Conny Aerts, conny.aerts@kuleuven.be
 
 Brno, 26 April 2021
 
 
 
 
 
 DIVING DEEP INTO STARS VIA ASTEROSEISMOLOGY !2 Take-home message Seismic
 waves offer 
 in-situ measurements of internal stellar physics:
 new look@SSE
 the art is to get the seismic info out of 
 the data…
 ©rtvnoord.nl ©PhysicsToday !3 99% of nuclear life Life determined 
 by uncalibrated 
 interior physics high-mass stars low- & intermediate-mass stars main sequence red giant main sequence supergiant Stellar interiors: poorly known Rotation? Convection? Mixing? Magnetism? !4 Asteroseismology to the rescue Pragmatic:
 use NRP,
 whatever
 their cause Courtesy:
 Péter Pápics Lots of open questions 
 in stellar evolution:
 nonradial oscillations 
 offer new tool
 !5 Stellar oscillations probe stellar interiors ©PhysicsToday Ingredients: temporal/spatial !6 NRPs = solutions of perturbed SSE in terms of periodic eigenfunctions : eigenmodes of the star Each mode described by spherical harmonic & frequency:
 
 
 
 
 Dominance of restoring force? 1. pressure (acoustic waves) 2. buoyancy (gravity waves) 3. Coriolis (inertial waves) 4. Lorentz (Alfvén waves) 5. tidal (tidal waves)
 Kepler! !7 Frequency regimes (Aerts, Mathis, Rogers, 2019, ARAA) p-modesg-modes !8 Green: l=0
 Red: l=1, n=3
 Blue: l=1, n= -20 From Aerts et al. (2019), ARAA Radialdisplacement Tangentialdisplacement ProbingKernel Red clump star Main sequence star Courtesy: Cole Johnston Courtesy: 
 Valentina
 Schmid Courtesy: Joey Mombarg Probing power: p/g-modes mass, chemistry, age: convection? mixing? rotation? Theoretical chemistry,
 luminosity, oscillations THEORY STELLAR MODEL FOR SPECIFIED INPUT PHYSICS !9 Data-driven modelling Kepler/K2/TESS high-R spectroscopy Gaia astrometry Observed chemistry,
 luminosity, oscillations OBSERVATIONS 16h 40m 17h 20m 18h 00m 18h 40m 19h 20m +50 +55 +60 +65 +70 CVZ North variability 
 classification
 from ML :
 clustering,
 deep learning
 … !10 Theoretical predictions Observed properties
 of identified modes Theoretical predictions
 for oscillations THEORY OBSERVATIONS STELLAR MODEL FOR SPECIFIED INPUT PHYSICS Kepler/K2/TESS high-R spectroscopy Gaia astrometry Two Major Aims:
 
 High-precision M, R, age (Z)
 
 Improve Input Physics: 
 AM, Dmix(r)
 mass, metallicity, age + convection? mixing? rotation? magnetism? !11 mass, metallicity, age + convection? mixing? rotation? magnetism? Aims of Asteroseismology Observed properties
 of identified modes Theoretical predictions
 for oscillations THEORY OBSERVATIONS STELLAR MODEL FOR SPECIFIED INPUT PHYSICS Kepler/K2/TESS high-R spectroscopy Gaia astrometry Two Major Aims:
 
 High-precision M, R, age (Z)
 
 Improve Input Physics: 
 AM, Dmix(r)
 ? ? ? 
 SOME APPLICATIONS:
 
 1) WEIGHING, SIZING, AGEING LOW-MASS STARS (“SERVICE”)
 2) INTERNAL ROTATION
 
 3) INTERNAL CHEMICAL MIXING !13 Helioseismology paved the way (Christensen-Dalsgaard, 2002, RMP) Courtesy: ESA/NASA SoHO ~ Limit of high 
 frequency waves:
 no rotation, 
 no magnetism !14 Low-mass stars: R, M, age Radius ~1-2%
 Mass~ 2-4%
 Age ~ 20% 
 model dependent: He? mixing?
 atomic diffusion? (see also Chaplin et al. 2014, Silva Aguirre et al. 2016,
 Verma et al. 2019, Bellinger et al. 2019, 2020…) 16 Cyg A !15 R, M, age for Exoplanet Research Courtesy of Nathalie Bathala Huber et al. (2013) Van Eylen et al. (2014, 2018), Campante et al. (2016), Chontos et al. (2019) Asteroseismology of Host Star: factor ~2 improvement
 for exoplanet radius + age delivery! Courtesy: 
 Ashley 
 Chontos !16 Seismic mass, radius, age, log g from scaling relations
 Teff from spectroscopy
 
