THERMAL PHASE VARIATIONS OF WASP-12b: DEFYING PREDICTIONS

By N. Cowan, P. Machálek, B. Croll, L. Shekhtman, Adam Burrows, D. Deming, T. Greene, J. Hora. 2011

143 citations recorded by the source corpus.

We report Warm Spitzer full-orbit phase observations of WASP-12b at 3.6 and 4.5 μm. This extremely inflated hot Jupiter is thought to be overflowing its Roche lobe, undergoing mass loss and accretion onto its host star, and has been claimed to have a C/O ratio in excess of unity. We are able to measure the transit depths, eclipse depths, thermal and ellipsoidal phase variations at both wavelengths. The large-amplitude phase variations, combined with the planet's previously measured dayside spectral energy distribution, are indicative of non-zero Bond albedo and very poor day–night heat redistribution. The transit depths in the mid-infrared—(Rp/R*)2 = 0.0123(3) and 0.0111(3) at 3.6 and 4.5 μm, respectively—indicate that the atmospheric opacity is greater at 3.6 than at 4.5 μm, in disagreement with model predictions, irrespective of C/O ratio. The secondary eclipse depths are consistent with previous studies: Fday/F* = 0.0038(4) and 0.0039(3) at 3.6 and 4.5 μm, respectively. We do not detect ellipsoidal variations at 3.6 μm, but our parameter uncertainties—estimated via prayer-bead Monte Carlo—keep this non-detection consistent with model predictions. At 4.5 μm, on the other hand, we detect ellipsoidal variations that are much stronger than predicted. If interpreted as a geometric effect due to the planet's elongated shape, these variations imply a 3:2 ratio for the planet's longest:shortest axes and a relatively bright day–night terminator. If we instead presume that the 4.5 μm ellipsoidal variations are due to uncorrected systematic noise and we fix the amplitude of the variations to zero, the best-fit 4.5 μm transit depth becomes commensurate with the 3.6 μm depth, within the uncertainties. The relative transit depths are then consistent with a solar composition and short scale height at the terminator. Assuming zero ellipsoidal variations also yields a much deeper 4.5 μm eclipse depth, consistent with a solar composition and modest temperature inversion. We suggest future observations that could distinguish between these two scenarios.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/db4b1d803633f2d4b1a965b7a1c4c06f0df82398

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In Astronomy and Astrophysics

1. N. Madhusudhan
2. Jon Fortney
3. A. Showman
4. D. Sing
5. D. Deming
6. H. Knutson
7. J. D'esert
8. M. Line

Citations in the corpus

• TRANSMISSION SPECTROSCOPY OF THE HOT JUPITER WASP-12b FROM 0.7 TO 5 μm (2013, methodology): “We also present reanalyses of WASP-12b transmission-spectroscopy observations using HST/WFC3 and broadband-photometry transit observations usingSpitzer, each previously discussed by Swain et al. (2013) and Cowan et al. (2012), respectively.”
• HST SPECTRAL MAPPING OF L/T TRANSITION BROWN DWARFS REVEALS CLOUD THICKNESS VARIATIONS (2013, unknown): “…via photometry and Doppler imaging (e.g. Budding 1977; Vogt et al. 1987; Lüftinger et al. 2010), and to translate precision Spitzer photometry to one-dimensional and two-dimensional brightness distributions for hot jupiters (e.g. Knutson et al. 2007; Cowan et al. 2012; Majeau et al. 2012).”
• THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA (2015, background): “This eastward shift in temperature was first predicted by Showman and Guillot (2002) and since observed in a a number of hot Jupiter’s (Knutson et al. 2007;2009;2012; Crossfield et al. 2010; Cowan et al. 2012; Lewis et al. 2013; Stevenson et al. 2014).”
• 3.6 AND 4.5 μm PHASE CURVES AND EVIDENCE FOR NON-EQUILIBRIUM CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HD 189733b (2012, background): “…et al. 2009c), HD 80606b Laughlin et al. (2009), HAT-P-7b (Borucki et al. 2009; Welsh et al. 2010), CoRoT-1b (Snellen et al. 2009), and WASP-12b (Cowan et al. 2012), with more sparsely sampled phase curves for three additional planets (51 Peg b, HD 209458b, and HD 179949b) from Cowan et al.…”
• STABILIZING CLOUD FEEDBACK DRAMATICALLY EXPANDS THE HABITABLE ZONE OF TIDALLY LOCKED PLANETS (2013, methodology): “Following Cowan et al. (2012b), we use the OLR maps from the GCMs to compute time-resolved, disk-integrated broadband thermal phase curves measured by a distant observer (Fig.”
• C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES (2012, methodology): “Using new observations in the Spitzer IRAC channels at 3.6 µm and 4.5 µm, in addition to existing data, Cowan et al. (2012) confirmed that their best fitting models required a high C/O ratio and the lack of a strong thermal inversion in the dayside atmosphere of WASP-12b (see Section 5.2.1 of Cowan…”
• A SYSTEMATIC RETRIEVAL ANALYSIS OF SECONDARY ECLIPSE SPECTRA. II. A UNIFORM ANALYSIS OF NINE PLANETS AND THEIR C TO O RATIOS (2013, methodology): “First, we retrieve the temperatures and abundances under the assumption of the Cowan et al. (2012) “null” hypothesis for the 4.5 µm flux.”
• A DETECTION OF WATER IN THE TRANSMISSION SPECTRUM OF THE HOT JUPITER WASP-12b AND IMPLICATIONS FOR ITS ATMOSPHERIC COMPOSITION (2015, methodology): “…dayside emission spectrum, and thermal phase variation (López-Morales et al. 2010; Fossati et al. 2010; Campo et al. 2011; Croll et al. 2011; Cowan et al. 2012; Crossfield et al. 2012; Haswell et al. 2012; Zhao et al. 2012; Föhring et al. 2013; Sing et al. 2013; Swain et al. 2013;…”
• SPITZER SECONDARY ECLIPSES OF THE DENSE, MODESTLY-IRRADIATED, GIANT EXOPLANET HAT-P- 20 b ?> USING PIXEL-LEVEL DECORRELATION (2014, methodology): “We have tested PLD with five sets of real data: GJ 436 (Ballard et al. 2010), CoRoT-2b (Deming et al. 2011), WASP-14b (Blecic et al. 2013), WASP-8b (Cubillos et al. 2013), and WASP-12b (Cowan et al. 2012; Stevenson et al. 2014).”
• ATMOSPHERIC HEAT REDISTRIBUTION ON HOT JUPITERS (2013, unknown): “Colored symbols with error bars are from published observations (Knutson et al. 2007, 2009a,b, 2012; Cowan et al. 2007, 2012; Borucki et al. 2009; Maxted et al. 2013).”
• ORBITAL PHASE VARIATIONS OF THE ECCENTRIC GIANT PLANET HAT-P-2b (2013, methodology): “The orbital period of HAT- P-2b (5.6334729 d) is more than 2.5 times that of other exoplanets with published full-orbit phase curve observations: WASP-12b (Cowan et al. 2012a) and HD 189733b (Knutson et al. 2012).”
• HST hot-Jupiter transmission spectral survey: evidence for aerosols and lack of TiO in the atmosphere of WASP-12b (2013, methodology): “Very hot Jupiters, with equilibrium temperatures greater than 2400 K, are observed to have low circulation efficiencies which leads to very large day/night temperature contrasts (Cowan et al. 2012).”