V/R VARIATIONS IN H-BETA EMISSION PROFILES OF BE STARS
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1991
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Abstract
The V/R ratio between the violet and red intensity peaks of the H/beta emission line of 33 southern Be stars was examined, covering periods from several years to several decades. 76% of our sample stars were found to be V/R variables. Long-term variables are characterized by quasiperiods mainly in the 2-13 years range with a mean T = 7 yr. Six short-term variables were found which are best characterized by V > R to V < R changes on time-scales of 6- 100 d. A statistical analysis of these data, including also data for 10 northern V/R variables, did not reveal any correlation of the quasiperiod T with the spectral type and projected rotational velocity (v sin i) of the central star. Long-term quasiperiods do not depend on the envelope size. However, only stars with small envelopes (r-beta less-than-or-similar-to 4r*) show short-term variations. We discuss several possible mechanisms for these variations and have concluded that the most satisfactory general interpretation for the long-term variations seems to be expansion and contraction of the envelope, triggered by a variable stellar wind. On the other hand, the short-term V/R variations could be caused by the rotation of inhomogeneities in the circumstellar envelope (blobs), possibly combined with atmospheric phenomena in the central star such as non-radial pulsations and/or anisotropic radiation fields.
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BE STARS, SPECTROSCOPY, EMISSION LINES