A stellar symphony: Asteroseismology reveal the interior of stars

Amazing stuff!

"... A Stellar Symphony

Although we cannot directly hear them with our own ears, stars are not silent. Like musical instruments, stars resonate with natural frequencies that astronomers can “hear” with the right tools. This field of research — known as asteroseismology — allows scientists to use these frequencies to probe the interiors of stars, just as earthquakes help scientists learn about Earth’s interior. ...

Keck Observatory’s KPF instrument precisely measures the motion of the stellar surface towards and away from the observer. Over four consecutive nights, the team used KPF to collect over 2,000 ultra-precise velocity measurements of the star — enabling them to catch the star’s vibrations in action. This is the first asteroseismic inference of the age and radius for a cool star using KPF.

“KPF’s fast readout mode makes it perfectly suited for detecting oscillations in cool stars,” ... “and it is the only spectrograph on Mauna Kea currently capable of making this type of discovery.” ..."

From the abstract:

"We present the first asteroseismic analysis of the K3 V planet host HD 219134 based on four consecutive nights of radial velocities collected with the Keck Planet Finder. We apply Gold deconvolution to the power spectrum to disentangle modes from side lobes in the spectral window and extract 25 mode frequencies with spherical degrees 0 ≤ ℓ ≤ 3.

We derive the fundamental properties using five different evolutionary-modeling pipelines and report a mass of 0.763 ± 0.020 (stat)  ± 0.007 (sys) M⊙, a radius of 0.748 ± 0.007 (stat)  ± 0.002 (sys) R⊙, and an age of 10.151 ± 1.520 (stat)  ± 0.810 (sys) Gyr. Compared to the interferometric radius 0.783 ± 0.005 R⊙, the asteroseismic radius is 4% smaller at the 4σ level—a discrepancy not easily explained by known interferometric systematics, modeling assumptions on atmospheric boundary conditions and mixing lengths, magnetic fields, or tidal heating.

HD 219134 is the first main-sequence star cooler than 5000 K with an asteroseismic age estimate and will serve as a critical calibration point for stellar spin-down relations.

We show that existing calibrated prescriptions for angular momentum loss, incorporating weakened magnetic braking with asteroseismically constrained stellar parameters, accurately reproduce the observed rotation period. Additionally, we revised the masses and radii of the super-Earths in the system, which support their having Earth-like compositions.

Finally, we confirm that the oscillation amplitude in radial velocity scales as (L/M)1.5 in K dwarfs, in contrast to the (L/M)0.7 relation observed in G dwarfs. These findings provide significant insights into the structure and angular momentum loss of K-type stars."

Listening to star music reveals a surprising secret about how the inside of a star works

Astronomers Tune Into the Music of a Nearby Star Unlocking a Surprising Discovery  (original news release) "By analyzing subtle stellar vibrations, researchers using the Keck Planet Finder uncovered hidden interior structures that challenge long-standing models"

K Dwarf Radius Inflation and a 10 Gyr Spin-down Clock Unveiled through Asteroseismology of HD 219134 from the Keck Planet Finder (open access)

Figure 4. Stellar mass, radius, and age derived from five independent asteroseismic modeling teams. The asteroseismic radius is compared against the interferometric radius based on an angular diameter measurement ...