We present the development of a Skipper Charge-Coupled Device (CCD) focal plane prototype for the SOAR Telescope Integral Field Spectrograph (SIFS). This mosaic focal plane consists of four 6k × 1k, 15 μm pixel Skipper CCDs mounted inside a vacuum dewar. We describe the process of packaging the CCDs so that they can be easily tested, transported, and installed in a mosaic focal plane. We characterize the performance of ∼ 650μm thick, fully-depleted engineering-grade Skipper CCDs in preparation for performing similar characterization tests on science-grade Skipper CCDs which will be thinned to 250μm and backside processed with an antireflective coating. We achieve a single-sample readout noise of 4.5 e− rms/pix for the best performing amplifiers and subelectron resolution (photon counting capabilities) with readout noise σ ∼ 0.16 e− rms/pix from 800 measurements of the charge in each pixel. We describe the design and construction of the Skipper CCD focal plane and provide details about the synchronized readout electronics system that will be implemented to simultaneously read 16 amplifiers from the four Skipper CCDs (4-amplifiers per detector). Finally, we outline future plans for laboratory testing, installation, commissioning, and science verification of our Skipper CCD focal plane.
The Southern Astrophysical Research (SOAR) 4.1m telescope, located in Cerro Pachón, Chile, has an active optics system that uses a Shack Hartmann wave front sensor to achieve optimal image correction and focus. This Calibration Wave Front Sensor (CWFS) has two detectors, one to acquire the star and the other to sense the wave front. In 2012 the acquisition camera failed, being replaced temporarily by an SBIG camera. We describe here a project to repair and upgrade the CWFS, extending the lifetime of this critical telescope component. The upgrade includes two new detectors and modifications to the existing software in order to communicate with the new cameras. Also, new mechanical supports were fabricated to mount the new cameras, and a new field flattener was designed for the acquisition camera. A laboratory rig with all the components was setup so to carry out extensive testing before installation on the telescope.
We present a fully-automated CCD testbench. The system performs all the tests in about 12 hours, and when done reduces the data, grading the device and presenting the results in the form of both a pdf report and web-based tables . All the data goes automatically to a database where both the raw and processed data can be visualized and compared with other devices, allowing for detector statistical graphs (number of devices over certain threshold in any given parameter, etc). The testbench was developed in the context of a FermiLab and CTIO collaboration for the packaging and characterization of the red and NIR science ccds for the Dark Energy Spectroscopic Instrument (DESI), where over 40 devices were tested. The system was further expanded at CTIO to be used with any ccd or detector controller. The characterization includes non-linearity (high and low), full well, flats and darks cosmetics (hot and dark pixels, bad columns,etc), dark current, noise, CTE, absolute QE and lateral diffusion.
Cerro Tololo Interamerican Observatory (CTIO) and the Southern Astrophysical Research Telescope (SOAR) are home to several telescopes, ranging from 4.2 to 0.9 meters in diameter. Every telescope has one or more working instruments, which are used every night of the year; keeping this vast amount of instruments (which includes a very big multi-ccd focal plane as well as visible and near infrared imagers and spectrographs) functioning in a way that ensures an appropriate science quality on each one of them is not a minor challenge. In order to help with this task we have developed an observatory-wide Detector and Instrument Quality Control system, which consist on a set of centralized tools: real time telemetry for all the instruments, automatic detector quality performance assessment, electronic logbooks, instrument software logging, image visualization, etc. All the data goes to databases and is available via web browsers.
We describe the design and implementation of a fourth version of the TripleSpec near-infrared spectrograph (TSpec4). This version of the instrument was designed for and first implemented on the 4-m Blanco telescope on Cerro Tololo, and subsequently converted for use on the 4-m Southern Astrophysical Research (SOAR) Telescope on Cerro Pachon. Details of the changed opto-mechanical design and mounting arrangements are discussed. An updated data pipeline provides reduced spectra from the instrument. We describe the required modifications and the performance of both implementations of TSpec4.
The move from the Blanco to SOAR required changing from operation at a classical Cassegrain f/8 focus to operation at a Nasmyth f/16 focus. The SOAR mount also employs a rotator and required accommodation to a significantly different back-focal distance inside the instrument. These changes were implemented by modifying the instrument fore-optics which feeds light onto the slit at f/10.6. The spectrograph and slit viewer optics are unchanged. A dichroic reflects infrared light toward the instrument while passing visible light to a SOAR facility guider; this removes the shortest wavelengths from the spectra and in turn required modification of the data reduction pipeline.
