Abundances of long-period variables: initial results

Abstract

The kinematics of the long-period variables (LPVs), both in the LMC (Hughes et al. 1991 AJ 101, 1304) and in the Galaxy (eg. Feast 1963 MNRAS 125, 367) shows that there exists an Age-Period relation for these objects. Low-resolution (FORS) spectra have been obtained for a sample of SMC, LMC and Galactic LPVs using the Anglo-Australian Telescope, with the ultimate aim of using the bandstrengths of the TiO bands, in combination with a temperature indicator derived from the continuum, to estimate their metallicities in a method similar to that used by Mould and Bessell (1982 ApJ 262, 142), but using the TiO bandhead at 8480 å. Metallicity estimates of these variables are essential, both in (1) verifying the finding of Wood et al. (1991 The Magellanic Clouds, eds. R.Haynes and D.Milne, (Kluwer: Dordrecht), p259) who theorise that the scatter in the mean Period-Luminosity and Period-Color relations of the LPVs in the LMC (Feast et al. 1989 MNRAS 241, 375) could be produced by a scatter in abundance, and (2) in investigating whether there exists a correlation between abundance, kinematics and period (age) for the LPVs in the LMC, as appears to be the case in the Galaxy.