Advancing cool-dwarf asteroseismology with Extremely Precise Radial Velocities (EPRVs)
Abstract
The tiny oscillation amplitudes in cool main-sequence stars (below 10 cm/s or, equivalently, a few ppm) fall below the detection threshold of space photometry. A viable alternative is offered by the lower stellar “noise” over the oscillation timescales in Doppler observations. Recent years have thus witnessed a resurgence of observing campaigns on K dwarfs using EPRV instruments on large-aperture telescopes. Notably, a pilot campaign with ESPRESSO@VLT on the K5 dwarf ϵ Indi demonstrated its potential for cool-dwarf asteroseismology, enabling detection of solar-like oscillations with a peak amplitude of 2.6 cm/s (just 14% of the solar value). This effectively opened a new domain in observational asteroseismology with profound implications for the field of stellar astrophysics. In this talk, I will present the main findings of our ongoing survey of seismic K dwarfs with ESPRESSO. We find growing evidence that oscillation amplitudes in K dwarfs scale as (L/M)^1.5, in contrast to the (L/M)^0.7 relation observed for G dwarfs. To explore this, we performed 3D hydrodynamical simulations to constrain the coupling between oscillations and near-surface convection over a broad T_eff interval. Our simulations also allow us to quantify granulation timescales and amplitudes, which could inform mitigation strategies in RV planet searches. Furthermore, we find that stellar models systematically underestimate the radii of K dwarfs by up to 5% compared to interferometric measurements. Using seismic constraints, we calibrated the mixing-length parameter, α_MLT, in this T_eff regime to reconcile modeled and empirical radii, with important implications for our understanding of the structure and interior physics of K dwarfs.