Asteroseismology & Exoplanets: A Kepler Success Story Daniel Huber SETI Institute / NASA Ames Research Center U Chicago Astronomy Colloquium April 2014
Collaborators Bill Chaplin, Andrea Miglio, Yvonne Elsworth, Tiago Campante & Rasmus Handberg (Birmingham) Jørgen Christensen-Dalsgaard, Hans Kjeldsen, Victor Silva Aguirre (Aarhus) Tim Bedding & Dennis Stello (Sydney) Ron Gilliland (PSU), Sarbani Basu (Yale), Steve Kawaler (Iowa State), Travis Metcalfe (SSI), Jaymie Matthews (UBC), Saskia Hekker (Amsterdam), Marc Pinsonneault & Jennifer Johnson (OSU), Eric Gaidos (Hawaii) Tom Barclay, Jason Rowe, Elisa Quintana & Jack Lissauer (NASA Ames / SETI) Josh Carter, Lars Buchhave, Dave Latham, Ben Montet & John Johnson (Harvard) Dan Fabrycky (Chicago) Josh Winn, Kat Deck & Roberto Sanchis-Ojeda (MIT) Andrew Howard, Howard Isaacson & Geoff Marcy (Hawaii, Berkeley)
The Kepler Space Telescope
launched in March 2009 0.95 m aperture 42 CCD s, 105 sq deg FOV Borucki et al. (2008), Koch et al. (2010)
Kepler Field of View Kepler Orbit Kepler obtained uninterrupted high-precision photometry of ~> 150,000 stars for 4 years to search for transiting exoplanets
Asteroseismology in a Nutshell
AstEroseismology?
AstEroseismology? unnamed author, sometime in 1995
What causes stellar oscillations? Oscillations in cool stars are driven by turbulent surface convection (opacity in hot stars)
Radial Order n displacement center surface number of nodes from the surface to the center of the star
Spherical Degree l l = 0
Spherical Degree l l = 2 l = 0
Δν ~ 135 µhz for the Sun sound speed cs Δν = (2 dr/cs) -1 (M/R 3 ) 1/2 (ω = n π c / L!) Ulrich (1986)
δν dcs/dr δν (Age) (individual frequencies) sound speed cs Δν = (2 dr/cs) -1 (M/R 3 ) 1/2 (ω = n π c / L!) Ulrich (1986)
νmax νmax ~ 3000 µhz for the Sun νmax νac g Teff 0.5 M R -2 Teff 0.5 Brown et al. (1991)
Spectroscopy Teff, log(g), [Fe/H] + Asteroseismology fix log(g) Δν α M 1/2 R -3/2 ν max α M R -2 T eff -1/2 log(g)seism R <~ 5% M <~ 10% Teff, R, M, [Fe/H], (Age) for single field stars!
Does asteroseismology work? interferometric radii Huber et al. (2012) 4% Empirical tests: interferometry, parallaxes, astrometric & eclipsing binaries, transits, cluster members Generally validated to ~5% and ~10% in R & M; better for dwarfs, worse for evolved giants seismic radii
The Kepler Revolution of Asteroseismology
1991: First confirmed detection of solar-like oscillations in a star other than the Sun Procyon Sun Brown et al. 1991 VIRGO/SOHO challenging using ground-based observations!
2014: Kepler??
2014: Kepler 16 Cyg A Sun
pre-2007 ~10 unevolved stars ~10 evolved stars
CoRoT ~10 unevolved stars ~2000 evolved stars
Kepler ~ 600 unevolved stars ~ 15000 evolved stars
Red Clump (He-core burning) RGB? (non He-core burning)
Probing the cores of Giants: Mixed Modes
Probing the cores of Giants: Mixed Modes l=1 l=1 l=1 Multiple l=1 peaks per order due to coupling of acoustic modes with gravity modes trapped in the stellar interior ( mixed modes )
Gravity mode period spacing Mean Density Bedding et al. 2011, Nature 481, 55 He-core burning non Hecore burning
The Exoplanet - Asteroseismology Synergy
Transits yield relative planet size
Transits & Planet Radii M & R + (RP/R ) 2 RP
Kepler-37: A Special Host Star ν max ~ 4300 µhz Δν ~ 179 µhz νmax, ~ 3000 µhz Δν ~ 135 µhz R = 0.772+/- 0.026 R Smallest solar-type star with detected oscillations yet!
