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The Long-Term Behaviour of BY Dra

Published online by Cambridge University Press:  12 April 2016

K.P. Panov
Affiliation:
Institute of Astronomy, Bulgarian Academy of Sciences, Zarigradsko Shose 72, 1748 Sofia, Bulgaria
M.S. Ivanovo
Affiliation:
Institute of Astronomy, Bulgarian Academy of Sciences, Zarigradsko Shose 72, 1748 Sofia, Bulgaria
J.S.W. Stegert
Affiliation:
Sternwarte der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

Extract

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BY Dra has been extensively monitored for flares and spot-modulation of brightness at the Bulgarian National Astronomical Observatory (Panov & Ivanova 1993). Its mean light level exhibited remarkable changes in the past, due to the emergence and disintegration of photospheric spots, and different cycles have been proposed for the long-term changes of the BY Dra activity. This star is still believed to be a good candidate for cyclic variations, presumably similar to the sunspot activity cycle. After a spectacular drop in brightness in 1965 — 1967, and a subsequent rise in the early 70s, the mean light remained approximately constant during 1977 - 1991. A brightening of BY Dra occurred in 1992.

In Fig. 1, the light curves are shown for 1991, 1992 and 1993 in the V-band and in BV. Phases were calculated with the ephemeris of Chugainov (1966):

JD (min. light) = 2438983.612 + 3.836 · E

From Fig. 1, it is apparent that the mean visual light, which was about V = 8.20 in 1991, increased in 1992 by 0m.10, and a further increase by another 0m.03 occurred in 1993. The phase of minimum light in 1992 indicates that the position of the spot remained approximately the same in stellar longitude as in 1991. However, in 1993 the position of the spot changed by almost half a period.

Type
Flares in Late-type Stars: Radio and Optical
Copyright
Copyright © Springer-Verlag 1995

References

Chugainov, P.F., 1966, IBVS No. 122 Google Scholar
Panov, K.P., Ivanova, M.S., 1993, ApSS 199, 265 Google Scholar