The wind speeds, dust content, and mass-loss rates of evolved AGB and RSG stars at varying metallicity

摘要

We present the results of our survey of 1612 MHz circumstellar OH maser emissionudfrom asymptotic giant branch (AGB) stars and red supergiants (RSGs) in the LargeudMagellanic Cloud. We have discovered four new circumstellar maser sources in theudLMC, and increased the number of reliable wind speeds from IR stars in the LMCudfrom 5 to 13. Using our new wind speeds, as well as those from Galactic sources,udwe have derived an updated relation for dust driven winds: vexp / ZL0:4. We compareudthe sub-solar metallicity LMC OH/IR stars with carefully selected samples ofudmore metal-rich OH/IR stars, also at known distances, in the Galactic Centre andudGalactic Bulge. For 8 of the Bulge stars we derive pulsation periods for the firstudtime, using near-IR photometry from the VVV survey. We have modeled our LMCudOH/IR stars and developed an empirical method of deriving gas-to-dust ratios andudmass loss rates by scaling the models to the results from maser profiles. We haveuddone this also for samples in the Galactic Centre and Bulge and derived a newudmass loss prescription that includes luminosity, pulsation period, and gas-to-dust ratioud_Mud= 1:06+3:5