EDP Sciences
Free access
Issue
A&A
Volume 379, Number 3, December I 2001
Page(s) 878 - 883
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011357
A&A 379, 878-883 (2001)
DOI: 10.1051/0004-6361:20011357

The light and period changes of RT Andromedae

A. Erdem, O. Demircan and M. Güre

Çanakkale Onsekiz Mart University, Faculty of Arts and Sciences, Department of Physics, 17100 Çanakkale, Turkey

(Received 11 June 2001 / Accepted 5 September 2001 )

Abstract
The nature of the long-term orbital period variation and the light level variation of RT And was studied based on all available photometric observations. The (O-C) diagram formed by all available times of eclipse minima could be either of a quasi-sinusoidal form superimposed on a parabolic form, or a long period sinusoidal form. The quasi-sinusoidal form with an amplitude of ~0.002 days and a period of ~65 years could be due to a cyclic magnetic activity modulation on the orbital period of the system. Applegate's theory (Applegate 1992), in this case, predicts an ~3 kG mean subsurface magnetic field for the primary component of the system. The parabolic form corresponds to a secular period decrease of about $3\times 10^{-9}
\textit{m}_{\odot} \rm yr^{-1}$ caused by mass loss from the system, and the long-period sinusoidal form with an amplitude of ~0.02 days and a period of ~105 years corresponds to a secular period change caused by the light-time effect due to an unseen third star in the system. It was estimated that the unseen third star should be a low mass (lower than $0.6 \textit{m}_{\odot}$) and faint ( ${\sim}5\fm$ fainter than the system RT And) star, whose detection is almost impossible. Future data will add information on the nature of the secular (O-C) variation. Secular light level variation of the system was found to be irregular and no correlation was detected with the orbital period variation.


Key words: stars: binaries: eclipsing -- stars: individual: RT And

Offprint request: A. Erdem, aerdem@bornova.ege.edu.tr

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