 Courtesy: Andrea Miglio K2 data: ecliptic
 
 TESS data: all sky Ages for Galactic Archaeology 
 Asteroseismic distances ~few% 
 (Silva Aguirre et al. 2012, Miglio et al. 2013, Stello et al. 2015, Huber et al. 2017, 
 Hon et al. 2019, Bellinger et al. 2019, Sharma et al. 2019, Jie Yu et al. 2020,…) 
 SOME APPLICATIONS:
 
 1) WEIGHING, SIZING, AGEING LOW-MASS STARS (“SERVICE”)
 2) INTERNAL ROTATION
 
 3) INTERNAL CHEMICAL MIXING !18 offers new way to study core masses, Dmix(r) & Ω(r)
 Pápics et al. (2017), Van Reeth et al. (2015,2016,2018), Saio et al. (2018), Gang Li et al. (2019,2020)
 g modes in intermediate-mass stars Courtesy:
 Péter Pápics !19 KIC11721304 With(out)
 Coriolis
 acceleration 
 (from Aerts et al. 2019 ARAA & Aerts 2021 RMP) Courtesy: Timothy Van Reeth Identification of (l,m) 
 & derivation of Ωcore depends on Ω Courtesy Timothy Van Reeth (Near-)Core rotation rate Observations Theory Asteroseismic estimates of Ωcore 
 !20 We cannot
 do this for
 the Sun…
 1210 stars Asteroseismic estimates of Ωcore 
 !21 ~1800 stars (Aerts, 2021, RMP) !22 Stars rotate quasi-rigidly
 when having a
 convective core
 
 AM transport to keep ~rigid rotation & agree with 
 AM of WDs 
 
 Magnetism/Tayler Instability:
 Fuller et al. (2019), Takahashi & Langer (2020)
 
 and/or
 
 IGWs: Rogers (2015);
 Edelmann et al. (2019); 
 Horst et al. (2020) Measuring Ωcore versus Ωenv 
 
 “Standard SSE” needs fixes… 
 (from Aerts, 2021, RMP) Courtesy: Philipp Edelmann 
 SOME APPLICATIONS:
 
 1) WEIGHING, SIZING, AGEING LOW-MASS STARS (“SERVICE”)
 2) INTERNAL ROTATION
 
 3) INTERNAL CHEMICAL MIXING !24 nuclear 
 burning 
 microscopic physics:
 radiative levitation
 & gravitational settling macroscopic physics:
 element transport, e.g. 
 rotation, waves, magnetism,…
 Chemical evolution !25 nuclear 
 physics 
 radiative
 levitation
 from atomic 
 physics micro- & macroscopic
 element transport:
 efficiency and timescales?
 diffusive treatment… ⦃ Chemical evolution inside star Element mixing: largest unknown in stellar evolution;
 of vast importance for chemical yields in stars with convective core !26 
 Deduced for sample of 26 SPB stars by Pedersen et al., 2021, under embargo
 
 Summary in
 Aerts (2021) Asteroseismic estimation of Dmix(r)
 Courtesy: 
 May Gade Pedersen Denv ? !27 Combined asteroseismology, astrometry, and spectroscopy of a sample of SPB stars (Pedersen et al. 2020, 2021 under embargo) Stellar evolution in action !28 He core at TAMS
 Cole Johnston 
 (2021, submitted) Fractional
 mass (in %) of 
 convective core
 EBsastero Asteroseismic & EB Core Masses
 Figures Courtesy: Cole Johnston Ongoing TESS/Gaia/Spectroscopic Surveys !29 SDSS-V (Pedersen et al. 2019;Bowman et al. 2019,
 2020; Dorn-Wallenstein et al. 2020) Onward to 
 high mass & 
 evolved BSG
 (incl. LMC)
 Mercator, La PalmaVLT-UVES TESS Gaia Onward to PLATO (2026+) !30 SDSS 8% Data Rate is Guest Observer program via open 
 ESA calls, incl. ToO option: welcome! 31 Much more to it: tidal, magneto-, pre-MS, binary mergers, 
 nonlinear,… asteroseismology
 Aerts, 2021, RMP, Vol.93, 015001: https://arxiv.org/abs/1912.12300
 general introduction & update for non-expert Figure courtesy:
 Aerts, Mathis, Rogers, 
 2019: ARAA, 57, 35, https://arxiv.org/abs/1809.07779