Periods and classifications of RR Lyrae stars in the globular cluster M15

TL;DR

This paper reports detailed measurements of periods, amplitudes, and classifications of 74 RR Lyrae stars in globular cluster M15, introduces a new Python tool for period detection, and discusses new variable star identifications.

Contribution

It presents a novel adaptive free-form fitting technique and a Python package for more accurate period determination of variable stars.

Findings

74 RR Lyrae stars analyzed with new period measurements

Identification of 5 Type II Cepheid variables with new periods

Development of the PIPS Python package for period detection

Abstract

We present measurements of the periods, amplitudes, and types of 74 RR Lyrae stars in the globular cluster M15 derived from Nickel 1 m telescope observations conducted at LickObservatory in 2019 and 2020. Of these RR Lyrae stars, two were previously reported but without a determination of the period. In addition, we identify five Type II Cepheid variable stars for which we report three novel period determinations, and a further 34 stars with uncertain classifications and periods. We discuss the development and subsequent application to our data of a new Python package, Period-determination and Identification Pipeline Suite(PIPS), based on a new adaptive free-form fitting technique to detect the periods of variable stars with a clear treatment of uncertainties.