Exploring RR Lyrae Variable Stars in the Vera C. Rubin Observatory Data Preview 1

TL;DR

This study analyzes known RR Lyrae stars in Vera C. Rubin Observatory DP1 data, comparing observed properties with stellar models to assess distance and metallicity estimations, highlighting current limitations and future improvements.

Contribution

It provides the first comparison of RR Lyrae properties in Rubin Observatory data with stellar models, evaluating metallicity and distance estimates and identifying calibration uncertainties.

Findings

PWZ relations yield accurate distances with minimal metallicity dependence.

PLZ distances are systematically overestimated due to calibration issues.

Future data releases will improve light curve sampling and parameter accuracy.

Abstract

We investigate the properties of known RR Lyrae in the Vera C. Rubin Observatory Data Preview 1 (DP1) fields and compare those with the predictions based on stellar pulsation models tailored to the Legacy Survey of Space and Time (LSST) filters. The cross-match of the DP1 data with two public variable star catalogs resulted in $\sim 600$ RR Lyrae with adequate light curve sampling in five (out of seven) DP1 fields. The majority of RR Lyrae are in the 47 Tucanae and Fornax fields. We estimated photometric metallicities for these RR Lyrae using the theoretical metallicity-color relation based on $gri$-band data, and find a good agreement with literature values where the light curve sampling is sufficient for fitting template light curves accurately. The distance modulus to all RR Lyrae in DP1 fields were determined using the theoretical period-luminosity-metallicity (PLZ) relations and the $W_{gr}$ period-Wesenheit-metallicity (PWZ) relation which has the smallest metallicity term. The distances based on PWZ relations are in good agreement with the literature values with a mean offset of $0.01\pm0.36$~mag. However, the PLZ-based distance moduli are systematically large which could be due to the theoretical calibration uncertainties that include evolved horizontal branch models. The predicted period-amplitude relations based on evolved models are also inconsistent with the amplitudes based on DP1 light curves. We conclude that the metallicity and distance estimates are sensitive to the template fitting to sparsely sampled light curves in DP1 data and future data release will significantly improve these determinations for RR Lyrae stars.