As the telescopes have similar apertures, the performance of the instrument is similar on both, though on SOAR image quality is somewhat better and details of the instrument’s optical properties differ also. Flexure performance differs as well due to the different instrument locations.
In recent years the V. M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory (CTIO) has been renovated for use as a platform for a completely new suite of instruments: DECam, a 520-megapixel optical imager, COSMOS, a multi-object optical imaging spectrograph, and ARCoIRIS, a near-infrared imaging spectrograph. This has had considerable impact, both internally to CTIO and for its wider community of observers. In this paper, we report on the performance of the renovated facility, ongoing improvements, lessons learned during the deployment of the new instruments, how practical operations have adapted to them, unexpected phenomena and subsequent responses. We conclude by discussing the role for the Blanco telescope in the era of LSST and the new generation of extremely large telescopes.
TripleSpec 4 (TS4) is a near-infrared (0.8um to 2.45um) moderate resolution (R ~ 3200) cross-dispersed spectrograph
for the 4m Blanco Telescope that simultaneously measures the Y, J, H and K bands for objects reimaged
within its slit. TS4 is being built by Cornell University and NOAO with scheduled commissioning in 2015.
TS4 is a near replica of the previous TripleSpec designs for Apache Point Observatory's ARC 3.5m, Palomar
5m and Keck 10m telescopes, but includes adjustments and improvements to the slit, fore-optics, coatings and
the detector. We discuss the changes to the TripleSpec design as well as the fabrication status and expected
sensitivity of TS4.
The Dark Energy Camera (DECam) is a new 520 Mega Pixel CCD camera with a 3 square degree field of view built for
the Dark Energy Survey (DES). DECam is mounted at the prime focus of the Blanco 4-m telescope at the Cerro-Tololo
International Observatory (CTIO). DES is a 5-year, high precision, multi-bandpass, photometric survey of 5000 square
degrees of the southern sky that started August 2013. In this paper we briefly review SISPI, the data acquisition and
control system of the Dark Energy Camera and follow with a discussion of our experience with the system and the
lessons learned after one year of survey operations.
KEYWORDS: Sensors, Telescopes, Near infrared, Control systems, Observatories, Astronomy, Signal detection, Interference (communication), Stars, Spectrographs
ARNICA and LonGSp are two NICMOS based near infrared instruments developed in the 90's by the Astrophysical Observatory of Arcetri. After more than 10 years from decommissioning we refurbished the two instruments
with a new read-out electronics and control software. We present the performances of the refurbished systems
and compare them with the historic behavior. Both instruments are currently used for testing purposes in the
Lab and at the telescope, we present some example applications.
The Dark Energy Camera (DECam) is a new 520 Mega Pixel CCD camera with a 3 square degree field of view designed
for the Dark Energy Survey (DES). DES is a high precision, multi-bandpass, photometric survey of 5000 square degrees
of the southern sky. DECam is currently being installed at the prime focus of the Blanco 4-m telescope at the Cerro-
Tololo International Observatory (CTIO). In this paper we describe SISPI, the data acquisition and control system of the
Dark Energy Camera. SISPI is implemented as a distributed multi-processor system with a software architecture based
on the Client-Server and Publish-Subscribe design patterns. The underlying message passing protocol is based on
PYRO, a powerful distributed object technology system written entirely in Python. A distributed shared variable system
was added to support exchange of telemetry data and other information between different components of the system. We
discuss the SISPI infrastructure software, the image pipeline, the observer console and user interface architecture, image
quality monitoring, the instrument control system, and the observation strategy tool.
The Dark Energy Survey Collaboration has completed construction of the Dark Energy Camera (DECam), a 3 square
degree, 570 Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be
used to perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the
remainder of the time, and after the survey, DECam will be available as a community instrument. All components of
DECam have been shipped to Chile and post-shipping checkout finished in Jan. 2012. Installation is in progress. A
summary of lessons learned and an update of the performance of DECam and the status of the DECam installation and
commissioning will be presented.
The Dark Energy Survey Camera (DECam) will be comprised of a mosaic of 74 charge-coupled devices (CCDs). The
Dark Energy Survey (DES) science goals set stringent technical requirements for the CCDs. The CCDs are provided by
LBNL with valuable cold probe data at 233 K, providing an indication of which CCDs are more likely to pass. After
comprehensive testing at 173 K, about half of these qualify as science grade. Testing this large number of CCDs to
determine which best meet the DES requirements is a very time-consuming task. We have developed a multistage
testing program to automatically collect and analyze CCD test data. The test results are reviewed to select those CCDs
that best meet the technical specifications for charge transfer efficiency, linearity, full well capacity, quantum efficiency,
noise, dark current, cross talk, diffusion, and cosmetics.
