Lars Bildsten Kavli Institute for Theoretical Physics University of California Santa Barbara Hearing the Stars! Happy Birthday David!!

KITP Residence: Opens January 2017

Though we know how stars evolve, we are only just beginning to probe rotation, interior states, hydrodynamics and magnetism in a meaningful way. Most observational progress is from the asteroseismic data from the Kepler and CoRoT satellites, while theoretical progress is driven by people and new computational tools. Matteo Cantiello (KITP), Joergen Christensen- Dalsgaard (Aarhus Univ.), Jim Fuller (Caltech/KITP), Phil Macias (UCSB=>UCSC), Chris Mankovich (UCSB=>UCSC), Kevin Moore (UCSB=>Claremont), Bill Paxton (KITP), Dennis Stello (U. Sydney) & Rich Townsend (U. Wisconsin)

After the Main Sequence: Red Giant Branch and Clump Stars M lifting degeneracy => stable He burning in core (Thomas 1967). Paxton et al. ‘11 Clump stars

Space-Based Photometry 27 cm diameter Launched December 2006 CoRoTKepler 95 cm diameter Launched March 2009

Non-Radial Stellar Oscillations P-modes (acoustic waves): In the high wavenumber limit=> Evenly spaced in Frequency (in Envelope!) G-modes (gravity waves): In the high wavenumber limit=> Evenly spaced in Period (in Core!)

Only Acoustic Waves seen in the Sun Christensen-Dalsgaard

Acoustic Waves (p-modes) in Giants Persistent convection in the outer parts of the giant excites standing acoustic waves (i.e. modes with n radial nodes for each l) The pulsation amplitudes were estimated (e.g. Christensen-Dalsgaard; Kjeldsen & Bedding ‘05) based on earlier solar work (c.f. Goldreich & Keeley ’77), but ground based tests were a challenge... as amplitudes were low... =>Measures mean density

CoRoT finds p-modes !

Kepler Observations Bedding et al. ‘10 (Kepler) Kepler

Bedding et al. ‘10 (Kepler) Large frequency spacing is well measured and collapsing these allows for identification of l=0, 1, 2 and often l=3 acoustic modes These give mean density measurements straight away! n~ WKB nearly valid

Highest Observed Frequency Huber et al Highest observed frequency is at the acoustic cutoff of the photosphere. Higher frequency waves have large damping due to wave escape Combined with frequency spacing, M and R inferred! However, internal state not probed...

Revealing the Population (CoRoT) Miglio et al. 2013

Highlights so Far Measured frequency spacing and maximum observed frequency give R, M and D for >10,000 stars across the galaxy. Great test for GAIA and new galactic science enabled. Useful diagnostics for extra-solar planets. Acoustic waves seen in nearly all evolved stars with amplitudes of parts per million. Where tested, distance estimates are ~10% accurate (Silva Aguirre+ ’13)

Degenerate Core => Burning Core Time spent on the Red Giant Branch (RGB) at L>30L  is comparable to that spent on the Red Clump. Hard to distinguish a clump star from an RGB star in the field, but let’s see what seismology can do.. Bildsten et al. ‘12

Inferring the State of the Stellar Core Bedding et al. ‘10 (Kepler) More modes are present than allowed for by acoustic waves! Most prevalent plethora is near the l=1 modes, which scatter away from simple expectations.

Propagation Diagrams and Mixed Modes Scuflaire ’74; Osaki ’75 and Aizenman et al. ’77 noted that the acoustic waves couple to the non-radial g-modes, which are uniformly spaced in period at: Coupling is strongest for l=1, and many g-modes exist between each successive acoustic mode

Burning vs. Degenerate Cores RGB Clump

Internal Gravity Waves in the Stellar Core then Detected A=p-dominated mode (n p,n g =8, 476) B=g-dominated mode (n p,n g =7, 505) The g-mode spectrum is very dense in the core, but the modes couple to the envelope well enough to emerge and be detected as oscillations evenly spaced in period. Very stable and long-lived CLOCK! Star near the RGB bump.

Mosser et al Bedding et al Distinction of stars on the Red Giant branch from those doing He burning in the core (clump stars)!! Discovered now in nearly all RGB stars (Stello et al. 2013) Luminosity

Solar Model “Trivially” Evolved Courtesy C. Mankovich Rotation rate in the core can impact the later evolution of the star, especially for massive stars Certainly sets rotation for the He burning core and eventually the white dwarf See also Tayar & Pinsonneault ‘13

RGB Power Spectrum: Rotation! Beck et al. ‘12 Stello et al G G G P

Inferred Core Rotation Mosser et al. 2012

Core loses 95% of its Angular Momentum after Leaving MS

Calculations with Magnetic Dynamos Still not enough angular momentum loss from the shrinking core! Cantiello et al. ‘14,

Conclusions New astronomical tools are revealing the interiors of stars in ways previously impossible. Rotation and Magnetism can now be explored, an important player in how stars finally collapse. Theory remains key in at least three ways: –Reliable physical modeling (MESA+GYRE) needed to fully interpret the data –Novel analytics and mechanisms (Cantiello et al. 2014; Fuller et al. 2014) to transport J –Recent theoretical (Fuller et al. 2015) work showed how dipole suppression arises from strong B in core (Stello et al. ‘16, Cantiello, Fuller, LB’16)

We now have a New way to Hear!

The width of one atom between earth and sun! The width of 10 nuclei over the earth’s diameter!