arXiv subjects

Ewine van Dishoeck

Publications and source records attributed to Ewine van Dishoeck.

At least 19 recordsLinked to original sources

arXiv2025

The Rich JWST Spectrum of the Western Nucleus of Arp 220: Shocked Hot Core Chemistry Dominates the Inner Disk

We present full 3-28 $\mathrm{μm}$ JWST MIRI/MRS and NIRSpec/IFU spectra of the western nucleus of Arp 220, the nearest ultraluminous infrared galaxy. This nucleus has long been suggested to possibly host an embedded Compton-thick AGN. Millimeter observations of the dust continuum suggest the presence of a distinct 20 pc core with a dust temperature of $T_\mathrm{d} \gtrsim 500~\mathrm{K}$, in addition to a 100 pc circumnuclear starburst disk. However, unambiguously identifying the nature of this core is challenging, due to the immense obscuration, the nuclear starburst activity, and the nearby eastern nucleus. With the JWST integral field spectrographs, we can, for the first time, separate the two nuclei across this full wavelength range, revealing a wealth of molecular absorption features towards the western nucleus. We analyse the rovibrational bands detected at 4-22 $\mathrm{μm}$, deriving column densities and rotational temperatures for 10 distinct species. Optically thick features of C$_2$H$_2$, HCN and HNC suggest that this molecular gas is hidden behind a curtain of cooler dust, and indicate that the column densities of C$_2$H$_2$ and HCN are an order of magnitude higher than previously derived from Spitzer observations. We identify a warm HCN component with rotational temperature $T_\mathrm{rot} = 330~\mathrm{K}$, which we associate with radiative excitation by the hot inner nucleus. We propose a geometry where the detected molecular gas is located in the inner regions of the starburst disk, directly surrounding the hot 20 $\mathrm{pc}$ core. The chemical footprint of the western nucleus is reminiscent of that of hot cores, with additional evidence for shocks. Despite the molecular material's close proximity to the central source, no evidence for the presence of an AGN in the form of X-ray-driven chemistry or extreme excitation is found.

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arXiv2025

MIRI-LRS spectrum of a cold exoplanet around a white dwarf: water, ammonia, and methane measurements

The study of the atmosphere of exoplanets orbiting white dwarfs is a largely unexplored field. With WD\,0806-661\,b, we present the first deep dive into the atmospheric physics and chemistry of a cold exoplanet around a white dwarf. We observed WD 0806-661 b using JWST's Mid-InfraRed Instrument Low-Resolution Spectrometer (MIRI-LRS), covering the wavelength range from 5 -- 12~$μ\rm{m}$, and the Imager, providing us with 12.8, 15, 18 and 21\,$μ$m photometric measurements. We carried the data reduction of those datasets, tackling second-order effects to ensure a reliable retrieval analysis. Using the \textsc{TauREx} retrieval code, we inferred the pressure-temperature structure, atmospheric chemistry, mass, and radius of the planet. The spectrum of WD 0806-661 b is shaped by molecular absorption of water, ammonia, and methane, consistent with a cold Jupiter atmosphere, allowing us to retrieve their abundances. From the mixing ratio of water, ammonia and methane we derive $\rm{C/O} = 0.34 \pm 0.06$, $\rm{C/N} = 14.4 ^{+2.5}_{-1.8}$ and $\rm{N/O} = 0.023 \pm 0.004$ and the ratio of detected metals as proxy for metallicity. We also derive upper limits for the abundance of CO and $\rm{CO_2}$ ($1.2\cdot10^{-6} \rm{\,and\,} 1.6\cdot10^{-7}$ respectively), which were not detected by our retrieval models. While our interpretation of WD\,0806-661\,b's atmosphere is mostly consistent with our theoretical understanding, some results -- such as the lack of evidence for water clouds, an apparent increase in the mixing ratio of ammonia at low pressure, or the retrieved mass at odds with the supposed age -- remain surprising and require follow-up observational and theoretical studies to be confirmed.

