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AR Lacertae: H chromospheric emission and radial velocities from long-term optical spectroscopy *
A. Frasca 1,
G. Marino 2,
S. Catalano 1 and
E. Marilli 1
Received 8 April 1999 / Accepted 27 April 2000
We present here the results of spectroscopic studies in the H 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 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 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 emission peaks in the subtracted spectra.
The observation of a H 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
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Online publication: June 20, 2000