On the possibility of magnetic starspots on the primary components of W Ursae Majoris type binaries.
Abstract
We examine the hypothesis that magnetic starspots occur in W UMa stars. Crude estimates of toroidal field strength in these rapidly-rotating stars suggest that the fields may be large enough (2-10 kilogauss) to permit spots to form. The probability of spot formation is larger on the primary component than on the secondary, especially in Rucinski's W type systems. It is shown that the existence of starspots on the primary component in W UMa systems can account for the apparent temperature excess of the secondary relative to the primary in W type systems, and for the much smaller variations in the light curve exhibited by Rucinski's A type systems. We predict upper limits on the amplitude of the distortions which can occur in the light curve of these systems due to starspot activity. The presence of starspots leads to flare activity, but flares with amplitudes as large as Amv = 1 mag are expected to occur very rarely, only once every few years in W UMa. Flares of amplitude 0.01 mag, may, however, occur sufficiently frequently to explain short-term deviations from mean light curves occurring within a single night's observations. Cycles of starspot activity appear to have periods of 5-10 years in two of these systems. Tidal effects may be important in determining preferred starspot longitudes. Subject heading: W Ursae Majoris stars
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1975
- DOI:
- 10.1086/153635
- Bibcode:
- 1975ApJ...198..563M
- Keywords:
-
- Binary Stars;
- Dynamo Theory;
- Starspots;
- Stellar Magnetic Fields;
- Stellar Rotation;
- Astronomical Models;
- Light Curve;
- Magnetic Effects;
- Main Sequence Stars;
- Mass Ratios;
- Stellar Temperature;
- Astrophysics