Abstract The Atacama Large Millimeter/submillimeter Array (ALMA) can probe the molecular content of planet-forming disks with unprecedented sensitivity. These observations allow us to build up an ...inventory of the volatiles available for forming planets and comets. Herbig Ae transition disks are fruitful targets due to the thermal sublimation of complex organic molecules (COMs) and likely H 2 O-rich ices in these disks. The IRS 48 disk shows a particularly rich chemistry that can be directly linked to its asymmetric dust trap. Here, we present ALMA observations of the IRS 48 disk where we detect 16 different molecules and make the first robust detections of H 2 13 CO , 34 SO, 33 SO, and c-H 2 COCH 2 (ethylene oxide) in a protoplanetary disk. All of the molecular emissions, aside from CO, are co-located with the dust trap, and this includes newly detected simple molecules such as HCO + , HCN , and CS. Interestingly, there are spatial offsets between different molecular families, including between the COMs and sulfur-bearing species, with the latter being more azimuthally extended and radially located further from the star. The abundances of the newly detected COMs relative to CH 3 OH are higher than the expected protostellar ratios, which implies some degree of chemical processing of the inherited ices during the disk lifetime. These data highlight IRS 48 as a unique astrochemical laboratory to unravel the full volatile reservoir at the epoch of planet and comet formation and the role of the disk in (re)setting chemical complexity.
Abstract Observations of disks with the Atacama Large Millimeter/submillimeter Array (ALMA) allow us to map the chemical makeup of nearby protoplanetary disks with unprecedented spatial resolution ...and sensitivity. The typical outer Class II disk observed with ALMA is one with an elevated C/O ratio and a lack of oxygen-bearing complex organic molecules, but there are now some interesting exceptions: three transition disks around Herbig Ae stars all show oxygen-rich gas traced via the unique detections of the molecules SO and CH 3 OH. We present the first results of an ALMA line survey at ≈337–357 GHz of such disks and focus this paper on the first Herbig Ae disk to exhibit this chemical signature—HD 100546. In these data, we detect 19 different molecules including NO, SO 2 , and CH 3 OCHO (methyl formate). We also make the first tentative detections of H 2 13 CO and 34 SO in protoplanetary disks. Multiple molecular species are detected in rings, which are, surprisingly, all peaking just beyond the underlying millimeter continuum ring at ≈200 au. This result demonstrates a clear connection between the large dust distribution and the chemistry in this flat disk. We discuss the physical and/or chemical origin of these substructures in relation to ongoing planet formation in the HD 100546 disk. We also investigate how similar and/or different this molecular makeup of this disk is to other chemically well-characterized Herbig Ae disks. The line-rich data we present motivate the need for more ALMA line surveys to probe the observable chemistry in Herbig Ae systems, which offer unique insight into the composition of disks ices, including complex organic molecules.
ABSTRACT
(Exo-)planets inherit their budget of chemical elements from a protoplanetary disc. The disc temperature determines the phase of each chemical species, which sets the composition of solids ...and gas available for planet formation. We investigate how gap structures, which are widely seen by recent disc observations, alter the thermal and chemical structure of a disc. Planet–disc interaction is a leading hypothesis of gap formation and so such changes could present a feedback that planets have on planet-forming material. Both the planet gap-opening process and the disc thermal structure are well studied individually, but how the gap-opening process affects disc thermal structure evolution remains an open question. We develop a new modelling method by iterating hydrodynamical and radiative transfer simulations to explore the gap-opening feedback on disc thermal structure. We carry out parameter studies by considering different planet locations rp and planet masses Mp. We find that for the same rp and Mp, our iteration method predicts a wider and deeper gap than the non-iteration method. We also find that the inner disc and gap temperature from the iteration method can vary strongly from the non-iteration or disc without planets, which can further influence dust-trap conditions, iceline locations, and distribution of various ices, such as H2O, CO2, and CO on large dust grains (‘pebbles’). Through that, a gap-opening planet can complicate the canonical picture of the non-planet disc C/O ratio and influence the composition of the next generation of planetesimals and planets.
Molecular line observations are powerful tracers of the physical and chemical conditions across the different evolutionary stages of star, disk, and planet formation. The high angular resolution and ...unprecedented sensitivity of the Atacama Large Millimeter Array (ALMA) enables the current drive to detect small-scale gas structures in protoplanetary disks that can be attributed directly to forming planets. We report high angular resolution ALMA Band 7 observations of sulphur monoxide (SO) in the nearby planet-hosting disk around the Herbig star HD 100546. SO is rarely detected in evolved protoplanetary disks, but in other environments, it is most often used as a tracer of shocks. The SO emission from the HD 100546 disk primarily originates from gas within the ≈20 au millimeter-dust cavity and shows a clear azimuthal brightness asymmetry of a factor of 2. In addition, the difference in the line profile shape is significant when these new Cycle 7 data are compared to Cycle 0 data of the same SO transitions. We discuss the different physical and chemical mechanisms that might cause this asymmetry and time variability, including disk winds, disk warps, and a shock triggered by a (forming) planet. We propose that SO is enhanced in the cavity by the presence of a giant planet. The SO asymmetry complements evidence for hot circumplanetary material around giant planet HD 100546 c that is traced via CO ro-vibrational emission. This work sets the stage for further observational and modelling efforts to detect and understand the chemical imprint of a forming planet on its parent disk.
