Most stars previously identified as Maunder minimum stars are old stars evolved off of the main sequence. Analysis of activity measurements from the California and Carnegie Planet Search program stars and Hipparcos parallaxes implies that the canonical age-chromospheric activity relation breaks down for stars older than ∼6 Gyr when activity is calculated from Mount Wilson S values. Stars only 1 magnitude above the main sequence exhibit significantly suppressed activity levels which have been mistaken for examples of Maunder minimum behavior.
@article{arxiv.astro-ph/0406338,
title = {Do We Know of Any Maunder Minimum Stars?},
author = {Jason T. Wright},
journal= {arXiv preprint arXiv:astro-ph/0406338},
year = {2009}
}