Temperature-Pressure Profile In The Upper Atmosphere Of HD 189733b: Detection Of The Thermosphere

Details Temperature-Pressure Profile In The Upper Atmosphere Of HD 189733b: Detection Of The Thermosphere Temperature-Pressure Profile In The Upper Atmosphere Of HD 189733b: Detection Of The Thermosphere

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011ess.....2.4013h&link_type=abstract

American Astronomical Society, ESS meeting #2, #40.13

Astronomy and Astrophysics

Astronomy

Scientific paper

We present transmission spectra of the hot-Jupiter HD 189733b taken with STIS aboard the Hubble Space Telescope. The spectra cover the wavelength range 5808 - 6300 Å with resolving power R = 5000. We detect the Na I line within the exoplanet’s atmosphere at the 10 σ confidence level with a 5 Å band of absorption (0.094 ± 0.0095 %) and use the data to measure the line absorption profile. We see only the narrow core of the line, with width < 45 Å, which could be due either to an obscuring high-altitude haze or a significantly sub-solar sodium abundance. We also observe that the effects of starspots on the absorption depths and profile are within errors in the sodium feature.
We use the absorption profile to probe the vertical structure of the upper atmosphere over approximately 7 scale heights. By comparing with model absorption profiles, we constrain the temperature at each atmospheric scale height, thus allowing us to construct a vertical temperature profile. We identify three temperature regimes clearly above the broadband Rayleigh signature; an 800±200 K region at 475-700 km, a 1300±300 K region at 700-925 km and a 2500±500 K region at 925-2215 km. We measure a white light radius of Rp/Rstar (z=0) = 0.15628. The temperature rises with higher altitudes, indicating an inversion characteristic of a thermosphere.
The absolute pressure scale depends on the species responsible for the Rayleigh signature and its abundance. We discuss plausible scenarios for this species and the atmospheric T-P profiles that result. We compare the sodium absorption depth with a solar abundance model and a feature at 8 microns, assuming this is water, and find that we cannot constrain the sodium abundance. However, a higher than solar sodium to water abundance ratio suggests that a super-solar abundance is likely.

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