SOXS (Son Of X-Shooter) will be a spectrograph for the ESO NTT telescope capable to cover the optical and NIR bands, based on the heritage of the X-Shooter at the ESO-VLT. SOXS will be built and run by an international consortium, carrying out rapid and longer term Target of Opportunity requests on a variety of astronomical objects. SOXS will observe all kind of transient and variable sources from different surveys. These will be a mixture of fast alerts (e.g. gamma-ray bursts, gravitational waves, neutrino events), mid-term alerts (e.g. supernovae, X-ray transients), fixed time events (e.g. close-by passage of minor bodies). While the focus is on transients and variables, still there is a wide range of other astrophysical targets and science topics that will benefit from SOXS. The design foresees a spectrograph with a Resolution-Slit product ≈ 4500, capable of simultaneously observing over the entire band the complete spectral range from the U- to the H-band. The limiting magnitude of R~20 (1 hr at S/N~10) is suited to study transients identified from on-going imaging surveys. Light imaging capabilities in the optical band (grizy) are also envisaged to allow for multi-band photometry of the faintest transients. This paper outlines the status of the project, now in Final Design Phase.
SOXS (Son of X-Shooter) will be the new medium resolution (R~4500 for a 1 arcsec slit), high-efficiency, wide band spectrograph for the ESO-NTT telescope on La Silla. It will be able to cover simultaneously optical and NIR bands (350-2000nm) using two different arms and a pre-slit Common Path feeding system. SOXS will provide an unique facility to follow up any kind of transient event with the best possible response time in addition to high efficiency and availability. Furthermore, a Calibration Unit and an Acquisition Camera System with all the necessary relay optics will be connected to the Common Path sub-system. The Acquisition Camera, working in optical regime, will be primarily focused on target acquisition and secondary guiding, but will also provide an imaging mode for scientific photometry. In this work we give an overview of the Acquisition Camera System for SOXS with all the different functionalities. The optical and mechanical design of the system are also presented together with the preliminary performances in terms of optical quality, throughput, magnitude limits and photometric properties.
The SPECtro-heliograph for the Transition REgion (SPECTRE) experiment is one of the instruments of the Solar Heliospheric Activity Research and Prediction Program (SHARPP) suite initially foreseen aboard the NASA mission Solar Dynamics Observatory (SDO) of the International Living With a Star (ILWS) program. The scientific objective of the SPECTRE experiment was to characterize the rapid evolution of plasma in the transition region of the solar atmosphere, producing full-disk 1.2 arcsec-resolution images of the solar atmosphere at the very critical 63 nm OV spectral line, characterizing a solar plasma temperature of about 250,000 K. Unfortunately, NASA very recently and unexpectedly, during the instrument Phase A study, decided not to proceed with the realization of SHARPP. The authors of this paper think that all the work done so far in the definition of SPECTRE should not be lost. So, they have decided to summarize in this paper the main characteristics of this instrument and the results of the analysis so far performed: the hope is that in a next future this work can be used again for realizing an instrument having similar characteristics.
The ASTRI mini-array, composed of nine small-size dual mirror (SST-2M) telescopes, has been proposed to be installed at the southern site of the Cherenkov Telescope Array (CTA), as a set of preproduction units of the CTA observatory. The ASTRI mini-array is a collaborative and international effort carried out by Italy, Brazil and South Africa and led by the Italian National Institute of Astrophysics, INAF. We present the main features of the current implementation of the Mini-Array Software System (MASS) now in use for the activities of the ASTRI SST-2M telescope prototype located at the INAF observing station on Mt. Etna, Italy and the characteristics that make it a prototype for the CTA control software system. CTA Data Management (CTADATA) and CTA Array Control and Data Acquisition (CTA-ACTL) requirements and guidelines as well as the ASTRI use cases were considered in the MASS design, most of its features are derived from the Atacama Large Millimeter/sub-millimeter Array Control software. The MASS will provide a set of tools to manage all onsite operations of the ASTRI mini-array in order to perform the observations specified in the short term schedule (including monitoring and controlling all the hardware components of each telescope and calibration device), to analyze the acquired data online and to store/retrieve all the data products to/from the onsite repository.
