas and denser HCO+ filaments inside the dust gap.
2) The HCO+ filaments extend from the outer disk towards the inner disk and star, indicating gas flowing across the gap.
3) Estimates of the gas flow rate through the filaments are sufficient to sustain the observed rate of accretion onto the star, supporting the interpretation that the filaments are planet-induced gap-crossing accretion streams.
This document presents an analysis of transit spectroscopy observations of three exoplanets - WASP-12 b, WASP-17 b, and WASP-19 b - using the Wide Field Camera 3 instrument on the Hubble Space Telescope. The observations achieved almost photon-limited precision but uncertainties in the transit depths were increased by the uneven sampling of the light curves. The final transit spectra for all three planets are consistent with the presence of a water absorption feature at 1.4 microns, though the amplitude is smaller than expected from previous Spitzer observations possibly due to hazes. Due to degeneracies between models, the data cannot unambiguously constrain the atmospheric compositions without additional observations.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
This document summarizes a study that estimates the dynamical surface mass density between 1.5 and 4 kpc from the Galactic plane using kinematics of thick disk stars. The authors derive an exact analytical expression for the surface density based on assumptions about the stellar population and Galactic potential. Their expression matches expectations of visible mass alone, with no evidence for additional dark matter required. They extrapolate a local dark matter density of 0±1 mM⊙ pc−3, excluding all current spherical dark matter halo models at over 4σ confidence. Only a highly prolate dark matter halo could potentially reconcile the observations with models, but this is unlikely according to ΛCDM.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
Olivine in an_unexpected_location_on_vesta_surfaceSérgio Sacani
The document reports on the discovery of olivine on the surface of the asteroid Vesta in unexpected locations, based on data from the Dawn spacecraft's VIR instrument. Specifically:
- Olivine was found in the northern hemisphere of Vesta, rather than the southern basins where mantle rocks were expected based on previous models.
- The olivine occurs in large patches hundreds of meters across mixed with howardite regolith, unlike in meteorites where it is a minor component of diogenites.
- The amount and distribution of olivine-rich material suggests a complex evolutionary history for Vesta and is not consistent with previous ideas of olivine occurrence being associated with diogenites
Detection of an atmosphere around the super earth 55 cancri eSérgio Sacani
We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near
infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent
star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness
of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length
and a very high scanning speed. We use our specialized pipeline to take into account systematics
introduced by these observational parameters when coupled with the geometrical distortions of the
instrument. We measure the transit depth per wavelength channel with an average relative uncertainty
of 22 ppm per visit and nd modulations that depart from a straight line model with a 6 condence
level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably
hydrogen-rich. Our fully Bayesian spectral retrieval code, T -REx, has identied HCN to be the
most likely molecular candidate able to explain the features at 1.42 and 1.54 m. While additional
spectroscopic observations in a broader wavelength range in the infrared will be needed to conrm
the HCN detection, we discuss here the implications of such result. Our chemical model, developed
with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a
high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic
than previously thought.
Molecular gas clumps_from_the_destruction_of_icy_bodies_in_beta_pictoris_debr...Sérgio Sacani
1) ALMA observations detected carbon monoxide gas orbiting in a debris disk around the young star Beta Pictoris, with a total mass equivalent to 0.0023 times the mass of Earth's Moon.
2) The gas is distributed asymmetrically, with 30% located in a single clump 85 AU from the star. This gas clump is aligned with the orbit of an inner planet in the system.
3) The gas must be continuously replenished, likely from the destruction of icy planetesimals and comets through collisions within the debris disk. The collisions may be enhanced in the gas clump due to resonances with an unseen giant planet or from remnants of a large collision between
A spectroscopic sample_of_massive_galaxiesSérgio Sacani
This document describes a study of 16 massive galaxies at z ~ 2 selected from the 3D-HST spectroscopic survey based on the detection of a strong 4000 Angstrom break in their spectra. Spectroscopy and imaging from HST/WFC3 are used to determine accurate redshifts, stellar population properties, and structural parameters. The sample significantly increases the number of spectroscopically confirmed evolved galaxies at z ~ 2 with robust size measurements. The analysis populates the mass-size relation and finds it is consistent with local relations but with smaller sizes by a factor of 2-3. A model is presented where the observed size evolution is explained by quenching of increasingly larger star-forming galaxies at a rate set by
Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydroth...Sérgio Sacani
Saturn’s moon Enceladus has an ice-covered ocean; a plume of material erupts from
cracks in the ice. The plume contains chemical signatures of water-rock interaction
between the ocean and a rocky core.We used the Ion Neutral Mass Spectrometer onboard
the Cassini spacecraft to detect molecular hydrogen in the plume. By using the instrument’s
open-source mode, background processes of hydrogen production in the instrument were
minimized and quantified, enabling the identification of a statistically significant signal of
hydrogen native to Enceladus.We find that the most plausible source of this hydrogen is
ongoing hydrothermal reactions of rock containing reduced minerals and organic materials.
The relatively high hydrogen abundance in the plume signals thermodynamic disequilibrium
that favors the formation of methane from CO2 in Enceladus’ ocean.
This study analyzed transit observations of the Neptune-mass exoplanet GJ 436b taken with the Hubble Space Telescope. The transmission spectrum was found to be featureless, ruling out cloud-free hydrogen-dominated atmosphere models with high significance. The flat transmission spectrum is consistent with either an atmosphere containing high-altitude clouds located at a pressure of around 1 millibar, or a relatively hydrogen-poor atmosphere with 3% hydrogen and helium by mass. Bayesian atmospheric modeling showed that cloudy hydrogen-dominated or high-metallicity hydrogen-poor atmospheres provide the best fits to the data. Further observations are needed to distinguish between these scenarios.
Team CO2 - Estimating Seismic Velocities and Attenuations of CO2 Saturated Sa...finite_parallel
The document discusses estimating seismic velocities and attenuations of CO2 saturated sandstones through laboratory experiments. Core rock samples are injected with CO2 and seismic P and S waves are shot through the samples to determine how velocities and attenuation change with different CO2 concentrations and effective stress regimes. The experiments aim to understand these relationships at a small scale so they can be applied to understanding larger field conditions. Key parameters like bulk modulus, density, pore pressure, and effective stress are also discussed in relation to how they impact seismic wave propagation through rocks.
SPECTROSCOPIC CONFIRMATION OF THE EXISTENCE OF LARGE, DIFFUSE GALAXIES IN THE...Sérgio Sacani
We recently identified a population of low surface brightness objects in the field of the z = 0.023 Coma cluster,
using the Dragonfly Telephoto Array. Here we present Keck spectroscopy of one of the largest of these “ultradiffuse
galaxies” (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption
features, including the Ca II H+K lines and the G-band, and no detected emission lines. Its radial velocity of
cz=6280±120 km s−1 is within the 1σ velocity dispersion of the Coma cluster. The galaxy has an effective
radius of 4.3 ± 0.3 kpc and a Sérsic index of 0.89 ± 0.06, as measured from Keck imaging. We find no indications
of tidal tails or other distortions, at least out to a radius of ∼2re. We show that UDGs are located in a previously
sparsely populated region of the size—magnitude plane of quiescent stellar systems, as they are ∼6 mag fainter
than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent
galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are
needed to determine whether the dark matter halos of UDGs are similar to those of galaxies with the same
luminosity or to those of galaxies with the same size.
VIMS images of the Huygens landing site on Titan acquired during Cassini flybys in October and December 2004 provide insight into surface features near the landing site with spatial resolutions of 14.4-19 km/pixel. Ratio images of the brightest and darkest spectra in the 2.03 μm window reveal a particularly contrasted structure north of the landing site, consistent with local enrichment in exposed water ice. The images also show a possible 150 km diameter impact crater with a central peak. While scattering from haze particles dominates Titan's spectrum, spectral ratios of bright and dark areas suggest differences in surface composition and/or topography related to DISR images of the site.
Evidence for plumes of water on Europa has previously been found using the Hubble Space Telescope using two
different observing techniques. Roth et al. found line emission from the dissociation products of water. Sparks et al.
found evidence for off-limb continuum absorption as Europa transited Jupiter. Here, we present a new transit
observation of Europa that shows a second event at the same location as a previous plume candidate from Sparks
et al., raising the possibility of a consistently active source of erupting material on Europa. This conclusion is
bolstered by comparison with a nighttime thermal image from the Galileo Photopolarimeter-Radiometer that shows
a thermal anomaly at the same location, within the uncertainties. The anomaly has the highest observed brightness
temperature on the Europa nightside. If heat flow from a subsurface liquid water reservoir causes the thermal
anomaly, its depth is ≈1.8–2 km, under simple modeling assumptions, consistent with scenarios in which a liquid
water reservoir has formed within a thick ice shell. Models that favor thin regions within the ice shell that connect
directly to the ocean, however, cannot be excluded, nor modifications to surface thermal inertia by subsurface
activity. Alternatively, vapor deposition surrounding an active vent could increase the thermal inertia of the surface
and cause the thermal anomaly. This candidate plume region may offer a promising location for an initial
characterization of Europa’s internal water and ice and for seeking evidence of Europa’s habitability.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
The x-ray diffraction analysis of soil samples from Rocknest at Gale Crater on Mars revealed:
1) Crystalline components including plagioclase, olivine, augite, pigeonite, and minor amounts of other phases.
2) 27±14% of the soil was amorphous material, likely containing multiple iron-bearing and volatile phases including possibly hisingerite.
3) The crystalline components are similar to martian basalts and meteorites, while the amorphous component is similar to soils on Earth like those on Mauna Kea, Hawaii.
This document discusses using geostatistical analysis to understand soil moisture dynamics at a small catchment scale. Daily soil moisture data from 111 sensors over 3.5 years was analyzed. Variogram analysis showed limitations in accurately estimating the nugget variance without paired sensors. Kriging interpolation was performed, but results were limited by inaccurate variograms that were sometimes unbounded with high sill and range values. The analysis demonstrated the importance of accurately estimating the nugget variance for robust geostatistical modeling of soil moisture dynamics.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
Shape of (101955) Bennu indicative of a rubble pile with internal stiffnessSérgio Sacani
The document describes new findings about the asteroid Bennu based on images from the OSIRIS-REx spacecraft. It finds that Bennu has a top-like shape with considerable macroporosity and prominent boulders, suggesting it is a rubble pile. However, it also has high-standing ridges and surface features indicating some level of internal stiffness. The shape and features suggest Bennu formed by reaccumulation and past fast spin, but now its interior allows surface cracking and mass wasting. Key parameters of Bennu such as size, volume, density are consistent with prior estimates from Earth-based radar.
Radial velocity monitoring has found the signature of a Msin i = 1:3 M planet located within the Habitable Zone of Proxima
Centauri, the Sun’s closest neighbor (Anglada-Escudé et al. 2016). Despite a hotter past and an active host star the planet Proxima b
could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016). Here we use a 3D Global Climate Model (GCM)
to simulate Proxima b’s atmosphere and water cycle for its two likely rotation modes (the 1:1 and 3:2 spin-orbit resonances) while
varying the unconstrained surface water inventory and atmospheric greenhouse eect (represented here with a CO2-N2 atmosphere.)
