Journal Article

NGC 2587: a sparse open cluster projected on to a populous star field

Andrés E. Piatti, Juan J. Clariá and Andrea V. Ahumada

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 397, issue 2, pages 1073-1083
Published in print August 2009 | ISSN: 0035-8711
Published online July 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.15069.x
NGC 2587: a sparse open cluster projected on to a populous star field

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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∼ 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: μα=−4.3 ± 3.6 mas yr−1 and μδ=−2.5 ± 3.4 mas yr−1. Adopting the theoretical metal content Z= 0.02, which provides the best global fit, we derive a cluster age of 500+60−50. Simultaneously, colour excesses E(BV) = 0.10 and E(VI) = 0.15 and an apparent distance modulus of VMV= 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 ∼9.8 kpc from the Galactic centre.

Keywords: techniques: photometric; galaxy: open clusters and associations: general; Galaxy: open clusters and associations: individual: (NGC 2587)

Journal Article.  5559 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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