The MACHO Project LMC Variable Star Inventory: Classical Cepheids and AGB Variables

The MACHO Project’s time-sampled photometric database contains thousands of LMC variable star lightcurves. We briefly review the Cepheid catalog. A third sequence is identified in the period–luminosity diagram, lying parallel to and fainter than the 1H and F mode sequences. These are excellent candidates to be Cepheids crossing the instability strip for the first time. However, we find no evidence for period-changes in the four-year MACHO lightcurves of these Cepheids. Anticipating the MACHO four-year LMC variable star catalog, we undertake a preliminary reconnaissance of the ∼18,500 year-one “red variables”. The vast majority are newly discovered low-amplitude variable stars, and may be on the asymptotic giant branch (AGB). We present the dual peaked differential luminosity function, period–frequency histograms, and the period– luminosity diagram. New AGB variables in the LMC clusters NGC 1783 and NGC 1898 are identified. We make a comparison with AGB variables in 47 Tuc and theoretical data; implications for the Mira PL relation are discussed. Lastly, we present the lightcurve of a carbon-rich AGB variable found near the LMC cluster NGC 2056 whose episodic fading is consistent with discrete mass-loss events. email: alves@igpp.llnl.gov