The Greenland Telescope (GLT) currently achieves a blind pointing accuracy of 2" rms, sufficient for 230GHz VLBI operations at Pituffik Space Base. Plans to relocate the antenna to Summit Station are underway to enable observations at ≥690GHz, which requires improving the pointing accuracy due to smaller beam sizes at higher frequencies. Since achieving the ALMA-standard referenced pointing accuracy of less than 1" for single-dish operations is impractical due to limited sensitivity, GLT’s strategy involves real-time adjustments using data from metrology sensors, following the Systematic Pointing Error Model (SPEM) by the antenna manufacturer (Vertex Antennentechnik). This paper highlights our metrology system’s role in predicting pointing corrections through real-time monitoring of inclinometers, linear, and temperature sensors. Additionally, we introduce a night-viable optical guidescope system for astrometric referencing of star-fields, aiming to enhance pointing precision for high-frequency VLBI with the GLT.
Past millimeter-wave galaxy surveys have probed the brightest starburst galaxies only and suffered heavily from confusion. The interpretation of existing surveys has also been hindered by the lack of reliable redshift indicators for measuring distances for the entire sample. Thanks to recent advances in mm-wave detector technologies we can now overcome these limitations, and conduct the first truly volumetric surveys of star-forming galaxies at mm-wavelengths down to the L∗ luminosities of typical galaxies, with ∼1000 redshift slices spanning most of the Cosmic star-forming volume (z∼1–12) with nearly uniform mass and luminosity selection. We describe an instrument concept capable of delivering such surveys with the technologies available today, which can be built and operated on a ground-based mm-wave facility in the near future. Such spectrometer cameras can resolve and redshift identify up to to 25,000 star-forming galaxies per year even when operated on a 10-m class telescope. On a larger aperture it can do the same faster or probe even deeper. We propose a loose, open-source collaboration to design, build, and operate one or several such cameras through the shared contributions of leading experts and telescopes from around the globe.
The Submillimeter Array (SMA) requires precise full-sky blind pointing for its eight 6m antennas, aiming for an error within 3′′, a fraction of the 34′′ FWHM beam at 345 GHz. SMA’s typical 2–3′′ rms pointing accuracy is crucial for efficient array operation, especially with 4 to 6 antenna relocations across 23 pads in various configurations each semester. Traditional calibration using optical guidescopes for mount model errors has shifted to interferometric pointing measurements on quasars, for full model acquisition and baseline calibration. Following every array reconfiguration, mechanical imperfections in antenna mounting lead to significant deviations in azimuth encoder offset and axis tilt parameters, complicating pointing accuracy. To overcome this, a three-layer feed-forward neural network, trained on over ten years of data for each antenna-pad configuration, predicts post-reconfiguration changes. This approach, currently under evaluation and refinement, aims to expedite re-calibration, indicating potential substantial reductions in calibration time and enhanced operational efficiency.
The Transneptunian Automated Occultation Survey (TAOS II) is a three robotic telescope project to detect stellar occultation events generated by TNOs. TAOS II aims to monitor about 10000 stars simultaneously at 20Hz to generate a significant event rate. The TAOS II cameras are designed to cover the 1.7 degree diameter field of view of the 1.3m telescopes with a mosaic of ten 4.5k × 2k e2v CIS 113 CMOS sensors. The CIS 113 has a back-illuminated thinned structure to provide similar performance to that of back-thinned CCDs. The CIS 113 device has 16 micron pixels with 8 outputs, with a plate scale about 0.63”/pixel. With the freedom of direct row and column addressing, star boxes with sizes of 8 × 8 pixels in each sensor can be sampled at 20 Hz or higher with a pixel rate of 1M pixel/sec per channel. The sensors, mounted on a single Invar plate, are cooled to an operating temperature of about 200K by a cryogenic cooler. The gap between two sensors is about 0.5mm. The control electronics consist of an analog part and a Xilinx FPGA based digital circuit. One FPGA is needed to control and process the signal from each CIS 113 chip. Two large PCBs were used to fanout signals from the 10 CMOS devices through the vacuum chamber wall. A synchronization circuit receives a pulse from the control building to ensure the timing error of exposures of the three cameras is within 1 ms. The cameras were delivered and installed on the TAOS telescopes in 2023 and series of tests and adjustments have been carried out to optimize the performance. In this presentation, the camera performance in the full frame mode and the window mode will be detailed. The synchronization and the adjustment among the three cameras will also be presented.
