New candidate EHB stars in the open cluster NGC 6791: Looking locally into the UV-upturn phenomenon

Abstract

Relying on U and B imagery at the Italian Telescopic, Nazionale Galileo (TNG), we report here the discovery of a sample of 13 new UV-bright post-HB candidate stars in the field of the Galactic open cluster NGC 6791. Owing to its super-solar metal content ([Fe/H] greater than or similar to 0.2 dex) and estimated age (t greater than or similar to 8 Gyr), this cluster represents the nearest and ideal stellar aggregate to match the distinctive properties of the evolved stellar populations possibly ruling the UV-upturn phenomenon in elliptical galaxies and bulges of spirals. Our ongoing spectroscopic follow-up of this unique UV-bright sample will allow us to assess - once cluster membership of the candidates is properly checked the real nature (e.g., sdB, sdO, AGB-manque or EHB stars) of these hot sources and their link with the ultraviolet excess emerging from low-mass, metal-rich evolutionary environments of external galaxies.