Performance Of Telescope Research Articles

Next-generation telescopes with curved focal surface for ultralow surface brightness surveys

ABSTRACT In spite of major advances in both ground- and space-based instrumentation, the ultralow surface brightness Universe (ULSB) still remains a largely unexplored volume in observational parameter space. ULSB observations provide unique constraints on a wide variety of objects, from the Zodiacal light all the way to the optical cosmological background radiation, through dust cirri, mass-loss shells in giant stars, LSB galaxies and the intracluster light. These surface brightness levels (>28–29 mag arcsec−2) are observed by maximizing the efficiency of the surveys and minimizing or removing the systematics arising in the measurement of surface brightness. Based on full-system photon Monte Carlo simulations, we present here the performance of a ground-based telescope aimed at carrying out ULSB observations, with a curved focal surface design. Its off-axis optical design maximizes the field of view while minimizing the focal ratio. No lenses are used, as their multiple internal scatterings increase the wings of the point spread function (PSF), and the usual requirement of a flat focal plane is relaxed through the use of curved CCD detectors. The telescope has only one unavoidable single refractive surface, the cryostat window, and yet it delivers a PSF with ultracompact wings, which allows the detection, for a given exposure time, of surface brightness levels nearly three orders of magnitude fainter than any other current telescope.

An International Survey of Front-end Receivers and Observing Performance of Telescopes for Radio Astronomy

This paper presents a survey of microwave front-end receivers installed at radio telescopes throughout the world. This unprecedented analysis was conducted as part of a review of front-end developments for Italian radio telescopes, initiated by the Italian National Institute for Astrophysics in 2016. Fifteen international radio telescopes have been selected to be representative of the instrumentation used for radio astronomical observations in the frequency domain from 300 MHz to 116 GHz. A comprehensive description of the existing receivers is presented and their characteristics are compared and discussed. The observing performances of the complete receiving chains are also presented. An overview of ongoing developments illustrates and anticipates future trends in front-end projects to meet the most ambitious scientific research goals.

Aberration correction based on wavefront sensorless adaptive optics in membrane diffractive optical telescope

The membrane diffractive optical telescopes are one of areas of active research of large aperture optical telescopes. However, due to the processing technology of thin membrane mirror, the changes of temperature and humidity, etc., the imaging performance of membrane diffractive optical telescope is degraded sharply and it is difficult to reach the design target. Adaptive optics (AO) technology is a potential solution to improve the imaging performance of this telescope. Our work is the first time to correct system aberration of hundred millimeter-level aperture membrane diffractive optical telescope based on AO technology. The point target and extended target imaging experiment of the telescope with WFSless AO system in the laboratory are accomplished. The experimental results demonstrate the effectiveness of AO correction in improving the imaging performance of membrane diffractive optical telescope. Especially when there are unexpected aberrations introduced in the telescope, such as disturbances caused by assembly and operation, AO correction will be an important guarantee for the telescope to maintain good imaging performance.

Real-time position calculation method for large-diameter radio telescope panel using angle sensor

<p indent="0mm">With diameter enlarging and frequency upgrading of the radio telescope, the telescope structure is more complex, and the telescope efficiency and steering are more and more sensitive to structural distortion. It is difficult if we adopt traditional compensation method to satisfy the telescope electrical performance requirements, so taking the initiative to adjust the main reflector telescope to compensate telescope performance is essential, but the common active surface adjustment technology does not well meet the important instantaneity index. To this end, this paper proposes a real-time position calculation method for large-diameter radio telescope panel using the angle sensor. The physical position and attitude of the telescope panel can be computed quickly through using the reading of the angle sensors, which can make the active adjustment of the telescope panel more efficient and the telescope electrical performance being better.

On-sky Performance of the CLASS Q-band Telescope

Abstract The Cosmology Large Angular Scale Surveyor (CLASS) is mapping the polarization of the cosmic microwave background (CMB) at large angular scales (2 &lt; ℓ ≲ 200) in search of a primordial gravitational wave B-mode signal down to a tensor-to-scalar ratio of r ≈ 0.01. The same data set will provide a near sample-variance-limited measurement of the optical depth to reionization. Between 2016 June and 2018 March, CLASS completed the largest ground-based Q-band CMB survey to date, covering over 31,000 square-degrees (75% of the sky), with an instantaneous array noise-equivalent temperature sensitivity of . We demonstrate that the detector optical loading (1.6 pW) and noise-equivalent power (19 ) match the expected noise model dominated by photon bunching noise. We derive a 13.1 ± 0.3 K pW−1 calibration to antenna temperature based on Moon observations, which translates to an optical efficiency of 0.48 ± 0.02 and a 27 K system noise temperature. Finally, we report a Tau A flux density of 308 ± 11 Jy at 38.4 ± 0.2 GHz, consistent with the Wilkinson Microwave Anisotropy Probe Tau A time-dependent spectral flux density model.

