Poster abstract
Westerlund 1: a 2D approach for the study of its elongated shape and its spatially varying IMF
Abstract
Westerlund 1 (Wd1) is the most massive compact young stellar cluster in the Local Group, comparable in mass to Super Star Clusters in starburst galaxies. As so, it is one of the few test cases in the Milky Way for the study of intense events of star formation over the entire range of stellar masses. Moreover, given its large total mass, Wd1 can also be considered as a prototype for the study of stellar dynamics in precursors of Globular Cluster.
I'll present a new approach in the study of Wd1 properties, which incorporates a 2D mapping of the incompleteness correction, and a new probabilistic technique to obtain an optimized field decontamination when using only photometric data. The cleaned colour-magnitude diagram, together with up-to-date MS and PMS stellar models, is used to derive basic properties of the cluster such as distance, extinction and age. We found values of d = 4 kpc, Ak = 0.9 mag and t = 4Myr.
Our new 2D approach furthermore facilitates an unbiased study of the spatial properties of Wd1, without any a priori assumption on the cluster symmetry and on the structure of the completeness pattern. Thanks to that we are able to investigate the local variations of the IMF slope which
indicate that mass segregation is present in Westerlund 1.
From the analysis of stellar density contours we infer that Wd1 has a quite elongated shape; we have already found indications of elongation in our previous study (Brandner et al., 2008) where, on the other hand, we assumed a spherical shape for the incompleteness pattern; the findings of the present work indicate that elongation is even more pronounced and then that an asymmetric incompleteness correction is necessary to correctly determine the shape of Wd 1.
The observed elongation points to the fact that the internal dynamics of Wd 1 is probably not trivial and probably the overall structure is not in dynamical equilibrium, a challenge for theoretical studies of clusters dynamical evolution.
I'll present a new approach in the study of Wd1 properties, which incorporates a 2D mapping of the incompleteness correction, and a new probabilistic technique to obtain an optimized field decontamination when using only photometric data. The cleaned colour-magnitude diagram, together with up-to-date MS and PMS stellar models, is used to derive basic properties of the cluster such as distance, extinction and age. We found values of d = 4 kpc, Ak = 0.9 mag and t = 4Myr.
Our new 2D approach furthermore facilitates an unbiased study of the spatial properties of Wd1, without any a priori assumption on the cluster symmetry and on the structure of the completeness pattern. Thanks to that we are able to investigate the local variations of the IMF slope which
indicate that mass segregation is present in Westerlund 1.
From the analysis of stellar density contours we infer that Wd1 has a quite elongated shape; we have already found indications of elongation in our previous study (Brandner et al., 2008) where, on the other hand, we assumed a spherical shape for the incompleteness pattern; the findings of the present work indicate that elongation is even more pronounced and then that an asymmetric incompleteness correction is necessary to correctly determine the shape of Wd 1.
The observed elongation points to the fact that the internal dynamics of Wd 1 is probably not trivial and probably the overall structure is not in dynamical equilibrium, a challenge for theoretical studies of clusters dynamical evolution.