Are Dust Disks and Circumstellar Gas Around Young A Stars Unrelated Phenomena?

Details Are Dust Disks and Circumstellar Gas Around Young A Stars Unrelated Phenomena? Are Dust Disks and Circumstellar Gas Around Young A Stars Unrelated Phenomena?

Jul 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004hst..prop10219n&link_type=abstract

HST Proposal ID #10219

Physics

Hst Proposal Id #10219 Star Formation

Scientific paper

Young stars with circumstellar material are common, but their properties vary greatly. Current studies strongly suggest that Beta Pictoris {A5 V} is an early solar system. If the high-density, high-velocity circumstellar gas falling toward Beta Pic were fueled by grazing comets or on-going erosion of debris located close to the star, we would expect to find evidence for warm dust in all Beta Pic-like systems. We have carried out detailed studies of the circumstellar environments of all nearby A-type stars. We have studied not only their circumstellar dust but also the characteristics of their circumstellar gas through absorption line spectroscopy. Based on our visible and IUE data, we identified about a dozen A-type stars with circumstellar gas. Among them, 7 have dynamic circumstellar gas similar to that found in the Beta Pic system, but none of them has detectable IRAS infrared excess. What is the origin of the dynamic circumstellar gas around young A-type stars? The STIS wavelength range covers many fine-structure lines that can only be seen at high densities, which are characteristic of circumstellar but not interstellar gas. We propose to observe these 7 stars with STIS to {a} verify the circumstellar gas detections from our previous visible and IUE studies, {b} determine the temperature and electron number density in the circumstellar gas, {c} derive accurate circumstellar gas column densities, and {d} study the possible causes of the variable circumstellar absorption lines {both red-shifted and blue-shifted have been seen in spectra of Beta Pic and our 7 target stars}.

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