ROSAT HRI observations of the intermediate-age open cluster IC 4756
Abstract
We have obtained an 88 kilosecond ROSAT HRI exposure of the intermediate-age open cluster IC 4756 with the purpose of detecting stars in the high luminosity tail (log L_X >= 10(29) erg s(-1) ) of its X-ray luminosity distribution. However, only 1 cluster member (HSS 201) out of the 60 members inside the central high-sensitivity region of the HRI field of view (FOV) was detected. This star has spectral type A8, suggesting a close binary system with a low mass X-ray emitting companion. We compare the distribution of upper limits for F and G-type dwarfs in IC 4756 with the X-ray distribution functions of the similarly aged Hyades and Praesepe clusters. The results of this statistical analysis are inconclusive for G-type stars, but suggest that at least F-type stars in IC 4756 are not as X-ray luminous as their Hyades counterparts, thus indicating intrinsic differences between the two clusters. Finally, our data indicate a deficit of very active binaries with respect to both Hyades and Praesepe, and older open clusters.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- September 1998
- Bibcode:
- 1998A&A...337..372R
- Keywords:
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- STARS: ACTIVITY;
- X-RAYS: STARS;
- OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: IC 4756