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Astron. Astrophys. 345, 137-148 (1999)

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The contact binary AW Ursae Majoris as a member of a multiple system

T. Pribulla 1, D. Chochol 1, H. Rovithis-Livaniou 2 and P. Rovithis 3

1 Astronomical Institute, Slovak Academy of Sciences, SK-059 60 Tatranská Lomnica, Slovakia (pribulla@; chochol@auriga.ta3.sk)
2 Section of Astrophysics, Department of Physics, University of Athens, GR-157 84 Zografos, Athens, Greece (elivan@atlas.uoa.gr)
3 Astronomical Institute, The National Observatory of Athens, P.O. Box 20048, GR-11810 Athens, Greece

Received 26 February 1998 / Accepted 22 December 1998

Abstract

New and published UBV photoelectric and spectroscopic observations of AW UMa are analyzed and interpreted by a triple or quadruple-star model. The derived inclination angle i = 78.3o, the photometric mass ratio q = 0.08 as well as all available radial velocities, corrected for the systemic velocity changes, were used to determine the masses of the components of the contact binary as [FORMULA] = (1.79[FORMULA]0.14) M[FORMULA] and [FORMULA] = (0.143[FORMULA]0.011) M[FORMULA]. These values set the binary on the ZAMS. Variations in the systemic velocity suggest the existence of a third body on a [FORMULA] = 398 days orbit with eccentricity [FORMULA] = 0.227[FORMULA]0.056. Assuming that the orbits of the contact binary and of the third body are coplanar, its mass is [FORMULA] = (0.85[FORMULA]0.13) M[FORMULA]. The long-term orbital period decrease is explained by mass transfer from the more massive to the less massive component accompanied by the angular momentum loss due to mass outflow from the outer Lagrangian point L2. The period decrease occurred either suddenly (in two period jumps 6200 days apart) or continuously. In the second case, the [FORMULA] residuals from the parabolic fit can be explained by the light-time effect caused by a fourth body on a [FORMULA] = 6250 days eccentric orbit ([FORMULA] = 0.63[FORMULA]0.24). For the most probable range of inclination of the possible fourth component orbit 60o [FORMULA] 40o, the range of its mass is 0.168 M[FORMULA]M[FORMULA].

Key words: stars: binaries: eclipsing – stars: binaries: spectroscopic – stars: individual: AW UMa

Send offprint requests to: T. Pribulla

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© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999
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