The 3.6-8.0 μm Broadband Emission Spectrum of HD 209458b: Evidence for an Atmospheric Temperature Inversion

By H. Knutson, D. Charbonneau, L. Allen. 2007

393 citations recorded by the source corpus.

We estimate the strength of the bandpass-integrated thermal emission from the extrasolar planet HD 209458b at 3.6, 4.5, 5.8, and 8.0 μm using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We observe a single secondary eclipse simultaneously in all four bandpasses and find relative eclipse depths of 0.00094 ± 0.00009, 0.00213 ± 0.00015, 0.00301 ± 0.00043, and 0.00240 ± 0.00026, respectively. These eclipse depths reveal that the shape of the inferred emission spectrum for the planet differs significantly from the predictions of standard atmosphere models; instead, the most plausible explanation would require the presence of an inversion layer high in the atmosphere leading to significant water emission in the 4.5 and 5.8 μm bandpasses. This is the first clear indication of such a temperature inversion in the atmosphere of a hot Jupiter, as previous observations of other planets appeared to be in reasonably good agreement with the predictions of models without such an inversion layer.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8ed53cf4f2ea89975a5821bddae61be0b62cb8ac

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In Astronomy and Astrophysics

1. Jon Fortney
2. N. Madhusudhan
3. D. Charbonneau
4. A. Showman
5. Sara Seager
6. D. Deming
7. J. Winn
8. H. Knutson

Citations in the corpus

• Hubble Space Telescope transmission spectroscopy of the exoplanet HD 189733b: high‐altitude atmospheric haze in the optical and near‐ultraviolet with STIS (2011, background): “From secondary eclipse measurements, the planet also has a well established thermal inversion layer (Knutson et al. 2008; Burrows et al. 2007).”
• KEPLER-18b, c, AND d: A SYSTEM OF THREE PLANETS CONFIRMED BY TRANSIT TIMING VARIATIONS, LIGHT CURVE VALIDATION, WARM-SPITZER PHOTOMETRY, AND RADIAL VELOCITY MEASUREMENTS (2011, background): “The Spitzer/IRAC photometry is known to be systematically affected by the so-called pixel-phase effect (see e.g., Charbonneau et al. 2005; Knutson et al. 2008).”
• MULTIWAVELENGTH CONSTRAINTS ON THE DAY–NIGHT CIRCULATION PATTERNS OF HD 189733b (2008, methodology): “We also see no evidence for the presence of the “detector ramp” effect (Charbonneau et al. 2005; Deming et al. 2006; Knutson et al. 2007; Harrington et al. 2007; Knutson et al. 2008; Charbonneau et al. 2008) in these data.”
• An HST optical-to-near-IR transmission spectrum of the hot Jupiter WASP-19b: detection of atmospheric water and likely absence of TiO (2013, background): “TiO has not been conclusively observed yet, even in HD 209458b which has been observed to have a stratosphere (Désert et al. 2008; Knutson et al. 2008).”
• Kepler-22b: A 2.4 EARTH-RADIUS PLANET IN THE HABITABLE ZONE OF A SUN-LIKE STAR (2011, methodology): “We remove the effect of the IRAC intrapixel sensitivity variations, or the “pixel phase” effect (see, e.g., Charbonneau et al. 2005; Knutson et al. 2008) by assuming a polynomial functional form for the intrapixel sensitivity (which depends on the x- and y-positions of the star on the array).”
• The TRAPPIST survey of southern transiting planets. I. Thirty eclipses of the ultra-short period planet WASP-43 b (2012, background): “…that we have to account for a ‘ramp’ effect (the log(t) term) similar to the well-documented sharp variation of theeffective gain of theSpitzer/IRAC detector at 8µm (e.g. Knutson et al. 2008), and also for a dependance of the measured flux with the exact position of the PSF center on the chip.”
• Exoplanet Atmospheres: Physical Processes (2010, methodology): “These properties led to the concept (Knutson et al. 2007a) that the ramp is due to charge trapping in the detector.”
• A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission (2014, methodology): “Astronomers have developed techniques to reduce data from space telescopes, in particular Spitzer, that substantially improved photometric precision by correcting for artifacts caused by the motion of the spacecraft (Knutson et al. 2008; Ballard et al. 2010; Stevenson et al. 2012).”
• Atmospheric Circulation of Hot Jupiters: Three-dimensional Circulation Models of HD 209458b and HD 189733b with Simplified Forcing (2008, neutral): “12 compares our light curves to the 8-µ m Spitzer IRAC light curve of HD189733b (Knutson et al. 2007b).”
• 3D mixing in hot Jupiters atmospheres. I. Application to the day/night cold trap in HD 209458b (2013, background): “For some transitinghot Jupiters, Spitzer IRAC secondary-eclipse observations indicate the presence of thermal inversions (stratospheres) on these planets’ daysides (Knutson et al. 2008).”
• 3.6 AND 4.5 μm PHASE CURVES AND EVIDENCE FOR NON-EQUILIBRIUM CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HD 189733b (2012, methodology): “…include an additional grey absorber at low pressures, which is required to reproduce the high-altitude temperature inversions observed in the atmospheres of a subset of hot Jupiters such as HD 209458b (e.g., Burrows et al. 2007; Knutson et al. 2008; Swain et al. 2009; Madhusudhan & Seager 2010).”
• THE ATMOSPHERIC SIGNATURES OF SUPER-EARTHS: HOW TO DISTINGUISH BETWEEN HYDROGEN-RICH AND HYDROGEN-POOR ATMOSPHERES (2008, background): “…temperatures (Deming et al. 2005; Charbonneau et al. 2005; Deming et al. 2006; Harrington et al. 2007; Deming et al. 2007; Demory et al. 2007; Knutson et al. 2008) as well as emission spectra (Grillmair et al. 2007; Richardson et al. 2007; Swain et al. 2007; Charbonneau et al. 2008) for…”
• Hubble Space Telescope hot Jupiter transmission spectral survey: a detection of Na and strong optical absorption in HAT-P-1b (2013, background): “…that these two atmospheres should be similar, as infrared observations indicate that the atmosphere of HD 209458b has a temperature inversion (Knutson et al. 2008; Burrows et al. 2007) while the atmosphere of HD 189733b does not (Grillmair et al. 2007; Charbonneau et al. 2008), the…”
• THE STATISTICS OF ALBEDO AND HEAT RECIRCULATION ON HOT EXOPLANETS (2009, background): “The most robust detection of this temperature inversion is for HD 209458b (Knutson et al. 2008), but this planet does not exhibit a large day-night brightness contrast at 8 µm (Cowan et al. 2007).”
• WATER, METHANE, AND CARBON DIOXIDE PRESENT IN THE DAYSIDE SPECTRUM OF THE EXOPLANET HD 209458b (2009, methodology): “Using the system ephemeris (Knutson et al. 2007) we determine that the bulk of the first two orbits (O1 & O2) coincides with the pre-ingress light curve, the third and part of the fourth orbit (O3 & O4) cover the occultation, while the fifth orbit (O5) is post-egress (see Fig.”