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Astron. Astrophys. 358, 1007-1021 (2000)


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AR Lacertae: H[FORMULA] chromospheric emission and radial velocities from long-term optical spectroscopy *

A. Frasca 1, G. Marino 2, S. Catalano 1 and E. Marilli 1

1 Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95125 Catania, Italy
2 Istituto di Astronomia, Università di Catania, Viale Andrea Doria 6, 95125 Catania, Italy

Received 8 April 1999 / Accepted 27 April 2000

Abstract

We present here the results of spectroscopic studies in the H[FORMULA] region of the active eclipsing binary AR Lac (G2IV+K0IV) obtained at Catania Astrophysical Observatory in 1989, 1990, 1994, 1996 and 1997. Accurate measurements of radial velocities by using the cross-correlation method have been made and a new orbital solution has been derived. The equivalent width of the H[FORMULA] emission core has been measured by subtraction of spectra synthesised from standard non-active stars of spectral types similar to those of the two components. We find chromospheric emission from both components in most of the spectra. No rotational modulation of the H[FORMULA] emission is apparent. The absorption excess observed near and during primary minima in 1997 is interpreted as the effect of a prominence-like structure anchored between the leading and the trailing hemisphere of the cool component. This interpretation is fully compatible with the radial velocities of the H[FORMULA] emission peaks in the subtracted spectra.

The observation of a H[FORMULA] flare in 1989 on the cool star is also reported and an estimate of the size of the magnetic structure involved in the event is proposed.

Key words: stars: activity – stars: binaries: eclipsing – stars: binaries: spectroscopic – stars: individual: AR Lac

* Based on observations collected at the Catania Astrophysical Observatory, Italy

Send offprint requests to: A. Frasca (afr@sunct.ct.astro.it)

© European Southern Observatory (ESO) 2000

Online publication: June 20, 2000

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