Hot Jupiter Atmospheres with the Spitzer Space Telescope

Open Access
Author:
Todorov, Kamen Orlinov
Graduate Program:
Astronomy and Astrophysics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 22, 2013
Committee Members:
  • Kevin Luhman, Committee Chair
  • L Drake Deming, Dissertation Advisor
  • Jason Wright, Committee Member
  • James Kasting, Committee Member
  • Aleksander Wolszczan, Committee Member
  • Suvrath Mahadevan, Committee Member
Keywords:
  • extrasolar planets
  • secondary eclipse
  • photometry
  • spectroscopy
Abstract:
I analyze Spitzer Space Telescope observations of seven transiting hot Jupiters during the time of secondary eclipse, the portion of the planet’s orbit when it is behind the star from the point of view of a Solar System observer. For six of them, HAT-P-3b, HAT-P-4b, HAT-P-6b, HAT-P-8b, HAT-P-12b and XO-4b, I analyze broadband photometric light curves at 3.6 and 4.5 μm. I compare the resulting eclipse depths, which are a measure of the planets’ dayside emission, to model emergent spectra by Burrows et al. and Fortney et al. The atmosphere of XO-4b has a strong temperature inversion, HAT-P-6b has weak or no temperature inversion, HAT-P-8b has a non-inverted atmosphere. The models are inconclusive about the temperature structure of the atmospheres of HAT-P-3b and HAT-P-4b. I find that HAT-P-3b, HAT-P-4b and HAT-P-8b have relatively inefficient heat transport from their day sides to their night sides. The models suggest moderate to low heat transport for XO-4b and HAT-P-6b. I discuss the physical implications of my results in the context of theoretical and empirical hypotheses on correlations related to the temperature-pressure structures of the atmospheres and the efficiency of energy transfer to the night side of the planet. In particular, I focus on the idea by Knutson et al. that planets with chromospherically active host stars may in general not have a stratosphere-like temperature inversions, while a quiet host star may lead to an inverted atmosphere. Another hypothesis I examine is that by Cowan and Agol and Perna et al. who suggest that the hottest planets have a narrow range of permitted heat redistribution efficiencies and, thus, high day-night contrasts. The seventh object I study is HD 189733b. I examine the time series spectroscopy during 18 eclipses between wavelengths of 5 and 14 μm. This is the most extensive data set observed for the emission spectrum of any exoplanet to date. Some of these data sets have been analyzed in the past by Grillmair et al., however eight of them are examined here for the first time. I use the latest analysis techniques to remove the systematic effects from the spectral light curves, and measure the secondary eclipse depths as a function of wavelength. I compare the results with three emergent spectrum models I compute using a modified version of a radiative transfer code by Richardson et al., and with the best fit model by Burrows et al. that Grillmair et al. adopt. I exclude isothermal and gray atmospheres with a high degree of confidence and confirm the water feature detected by Grillmair et al. I also comment on the physical implications on HD 189733b’s atmosphere and how the results of the complex Burrows forward model compares with the simpler Richardson models that can be used for retrieval.