Revealing the parameters of the open cluster Ruprecht 58

Abstract

We present results of a study that combines UBV I photometry, MK spectral classification and proper motions in the area of the, up to now unknown, open cluster Ruprecht 58 at the Puppis region. Star counts from the 2MASS data catalog to- gether with the analysis of CCD UBV I photometry demonstrate that it is a real open cluster with 9' size approximately. The cluster is placed at a distance of 3.9 kpc and is about 250 Myr old with mean reddening E(_B-V ) = 0:33 mag. Proper motions con¯rm Ruprecht 58 is a real cluster with mean absolute proper motions ¹®cos± = ¡2:77§0:45 mas/yr and ¹± = 4:54§0:45 mas/yr in the magnitude range 13:5 < V < 14:5 and ¹®cos± = ¡2:70 § 0:32 mas/yr and ¹± = 3:19 § 0:32 mas/yr in the range 14:5 < V < 16:0. The computation of the cluster mass spectrum slope yielded x = 1:8 in the mass range from ¼ 1:4 to ¼ 4m¯.