UPDATED 24μm PERIOD–LUMINOSITY RELATION DERIVED FROM GALACTIC CEPHEIDS

Abstract

In this work, we updated the catalog of Galactic Cepheids with $24\mu\mathrm{m}$ photometry by cross-matching the positions of known Galactic Cepheids to the recently released MIPSGAL point source catalog. We have added 36 new sources featuring MIPSGAL photometry in our analysis, thus increasing the existing sample to 65. Six different sources of compiled Cepheid distances were used to establish a $24\mu\mathrm{m}$ period-luminosity (P-L) relation. Our recommended $24\mu\mathrm{m}$ P-L relation is $M_{24\mu\mathrm{m}}=-3.18(\pm0.10)\log P - 2.46(\pm0.10)$, with an estimated intrinsic dispersion of 0.20 mag, and is derived from 58 Cepheids exhibiting distances based on a calibrated Wesenheit function. The slopes of the P-L relations were steepest when tied solely to the 10 Cepheids exhibiting trigonometric parallaxes from the Hubble Space Telescope and Hipparcos. Statistical tests suggest that these P-L relations are significantly different from those associated with other methods of distance determination, and simulations indicate that difference may arise from the small sample size.