Dr. Anupam Bhardwaj

Classical Cepheids, RR Lyrae, and the tip of the red giant branch (TRGB) are the most robust stellar standard candles that can provide independent primary calibrations of the cosmic distance ladder, leading to increasingly accurate and precise local determinations of the Hubble constant. Given the ongoing Hubble tension, it is critical to investigate all possible sources of systematic uncertainties in the Hubble constant measurements based on these stars of different ages and metallicities. I will present recent progress and our ongoing efforts to improve the calibration of these stellar standard candles in the Gaia era. Our new homogeneous, high-resolution spectroscopy from CFHT-ESPaDOnS/VLT-UVES and multiband time-series photometry of Population I Cepheid variable stars will be discussed along with their implications for the Hubble constant. For the Population II stars, I will present our most precise empirical calibrations of RR Lyrae variables based on infrared monitoring of globular clusters with the CFHT-WIRCam and Gemini-Flamingos2 instruments. We provide accurate RR Lyrae-based distances to dwarf spheroidal galaxies and old LMC clusters with our new observations, leading to an independent absolute zero-point for the TRGB and, in turn, a Hubble constant based on Population II stars. I will also discuss our ongoing theoretical efforts that complement the observational data to achieve high-precision distance measurements using stellar standard candles in the era of large telescopes.