HIGH-MASS-LOSS AGB STARS IN THE SOUTH GALACTIC CAP

Observations are presented for 61 Miras in the South Galactic Cap (b < - 30') which were selected on the basis of their IRAS 12/25-mum flux ratios as high-mass-loss candidates. JHKL photometry (over 1500 observ ations) was obtained for all of the stars, optical spectra for 49 and OH-maser detections for four. 58 of the Miras are oxygen-rich, and thr ee are carbon stars with thick shells. Periods have been determined fo r all of the stars for which they were not already known - they range from 166 to 700 d. The carbon Mira IZ Peg (AFGL 3099) shows two period s, of 488 and 345 d, respectively. Distances and mass-loss rates have been determined for all 61 stars. Mass-loss rates range from about 10( -7) to over 10(-5) M. yr-1; they are tightly correlated with K-[12] bu t not with the 12/25-mum flux ratio. The kinematic behaviour of the Mi ras is discussed on the basis of the new spectra and of published radi o observations of molecular lines. The kinematic properties are depend ent on the pulsation period, as is the height above the Galactic plane . These results are interpreted as indicating that there can be only a rather small fractional change to the pulsational period of a Mira du ring its lifetime as a Mira. A high asymmetric drift is determined for the Galactic Cap Miras in the period range from 250 to 350 d; possibl e reasons for this are discussed. Evidence is given that supports the view that almost all IRAS sources with a variability index of 9 are Mi ra variables. It is shown, however, that biases may result if sources selected on the basis of their variability indices are used for Galact ic structure studies. The current status of the period-luminosity and period-luminosity-colour relations is briefly reviewed. It is demonstr ated that the assumption sometimes made that local Miras are 0.25 mag fainter at K than those with the same period in the LMC is not support ed by observations. A comparison of Miras in the Cap with those in the 7-degrees < \b\ < 8-degrees field of the Bulge indicates no obvious d ifferences in period distribution or other properties.