ABSTRACT
Volatile elements play a crucial role in the formation of planetary systems. Their abundance and distribution in protoplanetary discs provide vital insights into the connection between ...formation processes and the atmospheric composition of individual planets. Sulfur, being one of the most abundant elements in planet-forming environments, is of great significance, and now observable in exoplanets with JWST. However, planetary formation models currently lack vital knowledge regarding sulfur chemistry in protoplanetary discs. Developing a deeper understanding of the major volatile sulfur carriers in discs is essential to building models that can meaningfully predict planetary atmospheric composition, and reconstruct planetary formation pathways. In this work, we combine archival observations with new data from the Atacama Large sub-Millimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX), covering a range of sulfur-bearing species/isotopologs. We interpret this data using the dali thermo-chemical code, for which our model is highly refined and disc-specific. We find that volatile sulfur is heavily depleted from the cosmic value by a factor of ∼1000, with a disc-averaged abundance of S/H ∼ 10−8. We show that the gas-phase sulfur abundance varies radially by ≳3 orders of magnitude, with the highest abundances inside the inner dust ring and coincident with the outer dust ring at r ∼ 150–230 au. Extracting chemical abundances from our models, we find OCS, H2CS, and CS to be the dominant molecular carriers in the gas phase. We also infer the presence of a substantial OCS ice reservoir. We relate our results to the potential atmospheric composition of planets in HD 100546, and the wider exoplanet population.
(Exo-)planets inherit their budget of chemical elements from a protoplanetary disk. The disk temperature determines the phase of each chemical species, which sets the composition of solids and gas ...available for planet formation. We investigate how gap structures, which are widely seen by recent disk observations, alter the thermal and chemical structure of a disk. Planet-disk interaction is a leading hypothesis of gap formation and so such changes could present a feedback that planets have on planet-forming material. Both the planet gap-opening process and the disk thermal structure are well studied individually, but how the gap-opening process affects disk thermal structure evolution remains an open question. We develop a new modelling method by iterating hydrodynamical and radiative transfer simulations to explore the gap-opening feedback on disk thermal structure. We carry out parameter studies by considering different planet locations rp and planet masses Mp. We find that for the same rp and Mp, our iteration method predicts a wider and deeper gap than the non-iteration method. We also find that the inner disk and gap temperature from the iteration method can vary strongly from the non-iteration or disk without planets, which can further influence dust-trap conditions, iceline locations, and distribution of various ices, such as H2O, CO2, and CO on large dust grains ("pebbles"). Through that, a gap-opening planet can complicate the canonical picture of the non-planet disk C/O ratio and influence the composition of the next generation of planetesimals and planets.
Millimeter wavelength observations of Class II protoplanetary disks often
display strong emission from hydrocarbons and high CS/SO values, providing
evidence that the gas-phase C/O ratio commonly ...exceeds 1 in their outer
regions. We present new NOEMA observations of CS $5-4$, SO $7_6-6_5$ and
$5_6-4_5$, C$_2$H $N=3-2$, HCN $3-2$, HCO$^+$ $3-2$, and H$^{13}$CO$^+$ $3-2$
in the DR Tau protoplanetary disk at a resolution of $\sim0.4''$ (80 au).
Estimates for the disk-averaged CS/SO ratio range from $\sim0.4-0.5$, the
lowest value reported thus far for a T Tauri disk. At a projected separation of
$\sim180$ au northeast of the star, the SO moment maps exhibit a clump that has
no counterpart in the other lines, and the CS/SO value decreases to $<0.2$ at
its location. Thermochemical models calculated with DALI indicate that DR Tau's
low CS/SO ratio and faint C$_2$H emission can be explained by a gas-phase C/O
ratio that is $<1$ at the disk radii traced by NOEMA. Comparisons of DR Tau's
SO emission to maps of extended structures traced by $^{13}$CO suggest that
late infall may contribute to driving down the gas-phase C/O ratio of its disk.
In current models used to interpret exoplanet atmospheric observations, the planet mass is treated as a prior and is estimated independently with external methods, such as RV or TTV techniques. This ...approach is necessary as available spectroscopic data do not have sufficient wavelength coverage and/or SNR to infer the planetary mass. We examine here the impact of mass uncertainties on spectral retrieval analyses for a host of atmospheric scenarios. Our approach is both analytical and numerical: we first use simple approximations to extract analytically the influence of each parameter to the wavelength-dependent transit depth. We then adopt a fully Bayesian retrieval model to quantify the propagation of the mass uncertainty onto other atmospheric parameters. We found that for clear-sky, gaseous atmospheres the posterior distributions are the same when the mass is known or retrieved. The retrieved mass is very accurate, with a precision of more than 10%, provided the wavelength coverage and S/N are adequate. When opaque clouds are included in the simulations, the uncertainties in the retrieved mass increase, especially for high altitude clouds. However atmospheric parameters such as the temperature and trace-gas abundances are unaffected by the knowledge of the mass. Secondary atmospheres are more challenging due to the higher degree of freedom for the atmospheric main component, which is unknown. For broad wavelength range and adequate SNR, the mass can still be retrieved accurately and precisely if clouds are not present, and so are all the other atmospheric/planetary parameters. When clouds are added, we find that the mass uncertainties may impact substantially the retrieval of the mean molecular weight: an independent characterisation of the mass would therefore be helpful to capture/confirm the main atmospheric constituent.
