NGC2587: a sparse open cluster projected on to a populous star field

PIATTI, ANDRÉS E.; CLARIÁ, JUAN J.; AHUMADA, ANDREA V.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2009 vol. 397 p. 1073 - 1083

0035-8711

We present CCD photometry in the Johnson U, B and V and Kron_Cousins I passbands for the open cluster NGC 2587. The sample consists of 4406 stars reaching down to  V approx. 21.0 . We developed a new method to clean statistically the colour-magnitude diagrams. NGC 2587 appears to be a sparse, relatively bright open cluster, with a few tens of members projected on to a populous star field. The comparatively bright F7/8 II type star HD 70927, located close to the cluster centre, seems not to be a member. Our analysis suggests that NGC 2587 is slightly younger than the Hyades and probably of solar metallicity. A cluster radius of roughly 8 arcmin was estimated from the radial stellar density profile. From 18 probable cluster members with measured proper motions, we derive the following mean values for NGC 2587:  mu (alpha) = -4.3+/-3.6 mas/yr and mu(delta) = -2.5+/-3.4 mas/yr.Adopting the theoretical metal content  Z= 0.02 , which provides the best global fit, we derive a cluster age of  500.Simultaneously, colour excesses  E(B-V) = 0.10  and  E(V-I) = 0.15  and an apparent distance modulus of  V-M= 12.50  are obtained.The interstellar extinction in the cluster direction is found to follow the normal law. NGC 2587 is located at a distance of (2.70+/-0.70) kpc from the Sun and approx. 9.8 kpc from the Galactic centre.