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A&A Supplement series, Vol. 121, April I 1997, 9-29

Received April 2; accepted June 26, 1996

Multicolour deep CCD photometric study of the moderately young southern open star clusters NGC 3228, NGC 4103, NGC 5662 and NGC 6087

R. Sagartex2html_wrap2240tex2html_wrap_inline2204gif - R.D. Cannontex2html_wrap2242

Send offprint request: R. Sagar

tex2html_wrap2244  Indian Institute of Astrophysics, Bangalore 560034, India
e-mail address:
tex2html_wrap2246  Anglo-Australian Observatory, P.O. Box 296, Epping NSW 2121, Australia
e-mail address:


CCD observations in the U, B, V, R and I passbands have been used to generate colour-colour and deep colour-magnitude diagrams for the young open star clusters NGC 3228, NGC 4103, NGC 5662 and NGC 6087. The sample consists of about 2000 stars reaching down to tex2html_wrap_inline2216. The interstellar extinction across the face of the imaged cluster regions seems to be uniform with average values of E(B-V) = 0.31, 0.34 and 0.22 mag for NGC 4103, NGC 5662 and NGC 6087 respectively. The distances to the clusters NGC 3228, NGC 4103, NGC 5662 and NGC 6087 have been estimated as tex2html_wrap_inline2220, tex2html_wrap_inline2222, tex2html_wrap_inline2224 and tex2html_wrap_inline2226 kpc respectively, while the corresponding ages estimated from the theoretical stellar evolutionary isochrones fitted to the bright proper motion cluster members are tex2html_wrap_inline2228, 30, 80 and 65 Myr respectively. Present data are consistent with the membership of the Cepheid variable V Cen to NGC 5662 and of S Norm to NGC 6087. Heavy contamination by foreground and background field stars has unfortunately made it impossible to reach definite conclusions about the faint luminosity function, and the data do not reach faint enough limits to investigate pre-main sequence stars.

keywords: HR diagram -- stars: evolution -- open clusters and associations: individual: NGC 3228, NGC 4103, NGC 5662, NGC 6087

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