The Submillimeter Array (SMA) is an array of 8 antennas operating at millimeter and submillimeter wavelengths on Maunakea, Hawaii, operated by the Smithsonian Astrophysical Observatory and Academia Sinica Institute of Astronomy and Astrophysics, Taiwan. Over the past several years, we have been preparing a major upgrade to the SMA that will replace the aging original receiver cryostats and receiver cartridges with all new cryostats and new 230 and 345 GHz receiver designs. This wideband upgrade (wSMA) will also include significantly increased instantaneous bandwidth, improved sensitivity, and greater capabilities for dual frequency observations. In this paper, we will describe the wSMA receiver upgrade and status, as well as the future upgrades that will be enabled by the deployment of the wSMA receivers.
The Transneptunian Automated Occultation Survey (TAOS II) is a three robotic telescope project to detect stellar occultation events generated by TransNeptunian objects (TNOs). TAOS II aims to monitor about 10000 stars simultaneously at 20Hz to generate a significant event rate. The TAOS II cameras are designed to cover the 1.7 degree diameter field of view of the 1.3m telescopes with a mosaic of ten 4.5k × 2k Teledyne e2v CIS 113 CMOS sensors. The CIS 113 has a back-illuminated thinned structure to provide similar performance to that of back-thinned CCDs. The CIS 113 device has 16 micron pixels with 8 outputs, with a plate scale about 0.63”/pixel. With the freedom of direct row and column addressing, star boxes with sizes of 8 × 8 pixels in each sensor can be sampled at 20 Hz or higher with a pixel rate of 1M pixel/sec per channel. The sensors, mounted on a single Invar plate, are cooled to an operating temperature of about 200K by a cryogenic cooler. The surfaces of the sensors were mounted to be within 30 microns to maintain a flat focal plane. The gap between two sensors is about 0.5mm. The control electronics consist of an analog part and a Xilinx FPGA based digital circuit. One FPGA controls and processes the signal from each CIS 113 chip. Two large PCBs were used to fanout signals from the 10 CMOS devices through the vacuum chamber wall. A synchronization circuit receives a pulse from the control center to ensure the timing accuracy of exposures of the three cameras is within 1 ms.
The Greenland Telescope (GLT), currently located at Thule Air Base, is a 12-m single dish telescope operating at frequencies of 86, 230 and 345 GHz. Since April 2018, the GLT has regularly participated in (sub-)mm VLBI observations of supermassive black holes as part of the Event Horizon Telescope (EHT) and the Global mm VLBI Array (GMVA). We present the status of scientific commissioning activities at the GLT, including most recently the 345 GHz first light and test observations. The antenna surface accuracy has been improved to ~25 microns through panel adjustments aided by photogrammetry, significantly increasing the antenna efficiency. Through all-sky spectral line pointing observations (SiO masers at 86 GHz and CO at 230 and 345 GHz), we have improved the radio pointing accuracy down to <~ 3" at all 3 frequencies. Due to the pandemic, we are in the process of transitioning GLT commissioning and observing activities to remote operations.
We describe the latest development of the control and monitoring system of the Greenland Telescope (GLT). The GLT is a 12-m radio telescope aiming to carry out the sub-millimeter Very Long Baseline Interferometry (VLBI) observations through the Event Horizon Telescope (EHT) and the Global Millimeter VLBI Array (GMVA), to image the shadows of super massive black holes. The telescope is currently located at the Thule Air Base for commissioning before deployed to the Summit Station. The GLT participated in the VLBI observing campaigns in 2018 and 2019 and fringes were successfully detected at 86 and 230 GHz. Our antenna control software was adapted from the Submillimeter Array (SMA), and as a result for single-dish observations we added new routines to coordinate it with other instruments. We are exploring new communication interfaces; we utilized both in-memory and on-disk databases to be part of the interfaces not only for hardware monitoring but also for engineering event logging. We plan to incorporate the system of the James Clerk Maxwell Telescope for the full Linux-based receiver control. The current progress of integrating our receivers, spectrometers, sub-reflector, and continuum detector into control is presented, together with the implementation of the commissioning software for spectral line pointing. We also describe how we built the anti-collision protection and the recovery mechanism for the sub-reflector hexapod.
A three-cartridge cryogenic receiver system is constructed for the Greenland Telescope Project. The system is equipped with a set of sub-millimeter receivers operating at 86, 230, and 345 GHz, as well as a complete set of instruments for calibration, control and monitoring. It is single pixel instrument built for VLBI observations. With the receiver system, the GLT has completed commissioning of its 12-m sub-millimeter antenna and participated in global very-long-baseline interferometry (VLBI) observations at Thule Air Base (TAB). This paper describes the receiver specification, construction, and verification.
