Period-luminosity relations of pulsating M giants in the solar neighbourhood and the Magellanic Clouds

TL;DR

This study analyzes pulsating M giants in the solar neighborhood and Magellanic Clouds, establishing period-luminosity relations, calibrating distances, and demonstrating the universality of RGB pulsation properties as precise distance indicators.

Contribution

It introduces a new method for determining absolute magnitudes from pulsation periods and calibrates the LMC distance modulus using Hipparcos parallaxes.

Findings

RGB pulsations detected in the solar neighborhood.

LMC distance modulus calibrated to 18.54 mag.

RGB pulsation properties are consistent and universal.

Abstract

We analyse the results of a 5.5-yr photometric campaign that monitored 247 southern, semi-regular variables with relatively precise Hipparcos parallaxes to demonstrate an unambiguous detection of Red Giant Branch (RGB) pulsations in the solar neighbourhood. We show that Sequence A' contains a mixture of AGB and RGB stars, as indicated by a temperature related shift at the TRGB. Large Magellanic Cloud (LMC) and Galactic sequences are compared in several ways to show that the P-L sequence zero-points have a negligible metallicity dependence. We describe a new method to determine absolute magnitudes from pulsation periods and calibrate the LMC distance modulus using Hipparcos parallaxes to find \mu (LMC) = 18.54 +- 0.03 mag. Several sources of systematic error are discussed to explain discrepancies between the MACHO and OGLE sequences in the LMC. We derive a relative distance modulus of the Small Magellanic Cloud (SMC) relative to the LMC of \Delta \mu = 0.41 +- 0.02 mag. A comparison of other pulsation properties, including period-amplitude and luminosity-amplitude relations, confirms that RGB pulsation properties are consistent and universal, indicating that the RGB sequences are suitable as high-precision distance indicators. The M giants with the shortest periods bridge the gap between G and K giant solar-like oscillations and M-giant pulsation, revealing a smooth continuity as we ascend the giant branch.