EDP Sciences
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Volume 482, Number 1, April IV 2008
Page(s) 173 - 178
Section Galactic structure, stellar clusters, and populations
DOI http://dx.doi.org/10.1051/0004-6361:20078352
Published online 04 March 2008

A&A 482, 173-178 (2008)
DOI: 10.1051/0004-6361:20078352

IRS 13N: a new comoving group of sources at the Galactic center

K. Muzic1, 2, R. Schödel3, A. Eckart1, 2, L. Meyer4, and A. Zensus2, 1

1  I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
    e-mail: muzic@ph1.uni-koeln.de
2  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3  Instituto de Astrofísica de Andalucía, Camino Bajo de Huétor 50, 18008 Granada, Spain
4  University of California, Division of Astronomy and Astrophysics, Los Angeles, CA 90095-4705, USA

(Received 25 July 2007 / Accepted 26 February 2008)

Context. The Galactic center IRS 13E cluster is located ~3.2'' from SgrA*. It is an extremely dense stellar association containing several Wolf-Rayet and O-type stars, at least four of which show a common velocity. Only half an arcsecond north of IRS 13E there is a complex of extremely red sources so-called IRS 13N. Their nature is still unclear. Based on analysis of their colors, there are two main possibilities: (1) dust-embedded sources older than few Myr or (2) extremely young objects with ages less than 1 Myr.
Aims. We present the first proper motion measurements of IRS 13N members and then give proper motions of four of IRS 13E stars resolved in the L'-band.
Methods. The L'-band (3.8 $\mu$m) observations were carried out using the NACO adaptive optics system at the ESO VLT. Proper motions were obtained by linear fitting the stellar positions extracted by StarFinder as a function of time, weighted by positional uncertainties.
Results. We show that six of seven resolved northern sources show a common proper motion, thus revealing a new comoving group of stars in the central half parsec of the Milky Way. The common proper motions of IRS 13E and IRS 13N clusters are significantly (>5$\sigma$) different. We also performed a fitting of the positional data for those stars onto Keplerian orbits, assuming SgrA* as the center of the orbit. Our results favor the very young stars hypothesis.

Key words: Galaxy: center -- infrared: stars -- astrometry -- open clusters and associations: indvidual: IRS 13N -- open clusters and associations: individual: IRS 13E

© ESO 2008