H. T. Diehl, E. Neilsen, R. Gruendl, T. M. Abbott, S. Allam, O. Alvarez, J. Annis, E. Balbinot, S. Bhargava, K. Bechtol, G. Bernstein, R. Bhatawdekar, S. Bocquet, D. Brout, R. Capasso, R. Cawthon, C. Chang, E. Cook, C. Conselice, J. Cruz, C. D'Andrea, L. da Costa, R. Das, D. DePoy, A. Drlica-Wagner, A. Elliott, S. Everett, J. Frieman, A. Fausti Neto, A. Ferté, I. Friswell, K. Furnell, L. Gelman, D. Gerdes, M. S. Gill, D. Goldstein, D. Gruen, D. Gulledge, S. Hamilton, D. Hollowood, K. Honscheid, D. James, M. Johnson, M. W. Johnson, S. Kent, R. Kessler, G. Khullar, E. Kovacs, A. Kremin, R. Kron, N. Kuropatkin, J. Lasker, A. Lathrop, T. Li, M. Manera, M. March, J. Marshall, M. Medford, F. Menanteau, I. Mohammed, M. Monroy, B. Moraes, E. Morganson, J. Muir, M. Murphy, B. Nord, A. Pace, A. Palmese, Y. Park, F. Paz-Chinchón, M. E. Pereira, D. Petravick, A. Plazas, J. Poh, T. Prochaska, A. Romer, K. Reil, A. Roodman, M. Sako, M. Sauseda, D. Scolnic, L. Secco, I. Sevilla-Noarbe, N. Shipp, J. Smith, M Soares-Santos, B. Soergel, A. Stebbins, K. Story, K. Stringer, F. Tarsitano, B. Thomas, D. Tucker, K. Vivas, A. Walker, M.-Y. Wang, C. Weaverdyck, N. Weaverdyck, W. Wester, C. Wethers, R. Wilkenson, H.-Y Wu, B. Yanny, A. Zenteno, Y. Zhang
The Dark Energy Survey (DES) is an operating optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES has completed its third observing season out of a nominal five. This paper describes DES “Year 4” (Y4) and “Year 5” (Y5), the survey strategy, an outline of the survey operations procedures, the efficiency of operations and the causes of lost observing time. It provides details about the quality of these two-season's data, a summary of the overall status, and plans for the final survey season.
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.
H. T. Diehl, E. Neilsen, R. Gruendl, B. Yanny, T. M. Abbott, J. Aleksić, S. Allam, J. Annis, E. Balbinot, M. Baumer, L. Beaufore, K. Bechtol, G. Bernstein, S. Birrer, C. Bonnett, D. Brout, C. Bruderer, E. Buckley-Geer, D. Capozzi, A. Carnero Rosell, F. Castander, R. Cawthon, C. Chang, L. Clerkin, R. Covarrubias, C. Cuhna, C. D'Andrea, L. da Costa, R. Das, C. Davis, J. Dietrich, A. Drlica-Wagner, A. Elliott, T. Eifler, J. Etherington, B. Flaugher, J. Frieman, A. Fausti Neto, M. Fernández, C. Furlanetto, D. Gangkofner, D. Gerdes, D. Goldstein, K. Grabowski, R. Gupta, S. Hamilton, H. Head, J. Helsby, D. Hollowood, K. Honscheid, D. James, M. Johnson, S. Jouvel, T. Kacprzac, S. Kent, R. Kessler, A. Kim, E. Krause, C. Krawiec, A. Kremin, R. Kron, S. Kuhlmann, N. Kuropatkin, O. Lahav, J. Lasker, T. Li, E. Luque, N. Maccrann, M. March, J. Marshall, N. Mondrik, E. Morganson, D. Mudd, A. Nadolski, P. Nugent, P. Melchior, F. Menanteau, D. Nagasawa, B. Nord, R. Ogando, L. Old, A. Palmese, D. Petravick, A. Plazas, A. Pujol, A. Queiroz, K. Reil, A. Romer, R. Rosenfeld, A. Roodman, P. Rooney, M. Sako, A. Salvador, C. Sánchez, E. Sánchez Álvaro, B. Santiago, A. Schooneveld, M. Schubnell, E. Sheldon, A. Smith, R. Smith, M. Soares-Santos, F. Sobreira, M. Soumagnac, H. Spinka, S. Tie, D. Tucker, V. Vikram, K. Vivas, A. Walker, W. Wester, M. Wiesner, H. Wilcox, P. Williams, A. Zenteno, Y. Zhang, Z. Zhang
The Dark Energy Survey (DES) is an operating optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES has completed its third observing season out of a nominal five. This paper describes DES “Year 1” (Y1) to “Year 3” (Y3), the strategy, an outline of the survey operations procedures, the efficiency of operations and the causes of lost observing time. It provides details about the quality of the first three season's data, and describes how we are adjusting the survey strategy in the face of the El Niño Southern Oscillation.
