Ultraviolet photometry from ANS: chromospheric emission of W Ursae Majoris and 44 i Bootis.
Abstract
We have obtained intermediate-bandwidth ultraviolet photometry of two W UMa-type binaries, W UMa (HD 83950) and 44 Boo (HD 133640). Observations at 1550 and 1800 Å, which measure chromospheric line emission in C IV and Si II and the continuous emission of layers near the temperature minimum, detect surface fluxes comparable to those measured to date for other late-type stars with strong surface activity. The surface brightnesses longward of 2000 Å, however, seem to be more or less consistent with the optical colors and surface brightnesses. For 44 Boo, which is a triple system, we have interpreted the wavelength dependence of the light curve to reach the following conclusions. The wide component, 44 Boo A, is most likely a G0V star near the zero-age main sequence. The eclipsing binary, 44 Boo B, cannot have the continuous spectrum of a star later than that of 44 Boo A by more than 5 subclasses, i.e., it is no later than . The eclipsing binary is underluminous by a factor of 2 for its color and has a color too blue for its mass and orbital period, properties which can be explained by a spot model.
- Publication:
-
The Astronomical Journal
- Pub Date:
- September 1981
- DOI:
- 10.1086/113019
- Bibcode:
- 1981AJ.....86.1387E