Speaker
Description
Asteroseismology is the study of oscillations in stars. Stars can sustain standing waves, meaning that the star is oscillating. These oscillations can be excited by different mechanisms. The opacity mechanism, acting in ionization zones, converts thermal energy into mechanical oscillations, whereas solar-like oscillations are stochastically excited and damped by turbulent convection in the outer layers, producing a broad spectrum of oscillation modes.
Observationally, oscillations manifest as small variations in stellar brightness and radial velocity, producing characteristic patterns of peaks in Fourier spectra. The oscillation frequencies are highly sensitive to the internal sound speed, density and temperature profiles of the star, as well as to rotation and magnetic fields. Asteroseismology therefore provides detailed tests of stellar structure and evolution models, constrains transport processes and energy generation under extreme conditions, and delivers precise stellar ages for galactic archaeology.
In this talk, I will present new and highly precise measurements of the G8 subgiant Beta Aql. The study is based on time-series radial velocities from the Danish-led SONG network, including SONG-Tenerife and, for the first time, SONG-Australia, combined with overlapping TESS photometry. The power spectrum reveals clear solar-like oscillations centered at 430 microhertz, with the TESS data showing lower signal-to-noise due to granulation. These simultaneous velocity and photometric observations are among the most precise ever obtained for a solar-type star.
Frequencies of 22 oscillation modes were extracted and modelled, yielding accurate estimates of Beta Aql’s mass and age and placing strong constraints on the mixing-length parameter. We determined a mass of 1.24 +/- 0.02 solar masses, and the asteroseismic age is consistent with classical estimates but with significantly higher precision.
I will also present new extended time-series observations of another solar-type subgiant, Mu Herculis, which we have monitored for 12 years with SONG. These data constitute one of the longest and most precise asteroseismic radial-velocity series ever obtained for a star other than the Sun. I will discuss what can be learned from such long-term monitoring and how future datasets from the ESA PLATO mission, scheduled for launch in the first part of 2027, will expand the reach of ground-based networks such as SONG.