The precise determination of the instrumental response function versus wavelength is a central ingredient in contemporary photometric calibration strategies. This typically entails propagating narrowband illumination through the system pupil, and comparing the detected photon rate across the focal plane to the amount of incident light as measured by a calibrated photodiode. However, stray light effects and reflections/ghosting (especially on the edges of filter passbands) in the optical train constitute a major source of systematic uncertainty when using a at-field screen as the illumination source. A collimated beam projector that projects a mask onto the focal plane of the instrument can distinguish focusing light paths from stray and scattered light, allowing for a precise determination of instrumental throughput. This paper describes the conceptual design of such a system, outlines its merits, and presents results from a prototype system used with the Dark Energy Camera wide field imager on the 4-meter Blanco telescope. A calibration scheme that blends results from at-field images with collimated beam projector data to obtain the equivalent of an illumination correction at high spectral and angular resolution is also presented. In addition to providing a precise system throughput calibration, by monitoring the evolution of the intensity and behaviour of the ghosts in the optical system, the collimated beam projector can be used to track the evolution of the filter transmission properties and various anti-reflective coatings in the optical system.
H. Diehl, T. M. Abbott, J. Annis, R. Armstrong, L. Baruah, A. Bermeo, G. Bernstein, E. Beynon, C. Bruderer, E. Buckley-Geer, H. Campbell, D. Capozzi, M. Carter, R. Casas, L. Clerkin, R. Covarrubias, C. Cuhna, C. D'Andrea, L. da Costa, R. Das, D. DePoy, J. Dietrich, A. Drlica-Wagner, A. Elliott, T. Eifler, J. Estrada, J. Etherington, B. Flaugher, J. Frieman, A. Fausti Neto, M. Gelman, D. Gerdes, D. Gruen, R. Gruendl, J. Hao, H. Head, J. Helsby, K. Hoffman, K. Honscheid, D. James, M. Johnson, T. Kacprzac, J. Katsaros, R. Kennedy, S. Kent, R. Kessler, A. Kim, E. Krause, R. Kron, S. Kuhlmann, A. Kunder, T. Li, H. Lin, N. Maccrann, M. March, J. Marshall, E. Neilsen, P. Nugent, P. Martini, P. Melchior, F. Menanteau, R. Nichol, B. Nord, R. Ogando, L. Old, A. Papadopoulos, K. Patton, D. Petravick, A. Plazas, R. Poulton, A. Pujol, K. Reil, T. Rigby, A. Romer, A. Roodman, P. Rooney, E. Sanchez Alvaro, S. Serrano, E. Sheldon, A. Smith, R. Smith, M. Soares-Santos, M. Soumagnac, H. Spinka, E. Suchyta, D. Tucker, A. Walker, W. Wester, M. Wiesner, H. Wilcox, R. Williams, B. Yanny, Y. Zhang
The Dark Energy Survey (DES) is a next generation optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES started its first observing season on August 31, 2013 and observed for 105 nights through mid-February 2014. This paper describes DES “Year 1” (Y1), the strategy and goals for the first year's data, provides an outline of the operations procedures, lists the efficiency of survey operations and the causes of lost observing time, provides details about the quality of the first year's data, and hints at the “Year 2” plan and outlook.
In an inauspicious start to the ultimately very successful installation of the Dark Energy Camera on the V. M. Blanco 4- m telescope at CTIO, the light-weighted Cer-Vit 1.3-m-diameter secondary mirror suffered an accident in which it fell onto its apex. This punched out a central plug of glass and destroyed the focus and tip/tilt mechanism. However, the mirror proved fully recoverable, without degraded performance. This paper describes the efforts through which the mirror was repaired and the tip/tilt mechanism rebuilt and upgraded. The telescope re-entered full service as a Ritchey- Chrétien platform in October of 2013.
To substantially upgrade the Blanco telescope a new Dark Energy Camera (DECam)5 was developed. The Blanco telescope was commissioned in 1974 before the benefits of modern heavy instruments were foreseen. Consequently, the mass of DECam is greater than the original instrument payload. DECam was installed on the Blanco in 20121, 2. The telescope mount was rebalanced about the declination assembly by redesigning the Cassegrain cage to accommodate a significant increase in balancing mass. Finite element analysis was used to both determine the structural integrity of the new telescope configuration and to predict the effects of this added mass on the relative displacement between the primary and secondary mirrors. The counterweight system is described.
