Lowell Observatory's Discovery Channel Telescope (DCT) is a 4.3-m telescope designed and constructed for optical and near infrared astronomical observation. The DCT is equipped with a cube at the RC focus capable of interfacing to five instruments along with the wave front sensing and guider systems at the f/6.1 RC focus. Over the period 2016 through mid-2018 the instrument cube ports were fully populated as several instruments new to the DCT were brought on-line (NIHTS, IGRINS, EXPRES). The primary and secondary mirrors of the telescope were re-aluminized, and the coating process modified. The facility operational modes have been refined to allow for greater flexibility and faster response to unexpected science opportunities. This report addresses operational methods, instrumentation integration, and the performance of the facility as determined from delivered science data, lessons learned, and plans for future work and additional instruments.
The Immersion GRating INfrared Spectrometer (IGRINS) was designed for high-throughput with the expectation of being a visitor instrument at progressively larger observing facilities. IGRINS achieves R∼45000 and > 20,000 resolution elements spanning the H and K bands (1.45-2.5μm) by employing a silicon immersion grating as the primary disperser and volume-phase holographic gratings as cross-dispersers. After commissioning on the 2.7 meter Harlan J. Smith Telescope at McDonald Observatory, the instrument had more than 350 scheduled nights in the first two years. With a fixed format echellogram and no cryogenic mechanisms, spectra produced by IGRINS at different facilities have nearly identical formats. The first host facility for IGRINS was Lowell Observatory’s 4.3-meter Discovery Channel Telescope (DCT). For the DCT a three-element fore-optic assembly was designed to be mounted in front of the cryostat window and convert the f/6.1 telescope beam to the f/8.8 beam required by the default IGRINS input optics. The larger collecting area and more reliable pointing and tracking of the DCT improved the faint limit of IGRINS, relative to the McDonald 2.7-meter, by ∼1 magnitude. The Gemini South 8.1-meter telescope was the second facility for IGRINS to visit. The focal ratio for Gemini is f/16, which required a swap of the four-element input optics assembly inside the IGRINS cryostat. At Gemini, observers have access to many southern-sky targets and an additional gain of ∼1.5 magnitudes compared to IGRINS at the DCT. Additional adjustments to IGRINS include instrument mounts for each facility, a glycol cooled electronics rack, and software modifications. Here we present instrument modifications, report on the success and challenges of being a visitor instrument, and highlight the science output of the instrument after four years and 699 nights on sky. The successful design and adaptation of IGRINS for various facilities make it a reliable forerunner for GMTNIRS, which we now anticipate commissioning on one of the 6.5 meter Magellan telescopes prior to the completion of the Giant Magellan Telescope.
The recent availability of large format near-infrared detectors with sub-election readout noise is revolutionizing our approach to wavefront sensing for adaptive optics. However, as with all near-infrared detector technologies, challenges exist in moving from the comfort of the laboratory test-bench into the harsh reality of the observatory environment. As part of the broader adaptive optics program for the GMT, we are developing a near-infrared Lucky Imaging camera for operational deployment at the ANU 2.3 m telescope at Siding Spring Observatory. The system provides an ideal test-bed for the rapidly evolving Selex/SAPHIRA eAPD technology while providing scientific imaging at angular resolution rivalling the Hubble Space Telescope at wavelengths λ = 1.3-2.5 μm.
MANIFEST is a facility multi-object fibre system for the Giant Magellan Telescope, which uses ‘Starbug’ fibre positioning robots. MANIFEST, when coupled to the telescope’s planned seeing-limited instruments, GMACS, and G-CLEF, offers access to: larger fields of view; higher multiplex gains; versatile reformatting of the focal plane via IFUs; image-slicers; and in some cases higher spatial and spectral resolution. The Prototyping Design Study phase for MANIFEST, nearing completion, has focused on developing a working prototype of a Starbugs system, called TAIPAN, for the UK Schmidt Telescope, which will conduct a stellar and galaxy survey of the Southern sky. The Prototyping Design Study has also included work on the GMT instrument interfaces. In this paper, we outline the instrument design features of TAIPAN, highlight the modifications that will be necessary for the MANIFEST implementation, and provide an update on the MANIFEST/instrument interfaces.
