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Abstract
The fundamental method for determining distances to astrophysical objects is through the measurement of their geometric parallaxes. Distance determinations beyond these geometric methods rely on standard candles, which have known intrinsic luminosities. The absolute calibration of the luminosities of stellar standard candles forms the first rung of the cosmic distance ladder used to determine the Hubble constant – the expansion rate of the Universe. Currently, the Hubble constant values based on a variety of standard candles observed with the Hubble/James Webb space telescopes, are in an intriguing discord with the measurement from the Planck space mission. This Hubble Tension points to new physics in the cosmological model and must be evaluated against all sources of measurement errors. One of the main systematic uncertainties is the absolute luminosity scales of stellar standard candles, which have not yet reached 1% accuracy despite unprecedented geometric distances of ~1.5 billion sources in the Gaia space mission data. This is mainly due to caveats associated with Gaia parallax offsets, lack of complementary multiband photometry and high-resolution spectroscopy, and highly debated effects of composition and age on the luminosities, among other uncertainties.
Our International Team aims to strategically address these shortcomings before the nominal five-year Gaia mission data release to achieve 1% calibration of stellar distance indicators. For this purpose, we are using state-of-the-art stellar evolution and pulsation models, multi-wavelength datasets from space and ground-based facilities together with machine-learning approaches, leveraging our team’s competences and expertise in a multidisciplinary context. The projects led by team members will provide cross-investigation of 1% precise luminosity scales of a variety of stellar standard candles with high accuracy and fidelity to firmly rule out (or confirm) measurement uncertainties as the origin of the Hubble tension. These precise luminosity calibrations will be the primary resource for the astronomical distance determination in the era of space and ground-based large observational facilities in the next-decade.