The Greenland Telescope project has recently participated in an experiment to image the supermassive black hole shadow at the center of M87 using Very Long Baseline Interferometry technique in April of 2018. The antenna consists of the 12-m ALMA North American prototype antenna that was modified to support two auxiliary side containers and to withstand an extremely cold environment. The telescope is currently at Thule Air Base in Greenland with the long-term goal to move the telescope over the Greenland ice sheet to Summit Station. The GLT currently has a single cryostat which houses three dual polarization receivers that cover 84-96 GHz, 213-243 GHz and 271-377 GHz bands. A hydrogen maser frequency source in conjunction with high frequency synthesizers are used to generate the local oscillator references for the receivers. The intermediate frequency outputs of each receiver cover 4-8 GHz and are heterodyned to baseband for digitization within a set of ROACH-2 units then formatted for recording onto Mark-6 data recorders. A separate set of ROACH-2 units operating in parallel provides the function of auto-correlation for real-time spectral analysis. Due to the stringent instrumental stability requirements for interferometry a diagnostic test system was incorporated into the design. Tying all of the above equipment together is the fiber optic system designed to operate in a low temperature environment and scalable to accommodate a larger distance between the control module and telescope for Summit Station. A report on the progress of the above electronics instrumentation system will be provided.
The Greenland Telescope completed its construction, so the commissioning phase has been started since December 2017. Single-dish commissioning has started from the optical pointing which produced the first pointing model, followed by the radio pointing and focusing using the Moon for both the 86 GHz and the 230 GHz receivers. After Venus started to rise from the horizon, the focus positions has been improved for both receivers. Once we started the line pointing using the SiO(2-1) maser line and the CO(2-1) line for the 86 GHz and the 230 GHz receivers, respectively, the pointing accuracy also improved, and the final pointing accuracy turned to be around 3" - 5" for both receivers. In parallel, VLBI commissioning has been performed, with checking the frequency accuracy and the phase stability for all the components that would be used for the VLBI observations. After all the checks, we successfully joined the dress rehearsals and actual observations of the 86 GHz and 230 GHz VLBI observations, The first dress rehearsal data between GLT and ALMA were correlated, and successfully detected the first fringe, which confirmed that the GLT commissioning was successfully performed.
The Greenland Telescope Project (GLT) has successfully commissioned its 12-m sub-millimeter. In January 2018, the fringes were detected between the GLT and the Atacama Large Millimeter Array (ALMA) during a very-long-baseline interferometry (VLBI) exercise. In April 2018, the telescope participated in global VLBI science observations at Thule Air Base (TAB). The telescope has been completely rebuilt, with many new components, from the ALMA NA (North America) Prototype antenna and equipped with a new set of sub-millimeter receivers operating at 86, 230, and 345 GHz, as well as a complete set of instruments and VLBI backends. This paper describes our progress and status of the project and its plan for the coming decade.
The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small (~1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (< 10−3 events per star per year) and short in duration (~200 ms), so many stars must be monitored at a high readout cadence in order to detect events. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astronomico Nacional at San Pedro Martir in Baja California, Mexico. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz. Construction of the site began in the fall of 2013, and the survey will begin by the end of 2018. This paper describes the observing system and provides an update on the status of the survey infrastructure.
We describe the control and monitoring system for the Greenland Telescope (GLT). The GLT is a 12-m radio telescope aiming to carry out the sub-millimeter Very Long Baseline Interferometry (VLBI) observations and image the shadow of the super massive black hole in M87. In November 2017 construction has been finished and commissioning activity has been started. In April 2018 we participated in the VLBI observing campaign for the Event Horizon Telescope (EHT) collaboration. In this paper we present the entire GLT control/monitoring system in terms of computers, network and software.
The GMT is an aplanatic Gregorian telescope consisting of 7 primary and secondary mirror segments that must be phased to within a fraction of an imaging wavelength to allow the 25.4 meter telescope to reach its diffraction limit. When operating in Laser Tomographic Adaptive Optics (LTAO) mode, on-axis guide stars will not be available for segment phasing. In this mode, the GMT’s Acquisition, Guiding, and Wavefront Sensing system (AGWS) will deploy four pickoff probes to acquire natural guide stars in a 6-10 arcmin annular FOV for guiding, active optics, and segment phasing. The phasing sensor will be able to measure piston phase differences between the seven primary/secondary pairs of up to 50 microns with an accuracy of 50 nm using a J-band dispersed fringe sensor. To test the dispersed fringe sensor design and validate the performance models, SAO has built and commissioned a prototype phasing sensor on the Magellan Clay 6.5 meter telescope. This prototype uses an aperture mask to overlay 6 GMT-sized segment gap patterns on the Magellan 6.5 meter primary mirror reimaged pupil. The six diffraction patterns created by these subaperture pairs are then imaged with a lenslet array and dispersed with a grism. An on-board phase shifter has the ability to simulate an arbitrary phase shift within subaperture pairs. The prototype operates both on-axis and 6 arcmin off-axis either with AO correction from the Magellan adaptive secondary MagAO system on or off in order to replicate as closely as possible the conditions expected at the GMT.
