Warm molecular layers in protoplanetary disks

By Y. Aikawa, G. V. Zadelhoff, E. F. Dishoeck, E. University, L. Observatory, T. O. S. University. 2002

179 citations recorded by the source corpus.

We have investigated molecular distributions in protoplanetary disks, adopting a disk model with a temperature gradient in the vertical direction. The model produces suciently high abundances of gaseous CO and HCO + to account for line observations of T Tauri stars using a sticking probability of unity and without assuming any non-thermal desorption. In regions of radius R > 10 AU, with which we are concerned, the temperature increases with increasing height from the midplane. In a warm intermediate layer, there are signicant amounts of gaseous molecules owing to thermal desorption and ecient shielding of ultraviolet radiation by the flared disk. The column densities of HCN, CN, CS, H2CO, HNC and HCO + obtained from our model are in good agreement with the observations of DM Tau, but are smaller than those of LkCa15. Molecular line proles from our disk models are calculated using a 2-dimensional non-local-thermal-equilibrium (NLTE) molecular-line radiative transfer code for a direct comparison with observations. Deuterated species are included in our chemical model. The molecular D/H ratios in the model are in reasonable agreement with those observed in protoplanetary disks.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/bbcaa33a394005732eb7d2c7167028ee43cd81b7

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. D. Wilner
2. S. Andrews
3. Jonathan P. Williams
4. E. Dishoeck
5. Simon Bruderer
6. C. Qi
7. T. Birnstiel
8. K. Oberg

In Atmospheric Science

1. E. Dishoeck
2. Simon Bruderer
3. K. Oberg
4. E. Bergin
5. V. Wakelam
6. C. Walsh
7. E. V. van Dishoeck
8. F. Hersant

In Spectroscopy

1. D. Wilner
2. S. Andrews
3. Jonathan P. Williams
4. E. Dishoeck
5. C. Qi
6. K. Oberg
7. Simon Bruderer
8. L. Testi

Citations in the corpus

• The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks (2009, methodology): “We adopt the standard disk model of D’Alessio et al. (1999), whose chemistry has been studied extensively (Aikawa et al. 2002; van Zadelhoff et al. 2003; Jonkheid et al. 2004).”
• A PARAMETRIC MODELING APPROACH TO MEASURING THE GAS MASSES OF CIRCUMSTELLAR DISKS (2013, background): “Consequently, a warm molecular layer, with nearly constant CO abundance, lies between the depleted midplane and dissociation surface (Aikawa et al. 2002; Woitke et al. 2009).”
• The Nature and Distribution of the Organic Material in Carbonaceous Chondrites and Interplanetary Dust Particles (2006, background): “…of young stellar objects (e.g., Qi et al., 2003) and theoretical models of collapsing interstellar cores (e.g., Aikawa et al., 2003), protoplanetary disks (e.g., Aikawa et al., 2002), and planetesimal mass distribution (e.g., Kortenkamp et al., 2001) that could affect the primordial asteroid belt.”
• CO emission from discs around isolated HAeBe and Vega-excess stars (2005, unknown): “…more complicated models of line emission from discs have been developed more recently which include the effects of chemistry, radiative transfer, different dust characteristics, more complex disc structures, and UV photodissociation (e.g. van Zadelhoff et al., 2001; Aikawa et al., 2002).”
• Resolved gas cavities in transitional disks inferred from CO isotopologs with ALMA (2015, background): “…CO emission into density is not trivial either: the CO abundance with respect to H2 varies throughout the disk due to photodissociation by the stellar UV radiation and freeze-out onto dust grains in the cold regions in the midplane and outer disk (van Zadelhoff et al. 2001; Aikawa et al. 2002).”
• UV-photoprocessing of interstellar ice analogs: New infrared spectroscopic results (2003, background): “This may cause most of the material in the outer disk to be exposed to the stellar photons and to become thoroughly photolyzed (Aikawa et al. 1996, 1999, 2002).”
• ISO Spectroscopy of Gas and Dust: From Molecular Clouds to Protoplanetary Disks (2004, background): “Ground-based millimeter CO surveys are hampered by freeze-out in the cold parts of the disk and photodissociation in the upper layers (e.g., Aikawa et al. 2002), whereas infrared CO lines probe only a small fraction of warm gas (e.g., Najita et al. 2003).”
• Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions (2010, background): “…(1973), and Watson & Salpeter (1972), numerous chemical models of molecular clouds (e.g., Hasegawa et al., 1992), protoplanetary disks (e.g., Aikawa et al., 2002), shells around late-type stars (e.g., Agúndez & Cernicharo, 2006), AGN tori (e.g., Meijerink et al., 2007), and planetary…”
• Circumstellar Dust Disks in Taurus-Auriga: The Submillimeter Perspective (2005, background): “Interpretation of these lines and those from trace molecular species require sophisticated models of the disk structure (e.g., Dartois, Dutrey, & Guilloteau 2003; Kamp & Dullemond 2004) and chemistry (e.g., van Zadelhoff et al. 2001, 2003; Aikawa et al. 2002; Qi et al. 2003).”
• Organic molecules in protoplanetary disks around T Tauri and Herbig Ae stars (2004, background): “The prevailing explanation of this depletion involves a combination of freeze-out of the molecules on grain surfaces in the cold midplane and their photodissociation by ultraviolet and/or X-rays in the upper atmosphere of disks (see Aikawa et al. 1999a, 2002; Bergin et al. 2003).”
• Photodesorption of water ice - A molecular dynamics study (2008, background): “Similarly, the cold midplanes of protoplanetary disks around young stars are largely devoid of gaseous molecules other than H2, H+3 and their isotopologues (e.g., Aikawa et al. 2002; Ceccarelli & Dominik 2005).”
• Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA (2015, background): “…inside the dust cavity: the CO abundance is not constant throughout the disk with respect to molecular hydrogen due to photodissociation by the UV radiation from the star and freeze out onto dust grains in colder regions close to the midplane (van Zadelhoff et al. 2001; Aikawa et al. 2002).”
• ALMA SURVEY OF LUPUS PROTOPLANETARY DISKS. I. DUST AND GAS MASSES (2016, background): “Physical-chemical models of protoplanetary disks have shown that a significant fraction of CO is sufficiently warm to avoid freeze-out and also sufficiently shielded from UV radiation to avoid photodissociation (Aikawa et al. 2002).”
• The Far-Ultraviolet Spectra of TW Hydrae. II. Models of H2 Fluorescence in a Disk (2004, background): “Cold gas at large radii is traced by observations of molecules such as CO and HCN (e.g., Aikawa et al. 2002).”
• Molecules with ALMA at Planet-forming Scales (MAPS). I. Program Overview and Highlights (2021, background): “Condensation fronts also exist in the vertical dimension, resulting in two-dimensional snow-surfaces (Aikawa et al. 2002; van ’t Hoff et al. 2017; Qi et al. 2019), due to vertical temperature gradients.”