SOXS (Son Of X-Shooter) will be a unique spectroscopic facility for the ESO-NTT 3.5-m telescope in La Silla (Chile), able to cover the optical/NIR band (350-1750 nm). The design foresees a high-efficiency spectrograph with a resolutionslit product of ~4,500, capable of simultaneously observing the complete spectral range 350 - 1750 nm with a good sensitivity, with light imaging capabilities in the visible band. This paper outlines the status of the project.
ASTRI SST-2M is an end-to-end telescope prototype developed by the Italian National Institute of Astrophysics (INAF) in the framework of the Cherenkov Telescope Array (CTA). The CTA observatory, with a combination of large-, medium-, and small-sized telescopes (LST, MST and SST, respectively), will represent the next generation of imaging atmospheric Cherenkov telescopes. It will explore the very high-energy domain from a few tens of GeV up to few hundreds of TeV.
The ASTRI SST-2M telescope structure and mirrors have been installed at the INAF observing station at Serra La Nave, on Mt. Etna (Sicily, Italy) in September 2014. Its performance verification phase began in autumn 2015. Part of the scheduled activities foresees the study and characterization of the optical and opto-mechanical performance of the telescope prototype.
In this contribution we report the results achieved in terms of kinematic model analysis, mirrors reflectivity evolution, telescopes positioning, flexures and pointing model and the thermal behavior.
The Italian National Institute for Astrophysics (INAF) is leading the Astrofisica con Specchi a Tecnologia Replicante Italiana (ASTRI) project whose main purpose is the realization of small size telescopes (SST) for the Cherenkov Telescope Array (CTA). The first goal of the ASTRI project has been the development and operation of an innovative end-to-end telescope prototype using a dual-mirror optical configuration (SST-2M) equipped with a camera based on silicon photo-multipliers and very fast read-out electronics. The ASTRI SST-2M prototype has been installed in Italy at the INAF “M.G. Fracastoro” Astronomical Station located at Serra La Nave, on Mount Etna, Sicily. This prototype will be used to test several mechanical, optical, control hardware and software solutions which will be used in the ASTRI mini-array, comprising nine telescopes proposed to be placed at the CTA southern site. The ASTRI mini-array is a collaborative and international effort led by INAF and carried out by Italy, Brazil and South-Africa. We present here the use cases, through UML (Unified Modeling Language) diagrams and text details, that describe the functional requirements of the software that will manage the ASTRI SST-2M prototype, and the lessons learned thanks to these activities. We intend to adopt the same approach for the Mini Array Software System that will manage the ASTRI miniarray operations. Use cases are of importance for the whole software life cycle; in particular they provide valuable support to the validation and verification activities. Following the iterative development approach, which breaks down the software development into smaller chunks, we have analysed the requirements, developed, and then tested the code in repeated cycles. The use case technique allowed us to formalize the problem through user stories that describe how the user procedurally interacts with the software system. Through the use cases we improved the communication among team members, fostered common agreement about system requirements, defined the normal and alternative course of events, understood better the business process, and defined the system test to ensure that the delivered software works properly. We present a summary of the ASTRI SST-2M prototype use cases, and how the lessons learned can be exploited for the ASTRI mini-array proposed for the CTA Observatory.