We find that a broad range of atmospheric compositions can allow surface liquid water. On a tidally-locked planet with a surface water
inventory larger than 0.6 Earth ocean, liquid water is always present (assuming 1 bar of N2), at least in the substellar region. Liquid
water covers the whole planet for CO2 partial pressures & 1 bar. For smaller water inventories, water can be trapped on the night side,
forming either glaciers or lakes, depending on the amount of greenhouse gases. With a non-synchronous rotation, a minimum CO2
pressure of 10 mbar (assuming 1 bar of N2) is required to avoid falling into a completely frozen snowball state if water is abundant.
If the planet is dryer, 0.5 bar of CO2 would suce to prevent the trapping of any arbitrary small water inventory into polar ice
caps. More generally, any low-obliquity planet within the classical habitable zone of its star should be in one of the climate regimes
discussed here.
We use our GCM to produce reflection/emission spectra and phase curves for the dierent rotations and surface volatile inventories.
We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes thanks to an angular
separation of 7=D at 1 m (with the E-ELT) and a contrast of 10 7. The magnitude of the planet will allow for high-resolution
spectroscopy and the search for molecular signatures, including H2O, O2, and CO2.
The observation of thermal phase curves, although challenging, can be attempted with JWST, thanks to a contrast of 210 5 at 10 m.
Proxima b will also be an exceptional target for future IR interferometers. Within a decade it will be possible to image Proxima b and
possibly determine whether this exoplanet’s surface is habitable.
Very regular high-frequency pulsation modes in young intermediate-mass starsSérgio Sacani
Asteroseismology probes the internal structures of stars by using their natural
pulsation frequencies1. It relies on identifying sequences of pulsation modes that can
be compared with theoretical models, which has been done successfully for many
classes of pulsators, including low-mass solar-type stars2, red giants3, high-mass stars4
and white dwarfs5. However, a large group of pulsating stars of intermediate mass—the
so-called δ Scuti stars—have rich pulsation spectra for which systematic mode
identification has not hitherto been possible6,7. This arises because only a seemingly
random subset of possible modes are excited and because rapid rotation tends to
spoil regular patterns8–10. Here we report the detection of remarkably regular
sequences of high-frequency pulsation modes in 60 intermediate-mass
main-sequence stars, which enables definitive mode identification. The space
motions of some of these stars indicate that they are members of known associations
of young stars, as confirmed by modelling of their pulsation spectra.
Curiosity at gale_crater_characterization_and_analysis_of_the_rocknest_sand_s...Sérgio Sacani
The Rocknest sand shadow analyzed by the Curiosity rover on Mars was similar to coarse-grained ripples analyzed by previous rovers. It consisted of an upper layer of very coarse sand grains armoring the surface, underlain by finer grains. Analysis found the sand was around 55% crystalline material of basaltic composition and 45% amorphous iron-rich glass. This amorphous component contained the volatiles detected and was similar to soils analyzed at other Mars sites, implying the materials were locally derived from similar basaltic sources globally on Mars.
The birth of_a_galaxy_propelling_reionisation_with_the_faintest_galaxiesSérgio Sacani
This document summarizes a study that uses cosmological radiation hydrodynamics simulations to model dwarf galaxy formation and properties at z > 7. The study finds that metal-enriched star formation can occur in halos down to masses of ~106 M, especially in neutral regions, and that these smallest galaxies provide nearly 30% of the ionizing photon budget needed for reionization despite only hosting up to 104 M of stars. The study also finds that the galaxy luminosity function flattens above MUV = -12 at z = 10 and that the fraction of ionizing radiation escaping into the intergalactic medium decreases from 50% to 5% over the halo mass range of log M/M⊙ = 7.0-8.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
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.
Detection of an atmosphere around the super earth 55 cancri eSérgio Sacani
We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near
infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent
star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness
of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length
and a very high scanning speed. We use our specialized pipeline to take into account systematics
introduced by these observational parameters when coupled with the geometrical distortions of the
instrument. We measure the transit depth per wavelength channel with an average relative uncertainty
of 22 ppm per visit and nd modulations that depart from a straight line model with a 6 condence
level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably
hydrogen-rich. Our fully Bayesian spectral retrieval code, T -REx, has identied HCN to be the
most likely molecular candidate able to explain the features at 1.42 and 1.54 m. While additional
spectroscopic observations in a broader wavelength range in the infrared will be needed to conrm
the HCN detection, we discuss here the implications of such result. Our chemical model, developed
with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a
high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic
than previously thought.
Molecular gas clumps_from_the_destruction_of_icy_bodies_in_beta_pictoris_debr...Sérgio Sacani
1) ALMA observations detected carbon monoxide gas orbiting in a debris disk around the young star Beta Pictoris, with a total mass equivalent to 0.0023 times the mass of Earth's Moon.
2) The gas is distributed asymmetrically, with 30% located in a single clump 85 AU from the star. This gas clump is aligned with the orbit of an inner planet in the system.
3) The gas must be continuously replenished, likely from the destruction of icy planetesimals and comets through collisions within the debris disk. The collisions may be enhanced in the gas clump due to resonances with an unseen giant planet or from remnants of a large collision between
A spectroscopic sample_of_massive_galaxiesSérgio Sacani
This document describes a study of 16 massive galaxies at z ~ 2 selected from the 3D-HST spectroscopic survey based on the detection of a strong 4000 Angstrom break in their spectra. Spectroscopy and imaging from HST/WFC3 are used to determine accurate redshifts, stellar population properties, and structural parameters. The sample significantly increases the number of spectroscopically confirmed evolved galaxies at z ~ 2 with robust size measurements. The analysis populates the mass-size relation and finds it is consistent with local relations but with smaller sizes by a factor of 2-3. A model is presented where the observed size evolution is explained by quenching of increasingly larger star-forming galaxies at a rate set by
Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydroth...Sérgio Sacani
Saturn’s moon Enceladus has an ice-covered ocean; a plume of material erupts from
cracks in the ice. The plume contains chemical signatures of water-rock interaction
between the ocean and a rocky core.We used the Ion Neutral Mass Spectrometer onboard
the Cassini spacecraft to detect molecular hydrogen in the plume. By using the instrument’s
open-source mode, background processes of hydrogen production in the instrument were
minimized and quantified, enabling the identification of a statistically significant signal of
hydrogen native to Enceladus.We find that the most plausible source of this hydrogen is
ongoing hydrothermal reactions of rock containing reduced minerals and organic materials.
The relatively high hydrogen abundance in the plume signals thermodynamic disequilibrium
that favors the formation of methane from CO2 in Enceladus’ ocean.
This study analyzed transit observations of the Neptune-mass exoplanet GJ 436b taken with the Hubble Space Telescope. The transmission spectrum was found to be featureless, ruling out cloud-free hydrogen-dominated atmosphere models with high significance. The flat transmission spectrum is consistent with either an atmosphere containing high-altitude clouds located at a pressure of around 1 millibar, or a relatively hydrogen-poor atmosphere with 3% hydrogen and helium by mass. Bayesian atmospheric modeling showed that cloudy hydrogen-dominated or high-metallicity hydrogen-poor atmospheres provide the best fits to the data. Further observations are needed to distinguish between these scenarios.
Team CO2 - Estimating Seismic Velocities and Attenuations of CO2 Saturated Sa...finite_parallel
The document discusses estimating seismic velocities and attenuations of CO2 saturated sandstones through laboratory experiments. Core rock samples are injected with CO2 and seismic P and S waves are shot through the samples to determine how velocities and attenuation change with different CO2 concentrations and effective stress regimes. The experiments aim to understand these relationships at a small scale so they can be applied to understanding larger field conditions. Key parameters like bulk modulus, density, pore pressure, and effective stress are also discussed in relation to how they impact seismic wave propagation through rocks.
SPECTROSCOPIC CONFIRMATION OF THE EXISTENCE OF LARGE, DIFFUSE GALAXIES IN THE...Sérgio Sacani
We recently identified a population of low surface brightness objects in the field of the z = 0.023 Coma cluster,
using the Dragonfly Telephoto Array. Here we present Keck spectroscopy of one of the largest of these “ultradiffuse
galaxies” (UDGs), confirming that it is a member of the cluster. The galaxy has prominent absorption
features, including the Ca II H+K lines and the G-band, and no detected emission lines. Its radial velocity of
cz=6280±120 km s−1 is within the 1σ velocity dispersion of the Coma cluster. The galaxy has an effective
radius of 4.3 ± 0.3 kpc and a Sérsic index of 0.89 ± 0.06, as measured from Keck imaging. We find no indications
of tidal tails or other distortions, at least out to a radius of ∼2re. We show that UDGs are located in a previously
sparsely populated region of the size—magnitude plane of quiescent stellar systems, as they are ∼6 mag fainter
than normal early-type galaxies of the same size. It appears that the luminosity distribution of large quiescent
galaxies is not continuous, although this could largely be due to selection effects. Dynamical measurements are
needed to determine whether the dark matter halos of UDGs are similar to those of galaxies with the same
luminosity or to those of galaxies with the same size.
VIMS images of the Huygens landing site on Titan acquired during Cassini flybys in October and December 2004 provide insight into surface features near the landing site with spatial resolutions of 14.4-19 km/pixel. Ratio images of the brightest and darkest spectra in the 2.03 μm window reveal a particularly contrasted structure north of the landing site, consistent with local enrichment in exposed water ice. The images also show a possible 150 km diameter impact crater with a central peak. While scattering from haze particles dominates Titan's spectrum, spectral ratios of bright and dark areas suggest differences in surface composition and/or topography related to DISR images of the site.
Evidence for plumes of water on Europa has previously been found using the Hubble Space Telescope using two
different observing techniques. Roth et al. found line emission from the dissociation products of water. Sparks et al.
found evidence for off-limb continuum absorption as Europa transited Jupiter. Here, we present a new transit
observation of Europa that shows a second event at the same location as a previous plume candidate from Sparks
et al., raising the possibility of a consistently active source of erupting material on Europa. This conclusion is
bolstered by comparison with a nighttime thermal image from the Galileo Photopolarimeter-Radiometer that shows
a thermal anomaly at the same location, within the uncertainties. The anomaly has the highest observed brightness
temperature on the Europa nightside. If heat flow from a subsurface liquid water reservoir causes the thermal
anomaly, its depth is ≈1.8–2 km, under simple modeling assumptions, consistent with scenarios in which a liquid
water reservoir has formed within a thick ice shell. Models that favor thin regions within the ice shell that connect
directly to the ocean, however, cannot be excluded, nor modifications to surface thermal inertia by subsurface
activity. Alternatively, vapor deposition surrounding an active vent could increase the thermal inertia of the surface
and cause the thermal anomaly. This candidate plume region may offer a promising location for an initial
characterization of Europa’s internal water and ice and for seeking evidence of Europa’s habitability.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
The x-ray diffraction analysis of soil samples from Rocknest at Gale Crater on Mars revealed:
1) Crystalline components including plagioclase, olivine, augite, pigeonite, and minor amounts of other phases.
