The Cepheid Period-Luminosity Relation (The Leavitt Law) at Mid-Infrared Wavelengths: IV. Cepheids in IC 1613

TL;DR

This study derives mid-infrared Period-Luminosity relations for Cepheids in IC 1613 using Spitzer data, providing a precise distance measurement and demonstrating the method's efficiency for galaxies up to 2 Mpc.

Contribution

It presents new mid-infrared PL relations for Cepheids in IC 1613 and shows their effectiveness for distance measurement with minimal observation time.

Findings

Measured apparent distance moduli at 3.6 and 4.5 microns are ~24.28 mag.

Derived a true distance modulus of 24.27 mag for IC 1613.

Spitzer can effectively observe Cepheids up to 2 Mpc with modest exposure times.

Abstract

We present mid-infrared Period-Luminosity relations for Cepheids in the Local Group galaxy IC1613. 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 4.5 microns. 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 4.5 microns, 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.