The Transneptunian Automated Occultation Survey (TAOS II) is a three robotic telescope project to detect the stellar occultation events generated by TransNeptunian Objects (TNOs). TAOS II project aims to monitor about 10000 stars simultaneously at 20Hz to enable statistically significant event rate. The TAOS II camera is designed to cover the 1.7 degrees diameter field of view of the 1.3m telescope with 10 mosaic 4.5k×2k CMOS sensors. The new CMOS sensor (CIS 113) has a back illumination thinned structure and high sensitivity to provide similar performance to that of the back-illumination thinned CCDs. Due to the requirements of high performance and high speed, the development of the new CMOS sensor is still in progress. Before the science arrays are delivered, a prototype camera is developed to help on the commissioning of the robotic telescope system. The prototype camera uses the small format e2v CIS 107 device but with the same dewar and also the similar control electronics as the TAOS II science camera. The sensors, mounted on a single Invar plate, are cooled to the operation temperature of about 200K as the science array by a cryogenic cooler. The Invar plate is connected to the dewar body through a supporting ring with three G10 bipods. The control electronics consists of analog part and a Xilinx FPGA based digital circuit. One FPGA is needed to control and process the signal from a CMOS sensor for 20Hz region of interests (ROI) readout.
The GMT-Consortium Large Earth Finder (G-CLEF) is the very first light instrument of the Giant Magellan Telescope (GMT). The G-CLEF is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. KASI (Korea Astronomy and Space Science Institute) is responsible for Flexure Control Camera (FCC) included in the G-CLEF Front End Assembly (GCFEA). The FCC is a kind of guide camera, which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within the GCFEA. The FCC consists of five optical components: a collimator including triple lenses for producing a pupil, neutral density filters allowing us to use much brighter star as a target or a guide, a tent prism as a focus analyzer for measuring the focus offset at the fiber mirror, a reimaging camera with three pair of lenses for focusing the beam on a CCD focal plane, and a CCD detector for capturing the image on the fiber mirror. In this article, we present the optical and mechanical FCC designs which have been modified after the PDR in April 2015.
Since the ALMA North America Prototype Antenna was awarded to the Smithsonian Astrophysical Observatory (SAO), SAO and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) are working jointly to relocate the antenna to Greenland. This paper shows the status of the antenna retrofit and the work carried out after the recommissioning and subsequent disassembly of the antenna at the VLA has taken place. The next coming months will see the start of the antenna reassembly at Thule Air Base. These activities are expected to last until the fall of 2017 when commissioning should take place. In parallel, design, fabrication and testing of the last components are taking place in Taiwan.
KEYWORDS: Telescopes, Stars, Space telescopes, Signal to noise ratio, Diffraction, Cameras, Scanning probe microscopy, Design for manufacturing, Astronomy, Sensors
The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small (~1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (< 10−3 events per star per year) and short in duration (~200 ms), so many stars must be monitored at a high readout cadence. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astronómico Nacional at San Pedro Mártir in Baja California, México. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz. Construction of the site began in the fall of 2013, and the survey will begin in the summer of 2017.
The Telescopio San Pedro Mártir project intends to construct a 6.5m telescope to be installed at the Observatorio Astronómico Nacional in the Sierra San Pedro Mártir in northern Baja California, Mexico. The project is an association of Mexican institutions, lead by the Instituto Nacional de Astrofísica, Óptica y Electrónica and the Instituto de Astronomía at the Universidad Nacional Autónoma de México, in partnership with the Smithsonian Astrophysical Observatory and the University of Arizona’s Department of Astronomy and Steward Observatory. The project is currently in the planning and design stage. Once completed, the partners plan to operate the MMT and TSPM as a binational astrophysical observatory.
