Galactic distributions of carbon- and oxygen-rich AGB stars revealed by the AKARI mid-infrared all-sky survey

TL;DR

This study uses the AKARI mid-infrared all-sky survey to analyze the spatial distributions of carbon-rich and oxygen-rich AGB stars in the Galaxy, revealing their different concentration patterns and implications for Galactic structure and chemical evolution.

Contribution

It provides a large-scale, quantitative analysis of AGB star distributions, highlighting differences between C-rich and O-rich stars and extending previous findings to the entire Galaxy.

Findings

O-rich AGB stars are concentrated toward the Galactic center.

C-rich AGB stars have a relatively uniform distribution within 8 kpc.

Results support previous studies and relate to Galactic metallicity gradient.

Abstract

Context: The environmental conditions for asympotic giant branch (AGB) stars to reach the carbon-rich (C-rich) phase are important to understand the evolutionary process of AGB stars. The difference between the spatial distributions of C-rich and oxygen-rich (O-rich) AGB stars is essential for the study of the Galactic structure and the chemical evolution of the interstellar medium (ISM). Aims: We quantitatively investigate the spatial distributions of C-rich and O-rich AGB stars in our Galaxy. We discuss the difference between them and its origin. Methods: We classify a large number of AGB stars newly detected by the AKARI id-infrared all-sky survey. In the color-color diagrams, we define their occupation zones based on the locations of known objects. We then obtain the spatial distributions of C-rich and O-rich AGB stars, assuming that they have the same luminosity for a given mass-loss rate. Results: We find that O-rich AGB stars are concentrated toward the Galactic center and that the density decreases with Galactocentric distance, whereas C-rich AGB stars show a relatively uniform distribution within about 8kpc of Sun. Conclusion: Our result confirms the trends reported in previous studies and extends them to a Galactic scale. We discuss the relations between our result, the Galactic metallicity gradient, and the chemical evolution of the ISM in our Galaxy.