Ground-based CCD astrometry with wide field imagers. II. A star catalogue for M67: WFI@2.2m MPG/ESO astrometry, FLAMES@VLT radial velocities

摘要

The solar-age open cluster M67 (C0847+120, NGC2682) is a touchstone instudies of the old Galactic disk. Despite its outstanding role, the census ofcluster membership for M67 at fainter magnitudes and their properties are notwell-established. Using the proprietary and archival ESO data, we have obtainedastrometric, photometric, and radial velocities of stars in a 34'x 33' fieldcentered on the old open cluster M67. The two-epoch archival observationsseparated by 4 years and acquired with the Wide Field Imager at the 2.2mMPG/ESO telescope have been reduced with our new astrometric techniques, asdescribed in the first paper of this series. The same observations served toderive calibrated BVI photometry in M67. Radial velocities were measured usingthe archival and new spectroscopic data obtained at VLT. We have determinedrelative proper motions and membership probabilities for ~2,400 stars. Theprecision of proper motions for optimally exposed stars is ~2 mas/yr, graduallydegrading down to ~5 mas/yr at V= 20. Our relatively precise proper motions atV>16 are first obtained in this magnitude range for M67. Radial velocities aremeasured for 211 stars in the same field. We also present a detailed comparisonwith recent theoretical isochrones from several independent groups. For M67area we provide positions, calibrated BVI photometry, relative proper motions,membership probabilities, and radial velocities. We demonstrate that theground-based CCD mosaic observations just a few years apart are producingproper motions, allowing a reliable membership determination. We produced acatalogue that is made electronically available to the astronomical community.