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J/A+A/287/817 Period changes in RT Lac (Keskin+ 1994)
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Luminosity variations and orbital period changes in RT Lacertae
Keskin V., Ibanoglu M.C., Akan C., Evren S., Tunca Z.
<Astron. Astrophys. 287, 817 (1994)>
=1994A&A...287..817K
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ADC_Keywords: Binaries, eclipsing; Stars, variable
Keywords: stars: binaries: close - stars: individual: RT Lac -
stars: activity - stars: chromospheres -
stars: magnetic field - stars: variable
Abstract:
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 3.5M_{sun}_. 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).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2 43 227 Up-dated times of primary and secondary
eclipses and residuals
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Byte-by-byte Description of file: table2
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Bytes Format Units Label Explanations
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1- 13 F13.5 d Min Time of minima in Julian day
16- 22 F7.1 --- E Integer eclipse cycle number
25- 31 F7.4 d O-C(I) Observed-calculated residual for primary
minima
34- 40 F7.4 d O-C(II) []? Observed-calculated residual for secondary
minima
43 A1 --- Ref References: (1) Hall & Kreiner (1980)
(2) Ibanoglu et al. (1980)
(3) Tunca et al. (1983)
(4) Evren (1989)
(5) This paper
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(End) Patricia Bauer [CDS] 25-Feb-1994