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From: "Don F. Figer"  figer@gc.astro.ucla.edu 
Subject: new abstract
Mime-Version: 1.0

% http://www.astro.ucla.edu/~figer  

\title{ The Pistol Star}

\author{\bf   Donald F. Figer$^1$, Francisco Najarro$^{2,5}$, Mark
Morris$^1$, 
Ian S. McLean$^1$, Thomas R. Geballe$^3$, Andrea M. Ghez$^1$, \&
Norbert Langer$^4$}

\institute{
$^1$ University of California, Los Angeles, Division of Astronomy \\
$^2$ Institut f\"ur Astronomie und Astrophysik der 
Universit\"at M\"unchen, Scheinerstr.\ 1,
D-81679 M\"unchen, Germany \\ 
$^3$ Joint Astronomy Centre, 660 N A'ohoku Place, University 
Park, Hilo, HI 96720 \\
$^4$Institut f\"ur Theoretische Physik und Astrophysik, 
Am Neuen Palais 10, D-14469 Potsdam, Germany \\
$^5$ CSIC, Instituto de Estructura de la Materia, Dpto. Fisica Molecular
Serrano 121, 28006 Madrid, Spain}

\vspace*{4mm}  \\ 


%  TEXT OF ABSTRACT below this line 
\begin{abstract}
We present new near-infrared data and an analysis which indicates that the
``Pistol Star'' is one of the most luminous stars known, 
adding another test point for massive star formation and stellar
evolution theories. 
We estimate an extinction of A_K = 3.2$\pm0.5$ using the near-infrared
colors of the star and surrounding stars in the young Quintuplet cluster. 
Using our wind/atmosphere code, we find two families of models which fit
the spectral energy
distribution and detailed line profiles. The lower luminosity models give L
= 10$^{6.6\pm0.2}$ \Lsun\
and \Teff\ = 10$^{4.15\pm0.01}$ K,
while the higher luminosity models give L = 10$^{7.2\pm0.2}$ \Lsun\ and
\Teff\ = 10$^{4.33\pm0.01}$ K;
the error in luminosity assumes an uncertainty of $\pm$0.5 in A_K, while
the error in \Teff\ is constrained
by detailed line modeling. 
The models also reveal a helium enriched surface. 
As previously existing stellar evolution models do not extend to such
high luminosities, we employ new evolutionary tracks for very massive stars
to determine
the initial mass and age of the Pistol Star, and estimate M$_{\rm initial}$
= 200$-$250 \Msun\
and an age of 1.7$-$2.1 Myrs.
The inferred luminosity and temperature place the star 
in a sparsely populated zone in the HR diagram where ``Luminous Blue
Variables'' (LBVs) are often found. 
This is consistent with our evolutionary models which predict that the star
is in
an unstable evolutionary stage. We interpret the star and its surrounding
nebula as an LBV which has
recently ejected large amounts of material. Our K-band speckle imaging data
reveal the star
to be single down to a projected separation of 110 AU.


\end{abstract}








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