The KPNO Nicholas U. Mayall 4-meter telescope is to be the host facility for the Dark Energy Spectroscopic Instrument (DESI). DESI will record broadband spectra simultaneously for 5000 objects distributed over a 3-degree diameter field of view; it will record the spectra of approximately 20 million galaxies and quasi-stellar objects during a five-year survey. This survey will improve the combined precision of measurement on the dark energy equation of state today (w0) and its evolution with redshift (wa) by approximately a factor of ten over existing spectroscopy baryon acoustic oscillation surveys (e.g., BOSS1) in both co-moving volume surveyed and number of galaxies mapped. Installation of DESI on the telescope is a complex procedure, involving a complete replacement of the telescope top end, routing of massive fiber cables, and installation of banks of spectrographs in an environmentally-controlled lab area within the dome. Furthermore, assembly of the instrument and major subsystems must be carried out on-site given their size and complexity. A detailed installation plan is being developed early in the project in order to ensure that DESI and its subsystems are designed so they can be safely and efficiently installed, and to ensure that all telescope and facility modifications required to enable installation are identified and completed in time.
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.
In preparation for the arrival of the Dark Energy Camera (DECam) at the CTIO Blanco 4-m telescope, both the hardware
and the software of the Telescope Control System (TCS) have been upgraded in order to meet the more stringent
requirements on cadence and tracking required for efficient execution of the Dark Energy Survey1. This upgrade was
also driven by the need to replace obsolete hardware, some of it now over half a century old.
In this paper we describe the architecture of the new mount control system, and in particular the method used to develop
and implement the servo-driver portion of the new TCS. This portion of the system had to be completely rethought,
when an initial approach, based on commercial off the shelf components, lacked the flexibility needed to cope with the
complex behavior of the telescope. Central to our design approach was the early implementation of extensive telemetry,
which allowed us to fully characterize the real dynamics of the telescope. These results then served as input to extensive
simulations of the proposed new servo system allowing us to iteratively refine the control model. This flexibility will be
important later when DECam is installed, since this will significantly increase the moving mass and inertia of the
telescope.
Based on these results, a fully digital solution was chosen and implemented. The core of this new servo hardware is
modern cRIO hardware, which combines an embedded processor with a high-performance FPGA, allowing the
execution of LabVIEW applications in real time.
The DES project is a 5 year imaging survey of the southern sky using the 4m Blanco Telescope at the Cerro Tololo
International Observatory in Chile. A new wide field camera with a 2.2 degree diameter field of view has been built to
undertake this survey. The alignment of the large lenses for this camera poses a significant challenge as they have to be
aligned to a tolerance of ±50 micrometers. This paper presents the assembly and alignment process of the full optical system along with the test results. Also included is the predicted imaging performance from the as-built system.
The Dark Energy Camera (DECam) has been installed on the V. M. Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. This major upgrade to the facility has required numerous modifications to the telescope and improvements in observatory infrastructure. The telescope prime focus assembly has been entirely replaced, and the f/8 secondary change procedure radically changed. The heavier instrument means that telescope balance has been significantly modified. The telescope control system has been upgraded. NOAO has established a data transport system to efficiently move DECam's output to the NCSA for processing. The observatory has integrated the DECam highpressure, two-phase cryogenic cooling system into its operations and converted the Coudé room into an environmentally-controlled instrument handling facility incorporating a high quality cleanroom. New procedures to
ensure the safety of personnel and equipment have been introduced.
KEYWORDS: Telescopes, Cameras, Mirrors, Control systems, Current controlled current source, Content addressable memory, Forward error correction, Actuators, Camera shutters, Chlorine
The Dark Energy Camera (DECam) is a new prime focus, wide-field imager for the V. M. Blanco 4-m telescope at CTIO. Instrumentation includes large, five-lens optical corrector mounted on hexapod mechanism for fine adjustment, filters, and a 519 Megapixel camera vessel; all integrated in a cage similar to the existing telescope prime focus structure. Currently Blanco allows a flip of this structure such that the f/8 secondary mirror, mounted on the back of the cage, points towards the primary mirror for Ritchey-Chretien observations. DECam will maintain this capability by attaching the existing F/8 mirror cell to the front of the new cage. Installation of this 8,600 kg instrument required the removal from the telescope of the primary mirror, the removal of the old prime focus assembly, and fine adjustment of large, over-constrained mechanisms followed by reassembly. A large facility shutdown was scheduled for this upgrade and several tools, fixtures, monitoring systems and procedures were developed in order to identify and then recover the optical alignment of the system, to control the distribution of stresses during tuning of the installation and to maintain the balance of the telescope with significant added mass. The final goal has been to maintain high performance of the telescope for both the existing f/8 Ritchey-Chretien focus mounted instruments and the new DECam instrument now in commissioning. The challenges presented in handling large elements, real-time monitoring, alignment, verification and feedback are described.