The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph that has been selected as
a first light instrument for the Giant Magellan Telescope (GMT) currently under construction at the Las Campanas
Observatory in Chile’s Atacama desert region. We designed G-CLEF as a general-purpose echelle spectrograph with
precision radial velocity (PRV) capability used for exoplanet detection. The radial velocity (RV) precision goal of GCLEF
is 10 cm/sec, necessary for detection of Earth-sized planets orbiting stars like our Sun in the habitable zone. This
goal imposes challenging stability requirements on the optical mounts and the overall spectrograph support structures.
Stability in instruments of this type is typically affected by changes in temperature, orientation, and air pressure as well
as vibrations caused by telescope tracking. For these reasons, we have chosen to enclose G-CLEF’s spectrograph in a
thermally insulated, vibration isolated vacuum chamber and place it at a gravity invariant location on GMT’s azimuth
platform. Additional design constraints posed by the GMT telescope include: a limited space envelope, a thermal
emission ceiling, and a maximum weight allowance. Other factors, such as manufacturability, serviceability, available
technology and budget are also significant design drivers. All of the previously listed considerations must be managed
while ensuring that performance requirements are achieved.
In this paper, we discuss the design of G-CLEF’s optical mounts and support structures including technical choices made
to minimize the system’s sensitivity to thermal gradients. A more general treatment of the properties of G-CLEF can be
found elsewhere in these proceedings1. We discuss the design of the vacuum chamber which houses the irregularly
shaped optical bench and optics while conforming to a challenging space envelope on GMT’s azimuth platform. We also
discuss the design of G-CLEF’s insulated enclosure and thermal control systems which maintain the spectrograph at
milli-Kelvin level stability while simultaneously limiting the maximum thermal emission into the telescope dome
environment. Finally, we discuss G-CLEF’s front-end assembly and fiber-feed system as well as other interface
challenges presented by the telescope, enclosure and neighboring instrumentation.
The scale and complexity of today’s ground based astronomy projects have justifiably required Principal Investigator’s and their project teams to adopt more disciplined management processes and tools in order to achieve timely and accurate quantification of the progress and relative health of their projects. Earned Value Management (EVM) is one such tool. Developed decades ago and used extensively in the defense and construction industries, and now a requirement of NASA projects greater than $20M; EVM has gained a foothold in ground-based astronomy projects. The intent of this paper is to de-mystify EVM by discussing the fundamentals of project management, explaining how EVM fits with existing principles, and describing key concepts every project can use to implement their own EVM system. This paper also discusses pitfalls to avoid during implementation and obstacles to its success. The authors report on their organization’s most recent experience implementing EVM for the GMT-Consortium Large Earth Finder (G-CLEF) project. G-CLEF is a fiber-fed, optical echelle spectrograph that has been selected as a first light instrument for the Giant Magellan Telescope (GMT), planned for construction at the Las Campanas Observatory in Chile’s Atacama Desert region.
The Transneptunian Automated Occultation Survey (TAOS II) is a three robotic telescope project to detect the stellar
occultation events generated by Trans Neptunian Objects (TNOs). TAOS II project aims to monitor about 10000 stars
simultaneously at 20Hz to enable statistically significant event rate. The TAOS II camera is designed to cover the 1.7
degree diameter field of view (FoV) of the 1.3m telescope with 10 mosaic 4.5kx2k CMOS sensors. The new CMOS
sensor has a back illumination thinned structure and high sensitivity to provide similar performance to that of the backillumination thinned CCDs. The sensor provides two parallel and eight serial decoders so the region of interests can be
addressed and read out separately through different output channels efficiently. The pixel scale is about 0.6"/pix with the
16μm pixels. The sensors, mounted on a single Invar plate, are cooled to the operation temperature of about 200K by a
cryogenic cooler. The Invar plate is connected to the dewar body through a supporting ring with three G10 bipods. The
deformation of the cold plate is less than 10μm to ensure the sensor surface is always within ±40μm of focus range. The
control electronics consists of analog part and a Xilinx FPGA based digital circuit. For each field star, 8×8 pixels box
will be readout. The pixel rate for each channel is about 1Mpix/s and the total pixel rate for each camera is about
80Mpix/s. The FPGA module will calculate the total flux and also the centroid coordinates for every field star in each
exposure.
