A dearth of OH/IR stars in the Small Magellanic Cloud

Steven R. Goldman (1), Jacco Th. van Loon (1), José F. Gómez (2), James A. Green (3,4), Albert A. Zijlstra (5), Ambra Nanni (6), Hiroshi Imai (7), Patricia A. Whitelock (8,9), Martin A. T. Groenewegen (10), Joana M. Oliveira (1)

1 - Astrophysics Group, Lennard-Jones Laboratories, Keele University, ST5 5BG, UK
2 - Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
3 - SKA Organisation, Jodrell Bank Observatory, Lower Withington, Macclesfield, Cheshire, SK11 9DL, UK
4 - CSIRO Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia
5 - Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
6 - Dipartimento di Fisica e Astronomia Galileo Galilei, vicolo dell'Osservatorio 3, 35122 Padova PD, Italy
7 - Department of Physics and Astronomy, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan
8 - South African Astronomical Observatory (SAAO), PO Box 9, 7935 Observatory, South Africa
9 - Astronomy Department, University of Cape Town, 7701 Rondebosch, South Africa
10 - Koninklijke Sterrenwacht van België,  Ringlaan 3, B-1180 Brussels, Belgium

We present the results of targeted observations and a survey of 1612-, 1665-, and 1667-MHz circumstellar OH maser emission from asymptotic giant branch (AGB) stars and red supergiants (RSGs) in the Small Magellanic Cloud (SMC), using the Parkes and Australia Telescope Compact Array radio telescopes. No clear OH maser emission has been detected in any of our observations targeting luminous, long-period, large-amplitude variable stars, which have been confirmed spectroscopically and photometrically to be mid- to late-M spectral type. These observations have probed 3 - 4 times deeper than any OH maser survey in the SMC. Using a bootstrapping method with LMC and Galactic OH/IR star samples and our SMC observation upper limits, we have calculated the likelihood of not detecting maser emission in any of the two sources considered to be the top maser candidates to be less than 0.05%, assuming a similar pumping mechanism as the LMC and Galactic OH/IR sources. We have performed a population comparison of the Magellanic Clouds and used Spitzer IRAC and MIPS photometry to confirm that we have observed all high luminosity SMC sources that are expected to exhibit maser emission. We suspect that, compared to the OH/IR stars in the Galaxy and LMC, the reduction in metallicity may curtail the dusty wind phase at the end of the evolution of the most massive cool stars. We also suspect that the conditions in the circumstellar envelope change beyond a simple scaling of abundances and wind speed with metallicity.

Reference: arXiv:1710.02184
Status: Manuscript has been accepted

Weblink: http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1710.02184

Comments: accepted in MNRAS

Email: sgoldman@stsci.edu