Volatile-carbon locking and release in protoplanetary disks
1 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
2 Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
3 Université de Grenoble Alpes, IPAG, 38000 Grenoble, France
4 CNRS, IPAG, 38000 Grenoble, France
5 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
6 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Received: 18 July 2015
Accepted: 17 May 2016
Aims. The composition of planetary solids and gases is largely rooted in the processing of volatile elements in protoplanetary disks. To shed light on the key processes, we carry out a comparative analysis of the gas-phase carbon abundance in two systems with a similar age and disk mass, but different central stars: HD 100546 and TW Hya.
Methods. We combine our recent detections of C0 in these disks with observations of other carbon reservoirs (CO, C+, C2H) and gas-mass and warm-gas tracers (HD, O0), as well as spatially resolved ALMA observations and the spectral energy distribution. The disks are modelled with the DALI 2D physical-chemical code. Stellar abundances for HD 100546 are derived from archival spectra.
Results. Upper limits on HD emission from HD 100546 place an upper limit on the total disk mass of ≤0.1 M⊙. The gas-phase carbon abundance in the atmosphere of this warm Herbig disk is, at most, moderately depleted compared to the interstellar medium, with [C]/[H]gas = (0.1−1.5) × 10-4. HD 100546 itself is a λBoötis star, with solar abundances of C and O but a strong depletion of rock-forming elements. In the gas of the T Tauri disk TW Hya, both C and O are strongly underabundant, with [C]/[H]gas = (0.2−5.0) × 10-6 and C / O > 1. We discuss evidence that the gas-phase C and O abundances are high in the warm inner regions of both disks. Our analytical model, including vertical mixing and a grain size distribution, reproduces the observed [C]/[H]gas in the outer disk of TW Hya and allows to make predictions for other systems.
Key words: astrochemistry / protoplanetary disks
Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 093.C-0926, 093.F-0015, 077.D-0092, 084.A-9016, and 085.A-9027.
Spectra and models are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A83
© ESO, 2016