cyberscience and hunting for planets beyond our solar system · “super-earth” jupiter analog...
TRANSCRIPT
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CyberScience and Hunting for
Planets Beyond our Solar System
Eric B. Ford, ICS Co-Hire, 2013
Astronomy & Astrophysics
Center for Astrostatistics
Center for Exoplanets & Habitable Worlds
Penn State Astrobiology Research Center
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From the Solar System to Exoplanets
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Hunting for Exoplanets
Credit: Frank Cianciolo/McDonald Observatory Credit: NOAO/WIYN
Hobby-Eberly Telescope (10m)
Habitable Zone Planet Finder
WIYN Telescope (3.5m)
NEID Spectrograph
Next-Generation Spectrographs being led by Penn
State’s Center for Exoplanets & Habitable Worlds
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Echelle Spectrometer
CCD
Echelle
Grating
Collimator
Starlight
From TelescopeEchelle Spectrograph
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Measure Shift of Absorption Lines to
Determine the Radial Velocity of Star
Image of Star’s Spectrum
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55 Cnc: An RV ClassicApsidal AlignmentApsidal Alignment
Butler+ 1996; Marcy+ 2002; McArthur+ 2004; Endl et al 2012; Nelson et al. 2014
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55 Cnc: Astroinformatics in Action
Near
1:3 MMR“Super-Earth”
Jupiter
Analog
• 1,418 RVs from 4 observatories, spanning over 23 years
• Self-consistent Bayesian Analysis w/ full N-body treatment
• ~40 model parameters
• Differential Evolution MCMC (ter Braak 2006; Nelson+ 2014)
• >6.4M models in Markov chains
N-body integration using Swarm-NG GPU (Dindar+ 2012)
Apsidal AlignmentApsidal Alignment
B. Nelson et al. 2014
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Candidate for update
i
Differential Evolution MCMC
x
y
ter Braak 2008; Veras & Ford 2009; Wright et al. 2010; Johnson et al. 2011; Carter et al. 2012; Nelson et al. 2014
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Candidate for update
i
j
k
Differential Evolution MCMC
x
y
ter Braak 2008; Veras & Ford 2009; Wright et al. 2010; Johnson et al. 2011; Carter et al. 2012; Nelson et al. 2014
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Proposed displacement ( )scaled
Candidate for update
i
j
k
Differential Evolution MCMC
x
y
ter Braak 2008; Veras & Ford 2009; Wright et al. 2010; Johnson et al. 2011; Carter et al. 2012; Nelson et al. 2014
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Proposed displacement ( )scaled
Candidate for update
Proposal
i
j
k
Differential Evolution MCMC
x
y
ter Braak 2008; Veras & Ford 2009; Wright et al. 2010; Johnson et al. 2011; Carter et al. 2012; Nelson et al. 2014
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i
j
k
Proposal
Differential Evolution MCMC
(correlated posterior)
x
y
ter Braak 2008; Veras & Ford 2009; Wright et al. 2010; Johnson et al. 2011; Carter et al. 2012; Nelson et al. 2014
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DEMCMC in Action (resonant case)
Johnson et al. 2011Nelson et al. 2014
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55 Cnc e: Mass of a Super-Earth
“Super-Earth”
1,086 RVs over 23 years
Self-consistent Bayesian Analysis
>6.4M models in Markov chain
N-body integration using
Swarm-NG GPU (Dindar+ 2012)
Apsidal AlignmentApsidal Alignment
Orbital Phase
Radia
l V
elo
city
Density (g/cm3)
Pro
bab
ility
Near
1:3 MMR
Jupiter
Analog Endl et al. 2012
B. Nelson et al. 2014
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55 Cnc d: A Jupiter Analog
Near
1:3 MMR“Super-Earth”
Jupiter
Analog
• 13.4 year orbital period
• Small, but non-zero eccentricity
• Very different inner planetary
system than our solar system
Apsidal AlignmentApsidal Alignment
B. Nelson et al. 2014
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What does it mean to “Discover a Planet”?
• Old Frequentist approach:
Reject the null hypothesis that a
simpler model without the planet could
reasonably explain your data
• Modern Bayesian approach:
The Evidence for a model with the
planet is significantly greater than the
alternative models.
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How Many Planets?
Bayesian Model Comparison
Evidence or Fully
marginalized
likelihood (FML)
Prior Likelihood
The probability of a radial velocity dataset {d} being
generated from some model M parameterized by {θ} is
given by…
To choose between two competing models M1 and M2,
take the ratio of the evidences for the two models
Bayes Factor
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How many planets?
• Bayesian Evidence
• Importance Sampling
• Importance Sampling with Finite Sample Size
• Truncate Importance Sampling Density
Nelson et al. 2015; see also Ford & Gregory 2007
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How many planets?
