Fiber modal noise is a performance limiting factor in high-precision radial velocity measurements with multi-mode fiber fed high-resolution spectrographs. Traditionally, modal noise is mitigated by agitating the fiber, this way redistributing the light that propagates in the fiber over many different modes. However, in case of fibers with only a limited number of modes, e.g. at near-infrared wavelengths or in adaptive-optics assisted systems, this method becomes very inefficient. The strong agitation that would be needed stresses the fiber and can lead to focal ratio degradation. As an alternative approach, we propose to use a classic optical double scrambler and to rotate the scrambler’s first fiber end during each exposure. Because of the rotating illumination pattern of the scrambler’s second fiber, the modes that are excited vary continuously. This leads to very efficient averaging of the modal pattern at the fiber exit and to a strong reduction of modal noise. In this contribution, we present a prototype design and first laboratory results of the rotating double scrambler.
Precise wavelength calibration is a critical issue for high-resolution spectroscopic observations. The ideal calibration source should be able to provide a very stable and dense grid of evenly distributed spectral lines of constant intensity. A new method which satisfies all mentioned conditions has been developed by our group. The approach is to actively measure the exact position of a single spectral line of a Fabry-Perot etalon with very high precision with a wavelength-tuneable laser and compare it to an extremely stable wavelength standard. The ideal choice of standard is the D2 absorption line of Rubidium, which has been used as an optical frequency standard for decades. With this technique, the problem of stable wavelength calibration of spectrographs becomes a problem of how reliably we can measure and anchor one etalon line to the Rb transition. In this work we present our self-built module for Rb saturated absorption spectroscopy and discuss its stability.
CubeSats are routinely used for low-cost photometry from space. Space-borne spectroscopy, however, is still the exclusive domain of much larger platforms. Key astrophysical questions in e.g. stellar physics and exoplanet research require uninterrupted spectral monitoring from space over weeks or months. Such monitoring of individual sources is unfortunately not affordable with these large platforms. With CUBESPEC we plan to offer the astronomical community a low-cost CubeSat solution for near-UV/optical/near-IR spectroscopy that enables this type of observations.
CUBESPEC is a generic spectrograph that can be configured with minimal hardware changes to deliver both low resolution (R = 100) with very large spectral coverage (200 - 1000 nm), as well as high resolution (R = 30 000) over a selected wavelength range. It is built around an off-axis Cassegrain telescope and a slit spectrograph with configurable dispersion elements. CUBESPEC will use a compact attitude determination and control system for coarse pointing of the entire spacecraft, supplemented with a fine-guidance system using a fast steering mirror to center the source on the spectrograph slit and to cancel out satellite jitter. An extremely compact optical design allows us to house this instrument in a 6U CubeSat with a volume of only 10 × 20 × 30 cm3 , while preserving a maximized entrance pupil of ca. 9 × 19 cm2 . In this contribution, we give an overview of the CUBESPEC project, discuss its most relevant science cases, and present the design of the instrument.
The BlackGEM Phase 1 array for optical synoptic surveys consists of three wide-field telescopes providing an 8.1 square degrees field-of-view sampled at 0.56". It will be installed at the ESO La Silla Observatory. Each unit telescope consists of a modified Dall-Kirkham (Wynne-Harmer) configuration with a 65cm parabolic primary mirror, a 23cm spherical secondary and a triplet corrector lens. The third lens in the triplet is motorized to double as an Atmospheric Dispersion Corrector. The 10cm x 10cm flat, achromatic focal plane contains a single STA1600 10.5k x 10.5k chip with 9 micron pixels, providing a 2.7 square degree field-of-view sampled at 0.56"/pix. The telescope is equipped with a 6 slot (u,g,q,r,i,z) filter wheel. Limiting magnitude (5 sigma) in dark conditions is q=23 in 300s integration in 1" seeing. The telescope structure is made from carbon-fibre for maximum stability. The secondary mirror is mounted on a piezo-stage for active control. Each telescope is mounted on the Fornax 200 mount. On La Silla each telescope will be housed in a clamshell dome, and be located on a 7m high double-walled cylinder to lift it above the ground-layer seeing. The outer cylinder will carry the dome and the inner cylinder the telescope.
The scientific program of BlackGEM is centered on optical afterglows of gravitational wave mergers, reacting to Advanced LIGO/Virgo triggers. The array will also perform a full southern sky survey (BG-SASS), covering 30000 square degrees (Dec < +30d) down to 22nd magnitude in all six filters at 1" resolution; a fast synoptic survey at 1 minute cadence for characterization of fast transients; bi-weekly all-sky q-band scan; and a twilight survey of the local universe.
