Acoustic Oscillations in Red Giants

Jim FullerCaltech/KITP

ACOUSTIC OSCILLATIONS IN RED GIANTS

QUIZ: IN WHICH DECADE WAS THE FIRST PULSATING RED GIANT

DISCOVERED?

Answer: 1596Mira’s variability discovered by David Fabricious

LUMINOSITY VARIATIONS FROM ACOUSTIC OSCILLATIONS

Chaplin & Miglio 2013

WHAT ARE ACOUSTIC OSCILLATIONS?

• Sound waves in star

• Waves are excited by convective motions

• Sound waves reflect, create global-scale standing waves, i.e., oscillation modes, at characteristic frequencies

CHARACTERISTIC FREQUENCIES

• Stellar dynamical frequency• Freefall frequency, orbital frequency at stellar surface

CHARACTERISTIC FREQUENCIES

• Acoustic cutoff frequency

• Characteristic atmospheric frequency

OSCILLATION FREQUENCIES

• Stars tend to oscillate at frequencies

• Oscillation spectrum exhibits peaks separated by

SPHERICAL HARMONICS

l

m

Chaplin & Miglio 2013

EVOLUTION UP GIANT BRANCH

• As stars evolve up RGB or AGB, their radii increase dramatically

• Mode frequencies and frequency spacing decrease

• Longer observation baselines needed

• Continuous data not needed

• Mode amplitudes increase

• Less sensitivity needed to detect oscillations

Mosser et al. 2013

Mosser et al. 2013

SCALING RELATIONS

Chaplin & Miglio 2013

LOWER RED GIANT BRANCH

Chaplin & Miglio 2013

ROTATIONAL SPLITTING

Mosser et al. 2012

UPPER RED GIANT BRANCH

Mosser et al. 2013

POWER OF PTF

• PTF has ability to detect oscillations in lots (millions?) of red giants

• With measurement of mode frequencies and spacings, PTF can characterize these stars

• Provides synergy with K2, GAIA, TESS, PLATO, LSST, etc.