J/ApJ/788/59 Parametric model for circumstellar disks gas mass (Williams+, 2014) ================================================================================ A parametric modeling approach to measuring the gas masses of circumstellar disks. Williams J.P., Best W.M.J. =2014ApJ...788...59W (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Models ; Stars, masses ; Effective temperatures Keywords: circumstellar matter - planets and satellites: formation - protoplanetary disks Abstract: The disks that surround young stars are mostly composed of molecular gas, which is harder to detect and interpret than the accompanying dust. Disk mass measurements have therefore relied on large and uncertain extrapolations from the dust to the gas. We have developed a grid of models to study the dependencies of isotopologue CO line strengths on disk structure and temperature parameters and find that a combination of ^13^CO and C^18^O observations provides a robust measure of the gas mass. We apply this technique to Submillimeter Array observations of nine circumstellar disks and published measurements of six well studied disks. We find evidence for selective photodissociation of C^18^O and determine masses to within a factor of about three. The inferred masses for the nine disks in our survey range from 0.7 to 6 M_Jup_, and all are well below the extrapolation from the interstellar medium gas-to-dust ratio of 100. This is consistent with the low masses of planets found around such stars, and may be due to accretion or photoevaporation of a dust-poor upper atmosphere. However, the masses may be underestimated if there are more efficient CO depletion pathways than those known in molecular clouds and cold cores. Description: Circumstellar disks are relatively small, faint objects that have, to date, required long integrations with millimeter wavelength interferometers to study their molecular gas content. Consequently, only a small number of disks have been imaged in isotopologue lines and most analyses have been tailored to the individual object. Driven by the moderately large sample size but low signal-to-noise level in our data here, we use a different approach. Rather than analyze each disk individually, we create a large grid of models that span a wide range of disk parameters, particularly in gas mass, and compare with the data in a uniform way. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table3.dat 131 18144 Parametric Model Output -------------------------------------------------------------------------------- See also: J/ApJ/784/62 : Circumstellar disks around binary stars in Taurus (Akeson+, 2014) Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 F3.1 Msun M* Stellar mass (0.5, 1.0) 5- 10 F6.4 Msun Mgas Gas mass (0.0001, 0.0003, 0.0010, 0.0030, 0.0100, 0.0300, 0.1000) 12- 14 F3.1 --- gamma Surface density power law index (0.0, 0.8, 1.5) 16- 18 I3 AU Rc Characteristic disk radius (30, 60, 100, 200) 20- 22 I3 K Tmid1 Inner midplane temperature (100, 200, 300) 24- 27 I4 K Tatm1 Inner atmopsheric temperature (500, 750, 1000, 1500) 29- 32 F4.2 --- q Radial power law index (0.45, 0.55, 0.65) 34- 35 I2 deg Inc Inclination (0, 45, 90) 37- 41 F5.3 --- ffreeze Mass fraction where CO is frozen out 43- 47 F5.3 --- fdissoc Mass fraction where CO is dissociated 49- 54 F6.3 Jy.km/s FCO10 Integrated intensity of CO J=1-0 line 56- 62 F7.3 Jy.km/s FCO21 Integrated intensity of CO J=2-1 line 64- 70 F7.3 Jy.km/s FCO32 Integrated intensity of CO J=3-2 line 72- 76 F5.3 Jy.km/s F13CO10 Integrated intensity of ^13^CO J=1-0 line 78- 83 F6.3 Jy.km/s F13CO21 Integrated intensity of ^13^CO J=2-1 line 85- 91 F7.3 Jy.km/s F13CO32 Integrated intensity of ^13^CO J=3-2 line 93- 97 F5.3 Jy.km/s FC18O10 Integrated intensity of C^18^O J=1-0 line 99-104 F6.3 Jy.km/s FC18O21 Integrated intensity of C^18^O J=2-1 line 106-111 F6.3 Jy.km/s FC18O32 Integrated intensity of C^18^O J=3-2 line 113-117 F5.3 Jy.km/s FC18O10l Integrated intensity limit of low abundance C^18^O J=1-0 line 119-124 F6.3 Jy.km/s FC18O21l Integrated intensity limit of low abundance C^18^O J=2-1 line 126-131 F6.3 Jy.km/s FC18O32l Integrated intensity limit of low abundance C^18^O J=3-2 line -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 06-Jul-2017