A {it Spitzer Space Telescope} far-infrared spectral atlas of compact
sources in the Magellanic Clouds. I. The Large Magellanic Cloud

Jacco Th. van Loon$^1$
Joana M. Oliveira$^1$
Karl D. Gordon$^2$
Margaret Meixner$^2$
Bernie Shiao$^2$
Martha L. Boyer$^2$
F. Kemper$^3$
Paul M. Woods$^3$
A. G. G. M. Tielens$^4$
Massimo Marengo$^{5,6}$
Remy Indebetouw$^{7,8}$
G. C. Sloan$^9$
C.-H. Rosie Chen$^7$

1 - Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG, UK
2 - Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
3 - Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
4 - Leiden Observatory, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands
5 - Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
6 - Department of Physics and Astronomy, Iowa State University, Ames IA, USA
7 - Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904, USA
8 - National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
9 - Department of Astronomy, Cornell University, Ithaca, NY 14853, USA

We present far-infrared spectra, $lambda$=52--93 $mu$m, obtained with the
{it Spitzer Space Telescope} in the Spectral Energy Distribution mode of its
MIPS instrument, of a representative sample of the most luminous compact
far-infrared sources in the Large Magellanic Cloud. These include carbon
stars, OH/IR Asymptotic Giant Branch (AGB) stars, post-AGB objects and
Planetary Nebulae, the R,CrB-type star HV,2671, the OH/IR red supergiants
WOH,G064 and IRAS,05280$-$6910, the three B[e] stars IRAS,04530$-$6916,
R,66 and R,126, the Wolf-Rayet star Brey,3a, the Luminous Blue Variable
(LBV) R,71, the supernova remnant N,49, a large number of young stellar
objects (YSOs), compact H,{sc ii} regions and molecular cores, and a
background galaxy at a redshift $zsimeq0.175$. We use the spectra to
constrain the presence and temperature of cold dust and the excitation
conditions and shocks within the neutral and ionized gas, in the circumstellar
environments and interfaces with the surrounding interstellar medium (ISM).
First, we introduce a spectral classification scheme. Then, we measure line
strengths, dust temperatures, and IR luminosities. Objects associated with
star formation are readily distinguished from evolved stars by their cold dust
and/or fine-structure lines. Evolved stars, including the LBV R,71, lack cold
dust except in some cases where we argue that this is swept-up ISM. This leads
to an estimate of the duration of the prolific dust-producing phase
(``superwind'') of several thousand years for both RSGs and massive AGB stars,
with a similar fractional mass loss experienced despite the different masses.
We tentatively detect line emission from neutral oxygen in the extreme RSG
WOH,G064, which suggests a large dust-free cavity with implications for the
wind driving. In N,49, the shock between the supernova ejecta and ISM is
revealed in spectacular fashion by its strong [O,{sc i}] $lambda$63-$mu$m
emission and possibly water vapour; we estimate that 0.2 M$_odot$ of ISM dust
was swept up. On the other hand, some of the compact H,{sc ii} regions
display pronounced [O,{sc iii}] $lambda$88-$mu$m emission. The efficiency
of photo-electric heating in the interfaces of ionized gas and molecular
clouds is estimated at 0.1--0.3%. We confirm earlier indications of a low
nitrogen content in the LMC. Evidence for solid state emission features is
found in both young and evolved objects, but the carriers of these features
remain elusive; some of the YSOs are found to contain crystalline water ice.
The spectra constitute a valuable resource for the planning and interpretation
of observations with the {it Herschel Space Observatory} and the {it
Stratospheric Observatory For Infrared Astronomy} (SOFIA).

Reference: The Astronomical Journal
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/0910.3339


Email: jacco@astro.keele.ac.uk