A Spitzer Space Telescope survey of extreme Asymptotic Giant Branch stars in M32

TL;DR

This study uses Spitzer infrared observations to identify and analyze dust-producing asymptotic giant branch stars in M32, revealing a significant population of obscured extreme AGB stars and estimating their contribution to dust and gas mass loss.

Contribution

First detection and characterization of a large population of extreme AGB stars in M32 using infrared data, highlighting their role in dust and gas enrichment.

Findings

Identified a sizeable population of extreme AGB stars in M32.

Measured the dust-injection rate from these stars.

Estimated the gas mass-loss rate associated with the AGB population.

Abstract

We investigate the population of cool, evolved stars in the Local Group dwarf elliptical galaxy M32, using Infrared Array Camera observations from the Spitzer Space Telescope. We construct deep mid-infrared colour-magnitude diagrams for the resolved stellar populations within 3.5 arcmin of M32's centre, and identify those stars that exhibit infrared excess. Our data is dominated by a population of luminous, dust-producing stars on the asymptotic giant branch (AGB) and extend to approximately 3 mag below the AGB tip. We detect for the first time a sizeable population of `extreme' AGB stars, highly enshrouded by circumstellar dust and likely completely obscured at optical wavelengths. The total dust-injection rate from the extreme AGB candidates is measured to be $7.5 \times 10^{-7}$ ${\rm M}_{\odot} \, {\rm yr}^{-1}$, corresponding to a gas mass-loss rate of $1.5 \times 10^{-4}$ ${\rm M}_{\odot} \, {\rm yr}^{-1}$. These extreme stars may be indicative of an extended star-formation epoch between 0.2 and 5 Gyr ago.