------------------------------------------------------------------------
From: Andrea Moneti  amoneti@aip.de 
To: gcnews@aoc.nrao.edu
Subject: submit quintp.tex A&A, in press
Mime-Version: 1.0


% astro-ph/0010558
%-----------------------------------------------------------------------------
% FILE     quint.tex - Quintuplet cluster spectroscopy paper
%-----------------------------------------------------------------------------

\documentclass{aa}
\usepackage{epsf}
\begin{document}

%-----------------------------------------------------------------------------
%%%%   My definitions

\title{Mid-infrared imaging
 and spectroscopy of the enigmatic cocoon stars in the Quintuplet
 Cluster}

\author{
   A.~Moneti\inst{1} \and
   S.~Stolovy\inst{2} \and
   J.A.D.L.~Blommaert\inst{3} \and
   D.F.~Figer\inst{4} \and 
   F.~Najarro\inst{5} 
       }

\offprints{A. Moneti}
\titlerunning{The Cocoon Stars in the Quintuplet Cluster}

\institute{Institut d'Astrophysique, 98bis Blvd. Arago, F-75014 Paris,
    France \\ email: moneti@iap.fr 
\and
    CalTech, Astronomy Dept., 105-24,  Pasadena, CA 91125, USA \\
    email: srs@astro.caltech.edu
\and
    ISO Data Centre, P.O.~Box 50727, E-28080 Madrid, Spain \\
    email: blommaert@iso.vilspa.esa.es
\and
    Space Telescope Science Institute, 3700 San Martin Drive,
    Baltimore, MD 21218, USA \\ email: figer@stsci.edu
\and
Instituto Estructura de la Materia, CSIC, Serrano 121, E-29006, 
    Madrid, Spain \\ email: najarro@isis.iem.csic.es}

\date{Received: 25.Sep.2000 / accepted: 27.Oct.2000}
\maketitle

%-----------------------------------------------------------------------------

\begin{abstract}

In an attempt to determine the nature of the enigmatic cocoon stars in the
Quintuplet Cluster, we have obtained mid-infrared imaging and
spectrophotometry of the cluster, using the CAM and SWS instruments on ISO,
using SpectroCam-10 on the Palomar 5m telescope, and NICMOS on HST.  The
spectra show smooth continua with various dust and ice absorption features.
These features are all consistent with an interstellar origin, and there is
no clear evidence for any circumstellar contribution to these features.  We
find no spectral line or feature that could elucidate the nature of these
sources.  Detailed modeling of the silicate absorption features shows that
they are best reproduced by the $\mu$ Cep profile, which is typical of the
interstellar medium, with $\tausil \simeq 2.9$.  The high spatial
resolution mid-IR images show that three of the five cocoon stars have
spatially extended and asymmetric envelopes, with diameters of $\sim
20,000\,$AUs.

A reddening law similar to that of Lutz (1999) but with silicate features
based on the $\mu$ Cep profile and normalized to our value of $\tausil$ is
used to deredden the observed spectrophotometry.  The dereddened energy
distributions are characterised by temperatures of 750--925 K, somewhat
cooler than determined from near IR data alone.  Models of optically thin
and geometrically thick dust shells, as used by Williams et al.~(1987) for
very dusty, late-type WC stars, reproduce the observed SEDs from 4 to
$17\mic$, and imply shell luminosities of $\log (L/\Lsun) \simeq 4.5$--4.9
for the brightest four components.  An analysis of the various suggestions
proposed to explain the nature of the cocoon stars reveals serious problems
with all the hypotheses, and the nature of these sources remains an enigma.

\end{abstract}

\keywords{
Galactic Centre -- Quintuplet Cluster -- extinction -- ISO
}

%-----------------------------------------------------------------------------



------------- End Forwarded Message -------------