The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

Scheltinga, Jeroen Terwisscha van; Hogerheijde, M. R.; Cleeves, L. Ilsedore; Loomis, Ryan A.; Walsh, Catherine; Öberg, Karin I.; Bergin, Edwin A.; Bergner, Jennifer B.; Blake, Geoffrey A.; Calahan, Jenny K.; Cazzoletti, P.; Dishoeck, E. F. van; Guzmán, Viviana V.; Huang, Jane; Kama, M.; Qi, Chunhua; Wilner, David J.

doi:10.3847/1538-4357/abc9ba

Cited by 27 publications

(16 citation statements)

References 67 publications

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“…Higher temperatures are found for the inner regions, however the snr of the data is low, as reflected by the large inferred uncertainties. Column densities across the 0.5 − 2 interval range between 4 × 10 12 − 4 × 10 13 cm −2 , in line with other protoplanetary disks (e.g., Pegues et al 2020;Terwisscha van Scheltinga et al 2021). A peak optical depth of ∼ 0.1 is derived for the 3 03 -2 20 transition, with the weaker transition showing a factor of ∼ 10 lower optical depth.…”

Section: H 2 Cosupporting

confidence: 78%

The chemical inventory of the planet-hosting disk PDS 70

Facchini,

Teague,

Bae

et al. 2021

Preprint

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As host to two accreting planets, PDS 70 provides a unique opportunity to probe the chemical complexity of atmosphere-forming material. We present ALMA Band 6 observations of the PDS 70 disk and report the first chemical inventory of the system. With a spatial resolution of 0. 4 − 0. 5 ( ∼ 50 au), 12 species are detected, including CO isotopologues and formaldehyde, small hydrocarbons, HCN and HCO + isotopologues, and Sbearing molecules. SO and CH 3 OH are not detected. All lines show a large cavity at the center of the disk, indicative of the deep gap carved by the massive planets. The radial profiles of the line emission are compared to the (sub-)mm continuum and infrared scattered light intensity profiles. Different molecular transitions peak at different radii, revealing the complex interplay between density, temperature and chemistry in setting molecular abundances. Column densities and optical depth profiles are derived for all detected molecules, and upper limits obtained for the non detections. Excitation temperature is obtained for H 2 CO. Deuteration and nitrogen fractionation profiles from the hydro-cyanide lines show radially increasing fractionation levels. Comparison of the disk chemical inventory to grids of chemical models from the literature strongly suggests a disk molecular layer hosting a carbon to oxygen ratio C/O>1, thus providing for the first time compelling evidence of planets actively accreting high C/O ratio gas at present time.

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Section: H 2 Cosupporting

confidence: 78%

The chemical inventory of the planet-hosting disk PDS 70

Facchini,

Teague,

Bae

et al. 2021

Preprint

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“…The temperature of the (outer) disk midplane is derived from the location of the snowlines of major species such as H 2 O and CO (Mathews et al 2013;Qi et al 2013;van 't Hoff et al 2017van 't Hoff et al , 2018Qi et al 2019;Leemker et al 2021). Additionally rotational diagrams are used to derive the temperature of intermediate layers in disks (e.g., Schwarz et al 2016;Loomis et al 2018;Pegues et al 2020;Terwisscha van Scheltinga et al 2021). In this work, we study the rarely observed J = 6 − 5 transition of 13 CO (E u = 111.1 K) in two transition disks: LkCa15 and HD 169142 with spatially resolved ALMA data.…”

