# VR CCD photometry of variable stars in globular cluster NGC 4147

## TL;DR

This study used CCD photometry to discover and classify 42 variable stars in globular cluster NGC 4147, including 28 newly detected variables, and estimated the cluster's metallicity and distance.

## Contribution

First time detailed CCD photometry and variable star detection in NGC 4147 using the 3.6m Devasthal telescope, including classification and metallicity estimation.

## Key findings

- 42 variable stars identified, 28 new detections
- Cluster metallicity consistent with Oosterhoff II type
- Distance estimates from RRab stars align with CMD measurements

## Abstract

We present results of a search for variable stars in a region of the globular cluster NGC 4147 based on photometric observations with 4k x 4k CCD imager mounted at the axial port of the recently installed 3.6 m Devasthal optical telescope at Aryabhatta Research Institute of Observational Sciences, Nainital, India. We performed time series photometry of NGC 4147 in V and R bands, and identified 42 periodic variables in the region of NGC 4147, 28 of which have been detected for the first time. Seventeen variable stars are located within the half light radius $\lesssim$ 0.48 arcmin, of which 10 stars are newly identified variables. Two of 10 variables are located within the core radius $\lesssim$ 0.09 arcmin. Based on the location in the $V/(V-R)$ colour magnitude diagram and variability characteristics, 7, 8, 5 and 1 newly identified probable member variables are classified as RRc, EA/E, EW and SX Phe, respectively. The metallicity of NGC 4147 estimated from light curves of RRab and RRc stars with the help of Fourier decomposition is found to be characteristics of Oosterhoff II. The distance derived using light curves of RRab stars is consistent with that obtained from the observed $V/(V-R)$ colour-magnitude diagram.