------------------------------------------------------------------------
 s2.tex  ApJL, accepted
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-MailScanner-Information: Please contact the postmaster@aoc.nrao.edu for more information
X-MailScanner: Found to be clean
X-MailScanner-SpamCheck: not spam, SpamAssassin (not cached, score=0,
	required 5, autolearn=disabled)
X-MailScanner-From: martins@mpe.mpg.de
X-Spam-Status: No

%astro-ph/0711.3344

\begin{document}

\title{On the nature of the fast moving star S2 in the Galactic Center 
\footnote{Based on observations collected at the ESO Very Large 
Telescope (programs 075.B
-0547, 076.B-0259, 077.B-0503, 078.B-0520 and 179.B-0261)}}

\author{F. Martins \altaffilmark{1}, S. Gillessen \altaffilmark{1}, F. 
Eisenhauer \altaffilmark{1}, R. Genzel \altaffilmark{1,2}, T. Ott 
\altaffilmark{1}, S. Tr


\altaffiltext{1}{Max Planck Institute of Extraterrestrial Physics, 
Postfach 1312, D-85741, Garching, Germany}
\altaffiltext{2}{Department of Physics, University of California, CA 
94720, Berkeley, USA}

\begin{abstract}
We analyze the properties of the star S2 orbiting the supermassive
black hole at the center of the Galaxy. A high quality SINFONI H and K band
spectrum obtained from coadding  23.5 hours of observation
between 2004 and 2007 reveals that S2 is an early B dwarf
(B0--2.5V). Using model atmospheres, we constrain its stellar and wind
properties. We show that S2 is a genuine massive star, and not the
core of a stripped giant star as sometimes speculated to resolve the
problem of star formation so close to the supermassive black hole. We
give an upper limit on its mass loss rate, and show that it is He
enriched, possibly because of the presence of a magnetic field.
\end{abstract}