The ALMA detection of CO rotational line emission in AGB stars in the Large Magellanic Cloud
Artikel i vetenskaplig tidskrift, 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.

outflows / radio continuum: stars

stars: AGB and post-AGB / stars: winds

Författare

M. A. T. Groenewegen

Royal Observatory of Belgium

Wouter Vlemmings

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

P. Marigo

Universita degli Studi di Padova

G. C. Sloan

Cornell University

STScI

The University of North Carolina at Chapel Hill

L. Decin

KU Leuven

M.W. Feast

South African Astronomical Observatory

University of Cape Town

S. R. Goldman

Keele University

Kay Justtanont

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

F. Kerschbaum

Universität Wien

M. Matsuura

Cardiff University

I. McDonald

University of Manchester

Hans Olofsson

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

R. Sahai

Jet Propulsion Laboratory, California Institute of Technology

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

NASA Goddard Space Flight Center

University of Maryland

L. Guzman-Ramirez

Leiden University

European Southern Observatory Santiago

O. C. Jones

STScI

E. Lagadec

Observatoire de la Cote d'Azur

M. Meixner

STScI

M.G. Rawlings

East Asian Observatory

S. Srinivasan

Academia Sinica

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 596 50- A50

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

DOI

10.1051/0004-6361/201629590