Ground-based CCD astrometry with the wide field imagers. III. WFI@ESO2.2m proper motion catalog of the globular cluster omega Centauri

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  • 10 October 2008
Abstract
omega Centauri is the most studied Globular Cluster due to its numerous puzzling features. Intensive spectroscopic follow-ups of stars located in different positions on the color-magnitude diagram may clarify some of these peculiarities. To be fairly sure to point cluster members during spectroscopic surveys, as well as to study space/radial distributions in the cluster outskirts without including field stars, a high-quality proper motion catalog of omega Cen is required, together with membership probability determination. The only available wide-field proper motion catalog of omega Cen is derived from photographic plates, and only for stars brighter than B~16. Using ESO/archive data, we have obtained a new, CCD-based, proper motion catalog for this cluster, extending down to B~20. We used the new high-precision astrometric software recently developed for WFI@ESO2.2m and presented in the first paper of this series. We achieved a very good cluster-field separation with a temporal base-line of only four years. We corrected our photometry for the sky concentration effects. We provide calibrated UBVRI wide-band photometry plus a narrow-band filter centered on H_alpha for nearly 360,000 stars. We can confirm that the omega Cen metal-poor and the metal-rich components share the same proper motion, and we show that also the metal-intermediate component exhibits the same mean motion of the other RGB stars. We provided also membership probability determination for the recently published omega Cen variable star catalogs. Our catalog extends the proper motion measurements below to the cluster turn-off luminosity, and covers a wide area (~33'x33') around the omega Cen center. Our catalog is now electronically available to the astronomical community.

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