Abstract

Contributed Talk - Plenary

A New Method for Distance-Reddening Calibration of Cepheids

Shubham Mamgain
Leibniz-Institut für Astrophysik Potsdam (AIP)

Since the discovery of the Leavitt Law, astronomy has changed forever. As a primary distance indicator, the Leavitt Law serves as a calibration tool for the secondary distance indicators of the cosmic distance ladder. Because the apparent magnitudes of observed Cepheids are affected by interstellar reddening and distance, incorrect estimates broaden the dispersion of the Leavitt Law and consequently perturb its zero point. This introduces uncertainty into the calibration of the distance ladder, which then propagates into a larger uncertainty in the Hubble constant. My research goal is to calibrate the Leavitt Law using two independent distance measurement methods: Gaia DR3 parallaxes and the Infrared Surface Brightness (IRSB) method. I developed a new method that utilizes BVIJHK photometric observations of Cepheids to constrain the systematic effects of reddening and distance for individual Cepheids. This ultimately provides the “true” absolute magnitudes, leading to a tighter period–luminosity (PL) relation with a more precise zero point. To validate the results, the calibrated distances and reddening values were compared with independent distance measurements for cluster Cepheids. The application of the developed algorithm to SMC Cepheids determined its distance to be 19.07 mag and additionally revealed the galaxy’s three-dimensional structure and reddening distribution.