Mid-IR period-magnitude relations for AGB stars

TL;DR

This study reveals that AGB stars follow consistent mid-infrared period-magnitude relations across different environments, with dust emission and mass-loss characteristics observable at 24 microns, aiding distance and stellar evolution studies.

Contribution

It demonstrates that mid-IR period-magnitude relations for AGB stars are similar across different galaxies and wavelengths, providing new insights into their dust emission and mass-loss properties.

Findings

AGB stars obey similar period-luminosity relations at mid-IR wavelengths in different galaxies.

Detection of dust shells around semi-regular variables at 24 microns.

Identification of a bifurcation in LMC colour-magnitude diagrams involving 24 micron magnitudes.

Abstract

Asymptotic Giant Branch variables are found to obey period-luminosity relations in the mid-IR similar to those seen at K_S (2.14 microns), even at 24 microns where emission from circumstellar dust is expected to be dominant. Their loci in the M, logP diagrams are essentially the same for the LMC and for NGC6522 in spite of different ages and metallicities. There is no systematic trend of slope with wavelength. The offsets of the apparent magnitude vs. logP relations imply a difference between the two fields of 3.8 in distance modulus. The colours of the variables confirm that a principal period with log P > 1.75 is a necessary condition for detectable mass-loss. At the longest observed wavelength, 24 microns, many semi-regular variables have dust shells comparable in luminosity to those around Miras. There is a clear bifurcation in LMC colour-magnitude diagrams involving 24 micron magnitudes.