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

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 <sup>1

1</sup> 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 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

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

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

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and data reduction
• 3. Radial velocities and orbital solution
• 4. Extraction of H emission
• 5. Results
  • 5.1. H equivalent width
  • 5.2. Radial velocity of the H emission
• 6. Discussion
  • 6.1. Primary eclipses
  • 6.2. Secondary eclipses
  • 6.3. The H flare on the cool component of AR Lac
• 7. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 20, 2000
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