Volume 375, Number 2, August IV 2001
|Page(s)||387 - 396|
|Section||Galactic structure, stellar clusters, and populations|
|Published online||15 August 2001|
An optical study of X-ray sources in the old open clusters NGC 752 and NGC 6940*
Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
Corresponding author: M. van den Berg, firstname.lastname@example.org
Accepted: 22 May 2001
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 H 209 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 VR 111 and VR 114 are likely not a result of magnetic activity as these stars lack strong Ca II H& K emission, while in VR 108 the level of activity could be enhanced. The short-period binary H 313 is a photometric variable; this supports the interpretation that it is a magnetically active binary. From the detection of the Li I 6707.8 Å line, we classify the giant in VR 84 as a first-ascent giant; this leaves its circular orbit unexplained. As a side-result we report the detection of Li I 6707.8 Å in the spectrum of the giant H 3 and the absence of this line in the spectrum of the giant H 11; this classifies H 3 as a first-ascent giant and H 11 as a core-helium-burning clump star, and confirms the faint extension of the red-giant clump in NGC 752.
Key words: stars: activity / stars: blue stragglers / stars: variables: general / open clusters and associations: individual: NGC 752, NGC 6940 / X-rays: stars
© ESO, 2001
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.