Physical properties of Be star envelopes from Balmer and Fe II emission lines

Abstract

The study obtains H-alpha, B-beta, H-gamma, and Fe II 6516 line profiles with resolution 0.45 A for 41 bright Be stars with a CCD detonator during two observing periods in 1989. Analysis of the structure of the emission profiles indicates that the Be star emitting envelope is most likely axially symmetric, consistent with a rotating, equatorial disk. A number of Be stars show either a 'wine bottle' structure or inflection points on one side of their H-alpha emission profiles, suggesting a two-component structure for the emitting envelope: an inner disk, possibly turbulent, and an outer extended disk. Differentially rotating disks producing weak H-alpha emission are closer to the central star where rotation broadens the line more strongly, relative to stars with extended envelopes which emit strongly but rotate more slowly. From the Balmer emission decrements it is found that Be star envelopes with Te near 10,000 K have electron densities in the range 10 exp 11 to 10 exp 13/cu cm. Be stars with weak Balmer emission have, on average, somewhat flatter Balmer decrements than stars with strong emission, suggesting envelopes with higher electron densities.