The Dark Energy Camera is a new prime-focus instrument to be delivered to the Blanco 4-meter telescope at the Cerro
Tololo Inter-American Observatory (CTIO) in 2011. Construction is in-progress at this time at Fermilab. In order to
verify that the camera meets technical specifications for the Dark Energy Survey and to reduce the time required to
commission the instrument while it is on the telescope, we are constructing a "Telescope Simulator" and performing full
system testing prior to shipping to CTIO. This presentation will describe the Telescope Simulator and how we use it to
verify some of the technical specifications.
K. Honscheid, J. Eiting, A. Elliott, J. Annis, M. Bonati, E. Buckley-Geer, F. Castander, L. da Costa, M. Haney, W. Hanlon, I. Karliner, K. Kuehn, S. Kuhlmann, S. Marshall, M. Meyer, E. Neilsen, R. Ogando, A. Roodman, T. Schalk, G. Schumacher, M. Selen, S. Serrano, J. Thaler, W. Wester
In this paper we describe the data acquisition and control system of the Dark Energy Camera (DECam),
which will be the primary instrument used in the Dark Energy Survey (DES). DES is a high precision multibandpath
wide area survey of 5000 square degrees of the southern sky. DECam currently under construction
at Fermilab will be a 3 square degree mosaic camera mounted at the prime focus of the Blanco 4m telescope
at the Cerro-Tololo International Observatory (CTIO). The DECam data acquisition system (SISPI) is
implemented as a distributed multi-processor system with a software architecture built on the Client-Server
and Publish-Subscribe design patterns. The underlying message passing protocol is based on PYRO, a
powerful distributed object technology system written entirely in Python. A distributed shared variable
system was added to support exchange of telemetry data and other information between different components
of the system. In this paper we discuss the SISPI infrastructure software, the image pipeline, the observer
interface and quality monitoring system, and the instrument control system.
Jacob Eiting, Ann Elliott, Klaus Honscheid, Jim Annis, Elizabeth Buckley-Geer, William Wester, Michael Haney, William Hanlon, Inga Karliner, Jon Thaler, Mark Meyer, Marco Bonati, German Schumacher, Kyler Kuehn, Stephen Kuhlmann, Terry Schalk, Stuart Marshall, Aaron Roodman
The Dark Energy Survey (DES) is a 5000 square degree survey of the southern galactic cap set to take place
on the Blanco 4-m telescope at Cerra Tololo Inter-American Observatory. A new 500 MP camera and control
system are being developed for this survey. To facilitate the data acquisition and control, a new user interface
is being designed that utilizes the massive improvements in web based technologies in the past year. The work
being done on DES shows that these new technologies provide the functionality and performance required to
provide a productive and enjoyable user experience in the browser.
The Dark Energy Camera is an wide field imager currently
under construction for the Dark Energy Survey.
This instrument will use fully depleted 250 μm thick
CCD detectors selected for their higher quantum efficiency
in the near infrared with respect to thinner devices.
The detectors were developed by LBNL using
high resistivity Si substrate. The full set of scientific
detectors needed for DECam has now been fabricated,
packaged and tested. We present here the results of
the testing and characterization for these devices and
compare these results with the technical requirements
for the Dark Energy Survey.
The Dark Energy Survey Collaboration is building the Dark Energy Camera (DECam), a 3 square degree, 520
Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be used to
perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the
remainder of the time, and after the survey, DECam will be available as a community instrument. Construction of
DECam is well underway. Integration and testing of the major system components has already begun at Fermilab and
the collaborating institutions.
KEYWORDS: Calibration, Galactic astronomy, Superposition, Mercury cadmium telluride, Photodiodes, Diodes, Signal to noise ratio, Sensors, Signal detection, Point spread functions
Image persistence can produce systematic errors, which remain significant in some applications even when buried in
noise. Ideally the image persistence amplitude, linearity and decay over time could be calibrated independently for each
pixel to levels well below the noise floor, however averaging multiple measurements to characterize persistence to this
accuracy is impractical due to the long time scales for the decay and the need to emulate the exposure and readout timing
of the observations to be calibrated. We examine a compromise where the initial persistence response is characterized
independently for each pixel but the latter parts of the decay are assumed to follow the mean decay curve. When
averaged spatially, persistence increases monotonically with stimulus amplitude until the photodiodes approach forward
bias. For several Teledyne 1.7 μm cutoff HgCdTe detectors tested, persistence is linear over most of the normal signal
range. We characterize the temporal response, and examine the dependence of charge emission time constants on total
stimulus duration. We describe the suppression of persistence by signal in the current frame and begin to examine the
superposition of the decay curves from multiple stimuli.
