Kama, M.M.KamaBruderer, S.S.Bruderervan Dishoeck, E. F.E. F.van DishoeckHogerheijde, M.M.HogerheijdeFolsom, C. P.C. P.FolsomMiotello, A.A.MiotelloFEDELE , DAVIDEDAVIDEFEDELEBelloche, A.A.BellocheGüsten, R.R.GüstenWyrowski, F.F.Wyrowski2020-06-162020-06-1620160004-6361http://hdl.handle.net/20.500.12386/26082Aims: 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. <BR /> Methods: We combine our recent detections of C<SUP>0</SUP> in these disks with observations of other carbon reservoirs (CO, C<SUP>+</SUP>, C<SUB>2</SUB>H) and gas-mass and warm-gas tracers (HD, O<SUP>0</SUP>), 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. <BR /> Results: Upper limits on HD emission from HD 100546 place an upper limit on the total disk mass of ≤0.1 M<SUB>☉</SUB>. 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]<SUB>gas</SUB> = (0.1-1.5) × 10<SUP>-4</SUP>. 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]<SUB>gas</SUB> = (0.2-5.0) × 10<SUP>-6</SUP> 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]<SUB>gas</SUB> in the outer disk of TW Hya and allows to make predictions for other systems. <P />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 <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A83">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A83STAMPAenArticle10.1051/0004-6361/2015269912-s2.0-84982817015000384722600026https://www.aanda.org/articles/aa/abs/2016/08/aa26991-15/aa26991-15.html2016A&A...592A..83KFIS/05 - ASTRONOMIA E ASTROFISICA