Circumstellar masers in the Magellanic Clouds

Results are presented of a search for 22 GHz H2O 6(16) --> 5(23), 43 GHz Si Ov=1(J = 1 --> 0), 86 GHz SiOv=1(J = 2 --> 1) and 129 GHz SiOv=1(J = 3 --> 2) maser emission from bright IRAS point sources in the Small and Large Mag ellanic Clouds - mostly circumstellar envelopes around obscured red supergi ants and Asymptotic Giant Branch stars (OH/IR stars). The aim of this effor t was to test whether the kinematics of the mass loss from these stars depe nds on metallicity. H2O maser emission was detected in the red supergiants IRAS 04553-6825 and IRAS 05280-6910, and tentatively in the luminous IR obj ect IRAS 05216-6753 and the AGE star IRAS 05329-6708, all in the LMC. SiOv= 1(J = 2 --> 1) maser emission was detected in IRAS 04553-6825. The double-p eaked H2O maser line profiles of IRAS 04553-6825 and IRAS 05280-6910, in co mbination with the OH (and SiO) maser line profiles, yield the acceleration of the outflows from these stars. The outflow velocity increases between t he H2O masing zone near the dust-formation region and the more distant OH m asing zone from v similar to 18 to 26 kms(-1) for IRAS 04553-6825 and from v similar to 6 to 17 km s(-1) for IRAS 05280-6910. 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 found to be very similar to those in the Galactic Centre. The expansion velocities i n the LMC appear to be similar to 20% lower than for similarly bright OH ma sers in the Galactic Centre, but the data are still consistent with no diff erence in expansion velocity. OH/IR stars in the LMC appear to have slower accelerating envelopes than OH/IR stars in the Galactic Centre. The masers in the LMC have blue-asymmetric emission profiles. This may be due to the a mplification of stellar and/or free-free radiation, rather than the amplifi cation of dust emission, and may be more pronounced in Low metallicity enve lopes. The SiO maser strength increases with the photometric amplitude at 2 .2 mum but is independent of the photometric amplitude at 10 mum. This sugg ests a strong connection between shocks in the dust-free SiO masing zone an d the dust formation process. The LMC masers obey the same trend as the Gal actic Centre masers. Appendices describe H2O maser emission from the modera tely mass-losing AGE star R Dor in tile Milky Way optical echelle spectrosc opy of IRAS 04553-6825, and the properties of circumstellar masers in the G alactic Centre.