Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...287..817k&link_type=abstract
Astronomy and Astrophysics 287, 817-823 (1994)
Astronomy and Astrophysics
Astrophysics
20
Stars: Binaries: Close, Stars: Individual (Rt Lac), Stars: Activity, Stars: Chromospheres, Stars: Magnetic Field, Stars: Variable
Scientific paper
The chromospherically active binary RT Lac was observed between 1978 and 1992. These observations showed that the mean brightness of the system varies with an amplitude of about 0.16min in blue and 0.11min in yellow light. The mean brightness at outside eclipses reached its maximum value at about 1986. During the observational time interval the mean colour of the system also varied by 0.06.min The up-dated O-C values have been interpreted as the consequence of a light-time effect. The analysis indicates that the eclipsing pair revolves around a third body with a period of 80.71yr. The projected distance of the eclipsing pair to the third body has been calculated to be approximately 176 times that of the separation between the eclipsing components. The lower limit estimated for the mass of the third body is at least 1.77 solar masses which is slightly greater than the mass of the more massive companion. It turns out that the smaller the inclination is, the greater the mass of the third body. If the inclination is decreased to 40deg the mass exceeds 3.5Msun_. Due to the lack of a photometric evidence, the nature of the third body should be questioned on the basis of stellar structure. When the light-time effect has been subtracted from all the photoelectric times of minima, an existence of cyclic variation in the orbital period revealed itself. The minimum of the O-C curve coincides with the maximum light of the system. The period and the mean brightness of the system seem to vary with the same cycle length of about 12.06yr. Since the light maximum coincides with the O-C curve's minimum, the outside spin of the more massive, active star should be greater than its inside spin according to the theory proposed by Applegate (1992).
Akan Can M.
Evren Serdar
Ibanoglu Cafer
Keskin Varol
Tunca Zeynel
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