RR Lyrae Variables in the Local Group Dwarf Galaxy NGC 147

TL;DR

This study investigates RR Lyrae stars in NGC 147 using ground-based and HST data, finding the presence of old stellar populations but highlighting limitations in determining detailed pulsation properties due to data quality.

Contribution

It provides a comparative analysis of different datasets for RR Lyrae detection in NGC 147 and discusses the challenges in characterizing their pulsation properties.

Findings

NGC 147 contains RR Lyrae variables, indicating an old stellar population.

Data quality limits the ability to determine pulsation properties.

Results serve as a reference for future RR Lyrae detection completeness.

Abstract

We investigate the RR Lyrae population in NGC 147, a dwarf satellite galaxy of M31 (Andromeda). We used both Thuan-Gunn g-band ground-based photometry from the literature and Hubble Space Telescope Wide Field Planetary Camera 2 archival data in the F555W and F814W passbands to investigate the pulsation properties of RR Lyrae variable candidates in NGC 147. These datasets represent the two extreme cases often found in RR Lyrae studies with respect to the phase coverage of the observations and the quality of the photometric measurements. Extensive artificial variable star tests for both cases were performed. We conclude that neither dataset is sufficient to confidently determine the pulsation properties of the NGC 147 RR Lyraes. Thus, while we can assert that NGC 147 contains RR Lyrae variables, and therefore a population older than ~10 Gyr, it is not possible at this time to use the pulsation properties of these RR Lyraes to study other aspects of this old population. Our results provide a good reference for gauging the completeness of RR Lyrae variable detection in future studies.