A photometric investigation of the young open cluster Trumpler 15

In this paper we present and analyse new CCD UBVRI photometry down to V ≈ 21 in the region of the young open cluster Trumpler 15, located in the Carina spiral feature. The cluster is rather compact and has a core radius of about 2 arcmin, which translates to about 1 pc at the distance of the cluster. We provide the first CCD investigation and update its fundamental parameters. We identify 90 candidate photometric members on the base of the position in the colour-colour and colour-magnitude diagrams. This sample allows us to obtain a distance of 2.4 ± 0.3 kpc from the Sun and a reddening E(B - V) = 0.52 ± 0.07. We confirm that the cluster is young, and fix a upper limit of 6 × 106 yr to its age. In addition, we draw attention to the lower part of the main sequence (MS) suggesting that some stars can be in contracting phase and on a gap in the MS, which we show to be a real feature, the B1-B5 gap found in other young open clusters. We finally study in detail the extinction toward Trumpler 15 concluding that it is normal and suggesting a value of 2.89 ± 0.19 for the ratio of total to selective absorption RV.