EDP Sciences
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Volume 374, Number 2, August I 2001
Page(s) 554 - 563
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20010741

A&A 374, 554-563 (2001)
DOI: 10.1051/0004-6361:20010741

Open clusters or their remnants: $\vec{B}$ and $\vec{V}$ photometry of NGC 1901 and NGC 1252

D. B. Pavani1, E. Bica1, C. M. Dutra1, H. Dottori1, B. X. Santiago1, G. Carranza2 and R. J. Díaz2

1  Universidade Federal do Rio Grande do Sul, IF, CP 15051, Porto Alegre 91501-970, RS, Brazil
2  Observatorio Astronómico de Córdoba, Laprida 854, 5000, Córdoba, Argentina

(Received 23 January 2001 / Accepted 21 May 2001)

Photometry in the B and V bands is presented for the southern stellar groups NGC 1901 and NGC 1252. NGC 1901 is often described as an open cluster while NGC 1252 consists of a concentration of about 20 stars centered $\approx$20$^{\prime}$ north of the original New General Catalogue coordinates, and at the southwest edge of the large region previously assigned to this object in the literature. NGC 1901 has a clear main sequence and shares similarities with the Hyades. We derive a reddening value E(B-V) = 0.04, a distance from the Sun $d_{\odot} = 0.45$ kpc (Z = -0.23 kpc) and an age 0.6 $\pm$ 0.1 Gyr. NGC 1901 is conclusively a physical system, dynamically comparable to or more evolved than the Hyades. The colour-magnitude diagram of NGC 1252 suggests a turnoff and main sequence, and a total of 12 probable members. We simulated the Galactic field colour-magnitude diagram in the same direction and found it to be a poor match to NGC 1252, suggesting that NGC 1252 is not a field fluctuation. Isochrone fitting to the probable members is consistent with E(B-V) = 0.02, $d_{\odot} = 0.64$ kpc (Z = -0.46 kpc) and an age 3 $\pm$ 1 Gyr. NGC 1252 cannot be ruled out as a physical group with the available data. If so, evidence is found that it is not a classical open cluster, but rather an open cluster remnant.

Key words: galaxy: open clusters and stellar associations -- galaxies: individual: NGC 1901, NGC 1252

Offprint request: D. B. Pavani, dpavani@if.ufrgs.br

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© ESO 2001