Instrument development for the 24m Giant Magellan Telescope (GMT) is described: current activities, progress, status, and schedule. One instrument team has completed its preliminary design and is currently beginning its final design (GCLEF, an optical 350-950 nm, high-resolution and precision radial velocity echelle spectrograph). A second instrument team is in its conceptual design phase (GMACS, an optical 350-950 nm, medium resolution, 6-10 arcmin field, multi-object spectrograph). A third instrument team is midway through its preliminary design phase (GMTIFS, a near-IR YJHK diffraction-limited imager/integral-field-spectrograph), focused on risk reduction prototyping and design optimization. A fourth instrument team is currently fabricating the 5 silicon immersion gratings needed to begin its preliminary design phase (GMTNIRS, a simultaneous JHKLM high-resolution, AO-fed, echelle spectrograph). And, another instrument team is focusing on technical development and prototyping (MANIFEST, a facility robotic, multifiber feed, with a 20 arcmin field of view). In addition, a medium-field (6 arcmin, 0.06 arcsec/pix) optical imager will support telescope and AO commissioning activities, and will excel at narrow-band imaging. In the spirit of advancing synergies with other groups, the challenges of running an ELT instrument program and opportunities for cross-ELT collaborations are discussed.
The Giant Magellan Telescope Project is in the construction phase. Production of the primary mirror segments is underway with four of the seven required 8.4m mirrors at various stages of completion and materials purchased for segments five and six. Development of the infrastructure at the GMT site at Las Campanas is nearing completion. Power, water, and data connections sufficient to support the construction of the telescope and enclosure are in place and roads to the summit have been widened and graded to support transportation of large and heavy loads. Construction pads for the support buildings have been graded and the construction residence is being installed. A small number of issues need to be resolved before the final design of the telescope structure and enclosure can proceed and the GMT team is collecting the required inputs to the decision making process. Prototyping activities targeted at the active and adaptive optics systems are allowing us to finalize designs before large scale production of components begins. Our technically driven schedule calls for the telescope to be assembled on site in 2022 and to be ready to receive a subset of the primary and secondary mirror optics late in the year. The end date for the project is coupled to the delivery of the final primary mirror segments and the adaptive secondary mirrors that support adaptive optics operations.
Instrument development for the 25 m class optical/infrared Giant Magellan Telescope (GMT) is actively underway. Two
instruments have begun their preliminary design phase: an optical (350-1000 nm) high resolution and precision radial
velocity echelle spectrograph (G-CLEF), and a near-IR (YJHK) diffraction-limited imager/integral-field-spectrograph
(GMTIFS). A third instrument will begin its design phase in early 2015: an optical (370-1000 nm) low-to-medium
resolution multi-object spectrograph (GMACS). Two other instrument teams are focusing on prototypes to demonstrate
final feasibility: a near-to-mid-IR (JHKLM) high resolution diffraction-limited echelle (GMTNIRS) spectrograph, and a
facility robotic multi-fiber-feed (MANIFEST). A brief overview of the GMT instrumentation program is presented:
current activities, progress, status, and schedule, as well as a summary of the facility infrastructure needed to support the
MANIFEST is a fibre feed system for the Giant Magellan Telescope that, coupled to the seeing-limited instruments
GMACS and G-CLEF, offers qualitative and quantitative gains over each instrument’s native capabilities in terms of
multiplex, field of view, and resolution. The MANIFEST instrument concept is based on a system of semi-autonomous
probes called “Starbugs” that hold and position hundreds of optical fibre IFUs under a glass field plate placed at the
GMT Cassegrain focal plane. The Starbug probes feature co-axial piezoceramic tubes that, via the application of
appropriate AC waveforms, contract or bend, providing a discrete stepping motion. Simultaneous positioning of all
Starbugs is achieved via a closed-loop metrology system.