VHE gamma-ray observation of Crab Nebula with HAGAR telescope array

HAGAR is a system of seven Non-imaging Atmospheric Cherenkov Telescopes located at Hanle in the Ladakh region of the Indian Himalayas at an altitude of 4270 meters {\it amsl}. Since 2008, we have observed the Crab Nebula to assess the performance of the HAGAR telescopes. We describe the analysis technique for the estimation of $\gamma$-ray signal amidst cosmic ray background. The consolidated results spanning nine years of the Crab nebula observations show long term performance of the HAGAR telescopes. Based on about 219 hours of data, we report the detection of $\gamma$-rays from the Crab Nebula at a significance level of about 20$\sigma$, corresponding to a time averaged flux of (1.64$\pm$0.09) $\times10^{-10}$ photons cm$^{-2}$ sec$^{-1}$ above 230 GeV. Also, we perform a detailed study of possible systematic effects in our analysis method on data taken with the HAGAR telescopes.

Subaru Portable Spectrophotometer: in-situ reflectivity measurement for large telescope mirror

The reflectivity of a telescope primary mirror is one of the fundamental parameters that determines the telescope performance. Due to a lack of suitable instruments, however, measuring the absolute value of the reflectivity, in particular wide spectral measurements in-situ, has been almost impossible. To solve this problem, we developed a portable spectrophotometer called the Subaru Portable Spectrophotometer (SPS). SPS covers a spectral range between 380 and 1000 nm with a resolution of 2 nm. Its dimension and weight enable in-situ measurement on the primary mirror. A modified V-N method is applied to SPS for obtaining the absolute reflectivity. A sequential measurement makes SPS compensate the instrumental drift. The great advantage of SPS is its capability of getting absolute spectral reflectivity in-situ, even after the primary mirror is mounted on a telescope. In the case of Subaru Telescope, SPS clarified the reflectivity of the primary mirror coated with aluminum 4 years ago. Periodic measurements have been on-going since the primary mirror recoating in 2017. It is now possible to study the telescope reflectivity degradation with SPS.

Ultra wideband and multi-beam signal receiving and processing system of QTT

The proposed 110-m full-steerable radio telescope (Qitai radio telescope, QTT) in Xinjiang is mainly used in the fields of basic scientific research, such as pulsar observation, gravitational wave and black hole detection, star formation, galactic origin. At the same time, it serves national projects such as China Lunar Exploration project and Mars exploration. In order to meet the scientific needs, QTT will be equipped with a variety of ultra-wideband, multi-beam, high-sensitivity receivers and signal processing systems, to treat the weak electromagnetic wave signal received by the radio telescope, such as amplification, filtering, frequency conversion and other processing and sending to the digital terminal and processed. As this system determines the operating bandwidth, instantaneous bandwidth and field of view of radio telescopes, and is closely related to sensitivity, as a key part of the large radio telescope, it plays an important role in the performance of telescopes. In this paper, the configuration scheme and main performance index of QTT UWB and multi-beam signal receiving and processing system are demonstrated in detail. This paper systematically discusses the preliminary technical scheme of QTT receiver and signal acquisition and processing system, and analyzes the key technical problems of signal receiving and processing system.

Accuracy Analysis of the Pointing and Focusing Calibration of the 5 m Terahertz Telescope for Dome A in Antarcticatwo

Pointing calibration and sub-reflector focusing are an important task of antenna measurement, which significantly contributes to the observational performance of a radio telescope. According to the requirements on the pointing accuracy and defocusing gain loss of the 5m Dome A Terahertz Explorer (DATE5), this paper has derived the requirements of signal-to-noise ratio for the pointing and sub-reflector focusing calibration observations, and selected several astronomical radio sources suitable for the pointing and focusing calibrations at the terahertz waveband in Antarctica, which include planets and ultra-compact HII regions. The effects of the atmospheric absorption and the source angular diameter on the accuracy of calibration measurements are analyzed. Simulations show that when the telescope operates in Antarctica, these sources can provide sufficient flux densities for verifying the pre-established pointing model and focusing model.

Status of the KM3NeT Mediterranean Sea neutrino telescope

The status and physics performance of the KM3NeT neutrino telescope in the Mediterranean Sea neutrino are presented.

