[P-EM11] 系外惑星

[PEM11-22] Technology development at the testbeds FACET and EXIST toward direct detection and characterization of exoplanets

*村上 尚史¹、米田 謙太²、須藤 星路¹、大平 泰広¹、淺野 瑞基¹、角田 亮平¹、西川 淳^2,3,4 (1.北海道大学、2.国立天文台、3.総合研究大学院大学、4.アストロバイオロジーセンター)

キーワード：地球型系外惑星、直接検出、コロナグラフ、波面センシング、波面制御

Direct detection of exoplanets requires a high-contrast observational system. A key component of the high-contrast observational system is a coronagraph which rejects diffracted light from bright central stars. However, the coronagraph cannot perfectly reject the stellar light, and the stellar suppression level would be limited by wavefront error due to irregularity of optical surfaces including a telescope primary mirror. The wavefront error causes stellar speckles in the coronagraphic image that would prevent us from directly detecting faint planets. Therefore, it is necessary to utilize a wavefront sensing technique to measure electric fields of the residual stellar speckles, so that a wavefront control system, such as deformable mirrors, can correct the wavefront error to create extremely dark region (so-called dark hole) in the coronagraphic image where detection of faint exoplanets becomes feasible. As a future ambitious scientific goal, a direct detection of Earth-like exoplanets in habitable zones around Sun-like stars has been envisioned to search for biosignatures (signs of life) via spectroscopic characterization. However, the direct detection of the Earth-like exoplanet would be extremely challenging since it is expected that a Sun-like star would roughly 10 billion times brighter than reflected light off an Earth-like exoplanet in visible wavelength region. We have been developing high-contrast observational technologies toward direct detection and characterization of Earth-like exoplanets. Recently, we have constructed two laboratory testbeds FACET (FAcility for Coronagraphic Elemental Technologies) and EXIST (EXoplanet Imaging System Testbed) to accelerate our technology development. These testbeds have optical-fiber-linked artificial light sources with various wavelengths in visible range for simulating target stars and planets. The FACET has several optical paths to demonstrate and evaluate various high-contrast techniques such as coronagraphic optical devices, wavefront sensing and control techniques, post-processing techniques and so on. The EXIST is an end-to-end laboratory simulator of a high-contrast observational system. At both testbeds, we use large-format spatial light modulators (SLMs), instead of deformable mirrors, as the wavefront control systems so that we can demonstrate novel wavefront control techniques assuming future large-format deformable mirrors. A main goal of these testbeds is to develop various high-contrast technologies that can operate over broad wavelength range or multiple spectral bands required for the spectroscopic characterization of exoplanets. In this presentation, we will describe an overview of these two testbeds, and report recent progress on our activities. Especially we will report our technology development of wavefront sensing and control techniques aiming to create dark holes simultaneously at multiple spectral bands toward direct detection and characterization of exoplanets envisioned in the future.