Asteroseismology of the Nearby K-Dwarf $\sigma$ Draconis using the Keck Planet Finder and TESS

TL;DR

This study successfully detected and analyzed solar-like oscillations in the nearby cool K-dwarf star σ Draconis using high-precision Doppler and photometric data, providing new insights into stellar oscillation amplitudes and ages.

Contribution

It presents the first combined velocity and luminosity asteroseismic observations of a cool dwarf star, demonstrating the potential of next-generation instruments for studying such stars.

Findings

Detected solar-like oscillations at 4-minute timescales in σ Draconis.

Measured oscillation amplitudes consistent with theoretical amplitude relations.

Estimated the star's age to be approximately 4.5 billion years.

Abstract

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 ($\nu_{\mathrm{max}}\sim4300\mu$Hz) 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 star to date with both velocity and luminosity observations of solar-like oscillations, having amplitudes of $5.9\pm0.8\,$cm$\,\text{s}^{-1}$ and $0.8\pm0.2$ ppm, respectively. These measured values are in excellent agreement with established luminosity-velocity amplitude relations for oscillations and provide further evidence that mode amplitudes for stars with $T_{\mathrm{eff}}<\,5500\,$K diminish in scale following a $(L/M)^{1.5}$ relation. By modeling the star's oscillation frequencies from photometric data, we measure an asteroseismic age of $4.5\pm0.9\,\rm{(ran)} \pm 1.2\,\rm{(sys)}$ Gyr. The 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.