6 research outputs found
Impact of planetary mass uncertainties on exoplanet atmospheric retrievals
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.Comment: 19 pages, 12 figures, Accepted in Ap
Azimuthal C/O variations in a planet-forming disk
The elemental carbon-to-oxygen ratio (C/O) in the atmosphere of a giant planet is a promising diagnostic of that planet’s formation history in a protoplanetary disk. Alongside efforts in the exoplanet community to measure the C/O ratio in planetary atmospheres, observational and theoretical studies of disks are increasingly focused on understanding how the gas-phase C/O ratio varies both with radial location and between disks. This is mostly tied to the icelines of major volatile carriers such as CO and H2O. Using ALMA observations of CS and SO, we have found evidence for an entirely unexpected type of C/O variation in the protoplanetary disk around HD 100546: an azimuthal variation from a typical, oxygen-dominated ratio (C/O ≈ 0.5) to a carbon-dominated ratio (C/O ≳ 1.0). We show that the spatial distribution and peculiar line kinematics of both CS and SO molecules can be well explained by azimuthal variations in the C/O ratio. We propose a shadowing mechanism that could lead to such a chemical dichotomy. Our results imply that tracing the formation history of giant exoplanets using their atmospheric C/O ratios will need to take into account time-dependent azimuthal C/O variations in a planet’s accretion zone
An ALMA molecular inventory of warm Herbig Ae disks: II. Abundant complex organics and volatile sulphur in the IRS 48 disk
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 molecule (COM) and likely
H2O-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 H213CO, 34SO, 33SO and
c-H2COCH2 (ethylene oxide) in a protoplanetary disk. All of the molecular
emissions, aside from CO, are colocated 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 sulphur-bearing species, with the latter being more azimuthally
extended and located radially further from the star. The abundances of the
newly detected COMs relative to CH3OH 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.Comment: Accepted to AJ, 21 pages, 7 figure
An ALMA molecular inventory of warm Herbig Ae disks: I. Molecular rings, asymmetries and complexity in the HD 100546 disk
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 CH3OH. We present
the first results of an ALMA line survey at 337 to 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
and CH3OCHO (methyl formate). We also make the first tentative detections of
H213CO and 34SO 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 outer disk. We discuss the physical and/or chemical origin of these
sub-structures in relation to ongoing planet formation in the HD 100546 disk.
We also investigate how similar and/or different the molecular make up of this
disk is to other chemically well-characterised Herbig Ae disks. The line-rich
data we present motivates the need for more ALMA line surveys to probe the
observable chemistry in Herbig Ae systems which offer unique insight into the
composition of disk ices, including complex organic molecules.Comment: Accepted to AJ, 25 pages, 11 figure
Spatially resolving the volatile sulfur abundance in the HD 100546 protoplanetary disc
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
Temperature-activated ion channels in neural crest cells confer maternal fever–associated birth defects
Birth defects of the heart and face are common, and most have no known genetic cause, suggesting a role for environmental factors. Maternal fever during the first trimester is an environmental risk factor linked to these defects. Neural crest cells are precursor populations essential to the development of both at-risk tissues. We report that two heat-activated transient receptor potential (TRP) ion channels, TRPV1 and TRPV4, were present in neural crest cells during critical windows of heart and face development. TRPV1 antagonists protected against the development of hyperthermia-induced defects in chick embryos. Treatment with chemical agonists of TRPV1 or TRPV4 replicated hyperthermia-induced birth defects in chick and zebrafish embryos. To test whether transient TRPV channel permeability in neural crest cells was sufficient to induce these defects, we engineered iron-binding modifications to TRPV1 and TRPV4 that enabled remote and noninvasive activation of these channels in specific cellular locations and at specific developmental times in chick embryos with radio-frequency electromagnetic fields. Transient stimulation of radio frequency-controlled TRP channels in neural crest cells replicated fever-associated defects in developing chick embryos. Our data provide a previously undescribed mechanism for congenital defects, whereby hyperthermia activates ion channels that negatively affect fetal development