Kepler-37: A Special Host Star P = 13.4 days R = 0.30+/- 0.06 R P = 21.3 days R = 0.74+/- 0.07 R P = 39.8 days R = 2.0+/- 0.1 R
Barclay et al. 2013, Nature 494, 452
Asteroseismic Planet Host Stars All Host Stars Host stars with asteroseismic detections Huber et al. (2013), ApJ 767, 127
An exotic host star: Kepler-56 red giant hosting 2 transiting planets 10.2d, 6.5R 21.4d, 9.8R
Kepler-56 Asteroseismology l=1 l=1 l=1 ~50 individual frequencies detected
Kepler-56 Asteroseismology l=1 l=1 l=1 ~50 individual frequencies detected mixed l=1 modes are split into triplets by rotation
Andrea Miglio University of Birmingham, UK
Kepler-56 Asteroseismology l=1 l=1 l=1 ~50 individual frequencies detected mixed l=1 modes are split into triplets because the star is inclined towards line of sight i ~ 45!
Kepler-56 Asteroseismology l=1 l=1 l=1? ~50 individual frequencies detected mixed l=1 modes are split into triplets because the star is inclined towards line of sight i ~ 45!
Keck/HIRES Radial Velocities wide companion! Planets b & c Radial velocity drift due to third companion on a wide orbit
torque by wide companion causes the orbital plane of the inner planets to precess (Mardling 2010, Kaib et al. 2011, Batygin 2012) Huber et al. 2013, Science 342, 331
The Big Picture: Stellar Properties of all Kepler Targets
Petigura et al. (2013) Planet occurrence rates (in and outside the Kepler field!) depend on our understanding of the Kepler parent sample So far, this is still mostly based on the Kepler Input Catalog (KIC)
Kepler Input Catalog The purpose of the KIC was to select targets for observations
Kepler Input Catalog Isochrones for ~95% of metallicities in the solar neighborhood Problem Areas The purpose of the KIC was to select targets for observations
Asteroseismology Spectroscopy ~15000 stars ~800 stars Photometry KIC ~130000 stars ~30000 stars
Old Catalog New Catalog Huber et al. (2014), ApJS 211, 2
Old Catalog (1) (1) Identification of new giant stars New Catalog (3) (3) (1) (2) (2) (2) Improved radii of cool dwarfs (3) Realistic metallicity distribution for solar-type dwarfs Huber et al. (2014), ApJS 211, 2
Unclassified Stars (not the Sun anymore!) Cool Dwarfs up to 90% smaller Huber et al. (2014), ApJS 211, 2
What does this mean for planet occurrence? Fressin et al. (2013) Howard et al. (2011)?? Petigura et al. (2013a)? Planet occurrence study in progress - stay tuned for new results!
The Future: Kepler s Ecliptic Plane Follow- Up Mission
Idea: Balance solar pressure around roll-angle (X-Y plane) of spacecraft, adjust with thruster firings ~80 day campaigns in each ecliptic field Howell et al. (2014)
Rich science fields: Young open clusters (Pleiades!) & moving groups (upper Sco), galactic fields ~20000-30000 targets per campaign (larger apertures mostly due to pointing precision); all targets are selected by the community http://keplerscience.arc.nasa.gov/k2/
K2 photometric performance (in fine-point) within a factor of 2 of Kepler!
Early Results: Transit and Eclipses WASP-28 Eclipsing Binary Stars
Early Results: Transit and Eclipses WASP-28 Eclipsing Binary Stars is back in Action!
(Unexpected?) Early Results: Asteroids Aviv Ofir, University of Göttingen
Early Results: Oscillating Giants Evolution Oscillation Frequency
Galactic Archeology K2 Asteroseismology will allow us to measure distances and ages for thousands of giants in the galaxy
Conclusions Kepler has opened up a new era in Asteroseismology; Stellar oscillations are used to characterize the host stars the smallest planets and most exotic planetary systems known to date! A better understanding of planet occurrence from Kepler relies on accurate stellar properties for all target stars, making use of different observational techniques (including asteroseismology); still lots of work ahead! The K2 Mission will continue Kepler s legacy in the ecliptic plane, both for exoplanet detections and asteroseismology; First results are very promising!