Compact, Wide-Angle Catadioptric Telescope Design for MWIR Imaging

In this work, the optical design of a compact diffraction-limited F/3.0 MWIR (3-5 µm) catadioptric telescope which consists of an aspheric primary mirror, a spherical secondary mirror, a ZnSe-ZnSe-Ge triplet lens and an air-spaced Si-Ge-Si corrector triplet lens placed before the focus is given. The calculated effective focal length, full field of view (FFOV) and angular magnification values for the designed telescope are 600 mm, 2.6° and -9.2, respectively. Zemax® calculations for the telescope MTF (modulation transfer function), PSF (point spread function), RMS (root-mean-square) wavefront error (WFE), optical path difference (OPD), Seidel aberrations, encircled energy, distortion and field curvature are discussed. The telescope performance analysis indicates that the telescope can achieve diffraction-limited image quality performance within the 2.6° full field-of-view. Additionally, the designed telescope can resolve at 50% contrast spatial frequency equal to 18.5 cycles/mm (at the on-axis FOV). Finally, a detailed tolerance analysis for the telescope design employing Monte Carlo and sensitivity analysis simulation features in Zemax® is provided.

3D Measurement Simulation and Relative Pointing Error Verification of the Telescope Mount Assembly Subsystem for the Large Synoptic Survey Telescope.

An engineering validation of a large optical telescope consists of executing major performing tests at the subsystem level to verify the overall engineering performance of the observatory. Thus, the relative pointing error verification of the telescope mount assembly subsystem is of special interest to guarantee the absolute pointing performance of the large synoptic survey telescope. This paper presents a new verification method for the relative pointing error assessment of the telescope mount assembly, based on laser tracker technology and several fiducial points fixed to the floor. Monte-Carlo-based simulation results show that the presented methodology is fit for purpose, even if floor movement occurs due to temperature variation during the measurement acquisition process. A further research about laser tracker technology integration into the telescope structure may suggest that such laser tracker technology could be permanently installed in the telescope in order to provide an active alignment system that aims to detect and correct possible misalignment between mirrors or to provide the required mirror positioning verification accuracy after maintenance activities. The obtained results show that two on-board laser tracker systems combined with eight measurement targets could result in measurement uncertainties that are better than 1 arcsec, which would provide a reliable built-in metrology tool for large telescopes.

Sequentially Assembled Reconfigurable Extended Joints: Self-Lockable Deployable Structure

AbstractAs focal length significantly affects the performance of a telescope, the performance of spatial telescopes in astrophysical missions is mainly limited by the launchers’ capabilities. An ap...

The Extreme Energy Events experiment: an overview of the telescopes performance.

The muon telescopes of the Extreme Energy Events (EEE) experiment are based on Multigap Resistive Plate Chambers (MRPC). The EEE network is composed, so far, of 53 telescopes, each made of three MRPC detectors; it is organized in clusters and single telescope stations distributed all over the Italian territory and installed in High Schools, covering an area larger than 3×105 km2. The study of Extensive Air Showers (EAS), that is one of the goal of the project, requires excellent performance in terms of time and spatial resolution, efficiency, tracking capability and long term stability. The data from two recent coordinated data taking periods, named Run 2 and Run 3, have been used to measure these quantities and the results are here reported, together with a comparison with expectations and with the results from a beam test performed in 2006 at CERN.

Vibration rejection of Tip-Tilt mirror using improved repetitive control

Abstract Mechanical vibrations in Tip-Tilt modes affect the closed-loop performance of astronomical telescopes. Large integration time of the image sensor can restrict the Tip-Tilt mirror control bandwidth, which is not sufficient to mitigate structural vibrations. This paper proposes an improved repetitive control (IRC) of the Tip-Tilt mirror based on Youla parameterization to mitigate telescope vibrations. As a learning-type control strategy, repetitive controllers can achieve optimal performance when frequencies of vibrations are provided. Although the control bandwidth of the Tip-Tilt mirror is not improved with this proposed controller, the disturbance attenuation is enhanced. Furthermore, vibrations rejection provided by this proposed control method is not restricted by an accurate model, because this repetitive controller is a plug-in type. To reduce the waterbed effect induced by the IRC, a new Q-filter based on moving average filter is proposed. Simulations and experiments demonstrate a clear improvement of performance for the IRC in comparison with the classical repetitive controller.

Performance investigation of the BAO 2.6 m telescope

Imaging performance of the BAO 2.6 m telescope is analyzed. In particular, the influence of the optical quality of the telescope's main mirror is considered. After a brief recall of the main parameters, which determine the performance of optical telescopes, detailed results of the mirror's optical quality investigation are presented. The contribution of the mirror's quality on the ultimate image quality, as well as its impact on the optical throughput in UVI passbands for a given seeing condition, is presented. Preliminary assessments of the other relevant factors responsible for image quality degradation have also been conducted.

