A new calibration of Galactic Cepheid Period-Luminosity relations from B to K bands, and a comparison to LMC PL relations

TL;DR

This study calibrates Galactic Cepheid Period-Luminosity relations across multiple bands and finds their slopes are universal, similar to LMC relations, supporting their use as standard candles regardless of galaxy metallicity.

Contribution

The paper provides a new calibration of Galactic Cepheid PL relations from B to K bands and compares them to LMC relations, confirming slope universality across these galaxies.

Findings

No significant difference in PL slopes between Galaxy and LMC.

Cepheid PL relations have universal slopes across studied bands.

Upper limit of 18.50 for LMC distance modulus derived.

Abstract

The universality of the Cepheid Period-Luminosity relations has been under discussion since metallicity effects have been assumed to play a role in the value of the intercept and, more recently, of the slope of these relations. The goal of the present study is to calibrate the Galactic PL relations in various photometric bands (from B to K) and to compare the results to the well-established PL relations in the LMC. We use a set of 59 calibrating stars, the distances of which are measured using five different distance indicators: Hubble Space Telescope and revised Hipparcos parallaxes, infrared surface brightness and interferometric Baade-Wesselink parallaxes, and classical Zero-Age-Main-Sequence-fitting parallaxes for Cepheids belonging to open clusters or OB stars associations. A detailed discussion of absorption corrections and projection factor to be used is given. We find no significant difference in the slopes of the PL relations between LMC and our Galaxy. We conclude that the Cepheid PL relations have universal slopes in all photometric bands, not depending on the galaxy under study (at least for LMC and Milky Way). The possible zero-point variation with metal content is not discussed in the present work, but an upper limit of 18.50 for the LMC distance modulus can be deduced from our data.