Case studies of transiting exoplanets

The observability of molecular features in the atmospheres of a few well studied exoplanets have been investigated with the NIRSpec Exoplanet Exposure Time Calculator (NEETC). All examples are based on one transit and one occultation with twice the transit/occultation duration spent on baseline observations. A variety of instrument configurations are tested to demonstarte how each science case have different needs and requirements.

Synthetic model spectra

The calculation of the synthetic spectra is based on radiative transfer models developed and tested in the context of both solar system and exoplanet atmosphere investigations (see e.g. Muñoz et al. 2012, Muñoz et al. 2013, and Munoz & Isaak 2015). The spectra for reflected and thermal emission are calculated at a star-planet-observer phase angle of zero, and integrate the signal over the whole planet disk.

We estimate the planet equilibrium temperature as Teq = Tstar (Rstar / 2a)1/2, where Tstar is the stellar effective temperature, Rstar  is the stellar radius and a is the orbital semi-major axis. For simplicity, we parameterize the temperature such that it is constant and equals to Teq from 1,000 bar to 0.1 bar. At higher altitudes, the implemented temperature drops exponentially with a scale pressure of 0.1 bar towards the limiting value of 2/3 Teq at the atmospheric top. The spectroscopic information for the gases is borrowed from HITEMP (Rothman et al. 2010) for the H2O molecule, and from HITRAN2012 (Rothman et al. 2013) for the other molecules. Absorption by the sodium and potassium atoms is parameterized as in (Iro et al. 2005). Temperature-dependent absorption due to H2-H2 and H2-He is included, with the corresponding cross sections from HITRAN2012.

The atmospheric models consider the effect of haze. The baseline implementation, thin haze, considers number densities that are equal to those of the gas. The variation, thick haze, considers aerosol densities one hundred times those in the baseline model. For the haze particles, a wavelength-dependent cross section of 10-28  (1 micron / lamdba)2 [cm2] is assumed. This cross section is comparable to that for Rayleigh scattering at wavelengths near 1 micron.

Case study planets

Note: Each planet will have a short description/ instroduction here, and a likn to the page with the simulated spectra.

GJ 436b

GJ 1214b

WASP 12b

WASP 43b