Are pre-MS stars older than we thought?

TL;DR

This paper compares ages of young star clusters derived from pre-main-sequence contraction with those from upper main-sequence evolution, finding the latter are significantly older, challenging current age estimates of pre-MS stars.

Contribution

It provides a consistent age ordering for young clusters using pre-main-sequence contraction and highlights discrepancies with traditional upper main-sequence age estimates.

Findings

Upper MS ages are 1.5 to 2 times older than pre-MS ages.

Increasing binary fraction among O-stars does not resolve the age discrepancy.

Abstract

We present a consistent age ordering for young clusters and groups determined using the contraction of stars through their pre-main-sequence phase. We compare these with ages derived from the evolution of the upper main-sequence stars, and find the upper MS ages are older by a factor 1.5 to 2. We show that increasing the binary fraction and number of equal-mass binaries amongst the O-stars compared to the rest of the MS cannot remove this discrepancy.