measuring stellar properties with asteroseismology and ... · asteroseismology and interferometry...
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Measuring Stellar Properties with Asteroseismology and Interferometry
Tim White Georg-August-Universität Göttingen
Solar-Seminar – Max Planck Instutut für Sonnensystemforschung – 29 April 2014
Kepler-186f
NASA Ames/SETI Institute/JPL-Caltech
• Show cover of Science article, transit.
• This planet is interesting because it is in the habitable zone and Earth-sized.
• How do we know it’s Earth-sized?
Science, April 18 2014, Vol 344, Page 277
R*=0.472±0.052 R
Rplanet=1.11±0.14 R
Planet Validation
Seager & Mallen-Ornélas 2003
Galaxy Formation
E. L. Wright (UCLA), The COBE Project, DIRBE, NASA
Source: Ivan Baldry Samland & Gerhard, 2003
Asteroseismology
Arentoft et al. 2008
figure by Daniel Huber
figure by Daniel Huber
figure by Daniel Huber
figure by Daniel Huber
Huber et al. 2011, ApJ, 743, 143
16 Cyg A
The Sun
Δν
νmax
From oscillations to stellar parameters
1) Scaling relations 2) Grid method 3) Detailed modelling
M, R, age
Δν, νmax [Fe/H] log(g)
Teff
ν1,…, νn [Fe/H] log(g) Teff, ...
M, R, age
Difficulty Precision
M, R
Δν νmax Teff
21
3
/
R
Mν
eff2ac
TR
Mνν max
Ideal gas Adiabatic Oscillations Isothermal Atmosphere
Tassoul (1980) Brown et al. (1991)
1) Scaling relations
Why care about scaling relations?
21
3
/
R
Mν
eff2ac
TR
Mνν max
• They tell you
– Density
– Surface gravity
– Radius
– Mass
Without the need for detailed modelling!
Why care about scaling relations?
From oscillations to stellar parameters
1) Scaling relations 2) Grid method 3) Detailed modelling
M, R, age
Δν, νmax [Fe/H] log(g)
Teff
ν1,…, νn [Fe/H] log(g) Teff, ...
M, R, age
Difficulty Precision
M, R
Δν νmax Teff
Huber et al. 2011, ApJ, 743, 143
A lot
From oscillations to stellar parameters
1) Scaling relations 2) Grid method 3) Detailed modelling
M, R, age
Δν, νmax [Fe/H] log(g)
Teff
ν1,…, νn [Fe/H] log(g) Teff, ...
M, R, age
Difficulty Precision
M, R
Δν νmax Teff
Kepler-21 Howell et al. 2012
Δν = 60.86 ± 0.55 μHz νmax = 1153 ± 32 μHz
Kepler-36 Carter et al. 2012
Δν = 67.9 ± 1.2 μHz νmax = 1250 ± 44 μHz
KIC 11772920 From the ensemble in Chaplin et al. 2011
Δν = 158.6± 3.6 μHz νmax = 3800 ±100 μHz
Frequency (μHz)
PSD
(p
pm
2 μ
Hz-1
)
8/LC artifact
Verifying Transiting Planets
• Can infer stellar density through shape of the transit light curve (Seager & Mallen-Ornélas 2003)
• Asterodensity profiling (e.g. Kipping 2014)
• Does asteroseismic density = transit density?
Asteroseismic density Inferred transit density
(Sliski & Kipping 2014)
Population Studies: CoRoT Giants
Mass
Frac
tio
n
Miglio et al. 2013
Simulations
Scaling relations Scaling relations
Population Studies:
Chaplin et al. 2011
Scaling relations Population synthesis modelling
Kepler Dwarfs
But can we trust the scaling relations?
Population Studies:
Chaplin et al. 2011
Scaling relations Population synthesis modelling
Kepler Dwarfs
But can we trust the scaling relations?
Two ways to check:
1.Stellar models
2.Independent observations
Density
Surface gravity
Mass
Radius
Models
• Make a grid of stellar models and determine their oscillation frequencies.
• For each model we know M and R.
• For each model we can measure Δν
• Is ?
21
3
/
R
Mν
White et al. 2011
White et al. 2011
Mass 0.7 M
2.0 M
• Observed frequencies are not high enough
• Departures from homology
Why not?
So Δνobs is not equal to
Mass 0.7 M
2.0 M
[Fe/H] -0.9 +0.5
[Fe/H] -0.9 +0.5
[Fe/H] -0.9 +0.5
Scatter in metallicity
[Fe/H] -0.9 +0.5
Scatter in mass
But can we trust the scaling relations?
