The young open cluster Markarian 50

Abstract

We report on a deep CCD UBV(RI) C photometric survey in the region of the young open cluster Markarian 50. The new photometric data allow us to extend the cluster membership down to V ≈ 17.5, about 2 mag deeper than any previous investigation. On the basis of these data we derive a distance d = 3460 ± 350 pc (V o - M v = 12.7 ± 0.2), which turns out to be only slightly lower than previous estimates. The cluster presents differential reddening, with E(B-V) values ranging from 0.69 to 1.1. The brightest member (HD 219460) is a double star, which we separate photometrically for the first time, providing individual magnitudes and colours for each component. One of them is a Wolf-Rayet (WR) star and, according to evolutionary models, the mass of its progenitor should be greater than ∼20 M⊙. The age obtained for the cluster is 7.5 ± 2 Myr and the mass function for the most massive stars (M > 1 M⊙) presents a slope x ≈ 1.0.