σ Draconis: The coolest nearby star with asteroseismology from the Keck Planet Finder and TESS

Asteroseismology of dwarf stars cooler than the Sun is very challenging due to the low amplitudes and rapid timescales of oscillations. Here, we present the asteroseismic detection of solar-like oscillations at 4-minute timescales in the nearby K-dwarf sigma Draconis using extreme precision Doppler velocity observations from the Keck Planet Finder and 20-second cadence photometry from NASA's Transiting Exoplanet Survey Satellite. The star is the coolest dwarf to date with asteroseismic observations from both ground and space. The measured oscillations show excellent agreement with established luminosity-velocity amplitude relations and provide further evidence that mode amplitudes for stars cooler than the Sun scale more steeply with stellar luminosity than expected. By modelling the star's oscillation frequencies from photometric data, we measure an asteroseismic age of 4.5 Gyr, in agreement with values from literature. These observations demonstrate the capability of next-generation spectrographs and precise space-based photometry to extend observational asteroseismology to nearby cool dwarfs, which are benchmarks for stellar astrophysics and prime targets for directly imaging planets using future space-based telescopes.