The lower main sequence of stars in the solar neighborhood: Model predictions versus observation

TL;DR

This study compares observed color-magnitude diagrams of nearby K-M dwarfs with theoretical models, revealing significant discrepancies especially for lower-mass stars, and identifies models that best match the data.

Contribution

It provides a detailed comparison between observational data and stellar models for the lower main sequence, highlighting model limitations and identifying the most accurate isochrones.

Findings

Most models show offsets from observational data for lower-mass stars.

Victoria-Regina and BaSTI isochrones match the data well.

Unresolved binaries and variable stars significantly affect the main sequence.

Abstract

We have used the Simbad database and VizieR catalogue access tools to construct the observational color-absolute magnitude diagrams of nearby K-M dwarfs with precise Hipparcos parallaxes (\sigma_\pi/\pi < 0.05). Particular attention has been paid to removing unresolved double/multiple and variable stars. In addition to archival data, we have made use of nearly 2000 new radial-velocity measurements of K-M dwarfs to identify spectroscopic binary candidates. The main sequences, cleaned from unresolved binaries, variable stars, and old population stars which can also widen the sequence due to their presumably lower metallicity, were compared to available solar-metallicity models. Significant ofsets of most of the model main-sequence lines are seen with respect to observational data, especially for the lower-mass stars. Only the location and slope of the Victoria-Regina and, partly, BaSTI isochrones match the data quite well.