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arXiv2024

JWST-IPA: Chemical Inventory and Spatial Mapping of Ices in the Protostar HOPS370 -- Evidence for an Opacity Hole and Thermal Processing of Ices

The composition of protoplanetary disks, and hence the initial conditions of planet formation, may be strongly influenced by the infall and thermal processing of material during the protostellar phase. Composition of dust and ice in protostellar envelopes, shaped by energetic processes driven by the protostar, serves as the fundamental building material for planets and complex organic molecules. As part of the JWST GO program, "Investigating Protostellar Accretion" (IPA), we observed an intermediate-mass protostar HOPS 370 (OMC2-FIR3) using NIRSpec/IFU and MIRI/MRS. This study presents the gas and ice phase chemical inventory revealed with the JWST in the spectral range of $\sim$2.9 to 28 $μ$m and explores the spatial variation of volatile ice species in the protostellar envelope. We find evidence for thermal processing of ice species throughout the inner envelope. We present the first high-spatial resolution ($\sim 80$ au) maps of key volatile ice species H$_{2}$O, CO$_{2}$, $^{13}$CO$_2$, CO, and OCN$^-$, which reveal a highly structured and inhomogeneous density distribution of the protostellar envelope, with a deficiency of ice column density that coincides with the jet/outflow shocked knots. Further, we observe high relative crystallinity of H$_{2}$O ice around the shocked knot seen in the H$_2$ and OH wind/outflow, which can be explained by a lack of outer colder material in the envelope along the line of sight due to the irregular structure of the envelope. These observations show clear evidence of thermal processing of the ices in the inner envelope, close to the outflow cavity walls, heated by the luminous protostar.

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arXiv2024

Report of the Kavli-IAU Workshop on Global Coordination, "Probing the Universe from far-infrared to millimeter wavelengths: future facilities and their synergies"

This Report summarizes findings and recommendations from the Kavli-IAU workshop on "Probing the Universe from far-infrared to millimeter wavelengths: future facilities and their synergies" which took place from 26 to 28 March 2024 in Pasadena, CA, USA. The workshop aimed to define the needs and potential synergies for different facilities at wavelengths from 30 μm to a few cm in the post-2030 era, considering both financial and programmatic limitations and exploring how to maximize the scientific insights from the data they will yield in the coming decades. This wavelength range provides unique probes of relatively cool, dense interstellar material central to studying the physics and chemistry of nascent stars, proton-planetary disks, and young forming exoplanets. On larger scales, these facilities probe dust and dense gas in galaxies and around highly obscured accreting supermassive black holes and are thus essential for characterizing feedback processes and galaxy evolution out to the highest redshifts. Solar system and time domain studies are also addressed. The main recommendations include the need for ALMA to develop an ALMA2040 vision; for ngVLA to maintain its momentum and schedule and further develop international partnerships; for far-IR astronomy to pursue a space-based observatory with urgency; and for large aperture, wide field millimeter/submillimeter telescopes to continue studies to mature science and technology.

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arXiv2023

The Disc Miner II: Revealing Gas substructures and Kinematic signatures from Planet-disc interaction through line profile analysis

