Distance estimate method for Asymptotic Giant Branch stars using Infrared Spectral Energy Distributions

TL;DR

This paper introduces a new infrared spectral energy distribution-based method for estimating distances to AGB stars in the Milky Way, enabling large-scale mapping of their distribution and Galactic structure.

Contribution

The paper presents a novel SED-based distance estimation technique for AGB stars, validated against VLBI and Gaia data, and applied to nearly 15,000 stars to reveal Galactic bar structure.

Findings

Strong correlation with VLBI and Gaia distances.

Statistical distances with ±35% error for 15,000 stars.

Identification of Galactic bar structure using AGB star distribution.

Abstract

We present a method to estimate distances to Asymptotic Giant Branch (AGB) stars in the Galaxy, using spectral energy distributions (SEDs) in the near- and mid-infrared. By assuming that a given set of source properties (initial mass, stellar temperature, composition, and evolutionary stage) will provide a typical SED shape and brightness, sources are color-matched to a distance-calibrated template and thereafter scaled to extract the distance. The method is tested by comparing the distances obtained to those estimated from Very Long Baseline Interferometry or Gaia parallax measurements, yielding a strong correlation in both cases. Additional templates are formed by constructing a source sample likely to be close to the Galactic center, and thus with a common, typical distance for calibration of the templates. These first results provide statistical distance estimates to a set of almost 15,000 Milky Way AGB stars belonging to the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey, with typical distance errors of $\pm 35$%. With these statistical distances a map of the intermediate-age population of stars traced by AGBs is formed, and a clear bar structure can be discerned, consistent with the previously reported inclination angle of 30$^\circ$ to the GC-Sun direction vector. These results motivate deeper studies of the AGB population to tease out the intermediate-age stellar distribution throughout the Galaxy, as well as determining statistical properties of the AGB population luminosity and mass-loss rate distributions.