On the Dayside Thermal Emission of Hot Jupiters

Astrophysics, abstract
astro-ph/0504212

From: Sara Seager [view email]

Date: Fri, 8 Apr 2005 17:03:19 GMT   (112kb)

We discuss atmosphere models of HD209458b in light of the recent day-side
flux measurement of HD209458b’s secondary eclipse by Spitzer-MIPS at 24
microns. In addition, we present a revised secondary eclipse IRTF upper limit
at 2.2 microns which places a stringent constraint on the adjacent H2O
absorption band depths. These two measurements are complementary because they
are both shaped by H2O absorption and because the former is on the Wien tail of
the planet’s thermal emission spectrum and the latter is near the thermal
emission peak. A wide range of models fit the observational data, confirming
our basic understanding of hot Jupiter atmospheric physics. Although a range of
models are viable, some models at the hot and cold end of the plausible
temperature range can be ruled out. One class of previously unconsidered hot
Jupiter atmospheric models that fit the data are those with C/O >~ 1 (as
Jupiter may have), which have a significant paucity of H2O compared to solar
abundance models with C/O = 0.5. The models indicate that HD209458b is in a
situation intermediate between pure in situ reradiation and very efficient
redistribution of heat; one which will require a careful treatment of
atmospheric circulation. We discuss how future wavelength-dependent and
phase-dependent observations will further constrain the atmospheric circulation
regime. In the shorter term, additional planned measurements for HD209458b,
especially Spitzer IRAC photometry, should lift many of the model degeneracies.
Multiwavelength IR observations constrain the atmospheric structure and
circulation properties of hot Jupiters and thus open a new chapter in
quantitative extrasolar planetology.

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