Image persistence can produce systematic errors, which remain significant in some applications even when buried in
noise. Ideally the image persistence amplitude, linearity and decay over time could be calibrated independently for each
pixel to levels well below the noise floor, however averaging multiple measurements to characterize persistence to this
accuracy is impractical due to the long time scales for the decay and the need to emulate the exposure and readout timing
of the observations to be calibrated. We examine a compromise where the initial persistence response is characterized
independently for each pixel but the latter parts of the decay are assumed to follow the mean decay curve. When
averaged spatially, persistence increases monotonically with stimulus amplitude until the photodiodes approach forward
bias. For several Teledyne 1.7 μm cutoff HgCdTe detectors tested, persistence is linear over most of the normal signal
range. We characterize the temporal response, and examine the dependence of charge emission time constants on total
stimulus duration. We describe the suppression of persistence by signal in the current frame and begin to examine the
superposition of the decay curves from multiple stimuli.
We report the performance of Triplespec from commissioning observations on the 200-inch Hale Telescope
at Palomar Observatory. Triplespec is one of a set of three near-infrared, cross-dispersed spectrographs
covering wavelengths from 1 - 2.4 microns simultaneously at a resolution of ~2700. At Palomar, Triplespec
uses a 1×30 arcsecond slit. Triplespec will be used for a variety of scientific observations, including
moderate to high redshift galaxies, star formation, and low mass stars and brown dwarfs. When used in
conjunction with an externally dispersed interferometer, Triplespec will also detect and characterize
extrasolar planets.
We compare a more complete characterization of the low temperature performance of a nominal 1.7um cut-off
wavelength 1kx1k InGaAs (lattice-matched to an InP substrate) photodiode array against similar, 2kx2k HgCdTe
imagers to assess the suitability of InGaAs FPA technology for scientific imaging applications. The data we present
indicate that the low temperature performance of existing InGaAs detector technology is well behaved and comparable
to those obtained for state-of-the-art HgCdTe imagers for many space astronomical applications. We also discuss key
differences observed between imagers in the two material systems.
We present the results of a detailed study of the noise performance of candidate NIR detectors for the proposed Super-Nova Acceleration Probe. Effects of Fowler sampling depth and frequency, temperature, exposure time, detector material, detector reverse-bias and multiplexer type are quantified. We discuss several tools for determining which sources of low frequency noise are primarily responsible for the sub-optimal noise improvement when multiple sampling, and the selection of optimum fowler sampling depth. The effectiveness of reference pixel subtraction to mitigate zero point drifts is demonstrated, and the circumstances under which reference pixel subtraction should or should not be applied are examined. Spatial and temporal noise measurements are compared, and a simple method for quantifying the effect of hot pixels and RTS noise on spatial noise is described.
We present the results of a study of the performance of InGaAs detectors conducted for the SuperNova Acceleration
Probe (SNAP) dark energy mission concept. Low temperature data from a nominal 1.7um cut-off wavelength 1kx1k
InGaAs photodiode array, hybridized to a Rockwell H1RG multiplexer suggest that InGaAs detector performance is
comparable to those of existing 1.7um cut-off HgCdTe arrays. Advances in 1.7um HgCdTe dark current and noise
initiated by the SNAP detector research and development program makes it the baseline detector technology for SNAP.
However, the results presented herein suggest that existing InGaAs technology is a suitable alternative for other future
astronomy applications.
We briefly describe the SOAR Optical Imager (SOI), the first light instrument for the 4.1m SOuthern Astronomical Research (SOAR) telescope now being commissioned on Cerro Pachón in the mountains of northern Chile. The SOI has a mini-mosaic of 2 2kx4k CCDs at its focal plane, a focal reducer camera, two filter cartridges, and a linear ADC. The instrument was designed to produce precision photometry and to fully exploit the expected superb image quality of the SOAR telescope over a 5.5x5.5 arcmin2 field with high throughput down to the atmospheric cut-off, and close reproduction of photometric pass-bands throughout 310-1050 nm. During early engineering runs in April 2004, we used the SOI to take images as part of the test program for the actively controlled primary mirror of the SOAR telescope, one of which we show in this paper. Taken just three months after the arrival of the optics in Chile, we show that the stellar images have the same diameter of 0.74" as the simultaneously measured seeing disk at the time of observation. We call our image "Engineering 1st Light" and in the near future expect to be able to produce images with diameters down to 0.3" in the R band over a 5.5' field during about 20% of the observing time, using the tip-tilt adaptive corrector we are implementing.
