Colour–Magnitude analysis of five old open clusters

¹ Università di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: ortolani@pd.astro.it
² Universidade Federal do Rio Grande do Sul, Dept. de Astronomia, CP 15051, Porto Alegre 91500-970, Brazil e-mail: bica@if.ufrgs.br
³ Universidade de São Paulo, Rua do Matão 1226, 05508-900 São Paulo, Brazil e-mail: barbuy@astro.iag.usp.br

Received: 6 November 2004
Accepted: 3 February 2005

Abstract

The Galileo Telescope was used to carry out BV photometry of five faint open clusters, for which no Colour Magnitude Diagrams were available in the literature. The clusters Berkeley 24, Berkeley 35, Berkeley 78, PWM 1, and PWM 4 are found to be old open clusters. Berkeley 24, Berkeley 35, and PWM 4 show a red clump. We fitted Padova isochrones to derive reddening and distance. The clusters Berkeley 35 and Berkeley 78 show low and 0.01 compatible with their relatively high Galactic latitudes, whereas higher values of , 0.94 and 0.62 are found for Berkeley 24, PMW1, PMW4. Their distances to the Sun are in the range kpc implying that they are at distances of 11.5 to 13.5 kpc from the Galactic center. The isochrone fitting show ages in the range 1.0 < Age (Gyr) < 6.3. Further discussion of the different methods used to derive age is given, in particular using the difference in magnitude between turn-off and giant clump, which gives lower ages. The contribution of the five old open clusters studied here, with basic parameters known, increases the overall sample to 108 objects. An important addition is the very old (6.3 Gyr) open cluster PWM 4.