The bottom of the white dwarf cooling sequence in the old open cluster NGC 2158

TL;DR

This study uses advanced telescope observations to identify the end of the white dwarf cooling sequence in NGC 2158, providing an age estimate consistent with main-sequence turn-off data and confirming theoretical predictions about white dwarf colors.

Contribution

It presents the first detection of the white dwarf cooling sequence's end in NGC 2158, refining age estimates and confirming theoretical models with deep photometry.

Findings

White dwarf cooling sequence ends at magnitude m_F606W = 27.5 +/- 0.15

Age of NGC 2158 estimated between 1.8 and 2.0 Gyr

Faintest white dwarfs turn toward bluer colors as predicted

Abstract

We use 10 orbits of Advanced Camera for Surveys observations to reach the end of the white dwarf cooling sequence in the solar-metallicity open cluster NGC 2158. Our photometry and completeness tests show that the end falls at magnitude m_F606W = 27.5 +/- 0.15, which implies an age between ~1.8 and ~2.0 Gyr, consistent with the age of 1.9 +/- 0.2 Gyr obtained from fits to the main-sequence turn-off. The faintest white dwarfs show a clear turn toward bluer colors, as predicted by theoretical isochrones.