We describe the distributed control system that we are developing for the Wideband frontend receiver system for Submillimeter Array (wSMA). This distributed control system is based on an array of Raspberry-Pi (RPi) modules, which is embedded in each subsystem. The RPis run the Linux operating system and they are integrated with Input/Output (I/O) circuits which carry out the control and monitoring functions. The distributed architecture gives rise to a low-cost and yet versatile and powerful setup, which can be built up gradually by adding subsystems, one at a time. In this paper, we will present, in more details, two RPi-controlled subsystems: the Local oscillator (LO) module and the scanning spectrometer.
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.
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.
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.
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 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 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 (GLT) is a 12m diameter antenna that is being developed from the ALMA North America prototype antenna, for VLBI observations and single-dish science approaching THz, at the Summit station in Greenland. The GLT is a collaboration between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics. We describe the control and monitoring software that is being developed for GLT. The present version of the software is ready for the initial tests of the antenna at Thule, including optical and radio pointing calibration, holography, and VLBI observations at 230 GHz.
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.
The Greenland Telescope project will deploy and operate a 12m sub-millimeter telescope at the highest point of the Greenland i e sheet. The Greenland Telescope project is a joint venture between the Smithsonian As- trophysical Observatory (SAO) and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA). In this paper we discuss the concepts, specifications, and science goals of the instruments being developed for single-dish observations with the Greenland Telescope, and the coupling optics required to couple both them and the mm-VLBI receivers to antenna. The project will outfit the ALMA North America prototype antenna for Arctic operations and deploy it to Summit Station,1 a NSF operated Arctic station at 3,100m above MSL on the Greenland I e Sheet. This site is exceptionally dry, and promises to be an excellent site for sub-millimeter astronomical observations. The main science goal of the Greenland Telescope is to carry out millimeter VLBI observations alongside other telescopes in Europe and the Americas, with the aim of resolving the event horizon of the super-massive black hole at the enter of M87. The Greenland Telescope will also be outfitted for single-dish observations from the millimeter-wave to Tera-hertz bands. In this paper we will discuss the proposed instruments that are currently in development for the Greenland Telescope - 350 GHz and 650 GHz heterodyne array receivers; 1.4 THz HEB array receivers and a W-band bolometric spectrometer. SAO is leading the development of two heterodyne array instruments for the Greenland Telescope, a 48- pixel, 325-375 GHz SIS array receiver, and a 4 pixel, 1.4 THz HEB array receiver. A key science goal for these instruments is the mapping of ortho and para H2D+ in old protostellar ores, as well as general mapping of CO and other transitions in molecular louds. An 8-pixel prototype module for the 350 GHz array is currently being built for laboratory and operational testing on the Greenland Telescope. Arizona State University are developing a 650 GHz 256 pixel SIS array receiver based on the KAPPa SIS mixer array technology and ASIAA are developing 1.4 THz HEB single pixel and array receivers. The University of Cambridge and SAO are collaborating on the development of the CAMbridge Emission Line Surveyor (CAMELS), a W-band `on- hip' spectrometer instrument with a spectral resolution of R ~ 3000. CAMELS will consist of two pairs of horn antennas, feeding super conducting niobium nitride filter banks read by tantalum based Kinetic Inductance Detectors.
The ALMA North America Prototype Antenna was awarded to the Smithsonian Astrophysical Observatory (SAO) in 2011. SAO and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), SAO’s main partner for this project, are working jointly to relocate the antenna to Greenland to carry out millimeter and submillimeter VLBI observations. This paper presents the work carried out on upgrading the antenna to enable operation in the Arctic climate by the GLT Team to make this challenging project possible, with an emphasis on the unexpected telescope components that had to be either redesigned or changed. Five-years of inactivity, with the antenna laying idle in the desert of New Mexico, coupled with the extreme weather conditions of the selected site in Greenland have it necessary to significantly refurbish the antenna. We found that many components did need to be replaced, such as the antenna support cone, the azimuth bearing, the carbon fiber quadrupod, the hexapod, the HVAC, the tiltmeters, the antenna electronic enclosures housing servo and other drive components, and the cables. We selected Vertex, the original antenna manufacturer, for the main design work, which is in progress. The next coming months will see the major antenna components and subsystems shipped to a site of the US East Coast for test-fitting the major antenna components, which have been retrofitted. The following step will be to ship the components to Greenland to carry out VLBI
The Submillimeter Array (SMA) is an 8-element interferometer which operates in the 180-700 GHz range located
atop Mauna Kea in Hawaii. It is a collaborative project between the Smithsonian Astrophysical Observatory
(SAO) and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) and is funded by the Smithsonian
Institution and the Academia Sinica. The University of Hawaii (UH) receives a fixed percentage of all
time on the telescopes of Mauna Kea. As such, the observing time at the SMA is shared among these partners
at the SAO:ASIAA:UH levels of 72:15:13. The nature of interferometric observing makes keeping track of these
partner shares challenging. Since a typical successful interferometric observation could last anywhere from 3-10
hours for it to have sufficient uv-coverage, it does not necessarily make sense to divide the observing time up
simply by counting hours. In this talk I will summarize the strategy devised at the SMA for keeping track of
partner time shares as well as the tools used to make these numbers transparent to all affiliations.