The Giant Magellan Telescope (GMT) is a 25.4-m diameter, optical/infrared telescope that is being built by an international consortium of universities and research institutions as one of the next generation of Extremely Large Telescopes. The primary mirror of GMT consists of seven 8.4 m borosilicate honeycomb mirror segments that are optically conjugate to seven corresponding segments in the Gregorian secondary mirror. Fabrication is complete for one primary mirror segment and is underway for the next two. The final focal ratio of the telescope is f/8.2, so that the focal plane has an image scale of 1.02 arcsec/mm. GMT will be commissioned using a fast-steering secondary mirror assembly comprised of conventional, rigid segments to provide seeing-limited observations. A secondary mirror with fully adaptive segments will be used in standard operation to additionally enable ground-layer and diffraction-limited adaptive optics. In the seeing limited mode, GMT will provide a 10 arcmin field of view without field correction. A 20 arcmin field of view will be obtained using a wide-field corrector and atmospheric dispersion compensator. The project has recently completed a series of sub-system and system-level preliminary design reviews and is currently preparing to move into the construction phase. This paper summarizes the technical development of the GMT sub-systems and the current status of the GMT project.
The Giant Magellan Telescope (GMT) is a 25.4-m optical/infrared telescope constructed from seven 8.4-m primary
mirror segments. The collecting area is equivalent to a 21.6-m filled aperture. The instrument development program was
formalized about two years ago with the initiation of 14-month conceptual design studies for six candidate instruments.
These studies were completed at the end of 2011 with a design review for each. In addition, a feasibility study was
performed for a fiber-feed facility that will direct the light from targets distributed across GMT's full 20 arcmin field of
view simultaneously to three spectrographs. We briefly describe the features and science goals for these instruments, and
the process used to select those instruments that will be funded for fabrication first. Detailed reports for most of these
instruments are presented separately at this meeting.
The Giant Magellan Telescope (GMT) is a 25-meter optical/infrared extremely large telescope that is being built by an
international consortium of universities and research institutions. It will be located at the Las Campanas Observatory,
Chile. The GMT primary mirror consists of seven 8.4-m borosilicate honeycomb mirror segments made at the Steward
Observatory Mirror Lab (SOML). Six identical off-axis segments and one on-axis segment are arranged on a single
nearly-paraboloidal parent surface having an overall focal ratio of f/0.7. The fabrication, testing and verification
procedures required to produce the closely-matched off-axis mirror segments were developed during the production of
the first mirror. Production of the second and third off-axis segments is underway.
GMT incorporates a seven-segment Gregorian adaptive secondary to implement three modes of adaptive-optics
operation: natural-guide star AO, laser-tomography AO, and ground-layer AO. A wide-field corrector/ADC is available
for use in seeing-limited mode over a 20-arcmin diameter field of view. Up to seven instruments can be mounted
simultaneously on the telescope in a large Gregorian Instrument Rotator. Conceptual design studies were completed for
six AO and seeing-limited instruments, plus a multi-object fiber feed, and a roadmap for phased deployment of the GMT
instrument suite is being developed.
The partner institutions have made firm commitments for approximately 45% of the funds required to build the
telescope. Project Office efforts are currently focused on advancing the telescope and enclosure design in preparation for
subsystem- and system-level preliminary design reviews which are scheduled to be completed in the first half of 2013.
The WIYN One Degree Imager (ODI) will provide a one degree field of view for the WIYN 3.5 m telescope located on
Kitt Peak near Tucson, Arizona. Its focal plane consists of an 8x8 grid of Orthogonal Transfer Array (OTA) CCD
detectors. These detectors are the STA2200 OTA CCDs designed and fabricated by Semiconductor Technology
Associates, Inc. and backside processed at the University of Arizona Imaging Technology Laboratory. Several lot runs
of the STA2200 detectors have been fabricated. We have backside processed devices from these different lots and
provide detector performance characterization, including noise, CTE, cosmetics, quantum efficiency, and some
orthogonal transfer characteristics. We discuss the performance differences for the devices with different silicon
thickness and resistivity. A fully buttable custom detector package has been developed for this project which allows
hybridization of the silicon detectors directly onto an aluminum nitride substrate with an embedded pin grid array. This
package is mounted on a silicon-aluminum alloy which provides a flat imaging surface of less than 20 microns peakvalley
at the -100 C operating temperature. Characterization of the package performance, including low temperature
profilometry, is described in this paper.
We present the as-built design overview and post-installation performance of the upgraded WIYN Bench Spectrograph.
