The 4.5 μm full-orbit phase curve of the hot Jupiter HD 209458b

Robert T. Zellem, Nikole K. Lewis, Heather A. Knutson, Caitlin Griffith, Adam Showman, Jonathan J. Fortney, Nicolas B. Cowan, Eric Agol, Adam Burrows, David Charbonneau, Drake Deming, Gregory Laughlin, Jonathan Langton

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Abstract

The hot Jupiter HD 209458b is particularly amenable to detailed study as it is among the brightest transiting exoplanet systems currently known (V-mag = 7.65; K-mag = 6.308) and has a large planet-to-star contrast ratio. HD 209458b is predicted to be in synchronous rotation about its host star with a hot spot that is shifted eastward of the substellar point by superrotating equatorial winds. Here we present the first full-orbit observations of HD 209458b, in which its 4.5 μm emission was recorded with Spitzer/IRAC. Our study revises the previous 4.5 μm measurement of HD 209458b's secondary eclipse emission downward by 35% to , changing our interpretation of the properties of its dayside atmosphere. We find that the hot spot on the planet's dayside is shifted eastward of the substellar point by 40.°9 ± 6.°0, in agreement with circulation models predicting equatorial superrotation. HD 209458b's dayside (T bright = 1499 ± 15 K) and nightside (T bright = 972 ± 44 K) emission indicate a day-to-night brightness temperature contrast smaller than that observed for more highly irradiated exoplanets, suggesting that the day-to-night temperature contrast may be partially a function of the incident stellar radiation. The observed phase curve shape deviates modestly from global circulation model predictions potentially due to disequilibrium chemistry or deficiencies in the current hot CH4 line lists used in these models. Observations of the phase curve at additional wavelengths are needed in order to determine the possible presence and spatial extent of a dayside temperature inversion, as well as to improve our overall understanding of this planet's atmospheric circulation.

Original languageEnglish (US)
Article number53
JournalAstrophysical Journal
Volume790
Issue number1
DOIs
StatePublished - Jul 20 2014

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Jupiter (planet)
Jupiter
planets
planet
extrasolar planets
orbits
night
curves
superrotation
stellar radiation
temperature inversions
stars
atmospheric circulation
temperature inversion
brightness temperature
eclipses
disequilibrium
lists
chemistry
wavelength

Keywords

  • atmospheric effects
  • methods: numerical
  • planets and satellites: general
  • planets and satellites: individual (HD 209458b)
  • techniques: photometric

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Zellem, R. T., Lewis, N. K., Knutson, H. A., Griffith, C., Showman, A., Fortney, J. J., ... Langton, J. (2014). The 4.5 μm full-orbit phase curve of the hot Jupiter HD 209458b. Astrophysical Journal, 790(1), [53]. https://doi.org/10.1088/0004-637X/790/1/53

The 4.5 μm full-orbit phase curve of the hot Jupiter HD 209458b. / Zellem, Robert T.; Lewis, Nikole K.; Knutson, Heather A.; Griffith, Caitlin; Showman, Adam; Fortney, Jonathan J.; Cowan, Nicolas B.; Agol, Eric; Burrows, Adam; Charbonneau, David; Deming, Drake; Laughlin, Gregory; Langton, Jonathan.

In: Astrophysical Journal, Vol. 790, No. 1, 53, 20.07.2014.

Research output: Contribution to journalArticle

Zellem, RT, Lewis, NK, Knutson, HA, Griffith, C, Showman, A, Fortney, JJ, Cowan, NB, Agol, E, Burrows, A, Charbonneau, D, Deming, D, Laughlin, G & Langton, J 2014, 'The 4.5 μm full-orbit phase curve of the hot Jupiter HD 209458b', Astrophysical Journal, vol. 790, no. 1, 53. https://doi.org/10.1088/0004-637X/790/1/53
Zellem, Robert T. ; Lewis, Nikole K. ; Knutson, Heather A. ; Griffith, Caitlin ; Showman, Adam ; Fortney, Jonathan J. ; Cowan, Nicolas B. ; Agol, Eric ; Burrows, Adam ; Charbonneau, David ; Deming, Drake ; Laughlin, Gregory ; Langton, Jonathan. / The 4.5 μm full-orbit phase curve of the hot Jupiter HD 209458b. In: Astrophysical Journal. 2014 ; Vol. 790, No. 1.
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abstract = "The hot Jupiter HD 209458b is particularly amenable to detailed study as it is among the brightest transiting exoplanet systems currently known (V-mag = 7.65; K-mag = 6.308) and has a large planet-to-star contrast ratio. HD 209458b is predicted to be in synchronous rotation about its host star with a hot spot that is shifted eastward of the substellar point by superrotating equatorial winds. Here we present the first full-orbit observations of HD 209458b, in which its 4.5 μm emission was recorded with Spitzer/IRAC. Our study revises the previous 4.5 μm measurement of HD 209458b's secondary eclipse emission downward by 35{\%} to , changing our interpretation of the properties of its dayside atmosphere. We find that the hot spot on the planet's dayside is shifted eastward of the substellar point by 40.°9 ± 6.°0, in agreement with circulation models predicting equatorial superrotation. HD 209458b's dayside (T bright = 1499 ± 15 K) and nightside (T bright = 972 ± 44 K) emission indicate a day-to-night brightness temperature contrast smaller than that observed for more highly irradiated exoplanets, suggesting that the day-to-night temperature contrast may be partially a function of the incident stellar radiation. The observed phase curve shape deviates modestly from global circulation model predictions potentially due to disequilibrium chemistry or deficiencies in the current hot CH4 line lists used in these models. Observations of the phase curve at additional wavelengths are needed in order to determine the possible presence and spatial extent of a dayside temperature inversion, as well as to improve our overall understanding of this planet's atmospheric circulation.",
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