Volume 642, October 2020
|Number of page(s)||15|
|Section||Interstellar and circumstellar matter|
|Published online||01 October 2020|
AB Aur, a Rosetta stone for studies of planet formation
I. Chemical study of a planet-forming disk
Observatorio Astronómico Nacional (OAN, IGN),
Calle Alfonso XII, 3.
2 Center for Astrophysics, Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA
3 CNRS / Institut de Recherche en Astrophysique et Planétologie, 14 avenue Edouard Belin, 31400 Toulouse, France
4 Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin d’Hères, France
5 Chalmers University of Technology, Department of Space, Earth and Environment, 412 93 Gothenburg, Sweden
6 Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago 763-0355, Chile
7 European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago 763-0355, Chile
8 Instituto de Astrofísica de Andalucía, (CSIC) Glorieta de la Astronomía s/n, 18008 Granada, Spain
Accepted: 25 July 2020
Context. AB Aur is a Herbig Ae star that hosts a prototypical transition disk. The disk shows a plethora of features connected with planet formation mechanisms, such as spiral arms, dust cavities, and dust traps. Understanding the physical and chemical characteristics of these features is crucial to advancing our knowledge of the planet formation processes.
Aims. We aim to characterize the gaseous disk around the Herbig Ae star AB Aur. A complete spectroscopic study was performed using NOEMA to determine the physical and chemical conditions with high spatial resolution.
Methods. We present new NOrthern Extended Millimeter Array (NOEMA) interferometric observations of the continuum and 12CO, 13CO, C18O, H2CO, and SO lines obtained at high resolution. We used the integrated intensity maps and stacked spectra to derive reliable estimates of the disk temperature. By combining our 13CO and C18O observations, we computed the gas-to-dust ratio along the disk. We also derived column density maps for the different species and used them to compute abundance maps. The results of our observations were compared with a set of Nautilus astrochemical models to obtain insight into the disk properties.
Results. We detected continuum emission in a ring that extends from 0.6′′ to ~2.0′′, peaking at 0.97′′ and with a strong azimuthal asymmetry. The molecules observed show different spatial distributions, and the peaks of the distributions are not correlated with the binding energy. Using H2CO and SO lines, we derived a mean disk temperature of 39 K. We derived a gas-to-dust ratio that ranges from 10 to 40 along the disk. Abundance with respect to 13CO for SO (~2 × 10−4) is almost one order of magnitude greater than the value derived for H2CO (1.6 × 10−5). The comparison with Nautilus models favors a disk with a low gas-to-dust ratio (40) and prominent sulfur depletion.
Conclusions. From a very complete spectroscopic study of the prototypical disk around AB Aur, we derived, for the first time, the gas temperature and the gas-to-dust ratio along the disk, providing information that is essential to constraining hydrodynamical simulations. Moreover, we explored the gas chemistry and, in particular, the sulfur depletion. The derived sulfur depletion is dependent on the assumed C/O ratio. Our data are better explained with C/O ~ 0.7 and S/H = 8 × 10−8.
Key words: astrochemistry / protoplanetary disks / planet-disk interactions / stars: variables: T Tauri, Herbig Ae/Be / radio continuum: stars / radio lines: planetary systems
© ESO 2020
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