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New optical positions and proper motions of late type stars associated with SiO masers
The 33 cm astrograph of the Bordeaux Observatory has been used to derivewith respect to AGK3 reference stars, accurate positions of late typevariable stars variable stars associated with strong SiO maser emission.It is suggested that selected maser stars can be used to link theHIPPARCOS system and the VLBI extragalactic reference frame. The propermotions of the program (SiO) and reference stars are derived and, forthe program stars, are compared to the McCormick catalog of propermotions.
| The influence of the envelope in the variations of transitory type Be stars
The contribution of the stellar envelope to variations oftransitory-type Be stars, which are alternately of types B and Be, isinvestigated. The Rojas-Herman classification is applied to thequantification of long-term stellar variation for a sample of Be starsbrighter than magnitude 7, and compared with the spectral properties ofthese stars. A relation is derived between the equivalent widths of theH-alpha and H-beta lines and the stellar U-B index. The U-B index isthen calibrated as a function of the Balmer discontinuity in order toseparate the contributions of the star and its envelope to the emission.The separate U-B indices derived for the star, which are characterizedby long-term variations, and the envelope, which is sensitive toshort-term variations, are observed to be additive, implying that theobserved flux is a convolution of the fluxes emitted by the star and itsenvelope.
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