The BlackGEM consortium consists of the Netherlands Research School for Astronomy (NOVA), Radboud University and KU Leuven as founding members and the University of Manchester, UC Davis, Tel Aviv University, the Weizmann Institute, the University of Canterbury and the Hebrew University Jerusalem as partners.
BlackGEM data will be processed on-line for transients and a full-source database using optimal photometry and the ZOGY image subtraction techniques. BlackGEM transients will be announced publically upon detection. All BlackGEM data will be cloud-based, including the 150Tb live database of the full source photometry.
BlackGEM Phase 1 is scheduled for installation on La Silla in Q2-Q3 2018 and start of operations of in Q4 2018. In Phase 2 (2019-2022) the array is to be expanded to 15 unit telescopes, providing a 40.5 square degree instantaneous field-of-view. An overview of the array, first results of the prototype and an update of the installation will be given.
In past decade, CMOS imagers are becoming increasingly popular in scientific imaging like astronomy. Large format image sensors are the detector of choice for the wide field imaging. The circuit integration capability of the CMOS imager is considered as an advantage while inducing the temperature variation over the sensor area. Dark current of the image sensor is strongly temperature-dependent signal and one of the limiting factors of the low light imaging. Here, we present per-pixel dark current measurement results and analysis of a 7638 x 5004 pixels front-side illuminated CMOS image sensor with a pixel pitch of 6 μm. In this work, global non- uniformity induced by the on-chip temperature variation is controlled by the Peltier junction device. This paper reports results of our dark current study for the temperature range 233 to 273 K with exposure of 0 to 300 s. A reasonably low dark current of 0.014 e-/pixel/s is achieved at 233 K temperature. The dark current spatial distributions at different temperatures are presented. We extracted the activation energy for the dark current in this lower temperature range. Using the Arrhenius law, dark current data analysis shows the Meyer-Neldel Relationship (MNR) between the Arrhenius pre-factor and the apparent activation energy.
We are characterizing a 7638 x 5004 front-side illuminated CMOS detector for astronomical application. Mod- ulation Transfer Function (MTF) of a detector is considered as an important figure of merit for accurate target positioning in astronomy. It states the upper limit of the image quality. MTF knowledge also provides a better understanding of the design trade-off. In this work, two-dimensional (2D) sub-micrometer scanning method is used to extract 2D MTF profile of our CMOS detector with a pixel pitch of 6μm. Our optical measurement setup focuses a collimated beam onto the imaging surface with a microscope objective. The spot was scanned in a raster over a single pixel. We generate an oversampled point spread function (PSF) of the detector which contains sub-pixel elements. 2D MTF map is calculated from the measured oversampled PSF. This 2D MTF map is used to characterize the resolving ability of our detector. We analyze the importance of the 2D MTF map to describe the full pixel MTF of the CMOS pixel having low fill-factor. 1D MTFs are calculated from the 2d MTF to do a quantitative comparison of the MTF in horizontal and vertical directions. This study emphasizes advantages and necessity of the 2D MTF for CMOS detector performance analysis, especially for anisotropic resolution.
Precise wavelength calibration is a persistent problem for highest precision Doppler spectroscopy. The ideal calibrator provides an extremely stable spectrum of equidistant, narrow lines over a wide bandwidth, is reliable over timescales of years, and is simple to operate. Unlike traditional hollow cathode lamps, etalons provide an engineered spectrum with adjustable line distance and width and can cover a very broad spectral bandwidth. We have shown that laser locked etalons provide the necessary stability with an ideal spectral format for calibrating precision Echelle spectrographs, in a cost-effective and robust package. Anchoring the etalon spectrum to a very precisely known hyperfine transition of rubidium delivers cm/s-level stability over timescales of years. We have engineered a fieldable system which is currently being constructed as calibrator for the MAROON-X, HERMES, KPF, FIES and iLocater spectrographs.
CubeSat technology is evolving rapidly. With the increased performance of these small spacecraft platforms, astronomical missions on CubeSats will be flown in the near future. These types of missions have very demanding requirements in terms of spacecraft pointing. At the KU Leuven university, we have developed a compact, highaccuracy attitude determination and control system for CubeSats. The system uses three reaction wheels and a star tracker to deliver high agility and accuracy. In this paper, we will discuss the test and calibration campaign that was carried out. This campaign was instrumental in achieving the performance required by astronomical missions.
We present a solution to the challenges of interfacing the ELT’s METIS to the telescope using a steerable hexapod structure. To guide the architectural choices, lumped physical models were derived from inverse kinematics in order to address the load distribution in each arm. Complete FE Analysis is carried on the optimal solutions of these models. The hexapod arms, which are high precision heavy duty linear actuators enduring forces in the excess of 30 tons, are designed using standard components whenever possible. An overall fully functional support structure design, satisfying the ESO/ELT and METIS requirements, is described.
