Asteroseismology of Kepler
Exoplanet Host Stars
Travis Metcalfe (SSI)
1992: first pulsar planets
3 planet system
2 = 4 x Earth mass
1 = 2 x Moon mass
Orbits closer than Mercury
1995: first radial velocity planet
0.5 x Jupiter mass
Orbit closer than Mercury
2001: first transiting planet
Orbit closer than Mercury
Size near Jupiter
Exoplanet atmospheres
Detections
- Sodium
- Carbon monoxide
- Water vapour
2004: first microlensing planet
Hosted by a tiny red dwarf
Orbit size similar to Mars
Mass similar to Jupiter
2008: first direct image
Mass = 3 x Jupiter
Orbit size = 3 x Neptune
Host star mass = 2 x Sun
2010: first habitable planet?
Gliese 581g
Mass = 3 x Earth
Orbit size = 0.4 x Mercury
Host star mass = 0.3 x Sun
Higher temperature = faster sound speed
Lighter gases = faster sound speed
Global oscillation properties
nmax
Elsworth & Thompson (2004)
Scaling relations
Mathur et al. (2012)
Grid-based methods
Mathur et al. (2012)
Fitting the frequencies
Metcalfe et al. (2012)
Asteroseismic Modeling Portal
http://amp.ucar.edu/
• Stellar evolution tracks
from ASTEC, pulsation
analysis with ADIPLS
• Parallel genetic algorithm
optimizes globally, local
analysis + SVD for errors
0.75 < M < 1.75
0.002 < Z < 0.05
0.22 < Y < 0.32
Science)
1.0Chaplin
< etaal. (2011,
< 3.0
Metcalfe et al. (2009), Woitaszek et al. (2009)
• Stellar age from match to
large separation, correct
surface effects empirically
Kepler-21: a love story
• 1.64±0.04 Re planet in a
2.8-day orbit around an
oscillating F subgiant
• Asteroseismic target prior
to exoplanet discovery,
expanded collaboration
• radius (1.86±0.04 R),
mass (1.34±0.06 M),
age (2.84±0.34 Gyr)
Howell et al. (2012)
Kepler-22: habitable super-Earth
• 2.38±0.13 Re planet with
290-d orbit in habitable
zone of G5 host star
• Spectroscopy and global
oscillation properties for
grid-based modeling
• radius (0.98±0.02 R),
mass (0.97±0.06 M),
age (~4 Gyr?)
Borucki et al. (2012)
Kepler-36: formation puzzle
Carter et al. (2012, Science)
Kepler-36: formation puzzle
• 1.5 and 3.7 Re planets in
13.8-d and 16.2-d orbits
(7:6 period ratio)
• Asteroseismology and
transit timing variations
yield planet densities
• Super-Earth and Neptune
(8:1 density ratio) in
neighboring orbits. How?
Carter et al. (2012, Science)
Kepler-##: smallest exoplanet
• 0.28 / 0.8 / 2.1 Re planets
in 13 / 21 / 39 day orbits
(no TTVs yet detected)
• radius (0.77±0.02 R),
mass (0.80±0.04 M),
age (~6 Gyr)
• Innermost planet is
smaller than Mercury
(similar to size of Moon)
Barclay et al. (submitted)
Future prospects
• Longer data sets will resolve mode splitting,
providing independent constraints on rotational
inclination and spin-orbit alignment.
• Extended time series will probe variations due to
magnetic cycles, and provide statistics on stellar
super-flares (with implications for habitability).
• Comparison with control sample of stars without
known planets may reveal correlations between
stellar composition and occurrence of planets.