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Astron. Astrophys. 356, 267-273 (2000)

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Orbital period variation in close binaries from radial velocity data and magnetic activity cycles

I. AR Lacertae: The test case

A. Frasca and A.F. Lanza

Osservatorio Astrofisico di Catania, Via S. Sofia, 78, Città Universitaria, 95125 Catania, Italy

Received 29 November 1999 / Accepted 4 February 2000


We check the possibility of detecting orbital period changes in non-eclipsing close binaries by means of spectroscopic orbit determinations. In order to test our method, we selected the eclipsing binary AR Lacertae for which the spectroscopically determined epochs of superior conjuctions can be compared with those provided by the light minima photometry. It is found that intermediate-resolution spectroscopy and IUE archive spectra can be used to build radial-velocity curves which allow us to estimate the epoch of superior conjunction [FORMULA] with an uncertainty of 0.01 days. We present the data-reduction procedure and the method of analysis, based on fitting a sinusoid to the radial-velocity curve, discussing the accuracy of [FORMULA]-value determinations and the possible sources of errors, notably those related to surface inhomogeneities, such as spots and faculae. The possibility of testing the hypothesis of a light-time effect for the orbital period modulation is also addressed by means of radial-velocity measurements.

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

Send offprint requests to: A. Frasca

Correspondence to: afr@sunct.ct.astro.it

© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000