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

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 c ompanion S 1040 and the eccentric binary on the subgiant branch S 1242 show magnetic activity in the form of Ca II H&K emission and Ha emission, sugge sting that their X-rays are coronal. The reason for the enhanced activity l evel 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 Ca II H&K emiss ion. A second spectral component is found in the spectrum of S 1082, most c learly in the variable Ha absorption profile. We interpret this as a signat ure of the proposed hot subluminous companion.