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Optical spectroscopy of X-ray sources in the old open cluster M67

Maureen van den Berg·Frank Verbunt·Robert D. Mathieu
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Abstract

We have obtained optical spectra of seven stars in the old galactic cluster M67 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 S1063 and S1113, the giant with the white dwarf companion S1040 and the eccentric binary on the subgiant branch S1242 show magnetic activity in the form of Ca II H&K emission and H-alpha emission, suggesting that their X-rays are coronal. The reason for the enhanced activity level in S1040 is not clear. The two wide, eccentric binaries S1072 and S1237 and the blue straggler S1082 do not show evidence for Ca II H&K emission. A second spectral component is found in the spectrum of S1082, most clearly in the variable H-alpha absorption profile. We interpret this as a signature of the proposed hot subluminous companion.

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Maureen van den Berg, Frank Verbunt, Robert D. Mathieu. 1999-04-16. Optical spectroscopy of X-ray sources in the old open cluster M67. https://arxiv.org/abs/astro-ph/9904217

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