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Issue A&A
Volume 437, Number 2, July II 2005
Page(s) 457 - 466
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20041792



A&A 437, 457-466 (2005)
DOI: 10.1051/0004-6361:20041792

uvby - H$_{\beta}$ CCD photometry and membership segregation of the open cluster NGC 2548; gaps in the Main Sequence of open clusters

L. Balaguer-Núñez1, 2, 3, C. Jordi1, 4 and D. Galadí-Enríquez5

1  Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Avda. Diagonal 647, 08028 Barcelona, Spain
    e-mail: Lola.Balaguer@am.ub.es
2  Shanghai Astronomical Observatory, CAS Shanghai 200030, PR China
3  Institute of Astronomy, Madingley Road, CB3 OHA Cambridge, UK
4  CER for Astrophysics, Particle Physics and Cosmology, associated with Instituto de Ciencias del Espacio-CSIC
5  Centro de Astrobiología (CSIC-INTA). Carretera de Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain

(Received 4 August 2004 / Accepted 14 March 2005 )

Abstract
Deep CCD photometry in the $uvby-{\rm H}_{\beta}$ intermediate-band system is presented for the cluster NGC 2548 (M 48). A complete membership analysis based on astrometric and photometric criteria is applied. The photometric analysis of a selected sample of stars yields a reddening value of $E(b-y)= 0.06\pm0.03$, a distance modulus of $V_0-M_V= 9.3\pm0.5$ (725 pc) and a metallicity of [ Fe/H $] = - 0.24 \pm0.27$. Through isochrone fitting we find an age of $\log t = 8.6 \pm0.1$ (400 Myr). Our optical photometry and $\it JHK$ from 2MASS are combined to derive effective temperatures of cluster member stars. The effective temperature distribution along the main sequence of the cluster shows several gaps. A test to study the significance of these gaps in the main sequence of the HR diagram has been applied. The method is also applied to several other open clusters (Pleiades, Hyades, NGC 1817 and M 67) to construct a sequence of metallicities and ages. The comparison of the results of each cluster gives four gaps with high significance (one of them, centred at 4900 K, has not been previously reported).


Key words: Galaxy: open clusters and associations: individual: NGC 2548 -- techniques: photometric -- astrometry -- methods: observational -- methods: data analysis

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