This Bench is currently fed by either of the general-use multi-fiber instruments at the WIYN 3.5m telescope on Kitt
Peak, the Hydra multi-object positioner, and the SparsePak integral field unit (IFU). It is very versatile, and can be
configured to accommodate low-order, echelle, and volume phase holographic gratings. The overarching goal of the
upgrade was to increase the average spectrograph throughput by ~60% while minimizing resolution loss (< 20%). In
order to accomplish these goals, the project has had three major thrusts: (1) a new CCD was provided with a nearly
constant 30% increase is throughput over 320-1000 nm; (2) two Volume Phase Holographic (VPH) gratings were
delivered; and (3) installed a new all-refractive collimator that properly matches the output fiber irradiance (EE90) and
optimizes pupil placement. Initial analysis of commissioning data indicates that the total throughput of the system has
increased 50-70% using the 600 l/mm surface ruled grating, indicating that the upgrade has achieved its goal.
Furthermore, it has been demonstrated that overall image resolution meets the requirement of <20% loss.
QUOTA is an 8Kx8K (16'x16') optical imager using four 4Kx4K orthogonal transfer CCDs arrays (OTAs). Each OTA
has 64 nearly independent CCDs having 480x494 12μm pixels. By reading out several of the CCDs rapidly (20 Hz), the
centroids of the stars in those CCDs can be used to measure image motion due to atmospheric effects, telescope shake,
and guide errors. Motions are fed back to the remaining 250 CCDs that continue to integrate normally, allowing a shift
of the collecting charge packets so that they always fall under the moving star images, thereby effecting low order
adaptive optics tip/tilt correction in the silicon to improve image quality. As a bonus, the stars that are read rapidly can
be studied for high speed photometric variability.
QUOTA was conceived to be a prototype for WIYN's 32Kx32K One Degree Imager (ODI), providing a means to test
and advance the technical developments for the larger imager (e.g., detectors, controllers, optics, coatings, cooling, and
software). QUOTA will have been to the WIYN 3.5-m telescope only twice in its current configuration, but it provided
a wealth of information that has been useful to the engineering of ODI. We focus on the areas in which ODI has
benefited from QUOTA in this report.
The Giant Magellan Telescope (GMT) is a 24.5m diameter optical/infrared telescope. Its seven 8.4m primary mirrors
give it a collecting area equivalent to a 21.4m filled aperture. The ten GMT partners are constructing the telescope at the
Las Campanas Observatory in Chile with first light planned for the end of 2018. In this paper, we describe the plans for
the first-generation focal plane instrumentation for the telescope. The GMTO Corporation has solicited studies for
instruments capable of carrying out the broad range of objectives outlined in the GMT Science Case. Six instruments
have been selected for 14 month long conceptual design studies. We briefly describe the features of these instruments
and give examples of the major science questions that they can address.
The One Degree Imager will be the future flagship instrument at the WIYN 3.5m observatory, once commissioned in
2011. With a 1 Gigapixel focal plane of Orthogonal Transfer Array CCD devices, ODI will be the most advanced optical
imager with open community access in the Northern Hemisphere. In this talk we will summarize the progress since the
last presentation of ODI at the SPIE 2008 meeting, focusing on optics procurement, instrument assembly and testing, and
The WIYN One Degree Imager (ODI) will provide a one degree field of view for the WIYN 3.5 m telescope located on Kitt Peak near Tucson, Arizona. Its focal plane will consist of an 8x8 grid of Orthogonal Transfer Array (OTA) CCD detectors with nearly one billion pixels. The implementation of these detectors into the focal plane has required the development of several novel packaging and characterization techniques, which are the subject of this paper. We describe a new packaging/hybridization method in which the CCD die are directly bonded to aluminum nitride ceramic substrates which have indium bump on one side and brazed pins on the other. These custom packages allow good thermal conductivity, a flat imaging surface, four side buttability, and in situ testing of the devices during backside processing. We describe these carriers and the backside processing techniques used with them. We have also modified our cold probing system to screen these OTA die at wafer level to select the best candidates for backside processing. We describe these modifications and characterization results from several wafer lots.
