The Dissipation of Molecular Gas in the Innermost Regions of Circumstellar Disks

Details The Dissipation of Molecular Gas in the Innermost Regions of Circumstellar Disks The Dissipation of Molecular Gas in the Innermost Regions of Circumstellar Disks

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21534604i&link_type=abstract

American Astronomical Society, AAS Meeting #215, #346.04; Bulletin of the American Astronomical Society, Vol. 42, p.527

Astronomy and Astrophysics

Astronomy

Scientific paper

Using the largest sample of far-ultraviolet (FUV) spectra of pre-main sequence objects to date, a sample which includes both accreting and non-accreting sources covering a significant age range, we present new results on the molecular gas content of the innermost region of the circumstellar disk.  We analyze the FUV spectra of 33 classical T Tauri stars (CTTS), including 20 new spectra obtained with the Advanced Camera for Surveys Solar Blind Channel (ACS/SBC) on the Hubble Space Telescope.  We also obtained FUV ACS/SBC spectra of 10 non-accreting sources surrounded by debris disks with ages between 10 and 125 Myr.  We use a feature in the FUV spectra which is due to H2 to study the evolution of the gas in the inner disk during the time in which planets form.  We find that the H2 feature is absent in non-accreting sources, but is detected in the spectra of CTTS and correlates with accretion luminosity. Since all young stars have active chromospheres which produce strong X-ray and UV emission capable of exciting H2 in the disk, the fact that the non-accreting sources show no H2 emission implies that the H2 gas in the inner disk has dissipated in the non-accreting sources, although dust remains at larger radii.  We find that the column density of H2 left in the inner regions of the debris disks in our sample is nine orders of magnitude below the surface density of the minimum mass solar nebula at 1 AU and discuss the implications of this result on the theory of solar system formation. This work was supported by NASA through grants from the Space Telescope Science Institute.

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