2) 27±14% of the soil was amorphous material, likely containing multiple iron-bearing and volatile phases including possibly hisingerite.
3) The crystalline components are similar to martian basalts and meteorites, while the amorphous component is similar to soils on Earth like those on Mauna Kea, Hawaii.
This document discusses using geostatistical analysis to understand soil moisture dynamics at a small catchment scale. Daily soil moisture data from 111 sensors over 3.5 years was analyzed. Variogram analysis showed limitations in accurately estimating the nugget variance without paired sensors. Kriging interpolation was performed, but results were limited by inaccurate variograms that were sometimes unbounded with high sill and range values. The analysis demonstrated the importance of accurately estimating the nugget variance for robust geostatistical modeling of soil moisture dynamics.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
Shape of (101955) Bennu indicative of a rubble pile with internal stiffnessSérgio Sacani
The document describes new findings about the asteroid Bennu based on images from the OSIRIS-REx spacecraft. It finds that Bennu has a top-like shape with considerable macroporosity and prominent boulders, suggesting it is a rubble pile. However, it also has high-standing ridges and surface features indicating some level of internal stiffness. The shape and features suggest Bennu formed by reaccumulation and past fast spin, but now its interior allows surface cracking and mass wasting. Key parameters of Bennu such as size, volume, density are consistent with prior estimates from Earth-based radar.
Radial velocity monitoring has found the signature of a Msin i = 1:3 M planet located within the Habitable Zone of Proxima
Centauri, the Sun’s closest neighbor (Anglada-Escudé et al. 2016). Despite a hotter past and an active host star the planet Proxima b
could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016). Here we use a 3D Global Climate Model (GCM)
to simulate Proxima b’s atmosphere and water cycle for its two likely rotation modes (the 1:1 and 3:2 spin-orbit resonances) while
varying the unconstrained surface water inventory and atmospheric greenhouse eect (represented here with a CO2-N2 atmosphere.)
We find that a broad range of atmospheric compositions can allow surface liquid water. On a tidally-locked planet with a surface water
inventory larger than 0.6 Earth ocean, liquid water is always present (assuming 1 bar of N2), at least in the substellar region. Liquid
water covers the whole planet for CO2 partial pressures & 1 bar. For smaller water inventories, water can be trapped on the night side,
forming either glaciers or lakes, depending on the amount of greenhouse gases. With a non-synchronous rotation, a minimum CO2
pressure of 10 mbar (assuming 1 bar of N2) is required to avoid falling into a completely frozen snowball state if water is abundant.
If the planet is dryer, 0.5 bar of CO2 would suce to prevent the trapping of any arbitrary small water inventory into polar ice
caps. More generally, any low-obliquity planet within the classical habitable zone of its star should be in one of the climate regimes
discussed here.
We use our GCM to produce reflection/emission spectra and phase curves for the dierent rotations and surface volatile inventories.
We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes thanks to an angular
separation of 7=D at 1 m (with the E-ELT) and a contrast of 10 7. The magnitude of the planet will allow for high-resolution
spectroscopy and the search for molecular signatures, including H2O, O2, and CO2.
The observation of thermal phase curves, although challenging, can be attempted with JWST, thanks to a contrast of 210 5 at 10 m.
Proxima b will also be an exceptional target for future IR interferometers. Within a decade it will be possible to image Proxima b and
possibly determine whether this exoplanet’s surface is habitable.
Very regular high-frequency pulsation modes in young intermediate-mass starsSérgio Sacani
Asteroseismology probes the internal structures of stars by using their natural
pulsation frequencies1. It relies on identifying sequences of pulsation modes that can
be compared with theoretical models, which has been done successfully for many
classes of pulsators, including low-mass solar-type stars2, red giants3, high-mass stars4
and white dwarfs5. However, a large group of pulsating stars of intermediate mass—the
so-called δ Scuti stars—have rich pulsation spectra for which systematic mode
identification has not hitherto been possible6,7. This arises because only a seemingly
random subset of possible modes are excited and because rapid rotation tends to
spoil regular patterns8–10. Here we report the detection of remarkably regular
sequences of high-frequency pulsation modes in 60 intermediate-mass
main-sequence stars, which enables definitive mode identification. The space
motions of some of these stars indicate that they are members of known associations
of young stars, as confirmed by modelling of their pulsation spectra.
Curiosity at gale_crater_characterization_and_analysis_of_the_rocknest_sand_s...Sérgio Sacani
The Rocknest sand shadow analyzed by the Curiosity rover on Mars was similar to coarse-grained ripples analyzed by previous rovers. It consisted of an upper layer of very coarse sand grains armoring the surface, underlain by finer grains. Analysis found the sand was around 55% crystalline material of basaltic composition and 45% amorphous iron-rich glass. This amorphous component contained the volatiles detected and was similar to soils analyzed at other Mars sites, implying the materials were locally derived from similar basaltic sources globally on Mars.
The birth of_a_galaxy_propelling_reionisation_with_the_faintest_galaxiesSérgio Sacani
This document summarizes a study that uses cosmological radiation hydrodynamics simulations to model dwarf galaxy formation and properties at z > 7. The study finds that metal-enriched star formation can occur in halos down to masses of ~106 M, especially in neutral regions, and that these smallest galaxies provide nearly 30% of the ionizing photon budget needed for reionization despite only hosting up to 104 M of stars. The study also finds that the galaxy luminosity function flattens above MUV = -12 at z = 10 and that the fraction of ionizing radiation escaping into the intergalactic medium decreases from 50% to 5% over the halo mass range of log M/M⊙ = 7.0-8.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
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.
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.
Molecular Gas Clumps from the Destruction of Icy Bodies in the β Pictoris Deb...GOASA
1) ALMA observations detected carbon monoxide gas orbiting in a debris disk around the young star Beta Pictoris, with a total mass equivalent to 0.0023 times the mass of Earth's Moon.
2) The gas is distributed asymmetrically, with 30% located in a single clump 85 AU from the star. This gas clump is aligned with the orbit of an inner planet in the system.
3) The gas must be continuously replenished, likely from the destruction of icy planetesimals and comets through collisions within the debris disk. The collisions may be enhanced in the gas clump due to resonances with an unseen giant planet or the remnants of a large collision between
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.
What determines the_density_structure_of_molecular_cloudsSérgio Sacani
This document analyzes column density probability distribution functions (PDFs) derived from Herschel observations of the Orion B, Aquila, and Polaris molecular clouds to understand what physical processes influence the density structure. The PDFs of Orion B and Aquila show a lognormal distribution at low densities transitioning to a power-law tail at high densities, indicating gravitational collapse. The Orion B PDF is broader, likely due to external compression. The quiescent Polaris subregion PDF is nearly lognormal, suggesting turbulence governs its density, while a filament subregion shows excess density above a visual extinction of 1, possibly from physical processes like magnetic fields. The document concludes that turbulence, gravity, collapse, and external compression
The SAMI Galaxy Sur v ey: galaxy spin is more strongly correlated with stella...Sérgio Sacani
We use the SAMI Galaxy Surv e y to examine the drivers of galaxy spin, λR e , in a multidimensional parameter space including stellar mass, stellar population age (or specific star formation rate), and various environmental metrics (local density, halo mass, satellite versus central). Using a partial correlation analysis, we consistently find that age or specific star formation rate is the primary parameter correlating with spin. Light-weighted age and specific star formation rate are more strongly correlated with spin than mass-weighted age. In fact, across our sample, once the relation between light-weighted age and spin is accounted for, there is no significant residual correlation between spin and mass, or spin and environment. This result is strongly suggestive that the present-day environment only indirectly influences spin, via the removal of gas and star formation quenching. That is, environment affects age, then age affects spin. Older galaxies then have lower spin, either due to stars being born dynamically hotter at high redshift, or due to secular heating. Our results appear to rule out environmentally dependent dynamical heating (e.g. g alaxy–g alaxy interactions) being important, at least within 1 R e where our kinematic measurements are made. The picture is more complex when we only consider high-mass galaxies ( M ∗ ≳ 10 11 M ). While the age-spin relation is still strong for these high-mass galaxies, there is a residual environmental trend with central galaxies preferentially having lower spin, compared to satellites of the same age and mass. We argue that this trend is likely due to central galaxies being a preferred location for mergers.
A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar f...Sérgio Sacani
The dwarf planets Sedna, Gonggong, and Quaoar are interesting in being somewhat smaller than
the methane-rich bodies of the Kuiper Belt (Pluto, Eris, Makemake), yet large enough to be
spherical and to have possibly undergone interior melting and differentiation. They also reside
on very different orbits, making them an ideal suite of bodies for untangling effects of size and
orbit on present day surface composition. We observed Sedna, Gonggong, and Quaoar with the
NIRSpec instrument on the James Webb Space Telescope (JWST). All three bodies were
observed in the low-resolution prism mode at wavelengths spanning 0.7 to 5.2 μm. Quaoar was
additionally observed at 10x higher spectral resolution from 0.97 to 3.16 μm using mediumresolution gratings. Sedna’s spectrum shows a large number of absorption features due to ethane
(C2H6), as well as acetylene (C2H2), ethylene (C2H4), H2O, and possibly minor CO2.
Gonggong’s spectrum also shows several, but fewer and weaker, ethane features, along with
stronger and cleaner H2O features and CO2 complexed with other molecules. Quaoar’s prism
spectrum shows even fewer and weaker ethane features, the deepest and cleanest H2O features, a
feature at 3.2 μm possibly due to HCN, and CO2 ice. The higher-resolution medium grating
spectrum of Quaoar reveals several overtone and combination bands of ethane and methane
(CH4). Spectra of all three objects show steep red spectral slopes and strong, broad absorptions
between 2.7 and 3.6 μm indicative of complex organic molecules. The suite of light
hydrocarbons and complex organic molecules are interpreted as the products of irradiation of
methane. The differences in apparent abundances of irradiation products among these three
similarly-sized bodies are likely due to their distinctive orbits, which lead to different timescales
of methane retention and to different charged particle irradiation environments. In all cases,
however, the continued presence of light hydrocarbons implies a resupply of methane to the
2
surface. We suggest that these three bodies have undergone internal melting and geochemical
evolution similar to the larger dwarf planets and distinct from all smaller KBOs. The feature
identification presented in this paper is the first step of analysis, and additional insight into the
relative abundances and mixing states of materials on these surfaces will come from future
spectral modeling of these data.
XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Proto...Sérgio Sacani
This document presents the first results from the JWST XUE program, which observed 15 protoplanetary disks in the NGC 6357 star-forming region using MIRI. For the disk XUE 1, located near massive stars, the following was found:
1) Abundant water, CO, CO2, HCN, and C2H2 were detected in the inner few AU, indicating an oxygen-dominated gas-phase chemistry similar to isolated disks.
2) Small crystalline silicate dust is present at the disk surface.
3) The column densities and chemistry are surprisingly similar to isolated disks despite the extreme radiation environment, implying inner disks can retain conditions conducive to rocky planet
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.
Formation of low mass protostars and their circumstellar disksSérgio Sacani
Understanding circumstellar disks is of prime importance in astrophysics, however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. Aims. We aim to elucidate the small scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. Methods. We carry out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent dense molecular cloud core to stellar densities. We study the birth of the protostar, the circumstellar disk, and its early evolution (< 6 yr after protostellar formation). Results. Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot (∼ 103 K), dense, and highly flared circumstellar disk. The protostar is embedded within the disk, such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock is shown to be supercritical whereas its equatorial counterpart is subcritical. We also f ind a remarkable convergence of our results with respect to initial conditions. Conclusions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger scale physics.
Herschel galactic plane_survey_the_global_distribution_of_ism_gas_componnentSérgio Sacani
This document summarizes a study using Herschel observations of the [C ii] 158μm line to analyze the distribution of different gas components in the Milky Way galaxy. The observations provide high-resolution maps of [C ii] emission across the Galactic plane. By comparing these maps to observations of HI, CO, and other tracers, the study finds that [C ii] emission is associated with spiral arms between 4-10 kpc from the Galactic center. It estimates that [C ii] traces dense photon-dominated regions (47%), CO-dark H2 gas (28%), cold atomic gas (21%), and ionized gas (4%). The study also analyzes the distribution of cold neutral medium versus
The pristine nature of SMSS 1605−1443 revealed by ESPRESSOSérgio Sacani
SMSS J160540.18−144323.1 is the carbon-enhanced metal-poor (CEMP) star with the lowest iron abundance ever measured, [Fe/H] =
−6.2, which was first reported with the SkyMapper telescope. The carbon abundance is A(C) ≈ 6.1 in the low-C band, as the majority of the stars
in this metallicity range. Yet, constraining the isotopic ratio of key species, such as carbon, sheds light on the properties and origin of these elusive
stars.
Aims. We performed high-resolution observations of SMSS 1605−1443 with the ESPRESSO spectrograph to look for variations in the radial
velocity (vrad) with time. These data have been combined with older MIKE and UVES archival observations to enlarge the temporal baseline. The
12C/
13C isotopic ratio is also studied to explore the possibility of mass transfer from a binary companion.
Methods. A cross-correlation function against a natural template was applied to detect vrad variability and a spectral synthesis technique was used
to derive 12C/
13C in the stellar atmosphere.
Results. We confirm previous indications of binarity in SMSS 1605−1443 and measured a lower limit 12C/
13C > 60 at more than a 3σ confidence
level, proving that this system is chemically unmixed and that no mass transfer from the unseen companion has happened so far. Thus, we confirm
the CEMP-no nature of SMSS 1605−1443 and show that the pristine chemical composition of the cloud from which it formed is currently imprinted
in its stellar atmosphere free of contamination.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
Artigo mostra resultados obtidos com o OSIRIS que mostra manchas brilhantes na superfície do cometa 67P/Churyumov-Gerasimenko, interpretadas como sendo gelo de água e provadas via experimentos de laboratório.
1. Astronomers detected a dense gas cloud falling into the supermassive black hole at the center of the Milky Way galaxy.
2. The cloud will reach its closest approach to the black hole, within 3,100 times the event horizon, in 2013. It has begun disrupting due to tidal forces.
3. Observing the cloud's disruption and interaction with the black hole's region in the coming years will provide insights into the feeding and accretion processes of supermassive black holes.
Titan’s aerosol and stratospheric ice opacities between 18 and 500 μm vertic...Sérgio Sacani
This document is an accepted manuscript for publication in Icarus that summarizes research analyzing data from the Cassini CIRS instrument to characterize Titan's stratospheric aerosols and ices between 18-500 μm. The research finds that aerosols are well-mixed from the surface to 300 km altitude, while nitrile ice clouds (likely HCN and HC3N) appear centered around 90 km. There is also evidence of an ice cloud layer at 60 km that may be C2H6 ice. Volume extinction coefficients derived from CIRS data are compared to those from DISR, finding particle size ratios consistent with sub-micron aerosols and ice particle effective radii of only a few microns.
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.
Evidence for a_complex_enrichment_history_of_the_stream_from_fairall_9_sightlineSérgio Sacani
This study analyzes absorption spectra of the Magellanic Stream (MS) toward the quasar Fairall 9, obtained using the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) and the Very Large Telescope Ultraviolet and Visible Echelle Spectrograph (VLT/UVES). The spectra reveal absorption from multiple velocity components of the MS, indicating multiphase gas. Surprisingly, the sulfur abundance is found to be high ([S/H] = -0.30), five times higher than other MS sightlines, while the nitrogen abundance is lower ([N/H] = -1.15). This points to a complex enrichment history, where the gas toward Fair
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
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.
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.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
Remote Sensing and Computational, Evolutionary, Supercomputing, and Intellige...University of Maribor
Slides from talk:
Aleš Zamuda: Remote Sensing and Computational, Evolutionary, Supercomputing, and Intelligent Systems.
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Inter-Society Networking Panel GRSS/MTT-S/CIS Panel Session: Promoting Connection and Cooperation
https://www.etran.rs/2024/en/home-english/
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
Travis Hills' Endeavors in Minnesota: Fostering Environmental and Economic Pr...Travis Hills MN
Travis Hills of Minnesota developed a method to convert waste into high-value dry fertilizer, significantly enriching soil quality. By providing farmers with a valuable resource derived from waste, Travis Hills helps enhance farm profitability while promoting environmental stewardship. Travis Hills' sustainable practices lead to cost savings and increased revenue for farmers by improving resource efficiency and reducing waste.
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
hematic appreciation test is a psychological assessment tool used to measure an individual's appreciation and understanding of specific themes or topics. This test helps to evaluate an individual's ability to connect different ideas and concepts within a given theme, as well as their overall comprehension and interpretation skills. The results of the test can provide valuable insights into an individual's cognitive abilities, creativity, and critical thinking skills
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptxMAGOTI ERNEST
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
Unlocking the mysteries of reproduction: Exploring fecundity and gonadosomati...AbdullaAlAsif1
The pygmy halfbeak Dermogenys colletei, is known for its viviparous nature, this presents an intriguing case of relatively low fecundity, raising questions about potential compensatory reproductive strategies employed by this species. Our study delves into the examination of fecundity and the Gonadosomatic Index (GSI) in the Pygmy Halfbeak, D. colletei (Meisner, 2001), an intriguing viviparous fish indigenous to Sarawak, Borneo. We hypothesize that the Pygmy halfbeak, D. colletei, may exhibit unique reproductive adaptations to offset its low fecundity, thus enhancing its survival and fitness. To address this, we conducted a comprehensive study utilizing 28 mature female specimens of D. colletei, carefully measuring fecundity and GSI to shed light on the reproductive adaptations of this species. Our findings reveal that D. colletei indeed exhibits low fecundity, with a mean of 16.76 ± 2.01, and a mean GSI of 12.83 ± 1.27, providing crucial insights into the reproductive mechanisms at play in this species. These results underscore the existence of unique reproductive strategies in D. colletei, enabling its adaptation and persistence in Borneo's diverse aquatic ecosystems, and call for further ecological research to elucidate these mechanisms. This study lends to a better understanding of viviparous fish in Borneo and contributes to the broader field of aquatic ecology, enhancing our knowledge of species adaptations to unique ecological challenges.
Unlocking the mysteries of reproduction: Exploring fecundity and gonadosomati...
Resolved gas cavities_in_transitional_disks_inferred_from_co_isotopologs_with_alma
1. arXiv:1511.07149v2[astro-ph.EP]2Dec2015
Astronomy & Astrophysics manuscript no. Paper˙final c ESO 2015
December 3, 2015
Resolved gas cavities in transitional disks inferred from CO
isotopologs with ALMA
N. van der Marel1, E.F. van Dishoeck1,2, S. Bruderer2, S.M. Andrews3, K.M. Pontoppidan4, G.J. Herczeg5, T. van
Kempen1, and A. Miotello1
1
Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, the Netherlands
2
Max-Planck-Institut f¨ur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
3
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
4
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
5
Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Haidijan district, Beijing 100871, China
ABSTRACT
Context. Transitional disks around young stars with large dust cavities are promising candidates to look for recently formed, embed-
ded planets. Models of planet-disk interaction predict that young planets clear a gap in the gas while trapping dust at larger radii.
Other physical mechanisms might also be responsible for cavities. Previous observations have revealed that gas is still present inside
these cavities, but the spatial distribution of this gas remains uncertain.
Aims. We present high spatial resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of 13
CO and
C18
O 3–2 or 6–5 lines of four well-studied transitional disks around pre-main-sequence stars with large dust cavities. The line and
continuum observations are used to set constraints on the the gas surface density, specifically on the cavity size and density drop inside
the cavity.
Methods. The physical-chemical model DALI was used to analyze the gas images of SR21, HD135344B (also known as
SAO 206462), DoAr44, and IRS 48. The main parameters of interest are the size, depth and shape of the gas cavity in each of
the disks. CO isotope-selective photodissociation is included to properly constrain the surface density in the outer disk from C18
O
emission.
Results. The gas cavities are up to three times smaller than those of the dust in all four disks. Model fits indicate that the surface
density inside the gas cavities decreases by a factor of 100 to 10000 compared with the surface density profile derived from the outer
disk. The data can be fit by either introducing one or two drops in the gas surface density or a surface density profile that increases
with radius inside the cavity. A comparison with an analytical model of gap depths by planet-disk interaction shows that the disk
viscosities are most likely low, between between 10−3
and 10−4
, for reasonable estimates of planet masses of up to 10 Jupiter masses.
Conclusions. The resolved measurements of the gas and dust in transition disk cavities support the predictions of models that describe
how planet-disk interactions sculpt gas disk structures and influence the evolution of dust grains. These observed structures strongly
suggest the presence of giant planetary companions in transition disk cavities, although at smaller orbital radii than is typically indi-
cated from the dust cavity radii alone.
Key words. Astrochemistry - Protoplanetary disks - Stars: formation - ISM: molecules
1. Introduction
Protoplanetary disks around young stars are the birth cra-
dles of planets (e.g., Williams & Cieza 2011). Disks with in-
ner dust cavities, also called transition disks, are good can-
didates to search for young planets that have recently been
formed and cleared out their orbit. Dust cavities have been in-
ferred from modeling of spectral energy distributions (SEDs)
(Espaillat et al. 2014, and references therein) and millimeter
interferometry (e.g., Brown et al. 2009; Andrews et al. 2011).
