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From: Jean-Pierre Maillard  maillard@iap.fr 
To: gcnews@zia.aoc.nrao.edu
Subject: submit IRS13 A&A, accepted

\documentstyle[apjfonts,emulateapj]{article}
\begin{document}
\title{The nature of the Galactic Center source IRS~13 revealed by high 
spatial resolution in the infrared}
\author{Jean-Pierre Maillard (1), Thibaut Paumard (1,2), Susan Stolovy (3),
           François Rigaut (4)}

\institute{(1) Institut d'Astrophysique de Paris (CNRS), 98b Blvd Arago, 
           75014 Paris, France
           (2) on leave from IAP, Max-Planck-Institut fuer extraterrestrische
           Physik, Postfach 1312, D-85741 Garching, Germany
           (3) Spitzer Science Center, CalTech, MS 220-6, Pasadena, CA 91125,
           USA
           (4) Gemini North Headquarter, Hilo, HI 96720, USA
}

\begin{abstract}
High spatial resolution observations in the 1 to 3.5 micron region of the
Galactic Center source known historically as IRS 13 are presented. They include
ground-based adaptive optics images in the H, Kp (2.12/0.4 micron) and L bands,
HST-NICMOS data in filters between 1.1 and 2.2 micron, and integral field
spectroscopic data from BEAR, an Imaging FTS, in the HeI 2.06 micron and the
Br$\gamma$ line regions. Analysis of all these data provides a completely new
picture of the main component IRS~13E, which appears as a cluster of seven
individual stars within a projected diameter of ~0.5'' (0.02 pc). The brightest
sources, 13E1, 13E2, 13E3 which is detected as a binary, and 13E4, are all
massive stars of different type. The star 13E1 is a luminous, blue object, with
no detected emission line. 13E2 and 13E4 are two hot, high-mass emission line
stars, 13E2 being at the WR stage and 13E4 a massive O-type star. In contrast,
13E3A and B are extremely red objects, proposed as other examples of dusty WR
stars, like IRS 21 (Tanner et al. 2002). All these sources have a common
westward proper motion indicating they are bounded. Two fainter sources,
detected after deconvolution of the AO images in the H and Kp bands, are also
identified. One, that we call 13E5, is a red source similar to 13E3A and B,
while the other one, 13E6, is probably a main sequence O star in front of the
cluster.  Considering this exceptional concentration of comoving massive hot
stars, IRS 13E is proposed as the remaining core of a massive star cluster,
which could harbor an intermediate-mass black hole (IMBH) (Portegies Zwart \&
McMillan 2002) of ~1300 M_sun. This detection plays in favor of a scenario,
first suggested by Gerhard (2001), in which the helium stars and the other hot
stars in the central parsec originate from the stripping of a massive cluster
formed several tens of pc from the center. This cluster would have spiraled
towards SgrA*, and IRS 13E would be its remnant. Furthermore, IRS 13E might be
the second black hole needed according to a model by Hansen \& Milosavljevic
(2003) to drag massive main-sequence stars, in the required timescale, very
close to the massive black hole.  The detection of a discrete X-ray emission
(Baganoff et al. 2003) at the IRS~13 position is examined in this context.
\end{abstract}