The Distance of the First Overtone RR Lyrae Variables in the MACHO LMC Database: A New Method to Correct for the Effects of Crowding

TL;DR

This paper introduces a new method to correct for crowding effects in RR Lyrae variables in the LMC, improving distance measurements by analyzing amplitude and period relations.

Contribution

It presents a novel approach using M3-like RR Lyrae properties and amplitude analysis to identify and correct for crowding effects in LMC distance estimations.

Findings

Derived an LMC distance modulus of 18.49±0.11

Identified crowding effects through amplitude differences

Improved distance measurement accuracy

Abstract

Previous studies have indicated that many of the RR Lyrae variables in the LMC have properties similar to the ones in the Galactic globular cluster M3. Assuming that the M3 RR Lyrae variables follow the same relationships among period, temperature, amplitude and Fourier phase parameter phi31 as their LMC counterparts, we have used the M3 phi31-logP relation to identify the M3-like unevolved first overtone RR Lyrae variables in 16 fields near the LMC bar. The temperatures of these variables were calculated from the M3 logP-logTe relation so that the extinction could be derived for each star separately. Since blended stars have lower amplitudes for a given period, the period amplitude relation should be a useful tool for identifying which stars are affected by crowding. We find that the low amplitude stars are brighter. We remove them from the sample and derive an LMC distance modulus 18.49+/-0.11.