The GMT-Consortium Large Earth Finder (G-CLEF) is an optical-band echelle spectrograph that has been selected as
the first light instrument for the Giant Magellan Telescope (GMT). G-CLEF is a general-purpose, high dispersion
spectrograph that is fiber fed and capable of extremely precise radial velocity measurements. The G-CLEF Concept
Design (CoD) was selected in Spring 2013. Since then, G-CLEF has undergone science requirements and instrument
requirements reviews and will be the subject of a preliminary design review (PDR) in March 2015. Since CoD review
(CoDR), the overall G-CLEF design has evolved significantly as we have optimized the constituent designs of the major
subsystems, i.e. the fiber system, the telescope interface, the calibration system and the spectrograph itself. These
modifications have been made to enhance G-CLEF’s capability to address frontier science problems, as well as to
respond to the evolution of the GMT itself and developments in the technical landscape. G-CLEF has been designed by
applying rigorous systems engineering methodology to flow Level 1 Scientific Objectives to Level 2 Observational
Requirements and thence to Level 3 and Level 4. The rigorous systems approach applied to G-CLEF establishes a well
defined science requirements framework for the engineering design. By adopting this formalism, we may flexibly update
and analyze the capability of G-CLEF to respond to new scientific discoveries as we move toward first light. G-CLEF
will exploit numerous technological advances and features of the GMT itself to deliver an efficient, high performance instrument, e.g. exploiting the adaptive optics secondary system to increase both throughput and radial velocity
measurement precision.
The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph, which has been selected
as a first light instrument for the Giant Magellan Telescope (GMT) currently under construction at the Las Campanas
Observatory. We designed G-CLEF as a general-purpose echelle spectrograph with a precision radial velocity (PRV)
capability goal of 0.1 m/s, which will enable it to detect/measure the mass of an Earth-sized planet orbiting a Solar-type
star in its habitable zone. This goal imposes challenging requirements on all aspects of the instrument and some of those
are best incorporated directly into the optical design process. In this paper we describe the preliminary optical design of
the G-CLEF instrument and briefly describe some novel solutions we have introduced into the asymmetric white pupil
echelle configuration.
One of the first light instruments for the Giant Magellan Telescope (GMT) will be the GMT-Consortium Large Earth
Finder (G-CLEF). It is an optical band echelle spectrograph that is fiber fed to enable high stability. One of the key
capabilities of G-CLEF will be its extremely precise radial velocity (PRV) measurement capability. The RV precision
goal is 10 cm/sec, which is expected to be achieved with advanced calibration methods and the use of the GMT adaptive
optics system. G-CLEF, as part of the GMT suite of instruments, is being designed within GMT's automated
requirements management system. This includes requirements flow down, traceability, error budgeting, and systems
compliance. Error budgeting is being employed extensively to help manage G-CLEF technical requirements and ensure
that the top level requirements are met efficiently. In this paper we discuss the G-CLEF error budgeting process,
concentrating on the PRV precision and instrument throughput budgets. The PRV error budgeting process is covered in
detail, as we are taking a detailed systems error budgeting approach to the PRV requirement. This has proven
particularly challenging, as the precise measurement of radial velocity is a complex process, with error sources that are
difficult to model and a complex calibration process that is integral to the RV measurement. The PRV budget combines
traditional modeling and analysis techniques, where applicable, with semi-empirical techniques, as necessary.
Extrapolation from existing PRV instruments is also used in the budgeting process.
The latest CCD science detectors have reached a size of 100 mm on its side. For delicate experiments, one needs to minimize or eliminate uncalibratable errors introduced by the instrument. This is especially critical in the case of any mechanical or electronic variations in large detectors caused by an unanticipated thermal behavior of the device, when operated at cryogenic temperatures. G-CLEF (GMT-Consortium Large Earth Finder) is an optical band echelle spectrograph that has been selected as the first light instrument for the Giant Magellan Telescope (GMT). As part of the Preliminary Design, we have developed a Finite Difference Model (FDM) that can predict the temperature profile of the CCD mounting plate. We present the model and the results we have obtained. This model is an important design tool for the optimization of the position for cold straps and heaters, when requirements such as temperature equalization or stability are considered.
The Giant Magellan Telescope active optics system is required to maintain image quality across a 20 arcminute diameter field of view. To do so, it must control the positions of the primary mirror and secondary mirror segments, and the figures of the primary mirror segments. When operating with its adaptive secondary mirror, the figure of the secondary is also controlled. Wavefront and fast-guiding measurements are made using a set of four probes deployed around the field of view. Through a set of simulations we have determined a set of modes that will be used to control fielddependent aberrations without degeneracies.
The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small (~1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (< 10-3 events per star per year) and short in duration (~200 ms), so many stars must be monitored at a high readout cadence. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astronómico Nacional at San Pedro Mártir in Baja California, México. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz. Construction of the site began in the fall of 2013.
The GMT-CfA, Carnegie, Catolica, Chicago Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph
that has undergone conceptual design for consideration as a first light instrument at the Giant Magellan Telescope. GCLEF
has been designed to be a general-purpose echelle spectrograph with precision radial velocity (PRV) capability.
