# Photometry of the Globular Cluster NGC 5466: Red Giants and Blue Stragglers

## TL;DR

This study provides detailed photometry of NGC 5466, detecting the red giant branch bump, analyzing stellar ratios and dynamical indicators, revealing insights into its stellar evolution and dynamical history, including mass loss and blue straggler distribution.

## Contribution

First detection of the red giant branch bump in NGC 5466 and analysis of stellar ratios and dynamical properties compared to theoretical models.

## Key findings

- Red giant branch bump detected at 0.2 mag fainter than expected.
- Cluster shows a very shallow mass function indicating significant mass loss.
- Blue stragglers are more centrally concentrated and consistent with dynamical friction expectations.

## Abstract

We present wide-field BVI photometry for about 11,500 stars in the low-metallicity cluster NGC 5466. We have detected the red giant branch bump for the first time, although it is at least 0.2 mag fainter than expected relative to the turnoff. The number of red giants (relative to main sequence turnoff stars) is in excellent agreement with stellar models from the Yonsei-Yale and Teramo groups, and slightly high compared to Victoria-Regina models. This adds to evidence that an abnormally large ratio of red giant to main-sequence stars is not correlated with cluster metallicity. We discuss theoretical predictions from different research groups and find that the inclusion or exclusion of helium diffusion and strong limit Coulomb interactions may be partly responsible. We also examine indicators of dynamical history: the mass function exponent and the blue straggler frequency. NGC 5466 has a very shallow mass function, consistent with large mass loss and recently-discovered tidal tails. The blue straggler sample is significantly more centrally concentrated than the HB or RGB stars. We see no evidence of an upturn in the blue straggler frequency at large distances from the center. Dynamical friction timescales indicate that the stragglers should be more concentrated if the cluster's present density structure has existed for most of its history. NGC 5466 also has an unusually low central density compared to clusters of similar luminosity. In spite of this, the specific frequency of blue stragglers that puts it right on the frequency -- cluster M_V relation observed for other clusters.