------------------------------------------------------------------------
 varcent.tex ApJ, April 2007, in press
Date: Fri, 5 Jan 2007 13:57:09 -0800
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% astro-ph/0701082

\documentstyle{article}
\begin{document}

\title{Photometric Stellar Variability in the Galactic Center}

\author{M. Rafelski, A. M. Ghez, S. D. Hornstein, J. R. Lu, M. Morris}
\affil{Division of Astronomy and Astrophysics, UCLA, Los Angeles, CA  
90095-1547}

\begin{abstract}

We report the results of a diffraction-limited, photometric variability
study of  the central 5$\tt''$ $\times$ 5$\tt''$ of the Galaxy  
conducted over the past 10 years
using speckle imaging techniques on the W. M. Keck I 10 m telescope.
Within our limiting magnitude of $m_{K} < 16$ mag for images made  
from a single
night of data, we find a minimum of 15 K[2.2 $\micron$]-band variable  
stars out of 131 monitored stars.
While large populations of binaries have been posited to exist in
this region, both to explain the presence of young stars in the  
vicinity of
a black hole and because of the high stellar densities, only two  
binaries are identified
in this study. First is the previously identified Ofpe/WN9 equal mass
eclipsing binary star IRS 16SW, for which we measure an orbital period
of $19.448 \pm 0.002$ days. In contrast to recent results, our data  
on IRS 16SW
show an asymmetric phased light curve with
a much steeper fall-time than rise-time,
which may be due to tidal deformations caused
by the proximity of the stars in their orbits.
Second is the WC 9 Wolf-Rayet star IRS 29N; its observed photometric  
variation over a
few year time-scale is likely due to episodic dust production in a
binary system containing two windy stars.
Our sample also includes 4 candidate
Luminous Blue Variable (LBV) stars (IRS 16NE, 16C, 16NW, 16SW).
While 2 of them show variability, none show the
characteristic of LBVs large increase or decrease in luminosity.  
However, our
time baseline is too short to rule them out as LBVs. Nonetheless, the  
lack of
evidence for these stars to be LBVs and their coexistence with a  
significant surrounding population
of well established Wolf-Rayet stars is consistent with needing only  
a single recent starburst
event at the Galactic center to account for all of the known, young,  
massive stars.
Among the remaining variable stars, the majority are early-type stars  
and three are
possibly variable due to line of sight extinction variations.
For the 7 OB stars at the center of our field of view that have well- 
determined 3-dimensional
orbits, we see no evidence of flares or dimming of their light, which
limits the possibility of a cold, geometrically-thin inactive  
accretion disk
around the supermassive black hole, Sgr A$^{*}$.

\end{abstract}

\end{document}

----------------------------------
Marc Rafelski
Graduate Student
UCLA Astronomy and Astrophysics
marcar@astro.ucla.edu
----------------------------------