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

Abstract

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 Lick Observatory 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.