Comparing, can see this is a special case:
• Truncated Importance Sampling Density
• Ratio Estimator (J. Berger; Ford & Gregory 2007)
Nelson et al. 2015; Ford & Gregory 2007
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Next Generation of Spectrographs for
Characterizing Earth-mass Planets
Credit: NEID.psu.edu
Hobby-Eberly Telescope (10m)
Habitable Zone Planet Finder
WIYN Telescope (3.5m)
NEID Spectrograph
HPF & NEID Spectrographs being built by Penn
State’s Center for Exoplanets & Habitable Worlds
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Next Generation of Spectrographs for
Characterizing Earth-mass Planets
HPF & NEID Spectrographs being built by Penn
State’s Center for Exoplanets & Habitable Worlds
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How to Separate Signals of
Planets & Stellar Activity?
X. DumusqueS. Berdyugina
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Principal Components Analysis to
Distinguish Stellar Activity & Planets
Results of PCA applied to ensembles of simulated spectra with
different types of stellar activity (plage or spots) or just kinematic
Doppler shifts.
Davis, Cisewski, Dumusque, Fischer, Ford, Robertson, Valenti in prep.
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Algorithmic Regression Path for
Sparse Principal Components Analysis
Red spectra from Dumusque 2014’s SOAP 2.0 model
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Measuring Planet Sizes
TESS (launch 2018)
Small Planets around Bright Stars
Kepler/K2 (launched 2009)
Frequency of Small Planets
ESANASA NASA/MIT
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NASA/Ames/JPL-Caltech
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Detecting a Transiting Planet
NASA/Kepler/Dana Berry
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Correlated noise afflicts Kepler light curves
Kepler lightcurve segment of Sun-like star
correlated noise even
on short timescales
R. Dawson, IAU 2015
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Accuracy & precision of transit times
improves by modeling correlated noise
Short timescale correlated noise accounted for by GP likelihood using Matern 5/2 radial kernel
(One of sixteen transits)
recovered - injected (minutes)
Model 1: Joint modeling of transits +
polynomials with white noise likelihood
Model 2: Joint modeling of transits +
polynomials with Gaussian process likelihood
Model 1
Model 2
Example
R. Dawson, IAU 2015
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Measuring the Day Side Properties of Exoplanets Using Gaussian-Process Regression
We use a distributed Product-of-Experts GP to
model the correlated noise in Hubble Space
Telescope observations of exoplanets’ day sides.
By using ACI to split the calculations over 15
physical CPUs with 20 threads each, we
complete a 2 week-long analysis in slightly over 1
hour. Published in Beatty et al.
(2017)
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Period-Radius Distribution of Kepler’s Planets
(including strong planet candidates)
Kepler/Burke+ 2015/Jontof-Hutter
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Planet Masses Measured
with Doppler Follow-up Observations
Kepler/Burke+ 2015/Jontof-Hutter
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Detection Biases Complicate
Interpretation of Exoplanet Populations
Especially for objects near threshold of detectability
M. Shabram 2015
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Bayesian Modeling of Exoplanet Populations
Population
Parameters
True Planet
Parameters
(radii, masses)
Observationsphotometry, RVs...
Wolfgang, Rogers & Ford 2016
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Hierarchical Bayesian Modeling to Infer the
Planetary Mass-Radius Relation
Wolfgang, Rogers & Ford 2016
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Hierarchical Modeling of
Exoplanet Populations
Foreman-Mackey et al. 2014
Shabram et al. 2014
Wolfgang et al. 2015
Wolfgang et al. 2016Morehead Ph.D. 2015
Period-Radius DistributionMultiplicity, Inclination &
Duration Distribution
Mass-Eccentricity Distribution
Mass-Radius Distribution (empirical)
Mass-Radius-Flux Distribution (w/ models)
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Modeling Exoplanet Populations
Foreman-Mackey et al. 2014
Shabram et al. 2014
Wolfgang et al. 2015
Wolfgang et al. 2016Morehead Ph.D. 2015
Period-Radius DistributionMultiplicity, Inclination &
Duration Distribution
Mass-Eccentricity Distribution
Mass-Radius Distribution (empirical)
Mass-Radius-Flux Distribution (w/ models)
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Approximate Bayesian Computing
• ABC is a “Likelihood-free” method
• Replaces specifying likelihood with:
– A forward model
– Defining a distance function between two
sets of observations
– Choosing a tolerance (i.e., maximum
distance that is “close enough”)
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ABC in Cartoons
R. Moorehead+ in prep.
Observations
HyperpriorSimulated
data sets
“posterior”
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R. Moorehead+ in prep.
ABC for a Normal Target Distribution
Iterationx
pdf(
x)
pdf(
x)
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R. Moorehead+ in prep.
ABC for a Normal Target Distribution
Iterationx
pdf(
x)
pdf(
x) Iterationmean std dev
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Characterizing Distribution of Orbital
Shapes & Inclinations with ABC
• The multiple planet
systems identified
by Kepler are
typically very nearly
coplanar.
R. Moorehead+ in prep.
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Questions?