The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IV. Helium content and relative age of multiple stellar populations within NGC 6352

TL;DR

This study uses multi-wavelength HST data to identify two stellar populations in NGC 6352, measuring their helium content difference and estimating a very small age difference, advancing understanding of globular cluster formation.

Contribution

It introduces a new method to estimate age differences between stellar populations in globular clusters using combined UV and optical data.

Findings

Two populations differ in helium by Delta Y=0.029+/-0.006.

Estimated age difference between populations is approximately 10+/-120 Myr.

Uncertainty in age difference increases to ~300 Myr when considering [Fe/H] and [alpha/Fe] variations.

Abstract

In this paper we combine WFC3/UVIS F275W, F336W, and F438W data from the "UV Legacy Survey of Galactic Globular Clusters: Shedding Light on Their Populations and Formation" (GO-13297) HST Treasury program with F606W, F625W, F658N, and F814W ACS archive data for a multi-wavelength study of the globular cluster NGC 6352. In the color-magnitude and two-color diagrams obtained with appropriate combination of the photometry in the different bands we separate two distinct stellar populations and trace them from the main sequence to the subgiant, red giant, horizontal and asymptotic giant branches. We infer that the two populations differ in He by Delta Y=0.029+/-0.006. With a new method, we also estimate the age difference between the two sequences. Assuming no difference in [Fe/H] and [alpha/Fe], and the uncertainties on Delta Y, we found a difference in age between the two populations of 10+/-120 Myr. If we assume [Fe/H] and [alpha/Fe] differences of 0.02 dex (well within the uncertainties of spectroscopic measurements), the total uncertainty in the relative age rises to ~300 Myr.