The ALMA detection of CO rotational line emission in AGB stars in the Large Magellanic Cloud
Journal article, 2016
Context. Low- and intermediate-mass stars lose most of their stellar mass at the end of their lives on the asymptotic giant branch (AGB). Determining gas and dust mass-loss rates (MLRs) is important in quantifying the contribution of evolved stars to the enrichment of the interstellar medium.
Aims. This study attempts to spectrally resolve CO thermal line emission in a small sample of AGB stars in the Large Magellanic Cloud (LMC).
Methods. The Atacama Large Millimeter Array was used to observe two OH/IR stars and four carbon stars in the LMC in the CO J = 2−1 line.
Results. We present the first measurement of expansion velocities in extragalactic carbon stars. All four C stars are detected and wind expansion velocities and stellar velocities are directly measured. Mass-loss rates are derived from modelling the spectral energy distribution and Spitzer/IRS spectrum with the DUSTY code. The derived gas-to-dust ratios allow the predicted velocities to agree with the observed gas-to-dust ratios. The expansion velocities and MLRs are compared to a Galactic sample of well-studied relatively low MLRs stars supplemented with extreme C stars with properties that are more similar to the LMC targets. Gas MLRs derived from a simple formula are significantly smaller than those derived from dust modelling, indicating an order of magnitude underestimate of the estimated CO abundance, time-variable mass loss, or that the CO intensities in LMC stars are lower than predicted by the formula derived for Galactic objects. This could be related to a stronger interstellar radiation field in the LMC.
Conclusions. Although the LMC sample is small and the comparison to Galactic stars is non-trivial because of uncertainties in their distances (hence luminosities), it appears that for C stars the wind expansion velocities in the LMC are lower than in the solar neighbourhood, while the MLRs appear to be similar. This is in agreement with dynamical dust-driven wind models.
stars: AGB and post-AGB / stars: winds
outflows / radio continuum: stars
Author
M. A. T. Groenewegen
Royal Observatory of Belgium
Wouter Vlemmings
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
P. Marigo
University of Padua
G. C. Sloan
Cornell University
The University of North Carolina System
Space Telescope Science Institute (STScI)
L. Decin
KU Leuven
M.W. Feast
South African Astronomical Observatory
University of Cape Town
S. R. Goldman
Keele University
Kay Justtanont
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
F. Kerschbaum
University of Vienna
M. Matsuura
Cardiff University
I. McDonald
University of Manchester
Hans Olofsson
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
R. Sahai
California Institute of Technology (Caltech)
J. T. van Loon
Keele University
P.R. Wood
Australian National University
A.A. Zijlstra
University of Manchester
J. Bernard-Salas
Open University
M. Boyer
National Aeronautics and Space Administration (NASA)
University of Maryland
L. Guzman-Ramirez
Leiden University
European Southern Observatory Santiago
O. C. Jones
Space Telescope Science Institute (STScI)
E. Lagadec
Observatoire de la Cote d'Azur
M. Meixner
Space Telescope Science Institute (STScI)
M.G. Rawlings
East Asian Observatory
S. Srinivasan
Academia Sinica
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 596 50- A50Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
DOI
10.1051/0004-6361/201629590