Recent Science Highlights

1 September 1995

(following information provided by Dr. Antonella Fruscione)

Dr. Geraldine J. Peters (Space Sciences Center, Univ. So. California) reports on a 60ks EUVE observation of the B7IVe star alpha Columbae. The observation began on March 5, 1995 and has revealed the likely detection of an emission line of Ne VII at 88.2 Å at about the 3-sigma level. Possible emission features of Si VI/Fe IX at 83.4 Å and Ne VII at 97.5 Å are also seen.

• Located at a distance of 46 pc roughly in the direction of the Canis Major interstellar tunnel, alpha Columbae displays a low column density of N(H)=2.34x10^18 cm^-2. It is the second nearest Be star (after alpha Eridani) and the one with the lowest ISM column density.
• According to the tables of line diagnostics published by Raymond & Smith, Mewe & Brown, and Landini & Monsignori-Fossi, the above emission lines would peak in a plasma of about 650,000 K. The line formation region in alpha Columbae thus has a significantly higher temperature than the star's photosphere (about 14,000 K), disk (about 10,000 K), or wind (about 40,000 K), and may reside either at a "boundary layer" where collapsing material from the inner disk impacts the photosphere or at the top/bottom periphery of a wind-compressed disk (Bjorkman & Cassinelli, 1993, ApJ, 409, 429) where a standing shock probably exists.
• Four IUE images acquired on March 6-8, 1995 confirm the strong presence of C IV and Si IV wind absorption similar to that reported in Marlborough & Peters (1986, ApJS, 62, 875). No wind variability was apparent. Since the star's radiation field is incapable of driving this wind, some other mechanism must be responsible for the mass loss.