The Curious Case of the Chromospherically (and Isochronally) Candescent K Stars

A significant fraction of apparently isochronally young, chromospherically active (UV-luminous) K and early-M stars appear to have anomalous kinematics and display weak X-ray emission. We demonstrate that the combination of UV excesses, X-ray fluxes, and newly available rotation rates from the TESS mission can potentially serve to assess the youth (or lack thereof) of these candidate pre-main sequence field stars. This approach holds promise for purposes of distinguishing between "bona fide" young, low-mass stars and "imposters"—overluminous, UV-bright ZAMS or evolved main sequence stars—and could shed light on why the latter might masquerade as the former.