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Register a new userPrime focus wide-field corrector designs with lossless atmospheric dispersion correction
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Wide-Field Corrector designs are presented for the Blanco and Mayall telescopes, the CFHT and the AAT. The designs are Terezibh-style, with 5 or 6 lenses, and modest negative optical power. They have 2.2-3 degree fields of view, with curved and telecentric focal surfaces suitable for fiber spectroscopy. Some variants also allow wide-field imaging, by changing the last WFC element. Apart from the adaptation of the Terebizh design for spectroscopy, the key feature is a new concept for a Compensating Lateral Atmospheric Dispersion Corrector, with two of the lenses being movable laterally by small amounts. This provides excellent atmospheric dispersion correction, without any additional surfaces or absorption. A novel and simple mechanism for providing the required lens motions is proposed, which requires just 3 linear actuators for each of the two moving lenses.
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By means of third-order optical theory as well as ray-tracing simulations we have investigated the feasibility of wide-field imaging atmospheric Cherenkov telescopes with a reflective prime-focus design. For a range of desired optical resolutions, we have determined the largest available field-of-view of single-piece spherical, single-piece parabolic, tessellated spherical, tessellated parabolic and Davies-Cotton designs, always considering a wide range of design parameters. The Davies-Cotton design exhibits a surprising similarity to the tessellated parabolic design in its qualitative behaviour. Also, elliptic telescope designs with better off-axis imaging properties than Davies-Cotton are presented. We show that by using f/2 optics it is possible to build prime-focus telescopes with a full field-of-view of 10 degree at 0.1 degree resolution.
High precision astrometry requires an accurate geometric distortion solution. In this work, we present an average correction for the Blue Camera of the Large Binocular Telescope which enables a relative astrometric precision of ~15 mas for the B_Bess
el and V_Bessel broad-band filters. The result of this effort is used in two companion papers: the first to measure the absolute proper motion of the open cluster M67 with respect to the background galaxies; the second to decontaminate the color-magnitude diagram of M67 from field objects, enabling the study of the end of its white dwarf cooling sequence. Many other applications might find this distortion correction useful.
We present an alternative Corrector-ADC design for GMT. The design consists of just 3 silica lenses, of maximum size 1.51m, and includes only a single low-precision asphere for 20 field-of-view, and none for 10. The polychromatic (360nm-1300nm) image quality is d80<0.043 at zenith and d80<0.20 for ZD<60 degrees. The monochromatic image quality is d80<0.1 everywhere, and typically ~0.05. The ADC action is achieved by tilt and translation of all three lenses; L1 and L2 via simple slide mechanisms each using a single encoded actuator, and L3 via a novel tracker-ball support and three actuators. There is also a small motion of M2 via the hexapod, automatically generated by the AGWS system. The ADC action causes a small non-telecentricity, but this is much less than the unavoidable chromatic effects shared with the baseline design. The ADC action also changes the distortion pattern of the telescope, but this can be used positively, to reduce the maximum image motion due to differential refraction by a factor of three. The transmission is superb at all wavelengths, because of the reduced number of air/glass surfaces, and the use only of fused silica.
The Prime Focus Spectrograph (PFS) is a new optical/near-infrared multi-fiber spectrograph design for the prime focus of the 8.2m Subaru telescope. PFS will cover 1.3 degree diameter field with 2394 fibers to complement the imaging capability of Hyper SuprimeCam (HSC). The prime focus unit of PFS called Prime Focus Instrument (PFI) provides the interface with the top structure of Subaru telescope and also accommodates the optical bench in which Cobra fiber positioners are located. In addition, the acquisition and guiding (A&G) cameras, the optical fiber positioner system, the cable wrapper, the fiducial fibers, illuminator, and viewer, the field element, and the telemetry system are located inside the PFI. The mechanical structure of the PFI was designed with special care such that its deflections sufficiently match those of the HSC Wide Field Corrector (WFC) so the fibers will stay on targets over the course of the observations within the required accuracy.
We present the technical specifications and first results of the ESA-funded, lunar monitoring project NELIOTA (NEO Lunar Impacts and Optical TrAnsients) at the National Observatory of Athens, which aims to determine the size-frequency distribution of small Near-Earth Objects (NEOs) via detection of impact flashes on the surface of the Moon. For the purposes of this project a twin camera instrument was specially designed and installed at the 1.2 m Kryoneri telescope utilizing the fast-frame capabilities of scientific Complementary Metal-Oxide Semiconductor detectors (sCMOS). The system provides a wide field-of-view (17.0 $times$ 14.4) and simultaneous observations in two photometric bands (R and I), reaching limiting magnitudes of 18.7 mag in 10 sec in both bands at a 2.5 signal-to-noise level. This makes it a unique instrument that can be used for the detection of NEO impacts on the Moon, as well as for any astronomy projects that demand high-cadence multicolor observations. The wide field-of-view ensures that a large portion of the Moon is observed, while the simultaneous, high-cadence, monitoring in two photometric bands makes possible, for the first time, the determination of the temperatures of the impacts on the Moons surface and the validation of the impact flashes from a single site. Considering the varying background level on the Moons surface we demonstrate that the NELIOTA system can detect NEO impact flashes at a 2.5 signal-to-noise level of ~12.4 mag in the I-band and R-band for observations made at low lunar phases ~0.1. We report 31 NEO impact flashes detected during the first year of the NELIOTA campaign. The faintest flash was at 11.24 mag in the R-band (about two magnitudes fainter than ever observed before) at lunar phase 0.32. Our observations suggest a detection rate of $1.96 times 10^{-7}$ events $km^{-2} h^{-1}$.
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