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From: Daniel Schaerer  schaerer@obs-mip.fr 
Mime-Version: 1.0
To: gcnews@aoc.nrao.edu
Subject: submit massive.tex Invited review to appear in "Active Galactic Nuclei, 
Dense Stellar Systems  and Galactic Environments", Eds. A.C. Baker, S. Lamb, 
J.J. Perry, ASP  Conf. Series, 1998
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\title{	Massive Star Evolution in Different Environments}
\author{  Daniel Schaerer$^{1,2,3}$} 
\institute{ {$^1$ Laboratoire d'Astrophysique, Observatoire
Midi-Pyr\'en\'ees,
	14, Av. E. Belin, F-31400 Toulouse, France (schaerer@obs-mip.fr) \\
	$^2$ Space Telescope Science Institute, 
	Baltimore, MD 21218, USA\\
	  $^3$  Geneva Observatory, CH-1290 Sauverny, Switzerland 
} \\
    % WRITE TEXT OF ABSTRACT HERE 
\begin{abstract}
We review the properties of massive star evolution in different
environments, where the major environmental factor is metallicity.
Comparisons between evolutionary models and observations
of massive OB, WR stars and related objects are presented. 
We also review several observations asking for future improvements of 
stellar models and theoretical developments in this respect.
We summarize evolutionary scenarios for the most massive stars and 
try to clarify recent questions regarding their evolutionary status
as core-H or core-He burning objects.

Another environmental effect, which might affect stellar evolution
is a cluster environment with a high stellar density.
As test cases of massive star evolution in dense clusters
we summarize recent work on the densest known resolved young 
clusters: R136, NGC 3603, and the three Galactic Center (GC) star 
clusters -- the central cluster, Quintuplet and the ``Arches'' cluster.
For the central cluster we present new comparisons between stellar
parameters 
of emission line stars derived by Najarro \etal (1994, 1997), 
and appropriate evolutionary models.
From their parameters we argue that most of these stars can be regarded 
as WNL stars, and do hence not necessarily represent a peculiar class. 
We suggest that some apparent differences with well known WR stars 
can be understood in terms of their core burning stage and/or
other changes due to a high metallicity.
% in the GC.
Based on our present knowledge 
we conclude that in young clusters with central stellar densities up to 
$\rho_c \sim 10^{5-6} \, \msun {\rm pc}^{-3}$
no compelling evidence for a secondary effect influencing the evolution 
of massive stars has yet been found.
\end{abstract}
{\bf  Invited review to appear in ``Active Galactic Nuclei, Dense
Stellar Systems 
	and Galactic Environments'', Eds.  A.C. Baker, S. Lamb, J.J. Perry, ASP 
	Conf.~Series, 1998.
	(Revised an extended 1998, original version august 1996) }
{\it Preprints from} {\tt    schaerer@obs-mip.fr}
%{\it or by anonymous ftp to} {\tt    ... }
{\it or on the web at} {\tt
http://www.obs-mip.fr/omp/astro/people/schaerer/Preprints.html }

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