Theoretical Spectra and Atmospheres of Extrasolar Giant Planets (Sudarsky, Burrows, Hubeny 2003) Nick Cowan March 2006 Nick Cowan March 2006

Outline Motivation Giants vs Dwarfs Numerical Techniques Atmospheric Composition Opacities Results & Discussion Motivation Giants vs Dwarfs Numerical Techniques Atmospheric Composition Opacities Results & Discussion

Motivation For ten years, we’ve been discovering extrasolar planets. In the last year, we’ve begun putting constraints on their thermal emission. We’d like to interpret these observations in the context of model spectra. We’d like to guide future searches with model spectra. For ten years, we’ve been discovering extrasolar planets. In the last year, we’ve begun putting constraints on their thermal emission. We’d like to interpret these observations in the context of model spectra. We’d like to guide future searches with model spectra.

Giants vs Dwarfs Giants are smaller than dwarfs (M < 13M J ) Giants are found orbiting a host star –Stellar illumination provides I - –Stellar illumination leads to non-equilibrium photochemistry in upper atmosphere –Diurnal variation in stellar flux leads to longitudinal variation in planetary spectrum Model the phase-averaged spectra for EGPs orbiting G0V hosts. Giants are smaller than dwarfs (M < 13M J ) Giants are found orbiting a host star –Stellar illumination provides I - –Stellar illumination leads to non-equilibrium photochemistry in upper atmosphere –Diurnal variation in stellar flux leads to longitudinal variation in planetary spectrum Model the phase-averaged spectra for EGPs orbiting G0V hosts.

Numerical Techniques TLUSTY (Hubeny 1988) –Complete Linearization (converges fast) –Accelerated Lambda Iteration (fast steps) Discontinuous Finite Element scheme Planar Geometry One-dimensional model (average over hemisphere) Forward scattering off condensates ≈ reduced cross-section. TLUSTY (Hubeny 1988) –Complete Linearization (converges fast) –Accelerated Lambda Iteration (fast steps) Discontinuous Finite Element scheme Planar Geometry One-dimensional model (average over hemisphere) Forward scattering off condensates ≈ reduced cross-section.

Atmospheric Composition EGP spectra are dominated by composition of upper atmosphere. –Condensation (from T-P curve) –Rainout (absence of certain constituents) –Photochemistry (destruction of species) Assume solar composition. Model includes 27 most abundant elements, combining to form ~300 molecules and ~100 condensates. EGP spectra are dominated by composition of upper atmosphere. –Condensation (from T-P curve) –Rainout (absence of certain constituents) –Photochemistry (destruction of species) Assume solar composition. Model includes 27 most abundant elements, combining to form ~300 molecules and ~100 condensates.

Opacities Rayleigh scattering Absorption & scattering by condensates Rayleigh scattering Absorption & scattering by condensates

Mie Scattering Treat particle as homogeneous sphere. Express incident wave in terms of spherical harmonics. Express scattered wave in terms of spherical Hankel functions of the first kind. Express transmitted wave in terms of Bessel functions of the first kind. Setting transverse components of E and B to zero, solve differential equations. Solution is a slowly converging infinite series. Treat particle as homogeneous sphere. Express incident wave in terms of spherical harmonics. Express scattered wave in terms of spherical Hankel functions of the first kind. Express transmitted wave in terms of Bessel functions of the first kind. Setting transverse components of E and B to zero, solve differential equations. Solution is a slowly converging infinite series.

Conclusions (Part I) 1.Planet-to-star flux ratio is very sensitive to wavelength and orbital distance. 2.EGP band fluxes, Bond and geometric albedos are not monotonic functions of orbital distance. 3.EGPs fall into classes of similar composition. 4.Mid-IR has favorable planet-to-star flux ratio, regardless of semi-major axis. 5.Scattering makes irradiated brown dwarfs much brighter than isolated ones. 6.Distant EGPs are brighter if young/massive. 1.Planet-to-star flux ratio is very sensitive to wavelength and orbital distance. 2.EGP band fluxes, Bond and geometric albedos are not monotonic functions of orbital distance. 3.EGPs fall into classes of similar composition. 4.Mid-IR has favorable planet-to-star flux ratio, regardless of semi-major axis. 5.Scattering makes irradiated brown dwarfs much brighter than isolated ones. 6.Distant EGPs are brighter if young/massive.

Conclusions (Part II) 7.There’s a bright feature around  m, specially for distant EGPs. 8.The feature shifts to shorter wavelengths with increasing illumination. 9.Scattering increases optical and near-IR flux, while grain absoprtion decreases mid-IR flux. 10.Increasing g increases flux red of 2.2  m, decreases flux blue of 2.2  m. 11.Na D & K resonance lines are important for roasters but not for more distant EGPs. 7.There’s a bright feature around  m, specially for distant EGPs. 8.The feature shifts to shorter wavelengths with increasing illumination. 9.Scattering increases optical and near-IR flux, while grain absoprtion decreases mid-IR flux. 10.Increasing g increases flux red of 2.2  m, decreases flux blue of 2.2  m. 11.Na D & K resonance lines are important for roasters but not for more distant EGPs.