We have defined the performance envelope of G-CLEF to address several of the highest science priorities in the Decadal
Survey1. The spectrograph optical design is an asymmetric, two-arm, white pupil design. The asymmetric white pupil
design is adopted to minimize the size of the refractive camera lenses. The spectrograph beam is nominally 300 mm,
reduced to 200 mm after dispersion by the R4 echelle grating. The peak efficiency of the spectrograph is >35% and the
passband is 3500-9500Å. The spectrograph is primarily fed with three sets of fibers to enable three observing modes:
High-Throughput, Precision-Abundance and PRV. The respective resolving powers of these modes are R~ 25,000,
40,000 and 120,000. We also anticipate having an R~40,000 Multi-object Spectroscopy mode with a multiplex of ~40
fibers. In PRV mode, each of the seven 8.4m GMT primary mirror sub-apertures feeds an individual fiber, which is
scrambled after pupil-slicing. The goal radial velocity precision of G-CLEF is ∂V <10 cm/sec radial. In this paper, we
provide a flowdown from fiducial science programs to design parameters. We discuss the optomechanical, electrical,
structural and thermal design and present a roadmap to first light at the GMT.
NIRMOS (Near-Infrared Multiple Object Spectrograph) is a 0.9 to 2.5 μm imager/spectrograph concept proposed for the
Giant Magellan Telescope1 (GMT). Near-infrared observations will play a central role in the ELT era, allowing us to
trace the birth and evolution of galaxies through the era of peak star formation. NIRMOS' large field of view, 6.5′ by
6.5′, will be unique among imaging spectrographs developed for ELTs. NIRMOS will operate in Las Campanas' superb
natural seeing and is also designed to take advantage of GMT's ground-layer adaptive optics system. We describe
NIRMOS' high-performance optical and mechanical design.
The f/5 instrumentation suite for the Clay telescope was developed to provide the Magellan Consortium observer community with wide field optical imaging and multislit NIR spectroscopy capability. The instrument suite consists of several major subsystems including two focal plane instruments. These instruments are Megacam and MMIRS. Megacam is a panoramic, square format CCD mosaic imager, 0.4° on a side. It is instrumented with a full set of Sloan filters. MMIRS is a multislit NIR spectrograph that operates in Y through K band and has long slit and imaging capability as well. These two instruments can operate both at Magellan and the MMT. Megacam requires a wide field refractive corrector and a Topbox to support shutter and filter selection functions, as well as to perform wavefront sensing for primary mirror figure correction. Both the corrector and Topbox designs were modeled on previous designs for MMT, however features of the Magellan telescope required considerable revision of these designs. In this paper we discuss the optomechanical, electrical, software and structural design of these subsystems, as well as operational considerations that attended delivery of the instrument suite to first light.
The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small ( 1 km diameter) objects in the Solar System and beyond. Such events are very rare (< 10−3 events per star per year) and short in duration ( 200 ms), so many stars must be monitored at a high readout cadence. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astron´omico Nacional at San Pedro Martir in Baja California, Mexico. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz.
Achieving the diffraction limit with the adaptive optics system of the 25m Giant Magellan Telescope will require that
the 7 pairs of mirror segments be in phase. Phasing the GMT is made difficult because of the 30-40cm gaps between the
primary mirror segments. These large gaps result in atmospheric induced phase errors making optical phasing difficult
at visible wavelengths. The large gaps between the borosilicate mirror segments also make an edge sensing system
prone to thermally induced instability. We describe an optical method that uses twelve 1.5-m square subapertures that
span the segment boundaries. The light from each subaperture is mapped onto a MEMS mirror segment and then a
lenslet array which are used to stabilize the atmospherically induced image motion. Centroids for stabilization are
measured at 700nm. The piston error is measured from the fringes visible in each of the 12 stabilized images at 2.2
microns. By dispersing the fringes we can resolve 2π phase ambiguities. We are constructing a prototype camera to be
deployed at the 6.5m Magellan Clay telescope.
The Giant Magellan Telescope adaptive optics system will be an integral part of the telescope, providing laser guide star
generation, wavefront sensing, and wavefront correction to most of the currently envisioned instruments. The system
will provide three observing modes: Natural Guidestar AO (NGSAO), Laser Tomography AO (LTAO), and Ground
Layer AO (GLAO).
