THE LARGE MAGELLANIC CLOUD BAR WEST FIELD

We present and analyze infrared photometry for an unbiased sample of 128 M giants in the Bar West field of the Large Magellanic Cloud. The mbol, J - K color-magnitude diagram is dominated by asymptotic giant branch stars (AGB) with properties similar to those of giants in intermediate-age clusters in the LMC. However, about 20% of the AGB population has properties similar to those of young, ≤ 100 Myr old, clusters. The luminosity function of all M giants, together with the C stars found in the same field, cuts off at an Mbol ∼ -6.0, about 1.5 mag brighter than the cutoff in the Galactic bulge. Although the field contains a rich population of luminous carbon stars, the brightest stars are all of M type. This also is characteristic of the LMC clusters. From the infrared colors we estimate a mean [Fe/H] = -0.5 ± 0.3 for the M stars in the Bar West field. This is nearly a factor of 10 lower than the mean [Fe/H] in Baade's window. The difference in metallicity is reflected in the fact that in Baade's window the M5-M7 giants dominate the light of all the M stars, whereas in the Bar West field the M0-M2 giants dominate. We find that it is easy to distinguish between Baade's window and the Bar West field in terms of the integrated photometric characteristics of their M giant populations. This result will be of importance in studying distant galaxies. The presence of two sequences of AGB stars can be interpreted as evidence for at least two major episodes of star formation in the Bar West field. The "young" population appears to have a measurably higher metallicity than the older population. The presence of yet an older population is indicated by the RR Lyrae variables found all over the LMC. This population would correspond with the oldest star clusters in the LMC.