AAS 201st Meeting, January, 2003
Session 25. Circumstellar Material and Mass Loss
Oral, Monday, January 6, 2003, 10:00-11:30am, 602-604

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[25.04D] Dust and Gas Around Young Stars

C. H. Chen (UCLA)

Asteroids, planets, and comets are believed to form within circumstellar disks of gas and dust around young stars (ages < 100 Myr). We have obtained 10 - 20 \mum images, using the Keck I telescope and FUSE spectra of Herbig Ae and main sequence stars to characterize the dust and gas in these systems. We report the following results: (1) For zeta Lep, we find that the majority of dust is located within 6 AU from the star. Since the Poytning-Robertson drag lifetime of grains around this star is 104 years, significantly shorter than the 300 Myr year age of the system, we infer the presence of parent bodies with a total mass 200 times that of the main asteroid belt in our solar system. (2) For the binary system sigma Herculis, which possess a Vega-like infrared excess, we observe circumstellar \ion{C}{2}*, \ion{N}{2}* and \ion{N}{2}**, blueshifted by as much as 40 km/sec. We propose that there is a radiatively driven wind, generated by sigma Her's high luminosity. In this model, the material in the wind is created through collisions between parent bodies at 20 AU from the star, the approximate distance at which blackbodies are in radiative equilibrium with the star and at which 3-body orbits become unstable. (3) For the pre main sequence star AB Aur, we measure a dust mass 6\times10-9 M\sun, significantly less than the 10-4 M\sun inferred from millimeter photometry, suggesting the presence of a cold optically thick disk. We find that models which include dust envelopes fit the data somewhat better than models which incorporate flared circumstellar disks.

The author(s) of this abstract have provided an email address for comments about the abstract: cchen@astro.ucla.edu

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