On the rotation properties of Be stars and their envelopes.
MENNICKENT R.E., VOGT N., BARRERA L.H., COVARRUBIAS R. and RAMIREZ A.
Abstract (from CDS):
We present the results of low resolution spectroscopy (4A) obtained at CTIO for a sample of 42 Be, 4 B and 3 O stars covering the λ3700-7000A spectral range. Equivalent widths of the Balmer lines were measured up to H10. We also give the V/R state of the Hα emission line. In addition, the peak separation and the width at the base of the Hβ and Hγ emission lines are tabulated for a total of 243 medium resolution (1A) spectra of 51 southern Be stars taken at the Manuel Foster Observatory, Chile. We analyzed our Hα equivalent widths (Wα) together with published data for a total of 122 Be and 2 Oe stars. An upper limit of Wα increasing with the projected rotational velocity vsini is shown by the data. The Wα values depend strongly on spectral type, being lower for later-type Be stars. This could indicate that the maximum strength of emission depends mainly on the spectral type and rotation velocity. The relation between Wα(max) and vsini, together with the observed excess in number of low vsini Be stars and the reported anti-correlation between photometric period and vsini give evidence for a considerable range of the true rotation velocities of Be stars: definitely there are intrinsically slow rotators among them. However, our results could also be interpreted in terms of anisotropic Hα emission coming from the disk. The analysis of the net equivalent widths and peak separations of Hα double emission line profiles strongly favor a disk type emitting envelope with a r–j rotation law with j=1.4±0.2 which do not depend on the spectral subtype. This result is interpreted as evidence of radial motions in the envelopes of Be stars. The mean radial extensions of the regions which emit Balmer lines were determined to range between 30% (H10) and 60% (Hβ) of the Hα emitting envelope in the case j=1. The mean electron density within the envelope has been found to vary only by a factor of 4. We compare our results with earlier investigations.
stars: emission-line, Be, rotation