The V. M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory is undergoing a number of improvements
in preparation for the delivery of the Dark Energy Camera. The program includes upgrades having potential to deliver
gains in image quality and stability. To this end, we have renovated the support structure of the primary mirror,
incorporating innovations to improve both the radial support performance and the registration of the mirror and telescope
top end. The resulting opto-mechanical condition of the telescope is described. We also describe some improvements to
the environmental control. Upgrades to the telescope control system and measurements of the dome environment are
described in separate papers in this conference.
Between February and April 2009 a number of ultrasonic anemometers, temperature probes and dust sensors were
operated inside the CTIO Blanco telescope dome. These sensors were distributed in a way that temperature and
3 dimensional wind speeds were monitored along the line of sight of the telescope. During telescope operations,
occasional seeing measurements were obtained using the Mosaic CCD imager and the CTIO site monitoring MASS-DIMM
system. In addition, also a Lunar Scintillometer (LuSci) was operated over the course of a few nights inside the
dome. We describe the instrumental setup and first preliminary results on the linkage of the atmospheric conditions
inside the dome to the overall image quality.
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.
As astronomical instruments have increased in complexity, cost and production time, sharing a major instrument
between telescopes has become an attractive alternative to duplication. This requires solving technical and logistical
problems of transportation, transferring operational support knowledge between on-site staffs, and developing effective
responses to in-service problems at a different site. The infrared camera NEWFIRM has been operated for two years on
the 4-m Mayall telescope of Kitt Peak National Observatory in Arizona. We have recently temporarily moved it to the 4-
m Blanco telescope of Cerro Tololo Interamerican Observatory in Chile for a limited period of operation. We describe
here our solutions to the challenges involved in relocating this major in-service cryogenic instrument, with an emphasis
on "lessons learned" to date.
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.
The Blanco 4-meter telescope has been in operation for over 30 years and is now subject to an extensive upgrade of its
control system, both of the hardware and software aspects. The motivation for the upgrade, besides the normal
replacement of obsolete components, is the preparation of the telescope for the installation of the DECAM instrument,
which makes greater operational demands than can't be met by the current system. The architecture of the new system is
in line with the designs proposed for modern telescopes like the Large Synoptic Survey Telescope (LSST), and its
implementation utilizes similar technologies as proposed for that project. In this paper we present a detailed description
of the upgraded system, including tape encoders, control algorithms, the use of trajectories to optimize motions,
communications middleware, and its performance as a whole.
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.
The Dark Energy Survey (DES) will produce high quality images covering over 5000 square degrees of the sky,
with precise photometric redshifts between z = 0.2 to z = 1.3, using g, r, i, z and Y filters. The Dark Energy
Camera (DECam), under construction for this survey, consists of wide field corrector optics and a CCD detector
array that will give a 2.2 square degree field of view. It will be placed at the prime focus of the Blanco 4-meter
telescope at the Cerro Tololo Inter-American Observatory in Chile. The Optical Science Laboratory (OSL) at
University College London (UCL) is undertaking the alignment of the five lenses in the imaging system. These
lenses range in diameter from 0.60 - 0.98 meters. The lenses must be held within tight tolerance limits in order
to meet the DES science requirements. The tolerances are especially driven by the accuracy in the measurement
of the weak lensing signal. This paper details the design for the cells that will hold the lenses and the alignment
procedure for the mounting of the lenses and cells. Also presented is the expected static shear distortion pattern
that will be generated and the impact of this pattern on the weak lensing signal measurement.
K. Honscheid, T. Abbott, J. Annis, E. Buckley-Geer, F. Castander, J. Eiting, M. Gladders, M. Haney, I. Karliner, D. Kau, K. Kuehn, S. Kuhlmann, T. Qian, M. Selen, J. Thaler, D. Tucker, A. Zhao
KEYWORDS: Control systems, Cameras, Telescopes, Databases, Image quality, Data acquisition, Charge-coupled devices, Camera shutters, Image processing, Computing systems
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). DECam will be a 3 sq. deg. 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 the SML inter-process communication software developed at CTIO [1].
