Vilnius photometry and Gaia astrometry of Melotte 105

Abstract

Archival Vilnius CCD photometric observations are presented for the heavily reddened star cluster Melotte 105, resulting in colour-magnitude diagrams and spectral class estimates. There is considerable lack of agreement between studies for reddening, age and distance for this cluster explaining why the archival data are being made available by this paper. The derived reddening E(B - V) = 0.34 +/- 0.04 mag and the distance V - MV = 12.9 +/- 0.3 mag are directly from the Vilnius photometry. The Gaia Data Release 2 (DR2) and Vilnius photometric data of the cluster were used to estimate the structural parameters of the cluster, probability of stellar membership in the cluster, the distance modulus and the cluster age. Lack of Y band observations prevented determination of metal abundance. The values of the colour excess and distance module are determined by two different methods (i.e., Q and Zero AgeMain Sequence or ZAMS methods). A distance modulus of 12.85 +/- 0.07 mag was derived by ZAMS fitting, in good agreement with the above estimate. ZAMS fitting indicates a reddening of 0.403 +/- 0.02 mag, within two sigma of the estimate above. The cluster's metallicity and age are estimated to be 0.24 dex and 240 +/- 25 Myr, respectively. The derived mass function is in good agreement with the Salpeter slope. The cluster space velocity components (U, V, W) were determined as (-3.90 +/- 3.34, -13.76 +/- 5.69, +3.45 +/- 0.41) km/s. Perigalactic and apogalactic distances were obtained as Rp = 6.85 and Ra = 7.44 kpc respectively. The maximum vertical distance from the Galactic plane was calculated as Zmax = 84 pc and the eccentricity of the orbit was determined as e = 0.042.