Inorbit performance of the Hard X-ray Telescope (HXT) on board the Hitomi (ASTRO-H) satellite

Hitomi (ASTRO-H) carries two Hard X-ray Telescopes (HXTs) that can focus X-rays up to 80 keV. Combined with the Hard X-ray Imagers (HXIs) that detect the focused X-rays, imaging spectroscopy in the high-energy band from 5 keV to 80 keV is made possible. We studied characteristics of HXTs after the launch such as the encircled energy function (EEF) and the effective area using the data of a Crab observation. The half power diameters (HPDs) in the 5--80 keV band evaluated from the EEFs are 1.59 arcmin for HXT-1 and 1.65 arcmin for HXT-2. Those are consistent with the HPDs measured with ground experiments when uncertainties are taken into account. We can conclude that there is no significant change in the characteristics of the HXTs before and after the launch. The off-axis angle of the aim point from the optical axis is evaluated to be less than 0.5 arcmin for both HXT-1 and HXT-2. The best-fit parameters for the Crab spectrum obtained with the HXT-HXI system are consistent with the canonical values.

Stray light characteristics of the diffractive telescope system

Diffractive telescope technology is an innovation solution in construction of large light-weight space telescope. However, the nondesign orders of diffractive optical elements (DOEs) may affect the imaging performance as stray light. To study the stray light characteristics of a diffractive telescope, a prototype was developed and its stray light analysis model was established. The stray light characteristics including ghost, point source transmittance, and veiling glare index (VGI) were analyzed. During the star imaging test of the prototype, the ghost images appeared around the star image as the exposure time of the charge-coupled device improving, consistent with the simulation results. The test result of VGI was 67.11%, slightly higher than the calculated value 57.88%. The study shows that the same order diffraction of the diffractive primary lens and correcting DOE is the main factor that causes ghost images. The stray light sources outside the field of view can illuminate the image plane through nondesign orders diffraction of the primary lens and contributes to more than 90% of the stray light flux on the image plane. In summary, it is expected that these works will provide some guidance for optimizing the imaging performance of diffractive telescopes.

Ray tracing method for the evaluation of grazing incidence x-ray telescopes described by spatially sampled surfaces.

The nested grazing incidence telescope can achieve a large collecting area in x-ray astronomy, with a large number of closely packed, thin conical mirrors. Exploiting the surface metrological data, the ray tracing method used to reconstruct the shell surface topography and evaluate the imaging performance is a powerful tool to assist iterative improvement in the fabrication process. However, current two-dimensional (2D) ray tracing codes, especially when utilized with densely sampled surface shape data, may not provide sufficient accuracy of reconstruction and are computationally cumbersome. In particular, 2D ray tracing currently employed considers coplanar rays and thus simulates only these rays along the meridional plane. This captures axial figure errors but leaves other important errors, such as roundness errors, unaccounted for. We introduce a semianalytic, three-dimensional (3D) ray tracing approach for x-ray optics that overcomes these shortcomings. And the present method is both computationally fast and accurate. We first introduce the principles and the computational details of this 3D ray tracing method. Then the computer simulations of this approach compared to 2D ray tracing are demonstrated, using an ideal conic Wolter-I telescope for benchmarking. Finally, the present 3D ray tracing is used to evaluate the performance of a prototype x-ray telescope fabricated for the enhanced x-ray timing and polarization mission.

The Sardinia Radio Telescope

[Abridged] The Sardinia Radio Telescope (SRT) is the new 64-m dish operated by INAF (Italy). Its active surface will allow us to observe at frequencies of up to 116 GHz. At the moment, three receivers, one per focal position, have been installed and tested. The SRT was officially opened in October 2013, upon completion of its technical commissioning phase. In this paper, we provide an overview of the main science drivers for the SRT, describe the main outcomes from the scientific commissioning of the telescope, and discuss a set of observations demonstrating the SRT's scientific capabilities. One of the main objectives of scientific commissioning was the identification of deficiencies in the instrumentation and/or in the telescope sub-systems for further optimization. As a result, the overall telescope performance has been significantly improved. As part of the scientific commissioning activities, different observing modes were tested and validated, and first astronomical observations were carried out to demonstrate the science capabilities of the SRT. In addition, we developed astronomer-oriented software tools, to support future observers on-site. The astronomical validation activities were prioritized based on technical readiness and scientific impact. The highest priority was to make the SRT available for joint observations as part of European networks. As a result, the SRT started to participate (in shared-risk mode) in EVN (European VLBI Network) and LEAP (Large European Array for Pulsars) observing sessions in early 2014. The validation of single-dish operations for the suite of SRT first light receivers and backends continued in the following years, and was concluded with the first call for shared-risk/early-science observations issued at the end of 2015.