Every AO observing mode will use the telescope’s segmented adaptive secondary mirror to deliver a corrected beam
directly to the instruments. High-order wavefront sensing for the NGSAO and LTAO modes is provided by a set of
wavefront sensors replicated for each instrument and fed by visible light reflected off the cryostat window. An infrared
natural guidestar wavefront sensor with open-loop AO correction is also required to sense tip-tilt, focus, segment piston,
and dynamic calibration errors in the LTAO mode. GLAO mode wavefront sensing is provided by laser guidestars over
a ~5 arcminute field of view, and natural guidestars over wider fields. A laser guidestar facility will project 120 W of
589 nm laser light in 6 beacons from the periphery of the primary mirror. An off-axis phasing camera and primary and
secondary mirror metrology systems will ensure that the telescope optics remain phased.
We describe the system requirements, overall architecture, and innovative solutions found to the challenges presented by high-order AO on a segmented extremely large telescope. Further details may be found in specific papers on each of the observing modes and major subsystems.
In 2003, the converted MMT’s wide-field f/5 focus was commissioned. A 1.7-m diameter secondary and a large refractive corrector offer a 1° diameter field of view for spectroscopy and a 0.5° diameter field of view for imaging. Stellar images during excellent seeing are smaller than 0.5" FWHM across the spectroscopic field of view, and smaller than 0.4" across the imaging field of view. Three wide-field f/5 instruments are now in routine operation: Hectospec (an R~1000 optical spectrograph fed by 300 robotically-positioned optical fibers), Hectochelle (an R~40,000 optical spectrograph fed by the same fibers), and Megacam (a 340 megapixel, 36 CCD optical imager covering a 25' by 25' format).
The Smithsonian Astrophysical Observatory uses the HRMA X- ray Detection System (HXDS) to calibrate the High-Resolution Mirror Assembly of the Advanced X-ray Astrophysics Facility AXAF. Apart from two high-purity-germanium solid-state detectors (SSDs) with good energy resolution and very high efficiency at higher energies, the detection system comprises seven flow proportional counters (FPCs) and one microchannel-plate High-Speed Imager. For the lower energy range, the FPCs are more appropriate. They have been calibrated at the radiometry laboratory of the Physikalisch- Technische Bundesandstalt, using the electron storage ring BESSY. For the determination of the absolute quantum efficiency two methods have been applied. First, the detector response was measured in the lower energy range 0.1 keV to 1.7 keV at several discrete energies using monochromatized radiation. The absolute photon flux has been determined by Si n-on-p photodiodes, calibrated against a cryogenic electrical-substitution radiometer used as primary detector source standard BESSY, which can be calculated very accurately. Combining both measurements the determination of the detection efficiency over the entire desired spectral range was possible with a typical relative uncertainty around 1 percent to 2 percent in the central energy range.
We report on the development and evaluation of a redesigned version of the Penning gas discharge source of x-ray and EUV radiation previously described by Finley et al. The most significant new features are the use of stronger permanent magnets and spill-proof quick- disconnect water cooling line fittings. Using aluminum cathodes and Ar discharge gas, and with a 0.5 mm by 5 mm exit aperture on the source, we obtained an absolute flux in the bright Al IV line at 129.73 A of order 5 multiplied by 1011 s-1 sr-1, and of order 5 multiplied by 109 s-1 sr-1 for the Ar I line at 56 A. Detailed spectral analysis of the lines near 56 A is reported. The application of this source to the prelaunch calibration of the AXAF x-ray astronomy observatory is discussed, with emphasis on use of the narrow line at 56 A for calibrating the spectral resolution of the AXAF transmission grating spectrometers.
The alignment and X-ray imaging performance of the Advanced X-ray Astrophysics Facility (AXAF) Verification Engineering Test Article-I(VETA-I) was measured by the VETA-I X-Ray Detection System (VXDS). The VXDS was based on the X-ray detection system utilized in the AXAF Technology Mirror Assembly (TMA) program, upgraded to meet the more stringent requirements of the VETA-I test program. The VXDS includes two types of X-ray detectors: (1) a High Resolution Imager (HRI) which provides X-ray imaging capabilities; and (2) sealed and flow proportional counters which, in conjunction with apertures of various types and precision translation stages, provide the most accurate measurement of VETA-I performance. Herein we give an overview of the VXDS hardware including X-ray detectors, translation stages, apertures, proportional counters and flow counter gas supply system and associated electronics. We also describe the installation of the VXDS into the Marshall Space Flight Central (MSFC) X-Ray Calibration Facility (XRCF). We discuss in detail the design and performance of those elements of the VXDS which have not been discussed elsewhere; translation systems, flow counter gas supply system, apertures and thermal monitoring system.
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