CCD photometry of the old open cluster M67

Abstract

We present a CCD photometric survey of the central one-half degree of the old open cluster, M67, in U, B, V, and I colors to magnitude V=20. Extensive comparison of our photometry with other published datasets shows excellent agreement, indicating that CCD photometry is capable of producing a uniform set of measurements consistent with the photometric system defined primarily by the Landolt standard sequence. The color-magnitude diagram of the cluster shows a well-defined main sequence extending at least to the limit of the photometry at Mv=10.55 and a substantial binary sequence. At least 38% of cluster stars are binaries. The current generation of theoretical isochrones cannot be fit to the observed sequences with the observational errors. We find a tendency for more massive members of the cluster to be more centrally concentrated, along with a turnover in the cluster luminosity function at low masses, which may be due to dynamical relaxation of the cluster. To the limit of our photometry, we find a mass of the cluster of 724 solar masses. In addition, we present a sample of stars of well-determined standard magnitudes that are suitable as photometric standards for further studies of this cluster and for general calibration of UBVI photometry using CCDs.

Absolute Magnitude Calibration for Red Giants Based on the Colour–Magnitude Diagrams of Galactic Clusters. III. Calibration with 2MASS

“…Finally, we de-reddened the V magnitudes and combined them with the true colour indices (V − J) 0 in the literature. Hence, we transformed the V , B − V and V − I data in Montgomery, Marschall, & Janes (1993) to obtain a set of (J 0 , (V − J) 0 ) data for the RGB of M67. It turned out that 21 of the stars in the bright stars catalogue in Montgomery et al (1993) were red giants.…”

“…For the cluster M67, we transformed the V , B − V, and V − I data of Montgomery et al (1993) to (V − K s ) 0 by the following equation of Yaz et al (2010), and then we evaluated the K s 0 magnitudes by the combination of V 0 magnitudes and (V − K s ) 0 colours:…”

The Wilson–Bappu effect: A tool to determine stellar distances

“…They derive, on the basis of the Colour Magnitude Diagram, 9.55 ≤ (m − M) V ≤ 9.65 mag. Montgomery et al (1993) performed a photometric survey of the central region of M 67. They compared their photometry with two theoretical isochrones to retrieve distance modulus and age for M 67.…”

Pal 1: Another Young Globular Cluster?

“…A further field at 10 arcmin from the cluster center has been secured in order to evaluate the background-foreground contamination. Saviane et al (1995) Montgomery et al (1993)). The red giant branch (RGB) falls between those of Rup 106 and M 67.…”