The warm gas atmosphere of the HD 100546 disk seen by Herschel - Evidence of a gas-rich, carbon-poor atmosphere?

By Simon Bruderer, E. Dishoeck, S. Doty, G. Herczeg. 2012

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(Abridged) Context. With the Herschel Space Observatory, lines of simple molecules (C+, O, and CO) have been observed in the atmosphere of protoplanetary disks. When combined with ground-based [CI], all principle forms of carbon can be studied. The absence of neutral carbon [CI], which is predicted by models to be strong, can then be interpreted together with [CII] and carbon monoxide. Aims. We study the gas temperature, excitation, and chemical abundance of the simple carbon-bearing species by the method of chemical-physical modeling. We explore the sensitivity of the lines to the entering parameters and constrain the region from which the line radiation emerges. Methods. Numerical models of the radiative transfer are used together with a chemical network simulation and a calculation of the gas energetics to obtain the gas temperature. We present our new model, which is based on our previous models but includes several improvements. Results. A model of the disk around the Herbig Be star HD 100546 is able to reproduce the CO ladder together with the atomic fine-structure lines of [OI] and either [CI] or [CII]. We find that the high-J lines of CO can only be reproduced by a warm atmosphere with Tgas>>Tdust. The high-J CO observable with PACS are dominated from regions within some tens of AU. Conclusions. Only a warm atmosphere with Tgas>>Tdust can reproduce the CO ladder. The CO ladder together with [O I] and the upper limit to [CI] can be reproduced by models with a high gas/dust ratio and a low abundance of volatile carbon. These models however produce too small amounts of [CII]. Models with a low gas/dust ratio and more volatile carbon also reproduce CO and [OI], are in closer agreement with observations of [CII], but overproduce [CI]. Due to the uncertain origin of the [CII] emission, we prefer the high gas/dust ratio models, indicating a low abundance of volatile carbon.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/bcda50108d78020ae4b995e650874ff12d8672ca

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Citations in the corpus

ALMA unveils rings and gaps in the protoplanetary system HD 169142: signatures of two giant protoplanets (2017, methodology): “The simulations presented here were generated using the thermo-chemical disk code dali (Dust and Lines, Bruderer et al. 2012; Bruderer 2013).”
Volatile carbon locking and release in protoplanetary disks. A study of TW Hya and HD 100546 (2016, methodology): “Studies that account for these processes have suggested that the gas is genuinely underabundant in carbon in the disks around HD 100546 and TW Hya (Bruderer et al. 2012; Bergin et al. 2013; Favre et al. 2013; Du et al. 2015).”
Resolved gas cavities in transitional disks inferred from CO isotopologs with ALMA (2015, methodology): “Because DALI considers only axisymmetric models, the millimeter continuum asymmetry is not fit: the total submillimeter flux, the VISIR 18 μm image and the SED are again used to constrain the dust density and dust cavity radius.”
Survival of molecular gas in cavities of transition disks - I. CO (2013, methodology): “Molecular excitation The main difference between Bruderer et al. (2012) and the present model is the non-LTE calculation of the molecular/atomic excitation.”
ALMA continuum observations of the protoplanetary disk AS 209. Evidence of multiple gaps opened by a single planet (2017, methodology): “For this purpose we use the dust radiative transfer code implemented into the thermo-chemical disk model DALI (Dust And LInes, Bruderer et al. 2012; Bruderer 2013).”
An ALMA Survey of Protoplanetary Disks in the σ Orionis Cluster (2017, methodology): “Using the code DALI (Bruderer et al. 2012), M16 investigated a range of realistic disk and stellar parameters, calculating selfconsistently the thermal and chemical structure of the disk up to an age of 1 Myr.”
The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime (2015, background): “For each gas-phase neutral-neutral reaction involving H2 which also possesses an activation barrier, we include a duplicate reaction involving hot H2 with a barrier reduced by the internal energy of the excited H2 (≈ 30,163 K, see, e.g., Bruderer et al. 2012, and references therein).”
Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA (2015, methodology): “With DALI we determine the density structure of the gas and dust that is consistent with the SED,dust continuum interferometry and the12CO observations.”
On the diversity and statistical properties of protostellar discs (2018, background): “…effects, deriving gas masses from dust masses currently appears to be more accurate than deriving the total gas mass from molecular emission such as CO (e.g. Bruderer et al. 2012; Favre et al. 2013; Bergin et al. 2014; Kama et al. 2016; McClure et al. 2016; Miotello et al. 2017; Yu et al. 2017).”
ALMA Survey of Lupus Protoplanetary Disks. II. Gas Disk Radii (2018, methodology): “Indeed, Facchini et al. (2017) combined the dust evolution models from Birnstiel et al. (2015) with the thermo-chemical code DALI (Bruderer et al. 2012; Bruderer 2013) to show that, at least for the case of the massive HD 163296 disk, the bulk of the difference between the gas and dust radii is due ”
Astrochemistry and compositions of planetary systems (2020, unknown): “2006), and protoplanetary disks (Gorti and Hollenbach 2004; Woitke et al. 2009; Kamp et al. 2010; Bruderer et al. 2012; Du and Bergin 2014).”