Inter-pixel crosstalk degrades the point spread function (PSF) of a scientific imager which affects quantitative interpretation of scientific image data. Compared to the CCD, crosstalk is larger in the CMOS image sensor. This problem is challenging due to constant downscaling of the CMOS technology and pixel size. In this work, we parametrized the inter-pixel crosstalk and also modeled it as an empirically quantifiable kernel. A CMOS image sensor with 6 μm pixel pitch is measured. Evidently the crosstalk value can change with the PSF centroid position inside a pixel, primarily due to the spatial extent of the beam, which causes some optical generation in the surrounding pixels. We demonstrate a crosstalk measurement method and its spatial variation with respect to the spot position. This sub-pixel scanning is conducted to measure any crosstalk variation with respect to the sub-pixel spot position. Notable asymmetry on the crosstalk value between rows and columns as well as in the four corners of the POI is observed. This variation shows how the signal is shared at the pixel boundaries. Several POIs (Pixel of interest) over the scan region are measured to analyze the crosstalk variations.
BlackGEM is an array of telescopes, currently under development at the Radboud University Nijmegen and at NOVA (Netherlands Research School for Astronomy). It targets the detection of the optical counterparts of gravitational waves. The first three BlackGEM telescopes are planned to be installed in 2018 at the La Silla observatory (Chile). A single prototype telescope, named MeerLICHT, will already be commissioned early 2017 in Sutherland (South Africa) to provide an optical complement for the MeerKAT radio array. The BlackGEM array consists of, initially, a set of three robotic 65-cm wide-field telescopes. Each telescope is equipped with a single STA1600 CCD detector with 10.5k x 10.5k 9-micron pixels that covers a 2.7 square degrees field of view. The cryostats for housing these detectors are developed and built at the KU Leuven University (Belgium). The operational model of BlackGEM requires long periods of reliable hands-off operation. Therefore, we designed the cryostats for long vacuum hold time and we make use of a closed-cycle cooling system, based on Polycold PCC Joule-Thomson coolers. A single programmable logic controller (PLC) controls the cryogenic systems of several BlackGEM telescopes simultaneously, resulting in a highly reliable, cost-efficient and maintenance-friendly system. PLC-based cryostat control offers some distinct advantages, especially for a robotic facility. Apart of temperature monitoring and control, the PLC also monitors the vacuum quality, the power supply and the status of the PCC coolers (compressor power consumption and temperature, pressure in the gas lines, etc.). Furthermore, it provides an alarming system and safe and reproducible procedures for automatic cool down and warm up. The communication between PLC and higher-level software takes place via the OPC-UA protocol, offering a simple to implement, yet very powerful interface. Finally, a touch-panel display on the PLC provides the operator with a user-friendly and robust technical interface. In this contribution, we present the design of the BlackGEM cryostats and of the PLC-based control system.
As the new control system of the Mercator Telescope is being finalized, we can review some technologies and design methodologies that are advantageous, despite their relative uncommonness in astronomical instrumentation. Particular for the Mercator Telescope is that it is controlled by a single high-end soft-PLC (Programmable Logic Controller). Using off-the-shelf components only, our distributed embedded system controls all subsystems of the telescope such as the pneumatic primary mirror support, the hydrostatic bearing, the telescope axes, the dome, the safety system, and so on. We show how real-time application logic can be written conveniently in typical PLC languages (IEC 61131-3) and in C++ (to implement the pointing kernel) using the commercial TwinCAT 3 programming environment. This software processes the inputs and outputs of the distributed system in real-time via an observatory-wide EtherCAT network, which is synchronized with high precision to an IEEE 1588 (PTP, Precision Time Protocol) time reference clock. Taking full advantage of the ability of soft-PLCs to run both real-time and non real-time software, the same device also hosts the most important user interfaces (HMIs or Human Machine Interfaces) and communication servers (OPC UA for process data, FTP for XML configuration data, and VNC for remote control). To manage the complexity of the system and to streamline the development process, we show how most of the software, electronics and systems engineering aspects of the control system have been modeled as a set of scripts written in a Domain Specific Language (DSL). When executed, these scripts populate a Knowledge Base (KB) which can be queried to retrieve specific information. By feeding the results of those queries to a template system, we were able to generate very detailed “browsable” web-based documentation about the system, but also PLC software code, Python client code, model verification reports, etc. The aim of this paper is to demonstrate the added value that technologies such as soft-PLCs and DSL-scripts and design methodologies such as knowledge-based engineering can bring to astronomical instrumentation.