Planet candidates have been found in cavities of several tran-
sition disks (Kraus & Ireland 2012; Quanz et al. 2013, 2015).
However, planet-disk interaction models indicate that dust cav-
ities are only an indirect consequence of planet clearing: a
planet will lower the gas surface density along its orbit, cre-
ating a gas gap with a pressure bump at its outer edge where
the millimeter-sized dust is trapped (e.g., Zhu et al. 2011;
Dodson-Robinson & Salyk 2011; Pinilla et al. 2012). The re-
sult is a millimeter-dust ring (or in particular cases an az-
imuthal asymmetry that is due to a Rossby-wave instability of
the pressure bump, van der Marel et al. 2013; Fukagawa et al.
2013; Casassus et al. 2013) and a gas cavity that can be up to
twice as small as the radius of the dust ring. Other mechanisms
that could cause a dust cavity or dust ring are photoevapora-
tion (Clarke et al. 2001) and instabilities at the edges of dead
zones (e.g., Reg´aly et al. 2012). Measuring the gas density in-
side the cavity is essential to distinguish between these mecha-
nisms: photoevaporation clears the dust and gas from the inside
out, dead zones do not change the gas density inside the cavity,
and planetary clearing creates a gas cavity. Furthermore, the de-
crease of gas surface density inside the gas cavity radius depends
on the mass of the companion and the disk viscosity. More gen-
erally, the fundamental properties of a disk are the gas-to-dust
ratio and gas surface density profile because the gas does not
necessarily follow the dust distribution.
The presence of gas inside the dust cavities was discovered
through accretion (e.g., Valenti et al. 1993; Najita et al. 2007)
and H2 emission (Bergin et al. 2003; Ingleby et al. 2009). Other
first indicators of warm molecular gas inside the cavities were
near-infrared observations of CO rovibrational lines, in several
1
2. N. van der Marel et al.: Gas cavities in transitional disks
cases revealing a gas cavity that was indeed smaller than the dust
cavity (Pontoppidan et al. 2008; Brittain et al. 2009; Salyk et al.
2009; Brown et al. 2012). As a result of a combination of high
critical densities and non-LTE excitation, rovibrational CO data
can be difficult to interpret, and derived gas masses are highly
model-dependent.
To properly derive the molecular gas densities, CO pure
rotational line observations are required. For a handful of
disks, pioneering interferometers such as SMA and PdBI have
revealed gas inside the cavity through CO rotational lines:
AB Aur (Pi´etu et al. 2005), GM Aur (Dutrey et al. 2008), and
HD 135344B (Lyo et al. 2011). Spatially resolved ALMA ob-
servations of 12
CO emission confirm the presence of gas in-
side the dust cavity for several other disks (van der Marel et al.
2013; Casassus et al. 2013; P´erez et al. 2014; Zhang et al. 2014;
Canovas et al. 2015). Using a disk model based on the dust struc-
ture derived from the SED and millimeter imaging, the 12
CO
data suggest a gas density decrease of one or two orders of
magnitude inside the dust cavity compared to the density pro-
file of the outer disk (van der Marel et al. 2015b). On the other
hand, the dust density decreased by at least three orders of mag-
nitude inside the cavity. For IRS 48 and J1604-2130, the gas
cavities are sufficiently empty so that 12
CO becomes optically
thin inside the dust cavity, and it was found that the gas cav-
ity radius is indeed smaller than the dust cavity (Bruderer et al.
2014; Zhang et al. 2014; van der Marel et al. 2015b), consistent
with predictions for the planet-disk interaction. The same result
was found for HD 142527 using CO isotopolog observations
(Perez et al. 2015).
Since detecting planets in disks is challenging, quantifying
the gas density structure of the disk inside the cavity can provide
important clues on the properties of embedded unseen planets.
The depth and shape of the gap depend primarily on the planet
mass and the disk viscosity (Zhu et al. 2011; Pinilla et al. 2012;
Fung et al. 2014). These models show that a planet does not cre-
ate a steep gas gap, but a gradual decrease over several AUs.
While spatially resolved 12
CO can provide some information
on the gas density profile, the emission remains optically thick
throughout most of the disk and is thus not a very good absolute
density tracer. Spatially resolved CO isotopolog observations are
required to constrain the outer disk mass and the gas cavity ra-
dius, as well as the depth and potentially the shape of the gas
surface density profile.
Converting CO emission into density is not trivial either:
the CO abundance with respect to H2 varies throughout the
disk due to photodissociation by the stellar UV radiation and
freeze-out onto dust grains in the cold regions in the mid-
plane and outer disk (van Zadelhoff et al. 2001; Aikawa et al.
2002). CO photodissociation is subject to self-shielding. As
CO isotopologs have lower abundances, they are not self-
shielded until deeper into a cloud or disk (Bally & Langer 1982;
van Dishoeck & Black 1988; Visser et al. 2009). Therefore, disk
models that do not include isotope-selective photodissociation
predict higher CO abundances than when this effect is included,
as recently demonstrated by Miotello et al. (2014). In addition,
the gas temperature is decoupled from the dust temperature in
the upper layers in the disk and at the directly heated cav-
ity wall (e.g., Kamp & Dullemond 2004; Jonkheid et al. 2004;
Gorti & Hollenbach 2008). For a proper interpretation of CO
emission, the physical and chemical structure of gas and dust
needs to be modeled. We make use of physical-chemical mod-
eling with DALI (Bruderer et al. 2012; Bruderer 2013), which
simultaneously solves the heating-cooling balance of the gas
and chemistry to determine the gas temperature, molecular abun-
dances, and molecular excitation for a given density structure.
In this paper, we present ALMA Cycle 1 and 2 observa-
tions of CO isotopologs 13
CO and C18
O at ∼ 0.2 − 0.25′′
res-
olution of four additional well-studied transitional disks: SR 21,
HD135344B, DoAr44, and IRS 48. For IRS 48, the 6–5 tran-
sitions are observed and for the other disks the lower 3–2
transitions. Previously derived models from 12
CO ALMA ob-
servations (Bruderer et al. 2014; van der Marel et al. 2015b) of
IRS 48, SR 21 and HD135344B are used as a starting point for
analyzing the isotopologs. With DALI we determine a gas den-
sity structure that is consistent with the CO observations, SED,
and continuum dust interferometry. Information on the hot gas
and dust from the literature is included. The goals of this study
are to determine the gas surface density profile, specificially the
size, depth, and shape of the gas density structure inside the dust
cavity, to constrain the properties of potential embedded planets.
The paper is structured as follows. In Sect. 2.1 we describe
the details of the ALMA observations. In Sect. 2.2 we present
moment maps of the 13
CO and 18
CO observations. The model-
ing approach is presented in Sect. 3. Section 4 presents the mod-
eling results. Section 5 discusses the implications for embedded
planets in the disk.
2. Data
The observations were obtained during ALMA Cycle 1 and 2 in
June and July 2014, with baselines ranging from 20 to 1100 m,
probing scales from 0.15 to 8 arcseconds. The sources and their
properties are summarized in Table 2.
2.1. Observational details
The disks SR 21, HD 135344B, and DoAr 44 were observed in
ALMA Cycle 1 program 2012.1.00158.S (PI van Dishoeck) in
Band 7 (∼335 GHz or 896 µm) with a resulting spatial resolu-
tion of 0.2–0.25”. The observations were taken in four spectral
windows of 3840 channels: three windows have a bandwidth of
469 MHz (channel width 122 kHz, equivalent to 0.1 km s−1
),
centered on the 13
CO 3–2, C18
O 3–2, and CN 3–2 transitions
with rest frequencies of 330.58796, 329.33056, and 340.24778
GHz, respectively. The fourth spectral window was centered on
342.15000 GHz with a bandwidth of 1875 MHz (channel width
488 kHz, equivalent to 0.5 km s−1
) aimed at higher continuum
sensitivity. The total continuum bandwidth was ∼3.2 GHz. For
HD135344B, the flux was calibrated using Ceres, and J1427-
4206 was used for calibration of both bandpass and gain. SR 21
and DoAr 44 were observed in one scheduling block, with Titan
as flux calibrator, J1517-2422 as bandpass calibrator, and J1625-
2527 as gain calibrator. In both objects, the flux calibrator (Ceres
resp. Titan) is highly resolved on long baselines. The gain cali-
bration on the flux calibrator was thus performed using a sub-
set of the antennas. The total on-source integration time was
30 minutes each for SR 21 and DoAr 44, and 54 minutes for
HD 135344B.
IRS 48 was observed in ALMA Cycle 2 program
2013.1.00100.S (PI van der Marel) in Band 9 (∼680 GHz or 440
µm) with a resulting spatial resolution of 0.15–0.2”. The obser-
vations were taken in four spectral windows of 1920 channels:
three windows with a bandwidth of 937.5 MHz (channel width
488 kHz or 0.3 km s−1
), centered on the 13
CO 6–5, C18
O 6–5
and H2CO 9–8 transitions with rest frequencies of 661.067276,
658.553278 and 674.80978 GHz, respectively. The fourth spec-
tral window was centered on 672 GHz with a bandwidth of 1875
2
3. N. van der Marel et al.: Gas cavities in transitional disks
Fig. 1. ALMA observations of the continuum, 13
CO and C18
O 3-2 lines of the first three targets. Top left: zero-moment 13
CO map.
Top middle: Continuum map. Top right: 13
CO spectrum integrated over the entire disk. Bottom left: zero-moment C18
O map.
Bottom middle: first moment 13
CO map (velocity map). Bottom right: C18
O spectrum integrated over the entire disk. The beam
is indicated in each map by a white ellipse in the lower left corner. The dotted white ellipse indicates the dust cavity radius.
MHz (channel width 977 kHz or 0.5 km s−1
) aimed at higher
continuum sensitivity. The total continuum bandwidth was ∼4.7
GHz. The flux was calibrated using J1517-243, the bandpass
with J1427-4206 and the gain with J1626-2951. J1700-2610 was
3
4. N. van der Marel et al.: Gas cavities in transitional disks
Fig. 2. ALMA observations of the continuum, the 13
CO and C18
O 6-5 lines of the fourth target. Top left: zero-moment 13
CO map.
Top middle: Continuum map. Top right: 13
CO spectrum integrated over the entire disk. Bottom left: zero-moment C18
O map.
Bottom middle: first moment 13
CO map (velocity map). Bottom right: C18
O spectrum integrated over the entire disk. The beam
is indicated in each map by a white ellipse in the lower left corner. The dotted white ellipse indicates the dust cavity radius.
Table 1. Stellar properties
Target SpT L∗ M∗ R∗ Teff
˙M d AV Ref.
