AGB Interlopers in YSO Catalogs Hunted out by NEOWISE

Asymptotic giant branch stars (AGBs) and young stellar objects (YSOs) often share the same domains in infrared (IR) color–magnitude or color–color diagrams leading to potential misclassification. We extracted a list of AGB interlopers from the published YSO catalogs using the periodogram analysis on the Near-Earth Object Wide Infrared Survey Explorer (NEOWISE) time series data. YSO IR variability is typically stochastic and linked to episodic mass accretion. Furthermore, most variable YSOs are at an early evolutionary stage, with significant surrounding envelope and/or disk material. In contrast, AGBs are often identified by a well-defined sinusoidal variability with periods of a few hundreds days. From our periodogram analysis of all known low-mass YSOs in the Gould Belt, we find 85 AGB candidates, out of which 62 were previously classified as late-stage Class III YSOs. Most of these new AGB candidates have similar IR colors to O-rich AGBs. We observed 73 of these AGB candidates in the H2O, CH3OH, and SiO maser lines to further reveal their nature. The SiO maser emission was detected in 10 sources, confirming them as AGBs because low-mass YSOs, especially Class III YSOs, do not show such maser emission. The H2O and CH3OH maser lines were detected in none of our targets.