CMOS imagers are becoming increasingly popular in astronomy. A very low noise level is required to observe extremely faint targets and to get high-precision flux measurements. Although CMOS technology offers many advantages over CCDs, a major bottleneck is still the read noise. To move from an industrial CMOS sensor to one suitable for scientific applications, an improved design that optimizes the noise level is essential. Here, we study the 1/f and thermal noise performance of the source follower (SF) of a CMOS pixel in detail. We identify the relevant design parameters, and analytically study their impact on the noise level using the BSIM3v3 noise model with an enhanced model of gate capacitance. Our detailed analysis shows that the dependence of the 1/f noise on the geometrical size of the source follower is not limited to minimum channel length, compared to the classical approach to achieve the minimum 1/f noise. We derive the optimal gate dimensions (the width and the length) of the source follower that minimize the 1/f noise, and validate our results using numerical simulations. By considering the thermal noise or white noise along with 1/f noise, the total input noise of the source follower depends on the capacitor ratio CG/CFD and the drain current (Id). Here, CG is the total gate capacitance of the source follower and CFD is the total floating diffusion capacitor at the input of the source follower. We demonstrate that the optimum gate capacitance (CG) depends on the chosen bias current but ranges from CFD/3 to CFD to achieve the minimum total noise of the source follower. Numerical calculation and circuit simulation with 180nm CMOS technology are performed to validate our results.
We present the MeerLICHT and BlackGEM telescopes, which are wide-field optical telescopes that are currently being built to study transient phenomena, gravitational wave counterparts and variable stars. The telescopes have 65 cm primary mirrors and a 2.7 square degree field-of-view. The MeerLICHT and BlackGEM projects have different science goals, but will use identical telescopes. The first telescope, MeerLICHT, will be commissioned at Sutherland (South Africa) in the first quarter of 2017. It will co-point with MeerKAT to collect optical data commensurate with the radio observations. After careful analysis of MeerLICHT's performance, three telescopes of the same type will be commissioned in La Silla (Chile) in 2018 to form phase I of the BlackGEM array. BlackGEM aims at detecting and characterizing optical counterparts of gravitational wave events detected by Advanced LIGO and Virgo. In this contribution we present an overview of the science goals, the design and the status of the two projects.
The Radboud University Nijmegen in collaboration with the NOVA Optical Infrared Instrumentation group at ASTRON is currently leading the development and realization of the BlackGEM observing facility. The BlackGEM science team aims to be the first to catch the optical counterpart of a gravitational wave event. The BlackGEM project will put an array of three medium-sized optical telescopes at the La Silla site of the European Southern Observatory in Chile. It is uniquely equipped to achieve a combination of wide-field and high sensitivity through its array-like approach. Each BlackGEM unit telescope is a modified Dall-Kirkham-type telescope consisting of a 65cm primary mirror, a 21cm spherical secondary mirror and a triplet corrector lens. The spatial resolution on the sky will be 0.56 asec/pixel and the total field-of-view per telescope is 2.7 square degrees. The main requirement is to achieve a 5-sigma sensitivity of 23rd magnitude within a 5-minute exposure under 15 m/s wind gust conditions. This demands a very stable optical system with tight control of all the error contributions. This has been realized with a spreadsheet based integrated instrument model. The model contains all relevant telescope instrument parameters and environmental conditions. The spreadsheet is partly used for performance calculations and partly used to combine and integrate the output from several other sources. The spreadsheet model calculates the overall performance based on an Exposure Time Calculator using the Noise Equivalent Area metric (NEA). The NEA is further budgeted over 7 main High Level Requirements. The spreadsheet model is coupled to 1) a ZEMAX telescope optical model 2) a telescope FEM analysis to predict the optomechanical response under various gravity, temperature and wind load conditions, 3) a Matlab Simulink thermal model to predict the transient temperature behaviour of the most important telescope elements and 4) a Matlab Simulink control model to predict the performance of the active M2 mirror. All outputs are collected in a system performance budget that readily shows the compliance with the main High Level Requirements.