A user-friendly and automatic illuminator with adjustable wavelength and optical power has been developed to obtain precision quantum efficiency (QE) curves of astronomical CCD as well as optical transmission measurements for cryogenic holographic gratings and other optical components. Integrating commercial components with custom mechanical parts and control software, this equipment is able to illuminate a target with light of controlled intensity and wavelength. This facility is primarily intended for testing of Volume Phase Holographic (VPH) gratings at low temperature as well as obtaining CCD quantum efficiencies. A Labview control application runs on a desktop computer allowing full automation of the spectrophotometer. The apparatus includes a Quartz-Tungsten light source, neutral density filters, a monochromator, visible and near-infrared power meters, as well as collimating and focusing optics. Rotation mechanisms allow the characterization of gratings for all angles of diffractions. For CCD testing, network commands allow the facility to get raw images, compute and record QE curves for further detector characterization.
Careful measurements for an engineering grade 2K2 2.5μm cut-off VIRGO detector in a sealed, cold enclosure have yielded dark current twenty five times less than previously reported for these devices, putting Raytheon detectors in contention for low background applications. Global reset followed by Sample Up the Ramp readout was used to allow zero point drifts at the exposure start to be separated from true dark current and mux glow. In a sub-array selected to be far from two photo-emitting defects, mean dark current stabilized 10 hours after power-on, at 0.025 e-/s/pix at 79K (-0.1K, +0.8K). Dark current showed no evidence of the onset of a floor in the 79-104K range, but the temperature dependence was softer than expected, implying a band gap that is 20% below nominal. Shot noise from the dark current will not dominate the 18 e- read noise, unless a substantial noise reduction is achieved through multiple sampling. Hundreds of non-destructive samples will be possible without impact from multiplexor glow, which contributes only 0.04e-/pix/read for a 6μs pixel. Reset Anomaly is dependent on exposure time, settling to -60e- for long exposures, and dominating dark current in exposures less than 2400s. Reference pixels do compensate for these effects, but imperfectly, requiring further study. Attempts to explain Reset Anomaly in terms of self heating were inconclusive.
The SOAR Optical Imager (SOI) is the commissioning instrument for the 4.2-m SOAR telescope, which is sited on Cerro Pachón, and due for first light in April 2003. It is being built at Cerro Tololo Inter-American Observatory, and is one of a suite of first-light instruments being provided by the four SOAR partners (NOAO, Brazil, University of North Carolina, Michigan State University). The instrument is designed to produce precision photometry and to fully exploit the expected superb image quality of the SOAR telescope, over a 6x6 arcmin field. Design goals include maintaining high throughput down to the atmospheric cut-off, and close reproduction of photometric passbands throughout 310-1050nm. The focal plane consists of a two-CCD mosaic of 2Kx4K Lincoln Labs CCDs, following an atmospheric dispersion corrector, focal reducer, and tip-tilt sensor. Control and data handling are within the LabVIEW-Linux environment used throughout the SOAR Project.
The new operations model for the CTIO Blanco 4-m telescope will use a small suite of fixed facility instruments for imaging and spectroscopy. The Infrared Side Port Imager, ISPI, provides the infrared imaging capability. We describe the optical, mechanical, electronic, and software components of the instrument. The optical design is a refractive camera-collimator system. The cryo-mechanical packaging integrates two LN2-cooled dewars into a compact, straightline unit to fit within space constraints at the bent Cassegrain telescope focus. A HAWAII 2 2048 x 2048 HgCdTe array is operated by an SDSU II array controller. Instrument control is implemented with ArcVIEW, a proprietary LabVIEW-based software package. First light on the telescope is planned for September 2002.
To meet the needs of the SOAR 4.2-m telescope first-generation instrument suite, as well as new instruments for the Blanco 4-m telescope, we developed a new camera controller system called ArcVIEW. In order to provide a strong foundation and rapid development cycle, we decided to build the system using National Instrument's LabVIEW environment. The advantages of this approach centers on the tools available for rapid prototyping, integration and testing of components.
Over the past 2 years, we have taken ArcVIEW from a design document to the point of controlling two new instruments being built at CTIO. The IR imager, ISPI, will complete final testing this semester and go into use on the Blanco telescope in September 2002.
The second instrument, the SOAR Optical Imager, is due for completion this semester and will be the commissioning instrument for the SOAR telescope, for which first light is expected in early 2003.
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