# Secular period variations of RR Lyrae stars in NGC 4147

## TL;DR

This study analyzes 58 years of photometric data on RR Lyrae stars in NGC 4147, revealing diverse period variations that align with theoretical models, while discussing the challenges in empirical validation.

## Contribution

It provides a long-term analysis of RR Lyrae period changes in NGC 4147 using the O-C diagram method, highlighting the complexity of empirical verification of stellar evolution theories.

## Key findings

- Three stars show significant period decrease.
- Two stars exhibit comparable period increase.
- Median period change is nearly zero, consistent with theory.

## Abstract

A compilation of photometric time-series data of NGC 4147 spanning 58 years, enabled to study the secular behaviour of the pulsation period in the population of RR Lyrae stars in the cluster. The traditional O-C diagram approach was employed. Three stars display a significant period decrease and two a comparable period increase. Nevertheless, the median value of the whole sample is nearly zero, which seems consistent with theoretical expectations. The limitations of empirical determinations of secular period changes in globular clusters to corroborate evolutionary theoretical predictions are discussed.