------------------------------------------------------------------------
From: Bob Blum  rblum@ctio.noao.edu 
To: gcnews@zia.aoc.nrao.edu
Subject: submit gcnews.tex ApJ, Nov 2003, in press

%astro-ph/0307291

\documentclass[12pt,preprint]{aastex}
\usepackage[nolists,tablesfirst]{endfloat}

\def\kms{km s$^{-1}$}

\def\pix{pix$^{-1}$}

\def\deg{$^\circ$}

\def\mic{{$\mu$m}}

\def\h2o{H$_2$O}

\def\ak{{\it $A_K$}}

\def\teff{$T_{\rm eff}$}

\def\mbol{$M_{\rm bol}$}

\def\aple{$\mathrel{\hbox{\rlap{\hbox{\lower4pt\hbox{$\sim$}}}\hbox{$<$}}}$}

\def\apge{$\mathrel{\hbox{\rlap{\hbox{\lower4pt\hbox{$\sim$}}}\hbox{$>$}}}$}

\begin{document}

\title{Really Cool Stars and the Star Formation History at the
Galactic Center}

\author{R. D. Blum{1},Solange V. Ram\'{\i}rez{2}, K. Sellgren{3}, K. 
Olsen{1}}

 \affil{Cerro Tololo Interamerican
Observatory, Casilla 603, La Serena, Chile\\ rblum@ctio.noao.edu}

 \affil{SIRTF Science
Center, JPL/Caltech, Pasadena, CA 91125,
USA\\solange@astro.caltech.edu}

 \affil{ Astronomy Department, The
Ohio State University, 140 West 18th Ave, Columbus, OH 43210, USA
\\sellgren@astronomy.ohio-state.edu}

\begin{abstract}

We present $\lambda$/$\Delta\lambda$ $=$ 550 to 1200 near infrared $H$
and $K$ spectra for a magnitude limited sample of 79 asymptotic giant
branch and cool supergiant stars in the central $\approx$ 5 pc
(diameter) of the Galaxy. We use a set of similar spectra obtained for
solar neighborhood stars with known \teff \ and \mbol \ that is in the
same range as the Galactic center (GC) sample to derive \teff \ and
\mbol \ for the GC sample. We then construct the Hertzsprung--Russell
(HRD) diagram for the GC sample. Using an automated maximum likelihood
routine, we derive a coarse star formation history of the GC.  We find
(1) roughly 75$\%$ of the stars formed in the central few pc are older
than 5 Gyr; (2) the star formation rate (SFR) is variable over time,
with a roughly 4 times higher star formation rate in the last 100 Myr
compared to the average SFR; (3) our model can only match dynamical
limits on the total mass of stars formed by limiting the IMF to masses
above 0.7 M$_\odot$. This could be a signature of mass segregation or
of the bias toward massive star formation from the unique star
formation conditions in the GC; (4) blue supergiants account for 12
$\%$ of the total sample observed, and the ratio of red to blue
supergiants is roughly 1.5; (5) models with isochrones with [Fe/H] =
0.0 over all ages fit the stars in our HRD better than models with
lower [Fe/H] in the oldest age bins, consistent with the finding of
Ramirez et al. (2000) that stars with ages between 10 Myr and 1 Gyr
have solar [Fe/H].

\end{abstract}

\end{document}