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|%astro-ph/|0604612

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\title{Near-IR Spectroscopy of OH/IR stars in the Galactic Centre}
\author{E. Vanhollebeke \inst{1} \and J.A.D.L. Blommaert \inst{1} \and
  M. Schultheis \inst{2} \and B. Aringer \inst{3} \and A. Lan\c{c}on 
\inst{4}}
\institute{\Leuven \and CNRS UMR6091, Observatoire de Besan\c{c}on,
  BP1615, F-25010 Besan\c{c}on, France \and \Wien \and \Strasbourg }

\offprints{E. Vanhollebeke, \email{evelien@ster.kuleuven.be}}

\date{Received / Accepted }

\abstract
{Galactic Centre (GC) OH/IR stars can be, based on the expansion
  velocities of their circumstellar shells, divided into two groups
  which are kinematically different and therefore are believed to
  have evolved from different stellar populations.}
{To study the metallicity distribution of the OH/IR stars population in
the GC on basis of a theoretical relation between EW(Na), EW(Ca)
and EW(CO) and the metallicity.}
{For 70 OH/IR stars in the GC, we obtained near-IR spectra.
 The equivalent line widths of
\ion{Na}{i}, \ion{Ca}{i}, \element[][12]{CO}(2,0) and the curvature of
the spectrum around 1.6~\micron\ due to water absorption are determined.}
{The near-IR spectrum of OH/IR stars is influenced by several physical
  processes. OH/IR stars are variable stars suffering high
  mass-loss rates. The dust that is formed around the stars strongly
  influences the near-IR spectra and reduces the  equivalent line widths
  of \ion{Na}{i}, \ion{Ca}{i}. A similar effect is caused by the water
  content in the outer atmosphere of the OH/IR star.
  Because of these effects, it is not possible with our low resolution
  near-infrared spectroscopy to determine the metallicities of these stars.}
{}

\keywords{Stars: AGB and post-AGB -- Stars:
  late-type -- Stars: mass-loss -- Galaxy: bulge --
Galaxy: center -- Infrared: stars}

-- 
Evelien Vanhollebeke		evelien.vanhollebeke@ster.kuleuven.be
Katholieke Universiteit Leuven		http://www.ster.kuleuven.be
Instituut voor Sterrenkunde             phone: +32-16-32.70.37
Celestijnenlaan 200 B          		fax:   +32-16-32.79.99
B-3001 Leuven


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