[Abridged] The aim of this work is to identify potential signatures from planet-disc interaction in the circumstellar discs around MWC 480, HD 163296, AS 209, IM Lup, and GM Aur, through the study of molecular lines observed as part of the ALMA large program MAPS. Extended and localised perturbations in velocity, line width, and intensity have been analysed jointly using the DISCMINER modelling framework, in three bright CO lines, 12CO, 13CO, and C18O $J=2-1$, to provide a comprehensive summary of the kinematic and column density substructures that planets might be actively sculpting in these discs. We find convincing evidence for the presence of four giant planets located at wide orbits in three of the discs in the sample: two around HD 163296, one in MWC 480, and one in AS 209. One of the planet candidates in HD 163296, P94, previously associated with velocity signatures detected in lower velocity resolution 12CO data, is confirmed and linked to localised velocity and line width perturbations in 13CO and C18O too. We highlight that line widths are also powerful tracers of planet-forming sites as they are sensitive to turbulent motions triggered by planet-disc interactions. In MWC 480, we identified non-axisymmetric line width enhancements around the radial separation of candidate planet-driven buoyancy spirals, which we used to narrow the location of the possible planet to an orbital radius of $R=245$ au and $\rm{PA}=193^\circ$. In the disc of AS 209, we found excess 12CO line widths centred at $R=210$ au, $\rm{PA}=151^\circ$, spanning around the immediate vicinity of a circumplanetary disc candidate proposed previously, which further supports its presence. Our simultaneous analysis of multiple tracers and observables aims to lay the groundwork for robust studies of molecular line properties focused on the search for young planets in discs.

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arXiv2022

CORINOS I: JWST/MIRI Spectroscopy and Imaging of a Class 0 protostar IRAS 15398-3359

The origin of complex organic molecules (COMs) in young Class 0 protostars has been one of the major questions in astrochemistry and star formation. While COMs are thought to form on icy dust grains via gas-grain chemistry, observational constraints on their formation pathways have been limited to gas-phase detection. Sensitive mid-infrared spectroscopy with JWST enables unprecedented investigation of COM formation by measuring their ice absorption features. We present an overview of JWST/MIRI MRS spectroscopy and imaging of a young Class 0 protostar, IRAS 15398-3359, and identify several major solid-state absorption features in the 4.9-28 $μ$m wavelength range. These can be attributed to common ice species, such as H$_2$O, CH$_3$OH, NH$_3$, and CH$_4$, and may have contributions from more complex organic species, such as C$_2$H$_5$OH and CH$_3$CHO. The MRS spectra show many weaker emission lines at 6-8 $μ$m, which are due to warm CO gas and water vapor, possibly from a young embedded disk previously unseen. Finally, we detect emission lines from [Fe II], [Ne II], [S I], and H$_2$, tracing a bipolar jet and outflow cavities. MIRI imaging serendipitously covers the south-western (blue-shifted) outflow lobe of IRAS 15398-3359, showing four shell-like structures similar to the outflows traced by molecular emission at sub-mm wavelengths. This overview analysis highlights the vast potential of JWST/MIRI observations and previews scientific discoveries in the coming years.

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arXiv2021

Molecules with ALMA at Planet-forming Scales. XX. The Massive Disk Around GM Aurigae

Gas mass remains one of the most difficult protoplanetary disk properties to constrain. With much of the protoplanetary disk too cold for the main gas constituent, H2, to emit, alternative tracers such as dust, CO, or the H2 isotopolog HD are used. However, relying on disk mass measurements from any single tracer requires assumptions about the tracer's abundance relative to \hh\ and the disk temperature structure. Using new Atacama Large Millimeter/submillimeter Array (ALMA) observations from the Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program as well as archival ALMA observations, we construct a disk physical/chemical model of the protoplanetary disk GM Aur. Our model is in good agreement with the spatially resolved CO isotopolog emission from eleven rotational transitions with spatial resolution ranging from 0.15'' to 0.46'' (24-73 au at 159 pc) and the spatially unresolved HD J=1-0 detection from Herschel. Our best-fit model favors a cold protoplanetary disk with a total gas mass of approximately 0.2 solar masses, a factor of 10 reduction in CO gas inside roughly 100 au and a factor of 100 reduction outside of 100 au. Despite its large mass, the disk appears to be on the whole gravitationally stable based on the derived Toomre Q parameter. However, the region between 70 and 100 au, corresponding to one of the millimeter dust rings, is close to being unstable based on the calculated Toomre Q of <1.7. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

