LONG-PERIOD VARIABLES IN THE SGR-I FIELD OF THE GALACTIC BULGE

We report 580 sets of JHKL observations of 63 long-period Mira-like va riables in the Sgr I clear field located in the Bulge of our Galaxy at 3 degrees from the Centre. These include 8 IRAS sources whose periods are given for the first time. No variable shows a period in excess of 700 d, The sample appears to be close to complete and it is demonstra ted that the apparent period distribution from a given survey is highl y dependent on the wavelength used. The colours and other properties o f the Sgr I Miras are compared with those in the LMC and the solar nei ghbourhood, Although the J - K colours of the shorter-period Sgr I Mir as are similar to those of their counterparts in the LMC, showing that they have similar temperatures at a given period, differences exist i n their J - H and H - K colours, At longer periods, the Sgr I Miras ap pear redder in all colour indices than the LMC relations and their ext rapolations. The apparent K-log P and m(bol)-log P relations for Miras in the Sgr I held are derived, The scatter about these relations is h igher in Sgr I than for the LMC because of the significant depth of th e Bulge in the line of sight. In conjunction with a simple model of th e Bulge, the K-log P and M(bol)-log P relations for LMC Miras are used to discuss the distance of the Sgr I field, the best value of which i s found to be 8.7 +/- 0.7 kpc (taking the distance modulus of the LMC to be 18.55 with s.e. 0.1. - 0.15), The value of R(0), the distance to the Galactic Centre, is 0.2 kpc greater if the Sgr I field is part of a bar lying in the Galactic Plane and inclined at 45 degrees to the l ine of sight.