PROBING THE INNER REGIONS OF PROTOPLANETARY DISKS WITH CO ABSORPTION LINE SPECTROSCOPY

Carbon monoxide (CO) is the most commonly used tracer of molecular gas in the inner regions of protoplanetary disks. CO can be used to constrain the excitation and structure of the circumstellar environment. Absorption line spectroscopy provides an accurate assessment of a single line of sight throu...

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Bibliographic Details
Published in:The Astrophysical journal 2013-03, Vol.766 (1), p.1-11
Main Authors: McJunkin, Matthew, France, Kevin, Burgh, Eric B, Herczeg, Gregory J, Schindhelm, Eric, Brown, Joanna M, Brown, Alexander
Format: Article
Language:English
Subjects:
ABSORPTION
ABSORPTION SPECTROSCOPY
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
CARBON MONOXIDE
Cobalt
Columns (structural)
DENSITY
Disks
EXCITATION
FAR ULTRAVIOLET RADIATION
HYDROGEN
INCLINATION
Planet formation
PROTOPLANETS
Stellar winds
T TAURI STARS
TELESCOPES
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Summary:Carbon monoxide (CO) is the most commonly used tracer of molecular gas in the inner regions of protoplanetary disks. CO can be used to constrain the excitation and structure of the circumstellar environment. Absorption line spectroscopy provides an accurate assessment of a single line of sight through the protoplanetary disk system, giving more straightforward estimates of column densities and temperatures than CO and molecular hydrogen (FF) emission line studies. We analyze new observations of ultraviolet CO absorption from the Hubble Space Telescope along the sightlines to six classical T Tauri stars. Gas velocities consistent with the stellar velocities, combined with the moderate-to-high disk inclinations, argue against the absorbing CO gas originating in a fast-moving disk wind. We conclude that the far-ultraviolet observations provide a direct measure of the disk atmosphere or possibly a slow disk wind. The CO absorption lines are reproduced by model spectra with column densities in the range N( super(12)CO) ~ 10 super(16)-10 super(18) cm super(-2) and N( super(13)CO) ~ 10 super(15)-10 super(17) cm super(-2), rotational temperatures T sub(rot)(CO) ~ 300-700 K, and Doppler b-values, b ~ 0.5-1.5 km s super(-1). We use these results to constrain the line-of-sight density of the warm molecular gas (n sub(CO) ~ 70-4000 cm super(-3)) and put these observations in context with protoplanetary disk models.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/766/1/12