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arXiv2021

Atmospheric characterization of terrestrial exoplanets in the mid-infrared: biosignatures, habitability & diversity

Exoplanet science is one of the most thriving fields of modern astrophysics. A major goal is the atmospheric characterization of dozens of small, terrestrial exoplanets in order to search for signatures in their atmospheres that indicate biological activity, assess their ability to provide conditions for life as we know it, and investigate their expected atmospheric diversity. None of the currently adopted projects or missions, from ground or in space, can address these goals. In this White Paper we argue that a large space-based mission designed to detect and investigate thermal emission spectra of terrestrial exoplanets in the MIR wavelength range provides unique scientific potential to address these goals and surpasses the capabilities of other approaches. While NASA might be focusing on large missions that aim to detect terrestrial planets in reflected light, ESA has the opportunity to take leadership and spearhead the development of a large MIR exoplanet mission within the scope of the "Voyage 2050" long-term plan establishing Europe at the forefront of exoplanet science for decades to come. Given the ambitious science goals of such a mission, additional international partners might be interested in participating and contributing to a roadmap that, in the long run, leads to a successful implementation. A new, dedicated development program funded by ESA to help reduce development and implementation cost and further push some of the required key technologies would be a first important step in this direction. Ultimately, a large MIR exoplanet imaging mission will be needed to help answer one of mankind's most fundamental questions: "How unique is our Earth?"

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arXiv2021

A dusty filament and turbulent CO spirals in HD135344B-SAO206462

Planet-disc interactions build up local pressure maxima that may halt the radial drift of protoplanetary dust, and pile it up in rings and crescents. ALMA observations of the HD135344B disc revealed two rings in the thermal continuum stemming from ~mm-sized dust. At higher frequencies the inner ring is brighter relative to the outer ring, which is also shaped as a crescent rather than a full ring. In near-IR scattered light images, the disc is modulated by a 2-armed grand-design spiral originating inside the ALMA inner ring. Such structures may be induced by a massive companion evacuating the central cavity, and by a giant planet in the gap separating both rings, that channels the accretion of small dust and gas through its filamentary wakes while stopping the larger dust from crossing the gap. Here we present ALMA observations in the J=(2-1)CO isotopologue lines and in the adjacent continuum, with up to 12km baselines. Angular resolutions of 0.03" reveal the tentative detection of a filament connecting both rings, and which coincides with a local discontinuity in the pitch angle of the IR spiral, proposed previously as the location of the protoplanet driving this spiral. Line diagnostics suggest that turbulence, or superposed velocity components, is particularly strong in the spirals. The 12CO(2-1) 3-D rotation curve points at stellocentric accretion at radii within the inner dust ring, with a radial velocity of up to ~6%+-0.5% Keplerian, which corresponds to an excessively large accretion rate of ~2E-6M_sun/yr if all of the CO layer follows the 12CO(2-1) kinematics. This suggests that only the surface layers of the disc are undergoing accretion, and that the line broadening is due to superposed laminar flows.

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arXiv2020

The TW Hya Rosetta Stone Project I: Radial and vertical distributions of DCN and DCO+

Molecular D/H ratios are frequently used to probe the chemical past of Solar System volatiles. Yet it is unclear which parts of the Solar Nebula hosted an active deuterium fractionation chemistry. To address this question, we present 0".2-0".4 ALMA observations of DCO+ and DCN 2-1, 3-2 and 4-3 towards the nearby protoplanetary disk around TW Hya, taken as part of the TW Hya Rosetta Stone project, augmented with archival data. DCO+ is characterized by an excitation temperature of ~40 K across the 70 au radius pebble disk, indicative of emission from a warm, elevated molecular layer. Tentatively, DCN is present at even higher temperatures. Both DCO+ and DCN present substantial emission cavities in the inner disk, while in the outer disk the DCO+ and DCN morphologies diverge: most DCN emission originates from a narrow ring peaking around 30~au, with some additional diffuse DCN emission present at larger radii, while DCO+ is present in a broad structured ring that extends past the pebble disk. Based on parametric disk abundance models, these emission patterns can be explained by a near-constant DCN abundance exterior to the cavity, and an increasing DCO+ abundance with radius. There appears to be an active deuterium fractionation chemistry in multiple disk regions around TW Hya, but not in the cold planetesimal-forming midplane and in the inner disk. More observations are needed to explore whether deuterium fractionation is actually absent in these latter regions, and if its absence is a common feature, or something peculiar to the old TW Hya disk.