For the DECam read-out and control system this software package was ported from LabVIEW to the Python
and C programming languages. A 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
architecture, new concepts used in the design of the infrastructure software and provide an overview of the
remaining components of the DES read-out and control system.
The CTIO V. M. Blanco 4-m telescope is to be the host facility for the Dark Energy Survey (DES), a large area optical
survey intended to measure the dark energy equation of state parameter, w. The survey is expected to use ~30% of the
telescope time over 5 years and use a new 520 megapixel CCD prime focus imaging system: the Dark Energy Camera
(DECam). The Blanco telescope will also be the southern hemisphere platform for NEWFIRM, a large area infrared
imager currently being commissioned at the Mayall Telescope at KPNO. As part of its normal cycle of continuing
upgrades and in preparation for the arrival of these new instruments, the Blanco telescope control system (TCS) will be
upgraded to provide a modern platform for observations and maximize the efficiency of survey operations. The
upgraded TCS will be based on that used at the SOAR telescope and will be a prototype of the TCS to be used by LSST.
It will be optimized for programmed and queued survey observations, will provide extended real-time telemetry of site
and facility characteristics, and will incorporate a distributed observer interface allowing for on- and off-site
observations and real time quality control. Hardware modifications will include the use of absolute tape encoders and a
modern servo control and power driver systems.
The DECam instrument, for the 4m Blanco telescope at CTIO, is a 5 lens element wide field camera giving a 2.2 degree
diameter field of view. The lenses are large, with the biggest being 980mm in diameter, and this poses challenges in
mounting and alignment. This paper reports the status of the production of the optics for the DECam wide field imager
Also presented are the design and finite element modelling of the cell design for the 5 lenses of the imager along with the
proposed alignment process.
We describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey.
DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo
International Observatory (CTIO). DECam includes a large mosaic CCD focal plane, a five element optical corrector,
five filters (g,r,i,z,Y), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of
62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of
view. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley
National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms,
and control system for DECam are underway; delivery of the instrument to CTIO is scheduled for 2010.
We describe a five element corrector for the prime focus of the 4 meter Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile that will be used in conjunction with a new mosaic CCD camera as part of the proposed Dark Energy Survey (DES). The corrector is designed to provide a flat focal plane and good images in the SDSS g, r, i, and z filters. We describe the performance in conjunction with the scientific requirements of the DES, particularly with regard to ghosting and weak-lensing point spread function (PSF) calibration.
A description of the plans and infrastructure developed for CCD testing and characterization for the DES focal plane detectors is presented. Examples of the results obtained are shown and discussed in the context of the device requirements for the survey instrument.
The CTIO V. M. Blanco 4-m telescope is to be the host facility for the Dark Energy Survey (DES), a large area optical
survey intended to measure the dark energy equation of state parameter, w, to a precision of ˜ 5%. The survey is
expected to take 5 years and use a new 520 megapixel CCD prime focus imaging system: the Dark Energy Camera
(DECam). In preparation for the arrival of DECam, we plan numerous upgrades to the telescope, including a new
telescope control system optimized for programmed and queued survey observations, modifications to the telescope
itself to improve reliability and performance, extended real-time telemetry of site and facility characteristics, and a
distributed observer interface allowing for on- and off-site observations and real time quality control. These upgrades
are specifically motivated by the scientific goals of the DES but will also improve community use of the telescope.
We describe the Nordic Optical Telescope's facility short- wavelength IR instrument, NOTCam. The instrument will be capable of wide-field and high-resolution imaging, long-slit and multi-object grism spectroscopy, coronography, and imaging-and spectro-polarimetry. First light will be in mid- 2000. Current progress is summarized and some problems we have encountered and overcome are discussed.
A telescope autoguider constructed of unmodified commercially available components for use with the 2.1-m focal reducer at McDonald Observatory is described. The system comprises a thermoelectrically cooled CCD camera with format 384 x 576 pixels, pixel size 23 microns square, readout noise 25 electrons/pixel, and dark current 10 electrons/sec pixel at -35 C; a 50-mm camera lens giving resolution about 1 arcsec/pixel; an IEEE-488 data bus; a MicroVAX 3200 computer workstation; and a serial-to-parallel converter permitting the computer to address the telescope drive system via four trail-rate controls. Also discussed are the top-down C-language programming approach, the data representation, the autoguiding and search algorithms, and ongoing work on the telescope control algorithm. It is suggested that the present system is versatile enough to be applicable to many similar telescopes.
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