Open clusters in the Third Galactic Quadrant

II. The intermediate age open clusters NGC 2425 and NGC 2635

¹ CAAUL, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal e-mail: andre@oal.ul.pt
² Departamento de Astronómia, Universidad de Chile, Casilla 36-D, Santiago, Chile
³ Yale University, Department of Astronomy, PO Box 208101, New Haven, CT 06520-8101, USA
⁴ Dipartimento di Astronomia, Università di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
⁵ Facultad de Ciencias Astronómicas y Geofísicas de la UNLP, IALP-CONICET, Paseo del Bosque s/n, La Plata, Argentina

Received: 16 April 2005
Accepted: 29 July 2005

Abstract

We analyse CCD broad band () photometric data obtained in the fields of the poorly studied open clusters NGC 2425 and NGC 2635. Both clusters are found to be of intermediate age thus increasing the population of open clusters known to be of the age of, or older than, the Hyades. More explicitly, we find that NGC 2425 is a 2.2 Gyr old cluster, probably of solar metallicity, located at 3.5 kpc from the Sun. NGC 2635 is a Hyades age (600 Myr) cluster located at a distance of 4.0 kpc from the Sun. Its Colour Magnitude Diagram reveals that it is extremely metal poor for its age and position, thus making it a very interesting object in the context of Galactic Disk chemical evolution models.