Section: Introductionmentioning

confidence: 99%

Gas temperature structure across transition disk cavities

Leemker,

Booth,

van Dishoeck

et al. 2022

Preprint

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Context.Most disks observed at high angular resolution show signs of substructures like rings, gaps, arcs, and cavities in both the gas and the dust. To understand the physical mechanisms responsible for these structures, knowledge about the gas surface density is essential. This, in turn, requires information on the gas temperature. Aims. The aim of this work is to constrain the gas temperature as well as the gas surface densities inside and outside the mm-dust cavities of two transition disks: LkCa15 and HD 169142, with dust cavities of 68 AU and 25 AU, respectively. Methods. We use some of the few existing ALMA observations of the J = 6 − 5 transition of 13 CO together with archival J = 2 − 1 data of 12 CO, 13 CO and C 18 O. The ratio of the 13 CO J = 6 − 5 to the J = 2 − 1 transition is used to constrain the temperature and is compared with that found from peak brightness temperature of optically thick lines. The spectra are used to resolve the innermost disk regions to a spatial resolution better than the beam of the observations. Furthermore, we use the thermochemical code DALI to model the temperature and density structure of a typical transition disk as well as the emitting regions of the CO isotopologues. Results. The 13 CO J = 6−5 and J = 2−1 transitions peak inside the dust cavity in both disks, indicating that gas is present in the dust cavities. The kinematically derived radial profiles show that the gas is detected down to 10 and 5 − 10 AU, much further in than the dust cavities in the LkCa15 and HD 169142 disks, respectively. For LkCa15, the steep increase towards the star in the 13 CO J = 6 − 5 transition, in contrast to the J = 2 − 1 line, shows that the gas is too warm to be traced by the J = 2 − 1 line and that molecular excitation is important for analysing the line emission. Quantitatively, the 6 − 5/2 − 1 line ratio constrains the gas temperature in the emitting layers inside the dust cavity to be up to 65 K, warmer than in the outer disk at 20−30 K. For the HD 169142, the lines are optically thick, complicating a line ratio analysis. In this case, the peak brightness temperature constrains the gas in the dust cavity of HD 169142 to be 170 K, whereas that in the outer disk is only 100 K. The data indicate a vertical structure in which the 13 CO 6 − 5 line emits from a higher layer than the 2 − 1 line in both disks, consistent with exploratory thermo-chemical DALI models. Such models also show that a more luminous central star, a lower abundance of PAHs and the absence of a dusty inner disk increase the temperature of the emitting layers and hence the line ratio in the gas cavity. The gas column density in the LkCa15 dust cavity drops by a factor > 2 compared to the outer disk, with an additional drop of an order of magnitude inside the gas cavity at 10 AU. In the case of HD 169142, the gas column density drops by a factor of 200−500 inside the gas cavity. Conclusions. The gas temperatures inside the dust cavities steeply increase towards the star and reach temperatures up to 65 K (LkCa15) an...

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“…The distribution of H 2 CO suggests that the bulk of the observed H 2 CO in the disc is formed via gas-phase reactions. This is indicated both by the o/p ratios measured in TW Hya (Terwisscha van Scheltinga et al, 2021) and by the vertical distribution of molecular emission in the edge-on disc of IRAS 04302 where H 2 CO mostly arises from an intermediate disc layer, the so called molecular layer (Podio et al, 2020b;van't Hoff et al, 2020). However, for IRAS 04302 H 2 CO emission is detected also in the outer disc midplane, where molecules are expected to be frozen onto the dust grain icy mantles.…”

Section: Organics As C-o-n Carriersmentioning

confidence: 77%

Exploring the link between star and planet formation with Ariel

Turrini,

Codella,

Danielski

et al. 2021

Preprint

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The goal of the Ariel space mission is to observe a large and diversified population of transiting planets around a range of host star types to collect information on their atmospheric composition. The planetary bulk and atmospheric compositions bear the marks of the way the planets formed: Ariel's observations will therefore provide an unprecedented wealth of data to advance our understanding of planet formation in our Galaxy. A number of environmental and evolutionary factors, however, can affect the final atmospheric composition. Here we provide a concise overview of which factors and effects of the star and planet formation processes can shape the atmospheric compositions that will be observed by Ariel, and highlight how Ariel's characteristics make this mission optimally suited to address this very complex problem.

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The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

Cited by 27 publications

References 67 publications

The chemical inventory of the planet-hosting disk PDS 70

The chemical inventory of the planet-hosting disk PDS 70

Gas temperature structure across transition disk cavities

Exploring the link between star and planet formation with Ariel

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