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.