Ground-based CCD astrometry with wide-field imagers^*,**,***

II. A star catalog for M 67: WFI@2.2 m MPG/ESO astrometry, FLAMES@VLT radial velocities

¹ Dipartimento di Astronomia, Universita di Padova, Vicolo dell' Osservatorio 2, 35122 Padova, Italy e-mail: [giampaolo.piotto;sandro.villanova]@unipd.it
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail: [bedin;jander]@stsci.edu
³ INAF – Osservatorio Astronomico di Collurania, via M. Maggini, 64100 Teramo, Italy e-mail: cassisi@oa-teramo.inaf.it
⁴ Grupo de Astronomía, Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción, Chile e-mail: svillanova@astro-udec.cl
⁵ Dept. of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA e-mail: imants@pha.jhu.edu
⁶ European Southern Observatory, Garching, Karl-Schwarzschild-Str. 2, 85748 Germany e-mail: lpasquin@eso.org
⁷ INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35132, Italy e-mail: yazan.almomany@oapd.inaf.it
⁸ Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263 129, India e-mail: sagar@aries.ernet.in

Corresponding author: rkant@aries.ernet.in

Received: 14 December 2007
Accepted: 25 February 2008

Abstract

Context. The solar-age open cluster M 67 (C0847+120, NGC 2682) is a touchstone in studies of the old Galactic disk. Despite its outstanding role, the census of cluster membership for M 67 at fainter magnitudes and their properties are not well-established.

Aims. Using proprietary and archival ESO data, we have obtained astrometric, photometric, and radial velocities of stars in a  arcmin² field centered on the old open cluster M 67.

Methods. The two-epoch archival observations separated by 4 years and acquired with the Wide-Field Imager at the 2.2 m MPG/ESO telescope were reduced with our new astrometric techniques, as described in the first paper in this series. The same observations served to derive calibrated BVI photometry in M 67. Radial velocities were measured using the archival and new spectroscopic data obtained at the VLT.

Results. We have determined relative proper motions and membership probabilities for ~2400 stars. The precision of proper motions for optimally exposed stars is 1.9 mas yr^-1, gradually degrading down to ~5 mas yr^-1 at . Our relatively precise proper motions at were first obtained in this magnitude range for M 67. Radial velocities were measured for 211 stars in the same field. We also present a detailed comparison with recent theoretical isochrones from several independent groups.

Conclusions. For the M 67 area, we provide positions, calibrated BVI photometry, relative proper motions, membership probabilities, and radial velocities. We demonstrate that ground-based CCD mosaic observations just a few years apart are producing proper motions, allowing reliable membership determination. We have produced a catalog that is electronically available to the astronomical community.