Abstract
Optical instrumentation with reliable performance is essential for the research of exoplanet atmosphere characteristics. However, due to long distances and weak signals, exoplanets are difficult to be imaged by traditional optical systems. To this end, a novel optical system based on transit spectroscopy is proposed in this paper. On the basis of the principle of the transit-spectroscopy method and the astronomical parameters of observed targets, the optional parameter ranges of a dedicated optical system are analyzed. The transit signal-to-noise ratio (SNR) is introduced for the determination of telescope aperture and throughput. Furthermore, an example of the optical system with a space telescope and spectrometer is proposed according to the above optical index, which is proven to meet the performance requirements. The optical system is required to cover the wavelength of 0.5–8 μm and the field of view (FOV) of 27.9″ within the diffraction limit. The collecting aperture should be greater than 2 m, and spectral resolutions of two spectrometer channels should approximately be 100 (2–4 μm) and 30 (4–8 μm). The point-spread function (PSF) of each channel at the minimal wavelength should cover 2 pixels. The telescope and dichroic system provide diffraction-limited input beams with the required aperture, FOV, and wavelength for the spectrometer slits. The simulation results of the optical system show that the spectral resolutions of the dual-channel spectrometer were 111–200 and 43–94. The image points of the spectrometer in each wavelength were smaller than the Airy spot within the slit FOV, and the full width at half-maximum (FWHM) of PSF at λmin provided 2 pixels of 18 μm sampling. The feasibility of the demonstrated optical parameters is proven by the design.
Highlights
With the increasing number of exoplanet discoveries, scientific issues such as verifying the habitability of exoplanets [1], and discussing the relationship between the properties of stars and planetary parameters [2] have become an astronomical research focus that requires the indepth exploration and characterization of exoplanets’ internal properties, such as the nature of their atmosphere [3]
To study the characteristics of an exoplanetary atmosphere, a novel optical system based on transit spectroscopy was designed
The optical-system indices were systematically analyzed on the basis of the principles of astronomy and optics, of which the transit signal-to-noise ratio (SNR) was introduced into the determination of telescope aperture and throughput
Summary
With the increasing number of exoplanet discoveries, scientific issues such as verifying the habitability of exoplanets [1], and discussing the relationship between the properties of stars and planetary parameters [2] have become an astronomical research focus that requires the indepth exploration and characterization of exoplanets’ internal properties, such as the nature of their atmosphere [3]. The contributions of this paper are summarized as follows: (1) in order to study the atmosphere characteristics of exoplanets, related optical instrument indices were systematically derived; (2) transit SNR is introduced to the determination of telescope aperture and throughput; and (3) to verify the feasibility of the optical indices, a novel optical system was designed. Transit spectroscopy is a widely applied method for spectral detection to obtain the atmospheric environmental characteristics of exoplanets. It has relatively low contrast demand (10–100 ppm) and an adequate number of available samples, which is conducive to studying warm and hot exoplanets with a short period and nearby orbit [7]. Information of planetary-atmosphere composition can be inferred from the spectral characteristics
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