The WIYN consortium is building the One Degree Imager (ODI) to be mounted to a Nasmyth port of the WIYN 3.5m
telescope, located at Kitt Peak, Arizona (USA). ODI will utilize both the excellent image quality and the one-degree
field of view that the telescope delivers. To accommodate the large field of view (~0.39m diameter unvignetted field
with 0.54m across the diagonal of the one-degree-square, partially vignetted field), 0.6m-class optics are required. The
ODI design consists of a two element corrector: one serves as a vacuum barrier to the cryostat, the other is an asphere;
two independently rotating bonded prism pairs for atmospheric dispersion compensation (ADC); nine independently
deployable filters via a simple pivoting motion; and a 971 mega-pixel focal plane consisting of 64 orthogonal transfer
array (OTA) devices.
This paper is an overview of the mechanical design of ODI and describes the optical element mounting and alignment
strategy, the ADC & filter mechanisms, plus the focal plane. Additionally, the project status will be discussed.
In accompanying papers Jacoby1 describes ODI's optical design, Yeatts2 describes the software and control system
design, and Harbeck3 gives a general update on the project.
The main advantage of the WIYN One Degree Imager (ODI) over other wide-field imagers will be its exceptional image quality. The fine pixel scale (0.11") provides uncompromised sampling of stellar PSFs under most conditions (seeing >0.3"). The telescope routinely delivers the site seeing (median ~ 0.7") which is often below 0.5" FWHM, and can be as low as 0.25". The ODI specifications require the optics to maintain native high quality images. A two-element, fused silica, corrector meets the geometric error budget of 0.10" images, but the first element requires a mildly aspheric surface. The other element serves as the dewar window. A pair of cemented prisms (fused silica plus PBL6Y) serve as an ADC, which is essential to meet the image quality requirements for many observing programs. We describe the optical design details and its performance, the tolerances required, and the trade-offs considered for anti-reflection coatings. This paper is an update to a preliminary three-element design.
The WIYN Consortium is building the One Degree Imager (ODI) for its 3.5m telescope, located at Kitt Peak, Arizona
(USA). ODI will utilize both the excellent image quality and the one degree field of view of the WIYN telescope. Image
quality will be actively improved by localised tip/tilt image motion stabilisation using a novel concept of Orthogonal
Transfer Array (OTA) CCDs, which are a new detector type jointly developed with the PanSTARRS project. Its anticipated
median image quality of ≤ 0.55" in the R band will make ODI a unique and competitive instrument in the landscape of the
next generation of large field imagers.
A conceptual design of ODI was presented earlier at SPIE.1 In the meantime, this concept matured, the ODI project has
been fully funded, and it has entered the construction phase. A prototype camera (QUOTA) with a field of view of 16'x16'
has already seen first star light in fall 2006. In this paper we report on the evolution of ODI's definition, the design of its
components, the status of the OTA detector development, and the path towards first light in early 2010. In accompanying
papers we detail the design of the ODI's optical corrector, the mechanical structures, and the software & instrument system
We describe the redesign and upgrade of the versatile fiber-fed Bench Spectrograph on the WIYN 3.5m telescope. The
spectrograph is fed by either the Hydra multi-object positioner or integral-field units (IFUs) at two other ports, and can
be configured with an adjustable camera-collimator angle to use low-order and echelle gratings. The upgrade, including
a new collimator, charge-coupled device (CCD) and modern controller, and volume-phase holographic gratings
(VPHG), has high performance-to-cost ratio by combining new technology with a system reconfiguration that optimizes
throughput while utilizing as much of the existing instrument as possible. A faster, all-refractive collimator enhances
throughput by 60%, nearly eliminates the slit-function due to vignetting, and improves image quality to maintain
instrumental resolution. Two VPH gratings deliver twice the diffraction efficiency of existing surface-relief gratings: A
740 l/mm grating (float-glass and post-polished) used in 1st and 2nd-order, and a large 3300 l/mm grating (spectral
resolution comparable to the R2 echelle). The combination of collimator, high-quantum efficiency (QE) CCD, and VPH
gratings yields throughput gain-factors of up to 3.5.
The orthogonal-transfer array (OTA) is a new CCD architecture designed to provide wide-field tip-tilt correction of astronomical images. The device consists of an 8x8 array of small (~500x500 pixels) orthogonal-transfer CCDs (OTCCD) with independent addressing and readout of each OTCCD. This approach enables an optimum tip-tilt correction to be applied independently to each OTCCD across the focal plane. The first design of this device has been carried out at MIT Lincoln Laboratory in support of the Pan-STARRS program with a collaborative parallel effort at Semiconductor Technology Associates (STA) for the WIYN Observatory. The two versions of this device are functionally compatible and share a common pinout and package. The first wafer lots are complete at Lincoln and at Dalsa and are undergoing wafer probing.