We present the proposal for the physical instrument model of the SOXS (Son OF X-Shooter) spectroscopic facility
mainly devoted to the follow-up observation of transient sources. A dedicated suitable instrument to exploit the science
of these transients is lacking, resulting in severe science “dissipation”. SOXS will cover the optical/NIR band (0.35-1.75
μm) with a medium resolution (R~4500), down to the limiting magnitude of R~20-20.5 (1 hr at S/N~10) that is perfectly
suited to study transients from on-going imaging surveys. Imaging capabilities in the optical are also foreseen to allow
for multi-band photometry of the faintest transients with a field of view of at least 2arcmin. We propose to implement a
physical modelling approach in order to link the instrument parameters and behaviour to physical quantities, thus
providing a description of the instrument that can be connected with measurements. The method has been already
successfully applied to the X-shooter instrument. The X-shooter physical model is based on a kernel optical ray-tracing
realised by means of matrix optics representation, which can handle a large number of wavelengths. This can be
extended to the SOXS design. The foreseen applications of the SOXS physical model are broad, ranging from support to
detailed instrument design and development of the data reduction software, wavelength calibration, evaluation of
instrument performance as a function of the model parameters, instrument alignment, and support during the
commissioning phase and as a tool for quality check during operations.
ASTRI SST-2M is an end-to-end prototype of Small Size class of Telescope proposed for the Cherenkov Telescope Array (CTA). Currently under completion at the Serra La Nave observing station (Mt. Etna, Catania, Italy), the ASTRI SST- 2M telescope is the first imaging dual-mirror telescope ever realized for Cherenkov telescopes. A mini-array of nine such telescopes will form the ASTRI mini-array proposed as a precursor and initial seed of CTA to be installed at the final CTA southern site. ASTRI SST-2M is equipped with an active optics system, controlling both the segmented primary mirror and the monolithic secondary mirror, which allows optical re-alignment during telescope slew. We describe the hardware and software solution that have been implemented for optics control and the models we developed for the system.
ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) SST-2M is an end-to-end prototype of Small Size
class of Telescope for the Cherenkov Telescope Array. It will apply a dual mirror configuration to Imaging Atmospheric
Cherenkov Telescopes. The 18 segments composing the primary mirror (diameter 4.3 m) are equipped with an active
optics system enabling optical re-alignment during telescope slew. The secondary mirror (diameter 1.8 m) can be moved
along three degrees of freedom to perform focus and tilt corrections. We describe the kinematic model used to predict the
system performance as well as the hardware and software design solution that will be implemented for optics control.
ASTRI SST-2M is a prototype dual mirror Small Size class of Telescope for the Cherenkov Telescope Array (CTA). Its
innovative design based on a Schwarzschild-Couder configuration will permit use Silicon Photo-multipliers as focalplane
detectors. The dual mirror configuration is a challenge for the realization of both the primary and secondary.
Accurate tests and characterization are mandatory to understand the behavior of the optical configuration, its limits and
the possibility of improvements of the full CTA array. Moreover, optical alignment requires solutions and procedures
that have not been used so far on Cherenkov telescopes. The aim of paper is to provide an analysis of these topics in the
context of the ASTRI SST-2M telescope.
The design and performance of a Fizeau interferometer with long focal length and large field of view are discussed. The optical scheme presented is well suited for very accurate astrometric measurements from space, being optimised, in terms of geometry and aberrations, to observe astronomical targets down to the visual magnitude mV=20, with a measurement accuracy of 10 microarcseconds at mV=15.
This study is in the context of the next generation astrometric space missions, in particular for a mission profile similar to that of the Gaia mission of the European Space Agency.
Beyond the accuracy goal, the great effort in optical aberrations reduction, particularly distortion, aims at the optimal exploitation of data acquisition done with CCD arrays working in Time Delay Integration mode. The design solution we present reaches the astrometric goals with a field of view of 0.5 square degrees.
We describe a software tool developed to simulate the behaviour of the angle between two lines of sight in a dual view telescope assembly (usually referred to as basic angle) due to optical misalignments induced by thermo-mechanical fluctuations. The tool applies to a variety of reflective optical designs. In principle, not only the basic angle behaviour can be simulated, but also other optical parameters. As a practical example, we present and discuss results obtained from application of our software to the case of the Gaia baseline optical design. We show that the final error can be severely degraded by fluctuations of the basic angle due to thermo-mechanical effects.