(L⊙) (M⊙) (R⊙) (K) (M⊙ yr−1
) (pc) (mag)
HD135344B F4 7.8 1.6 2.2 6590 6 · 10−9
140 0.3 1,2,3
SR21 G3 10 1.0 3.2 5830 < 1 · 10−9
120 6.3 4,5,6
DoAr44 K3 1.4 1.3 1.75 4730 9 · 10−9
120 2.2 5,6
IRS48 A0 14.3 2.0 1.3 10000 4 · 10−9
120 11.5 7,8
1) Prato et al. (2003), 2) Andrews et al. (2011), 3) Espaillat et al. (2010), 4) Dunkin et al. (1997), 5) Pontoppidan et al. (2008), 6) Grady et al.
(2009), 7) Brown et al. (2012), 8) Salyk et al. (2013)
Table 2. Properties of the ALMA observations
Target Derived position Beam Beam rms13CO
a
rmsC18O
a
rmscont PA ib
LSR
(J2000) size (”) PA (◦
) (mJy beam−1
) (mJy beam−1
) (mJy beam−1
) (◦
) (◦
) (km/s)
HD135344B 15:15:48.42 -37:09:16.36 0.26×0.21 46 9.8 14 0.26 63 16 7.25
SR21 16:27:10.27 -24:19:13.04 0.25×0.19 -65 6.4 8.9 0.12 14 16 3.0
DoAr44 16:31:33.46 -24:27:37.53 0.25×0.19 -65 6.8 8.9 0.14 30 20 4.35
IRS48 16:27:37.18 -24:30:35.39 0.19×0.15 87 23 25 0.59 100 50 4.55
Notes. (a)
Measured in 0.5 km s−1
bins (b)
Derived from the 13
CO channel maps.
set as secondary gain calibrator, but not used in the final calibra-
tion. The total on-source integration time was 52 minutes.
The data were calibrated and imaged in CASA version 4.2.1.
Given the high signal-to-noise ratio of these observations, am-
plitude and phase self-calibration was performed after standard
phase referencing. The data were cleaned using Briggs weight-
ing with a robust factor of 0.5, resulting in a beam size of
∼ 0.25” × 0.20” (Cycle 1 data) and ∼ 0.19” × 0.15” (Cycle 2
data). Table 2 lists the observational properties of the continuum
and spectral line maps of the imaging results.
2.2. Continuum and line maps
Figures 1 and 2 show the zero-moment 13
CO and C18
O maps
and spectra and the velocity map (first moment) of the 13
CO
and the continuum. The spectrum was extracted from the re-
gion of the zero-moment map size. Channel maps of the 13
CO
emission are given in the Appendix. Three of the four sources,
HD135344B, DoAr44, and IRS48, show a clear hole in the
13
CO and C18
O images (Figs. 1 and 2) that was not seen in
12
CO (van der Marel et al. 2015b). IRS48 shows a full gas ring
in 13
CO, which does not suffer from foreground absorption
found in the 12
CO (Bruderer et al. 2014). On the other hand,
the foreground absorption seen in the 12
CO emission of SR 21
(van der Marel et al. 2015b) also affects the 13
CO spectra.
All CO data reveal rotating gas disks with inclination
>15◦
, with a double-peaked velocity profile. The gas rings for
HD135344B, DoAr44, and IRS 48 are in all cases smaller than
the continuum cavities, as shown directly in the 13
CO panels in
Figs. 1 and 2 and in the radial cuts in Fig. 3. The emission in-
side the gas cavities is at least a factor of 2 lower than in the
surrounding rings. In contrast, SR 21 does not appear to have a
4
5. N. van der Marel et al.: Gas cavities in transitional disks
cavity in the gas at this spatial resolution. The peak S/N in the
integrated maps is 12-30 for 13
CO and 5-20 for C18
O.
The 13
CO channel maps and velocity maps are used to derive
the stellar position, the position angle, inclination, and source ve-
locity, which are within errors consistent with the values derived
from the 12
CO data (van der Marel et al. 2015b). The derived pa-
rameters are given in Table 2.
The continuum images show ring-like structures for SR21,
HD135344B, and DoAr44 and a highly asymmetric structure for
IRS 48, as seen in previous Cycle 0 data (van der Marel et al.
2013). The S/N on the continuum ranges between 130 and 500
for the different disks. The Band 7 continuum data of SR21
and HD135344B show minor azimuthal asymmetries with a
contrast lower than a factor 2, similar to the Band 9 contin-
uum (P´erez et al. 2014; van der Marel et al. 2015b), although the
asymmetry in SR21 appears to be less pronounced in Band 7
than in Band 9. The Band 9 and Band 7 continuum images are
compared and analyzed in Pinilla et al. (2015). The continuum
emission in IRS 48 is discussed in van der Marel et al. (2015a).
Fig. 3. Normalized intensity cuts through the major axis of each
disk of the 13
CO 3-2 emission (red) and the dust continuum
emission (blue). In case of IRS48, the deprojected intensity cut
of the minor axis is taken so as to cover the (asymmetric) contin-
uum profile. The cuts clearly reveal that the gas cavity radii are
smaller than the dust cavity radii.
3. Modeling
3.1. Physical model
As a starting point for our models we adopted the physical
structure suggested by Andrews et al. (2011), as implemented
by Bruderer (2013) and fully described in van der Marel et al.
(2015b). The surface density Σ(r) is assumed to be a ra-
dial power-law with an exponential cut-off following the time-
dependent viscosity disk model ν ∼ rγ
with γ = 1
(Lynden-Bell & Pringle 1974; Hartmann et al. 1998)
Σ(r) = Σc
r
rc
−γ
exp
−
r
rc
2−γ
. (1)
The gas and dust follow the same density profile, but the gas-to-
dust ratio is varied throughout the disk, as shown in Fig. 4. Inside
the cavity, the dust density is zero, except for the inner disk,
which is set by δdust. The gas density inside the cavity is varied
with drops δgas. In the outer disk, the gas-to-dust ratio is fit by
a constant number. The vertical structure is defined by the scale
height hc and the flaring angle ψ, following h(r) = hc(r/rc)ψ
. The
fraction of large grains fls and the scale height of the large grains
χ are used to describe the settling. More details on the star, the
adopted stellar UV radiation, the dust composition, and vertical
structure are given in van der Marel et al. (2015b).
3.2. Model-fitting approach
The best-fit models from Table 4 in van der Marel et al. (2015b)
were used as initial model for the vertical structure and dust den-
sity structure for SR21 and HD135344B, based on a combina-
tion of SED, dust 690 GHz continuum visibility, and 12
CO 6–5
modeling. These models were fit by eye, starting from a surface
density and cavity size consistent with the millimeter visibility
curve, followed by small adjustments on the inner disk parame-
ter (δdust) and vertical structure to fit the SED. For the fit to the
12
CO data, the gas surface density was taken initially assuming
a gas-to-dust ratio of 100, and the amount of gas inside the cav-
ity was subsequently constrained by varying the δgas parameter,
where Σgas = δgasΣgas for r < rcav. The dust density inside the
cavity (between rgap and rcavdust) was set to be entirely empty of
dust grains. SR21 is an exception: a small amount of dust was
included between 7 and 25 AU, following van der Marel et al.
(2015b). The dust structure of DoAr44 is analyzed in a similar
way in Appendix B through SED and dust 345 GHz continuum
visiblity modeling. For IRS48, we used the model derived by
Bruderer et al. (2014), although we chose to use an exponential
power-law density profile instead of a normal power-law, to be
consistent with the other three disks in this study.
With the new CO isotopolog data, we used the initial dust
structure model and only varied a small number of parameters
to fit the CO emission by eye by subsequent adjustments of the
surface density, gas-to-dust ratio, outer radius, and the δ parame-
ters to fit the amount of gas inside the cavity. These are shown to
be the most relevant parameters by our previous modeling. We
did not use a χ2
or Markov chain Monte Carlo (MCMC) method
because the computational time of the models is too long and the
number of parameters too large. Formal uncertainties of model
parameters, the uniqueness of the fit and correlation between pa-
rameters cannot be computed directly, but the density and δ pa-
rameters are estimated to be within an order of magnitude and
the radial parameters to within 5 AU based on a small model grid
(see also Figs. 5 and C.1).
The outer disk CO emission and submillimeter continuum
flux were fit simultaneously by varying Σc and the gas-to-dust
ratio. The outer radius rout was set by fitting the CO spectrum
(the maxima in the spectra or double peaks that arise from the
Keplerian motion) and provides outer boundaries for computing
the gas masses. Using this surface density profile, the emission
inside the cavity is constrained by the δ parameters (Fig. 4). The
near-infrared excess determines the dust density in the inner disk
through δdust. The gas cavity radius rcavgas and drop δgas2 were fit
5
6. N. van der Marel et al.: Gas cavities in transitional disks
Fig. 4. Generic surface density profile for the gas and dust.
Table 3. Results for the gas density profile of each transition
disk.
Parameter HD SR DoAr IRS
13(a)
21 44 48
Surface rc (AU) 25 15 25 60
density Σc (g cm−2
) 120 400 60 0.5
gas-to-dust ratio 80 100 100 12
M(b)
dust
(10−3
M⊙) 0.13 0.075 0.05 0.015
M(b)
gas (10−3
M⊙) 15 7.7 2.5 0.55
Radial rcavgas (AU) (d)
30 7 16 25
structure δgas2
(d)
2·10−4
10−20 (c)
≤ 10−4
≤ 10−3
rcavdust (AU) 40 25 32 60
δgas
(d)
1 5 · 10−2
10−2
1
rout (AU) 125 60 60 90
Inner rsub (AU) 0.18 0.18 0.08 0.4
disk rgap (AU) 0.25 1.0 1.0 1.0
δdust (AU) 2·10−4
1·10−6
1·10−2
1·10−3
Vertical hc (rad) 0.15 0.07 0.1 0.14
structure ψ 0.05 0.15 0.1 0.22
fls 0.95 0.85 0.85 0.85
χ 0.8 0.2 0.2 0.2
Notes. a) HD13=HD135344B. b) The masses are only constrained
within rout for the detected surface brightness. c) The drop inside 7
AU could not be constrained by the ALMA data; we adopt the value
from CO rovibrational spectroastrometry by Pontoppidan et al. (2008).
d) The uncertainties on the gas cavity size are typically 5 AU and
lower than one order of magnitude on the depth of the drop.
to the CO emission. In some cases, an additional drop in gas
surface density is required between rcavgas and the dust cavity
radius rcavdust. This drop is indicated by δgas.
The main parameters that are varied are the gas cavity ra-
dius rcavgas and the drop in gas density δgas2 between rsub and
rcavgas. The CO isotopologs provide better constraints on the den-
sity than the 12
CO because they are less optically thick (13
CO) or
even optically thin (C18
O). The effects of isotope-selective pho-
todissociation are properly considered in the modeling and are
discussed in Sect. 4.3.
4. Results
Data and models are compared through the spectra and the zero-
moment maps (intensity maps) of both 13
CO and C18
O. For each
target we show the direct comparison of the images of the inten-
sity map of the best-fit model and the constraint on both rcavgas
and δgas2 through spectra and intensity cuts through the major
and minor axis of the zero-moment map.