The optical design for the WIYN One Degree Imager (ODI) is based on well-known princples for the design of secondary focus correctors of Ritchey-Chrétien telescopes. It started as the classical two element plus/minus pair of lenses required to correct moderate and wide fields of view whilst working with wide spectral regions. However, since this corrector is required to cover a one degree square and plane field of view, accommodate filters and an atmospheric dispersion compensator, it evolved into three elements. In order to avoid the addition of more glass than was absolutely necessary the third element was designed to serve the dual function of field flattener and dewar window. The final form presented here is plus/minus/minus in power distribution with well-separated elements. The ADC is situated between the first and second elements with filter between the second and third elements in an accessible position. Theoretically the worst-case image given is 90% of the ensquared energy into 2 by 2 pixels in the corner of the one degree square field.
The WIYN One Degree Imager (ODI) will be a well-sampled (0.11” per pixel) imager that provides a full one degree square field of view (32K×32K pixels). ODI will utilize high resistivity, red sensitive, orthogonal transfer (OT) CCDs to provide rapid correction for image motion arising from telescope shake, guider errors, and atmospheric effects. ODI will correct the full field of view by deploying 64 array packages having a total of 4096 independently controllable OTCCDs that can correct individually for local (2 arcmin) image motion. Each array package is an orthogonal transfer array (OTA) of 64 CCDs arranged in an 8×8 grid. Each CCD has 512×512 pixels. We expect the median image quality at the WIYN 3.5m telescope in RIZ to be 0.52”, 0.43”, and 0.35” FWHM. ODI makes optimal use of the WIYN telescope, which has superb optics, excellent seeing characteristics, a natural 1.4 degree field of view (with a new corrector), and can serve as a pathfinder for LSST in terms of detectors, data pipelines, operations strategies, and scientific motivation.
We describe progress in removing image motion over large fields of view. A camera using a new type of CCD has been commissioned and we report first results which are very promising for wide field imaging. We are embarking on a project to build a new type of astronomical CCD which should provide image motion compensation over arbitrarily large fields of view, very fast readout, autoguiding capability, good red sensitivity, and should be significantly less expensive than the present generation of CCDs.
Imaging surveys of the bright 5007 angstrom line in nearby early-type galaxies and the bulges of spirals have catalogued many planetary nebulae. Planetary nebulae arise from the late stages of evolution of low mass stars and are thus representative of a large fraction of the stellar population by number. In about 80 percent of planetary nebulae the abundances of the well observed lighter elements are not affected by the nucleo synthesis which occurs on the Asymptotic Giant Branch, so the nebular abundances can be related to those of the progenitor star. Planetary nebular abundances compared with those of H II regions in spirals, as indicators of abundance gradients and enrichment history. Planetary nebulae provide point probes of the stellar abundance and, in contrast to integrated line of sight stellar spectra, can be used to measure the abundance spread.
The confluence of advances in telescope and spectrograph design computing power, pathfinding imaging capabilities on the ground and in space, and the maturity of many astrophysical fields, allow us to look beyond the study of a few unique objects and towards the systematic study of large samples in order to completely characterize their properties, formation history, and cosmological significance. These studies require spectroscopic observations to probe the kinematics, chemical composition, dynamics, ages, masses and evolutionary histories of astronomical objects. Examples of three fundamental science goals are described that demand a wide-field system on a large telescope.
We have obtained high speed image motion data from the 3.5M WIYN telescope at Kitt Peak as part of commissioning and characterizing efforts. These data come from a small frame transfer CCD feeding dedicated centroiding hardware called FastTrack, which provides x and y data pairs at frequencies > Hertz. In this paper we use power spectra from these data to investigate telescope structure resonance and characterize the site + telescope performance for gains by implementing tip-tilt correction at WIYN. At frequencies below 20hz the image motion power spectra are consistent with Kolmogorov turbulence models but show excess power at higher frequencies. Over the past 2 years the FastTrack data have consistently shown that image improvements of 0.10-0.20 arcseconds can be obtained with a simple tip-tilt systems that fully corrects frequencies 20Hz and lower. The FastTrack power spectra have also revealed a complex structure of coherent frequencies between 22 and 28 Hertz, similar to what has been seen on other light weight stiff telescopes. In other tests, we have used simultaneous star trail data to estimate the isokinetic angle for frequencies below 10hz. We have found that the one dimensional correlation remains above 0.8 within an angular radius of approximately 240 arcseconds. These data show that a high speed tip-tilt system can net significant improvements to image quality at WIYN over a relatively large field.
