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 IRS13N_abstract.tex A&A, 2008, in press
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%arXiv:0802.4004

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\title{IRS$\,$13N: a new comoving group of sources at the Galactic Center}
\subtitle{}
\author{K. Muzic$^{1,2}$, R. Sch\"odel$^3$, A. Eckart$^{1,2}$, L. 
Meyer$^4$, A. Zensus$^{2,1}$}
\institute{1) I. Physikalisches Institut, Universit\"at zu K\"oln,
          Z\"ulpicher Str. 77,
          50937 K\"oln, Germany\\
          2) Max-Planck-Institut f\"ur Radioastronomie,
          Auf dem H\"ugel 69,
      53121 Bonn, Germany\\
          3) Instituto de Astrof\'isica de Andaluc\'ia,
             Camino Bajo de Huétor 50,
             18008 Granada, Spain \\
          4) University of California, Division of Astronomy and 
Astrophysics,
         Los Angeles, CA 90095-4705\\
          \email{muzic@ph1.uni-koeln.de} }

\date{Received  / Accepted }
\begin{document}
\abstract
{The Galactic Center IRS$\,$13E cluster is located $\sim$3.2'' from 
SgrA*. It is an extremely
dense stellar association containing several Wolf-Rayet and O-type 
stars, at least four of which show
a common velocity. Only half an arcsecond north from IRS$\,$13E
there is a complex of extremely red sources, so-called IRS$\,$13N. Their 
nature is
still unclear. Based on the analysis
of their colors, there are two main possibilities:
(1) dust embedded sources older than few
Myr, or (2) extremely young objects with ages less than 1Myr.}
{We present the first proper motion measurements of IRS$\,$13N members, 
and additionally give
proper motions of four of IRS$\,$13E stars resolved in the L'-band.}
{The L'-band (3.8$\mu$m) observations have been carried out using the 
NACO adaptive
optics system at the ESO VLT.
Proper motions
have been obtained by linear fitting of the stellar positions
extracted by StarFinder as a function of time, weighted by positional 
uncertainties.}   {We show that six of seven resolved northern sources 
show a common proper motion, thus revealing
a new comoving group of stars in the central half parsec of the Milky 
Way. The common proper motions
of IRS$\,$13E and IRS$\,$13N clusters are significantly 
($>$5$\,$$\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.}
{}
\keywords{Galaxy:center -- infrared:stars}
\end{document}