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Session 96 - Cepheids and Supergiant Variable Stars.
Display session, Thursday, January 16
Metropolitan Ballroom,

[96.11] A Test for the Metallicity Dependence of the Cepheid Period-Luminosity Relation in the Near Infrared and a New Distance to M31

T. M. Webb, D. L. Welch, C. Wilson (McMaster), P. Stetson (DAO)

We present new JHK' photometry for previously discovered M31 Cepheids within the Baade and Swope fields I, III, and IV. The data were obtained over 6 nights in August 1993 and 3 nights in October 1994 using the RedeyeN camera of CFHT in conditions of FWHM=0.65 arcsec seeing. The Cepheids were chosen to be a subset of those observed by Freedman amp; Madore (1990). Some of the Cepheids in this subset were resolved into multiple objects. The correct stars were identified by variation (when multiple-epoch observations were available), and by their position on the JHK' color-color plane. The total absorption at K' is a factor of 4 lower than that for I, the longest wavelength in the previous study.

We present an improved true distance modulus estimate for M31 and an investigation of the dependence of the Cepheid infrared P-L relation on metal abundance. Theoretical predictions and empirical studies of the latter have been contradictory in the past a nd the systematic errors affecting the calibration are expected to be much smaller in the infrared.

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