The Period-Luminosity Relation of Red Supergiant Stars in the Small Magellanic Cloud

TL;DR

This study analyzes the period-luminosity relation of Red Supergiant stars in the Small Magellanic Cloud using long-term photometric data, revealing similar relations across galaxies and suggesting a pulsation mode.

Contribution

It provides new infrared P-L relations for RSGs in SMC and compares them with other galaxies, proposing the first overtone radial mode as the pulsation mode.

Findings

RSGs in SMC follow similar P-L relations to those in LMC, M33, but differ from the Galaxy.

Infrared P-L relations are reliably derived, especially in Spitzer/IRAC bands.

The pulsation mode of RSGs in SMC is likely the first overtone radial mode.

Abstract

The characteristics of light variation of RSGs in SMC are analyzed based on the nearly 8-10 year long data collected by the ASAS and MACHO projects. The identified 126 RSGs are classified into five categories accordingly: 20 with poor photometry, 55 with no reliable period, 6 with semi-regular variation, 15 with Long Secondary Period (LSP) and distinguishable short period and 30 with only LSP. For the semi-regular variables and the LSP variables with distinguishable short period, the Ks band period-luminosity (P-L) relation is analyzed and compared with that of the Galaxy, LMC and M33. It is found that the RSGs in these galaxies obey similar P-L relation except the Galaxy. In addition, the P-L relations in the infrared bands, namely the 2MASS JHKs, Spitzer/IRAC and Spitzer/MIPS 24 {\mu}m bands, are derived with high reliability. The best P-L relation occurs in the Spitzer/IRAC [3.6] and [4.5] bands. Based on the comparison with the theoretical calculation of the P-L relation, the mode of pulsation of RSGs in SMC is suggested to be the first overtone radial mode.