New BVIc Photometry of Low-mass Pleiades Stars: Exploring the Effects of Rotation on Broadband Colors

TL;DR

This study provides new BVIc photometry for low-mass Pleiades stars, revealing a significant correlation between stellar rotation rates and their positions in the color-magnitude diagram, challenging existing models of stellar evolution.

Contribution

It offers the first extensive empirical photometric catalog for low-mass Pleiades stars and links rotation to CMD displacement, improving understanding of stellar evolution at 100 Myr.

Findings

Mid K and early M stars are displaced below the ZAMS in the CMD.

Rapid rotators show larger displacements in the B-V CMD.

New photometry doubles the number of well-calibrated low-mass stars in the Pleiades.

Abstract

We present new BVIc photometry for 350 Pleiades proper-motion members with 9 < V < 17. Importantly, our new catalog includes a large number of K and early-M type stars, roughly doubling the number of low-mass stars with well calibrated Johnson/Cousins photometry in this benchmark cluster. We combine our new photometry with existing photometry from the literature to define a purely empirical isochrone at Pleiades age (~100 Myr) extending from V=9 to 17. We use the empirical isochrone to identify 48 new probable binaries and 14 likely non-members.The photometrically identified single stars are compared against their expected positions in the color-magnitude diagram (CMD). At 100 Myr, the mid K and early M stars are predicted to lie above the zero-age main sequence (ZAMS) having not yet reached the ZAMS. We find in the B-V vs. V CMD that mid K and early M dwarfs are instead displaced below (or blueward of) the ZAMS. Using the stars' previously reported rotation periods, we find a highly statistically significant correlation between rotation period and CMD displacement, in the sense that the more rapidly rotating stars have the largest displacements in the B- V CMD.