University of Wisconsin

Space Astronomy Laboratory

ASTRO - 2

WUPPE PROGRAM CLASS 3.3

CLOSE BINARY STARS

Objects:
#3308 68 Herculis
#3315 44i Bootis
#3815 HD 153919
UW Astronomer: Geoff Fox


Close binaries are stars that are physically so close to each other that they actually influence each other's evolution. Astronomers know that the more massive a star is the more rapidly it evolves. However, there is one class of objects for which this does not seem to be the case. These stars are called Algol systems where the more massive star is less evolved than its companion. We believe that the system has undergone an epoch of mass transfer where the more evolved star actually "donated" mass to the younger star such that the less evolved star has become the more massive object. There are stars which are even physically closer to each other than Algol systems; these are called W Ursae Majoris stars. The stars which are members of this class of objects are actually in contact with each other; they share a common envelope of gas. Naturally, such close proximities will produce various asymmetries which range from distortions in the shapes of the stars to the reflection from one or both of the photospheres (surfaces) of the illuminating radiation from the other star, to light scattering in a stream of gas extending from one star to the other. A third type of close binary is the massive x-ray binary. This binary system consists of an O and B type supergiant and a neutron star or black hole that acts as the x-ray source. We believe that matter from the supergiant may be accreting on the neutron star. WUPPE will be looking at three close binary systems, 68 Herculis, 44i Bootis, and HD 153919. We hope to be able to study the effects due to scattering processes in the distorted atmospheres of these objects in an attempt to learn more about the evolution of these stars.