Abstract
HD 135344B is an accreting (pre-) transition disk that displays the emission of warm CO extending tens of AU inside its 30 AU dust cavity. We used the dust radiative transfer code MCFOST and the thermochemical code ProDiMo to derive the disk structure from the simultaneous modeling of the spectral energy distribution (SED), VLT/CRIRES CO P(10) 4.75 micron, Herschel/PACS [O I] 63 micron, Spitzer-IRS, and JCMT 12CO J=3-2 spectra, VLTI/PIONIER H-band visibilities, and constraints from (sub-)mm continuum interferometry and near-IR imaging. We found a disk model able to describe the current observations simultaneously. This disk has the following structure. (1) To reproduce the SED, the near-IR interferometry data, and the CO ro-vibrational emission, refractory grains (we suggest carbon) are present inside the silicate sublimation radius (0.08<R<0.2 AU). (2) The dust cavity (R<30 AU) is filled with gas, the surface density of this gas must increase with radius to fit the CO P(10) line profile, a small gap of a few AU in the gas is compatible with current data, and a large gap in the gas is not likely. (4) The gas/dust ratio inside the cavity is > 100 to account for the 870 micron continuum upper limit and the CO P(10) line flux. (5) The gas/dust ratio at 30<R<200 AU is < 10 to simultaneously describe the [O I] 63 micron line flux and the CO P(10) line profile. (6) In the outer disk, most of the mass should be located in the midplane, and a significant fraction of the dust is in large grains. Conclusions: Simultaneous modeling of the gas and dust is required to break the model degeneracies and constrain the disk structure. An increasing gas surface density with radius in the inner dust cavity echoes the effect of a migrating Jovian planet. The low gas mass (a few MJupiter) in the HD 135344B's disk suggests that it is an evolved disk that has already lost a large portion of its mass.
Highlights
Observations of young stars of different ages reveal that protoplanetary disks evolve from optically thick, gas-rich disks to optically thin, gas-poor debris disks
(1) To simultaneously reproduce the spectral energy distributions (SED), the near-IR interferometry data, and the CO ro-vibrational emission, refractory grains are present inside the silicate sublimation radius (0.08 < R < 0.2 AU). (2) The dust cavity (R < 30 AU) is filled with gas, the surface density of the gas inside the cavity must increase with radius to fit the CO ro-vibrational line profile, a small gap of a few AU in the gas distribution is compatible with current data, and a large gap of tens of AU in the gas does not appear likely
In our models of HD 135344B, we have found that the CO ro-vibrational line profile is the result of the combination of two contributions: (1) the emission from the gas inside the dust cavity and (2) the emission from the gas located in the inner rim of the outer disk
Summary
Observations of young stars of different ages reveal that protoplanetary disks evolve from optically thick, gas-rich disks to optically thin, gas-poor debris disks (e.g., see review by Williams & Cieza 2011). Infrared space observatories have unveiled several young stars with spectral energy distributions (SED) characterized by IRexcess at >10 μm and significantly reduced excesses at shorter wavelengths (e.g., Strom et al 1989; Calvet et al 2005; Sicilia-Aguilar et al 2006; Hernández et al 2006; Espaillat et al 2007; Fang et al 2009; Merín et al 2010; Rebull et al 2010; Cieza et al 2010) These sources are commonly named “transition disks”, because they are believed to be the objects in the transition phase between a young star with an optically thick gas-rich disk and a star with an optically thin gas-poor debris disk. Follow-up imaging of several transition disks with sub-mm interferometers have confirmed that transition disks have a deficit of sub-mm continuum emission at a few mJy levels inside tens of AU (e.g., Piétu et al 2007; Brown et al 2009; Hughes et al 2009; Andrews et al 2011; Isella et al 2012), providing further evidence for such inner disk cavities, at least on the large dust grains
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