Issue |
A&A
Volume 484, Number 2, June III 2008
|
|
---|---|---|
Page(s) | 371 - 379 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:200809469 | |
Published online | 16 April 2008 |
Spatially resolved dusty torus toward the red supergiant WOH G64 in the Large Magellanic Cloud *,**
1
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: kohnaka@mpifr-bonn.mpg.de
2
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
Received:
28
January
2008
Accepted:
14
March
2008
Aims. We present N-band spectro-interferometric observations of the red
supergiant WOH G64 in the Large Magellanic Cloud (LMC) using MIDI at
the Very Large Telescope Interferometer (VLTI).
While the very high luminosity (∼
) previously
estimated for WOH G64 suggests that it is a very massive star with an
initial mass of ~40
, its low effective temperature (~3200 K)
is in serious disagreement with the current stellar evolution theory.
Methods. WOH G64 was observed with VLTI/MIDI using the UT2-UT3 and UT3-UT4 baseline configurations.
Results.
The dust envelope around WOH G64 has been spatially resolved with a
baseline of ~60 m – the first MIDI observations to resolve an
individual stellar source in an extragalactic system.
The observed N-band visibilities show a slight decrease from 8 to
~10 μm and a gradual increase longward of ~10 μm,
reflecting the 10 μm silicate feature in self-absorption.
This translates into a steep increase of the uniform-disk diameter from 8 to
10 μm (from 18 to 26 mas) and a roughly constant diameter above
10 μm.
The visibilities measured at four position angles differing by ~60°
but at approximately the same baseline length (~60 m) do not show
a noticeable difference, suggesting that the object appears nearly
centrosymmetric.
The observed N-band visibilities and spectral energy distribution
can be reproduced by an optically and geometrically thick silicate torus
model viewed close to pole-on.
The luminosity of the central star is derived to be
∼
, which is by a factor of 2 lower than the
previous estimates based on spherical models.
We also identify the H2O absorption features at 2.7 and 6 μm in
the spectra obtained with the Infrared Space Observatory and
the Spitzer Space Telescope.
The 2.7 μm feature originates in the photosphere and/or the extended
molecular layers,
while the 6 μm feature is likely to be of
circumstellar origin.
Conclusions.
The lower luminosity newly derived from our MIDI observations and
two-dimensional modeling
brings the location of WOH G64 on the H-R diagram
in much better agreement with theoretical evolutionary tracks
for a 25 star. However, the effective temperature is still
somewhat too cool for the theory.
The low effective temperature of WOH G64 places it very close to or even
beyond the Hayashi limit, which implies that this object may be experiencing
unstable, violent mass loss.
Key words: infrared: stars / techniques: interferometric / stars: supergiants / stars: late-type / stars: circumstellar matter / stars: individual: WOH G64
© ESO, 2008
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