The ALMA detection of CO rotational line emission in AGB stars in the Large Magellanic Cloud
- Author(s)
- Martin A. T. Groenewegen, Wouter H. T. Vlemmings, Paola Marigo, G. C. Sloan, Leen Decin, Franz Kerschbaum, Hans Olofsson
- Abstract
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.- Organisation(s)
- Department of Astrophysics
- External organisation(s)
- Cornell University, Royal Observatory of Belgium, Chalmers University of Technology, University of Padova, Katholieke Universiteit Leuven, Stockholm Observatory
- Journal
- Astronomy & Astrophysics
- Volume
- 596
- No. of pages
- 12
- ISSN
- 0004-6361
- DOI
- https://doi.org/10.1051/0004-6361/201629590
- Publication date
- 12-2016
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103003 Astronomy, 103004 Astrophysics
- Keywords
- ASJC Scopus subject areas
- Astronomy and Astrophysics, Space and Planetary Science
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/f7e60fe2-63e0-4580-8d45-c8ed81e53334