In three of the four targets an inner gas cavity (smaller than
the dust cavity) was required to fit the data. In SR21 the 7
AU cavity previously derived from rovibrational emission was
adopted, but no gas cavity is resolved at the spatial resolution
of ∼ 0.2” (24 AU) in our observations. In all disks, the depth is
constrained to within an order of magnitude and the cavity size
to within ±5 AU, mainly through the comparison of the spatially
resolved emission, but further confirmed by the line wings in
the spectra. In the intensity cuts in Fig. 5 the δgas2 parameter is
varied. The comparison shows that the uncertainty on the den-
sity drop is lower than an order of magnitude. In Appendix C we
show the intensity cuts for larger and smaller gas cavity radii, re-
spectively. These plots show that the uncertainty on the gas cav-
ity radius is typically 5 AU and the uncertainty on the depth is
lower than one order of magnitude. Furthermore, in both SR21
and DoAr44 an additional drop δgas between rcavgas and rcavdust is
required to fit the data.
The models of the 12
CO fits of van der Marel et al. (2015b)
match the isotopolog data in the outer disk remarkably well.
Only minor corrections in surface density and gas-to-dust ratio
were required to fit the new data. However, inside the cavity the
previously derived results for the gas surface density were found
to be inconsistent. A modest drop in the gas density inside the
dust cavity radius rcav was sufficient to explain the 12
CO data, but
no gas cavity was seen. Since the gas cavity becomes visible in
the isotopolog data and turns out to be smaller than the dust cav-
ity radius, the gas cavity radius rcavgas could be fit independently
of the depth.
4.1. Results for individual targets
HD135344B
HD135344B shows a clear gas cavity, both in 13
CO and C18
O
images, which is significantly smaller than the dust cavity (see
top two panels of Fig. 1). The modeling constrains the gas cav-
ity radius to 30 AU (dust cavity radius is 40 AU), and the drop
is 2 · 10−4
(top right panels in Fig. 5). Previously, the model
based on the 12
CO data required δgas of 10−1
− 10−2
for a cav-
ity radius of 40 AU. A 30 AU gas cavity was also derived
in van der Marel et al. (2015b) considering the inner radius of
the small dust grains derived from the scattered-light emission
(Garufi et al. 2013), but a δgas value as low as ∼ 10−4
under-
produces the 12
CO emission inside the cavity. As the 12
CO is
optically thick and mainly traces the temperature at the τ = 1
surface, this new result suggests that the temperature structure
is somewhat higher than in our model, perhaps because of some
residual dust in the cavity (increasing the CO abundance by its
shielding and changing the heating-cooling balance) or the ver-
tical structure (shadowing on the outer disk) (see Bruderer 2013,
for a detailed discussion).
The residual of the 13
CO emission (left panels in Fig. 5)
shows that the model overpredicts the emission in the outer disk
(>0.5”). On the other hand, the C18
O residual underpredicts the
emission in the outer disk. The residuals are spatially insignif-
icant, but integrated over the whole disk, they are most likely
related to real structure, suggesting an outer gas ring with a
6
7. N. van der Marel et al.: Gas cavities in transitional disks
Fig. 5. Modeling results and observations of the 13
CO and C18
O emission for the best-fitting models in derotated images and spectra.
The left panels show the direct image comparison of the zero-moment map: derotated observations, model, convolved model, and
residual. In the residual map the overlaid contours indicate the 3σ levels, where dashed lines are negative. The central panels show
the gas density profiles with different δgas2 drops as solid lines and the dust density profile as dashed lines. The right panels show
the resulting intensity cuts for the major and minor axis for both 13
CO and C18
O. The best-fitting model is indicated in red, other
δgas2 values in blue. The drop in density can be constrained to within an order of magnitude.
7
8. N. van der Marel et al.: Gas cavities in transitional disks
possible gap. The radius of ∼ 100 AU coincides with a sug-
gested planet that is launching one of the spiral arms observed in
scattered-light observations (Muto et al. 2012). If there is indeed
a planet at this large orbit, it is expected to clear a gap in the gas,
which might explain the structure in the outer disk. As the focus
of this study is on the emission inside the dust cavity, this is not
investigated further.
SR21
Unlike the other disks, the CO emission in SR21 does not appear
to have a cavity. Rovibrational CO emission suggests a gas cav-
ity of 7 AU radius (Pontoppidan et al. 2008) that remains unre-
solved at the ALMA spatial resolution (14 AU diameter∼0.12”).
The physical model includes this 7 AU cavity. The 12
CO emis-
sion already indicated a drop in density between 7 AU and the
dust cavity radius of 25 AU. The intensity cuts of the CO iso-
topologs also suggests a drop in density considering the strength
of the emission (right panels in Fig. 5). According to the model
fitting, this drop is of about two orders of magnitudes.
DoAr44
DoAr44 is the only disk in this study with a symmetric dust ring.
The dust cavity radius was found to be 32 AU (see Appendix
B), using the same modeling approach as in van der Marel et al.
(2015b). The cavity size and disk mass are similar to previous
studies of SMA 345 GHz continuum data (Andrews et al. 2011).
The drop in dust density inside the cavity (δdustcav) is at least a
factor 1000. The CO isotopolog intensity maps have a lower S/N
than the other disks, probably because of the lower disk mass,
but still show a gas cavity that is only half the size of the dust
cavity: 16 AU. The δgas2 inside 16 AU is at most 10−4
. An ad-
ditional drop in gas density between 16 and 32 AU of 10−2
is
required to fit the emission (right panels in Fig. 5).
IRS48
The CO isotopolog emission in IRS48 confirms the presence of
a gas cavity with a considerably smaller radius than that of the
peak of the dust asymmetry (60 AU), as found by Bruderer et al.
(2014), consistent with the 30 AU gas ring found in rovibra-
tion CO emission (Brown et al. 2012). To be consistent with the
models of the other disks, we assumed a radial power-law with
exponential cut-off instead of a simple power-law as done by
Bruderer et al. (2014), but a similar vertical structure, density
structure, and mass are found as in their study. Because DALI
considers only axisymmetric models, the millimeter continuum
asymmetry is not fit: the total submillimeter flux, the VISIR
18µm image and the SED are again used to constrain the dust
density and dust cavity radius. The gas cavity radius is found
to be 25 instead of the 20 AU found by Bruderer et al. (2014),
but this is within the uncertainty on the radius, and no additional
drop between 25 and 60 AU in density is required to fit the emis-
sion (right panels in Fig. 5).
13
CO shows a full ring of emission. However, the emission
is weaker at the location of the dust trap, as seen in the residual
image (left panels in Fig. 5). The 13
CO emission is barely opti-
cally thick at the dust trap radius of 60 AU (the τ = 1 surface is
at the midplane), and the drop in emission is most likely due to
the continuum optical depth or a drop in temperature caused by
the local increase of dust density. The S/N of the C18
O emission
is too low to show the gas ring or this local drop in emission, but
the data were used to set constraints on the gas density.
4.2. Gradual drop
The structure with two gas density drops inside the cavity found
in DoAr44 and SR21 (and previously in IRS 48, Bruderer et al.
2014) has been interpreted as the result of multiple planets at
different orbits. An alternative explanation is a gradual drop or
increasing surface density profile inside the cavity. To investi-
gate this, we ran additional models and replaced the exponential
power-law Σ(r) by an increasing exponential law between rcavdust
and rcavgas, motivated by planet-disk interaction models, follow-
ing
Σ(r) = Σ(rcav) · e(r−rcav2)/w
, (2)
where the width w is given by
w =
rcav − rcav2
ln(Σ(rcav)/δgas2Σ(rcav2)
. (3)
The width was chosen to connect Σ(r) at rcavdust and rcavgas, fit-
ting δgas2, and no new parameters were introduced. This straight
connection is further motivated by the shape of the gaps in Fig.
7 in de Juan Ovelar et al. (2013) of planet-disk interaction mod-
els. Using the above relation and the derived cavity radii, the
drop in density is derived again for the best-fitting model (see
Fig. 6). The best-fitting values are within a factor of 2 of the
δgas2 values in the vertical drop model (Table 3): we find 2·10−4
,
10−3
, 2·10−4
, and 5·10−2
for HD135344B, SR21, DoAr44, and
IRS48 respectively, although IRS48 is a poor fit compared to the
double-drop model. However, the outer radius of the slope (rcav)
of 60 AU has been constrained from the SED and VISIR image
instead of from the millimeter continuum, as in the other disks,
because of the asymmetric structure. This makes this approach
rather uncertain. Another possibility is that a combination with
other clearing mechanisms is responsible for the different drop
shapes.
4.3. Isotope-selective photodissociation
The main process regulating the survival of CO in disks, pho-
todissociation, does not equally affect different CO isotopologs
(van Dishoeck & Black 1988). 12
CO becomes optically thick
at low column densities and shields itself throughout the disk
from the photodissociating flux. On the other hand, less abun-
dant isotopologs, like C18
O, are not self-shielded until much
deeper into the disk and continue to be photodissociated. This
results in regions where C18
O is less abundant than predicted
by a constant [16
O/18
O] ratio found in the interstellar medium.
Accordingly, this leads to reduced C18
O line intensities. The im-
portance of isotope-selective effects varies depending on disk
parameters, dust properties, and the stellar far-ultraviolet field
(Miotello et al. 2014). The UV field is calculated at each position
in the DALI model taking into account the local dust density.
For this reason, isotope-selective photodissociation has been
implemented in the modeling of all disks in our sample. Isotope-
selective effects are substantial only for C18
O line emission and
in the outer disk regions, where the bulk of the gas phase CO
is located (Fig. 7). The effect on the outer disk emission is not
detectable for SR21. On the other hand, IRS48 has an even lower
disk mass but shows a significant difference. This may be related
to the low gas-to-dust ratio in this disk. This shows that isotope-
selective photodissociation depends on the combination of disk
and stellar parameters and not only on the total disk gas mass.
Interestingly, isotope-selective photodissociation only af-
fects the CO isotopolog emission in the outer disk (instead of
8
9. N. van der Marel et al.: Gas cavities in transitional disks
Fig. 6. Comparison of the intensity cuts between the best-fit
models (blue) and a gradual model (red) as defined in Eq. 2.
The right panel gives the density profile. All disks except IRS48
can be fit equally well with this gradual increase profile.
inside the cavity), probably because of the lower CO column
densities and the temperatures. In these conditions the isotope-
selective photodissociation is more effective. A similar result
was found in full disks, where the regions strongly affected by
isotope-selective processes were located in the outer colder re-
gions (Miotello et al. 2014). However, this is only true for con-
ditions in these four disks. Possible effects in more extreme sce-
narios cannot be excluded.
5. Discussion
The main outcome of Fig. 3 and the modeling is that all four
transition disks have gas inside the cavity, with a gas cavity
that is smaller than the dust cavity (for SR21 adopted from
Pontoppidan et al. (2008)). The CO isotopologs confirm the
main result from the 12
CO data: gas is present inside the dust
cavities and decreases less in density than the millimeter-dust.
