NGC 2587: a sparse open cluster projected on to a populous star field |
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Authors: | André s E. Piatti,Juan J. Clariá , Andrea V. Ahumada |
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Affiliation: | Instituto de Astronomía y Física del Espacio, CC 67, Suc. 28, 1428 Ciudad de Buenos Aires, Argentina;Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, X5000BGR Córdoba, Argentina;European Southern Observatory, Alonso de Córdova 3107, Santiago, Chile |
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Abstract: | 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 ( B − V ) = 0.10 and E ( V − I ) = 0.15 and an apparent distance modulus of V − MV = 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. |
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Keywords: | techniques: photometric galaxy: open clusters and associations: general Galaxy: open clusters and associations: individual: (NGC 2587) |
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