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Astron. Astrophys. 338, 139-150 (1998)


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A spectroscopic study of the long-period binary star WY Geminorum

Laurits Leedjärv

Tartu Observatory, Tõravere, EE 2444, Estonia (leed@aai.ee)

Received 30 January 1998 / Accepted 10 June 1998

Abstract

The long-period VV Cephei type binary star WY Gem, consisting of a M2 supergiant and an early B type main-sequence star, has been monitored spectroscopically on the 1.5-meter telescope of Tartu Observatory from 1984 to 1997. The H[FORMULA] emission line has undergone significant variations, with equivalent width decreasing from a value of about 20 Å  in 1980s down to 3-5 Å  in 1996-1997. Strong emission lines of Fe II , present in 1985, have almost vanished by now. At the same time, the forbidden emission lines of [Fe II ] and [S II ] have not changed remarkably. Radial velocities of the M2 supergiant have been measured, and together with the data available from literature, they are used for deriving approximate orbital elements of WY Gem. Although the observational data have large scatter, it is likely that WY Gem has a long-period ([FORMULA] yr), very eccentric orbit ([FORMULA]), with periastron passage occuring in 1983. Such elements are confirmed by the variations of the emission lines of H[FORMULA] and Fe II , as well as by photometric observations. Near the time of periastron passage, the hot (B type) star probably accretes some amount of the supergiant's wind, and even an accretion disk could be formed. The observed H[FORMULA] profiles, in principle, are consistent with those computed as arising in a rotating disk. The extent of the disk has decreased since 1984.

Key words: stars: binaries: spectroscopic – stars: individual: WY Gem – stars: supergiants


© European Southern Observatory (ESO) 1998

Online publication: September 8, 1998

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