We are currently investigating the feasibility of a 1.6 m telescope with a laser-guide star adaptive optics (AO) system. The telescope, if successfully commissioned, would be the first dedicated adaptive optics observatory in South Korea. The 1.6 m telescope is an f/13.6 Cassegrain telescope with a ...
We are currently investigating the feasibility of a 1.6 m telescope with a laser-guide star adaptive optics (AO) system. The telescope, if successfully commissioned, would be the first dedicated adaptive optics observatory in South Korea. The 1.6 m telescope is an f/13.6 Cassegrain telescope with a focal length of 21.7 m. This paper first reviews atmospheric seeing conditions measured over a year in 2014~2015 at the Bohyun Observatory, South Korea, which corresponds to an area from 11.6 to 21.6 cm within 95% probability with regard to the Fried parameter of 880 nm at a telescope pupil plane. We then derive principal seeing conditions such as the Fried parameter and Greenwood frequency for eight astronomical spectral bands (V/R/I/J/H/K/L/M centered at 0.55, 0.64, 0.79, 1.22, 1.65, 2.20, 3.55, and $4.77{\mu}m$). Then we propose an AO system with a laser guide star for the 1.6 m telescope based on the seeing conditions. The proposed AO system consists of a fast tip/tilt secondary mirror, a $17{\times}17$ deformable mirror, a $16{\times}16$ Shack-Hartmann sensor, and a sodium laser guide star (589.2 nm). The high order AO system is close-looped with 2 KHz sampling frequency while the tip/tilt mirror is independently close-looped with 63 Hz sampling frequency. The AO system has three operational concepts: 1) bright target observation with its own wavefront sensing, 2) less bright star observation with wavefront sensing from another bright natural guide star (NGS), and 3) faint target observation with tip/tilt sensing from a bright natural guide star and wavefront sensing from a laser guide star. We name these three concepts 'None', 'NGS only', and 'LGS + NGS', respectively. Following a thorough investigation into the error sources of the AO system, we predict the root mean square (RMS) wavefront error of the system and its corresponding Strehl ratio over nine analysis cases over the worst ($2{\sigma}$) seeing conditions. From the analysis, we expect Strehl ratio >0.3 in most seeing conditions with guide stars.
We are currently investigating the feasibility of a 1.6 m telescope with a laser-guide star adaptive optics (AO) system. The telescope, if successfully commissioned, would be the first dedicated adaptive optics observatory in South Korea. The 1.6 m telescope is an f/13.6 Cassegrain telescope with a focal length of 21.7 m. This paper first reviews atmospheric seeing conditions measured over a year in 2014~2015 at the Bohyun Observatory, South Korea, which corresponds to an area from 11.6 to 21.6 cm within 95% probability with regard to the Fried parameter of 880 nm at a telescope pupil plane. We then derive principal seeing conditions such as the Fried parameter and Greenwood frequency for eight astronomical spectral bands (V/R/I/J/H/K/L/M centered at 0.55, 0.64, 0.79, 1.22, 1.65, 2.20, 3.55, and $4.77{\mu}m$). Then we propose an AO system with a laser guide star for the 1.6 m telescope based on the seeing conditions. The proposed AO system consists of a fast tip/tilt secondary mirror, a $17{\times}17$ deformable mirror, a $16{\times}16$ Shack-Hartmann sensor, and a sodium laser guide star (589.2 nm). The high order AO system is close-looped with 2 KHz sampling frequency while the tip/tilt mirror is independently close-looped with 63 Hz sampling frequency. The AO system has three operational concepts: 1) bright target observation with its own wavefront sensing, 2) less bright star observation with wavefront sensing from another bright natural guide star (NGS), and 3) faint target observation with tip/tilt sensing from a bright natural guide star and wavefront sensing from a laser guide star. We name these three concepts 'None', 'NGS only', and 'LGS + NGS', respectively. Following a thorough investigation into the error sources of the AO system, we predict the root mean square (RMS) wavefront error of the system and its corresponding Strehl ratio over nine analysis cases over the worst ($2{\sigma}$) seeing conditions. From the analysis, we expect Strehl ratio >0.3 in most seeing conditions with guide stars.
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제안 방법
6 m telescope with a laser-guide star adaptive optics (AO) system. The AO system was designed based on the astronomical seeing conditions measured over a year at the Bohyun observatory, South Korea. Following an extensive investigation into the errors sources of the adaptive optics system with a sodium laser guide star, we concluded that we can achieve a Strehl ratio > 0.
4µm) for NGS and LGS cases. The prediction considers a wide range of parameters and error sources, including the strength and profile of the atmospheric turbulence, the fitting error caused by the finite spatial resolutions of the wavefront sensor and deformable mirror, wavefront sensor noise propagating through the wavefront reconstruction algorithm, servo lag resulting from the finite bandwidth of the control loop, and the anisoplanatism for a given constellation of natural and/or laser guide stars [6-10].
대상 데이터
One of the site candidates for the 1.6 m telescope is the Bohyun observatory located at 36.1648°N and 128.977°E with altitude 1124 m.
The telescope, if successfully commissioned, would be the first dedicated adaptive optics observatory in South Korea. The 1.6 m telescope is an f/13.6 Cassegrain telescope with a focal length of 21.7 m. The AO system consists of a tip/ tilt secondary mirror, a deformable mirror, two scientific cameras (CCD and IR detector), a Shack-Hartman wavefront sensor, a laser guide star, and a data processing or control system (Fig.
7 m. The AO system consists of a tip/ tilt secondary mirror, a deformable mirror, two scientific cameras (CCD and IR detector), a Shack-Hartman wavefront sensor, a laser guide star, and a data processing or control system (Fig. 1).
6 m telescope. The AO system consists of a tip/tilt secondary mirror, a deformable mirror, two scientific cameras (CCD and IR detector), a Shack-Hartman wavefront sensor, a sodium laser, and a data processing or control system. The adaptive optics system set is installed on an optical bench located on one of the Nasmyth ports, as shown in Fig.
The telescope is an f/13.6 Nasmyth-Cassegrain telescope on an alt-azimuth mount, which is a simple two-axis mount for supporting and rotating an instrument about two perpendicular axes - one vertical and the other horizontal. As in the Cassegrain telescope, the light falls on a concave primary mirror and then is reflected toward a convex secondary mirror.
The telescope is equipped with a laser launch telescope with a sodium laser, an AO system set, and two scientific cameras (a CCD and an IR detector). The laser launch telescope with the laser head is mounted on the center frame, the laser electric control box is mounted on one of the Nasmyth platforms, and the optical bench including the AO system is set on the other Nasmyth port.
This paper first presents the system design of the AO system based on the seeing conditions measured at the Bohyun Observatory, South Korea, which is one of the telescope site candidates. We then investigate the imaging performance of the telescope in terms of the Strehl ratio predicted at four wave bands (V/I/J/K/L centered at 0.
성능/효과
In this simulation, we assumed that the total optics transmittance is 50% and the WFS bandwidth (∆λ) is 80 nm, which are common values in adaptive optics systems.
후속연구
However, the intensity of the laser guide star depends on the density of sodium atoms at the mesosphere, which strongly varies locally and temporally. Further study is under preparation to predict the sodium density above the observatory and to predict the AO performance accordingly.
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