On open cluster physical parameters from 2MASS data

The near infrared range has opened a new window to study stellar populations in the Galaxy, in the Local Groud and beyond. Despite the large and growing use of these data, insufficient efforts have been made in the direction to calibrate stellar physical parameters such as age, reddening and distance. This can also be achieved using near infrared and optical data together. Furthermore, the huge amounts of photometric data available now and in the incoming years, demand the development of automated and statistical isochrone fittings to cope with such data. With this in mind, we analyse 2MASS data in order to determine physical parameters for a sample of 9 open clusters. As a first step, we determined the age, reddening and distance values for each cluster applying the classical isochrone fitting (by eye). Subsequently, we employed an automated procedure which compares synthetic colour-magnitude diagrams to observed ones, making use of the likelihood statistics to find the best solution. We also carried out structural analyses of the clusters using stellar radial density profiles. Both classical and statistical isochrone fittings revealed that there can be disagreement between physical parameters obtained from near infrared data analysis and the literature corresponding ones, most based on optical and UV data. Concerning the observed cluster structures, they were studied for the first time. We found evidence of various dynamical stages in the sample.

► We employ 2MASS near infrared data to determine astrophysical parameters (age, reddening and distance) for 9 OCs by means of colour-magnitude diagram analyses. ► Solutions from classical isochrone fitting were used as input values for refined automated isochrone fittings. ► The automated procedure compared synthetic CMDs to observed ones using likelihood statistics. ► Radial density profile analyses provided structural parameters which, associated to CMD analyses, inferred evolutionary stages. ► Some near infrared parameters were different form the literature (optical) ones..