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Astron. Astrophys. 347, 866-875 (1999)

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Optical spectroscopy of X-ray sources in the old open cluster M 67 *

M. van den Berg 1, F. Verbunt 1 and R.D. Mathieu 2

1 Astronomical Institute, P.O. Box 80000, 3508 TA Utrecht, The Netherlands
2 Department of Astronomy, University of Wisconsin, Madison, WI 53706, USA

Received 21 January 1999 / Accepted 15 April 1999

Abstract

We have obtained optical spectra of seven stars in the old galactic cluster M 67 that are unusual sources of X-rays, and investigate whether the X-ray emission is due to magnetic activity or to mass transfer. The two binaries below the giant branch S 1063 and S 1113, the giant with the white dwarf companion S 1040 and the eccentric binary on the subgiant branch S 1242 show magnetic activity in the form of CaII H&K emission and H[FORMULA] emission, suggesting that their X-rays are coronal. The reason for the enhanced activity level in S 1040 is not clear. The two wide, eccentric binaries S 1072 and S 1237 and the blue straggler S 1082 do not show evidence for CaII H&K emission. A second spectral component is found in the spectrum of S 1082, most clearly in the variable H[FORMULA] absorption profile. We interpret this as a signature of the proposed hot subluminous companion.

Key words: stars: activity – stars: binaries: general – Galaxy: open clusters and associations: individual: M 67 – X-rays: stars

* Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias

Send offprint requests to: Maureen van den Berg

Correspondence to: m.c.vandenberg@astro.uu.nl

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© European Southern Observatory (ESO) 1999

Online publication: June 6, 1999
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