With the new optically thin isotopolog data, the density profiles
are now much better constrained than those based on 12
CO data
alone (van der Marel et al. 2015b).
Two other transition disks have been sufficiently spatially
resolved in CO and continuum to also confirm a gas cav-
Fig. 7. Comparison of the spectra of the C18
O emission with
(red, ISO) and without (blue, NOISO) implementing isotope-
selective photodissociation. HD135344B, SR21, and IRS48 dif-
fer by up to a factor of 2, while no difference is seen for DoAr44.
ity smaller than the dust cavity: HD142527 (Fukagawa et al.
2013; Perez et al. 2015) and J1604-2130 (Zhang et al. 2014;
van der Marel et al. 2015b). To date, no counterexample has
been found for which the gas follows the same distribution as
the dust. This hints at the exciting possibility that the origin of
transition disks indeed lies in embedded planets that have cleared
their orbit in the gas and trapped the millimeter-dust at the edge.
An upper limit on any embedded companions has been de-
rived for HD135344B using direct imaging in Vicente et al.
(2011): less than 1 brown dwarf mass at >37 AU radius. For
SR21, companions with q > 0.01 or > 10MJup are ruled out
for 11-21 AU orbital radius according to near-infrared aperture
masking interferometry (Andrews et al. 2011). For the other two
disks no limits on companions are known. Unfortunately, the de-
rived limits are outside the orbital range suggested by our gas
cavity radii, assuming the companion orbital radius is close to
the gas cavity radius.
The difference between gas and dust cavity radius can
be compared with modeling results of planet-disk interaction
by de Juan Ovelar et al. (2013). They show a relation between
the observed dust cavity wall in the near-infrared (SPHERE-
ZIMPOL predictions), tracing the small dust grains, and the
millimeter-dust cavity wall as observed by ALMA. Simulations
were run for different planet masses at different radii (Fig. 8 and
Eq. 1 in de Juan Ovelar et al.). The simulations were performed
assuming a viscosity of α ∼ 10−3
for a disk of 0.05 M⊙. The
ratio between the two radii f(Mp) is found to follow
f(Mp) = c ·
Mp
MJup
γ
, (4)
with c ∼ 0.85, and γ ∼ [−0.22, −0.18, −0.16] for planet orbital
radius = [20, 40, 60] AU, respectively. Assuming that the small
dust grains follow the gas, this relation can be directly applied to
our cavity radii. The gas-to-dust cavity radii ratios for our targets
are 0.75, 0.28, 0.5, and 0.42 for HD135344B, SR21, DoAr44,
and IRS48, respectively, with gas cavity radii of 30, 7, 16, and
9
10. N. van der Marel et al.: Gas cavities in transitional disks
25 AU. Using the γ = −0.22 relation (closest to our gas cavity
radii), planet masses are predicted to be 2, 11, and 25 MJup for
HD135344B, DoAr44, and IRS48. For SR21, we extrapolate γ
for the 7 AU gas cavity radius to be -0.26, resulting in a planet
mass of 71 Jupiter masses. The derived masses remain uncertain
because of the fixed viscosity in the models: a lower viscosity
would result in lower masses.
Another way to compare the observations with planet-disk
interaction models is using the δgas2 drop value. The outcome of
the gradual drop model is particularly interesting because it bet-
ter resembles the shape of the gap carved by a planet, as seen in
planet-disk interaction simulations (Crida et al. 2006; Zhu et al.
2011; de Juan Ovelar et al. 2013; Fung et al. 2014). Fung et al.
(2014) have derived an analytical prescription based on the out-
come of numerical simulations of the depth of the gap, which
can set constraints on the mass of the planet in combination with
the viscosity in their Eq. 14:
Σgap/Σ0 = 4.7 × 10−3 q
5 × 10−3
−1 α
10−2
1.26 h/r
0.05
6.12
, (5)
with q the mass ratio between planet and star, α the viscosity
parameter, h/r the scale height, and Σgap/Σ0 the drop in density,
or δgas2. The equation is only valid for q = 10−4
− 10−2
. A simi-
lar relation was recently derived by Kanagawa et al. (2015). The
derived parameters can thus provide an estimate for the planet
mass, assuming a certain viscosity value. The relation has a very
strong dependence on h/r because of the strong dependencies
of the torque on the disk angular frequency. We note that the
disks of these simulations are isothermal to make h/r constant
as a function of radius. Since the gas temperature has in real-
ity a strong vertical gradient that is due to the UV heating, es-
pecially at the cavity wall, this makes Eq. 5 uncertain. On the
other hand, these processes occur close to the midplane, and the
isothermal approximation is not entirely incorrect. In applying
the relation to our findings, h/r is only marginally constrained
by our models because of the degeneracies in SED modeling. As
h/r = cs/vk, with the sound speed cs ∝
√
T and vk the Keplerian
velocity, it can also be computed directly from the derived mid-
plane temperatures. We find h/r in our models at the gas cavity
radius of 0.077, 0.063, 0.048, and 0.11 for HD135344B, SR21,
DoAr44, and IRS48, respectively, which is generally not too dif-
ferent from the h/r derived from our radiative transfer modeling.
Using these values for h/r in combination with the δgas2 values
derived for the gradual drop models for our disks, planet masses
can be derived for α between 10−2
and 10−4
. For α = 10−2
, the
q-values are > 0.01 (except for DoAr44), which is beyond the
range for which the analytical relation was derived. Higher q-
values, implying substellar mass companions, would result in
eccentric gaps and/or entire disruption of the disk, which is why
the relation is no longer valid. For reasonable planet masses (up
to 10 Jupiter masses) that are consistent with the upper limits
for companions mentioned above, this implies low viscosity val-
ues between α ∼ 10−3
and 10−4
, much lower than found in the
TW Hya and HD163296 disks based on turbulent broadening
(Hughes et al. 2011).
The estimates derived here remain highly uncertain because
of the uncertainties in our modeling and the assumptions in the
numerical models: the relation was empirically derived based
on the outcome of numerical simulations with several important
limitations: the vertical structure is isothermal, accretion onto
the planet is ignored, and the dust and gas are coupled, which is
not true for a realistic physical disk. However, the δgas or Σgap/Σ0,
has been measured for the first time with an accuracy of better
than an order of magnitude with these new observations. This
parameter is inversely linear with q or planet mass and sets a
constraint on the properties of these potential embedded planets.
6. Conclusions
We have analyzed high spatial resolution ALMA submillimeter
observations of 13
CO and C18
O line emission from four transi-
tion disks using full physical-chemical modeling. Using a pre-
viously derived surface density model of the dust, based on the
SED and millimeter continuum visibilities, a physical model of
the gas and dust was derived for each of the disks. The structure
and amount of gas inside the cavity is the main point of interest
as it gives direct information about potential embedded planets.
1. All four disks show a gas cavity that is up to twice as small
in radius as the dust cavity. Two other examples are known
from the literature.
2. All disks can be fit to a gas density model with one or two
drops in the gas density inside the cavity.
3. The gas density inside the cavity drops by at least a factor of
1000 compared to the gas surface density profile of the outer
disk.
4. An alternative model with a gradual increase of surface den-
sity with radius inside the cavity fits the data equally well for
three of the four disks.
5. The derived values of the gas mass from the CO isotopologs
are within a factor of a few compared to previously derived
values from spatially resolved 12
CO observations, submil-
limeter continuum, and a gas-to-dust ratio of 100. The iso-
topologs are crucial for the gas density profile inside the cav-
ity, however.
6. The depth of the gas density drop indicates that the viscosi-
ties in these disks are low for reasonable companion masses.
These spatially resolved isotopolog data point to embedded plan-
ets as by far the most likely explanation.
Acknowledgements. The authors would like to thank P. Pinilla for useful dis-
cussions. Astrochemistry in Leiden is supported by the Netherlands Research
School for Astronomy (NOVA), by a Royal Netherlands Academy of Arts
and Sciences (KNAW) professor prize, and by the European Union A-ERC
grant 291141 CHEMPLAN. This paper makes use of the following ALMA
data: ADS/JAO.ALMA/2012.1.00158.S and ADS/JAO.ALMA/2013.1.00100.S.
ALMA is a partnership of ESO (representing its member states), NSF (USA)
and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan),
in cooperation with the Republic of Chile. The Joint ALMA Observatory is op-
erated by ESO, AUI/NRAO and NAOJ.
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Appendix A: Channel maps
In this section we present the 13
CO channel maps for each observed target.
Fig. A.1. 13
CO channel maps for each observed target. Overlaid in white contours are the Keplerian velocity profiles for the derived
inclination and the given stellar mass.
12
13. N. van der Marel et al.: Gas cavities in transitional disks
Appendix B: Dust model DoAr44
Unlike the other disks, the dust surface density profile of DoAr44 was not yet constrained by ALMA data from previous papers.
Using the same approach as in van der Marel et al. (2015b), a model was found by fitting the SED, the 345 GHz continuum visibility
curve, and the 345 GHz continuum intensity cuts. The cavity size is 32 AU, similar to the previous result by Andrews et al. (2011).
The depth of the dust density inside the cavity was constrained by varying the δdustcav between rgap and rcavdust. It was found that the
dust density drops by at least a factor 103
, similar to the other disks.
Fig. B.1. Modeling results and observations of DoAr44 of the dust surface density, comparing δdustcav ranging between 10−2
and 10−4
as indicated in the right panel. The observations are plotted in black. Left: Spectral energy distribution. Middle left:
Amplitude of the 345 GHz continuum visibility for the deprojected baselines. The null line is indicated with a dashed line. Middle
right: Normalized intensity cuts through the major (bottom) and minor (top) axis of the 345 GHz continuum image. The model
images are convolved with the same beam as the ALMA observations. Right: The dust surface density profile. Indicated are the
δdust , the drop in density to fit the inner disk through the near-infrared emission, and δdustcav , the minimum drop in dust density
inside the cavity needed to fit the observations.
Appendix C: Additional models
Figure C.1 shows the modeling results for 13
CO for the baseline model (Table 3) for different gas cavity sizes. The plots show that
the gas cavity radius is determined to within an uncertainty of 5 AU.
Fig. C.1. Modeling results for different cavity sizes for three of the four sources. The plots show the 13
CO intensity cuts of the data
(black) and the models (colors) for different density drops δgas2. The central panel uses the gas cavity size rcavgas of the final model
(see Table 3), the left panel the results for a 5 AU smaller gas cavity, and the right panel the results for a 5 AU larger cavity. For
SR21 the 7 AU radius remains unresolved in the ALMA data so the radius is not explored. The plots reveal that the gas cavity radius
is determined to within 5 AU uncertainty.
13
14. N. van der Marel et al.: Gas cavities in transitional disks
Fig. C.1. Continued.
14