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arXiv2020

The Leiden Atomic and Molecular Database (LAMDA): Current Status, Recent Updates, and Future Plans

The Leiden Atomic and Molecular Database (LAMDA) collects spectroscopic information and collisional rate coefficients for molecules, atoms, and ions of astrophysical and astrochemical interest. We describe the developments of the database since its inception in 2005, and outline our plans for the near future. Such a database is constrained both by the nature of its uses and by the availability of accurate data: we suggest ways to improve the synergies among users and suppliers of data. We summarize some recent developments in computation of collisional cross sections and rate coefficients. We consider atomic and molecular data that are needed to support astrophysics and astrochemistry with upcoming instruments that operate in the mid- and far-infrared parts of the spectrum.

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arXiv2020

Missing water in Class I protostellar disks

Water is a key volatile that provides insights into the initial stages of planet formation. The low water abundances inferred from water observations toward low-mass protostellar objects may point to a rapid locking of water as ice by large dust grains during star and planet formation. However, little is known about the water vapor abundance in newly formed planet-forming disks. We aim to determine the water abundance in embedded Keplerian disks through spatially-resolved observations of H$_2^{18}$O lines to understand the evolution of water during star and planet formation. We present H$_2^{18}$O line observations with ALMA and NOEMA millimeter interferometers toward five young stellar objects. NOEMA observed the 3$_{1,3}$ - $2_{2,0}$ line (E$_{\rm up}$ = 203.7 K) while ALMA targeted the $4_{1,4}$ - $3_{2,1}$ line (E$_{\rm up}$ = 322.0 K). Water column densities are derived considering optically thin and thermalized emission. Our observations are sensitive to the emission from the known Keplerian disks around three out of the five Class I objects in the sample. No H$_2^{18}$O emission is detected toward any of our five Class I disks. We report upper limits to the integrated line intensities. The inferred water column densities in Class I disks are N < 10$^{15}$ cm$^{-2}$ on 100 au scales which include both disk and envelope. The upper limits imply a disk-averaged water abundance of $\lesssim 10^{-6}$ with respect to H$_2$ for Class I objects. After taking into account the physical structure of the disk, the upper limit to the water abundance averaged over the inner warm disk with $T>$ 100 K is between 10$^{-7}$ up to 10$^{-5}$. Water vapor is not abundant in warm protostellar envelopes around Class I protostars. Upper limits to the water vapor column densities in Class I disks are at least two orders magnitude lower than values found in Class 0 disk-like structures.

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arXiv2019

ESA's Voyage 2050 Long-term Plan for Education and Public Engagement: White Paper

This white paper responds to the Voyage 2050 Call for White Papers from the Science Programme of the European Space Agency (ESA) and argues that education, communication and public engagement (hereafter EPE) should have priority in the Voyage 2050 planning cycle. The ESA Science's Voyage 2050 missions promise insights into the big existential questions of our era: the prevalence of life in the Universe; the nature of space and time; and the intertwined nature of matter, energy and gravity. It is likely that innovations in the acquisition, handling and processing of vast data sets will drive these themes to scientific maturity in the next decades. They offer us a timely opportunity to underline the relevance of space sciences to everyday life and thinking. More generally, space science is maturing to the point where it contributes to every major aspect of our cultural discourse. Citizens need information, resources and opportunities to actively participate in that discourse, and ESA Science can provide these. This white paper is a modest attempt to support ESA Science improve its engagement with society. It focuses on issues and topics to improve ESA Science's Education and Public Engagement activities. It does not dwell on the topics that ESA already excels at; hence this White Paper provides a critical review of what should and could be improved. We believe ESA's Voyage 2050 programme teams have a responsibility to represent Europe's social and cultural diversity, and our suggestions are conceived in that spirit: to support ESA Science's complex task of engaging a hugely diverse audience in the complex issues of planning, building and operating fascinating space missions.

