EXOFAST: A Fast Exoplanetary Fitting Suite in IDL

By Jason Eastman, S. Gaudi, E. Agol. 2012

539 citations recorded by the source corpus.

We present EXOFAST, a fast, robust suite of routines written in IDL that is designed to fit exoplanetary transits and radial velocity variations simultaneously or separately and characterize the parameter uncertainties and covariances with a differential evolution Markov chain Monte Carlo method. We describe how our code incorporates both data sets to derive simultaneously stellar parameters along with the transit and RV parameters, resulting in more self-consistent results on an example fit of the discovery data of HAT-P-3b that is well-mixed in under 5 minutes on a standard desktop computer. We describe in detail how our code works and outline ways in which the code can be extended to include additional effects or generalized for the characterization of other data sets—including non-planetary data sets. We discuss the pros and cons of several common ways to parameterize eccentricity, highlight a subtle mistake in the implementation of MCMC that could bias the inferred eccentricity of intrinsically circular orbits to significantly non-zero results, discuss a problem with IDL’s built-in random number generator in its application to large MCMC fits, and derive a method to analytically fit the linear and quadratic limb darkening coefficients of a planetary transit. Finally, we explain how we achieved improved accuracy and over a factor of 100 improvement in the execution time of the transit model calculation. Our entire source code, along with an easy-to-use online interface for several basic features of our transit and radial velocity fitting, are available online at http://astroutils.astronomy.ohio-state.edu/exofast.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d0dccde3c7453ba7915dffb0399cda7033133391

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In Astronomy and Astrophysics

1. Jon Fortney
2. N. Madhusudhan
3. D. Charbonneau
4. J. Johnson
5. J. Winn
6. D. Deming
7. Timothy Morton
8. D. Sing

In Instrumentation

1. Jon Fortney
2. D. Charbonneau
3. Timothy Morton
4. J. Johnson
5. J. Winn
6. J. Southworth
7. D. Sing
8. N. Madhusudhan

Citations in the corpus

• ECCENTRICITY FROM TRANSIT PHOTOMETRY: SMALL PLANETS IN KEPLER MULTI-PLANET SYSTEMS HAVE LOW ECCENTRICITIES (2015, background): “We do not sample directly in e and ω, as this biases the eccentricity results for nearly circular orbits due to the boundary at zero (Lucy & Sweeney 1971; Eastman et al. 2013).”
• Barycentric Corrections at 1 cm s-1 for Precise Doppler Velocities (2014, methodology): “They are now included as part of the EXOFAST package (Eastman et al. 2013)9 and can also be found at exoplanets.org10, along with the RVLIN (Wright & Howard 2009) and BOOTTRAN (Wang et al. 2012) orbit-fitting packages.”
• THE KEPLER-10 PLANETARY SYSTEM REVISITED BY HARPS-N: A HOT ROCKY WORLD AND A SOLID NEPTUNE-MASS PLANET (2014, methodology): “To derive the Kepler-10 system parameters, a Bayesian combined analysis of the Kepler short-cadence photometry and HARPS-N RV measurements was performed using a Differential Evolution Markov Chain Monte Carlo method (DE- MCMC; Eastman et al. 2013; Ter Braak 2006).”
• A Guide to Realistic Uncertainties on the Fundamental Properties of Solar-type Exoplanet Host Stars (2020, methodology): “…et al. 2008, Yonsai—Yale, Spada et al. 2013, etc.) and a variety of tools have been developed to simplify the inference such as isochrones (Morton 2015), isoclassify (Huber 2017; Berger et al. 2020), PARAM (da Silva et al. 2006; Rodrigues et al. 2014), and exofast (Eastman et al. 2013, 2019).”
• FRIENDS OF HOT JUPITERS. I. A RADIAL VELOCITY SEARCH FOR MASSIVE, LONG-PERIOD COMPANIONS TO CLOSE-IN GAS GIANT PLANETS (2013, methodology): “(degrees) (m s−1) (m s−1day−1) (m s−1) MJup (degrees) WASP-7b 0.034 +0.045 −0.024 109 +170 −55 0.003 +0.026 −0.02 0.011 +0.055 −0.025 111.3 +7.3 −7.5 0.03 ±0.04 34.6 +4.5 −3.8 1.131 +0.092 −0.089 86± 8 Misaligned 3, 39 WASP-8b 0.3044 +0.0039 −0.004 274.215 +0.084 −0.082 0.02237 +0.00032 −0.00031 -0.”
• HST hot-Jupiter transmission spectral survey: detection of potassium in WASP-31b along with a cloud deck and Rayleigh scattering (2014, result): “We then compared these uncertainties to the results of a MCMC analysis (Eastman et al. 2013), which does not assume any functional form for this probability distribution.”
• HST hot-Jupiter transmission spectral survey: evidence for aerosols and lack of TiO in the atmosphere of WASP-12b (2013, methodology): “We used the Markov Chain Monte Carlo (MCMC) suite EXOFAST from Eastman et al. (2013) to perform the joint fit.”
• RadVel: The Radial Velocity Modeling Toolkit (2018, background): “…Monte Carlo 1 a non-exhaustive list includes RVLIN (Wright & Howard 2009), Systemic (Meschiari et al. 2009; Meschiari & Laughlin 2010), EXOFAST (Eastman et al. 2013), rvfit (Iglesias-Marzoa et al. 2015), and ExoSOFT (Mede & Brandt 2017) (MCMC) sampling techniques and robust convergence…”
• A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission (2014, methodology): “To quantify this, we fit the recovered light curves with a Mandel & Agol (2002) model (once again as implemented by Eastman et al. 2013) and compared our recovered parameters to our inputs.”
• AN ANCIENT EXTRASOLAR SYSTEM WITH FIVE SUB-EARTH-SIZE PLANETS (2015, methodology): “The eccentricity vectors were assigned uniform priors in the range [−1, 1], although we have included an 1/e correction which has the effect of enforcing a uniform prior in eccentricity (Eastman et al. 2013).”
• Accurate Empirical Radii and Masses of Planets and Their Host Stars with Gaia Parallaxes (2016, methodology): “EXOFAST uses MCMC to robustly determine system parameter uncertainties.”
• CHARACTERIZING K2 PLANET DISCOVERIES: A SUPER-EARTH TRANSITING THE BRIGHT K DWARF HIP 116454 (2014, methodology): “We fit the transit light curve with a Mandel & Agol (2002) model, as implemented by Eastman et al. (2013), with quadratic limb darkening coefficients held at the values given by Claret & Bloemen (2011).”
• The Apparently Decaying Orbit of WASP-12b (2017, methodology): “2 For this purpose we used the online code of Eastman et al. (2013): http://astroutils.astronomy.ohio-state.edu/exofast/limbdark.shtml”