UVIT-HST-Gaia-VISTA study of KRON 3 in the Small Magellanic Cloud: A cluster with an extended red clump in UV

TL;DR

This study combines multi-wavelength data from UV to near-infrared to analyze the star cluster Kron 3 in the Small Magellanic Cloud, revealing an extended red clump and insights into its stellar population.

Contribution

It reports the first identification of NUV-bright red clump stars and demonstrates the intrinsic extension of the red clump in Kron 3 using combined UV and optical data.

Findings

Extended red clump is intrinsic, not due to contamination or reddening.

NUV-bright red clump stars identified with specific temperature and luminosity ranges.

Variations in UV magnitudes likely caused by mass loss, helium abundance, age, and metallicity differences.

Abstract

We have demonstrated the advantage of combining multi-wavelength observations, from the ultraviolet (UV) to near-infrared, to study Kron 3, a massive star cluster in the Small Magellanic Cloud. We have estimated the radius of the cluster Kron 3 to be 2.'0 and for the first time, we report the identification of NUV-bright red clump (RC) stars and the extension of the RCin colour and magnitude in the NUV vs (NUV-optical) colour-magnitude diagram (CMD). We found that extension of the RC is an intrinsic property of the cluster and it is not due to contamination of field stars or differential reddening across the field. We studied the spectral energy distribution of the RC stars and estimated a small range in temperature ~5000 - 5500K, luminosity ~60 - 90 Land radius ~8.0 - 11.0 Supporting their RC nature. The range of UV magnitudes amongst the RC stars (~23.3 to 24.8 mag) is likely caused by the combined effect of variable mass loss, variation in initial helium abundance (Y_ini=0.23 to 0.28), and a small variation in age (6.5-7.5 Gyr) and metallicity ([Fe/H]=-1.5 to -1.3). Spectroscopic follow-up observations of RC stars in Kron 3 are necessary to confirm the cause of the extended RC.