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Astron. Astrophys. 360, 529-538 (2000)

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Photometric and integrated spectral study of the young open clusters Pismis 22, NGC 6178, NGC 6216 and Ruprecht 130 * **

A.E. Piatti 1, J.J. Clariá 1 and E. Bica 2

1 Observatorio Astronómico, Laprida 854, 5000 Córdoba, Argentina
2 Universidade Federal do Rio Grande do Sul, Depto. de Astronomía, CP 15051, Porto Alegre, 91500-970, Brazil

Received 4 April 2000 / Accepted 5 June 2000


We present CCD observations in the B, V, and I passbands obtained for stars in the fields of the open clusters Pismis 22, NGC 6178, NGC 6216, and Ruprecht 130, projected not far from the Galactic centre ([FORMULA]l [FORMULA] [FORMULA] 30o, [FORMULA]b[FORMULA] [FORMULA] 2o). The sample consists of about 790 stars reaching down to V [FORMULA] 18-19 mag. From the analysis of the colour magnitude diagrams, we confirmed the physical reality of the clusters and derived their reddening, distance and age. In addition, we obtained flux-calibrated integrated spectra in the range 3500-9200 Å for the cluster sample. The equivalent widths of the Balmer lines provided us with age estimates, while the comparison with template spectra allowed us to derive both foreground reddening and age. The photometric and spectroscopic results reveal that the four studied objects are young open clusters with ages ranging between 35 and 50 Myr. The clusters, located between 1.0 kpc and 4.3 kpc from the Sun, are affected by different amounts of interstellar visual absorption (0.6 [FORMULA] Av [FORMULA] 6.0).

Key words: Galaxy: open clusters and associations: general – Galaxy: open clusters and associations: individual: NGC 6178, NGC 6216, Pismis 22, Ruprecht 130

* Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la Repúbica Argentina and the National Universities of La Plata, Córdoba, and San Juan, Argentina, and at the University of Toronto (David Dunlap Observatory) 24-inch telescope, Las Campanas, Chile.
** Tables 3-6 are only available in electronic form at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr//pub/cats/J/A+A/360/529 ( or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/360/529

Send offprint requests to: A.E. Piatti (andres@mail.oac.uncor.edu)

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© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000