A new concept CCD camera is currently under development at the XUVLab of the Department of Astronomy and Space Science of the University of Florence. This CCD camera is the proposed detector for the space- and ground-based solar corona observations. This camera will be the detector for the polarimetric channels of the UVC coronagraph of the HERSCHEL rocket mission to observe the solar corona in an optical broadband. The ground-based application consists in a UVC prototype for coronagraphic measurements from Earth in the visible range. Within this project, a CCD camera with innovative features has been produced: the camera controller allows the fine tuning of all the parameters related to charge transfer and CCD readout, i.e., the use of virtually any CCD sensor, and it implements the new concept of high level of versatility, easy management, TCP/IP remote control and display.
The HERSCHEL (HElium Resonance Scattering in the Corona and HELiosphere) Sun-Earth Sub-Orbital Program is a proposed sounding-rocket payload designed to investigate helium coronal abundance and solar wind acceleration from a range of solar source structures by obtaining simultaneous observations of the electron, proton and helium solar coronae. HERSCHEL will provide the first measurements of the coronal helium abundance in source regions of the solar wind, thus bringing key elements to our understanding of the Sun-Earth connections. The HERSCHEL instrument package consists of the Extreme Ultraviolet Imaging Telescope (EIT) for on-disk coronal observations and the Ultraviolet and Visible-light Coronagraphic Imager (UVCI) for off-limb observations of the corona. The UVCI is an externally occulted, reflecting coronagraph with an off-axis Gregorian telescope. UVCI will be able to take coronal images at heliocentric heights comprised between 1.2 to 3.5 solar radii of a) K-corona polarized brightness (pB); b) H I Lyman-α, 121.6 nm, line-emission; c) He II Lyman-α, 30.4 nm, line. The key element in the UVCI instrument concept is that the mirrors with multilayer coatings optimized for 30.4 nm still have good reflectivity at 121.6 nm and in the visible. The optical design concept for the UVCI instrument will be discussed, together with its expected optical and throughput performances.
Deposition and characterization results of multilayer coatings optimized for HeII 30.4 nm high reflectivity will be presented. Additional characterization of reflectivity at HI Ly-α and in the visible spectral range has been also accomplished in order to investigate the performances of such coatings in view of their application to the UVCI instrument on board of ESA payload SOLO and to HERSCHEL, a sounding rocket experiment.
The Ultraviolet and Visible-light Coronagraph Imager (UVCI) proposed for the European Space Agency (ESA) Solar Orbiter mission, is designed to image the visible and the ultraviolet coronal emissions, in order to diagnose the solar corona. The UVCI is an externally occulted reflection coronagraph that obtains monochromatic images in the neutral hydrogen HI 121.6 nm and in the single ionized helium HeII 30.4 nm lines, and measures the polarized brightness (pB) of the K-corona in broadband visible light. One of the most stringent requirements in the design of a coronagraph is the stray light rejection. The stray light is produced by solar disk radiation which is several order of magnitude brighter than the coronal radiation in both visible and UV. The solar disk radiation enters the instrument through the external aperture and stray light is produced by diffraction off the edges of the apertures and of the optical components, non-specular reflections off the mirror surfaces, and scattering off the mechanical structure. In this paper, the features in the optical design that contribute to the stray light reduction are described, and an analysis of all possible stray light contributions is performed on the optical configuration of the UVCI sounding rocket prototype (UVC-SR). From this analysis, a stray light model has been developed and its results are compared with the minimum measurable signal expected from the solar corona.
