The Local Group Galaxy NGC 6822 and its Asymptotic Giant Branch Stars

TL;DR

This study presents detailed JHKs photometry of NGC 6822's central regions, analyzing AGB star populations, their period-luminosity relations, and implications for distance measurement and stellar evolution in the galaxy.

Contribution

It provides new near-infrared photometric data and period analyses of AGB stars in NGC 6822, comparing their properties with those in other Local Group galaxies.

Findings

The bolometric period-luminosity relation slope for C-rich Miras matches the LMC.

Distance estimates from Miras agree with previous measurements.

C-rich Mira period distribution resembles that in the Magellanic Clouds.

Abstract

JHKs photometry is presented from a 3.5 year survey of the central regions of the irregular galaxy NGC6822. The morphology of the colour-magnitude and colour-colour diagrams is discussed with particular reference to M, S and C-type AGB stars and to M-supergiants. Mean JHKs magnitudes and periods are given for 11 O-rich and 50 presumed C-rich Miras. Data are also listed for 27 large amplitude AGB stars without periods and for 69 small amplitude AGB variables. The slope of the bolometric period-luminosity relation for the C-rich Miras is in good agreement with that in the LMC. Distance moduli derived from the C- and O-rich Miras are in agreement with other estimates. The period distribution of C-rich Miras in NGC6822 is similar to that in the Magellanic Clouds, but differs from that in the dwarf spheroidals in the Local Group. In the latter there is a significant proportion of large amplitude, short period variables indicating a population producing old carbon-rich AGB stars.