THE CEPHEID PERIOD-LUMINOSITY RELATION (THE LEAVITT LAW) AT MID-INFRARED WAVELENGTHS. IV. CEPHEIDS IN IC 1613

Abstract

We present mid-infrared Period-Luminosity relations for Cepheids in the Local Group galaxy IC 1613. Using archival IRAC imaging data from Spitzer we were able to measure single-epoch magnitudes for five, 7 to 50-day, Cepheids at 3.6 and 4.5µm. When fit to the calibrating relations, measured for the Large Magellanic Cloud Cepheids, the data give apparent distance moduli of 24.29±0.07 and 24.28±0.07 at 3.6 and 4.5µm, respectively. A multi-wavelength fit to previously published BVRIJHK apparent moduli and the two IRAC moduli gives a true distance modulus of 24.27±0.02 mag with E(B-V) = 0.08 mag, and a corresponding metric distance of 715 kpc. Given that these results are based on single-phase observations derived from exposures having total integration times of only 1,000 sec/pixel we suggest that Cepheids out to about 2 Mpc are accessible to Spitzer with modest integration times during its warm mission. We identify the main limiting factor to this method to be crowding/contamination induced by the ubiquitous population of infrared-bright AGB stars. 1.