The Ultraviolet and Visible-light Coronagraph (UVC) is one of the solar remote-sensing instruments proposed for the model payload of the Solar Orbiter mission. The Solar Orbiter is one of the two 'Flexible' missions selected in September 2000 by the European Space Agency (ESA) for the definition study phase. A novel orbital design takes the orbiter as close as 0.21 astronomical units (AU) to the Sun, with heliographic latitudes as high as 38 degrees for observations of the solar polar regions at very high spatial resolution. From this vantage point, the UVC can, at the same time, image the visible and ultraviolet coronal emissions and diagnose, with unprecedented temporal and spatial resolution (down to 1200 km) the full solar corona. The UVC's optical design, presented here, consists of an externally occulted, off-axis Gregorian with multilayer-coated optics. The UVC can obtain monochromatic images in the neutral hydrogen HI Lyman (alpha) , (lambda) 121.6 nm, and single-ionized helium HEII Lyman (alpha) , (lambda) 30.4 nm, lines and measure the polarized brightness (pB) of the visible K-corona. The ultraviolet Lyman (alpha) lines are separated with two multilayer coatings mirror and an extreme-ultraviolet transmission filter. The mirrors' coating optimized for 30.4 nm still has a good reflectivity at 121.6 nm and visible. The optical performances, resulting from ray-tracing calculations, are presented here, along with the expected system response to the coronal signal.
KEYWORDS: Sensors, Mirrors, Telescopes, Contamination, Near infrared, Optical design, Optical filters, Signal to noise ratio, Optical instrument design, K band
In this paper a preliminary design for a prime focus corrector to be mounted at the Telescopio Nazionale Galileo (TNG) is presented. The telescope is located on La Palma and has a primary mirror of 3.5 m with a hyperbolic sag. Two optical designs have been considered in order to exploit detectors with 1k by 1k and 2k by 2k pixels. Each design makes use of four lenses, tow of which are aspherical. The first lens diameters are respectively, of 140 mm and 320 mm for the two kinds of detectors. For both designs the telescope pupil is deliberately not re-imaged, and therefore it will not be possible to insert a cold stop. For such a reason particular care has been dedicated to the telescope thermal background study, in order to optimize the baffling system. The optics is able to correct fields of 11 feet by 11 feet and of 60 feet by 60 feet, depending on the design. It should be considered that the particular geometry of the focal plane array mosaic does not permit a full exploitation of the entire field, being based on a combination of four detectors. The selected chips are HgCdTe manufactured by Rockwell, i.e. Hawaii I in the 1k by 1k case and Hawaii I in the 1k by 1k case and Hawaii II in the 2k by 2k case.
We present in this paper a preliminary design of a near IR wide field imager for the prime focus of the ESO 3.6 meter telescope. Such a design was developed in response to the increasing demand in the astronomical community for a fast and efficient Near IR survey facility taking profit of the small pitch 1k2 and 2k2 Hybrid Focal Plane Arrays recently made available. The prime focus is a privileged location for high throughput instrument since it allows to design imagers with a relatively small amount of optical elements . At the prime focus however the plate scale is constrained to a narrow range of possibility by the F/number of primary mirror since the need to correct for aberrations does not leave much freedom for focal elongation. The ESO 3.6 telescope has a F/3 primary mirror. Unlike most of the new technology telescope of the same size, e.g. NTT or TNG, that have F/2.2 primaries, the longer focal length of the ESO 3.6 allows to reach plate scales of the order of about 15.2 as/mm, matching the scientific requirement for wide field NIR surveys. The Camera consist in a prime focus corrector made of 4 spherical lenses in fused silica providing a corrected field of 45 arcmin 0. The limited number of optical elements maximizes the throughput but does not allow to re-image the telescope pupil to position a cold stop. Therefore a detailed mode of the telescope thermal background has been sued to optimized the baffling system. Only a non-contiguous fraction of the corrected field is covered by 4 Rockwell HAWAII II 2k2 HgCdTe chips.
