RR Lyrae Variables in NGC 2808

TL;DR

This study presents the first detailed time-series photometry of RR Lyrae variables in NGC 2808, providing insights into its bimodal horizontal branch, formation history, and possible links to a dwarf galaxy, enhancing understanding of globular cluster evolution.

Contribution

First calibrated CCD photometry of RR Lyrae stars in NGC 2808 over twenty years, revealing new variables and informing models of its unique horizontal branch features.

Findings

Discovered new RR Lyrae variables in NGC 2808.

Analyzed the effects of helium enrichment and differential reddening.

Discussed the cluster's Oosterhoff classification and its galactic context.

Abstract

NGC 2808 is a unique globular cluster with not only a bimodal-horizontal branch (HB) but also with gaps on the blue horizontal branch. Adequate interpretation of the nature of the detected peculiarities in "bimodal" and "gap" clusters is of paramount importance for understanding the nature of the second parameter phenomenon and scenarios for the formation of the Galaxy. Although RR Lyrae variables are HB stars that can provide powerful constraints to models on the origin of bimodal HBs, unfortunately, until recently, only one RR Lyrae variable was known in this cluster. Here we present the first calibrated time-series CCD photometry for newly discovered fundamental mode RR Lyrae variables in NGC 2808, with observations over a range of twenty years. Investigations of RR Lyrae variable stars in this peculiar, bimodal-horizontal branch globular cluster are carried out to account for its formation, and the effects of helium enrichment and differential reddening. The Oosterhoff classification of NGC$\,$2808, which has recently been associated with a previously unknown dwarf galaxy in Canis Major, is also discussed.