AGB Variables in Local Group Dwarf Irregular Galaxies

TL;DR

This paper studies Mira variables in Local Group dwarf irregular galaxies, exploring their potential as distance indicators and their evolutionary insights, especially regarding hot bottom burning and mid-infrared characteristics.

Contribution

It provides new understanding of Mira variables' properties in dwarf irregular galaxies and their implications for stellar evolution and distance measurement techniques.

Findings

Short period Miras are promising distance indicators with low extinction.

The K period-luminosity relation slope change is due to hot bottom burning.

Mid-infrared period-luminosity relation splits into two sequences.

Abstract

The near and mid-infrared characteristics of large amplitude, Mira, variables in Local Group dwarf irregular galaxies (LMC, NGC 6822, IC 1613, Sgr dIG) are described. Two aspects of these variables are discussed. First, the short period (P < 420 days) Miras are potentially powerful distance indicators, provided that they have low circumstellar extinction, or can be corrected for extinction. These are the descendants of relatively low mass stars. Secondly, the longer period stars, many of which undergo hot bottom burning, are poorly understood. These provide new insight into the evolution of intermediate mass stars during the high mass-loss phases, but their use as distance indicators depends on a much firmer understanding of their evolution. The change in slope of the K period luminosity relation for O-rich stars that is seen around 400 to 420 days in the LMC is due to the onset of hot bottom burning. It will be sensitive to metallicity and should therefore be expected at different periods in populations with significant differences from the LMC. The [4.5] period-luminosity relation splits into two approximately parallel sequences. The fainter one fits stars where the mid-infrared flux originates from the stellar photosphere, while the brighter one fits observations dominated by the circumstellar shell.