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

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

Abstract

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 μm) 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 (>5σ) 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.