2001A&A...375..387V

We observed the optical counterparts of X-ray sources in the old open clusters NGC 752 and NGC 6940 to search for the origin of the X-rays. The photometric variability reported earlier for the blue straggler H209 is not confirmed by our light curves, nor is an indication for variability seen in the spectra; thus its X-rays remain unexplained. The X-rays of VR111 and VR114 are likely not a result of magnetic activity as these stars lack strong Ca II H&K emission, while in VR108 the level of activity could be enhanced. The short-period binary H313 is a photometric variable; this supports the interpretation that it is a magnetically active binary. From the detection of the Li I 6707.8Å line, we classify the giant in VR84 as a first-ascent giant; this leaves its circular orbit unexplained. As a side-result we report the detection of Li I 6707.8Å in the spectrum of the giant H3 and the absence of this line in the spectrum of the giant H11; this classifies H3 as a first-ascent giant and H11 as a core-helium-burning clump star, and confirms the faint extension of the red-giant clump in NGC 752.