Extrasolar Super-Earth Transit Spectra
Taken from Howe and Burrows (2012)

Library of Selected Theoretical Transit Spectra of Extrasolar "Super-Earths"

Description: The files on this page are described in the paper Theoretical Transit Spectra of GJ 1214b and Other "Super-Earths" by Howe and Burrows (2012), submitted to the Astrophysical Journal. These files contain transit spectra for super-Earths as a function of mass, radius, equilibrium temperature, and atmospheric composition, including haze. A spectral range of 0.3 to ~10 microns is provided.

We have computed these models based on the assumptions of an observed mass and radius of the exoplanet. This will not be the physical radius, but will be the effective radius based on the observed absorption depth in a given wave band. To compute the models we assume the observed radius as a fiducial value for the physical radius, and then normalize the resultant spectrum to this value. The models on this page are normalized in a wave band from 0.7 to 1.0 microns.

Should you employ these theoretical models in a talk, publication, proposal, or other document, we would appreciate it if you would refer to this paper. In addition to the models included here, we can provide models for specific objects upon request. Feel free to contact Alex Howe or Adam Burrows if you have questions or requests.

Contents: All of the models are computed for a silicate-iron planet orbiting a Sun-like star. They include equilibrium temperatures of 400 K, 700 K, and 1000 K and a variety of models for opaque clouds and translucent hazes. Each model set includes atmospheres with solar, 0.3x solar, and 3x solar metallicities, and pure water, carbon dioxide, and methane. The models are named according to the format:
"(mass in Earth masses)me_(temperature)k_(atmosphere composition)_(cloud top pressure).dat"1

Format: The parameters assumed for the calculations are to be found in the headers to the files. The remainder of each file consists of the spectra data as follows:

  • Column 1: Wavelength of light in microns.
  • Column 2: Apparent radius in stellar radii.
  • Column 3: Transit depth as a fraction.
  • Column 4: Pressure at the effective radius (tau=0.56) in millibars (analytic model).
  • Column 5: Pressure at the effective radius (tau=0.56) in millibars (numerical calculations).
  • Column 6: Vertical optical depth of the haze at 0.85 microns (the midpoint of the normalization band).

  • These models are found in the paper and are described in the filenames. Models with haze are named according to the format:
    "(atmophere composition).(haze type).(number density).(particle size in microns)mu.(cloud top pressure).dat".

    Venus: The upcoming transit of Venus on June 5-6, 2012 provides a unique opportunity to test the techniques of transit spectroscopy. To that end, we have provided a selection of spectra for the transit of Venus incorporating a range of haze models informed by Ehrenreich et al. (A&A, 572, L2, 2011). These models do not account for limb darkening or refraction effects, but should demonstrate the effectivenesss of our calculations to predict the atmospheric compositions of exoplanets. Note that the effective radii in these files are based on the angular dimensions of the Sun and Venus rather than their linear dimensions.

    1Note that file names containing "1,0", "0,3", and "3,0" refer to 1x, 0.3x, and 3x solar metallicities, respectively, and "mubar" refers to microbars. In all cases, hazes are assumed to extend downward for two orders of magnitude in pressure (4.6 scale heights) with a uniform density.
    2A polymer based on the general formula (CH)n produced by UV photochemistry of methane and suggested to occur on Jupiter and giant exoplanets (Sudarsky, Burrows, & Hubeny 2003).
    3A complex heteropolymer produced by UV photochemistry of methane in the presence of nitrogen and oxygen compounds and thought to occur in the atmosphere Titan and on the surfaces of other outer solar system bodies (Khare et al. 1984).