Circumstellar masers in the Magellanic Clouds

Abstract

We have searched for 22 GHz H2O and 43/86/129 GHz SiO masers in bright IRAS point sources in the SMC and LMC, to test whether the kinematics of the mass loss from these stars depends on metallicity. H2O masers were detected in the red supergiants IRAS04553-6825 and IRAS05280-6910, and tentatively in the luminous IR object IRAS05216-6753 and the AGB star IRAS05329-6708. SiO masers were detected in IRAS04553-6825. The outflow velocity increases between the H2O masing zone near the dust-formation region and the more distant OH masing zone from 18 to 26 km/s for IRAS04553-6825 and from 6 to 17 km/s for IRAS05280-6910. The total sample of LMC targets is analysed in comparison with circumstellar masers in the Galactic Centre. The photon fluxes of circumstellar masers in the LMC are very similar to those in the Galactic Centre. The expansion velocities in the LMC appear to be 20% lower than for similarly bright OH masers in the Galactic Centre, but the data are consistent with no difference in expansion velocity. OH/IR stars in the LMC appear to have slower accelerating envelopes than OH/IR stars in the Galactic Centre. Masers in the LMC have blue-asymmetric emission profiles. This may be due to the amplification of stellar and/or free-free radiation, rather than the amplification of dust emission, and may be more pronounced in low metallicity envelopes. SiO maser strength increases with the photometric amplitude at 2.2 micron but is independent of the photometric amplitude at 10 micron. This suggests a strong connection between shocks in the dust-free SiO masing zone and the dust formation process. Appendices describe H2O maser emission from R Dor in the Milky Way, optical echelle spectroscopy of IRAS04553-6825, and the properties of masers in the Galactic Centre (Abridged).