Two ways to check:
1.Stellar models
2.Independent observations
Independent Measurements
• Interferometric radii
• Dynamical masses
• Transit densities
Interferometry Point source
Interferometry Point source
Interferometry Point source Resolved disc
Fringe visibility is a function of source size, baseline length, and wavelength
Visibility
0.2 mas
0.5 mas 1.5 mas
λ
B
PAVO at the CHARA Array
0.2 mas
0.5 mas 1.5 mas
λ
B
PAVO (visible)
MIRC (infrared)
θLD = 0.753±0.009 mas R = 1.48±0.02 R
White et al. 2013
Interferometry of Kepler and CoRoT stars
Huber et al. 2012
Asteroseismology of Kepler and CoRoT stars
Huber et al. 2012
Density
Surface gravity
Mass
Radius
Huber et al. 2012
Giants dominated by parallax uncertainties
Measured Radius
From scaling relations
16 Cyg
16 Cyg A
16 Cyg B
Metcalfe et al. 2012
θLD = 0.539±0.007 mas R = 1.22±0.02 R
White et al. 2013
θLD = 0.490±0.006 mas R = 1.12±0.02 R
White et al. 2013
Huber et al. 2012
Measured Radius
From scaling relations
White et al. 2013
PAVO (visible)
MIRC (infrared)
θLD = 0.753±0.009 mas R = 1.48±0.02 R
White et al. 2013
θ Cyg
Guzik et al. 2011
Let’s have another look at the Δν scaling relation
using the brightest stars with
independent measurements of mass and radius
α Cen A R=1.225±0.004 R
(interf. + parallax, Kervella et al. 2003, Söderhjelm 1999)
M=1.105±0.007 M (binary orbit, Pourbaix et al. 2002)
Δν = 105.7±0.3 μHz (Bedding et al. 2004)
α Cen B R=0.864±0.005 R
(interf. + parallax, Kervella et al. 2003, Söderhjelm 1999)
M=0.934±0.006 M (binary orbit, Pourbaix et al. 2002)
Δν = 161.7±0.2 μHz (Kjeldsen et al. 2005)
Procyon A R=2.059±0.015 R
(interf. + parallax, Kervella et al. 2004, van Leeuwen 2007)
M=1.461±0.025 M (binary orbit, Girard et al. 2000, Gatewood & Han 2006)
Δν = 55.9±0.3 μHz (Bedding et al. 2010)
TrES-2 (Kepler-1) ρ=1.105±0.011 ρ
(transit, Southworth, 2011)
Δν = 141.0±1.4 μHz (Huber et al. 2013)
HAT-P-7 (Kepler-2) ρ=0.2023±0.0024 ρ
(transit, Southworth, 2011)
Δν = 59.2±0.6 μHz (Huber et al. 2013)
HD 17156
Δν = 83.44±0.15 μHz (Gilliland et al. 2011) 2011) al. et Nutzman (transit, ρ3710 0150
0130.
..
ρ
16 Cyg A R=1.22±0.02 R
(interf. + parallax, White et al. 2013, van Leeuwen 2007)
M=1.06±0.03 M (H-R diagram, Casagrande et al. 2011)
Δν = 103.5±0.1 μHz (Metcalfe et al. 2012)
16 Cyg B R=1.12±0.02 R
(interf. + parallax, White et al. 2013, van Leeuwen 2007)
M=1.04±0.04 M (H-R diagram, Casagrande et al. 2011)
Δν = 117.0±0.1 μHz (Metcalfe et al. 2012)
θ Cyg R=1.49±0.02 R
(interf. + para., White et al. 2013, van Leeuwen 2007)
M=1.39±0.02 M (H-R diagram, Casagrande et al. 2011)
Δν = 84.0±0.4 μHz (Guzik et al. 2011)
Giants?
Huber et al. 2012
Giants dominated by parallax uncertainties
Measured Radius
From scaling relations
KIC 8410637
• Giant in an eclipsing binary (Hekker et al. 2010)
– Δν = 4.57 ± 0.03 μHz
• Mass and radius determined by Frandsen et al. 2013
– M = 1.557 ± 0.028 M
– R = 10.74 ± 0.11 R
KIC 8410637
What we need:
We need the brightest stars with the best measurements.
• Better parallaxes Gaia
• Asteroseismology of nearby, bright stars K2, SONG, TESS, PLATO
• Interferometry AO system at CHARA
• Dynamical masses