In todays era of ever growing telescope apertures, there remains a specific niche for meter-class telescopes, provided they are equipped with efficient and dedicated instruments. In case these telescopes have permanent and long-term availability, they turn out very useful for intensive monitoring campaigns over a large range of time-scales. Flexible scheduling and time allocation allow small telescopes to rapidly seize new opportunities or provide immediate follow-up observations to complement data from large ground-based or space-borne facilities. The Mercator telescope, a 1.2-m telescope, installed at the Roque de Los Muchachos Observatory on La Palma (Canary Islands, Spain), successfully targets this niche of intensive monitoring and flexible scheduling. Mercator is already in operation since 2001 and has seen several upgrades in the mean time. In this contribution we give an update about the actual telescope status and its performance. We also present the Mercator instrument suite that currently consists of two instruments. The workhorse instrument is HERMES, a very efficient and stable fibre-fed high-resolution spectrograph. Recently, the MAIA imager was commissioned. This is a three- channel photometric instrument that observes a large field simultaneously in the different color bands. The MAIA detectors are unique 6k x 2k frame transfer devices which also allow for fast and continuous monitoring of variable phenomena.We discuss two important upcoming upgrades: a long-awaited automatic mirror cover and, more importantly, an entirely new telescope control system (TCS). This TCS is based on modern PLC technology, and relies on OPC UA and EtherCAT communication. Only commercially off-the-shelve hardware will be used for controlling the telescope. As a test case and as a precursor of the full TCS, such PLC systems are already deployed at Mercator to steer the Nasmyth mirror mechanism and to control the MAIA instrument. Finally, we also give an overview of the exploitation scheme of the telescope, the scheduling software that we developed to guarantee that time series or time-critical observations can be acquired in an efficient way, and how this all serves the most important research themes for Mercator, mainly in the domain of stellar astrophysics.
Modern Programmable Logic Controllers (PLCs) have become an attractive platform for controlling real-time aspects of astronomical telescopes and instruments due to their increased versatility, performance and standardization. Likewise, vendor-neutral middleware technologies such as OPC Unified Architecture (OPC UA) have recently demonstrated that they can greatly facilitate the integration of these industrial platforms into the overall control system. Many practical questions arise, however, when building multi-tiered control systems that consist of PLCs for low level control, and conventional software and platforms for higher level control. How should the PLC software be structured, so that it can rely on well-known programming paradigms on the one hand, and be mapped to a well-organized OPC UA interface on the other hand? Which programming languages of the IEC 61131-3 standard closely match the problem domains of the abstraction levels within this structure? How can the recent additions to the standard (such as the support for namespaces and object-oriented extensions) facilitate a model based development approach? To what degree can our applications already take advantage of the more advanced parts of the OPC UA standard, such as the high expressiveness of the semantic modeling language that it defines, or the support for events, aggregation of data, automatic discovery, ... ? What are the timing and concurrency problems to be expected for the higher level tiers of the control system due to the cyclic execution of control and communication tasks by the PLCs? We try to answer these questions by demonstrating a semantic state machine model that can readily be implemented using IEC 61131 and OPC UA. One that does not aim to capture all possible states of a system, but rather one that attempts to organize the course-grained structure and behaviour of a system. In this paper we focus on the intricacies of this seemingly simple task, and on the lessons that we’ve learned during the development process of such a “PLC-friendly” state machine model.
The quality of space telescope observations greatly depends on the pointing performance of the spacecraft. In
this paper, recent advances in star tracker algorithms are discussed. This paper discusses efficient star tracker
algorithms that improve the pointing performance of the satellite, resulting in observations of higher quality.
Furthermore, the greatly reduced computational cost of these algorithms facilitates the inclusion of astronomical
payload measurements in the attitude determination and control loop. When the payload is used as an additional
star tracker, the pointing performance of the spacecraft increases drastically, which in its turn improves the quality
of the scientific measurements. Simulations show that with these improvements, the absolute pointing error of
the spacecraft can be reduced considerably.
We have developed an observing scheduling and archive system for the 1.2 meter Mercator Telescope. The goal
was to optimize the specific niche of this modern small telescope in observational astrophysics: the building-up
of long-term time series of photometric or high-resolution spectroscopic data with appropriate sampling for any
given scientific program. This system allows PIs to easily submit their technical requirements and keep track of
the progress of the observing programmes. The scheduling system provides the observer with an optimal schedule
for the night which takes into account the current observing conditions as well as the priorities and requirements
of the programmes in the queue. The observer can conveniently plan an observing night but also quickly adapt
it to changing conditions. The archiving system automatically processes new files as they are created, including
reduced data. It extracts the metadata and performs the normalization. A user can query, inspect and retrieve
observing data. The progress of individual programmes, including timeline and reduced data plots can be seen at
any time. Our MESA project is based on free and open source software (FOSS) using the Python programming
language. The system is fully integrated with the Mercator Observing Control System1 (MOCS).
