Pre-main-sequence isochrones -- I. The Pleiades benchmark

TL;DR

This paper critically evaluates pre-main-sequence isochrones by comparing model predictions to Pleiades observations, revealing systematic flux overestimations at low temperatures and emphasizing the importance of using natural photometric systems for accurate model-data comparisons.

Contribution

It introduces a benchmark for pre-main-sequence models using Pleiades data and provides system response models for the Wide-Field Camera, improving model validation accuracy.

Findings

Models overestimate flux below 4000 K at 0.5 microns

Optical age estimates for young stars are underestimated

Using natural photometric systems reduces transformation errors

Abstract

We present a critical assessment of commonly used pre-main-sequence isochrones by comparing their predictions to a set of well-calibrated colour-magnitude diagrams of the Pleiades in the wavelength range 0.4 to 2.5 microns. Our analysis shows that for temperatures less than 4000 K the models systematically overestimate the flux by a factor two at 0.5 microns, though this decreases with wavelength, becoming negligible at 2.2 microns. In optical colours this will result in the ages for stars younger than 10 Myr being underestimated by factors between two and three. We show that using observations of standard stars to transform the data into a standard system can introduce significant errors in the positioning of pre-main-sequences in colour-magnitude diagrams. Therefore we have compared the models to the data in the natural photometric system in which the observations were taken. Thus we have constructed and tested a model of the system responses for the Wide-Field Camera on the Isaac Newton Telescope. As a benchmark test for the development of pre-main-sequence models we provide both our system responses and the Pleiades sequence.