We report the measurement results and compensation of the antenna elevation angle dependences of the Submillimeter
Array (SMA) antenna characteristics. Without optimizing the subreflector (focus) positions as a
function of the antenna elevation angle, antenna beam patterns show lopsided sidelobes, and antenna efficiencies
show degradations. The sidelobe level increases and the antenna efficiencies decrease about 1% and a few %,
respectively, for every 10° change in the elevation angle at the measured frequency of 237 GHz. We therefore
obtained the optimized subreflector positions for X (azimuth), Y (elevation), and Z (radio optics) focus axes at
various elevation angles for all the eight SMA antennas. The X axis position does not depend on the elevation
angle. The Y and Z axes positions depend on the elevation angles, and are well fitted with a simple function for
each axis with including a gravity term (cosine and sine of elevation, respectively). In the optimized subreflector
positions, the antenna beam patterns show low level symmetric sidelobe of at most a few%, and the antenna
efficiencies stay constant at any antenna elevation angles. Using one set of fitted functions for all antennas,
the SMA is now operating with real-time focusing, and showing constant antenna characteristics at any given
APEX, the Atacama Pathfinder Experiment, has been successfully commissioned and is in operation now. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the world's outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of 17-18 μm makes APEX suitable for observations up to 200 μm, through all atmospheric submm windows accessible from the ground.
The holography program to measure and set the surfaces of the antennas of the Submillmeter Array (SMA) has been very successful, with the best antenna meeting the stringent 12 μm rms specification. The surfaces of the 6-meter diameter antennas
of the 8 element array have been set to accuracies of 12-25 μm, and are under constant improvement. This allows efficient operation in the 660 GHz band, currently the highest frequency band of observations. The system used to make routine near-field holographic measurements at 232.4 GHz -- the primary method of obtaining surface error maps -- is now fully integrated into the SMA. The measurements are carried out remotely from Cambridge. A sequence of upto 4 rounds of measurements and adjustments is needed to achieve the design specification of 12 μm rms starting typically from 65 μm rms. The last sets of adjustments incorporate corrections for panel flexures, allowed by the 4 points of adjustment for most of the panels, and the high spatial resolution (~ 8 cm) of the surface error maps. Repeat measurements indicate a surface stability time scale of ~ 1 year including antenna transport between stations. Celestial holography to characterize gravitational deformations and careful efficiency measurements to validate the holographic measurements are in progress.
The Submillimeter Array (SMA) is a new radio interferometer consisting
of 8 antennas of 6 meters diameter each, recently deployed in operation at the summit of Mauna Kea in Hawaii. The antennas currently operate at 230, 345 and 690 GHz bands and have high enough surface accuracy to allow operations at 890 GHz. At the highest frequencies, the FWHM primary beam size of each antenna will be about 12" which imposes a stringent requirement for single-dish pointing accuracy of 1". We summarize the current status of pointing of the SMA antennas and the methods we have implemented to derive the pointing model parameters. We discuss the stability of the pointing models over time scales of several weeks. The difference between the radio and optical pointing offsets is a function of elevation only, and can be calibrated by observing a common source or a pair of neighboring sources. We present results of such a calibration and its
application to improve the radio pointing performance during submillimeter observations.
We present the current status of the antenna control software for the Submillimeter array. This software is responsible for pointing and tracking astronomical sources and four antenna pointing calibration. We describe the various stages of the calculations, starting with source- lookup from catalogs and resulting in antenna coordinates commanded to the servo computers. We also present some preliminary results on the pointing calibration of the antenna mounts using an optical guide-scope.