Expanding the frontiers of cool-dwarf asteroseismology with ESPRESSO. Detection of solar-like oscillations in the K5 dwarf $\epsilon$ Indi

Abstract

Fuelled by space photometry, asteroseismology is vastly benefitting the study of cool main-sequence stars, which exhibit convection-driven solar-like oscillations. Even so, the tiny oscillation amplitudes in K dwarfs continue to pose a challenge to space-based asteroseismology. A viable alternative is offered by the lower stellar noise over the oscillation timescales in Doppler observations. In this letter we present the definite detection of solar-like oscillations in the bright K5 dwarf $\epsilon$ Indi based on time-intensive observations collected with the ESPRESSO spectrograph at the VLT, thus making it the coolest seismic dwarf ever observed. We measured the frequencies of a total of 19 modes of degree $\ell =0$--2 along with ${\nu }_{\max }=5305\pm 176\mu \mathrm{Hz}$ and $\Delta \nu =201.25\pm 0.16\mu \mathrm{Hz}$. The peak amplitude of radial modes is $2.6\pm 0.5\mathrm{cm}{\mathrm{s}}^{-1}$, or a mere $\sim 14\%$ of the solar value. Measured mode amplitudes are $\sim 2$ times lower than predicted from a nominal $L/M$ scaling relation and favour a scaling closer to $(L/M{)}^{1.5}$ below $\sim 5500\mathrm{K}$, carrying important implications for our understanding of the coupling efficiency between pulsations and near-surface convection in K dwarfs. This detection conclusively shows that precise asteroseismology of cool dwarfs is possible down to at least the mid-K regime using next-generation spectrographs on large-aperture telescopes, effectively opening up a new domain in observational asteroseismology.

Accepted for publication in Astronomy & Astrophysics Letters

References in corpus (24)

• The Transiting Exoplanet Survey Satellite
• The K2 Mission: Characterization and Early results
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Standing on the shoulders of Dwarfs: the $Kepler$ asteroseismic LEGACY sample I - oscillation mode parameters
• CoRoT reveals a magnetic activity cycle in a Sun-like star
• A new correction of stellar oscillation frequencies for near-surface effects
• An ancient extrasolar system with five sub-Earth-size planets
• A multi-site campaign to measure solar-like oscillations in Procyon. I. Observations, Data Reduction and Slow Variations
• The amplitude of solar oscillations using stellar techniques
• Excitation of solar-like oscillations across the HR diagram
• Stellar chromospheric activity of 1,674 FGK stars from the AMBRE-HARPS sample I. A catalogue of homogeneous chromospheric activity
• DIAMONDS: a new Bayesian Nested Sampling tool. Application to Peak Bagging of solar-like oscillations
• PLATO as it is: a legacy mission for Galactic archaeology
• Solar-like oscillations in the G8 V star tau Ceti
• Detection of the nearest Jupiter analog in radial velocity and astrometry data
• Why should we correct reported pulsation frequencies for stellar line-of-sight Doppler velocity shifts?
• Asteroseismology of the visual binary 70 Ophiuchi
• Precision angular diameters for 16 southern stars with VLTI/PIONIER
• Asteroseismic stellar activity relations
• Precise Dynamical Masses of Epsilon Indi Ba and Bb: Evidence of Slowed Cooling at the L/T Transition
• The KOBE experiment: K-dwarfs Orbited By habitable Exoplanets. Project goals, target selection and stellar characterization
• On the origin of the dichotomy of stellar activity cycles
• The relationship between photometric and spectroscopic oscillation amplitudes from 3D stellar atmosphere simulations
• Constraints on the nearby exoplanet $\epsilon$ Ind Ab from deep near/mid-infrared imaging limits