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. 2014 Mar 24;372(2014):20130083.
doi: 10.1098/rsta.2013.0083. Print 2014 Apr 28.

Infrared spectroscopy of exoplanets: observational constraints

Thérèse Encrenaz  1
Affiliations

Infrared spectroscopy of exoplanets: observational constraints

Thérèse Encrenaz. Philos Trans A Math Phys Eng Sci. .

Abstract

The exploration of transiting extrasolar planets is an exploding research area in astronomy. With more than 400 transiting exoplanets identified so far, these discoveries have made possible the development of a new research field, the spectroscopic characterization of exoplanets' atmospheres, using both primary and secondary transits. However, these observations have been so far limited to a small number of targets. In this paper, we first review the advantages and limitations of both primary and secondary transit methods. Then, we analyse what kind of infrared spectra can be expected for different types of planets and discuss how to optimize the spectral range and the resolving power of the observations. Finally, we propose a list of favourable targets for present and future ground-based observations.

Keywords: exoplanets; infrared spectroscopy; molecular spectroscopy; transits.

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Figures

Figure 1.
Figure 1.
Reflected/scattered components and thermal components of exoplanets' spectra: (a) HD209458b and HD189733b, calculated for an albedo of 0.03; (b) GJ 1214b, calculated for two values of the albedo, a=0.03 and a=0.3. In view of the small planet–star distance, fast rotation is assumed in all cases. The figure is adapted from [23]. (Online version in colour.)
Figure 2.
Figure 2.
Transmission of main candidate molecules (H2O, CO2, CO, CH4, NH3) between 2 and 18 μm. Calculations use a line-by-line model with, for each gas, a pressure of 1 atm and a column density of 10 cm-amagat. (a) T=300 K and (b) T=1200 K. The spectral resolution is 10 cm−1, which corresponds to a resolving power of 67 at 16 μm, 100 at 10 μm and 500 at 2 μm. The figure is adapted from [23]. (Online version in colour.)
Figure 3.
Figure 3.
Molecular signatures expected in the K, L and M filters. The transmission is calculated as in figure 2, with a spectral resolution of 33 cm−1 (R= 150 at 2 μm and 75 at 4 μm). These conditions are appropriate for ground-based observations with an 8 m telescope (see table 4). (Online version in colour.)
See this image and copyright information in PMC

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