Issue |
A&A
Volume 442, Number 2, November I 2005
|
|
---|---|---|
Page(s) | 597 - 613 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20053528 | |
Published online | 07 October 2005 |
Dust-enshrouded giants in clusters in the Magellanic Clouds
1
Astrophysics Group, School of Physical & Geographical Sciences, Keele University, Staffordshire ST5 5BG, UK e-mail: jacco@astro.keele.ac.uk
2
School of Physics and Astronomy, University of Manchester, Sackville Street, PO Box 88, Manchester M60 1QD, UK
Received:
27
May
2005
Accepted:
13
July
2005
We present the results of an investigation of post-Main Sequence
mass loss from stars in clusters in the Magellanic Clouds, based around an
imaging survey in the -band (3.8 μm) performed with the VLT at
ESO. The data are complemented with
(ESO and 2MASS) and mid-IR
photometry (TIMMI2 at ESO, ISOCAM on-board ISO, and data from IRAS and MSX).
The goal is to determine the influence of initial metallicity and initial mass
on the mass loss and evolution during the latest stages of stellar evolution.
Dust-enshrouded giants are identified by their reddened near-IR colours and
thermal-IR dust excess emission. Most of these objects are Asymptotic Giant
Branch (AGB) carbon stars in intermediate-age clusters, with progenitor masses
between 1.3 and ~5
. Red supergiants with circumstellar dust
envelopes are found in young clusters, and have progenitor masses between 13
and 20
. Post-AGB objects (e.g., Planetary Nebulae) and massive stars
with detached envelopes and/or hot central stars are found in several
clusters. We model the spectral energy distributions of the cluster IR
objects, in order to estimate their bolometric luminosities and mass-loss
rates. The IR objects are the most luminous cluster objects, and have
luminosities as expected for their initial mass and metallicity. They
experience mass-loss rates in the range from a few 10-6 up to 10-4
yr-1 (or more), with most of the spread being due to
evolutionary effects and only a weak dependence on progenitor mass and/or
initial metallicity. About half of the mass lost by 1.3–3
stars is
shed during the superwind phase, which lasts of order 105 yr. Objects with
detached shells are found to have experienced the highest mass-loss rates, and
are therefore interpreted as post-superwind objects. We also propose a simple
method to measure the cluster mass from
-band images.
Key words: stars: AGB and post-AGB / Sun: evolution / stars: mass-loss / supergiants / Magellanic Clouds / infrared: stars
© ESO, 2005
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