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From: Jihane Moultaka  moultaka@ph1.uni-koeln.de 
To: gcnews@zia.aoc.nrao.edu
Subject: submit moultakaGC1.tex A&A, in press

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\begin{document}

\authorrunning{Moultaka et al.}
\titlerunning{Interstellar Matter and Circumstellar Matter in the
  Central Parsec of the Milky Way}
\title{Dust Embedded Sources at the Galactic Center}
\subtitle{2 to 4$\mu$m imaging and spectroscopy in the central parsec}
\author{J. Moultaka$^1$, A. Eckart$^1$, T. Viehmann$^1$, N. Mouawad$^1$,
C. Straubmeier$^1$, T. Ott$^2$, R. Sch\"odel$^1$}
\institute{1) I Physikalishes Institut,
           Z\"ulpicher Str. 77,
           50937 K\"oln, Germany \\
           2) Max Planck Institut f\"ur extraterrestrische Physik,
           Giessenbachstrasse, 85748 Garching, Germany\\
           \email{email: moultaka@ph1.uni-koeln.de} }


\date{Received  / Accepted }

\abstract{
\noindent

We present the first L-band spectroscopic observations for a dozen stellar
sources in the central $0.5$~pc of the GC stellar cluster that are
bright in the 2-4 $\mu$m wavelength domain.  The L-band data were
taken with ISAAC at the VLT UT1 (Antu).  With the aid of additional
K-band spectroscopic data, we derive optical depth spectra of the
sources after fitting their continuum emission with a single reddened
blackbody continuum.  We also derive intrinsic source spectra by
correcting the line of sight extinction via the optical depth spectrum
of a late type star that is most likely not affected by local dust
emission or extinction at the Galactic Center. The good agreement
between the two approaches shows that the overall variation of the
line-of-sight extinction across the central $0.5$~pc is $\Delta
A_{\mathrm{K}}\leq0.5$~mag.  The extinction corrected spectra of the
hot He-stars are in good agreement with pure Rayleigh Jeans continuum
spectra.  The intrinsic spectra of all other sources are in agreement
with continuum emission and absorption features due to the dust
in which they are embedded.  We interprete both facts as evidence that
a significant amount of the absorption takes place within the central
parsec of the Galactic Center and is most likely associated with the
individual sources there. We find absorption features at $3.0\mu m$,
 $3.4\mu m$, and $3.48\mu m$ wavelength. Correlations
between all
three features show that they are very likely to arise in
the ISM of the central $0.5$~pc.
Spacially highly
variable hydrogen emission lines seen towards the individual sources
give evidence of the complex density and temperature structure of the
mini-spiral. In the cases of the sources with featureless K-band
spectra like IRS~21 and IRS~1W, they are consistent with
massive hot stars embedded in the bow shock created by their motion
through the dust and gas of the mini-spiral.  It is likely that the
bow shock scenario may be applicable to most of the dust embedded
sources in the central stellar cluster. Spectroscopy of high
MIR-excess sources 0.5'' north of the IRS~13 complex is largely
consistent with them being YSOs. However, a bow-shock nature of these
sources cannot be excluded.  The L-band spectrum at the location of
SgrA*, is consistent with that of a hot O-type star, such as S2, which
was very close to Sgr~A* at the time of our observations.
\keywords{Galaxy: center - galaxies: nuclei - infrared: stars - infrared:
ISM
extinction}

}
\end{document}