Ultraviolet photometry from the orbiting astronomical observatory XXII. Ultraviolet light variation ofβ Lyrae

Six-color ultraviolet light curves of the complex eclipsing binary system Lyr were obtained with the OAO-2 Wisconsin Experiment Package. The filters had a typical width at half maximum of 150 to 200 Å and centered at 1430, 1550, 1910, 2460, 2980 and 3320 Å. The most striking characteristics of the ultraviolet light curves are that the secondary minimum deepens at shorter wavelengths. This indicates that we arenot observing the eclipse effect of two stars having roughly a Planckian distribution of energy. In combination with the high resolution far ultraviolet spectra of Lyr recently obtained withCopernicus (OAO-3) Princeton Telescope Spectrometer, it is concluded that the far ultraviolet light curves are dominated by emission from the high temperature gas surrounding the binary system. The ultraviolet observations with OAO-2 andCopernicus are consistent with a model in which the enigmatic secondary component involves a gravitationally collapsed object, i.e., a black hole; however, alternative models are also admissible.     

Oscillations and pulsations in the sun and stars (invited review)

The discovery of the solar global oscillations, and their identification to many radial and nonradial eigenmodes of the Sun, have opened a new important field of research called solar seismology, in which we may probe the internal structure of the Sun by using its oscillations. In recent years, pulsations and oscillation-related phenomena have also been discovered in many stars which were hitherto regarded as non-pulsating stars. They include white dwards (ZZ Ceti-stars), Ap-stars, early-type stars with slow and rapid rotation (53 Per and Oph-stars, respectively). Developments in high spectral and high time-resolution observations will be expected to reveal variability in many other stars as well, in near future.In this review, the general properties of stellar eigenmode oscillations are first discussed. Recent observational and theoretical developments in the solar seismology and on pulsations and oscillations of newly discovered variable stars will then be reviewed.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.