The old anticentre open cluster Berkeley 32: membership and fundamental parameters

Abstract

We have obtained medium-low resolution spectroscopy and BV I CCD imaging of Berkeley 32, an old open cluster which lies in the anticentre direc tion. From the radial velocities of 48 stars in the cluster direction we found that 31 of them, in crucial evolutionary phases, are probable cluster members, with an average radial velocity of +106.7 (� = 8.5) km s 1 . From isochrone fitting to the colour magnitude diagrams of Be rkeley 32 we have obtained an age of 6.3 Gyr, (m − M)0= 12.48 and E(B − V ) = 0.10. The best fit is obtained with Z=0.008. A consistent distance, (m − M)0 ≃ 12.6 ± 0.1, has been derived from the mean magnitude of red clump stars with confirmed membership; we ma y assume (m − M)0 ≃ 12.55 ± 0.1 The colour magnitude diagram of the nearby field observed to c heck for field stars contamination looks intriguingly similar to that of the Canis Major overdensity.