Searching for Circumstellar Gas around Low Mass Pre-Main Sequence Stars: Cycle 4 Medium

Details Searching for Circumstellar Gas around Low Mass Pre-Main Sequence Stars: Cycle 4 Medium Searching for Circumstellar Gas around Low Mass Pre-Main Sequence Stars: Cycle 4 Medium

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994hst..prop.5317w&link_type=abstract

HST Proposal ID #5317

Computer Science

Hst Proposal Id #5317 Cool Stars Early Evolution

Scientific paper

We seek evidence of the presence of gas disks around low mass pre-main sequence stars. We know that the dust disks disappear rapidly, changing from optically thick to undetectable in less than 1 Myr. Few stars older than 10 Myr retain dust disks. The gas may linger longer, but there is yet no evidence for circumstellar gas around naked (dustless) T Tauri stars. We propose to search for H2 emission from the UV Lyman band, which arises from fluorescently excited molecular hydrogen at 1000-2000K. Such emission has been seen in T Tauri, and in Herbig-Haro objects. With the GHRS we can detect H2 emission a fraction of a percent of the intensity observed in T Tauri. This UV search is more sensitive than radio and infrared searches for molecular gas. We propose to observe 4 early-mid G stars ranging in age from 1 to 200 Myr. Some have dust disks, most do not. These observations will permit us to discriminate between scenarios where the disk dissipates completely, and one where the dust accumulates into planetesimals while the gaseous disk remains in place. Disk mass estimates based on the H2 will permit estimation of the true timescales for the dissipation of the circumstellar disks; non-detection will indicate that either the gas also dissipates quickly, or that the optically thin circumstellar gas disks do not extend in close to the st This investigation may constrain theories of planetary accumulation.

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