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arXiv2017

Report of the Kavli IAU Workshop on Global Coordination: Future Space-Based Ultraviolet-Optical-Infrared Telescopes

International efforts play a key role in driving all areas of astrophysics. Strategic planning is essential to explore possible partnerships and joint projects that otherwise could not be afforded, and to maximize their scientific return. For these reasons, the International Astronomical Union (IAU) established in 2016 the Working Group on Global Coordination of Ground and Space Astrophysics. The Working Group held a Kavli IAU Workshop on "Global Coordination: Future Space-Based Ultraviolet-Optical-Infrared Telescopes" in July 2017, bringing together scientific leaders from 17 countries to discuss compelling science drivers, technical requirements, political constraints, and opportunities for a future large-scale UV/optical/Infrared space mission. This report summarizes the workshop and recommends that astronomers worldwide intensify their activities to explore the possibilities for science with such a mission, including consideration of instrumentation and technology definition and development, construction, launch, data analysis, and complementary science. The workshop presentations are available at https://www.strw.leidenuniv.nl/KavliIAU2017.

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arXiv2016

Mass measurements in protoplanetary disks from hydrogen deuteride

The total gas mass of a protoplanetary disk is a fundamental, but poorly determined, quantity. A new technique \citep{bergin+13} has been demonstrated to assess directly the bulk molecular gas reservoir of molecular hydrogen using the HD J=1-0 line at 112 $μ$m. In this work we present a {\it Herschel} Space Observatory\footnote{Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.} survey of six additional T Tauri disks in the HD line. Line emission is detected at $>$3$σ$ significance in two cases: DM Tau and GM Aur. For the other four disks, we establish upper limits to the line flux. Using detailed disk structure and ray tracing models, we calculate the temperature structure and dust mass from modeling the observed spectral energy distributions, and include the effect of UV gas heating to determine the amount of gas required to fit the HD line. The range of gas masses are 1.0-4.7$\times10^{-2}$ for DM Tau and 2.5-20.4$\times10^{-2}$ for GM Aur. These values are larger than those found using CO for GM Aur, while the CO-derived gas mass for DM Tau is consistent with the lower end of our mass range. This suggests a CO chemical depletion from the gas phase of up to a factor of five for DM Tau and up to two orders of magnitude for GM Aur. We discuss how future analysis can narrow the mass ranges further.

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arXiv2015

Volatile snowlines in embedded disks around low-mass protostars

(Abridged*) Models of the young solar nebula assume a hot initial disk with most volatiles are in the gas phase. The question remains whether an actively accreting disk is warm enough to have gas-phase water up to 50 AU radius. No detailed studies have yet been performed on the extent of snowlines in an embedded accreting disk (Stage 0). Quantify the location of gas-phase volatiles in embedded actively accreting disk system. Two-dimensional physical and radiative transfer models have been used to calculate the temperature structure of embedded protostellar systems. Gas and ice abundances of H$_2$O, CO$_2$, and CO are calculated using the density-dependent thermal desorption formulation. The midplane water snowline increases from 3 to 55 AU for accretion rates through the disk onto the star between $10^{-9}$-$10^{-4} \ M_{\odot} \ {\rm yr^{-1}}$. CO$_2$ can remain in the solid phase within the disk for $\dot{M} \leq 10^{-5} \ M_{\odot} \ {\rm yr^{-1}}$ down to $\sim 20$ AU. Most of the CO is in the gas phase within an actively accreting disk independent of disk properties and accretion rate. The predicted optically thin water isotopolog emission is consistent with the detected H$_2^{18}$O emission toward the Stage 0 embedded young stellar objects, originating from both the disk and the warm inner envelope (hot core). An accreting embedded disk can only account for water emission arising from $R < 50$ AU, however, and the extent rapidly decreases for low accretion rates. Thus, the radial extent of the emission can be measured with ALMA observations and compared to this limit. Volatiles sublimate out to 50 AU in young disks and can reset the chemical content inherited from the envelope in periods of high accretion rates. A hot young solar nebula out to 30 AU can only have occurred during the deeply embedded Stage 0, not during the T-Tauri phase of our early solar system.

