SCYON Abstract

Received on June 1 2010

Internal dynamics and membership of the NGC 3603 Young Cluster from microarcsecond astrometry

AuthorsBoyke Rochau (1), Wolfgang Brandner (1), Andrea Stolte (2), Mario Gennaro (1), Dimitrios Gouliermis (1), Nicola Da Rio (1), Natalia Dzyurkevich (1), and Thomas Henning (1)
Affiliation(1) Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg
(2) I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln
To appear inAstrophysical Journal Letters
Contactrochau@mpia.de
URLhttp://stacks.iop.org/2041-8205/716/L90
Links NGC 3603 Young Cluster

Abstract

We have analyzed two epochs of HST/WFPC2 observations of the young Galactic starburst cluster in NGC 3603 with the aim to study its internal dynamics and stellar population. Relative proper motions measured over 10.15 yrs of more than 800 stars enable us to distinguish cluster members from field stars. The best-fitting isochrone yields Av=4.6-4.7 mag, a distance of 6.6-6.9 kpc, and an age of 1 Myr for NGC 3603 Young Cluster (NYC). We identify pre-main-sequence/main-sequence transition stars located in the short-lived radiative-convective gap, which in the NYC occurs in the mass range 3.5-3.8 Msun. We also identify a sparse population of stars with an age of 4 Myr, which appear to be the lower mass counterparts to previously discovered blue supergiants located in the giant HII region NGC 3603. For the first time, we are able to measure the internal velocity dispersion of a starburst cluster from 234 stars with I < 18.5 mag to σpm1D=141+/-27 μas/yr (4.5+/-0.8 km/s at a distance of 6.75 kpc). As stars with masses between 1.7 and 9 Msun all exhibit the same velocity dispersion, the cluster stars have not yet reached equipartition of kinetic energy (i.e., the cluster is not in virial equilibrium). The results highlight the power of combining high-precision astrometry and photometry, and emphasize the role of NYC as a benchmark object for testing stellar evolution models and dynamical models for young clusters and as a template for extragalactic starburst clusters.