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Astron. Astrophys. 319, 211-224 (1997)

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Environments of active close binaries

II. GK Hydrae and TY Pyxidis

A.G. Gunn 1, J.G. Doyle 1 and E.R. Houdebine 2

1 Armagh Observatory, Armagh, BT61 9DG, Northern Ireland
2 Solar System Division, ESA Space Science Department, ESTEC Postbus 299, 2200 AG Noordwijk, The Netherlands

Received 27 February 1996 / Accepted 31 May 1996


High-resolution spectroscopic observations were obtained for two eclipsing active close binary systems, GK Hydrae and TY Pyxidis. For GK Hya excess emission was observed in the Balmer lines and Mg I b lines while TY Pyx showed excess emission in the Balmer lines and Ca II H&K lines. The emission from GK Hya arises from a global phenomenon associated solely with the secondary component. The lack of significant He I D3 excess absorption and an analysis of the flux ratio in the Balmer lines suggest that the emission originates in prominence-like material seen off the limb of the star. A marginal broad excess absorption band centered around the Balmer emission peaks may be caused by this material absorbing the stellar continuum against the disk with high (350 km s-1) line-of-sight turbulent velocities. The inference that plage-like regions and associated star-spots are not substantial on this star is in agreement with the lack of spot modulation in the photometric light curve. For TY Pyx the majority of the H [FORMULA] excess and a larger proportion of the Ca II core emission could be attributed to a global phenomenon on the primary. Analysis suggests that very large volumes are responsible for the emission, however, there is no observational evidence for the existence of discrete extended structures around TY Pyx.

Key words: star: binaries: spectroscopic – stars: GK Hya; Ty Pyx – stars: activity – stars: chromospheres - stars: magnetic field

Send offprint requests to: A.G. Gunn

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998