Near-infrared Observations of Cepheid Variables in the Large Magellanic Cloud (Abstract)

Volume 38 number 2 (2010)

Lucas Macri

Abstract

(Abstract only) I present preliminary results of near-infrared observations of Cepheid variables in the Large Magellanic Cloud, obtained with the CPAPIR camera at the Cerro Tololo 1.5-m telescope. The observations were carried out with two goals: (a) to better characterize the Cepheid Period-Luminosity (P-L) relation at near-infrared wavelengths, especially for periods below 10 days; (b) to determine if the P-L relations are linear or non-linear in these bandpasses. Several analyses of OGLE-II observations of Cepheid variables in the Large Magellanic Cloud have detected a non-linearity or “break” in the slope of the optical (V and I) P-L relations at a period around 10 days. Theoretical models indicate the non-linearity may be due to changes in the interaction of the hydrogen ionization front and the stellar photosphere as a function of global stellar parameters, such as mass and metal abundance. Models predict that the non-linearity becomes most pronounced at abundances similar to that of the Large Magellanic Cloud. In this talk, I will show representative light curves for a small subset of our nearly 1,200 Cepheid variables and I will present preliminary PL relations in the J and K bands as well as color-magnitude diagrams for Cepheid variables and field stars.