The Galileo Telescope is a Ritchey-Chretienne telescope with an aperture of 3.58 meters and is located in La Palma Island. Since the first light in June 1998, several nights have been used to calibrate and to test the active optics systems, an operation involving also the control and reduction software and the optics of the de-rotator system. At the moment the active optics system routinely works at the beginning of the nights to support both technical and scientific observations. The ultimate tests on the control system are here reported and its performances are analyzed in order to quantify the final optical quality. Also a brief report on the effects of the serrourier temperature is reported. A comparison between Shack-Hartmann analysis performed on the rotator adapter bench and wavefront analysis on the instrument focal plane (at Nasmith station) is also reported. Some images taken in the visible and near infrared ranges during the same night are shown.
The Telescope Nazionale Galileo (TNG) telescope is now operational. One of its main goals is to provide high quality images, in a wide range of operating conditions and for several observing modes. Telescope pointing and tracking performances can heavily affect achievement of this requirement, and particular care must be taken in order to reach the highest possible accuracy. Control of the three axes is implemented in one VME controller (minimizing data exchange through the TNG LAN), and telescope mount positions are computed from object coordinates taking into account physical and environmental aspects which alter the object apparent position. Improvement of telescope pointing and tracking performances is obtained by two means. Systematic errors are mostly corrected using a model compensation, that can be introduced in the coordinates transformation flow. The telescope model is derived by off-line analysis of the pointing errors on a specific set of data. In this way we could improve the pointing and tracking performances up to now by a factor of about 30. Tracking drift given by non- systematic and residuals of systematic errors is corrected using a guide camera, which mounts a 800 X 576 CCD (0.35 arcsec/pixel scale). Guide stars are selected from an on- line available star catalogue. Light from the selected star is focused on the guide camera by moving a probe housed in the rotator-adapter module. Tracking drift computation is performed on a two-axes scheme (Right Ascension and Declination), with sub-pixel accuracy. Here the first results of the telescope pointing and tracing accuracy are presented.
KEYWORDS: Mirrors, Telescopes, Control systems, Active optics, Computer programming, Temperature metrology, Lanthanum, Thermal effects, Space telescopes, Switches
Sometimes during a scientific data acquisition the focus of a telescope may change, especially for medium- and long-time exposures. This is mainly due to temperature changes inducing an expansion of the serrourier truss, and more generally, due to elastic structural flexures. Modelization and control of defocusing effect is an important topic in telescopes with great magnification ratio. In the Telescopio Nazionale Galileo case, a 3.5 meters class telescope located in La Palma island, a temperature change of 1 degree induces a 0.9 arcsec image blue. In such a case a control of defocus during an acquisition is essential to obtain sub-arcsec images, thus exploiting the site seeing. The secondary mirror of Galileo telescope is actively controlled via a hexapod actuator. Both systems, the hexapod secondary support and the control system, have been completed and tested at the telescope. The results show that positioning of the mirror is smooth enough, introducing an image movement of about 0.1 arcesc and allowing in such a way the on-line correction also during scientific operations.
KEYWORDS: Telescopes, Control systems, Active optics, Local area networks, Human-machine interfaces, Interfaces, Operating systems, Data archive systems, Databases, CCD cameras
Since March 1997, the TNG Telescope is int its Commissioning phase. In this paper, we describe the structure of the control software of TNG and the on-going activity of the software integration team. The Telescope Communication Network has been completely installed, the control software has been set up and the integration phase is currently in progress. The TNG control software has been designed having in mind the needs of a modern telescope control system: it is based on stable and widespread industry standards; its architecture is fully modular and intrinsically open in order to allow future enhancements and/or modifications of its components. Moreover, the code was written paying a particular attention to its portability. All these characteristics make the TNG control system open to future technology evolutions, both hardware and software-wise. The TNG control software provides a coherent environment where the information flow is constantly guided and controlled through its path across the system. Despite the multiplicity and non-homogeneity of the different subsystems, TNG provides the operator a common framework from the raw data gathering, to the real-time applications, up to the operator interface and archiving system. This was made designing and building a set of layers of increasing abstraction that were mapped onto the various physical components. A brief description of the steps followed during the integration of a number of subsystems will be given.
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