Classification Study of WISE Infrared Sources: Identification of Candidate Asymptotic Giant Branch Stars

TL;DR

This study develops a method to identify candidate asymptotic giant branch stars in the Milky Way using WISE infrared data, establishing selection criteria based on color and brightness, and estimating their distribution within the galaxy.

Contribution

The paper introduces a new selection method for AGB star candidates using WISE and 2MASS data, including specific color and brightness criteria, and provides their estimated galactic distribution.

Findings

Identified 0.47 million candidate AGB stars in the Galaxy.

Candidates are mostly located within 8 kpc of the Galactic center.

Proposed optical spectroscopy for verification of C-rich AGB stars.

Abstract

In the WISE all-sky source catalogue there are 76 million mid-infrared (MIR) point sources that were detected at the first three WISE bands and have association with only one 2MASS near-IR source within 3 arcsec. We search for their identifications in the SIMBAD database and find 3.2 million identified sources. Based on these known sources, we establish three criteria for selecting candidate AGB stars in the Galaxy, which are three defined occupation zones in a color-color diagram, Galactic latitude |gb|< 20 deg, and "corrected" WISE third-band W3c < 11. Applying these criteria to the WISE+2MASS sources, 1.37 million of them are selected. We analyze the WISE third-band W3 distribution of the selected sources, and further establish that W3 < 8 is required in order to exclude a large fraction of normal stars in them. We therefore find 0.47 million candidate AGB stars in our Galaxy from the WISE source catalogue. Using W3c, we estimate their distances and derive their Galactic distributions. The candidates are generally located around the Galactic center uniformly, with 68% (1-sigma) of them within approximately 8 kpc. We discuss that optical spectroscopy can be used to verify the C-rich AGB stars in our candidates, and they will be good targets for the LAMOST survey that is planned to start from fall of 2012.