The 1.2m optical Mercator Telescope (based at the Roque de Los Muchachos Observatory at La Palma) is currently
in the commissioning phase of a third permanently installed instrument called MAIA (Mercator Advanced
Imager for Asteroseismology), a three-channel frame-transfer imager optimized for rapid photometry. Despite
having three cryostats, MAIA is designed as a highly compact and portable instrument by using small Stirling-type
cryocoolers, and a single PLC in charge of all temperature control loops, cryocooler interaction, telemetry
acquisition and other instrument control related tasks. To accommodate MAIA at the Nasmyth B focal station of
the telescope, a new mechanism for the tertiary mirror had to be built since the former mechanism only allowed
motor controlled access to the Cassegrain and Nasmyth A focal stations. A second PLC has been installed in
order to control the two degrees of freedom of this mirror mechanism by interfacing with its motor controllers,
high-precision optical encoders, and limit switches. This PLC is not dedicated to the tertiary mirror control but
will serve as a general purpose controller for various tasks related to the telescope and the observatory, as part
of a new Telescope Control System primarily based on PLCs and OPC UA communication technology. Due to
the central location of the PLC inside the observatory, the position control loops of the mirror mechanism are
distributed using EtherCAT as the communication fieldbus. In this paper we present the design and the first
commissioning results of both the MAIA instrument control and the tertiary mirror control.
Originally, the Mercator telescope (Roque de Los Muchachos Observatory, La Palma) only had one Cassegrain
and one Nasmyth focal station available. Both foci are currently occupied and the exploitation scheme of the
Mercator telescope does not allow regular instrument changes. To accommodate our new three-channel imager
MAIA and to allow
exible scheduling with rapid follow-up of transient phenomena, we have designed and built
a new mechanism for the Nasmyth mirror that enables the use of the second Nasmyth focal station and of two
compact intermediate foci at the front and the rear side of the telescope tube. This mechanism uses high-precision
gears, bearings and optical encoders to allow for
exible and very accurate positioning of the Nasmyth mirror
along the rotation and tilt axes. It is controlled by a programmable logic controller (PLC) that is the precursor
of a completely new PLC and OPC-UA based telescope control system. We present the design, the construction
and the performance of this new Nasmyth mirror mechanism.
Proc. SPIE. 8451, Software and Cyberinfrastructure for Astronomy II
KEYWORDS: Observatories, Telescopes, Data modeling, Databases, Control systems, Software development, Photonic integrated circuits, Optical proximity correction, OLE for process control, Software frameworks
As an emerging Service Oriented Architecture (SOA) specically designed for industrial automation and process
control, the OPC Unied Architecture specication should be regarded as an attractive candidate for controlling
scientic instrumentation. Even though an industry-backed standard such as OPC UA can oer substantial added
value to these projects, its inherent complexity poses an important obstacle for adopting the technology. Building
OPC UA applications requires considerable eort, even when taking advantage of a COTS Software Development
Kit (SDK). The OPC Unied Architecture Framework (UAF) attempts to reduce this burden by introducing
an abstraction layer between the SDK and the application code in order to achieve a better separation of the
technical and the functional concerns. True to its industrial origin, the primary requirement of the framework
is to maintain interoperability by staying close to the standard specications, and by expecting the minimum
compliance from other OPC UA servers and clients. UAF can therefore be regarded as a software framework
to quickly and comfortably develop and deploy OPC UA-based applications, while remaining compatible to
third party OPC UA-compliant toolkits, servers (such as PLCs) and clients (such as SCADA software). In the
rst phase, as covered by this paper, only the client-side of UAF has been tackled in order to transparently
handle discovery, session management, subscriptions, monitored items etc. We describe the design principles
and internal architecture of our open-source software project, the rst results of the framework running at the
Mercator Telescope, and we give a preview of the planned server-side implementation.
The Mercator Advanced Imager for Asteroseismology (MAIA) is being designed particularly for asteroseismology
of hot subdwarf stars on the 1.2m Mercator Telescope. In order to achieve the required precision on the pulsation
amplitude ratios, the photometric variations must be measured simultaneously in several bands with respect to
constant reference stars in the field. MAIA is an optical imager to observe simultaneously in three color bands,
corresponding approximately with an SDSS u, g, r+i+z photometric system. The fully dioptric design uses
a common collimator, two dichroic beam splitters (cut-offs at 390nm and 550nm) and three cameras. Each
camera holds a fast frame-transfer CCD cooled down to -90°C with a compact Stirling cryocooler. All lenses
are axially and radially constrained by a calibrated spring load, with radial adjustment mechanisms to calibrate
the centering of each lens. The differential thermal expansion of the optical system is compensated by the
thermal expansion of the different materials in the mechanical mountings, resulting in a design that is insensitive
to thermal variations. Specific care has been taken to reduce the effect of manufacturing tolerances on the
performance of the instrument. The tilt angle of two of the beam splitters is adjustable in two dimensions to
compensate for remaining misalignment in the optical system. Finite element models have been constructed to
verify that the structural flexure and structural dynamics are within the requirements. A tool has been developed
to estimate the performance of the instrument based on the design parameters. Various commercial software
tools have been used to optimize the workflow in this complex system design.
