2025ApJ...990..113M

We present initial results from a planned 10 yr survey of Ca II H and K emission, using observations made with the Astrophysical Research Consortium 3.5 m Telescope at Apache Point Observatory. The primary goal of the survey is to investigate activity cycles in low-mass stars. The sample includes stars chosen from the legacy Mount Wilson Observatory (MWO) survey carried out by Olin Wilson more than 50 yr ago, together with newly identified planet-hosting stars and a select sample of early to mid M dwarfs. This paper presents the first 4 yr of data, comprising 1040 observations of 271 stars, with a specific focus on K and M stars. We identify a subsample of 153 stars for continuing observations over the full 10 yr survey. Early results indicate that our data are consistent with the MWO cycle periods over a time span of more than 50 yr; that there is a bifurcation in activity in the late K range with separate populations of low- and high-activity stars at lower masses; and that M dwarf planet hosts tend to be mainly found in the population of low-activity stars, even in the unbiased (by activity) TESS sample, potentially indicating a link between activity and planet formation. We have also found indications of possible cyclic variability in some of the lower-mass stars in the sample. Our ultimate goal is to link the activity cycle and rotation periods in a robust sample of stars spanning the FGKM spectral types and to investigate the implications for the underlying magnetic dynamo.