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Session 44 - Circumstellar Material.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
Ultraviolet observations with the Goddard High Resolution Spectrograph (GHRS) aboard on the Hubble Space Telescope clearly indicate circumstellar gas around 2 And (HD 217782). This star is one of the 62 A stars in our volume-limited search for proto-planetary systems. It also has been thought to be a Lambda Boo star like Beta Pictoris, a well-known proto-planetary system.
While others interpret the unusually large Ca II column density in the line-of-sight toward 2 And as caused by a cold (T=80 K) diffuse interstellar cloud, we suggest that there is also circumstellar gas around this nearby (d=29 pc) star based on our high-dispersion IUE Fe II spectra. To confirm our circumstellar gas detection, we recently obtained GHRS/Echelle-B spectra of the ultraviolet resonance multiplets of Fe II near 2600 Å\ and Al III near 1860 Åwhich have far higher resolution and S/N than our previous IUE data. From the presence of absorptions from fine-structure levels of Fe II, we estimate that the density in the circumstellar gas is about 10^4 to 10^5 cm^-3, which is inconsistent with any diffuse interstellar cloud in the nearby region. We also detect weak Al III circumstellar absorption at \lambda\lambda1854,1862, which must arise in a shocked region about 2 And. Under ``normal" circumstances, 2 And, an A star, is too cool to have sufficient Al III ionizing flux. Our detailed study of this system allows us to understand Beta Pic better. We also discuss the role of accretion in circumstellar disks and the Lambda Boo phenomenon in this paper.
