Variable Stars in Large Magellanic Cloud Globular Clusters II: NGC 1786

TL;DR

This study analyzes variable stars in the Large Magellanic Cloud globular cluster NGC 1786, focusing on RR Lyrae stars and their Oosterhoff classification, using new BV photometry and Fourier analysis to explore their properties and classifications.

Contribution

It provides a detailed photometric survey of variable stars in NGC 1786 and examines the complexity of its Oosterhoff classification, contributing new data and analysis methods.

Findings

Identified 65 variable stars, including RR Lyrae, Cepheids, eclipsing binaries, and Delta Scuti variables.

Derived physical properties of RR Lyrae stars through Fourier analysis.

Indicated that NGC 1786's Oosterhoff classification is ambiguous and not straightforward.

Abstract

This is the second in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to study how RR Lyrae stars in Oosterhoff-intermediate systems compare to their counterparts in Oosterhoff I/II systems. In this paper, we present the results of our new time-series BV photometeric study of the globular cluster NGC 1786. A total of 65 variable stars were identified in our field of view. These variables include 53 RR Lyraes (27 RRab, 18 RRc, and 8 RRd), 3 classical Cepheids, 1 Type II Cepheid, 1 Anomalous Cepheid, 2 eclipsing binaries, 3 Delta Scuti/SX Phoenicis variables, and 2 variables of undetermined type. Photometeric parameters for these variables are presented. We present physical properties for some of the RR Lyrae stars, derived from Fourier analysis of their light curves. We discuss several different indicators of Oosterhoff type which indicate that the Oosterhoff classification of NGC 1786 is not as clear cut as what is scene in most globular clusters.