A lithium depletion boundary age of 22 Myr for NGC 1960

TL;DR

This study determines the age of the open cluster NGC 1960 as approximately 22 million years by analyzing the lithium depletion boundary, providing a robust calibration for young cluster age estimates.

Contribution

First LDB age estimate for NGC 1960, confirming consistency with isochrone-based ages and advancing calibration of young cluster ages.

Findings

LDB age of 22 +/- 4 Myr for NGC 1960

Good agreement between LDB and isochrone ages

NGC 1960 is the youngest cluster with a well-defined LDB

Abstract

We present a deep Cousins RI photometric survey of the open cluster NGC 1960, complete to R_C \simeq 22, I_C \simeq 21, that is used to select a sample of very low-mass cluster candidates. Gemini spectroscopy of a subset of these is used to confirm membership and locate the age-dependent "lithium depletion boundary" (LDB) --the luminosity at which lithium remains unburned in its low-mass stars. The LDB implies a cluster age of 22 +/-4 Myr and is quite insensitive to choice of evolutionary model. NGC 1960 is the youngest cluster for which a LDB age has been estimated and possesses a well populated upper main sequence and a rich low-mass pre-main sequence. The LDB age determined here agrees well with precise age estimates made for the same cluster based on isochrone fits to its high- and low-mass populations. The concordance between these three age estimation techniques, that rely on different facets of stellar astrophysics at very different masses, is an important step towards calibrating the absolute ages of young open clusters and lends confidence to ages determined using any one of them.