The WIYN 3.5 meter telescope is situated on the southwest ridge of Kitt Peak yielding excellent atmosphere seeing conditions. As such, the telescope and enclosure design was directed towards exploiting this feature. The primary mirror was spun cast and figured by the Steward Observatory Mirror Laboratory and the secondary mirror by Contraves. In both cases the performance exceeded the design specifications. The borosilicate primary is actively temperature controlled to within 0.2 C of the desired temperature, typically 0.5 degrees C below the ambient air. The telescope structure is also temperature controlled and the enclosure is opened to the outside ion all sides, which all heat sources are vented to ducts carrying air downwind of the facility. The primary mirror is actively controlled for low order aberrations by 66 axial actuators which are adjusted open loop via force matrix look-up tables and closed loop via real-time wavefront curvature sensing measurements. The active optics also included real-time collimation and focus control. The telescope drive and guider are capable of providing tracking to a few hundredths of a second of arc. By employing active telescope control at this level, it is possible to maintain telescope and local wavefront distortion to a level where atmospheric effects dominate the image quality. Since a significant fraction of the power in the atmospheric disturbances is contained in image motion the first step in adaptive optics control will be simple tip tilt. Studies of higher order AO system are being carried out, as well as additional test characterizing the telescope and site. It is intended to continue such studies in an attempt to establish long term variances.
A new generation wide-field imager is being developed and will be put into service at sites in North and South America. Driven by the requirement for larger imaging areas and more pixels but limited by manufacturing process constraints, manufacturers are developing 2, 3, and 4-side buttable CCDs that can be tiled to achieve large imaging areas as opposed to developing a single large CCD. NOAO has designed, fabricated, and tested a wide-field imager called Mosaic that tiles 8 CCDs to produce an imaging area slightly greater than 123 mm X 123 mm. Several successful science observation runs have been completed using Mosaic at the KPNO Mayall 4 m and .9 m telescopes. A second Mosaic Wide-Field Imager is presently being manufactured and will be deployed at the CTIO Blanco 4 m telescope early next year. This report will focus on the mechanical design aspects of the Mosaic Imager and the upgrade path to achieve the scientific requirements will be discussed.
NOAO is testing Scientific Imaging Technologies, Inc. (SITe) thinned backside 2k by 4k charge coupled devices (CCDs) to be used at KPNO and CTIO. NOAO's Mosaics will use as the basic 'tile' the SITe ST-002A CCD Imager. These CCDs will be used to upgrade the wide field Mosaic imager now in use at KPNO's 4- Meter Mayall telescope and 0.9-Meter telescope. SITe 2k by 4k CCDs will also be used in MOSAIC II now under construction for CTIO's 4-Meter Blanco telescope. Additionally NOAO will implement 2 Mini-Mosaics in the two device 4K by 4K configuration. The first of the ST-002As arrived in mid August 97 and this paper will discuss test results of all devices received and tested prior to publication. Additionally this paper will discuss the mounting methods of Mosaics. This will include; geometric stability, techniques used for measuring CCD surface flatness and co-planer requirements for NOAO's Mosaic Instruments.
The Kitt Peak Mayall 4-m telescope required a new prime focus corrector having a flat focal plane covering 36 arcmin on a side (51 arcmin diagonal) to accommodate the Mosaic 8K X 8K CCD system. The scientific requirements for the new corrector included atmospheric dispersion compensation (ADC), excellent near-UV efficiency, excellent image quality, and extremely low scattered light and ghosting. The optical system designed to meet these demands exhibits excellent and stable performance through its first year of operation. This paper describes the innovative design and engineering aspects of the corrector. Science verification data are presented to demonstrate some of the attributes of the new corrector.