Theoretical Spectra and Light Curves of Close‐in Extrasolar Giant Planets and Comparison with Data

Abstract

We present theoretical atmosphere, spectral, and light-curve models for extrasolar giant planets (EGPs) undergoing strong irradiation for which Spitzer planet/star contrast ratios or light curves have been published (circa 2007 June). These include HD 209458b, HD 189733b, TrES-1, HD 149026b, HD 179949b, and And b. By comparing models with data, we find that a number of EGP atmospheres experience thermal inversions and have stratospheres. This is particularly true for HD 209458b, HD 149026b, and And b. This finding translates into qualitative changes in the planet/star contrast ratios at secondary eclipse and in close-in EGP orbital light curves. Moreover, the presence of atmospheric water in abundance is fully consistent with all the Spitzer data for the measured planets. For planets with stratospheres, water absorption features invert into emission features and mid-infrared fluxes can be enhanced by a factor of 2. In addition, the character of near-infrared planetary spectra can be radically altered. We derive a correlation between the importance of such stratospheres and the stellar flux on the planet, suggesting that close-in EGPs bifurcate into two groups: those with and without stratospheres. From the finding that TrES-1 shows no signs of a stratosphere, while HD 209458b does, we estimate the magnitude of this stellar flux breakpoint. We find that the heat redistribution parameter, P n , for the family of close-in EGPs assumes values from $0.1 to $0.4. This paper provides a broad theoretical context for the future direct characterization of EGPs in tight orbits around their illuminating stars.

Characterizing the Atmospheres of Hot Jupiters: From Spectra to Multi-Color Maps

“…Unfortunately neither υ Andromedae b nor HD 179949b are eclipsing, making it difficult to check directly for the presence of a temperature inversion. A better test would be to measure the day-night temperature difference for HD 209458b, which clearly does have a temperature inversion, or HD 149026b, whose high 8 μm brightness temperature ) strongly favors the presence of a temperature inversion (Fortney et al 2006a, Burrows et al 2008. We have obtained such observations of both planets, and will report on the results in a future paper.…”

“…The black line corresponds to the default model (no temperature inversion) with a redistribution parameter Pn = 0.1, which describes the case where 10% of the incident energy is redistributed to the night side. The grey line correspond to a model with Pn = 0.1 and an additional optical absorber at high altitudes, which produces a thermal inversion around pressures of 0.001 bar (Burrows et al 2007(Burrows et al , 2008. Squares show the values for these models after integrating over the Spitzer bandpasses.…”

“…2) from Knutson et al (2008c). These models employ the same formalism described 258 H. A. Knutson in Burrows et al (2007Burrows et al ( , 2008, which uses a dimensionless redistribution parameter P n that, in approximate fashion, accounts for the cooling of the dayside and the warming of the nightside by zonal winds near an optical depth of order unity. The larger P n is, the cooler is the dayside atmosphere and the lower the emergent planetary flux at superior conjunction.…”

Two Classes of Hot Jupiter Atmospheres

“…• HD 189733b (Charbonneau et al 2008;Barman 2008) • TrES-1 (Charbonneau et al 2005;Fortney et al 2005;Burrows et al 2005Burrows et al , 2008 The observed inversion for XO-1b is particularly interesting, as its irradiation level is quite similar to that of HD 189733b. Why does one have an inversion and the other does not?…”

Transiting Exoplanets with JWST

“…See also [30,26,27,28]. Hot planets such as Ups And are on one side of a temperature-driven chemical composition boundary, while cooler planets such as HD 209458b are on the cooler side.…”