Spectrophotometric parallaxes with linear models: Accurate distances for luminous red-giant stars

Understand

With contemporary infrared spectroscopic surveys like APOGEE, red-giant stars can be observed to distances and extinctions at which Gaia parallaxes are not highly informative.

• Yet the combination of effective temperature, surface gravity, composition, and age - all accessible through spectroscopy - determines a giant's luminosity.
• Therefore spectroscopy plus photometry should enable precise spectrophotometric distance estimates.
• Here we use the APOGEE-Gaia-2MASS-WISE overlap to train a data-driven model to predict parallaxes for red-giant branch stars with $0<\log g\leq2.2$ (more luminous than the red clump).