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Astron. Astrophys. 363, 958-969 (2000)

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5. Conclusions

We have conducted a photometric and spectroscopic optical follow-up of 12 X-ray sources detected by ROSAT in the center field of the Coma Berenices open cluster. VRI colours, spectral types, chromospheric activity and radial velocities were derived for all the stellar candidates observed. Four of these stars exhibit both photometric and spectroscopic properties which are marginally compatible with cluster membership. Their proper motions are, however, much higher than the cluster's value, implying that they do not belong to it. We have discussed their probable nature on the basis of the available information, but higher resolution spectroscopy and photometric monitoring would be needed to better ascertain their stellar properties. Changes in radial velocities indicate that five of the stellar objects in the sample could be binaries, and one of them has turned out to be a K6 W-type W UMa contact binary exhibiting one of the shortest periods known for this kind of systems.

Coma Berenices appears then to be an open cluster with not enough mass to retain its less massive original stars. Additional X-ray/optical observations are needed to investigate the existence and distribution of late-type stars outside the cluster core.

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© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000
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