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arXiv2015

Resolving structure of the disk around HD100546 at 7 mm with ATCA

There is much evidence that planet formation is occurring in the disk around the Herbig Be star HD100546. To learn more about the processes occurring in this disk we conducted high resolution imaging at 43/45 GHz with the Australia Telescope Compact Array (ATCA). Multiple array configurations were used, providing a best spatial resolution of $\sim$ 0.15 arcsec, or 15 AU at HD100546's distance of $\sim$ 100 pc. Significant structure is revealed, but its precise form is dependent on the $u-v$ plane sampling used for the image reconstruction. At a resolution of $\leq$ 30 AU we detected an inner gap in the disk with a radius of $\sim$ 25 AU and a position angle approximately along the known disk major axis. With different weighting, and an achieved resolution of $\sim$ 15 AU, emission appears at the centre and the disk takes on the shape of an incomplete ring, much like a horseshoe, again with a gap radius of $\sim$ 25 AU. The position angle of the disk major axis and its inclination from face-on are determined to be $140^{\circ}\pm5^{\circ}$ and $40^{\circ}\pm5^{\circ}$ respectively. The $\sim$ 25 AU gap radius is confirmed by a null in the real part of the binned visibilities at 320$\pm$10 k$λ$, whilst the non-axisymmetric nature is also confirmed through significant structure in the imaginary component. The emission mechanism at the central peak is most likely to be free-free emission from a stellar or disk wind. Overall our data support the picture of at least one, but probably several, giant planets orbiting HD100546 within 25 AU.

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arXiv2015

Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA

Transitional disks with large dust cavities are important laboratories to study planet formation and disk evolution. Cold gas may still be present inside these cavities, but the quantification of this gas is challenging. The gas content is important to constrain the origin of the dust cavity. We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of 12CO 6--5 and 690 GHz (Band 9) continuum of five well-studied transitional disks. In addition, we analyze previously published Band 7 observations of a disk in 12CO 3--2 line and 345 GHz continuum. The observations are used to set constraints on the gas and dust surface density profiles, in particular the drop delta-gas of the gas density inside the dust cavity. The physical-chemical modeling code DALI is used to analyze the gas and dust images simultaneously. We model SR21, HD135344B, LkCa15, SR24S and RXJ1615-3255 (Band 9) and J1604-2130 (Band 7). The SED and continuum visibility curve constrain the dust surface density. Subsequently, the same model is used to calculate the 12CO emission, which is compared with the observations through spectra and intensity cuts. The amount of gas inside the cavity is quantified by varying the delta-gas parameter. Model fits to the dust and gas indicate that gas is still present inside the dust cavity for all disks but at a reduced level. The gas surface density drops inside the cavity by at least a factor 10, whereas the dust density drops by at least a factor 1000. Disk masses are comparable with previous estimates from the literature, cavity radii are found to be smaller than in the 345 GHz SubMillimeter Array (SMA) data. The derived gas surface density profiles suggest clearing of the cavity by one or more companions in all cases, trapping the millimeter-sized dust at the edge of the cavity.

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