U Cephei: effects of disk, hot spot, and stream on primary eclipse light curves.
Abstract
Large variations of extra light as a function of orbital phase are analyzed in 1974-1978 eclipse observations of U Cep. Light losses near first contact result from the projection of an optically thick (10,000 K) stream onto the B star (13,500 K) photosphere. By phase 0.965 the stream is eclipsed, leaving a light excess produced by a small hot spot (equal to or greater than 20,000 K) and an 'accretion disk'. From shortly after third contact to last contact, large light losses occur as the disk (12,000 K) is projected against the B star. The visible light from the hot spot is less than the luminosity excess produced by the disk, when radiation in all directions is included. A brief discussion of photometric activity observed in U Cep since 1974 is given, and orbital period changes since 1972 and their bearing on mass and angular momentum exchange are summarized. Finally, a simple physical mechanism is discussed that may account for optically thick light perturbations seen in U Cep since 1974.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1980
- DOI:
- 10.1086/158338
- Bibcode:
- 1980ApJ...241..257O
- Keywords:
-
- Cepheid Variables;
- Eclipsing Binary Stars;
- Light Curve;
- Stellar Mass Accretion;
- B Stars;
- Optical Thickness;
- Stellar Envelopes;
- Stellar Spectrophotometry;
- Ultraviolet Radiation;
- Astrophysics;
- Accretion:Eclipsing Binaries;
- Eclipsing Binaries:Light Curves;
- Eclipsing Binaries:Period Changes