Revealing the parameters of the open cluster Ruprecht 58

We present results of a study that combines UBVI 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 together with the analysis of CCD UBVI 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 confirm Ruprecht 58 is a real cluster with mean absolute proper motions μαcosδ = −2.77 ± 0.45 mas/yr and μδ = 4.54 ± 0.45 mas/yr in the magnitude range 13.5 < V < 14.5 and μαcosδ = −2.70 ± 0.32 mas/yr and μδ = 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 ≈1.4 to ≈4m⊙.