The Mercator Advanced Imager for Asteroseismology (MAIA) is being designed particularly for asteroseismology
of hot subdwarf stars. In order to achieve the required precision on the pulsation amplitude ratios, the photometric
variations must be measured simultaneously in several bands with respect to constant reference stars in the
field. MAIA is an optical imager to observe simultaneously in three color bands, corresponding approximately
with an SDSS u, g, r+i+z photometric system. The fully dioptric design uses a common collimator, two dichroic
beam splitters (cut-offs at 390nm and 550nm) and three cameras. MAIA covers a wide field of view (FoV)
of 9.4' x 14.1' with a sampling of 0.27"/pix on the 1.2m Mercator Telescope. When replacing the collimator
and with a modest reduction of the FoV, its host can also be used on larger telescopes. Each camera holds a
fast-frame-transfer charge coupled device (CCD), cooled by three four-stage Peltier elements to -70 °C. The
mechanical design minimizes structural flexure. Selected optical elements are mounted in quasi-isostatic lens
mounts to minimize the effects of temperature variations.
A new control system is currently being developed for the 1.2-meter Mercator Telescope at the Roque de Los Muchachos Observatory (La Palma, Spain). Formerly based on transputers, the new Mercator Observatory Control System (MOCS) consists of a small network of Linux computers complemented by a central industrial controller and an industrial real-time data communication network. Python is chosen as the high-level language to develop flexible yet powerful supervisory control and data acquisition (SCADA) software for the Linux computers. Specialized applications such as detector control, auto-guiding and middleware management are also integrated in the same Python software package. The industrial controller, on the other hand, is connected to the majority of the field devices and is targeted to run various control loops, some of which are real-time critical. Independently of the Linux distributed control system (DCS), this controller makes sure that high priority tasks such as the telescope motion, mirror support and hydrostatic bearing control are carried out in a reliable and safe way. A comparison is made between different controller technologies including a LabVIEW embedded system, a PROFINET Programmable Logic Controller (PLC) and motion controller, and an EtherCAT embedded PC (soft-PLC). As the latter is chosen as the primary platform for the lower level control, a substantial part of the software is being ported to the IEC 61131-3 standard programming languages. Additionally, obsolete hardware is gradually being replaced by standard industrial alternatives with fast EtherCAT communication. The use of Python as a scripting language allows a smooth migration to the final MOCS: finished parts of the new control system can readily be commissioned to replace the corresponding transputer units of the old control system with minimal downtime. In this contribution, we give an overview of the systems design, implementation details and the current status of the project.
HERMES, a fiber-fed , high-resolution echelle spectrograph is currently in its integration phase at the 1.2-meter Mercator Telescope at the Roque de Los Muchachos Observatory on La Palma (Spain). The design of HERMES, optimized for high efficiency and high instrumental stability, is based on a large R2.7 echelle grating. It is operating in quasi-Littrow white-pupil configuration, with a double-prism as cross-disperser. It records the complete spectrum from 377 to 900 nm on one 2048×4608 pixel CCD in a single exposure. HERMES offers 1) a high-resolution and high-efficiency observation mode through a 80-μm optical fiber (2.5 arcsec sky aperture) equipped with a two-slice image slicer, resulting in a spectral resolution of R=85000 and a peak-efficiency above 25%; and 2) a high-stability mode through a 60-μm fiber (2.15 arcsec sky aperture, R=55000) equipped with a double fiber scrambler for improved spectrograph illumination stability. This mode is intended for high-precision radial velocity measurements and it offers the possibility of recording simultaneously the spectrum of a wavelength calibration lamp interlaced with the science spectrum. This allows for precise tracking of instrumental drifts during integration. To increase instrumental stability further, the spectrograph will be housed in a temperature and pressure controlled chamber. This spectrograph mounted on a flexible-scheduling telescope has a wide astronomical scope, going from asteroseismology to binary star research and chemical studies of stars and circumstellar material. In this contribution we present the final design of HERMES and we report on the project status.
HERMES is a high-resolution fiber-fed echelle spectrograph combining high throughput with high instrumental stability. The optical design is based on a large R2.7 echelle grating, operating in quasi-Littrow and white-pupil configuration, using a double-prism cross-disperser. It records the complete spectrum from 380 to 900 nm in a single exposure on a monolithic 2kx4.5k pixels CCD. HERMES offers 1) a high-resolution and high-efficiency observation mode through a 80-μm optical fiber (2.5 arcsec sky aperture) equipped with a two-slice image slicer, resulting in a resolution of λ/Δλ = 85000 and a peak-efficiency higher than 25%; and 2) a high-stability mode through a 60-μm fiber (2.15 arcsec sky aperture, R = 55000) equipped with a double fiber scrambler for improved spectrograph illumination stability. The latter mode is intended for high-precision radial velocity measurements and it offers the possibility of recording the spectrum of a wavelength calibration lamp simultaneously and interlaced with the stellar spectrum for precise tracking of instrumental drifts. To optimize instrumental stability, the spectrograph will be housed in a temperature and pressure controlled chamber, and it will operate in one fixed optical configuration. This instrument has a wide astronomical scope, going from asteroseismology to binary star research and chemical studies of stars and circumstellar material. HERMES is currently under construction and will be mounted on the 1.2-meter Mercator Telescope at the Roque de Los Muchachos Observatory on La Palma.
