A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission

By Andrew Vanderburg, J. Johnson. 2014

464 citations recorded by the source corpus.

The original Kepler mission achieved high photometric precision thanks to ultrastable pointing enabled by use of four reaction wheels. The loss of two of these reaction wheels reduced the telescope’s ability to point precisely for extended periods of time, and as a result, the photometric precision has suffered. We present a technique for generating photometric light curves from pixel-level data obtained with the two-wheeled extended Kepler mission, K2. Our photometric technique accounts for the nonuniform pixel response function of the Kepler detectors by correlating flux measurements with the spacecraft’s pointing and removing the dependence. When we apply our technique to the ensemble of stars observed during the Kepler Two-Wheel Concept Engineering Test, we find improvements over raw K2 photometry by factors of 2–5, with noise properties qualitatively similar to Kepler targets at the same magnitudes. We find evidence that the improvement in photometric precision depends on each target’s position in the Kepler field of view, with worst precision near the edges of the field. Overall, this technique restores the median-attainable photometric precision within a factor of two of the original Kepler photometric precision for targets ranging from 10th to 15th magnitude in the Kepler bandpass, peaking with a median precision within 35% to that of Kepler for stars between 12th and 13th magnitude in the Kepler bandpass.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

• A SYSTEMATIC SEARCH FOR TRANSITING PLANETS IN THE K2 DATA (2015, methodology): “Following Vanderburg & Johnson (2014), we choose the aperture size with the minimum CDPP (Christiansen et al. 2012) with a 6 hour window.3 All previous methods for analyzing K2 data involve some sort of “correction” or “de- trending” step based on measurements of the pointing of the spacecraft…”
• Precise time series photometry for the Kepler-2.0 mission (2014, methodology): “At the time of writing, photometric precision estimates for K2 are available from H14 and (Vanderburg & Johnson 2014, hereafter VJ14).”
• THE K2 ECLIPTIC PLANE INPUT CATALOG (EPIC) AND STELLAR CLASSIFICATIONS OF 138,600 TARGETS IN CAMPAIGNS 1–8 (2015, background): “Methodologies to account for systematic variability caused by the spacecraft thruster firings are continuously being developed (Vanderburg & Johnson 2014; Aigrain et al. 2015; Angus et al. 2016; Huang et al. 2015; Lund et al. 2015) and have demonstrated that the photometric precision of K2 is at…”
• WASP-47: A HOT JUPITER SYSTEM WITH TWO ADDITIONAL PLANETS DISCOVERED BY K2 (2015, methodology): “We began processing the short cadence data following Vanderburg & Johnson (2014) to estimate the correlation between K2’s pointing and the measured flux (which we refer to as the K2 flat field).”
• One of the closest exoplanet pairs to the 3:2 mean motion resonance: K2-19b and c (2015, background): “This leads to a major source of systematic noise in the lightcurve (Vanderburg & Johnson 2014), the removal of which is the key part of our detrending method.”
• K2 Variable Catalogue: Variable Stars and Eclipsing Binaries in K2 Campaigns 1 and 0 (2015, methodology): “Having applied this detrending method to our set of K2 lightcurves we were in a position to test it’s overall performance as compared to the other methods available for K2 data (e.g. Aigrain et al. 2015; Vanderburg & Johnson 2014).”
• The CARMENES search for exoplanets around M dwarfs (2018, methodology): “For GJ 1265 (EPIC 205913009) we employed photometric time series from the K2 space mission during its Campaign 3 (Vanderburg & Johnson 2014) from November 2014 to February 2015.”
• A NEARBY M STAR WITH THREE TRANSITING SUPER-EARTHS DISCOVERED BY K2 (2015, methodology): “The algorithm described in Vanderburg & Johnson (2014) was developed for the K2 engineering campaign (C0), where the time baseline was short enough that drifts in stellar position along the y′ direction could be ignored.”
• ZODIACAL EXOPLANETS IN TIME (ZEIT). III. A SHORT-PERIOD PLANET ORBITING A PRE-MAIN-SEQUENCE STAR IN THE UPPER SCORPIUS OB ASSOCIATION (2016, methodology): “Vanderburg & Johnson (2014) present a method for mitigating or removing this noise, however it is not optimized for highly variable stars, e.g., the young stars of Upper Scorpius.”
• ROTATION IN THE PLEIADES WITH K2. I. DATA AND FIRST RESULTS (2016, methodology): “(4) The ‘self-flat-fielding’ approach used by Vanderburg & Johnson (2014) as obtained from MAST.”
• Identifying Exoplanets with Deep Learning: A Five-planet Resonant Chain around Kepler-80 and an Eighth Planet around Kepler-90 (2017, methodology): “This process is illustrated in Figure 3 of Vanderburg & Johnson (2014).”
• White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Line Widths: Kepler Observations of 27 Pulsating DA White Dwarfs through K2 Campaign 8 (2017, methodology): “We subsequently used the KEPSFF task by Vanderburg & Johnson (2014) to mitigate the K2 motion-correlated systematics.”
• 197 CANDIDATES AND 104 VALIDATED PLANETS IN K2's FIRST FIVE FIELDS (2016, methodology): “…of planet candidates (Foreman-Mackey et al. 2015; Adams et al. 2016; Vanderburg et al. 2016), and a growing sample of validated and/or confirmed planets (e.g., Vanderburg & Johnson 2014; Crossfield et al. 2015; Huang et al. 2015; Montet et al. 2015; Sanchis-Ojeda et al. 2015; Sinukoff et al. 2016).”
• EVEREST: PIXEL LEVEL DECORRELATION OF K2 LIGHT CURVES (2016, methodology): “In particular, the K2SFF pipeline (Vanderburg & Johnson 2014) decorrelates K2 aperture photometry with the centroid position of the stellar images.”
• SPITZER OBSERVATIONS CONFIRM AND RESCUE THE HABITABLE-ZONE SUPER-EARTH K2-18b FOR FUTURE CHARACTERIZATION (2016, methodology): “…conceivable because the detected signals are well below the noise floor of the uncorrected K2 photometry and outliers well above the median light curve scatter are common in the corrected K2 photometry despite stateof-the-art detrending (e.g., Vanderburg & Johnson 2014; Foreman-Mackey et al. 2015).”