Nonradial and radial oscillations observed in non-emission line OB dwarfs and giants

Abstract

Only a decade ago, this talk could have concerned only the β Cephei stars which however populate a much more precisely defined strip in the Hertzsprung-Russel diagram (MED). But recent reconnaissance surveys (Smith 1977; Smith and Penrod 1984; Waelkens and Rufener 1985; Baade, in preparation) show that perhaps only one, if any, sizeable region of the upper HRD is devoid of nonradially pulsating stars. The identification of the driving mechanism is still pending (cf. the parallel talk by Osaki), and apparently our knowledge about the internal structure of OB stars is incomplete. But, turning that argument around, it also is indicative of how much may be learned about OB stars from and through the solution of that fundamental problem. This seismologial potential, the ubiquity of the phenomenon, and the effect, as suggested by recent observations of some stars, of the pulsations on the mass loss of OB stars make the oscillations of OB stars one of the most important problems of current astrophysics. On the observational side, rotationally broadened spectral lines, large amplitudes, comparatively long periods, and high luminosities permit information to be gathered which otherwise is accessible only for the sun.

3 Vulpeculae - A nonradial pulsator in a one-year binary system

“…The spectral line-profile variations, the intrinsic velocity variations, and the possibility of low-amplitude phototometric variations are all reminiscent of the variations observed in other late O-type and the middle B-type stars on, or slightly above, the main sequence. We suggest that 3 Vul is a member of the "53 Persei" class of nonradially pulsating variables (Smith 1977(Smith , 1980(Smith , 1988Waelkens & Rufener 1985) or of some related group of variable stars (Baade 1986(Baade , 1989. There is uncertainty as to how the 53 Persei variables are to be defined, how they are related to the ß Canis Majoris variables, and whether there are other distinct classes of variables at the blue end of the main sequence.…”

The Galactic bulge and halo

“…Their sample is likely to be most incomplete toward the galactic center, where high reddening makes it difficult both to find clusters and measure their properties well, but the modal distance from the galactic center for this sample is still only 3 kpc. Baade (1951Baade ( , 1958 detected RR Lyrae variables in his window at /= I o , b=-3.9°. Their presence was one of the reasons why he postulated that the galactic bulge was an example of "Population II."…”

On the period and nature of the light and radial-velocity variations of HD 25799

“…Light, line-profile, and sometimes velocity variations with periods in the range 0.5 to 2 days are common among early-type B stars (Baade 1986;Percy 1986), and there are many points in common between the light and velocity variations seen in these stars and those of HD 25799. These include changes in the amplitude and shape of the light curve, the presence of second harmonics in the light curve, and the relative phasing of the light and velocity curves.…”