We present the Mercator Telescope together with the P7-2000 photometer as its first-light instrument. Mercator is a 1.2-meter Ritchey-Chretien telescope, installed at the Roque De Los Muchachos Observatory on La Palma and fully operational since Spring 2001. The Geneva Observatory developed this telescope and a twin, known as the Euler Telescope, was already inaugurated at the La Silla Observatory in 1998. Mercator is an alt-azimuthal telescope designed for semi-automatic operation and high operational robustness. P7 is a high-precision 2-channel differential photometer, built by the Geneva Observatory and in permanent use for over 25 years on various telescopes. It allows quasi-simultaneous observations in the 7 filters of the Geneva photometric system with a variable sampling rate up to 100 samples per second. This vintage instrument was completely refurbished in 2000 to function in an automatic mode on the Mercator Telescope. Electronics were completely renewed and are now based on a digital signal processor (DSP), which controls the instrument and performs basic data reduction. The optical system was left unmodified, apart from the addition of a field camera that is also used for auto-guiding. We also added instrument temperature control and a mechanical derotator. Since the 7 filters are acquired simultaneously and the absolute calibration of the colors is strictly homogeneous, the Mercator-P7 combination is a unique tool to study stellar variability on many different timescales. The current scientific program focuses on multi-periodic phenomena in early-type stars with the goal to identify the frequency spectrum and to constrain stellar models by asteroseismology studies. More than 43000 observations have been performed since 2001 and a precision of few milli-magnitudes is routinely achieved. Our photometric measurements result in the continuous calculation of the atmospheric extinction coefficients and these data are available online for other observers as well. In this paper, we describe the telescope, the photometer and their software, followed by the presentation of some first results. Finally, we discuss an upcoming upgrade and the complete instrumentation plan for Mercator.
Hermes, a high-resolution fiber-fed echelle spectrograph is currently under development for the 1.2-meter Mercator Telescope at the Roque De Los Muchachos Observatory on La Palma. The optical design is based on a large R2.6 echelle grating, operating in quasi-Littrow and white-pupil configuration, and a double-prism cross-disperser. This instrument records the complete optical spectrum from 380 to 875 nm in one single exposure on a 2k x 4k CCD. Order separation is sufficiently large to record two interleaved spectra simultaneously through two 60-mm core fibers: one spectrum of the object and one of the nearby sky or, alternatively, of a wavelength calibration lamp for high-precision radial velocity measurements. This type of observations also benefits from the high instrumental stability, owing to bench-mounting the spectrograph with a fixed configuration in a precisely temperature and humidity controlled chamber. Modest telescope size calls for high detection efficiency and great efforts in the design of both the fiber link and the spectrograph itself go in that direction. We aim at a peak-efficiency larger than 25% for the complete system. With a large fiber aperture of 2.3 arcsec, the resolving powerλ/ΔλΑ is 50000, a value that can be increased to 90000 with an adjustable slit at the fiber exit. This instrument mounted on a flexible telescope has a wide astronomical scope, going from asteroseismology to binary star research and chemical studies of stars and circumstellar material. We present the spectrograph design and we report on the project status.
In this paper we present the development of a CCD imager for the modern 1.2m MERCATOR telescope dedicated to long term monitoring of variable astrophysical phenomena. This instrument is a result of the collaboration of the Observatory of Geneva with the Institute of Astronomy in Leuven. After a technical description of the main components of the CCD camera system, the text will focus on the automatization of the observations and subsequent data reduction. The telescope itself is an altazimuth mounted 1.2 m Ritchey-Chretien telescope and is operated in a semi-automatic mode. The system executes a predefined sequence of observations, that only need
occasional checking of data quality by the astronomer. The observation software is written in a FORTRAN based interpreter language (INTER) running on a UNIX system that communicates with the astronomer via GUIs implemented in Perl/Tk. The data reduction is integrated into one package and includes pre-reduction, photometric and astrometric calibration, extraction, catalogue preparation and archiving. This allows to have a GUI driven reduction that is both flexible and robust. The preliminary reduced data give the astronomers an indication of the quality of their observations, so that they can adjust their program or camera settings during the same night.