The Spitzer Space Telescope currently operates in the "Beyond Era", over nine years past an original cryogenic mission. As the astronomy community continues to advance scientific boundaries and push beyond original specifications, the stability of the Infrared Array Camera (IRAC) instrument is paramount. The Instrument Team (IST) monitors the pointing accuracy, temperature, and calibration and provides the information in a timely manner to observers. The IRAC IST created a calibration trending web page, available to the general astronomy community, where the team posts updates of three most pertinent scientific stability measures of the IRAC data: calibration, bias, and bad pixels. In addition, photometry and telescope properties from all the staring observations (>1500 as of April 2018) are trended to examine correlations with changes in the age or thermal properties of the telescope. A long, well-sampled baseline established by consistent monitoring outside anomalies and space weather events allows even the smallest changes to be detected.
The Thermal Infrared imager for the GMT which provides Extreme contrast and Resolution (TIGER) is intended as a
small-scale, targeted instrument capable of detecting and characterizing exoplanets and circumstellar disks, around both
young systems in formation, and more mature systems in the solar neighborhood. TIGER can also provide general
purpose infrared imaging at wavelengths from 1.5-14 μm. The instrument will utilize the facility adaptive optics (AO)
system. With its operation at NIR to MIR wavelengths (where good image quality is easier to achieve), and much of the
high-impact science using modestly bright guide stars, the instrument can be used early in the operation of the GMT.
The TIGER concept is a dual channel imager and low resolution spectrometer, with high contrast modes of observations
to fulfill the above science goals. A long wavelength channel (LWC) will cover 7-14 μm wavelength, while a short
wavelength channel (SWC) will cover the 1.5-5 μm wavelength region. Both channels will have a 30° FOV. In addition
to imaging, low-resolution spectroscopy (R=300) is possible with TIGER for both the SWC and LWC, using insertable
grisms.
The dominant non-instrumental background source for space-based infrared observatories is the zodiacal light
(ZL). We present Spitzer Infrared Array Camera (IRAC) measurements of the ZL at 3.6, 4.5, 5.8, and 8.0 μm,
taken as part of the instrument calibrations. We measure the changing surface brightness levels in approximately
weekly IRAC observations near the north ecliptic pole over the period of roughly 8.5 years. This long time
baseline is crucial for measuring the annual sinusoidal variation in the signal levels due to the tilt of the dust disk
with respect to the ecliptic, which is the true signal of the ZL. This is compared to both Cosmic Background
Explorer Diffuse Infrared Background Experiment data and a ZL model based thereon. Our data show a few
percent discrepancy from the Kelsall et al.(1998)1 model including a potential warping of the interplanetary dust
disk and a previously detected overdensity in the dust cloud directly behind the Earth in its orbit. Accurate
knowledge of the ZL is important for both extragalactic and Galactic astronomy including measurements of the
cosmic infrared background, absolute measures of extended sources, and comparison to extrasolar interplanetary
dust models. IRAC data can be used to further inform and test future ZL models.
Significant improvements in our understanding of various photometric effects have occurred in the more than nine years
of flight operations of the Infrared Array Camera aboard the Spitzer Space Telescope. With the accumulation of
calibration data, photometric variations that are intrinsic to the instrument can now be mapped with high fidelity. Using
all existing data on calibration stars, the array location-dependent photometric correction (the variation of flux with
position on the array) and the correction for intra-pixel sensitivity variation (pixel-phase) have been modeled
simultaneously. Examination of the warm mission data enabled the characterization of the underlying form of the pixelphase
variation in cryogenic data. In addition to the accumulation of calibration data, significant improvements in the
calibration of the truth spectra of the calibrators has taken place. Using the work of Engelke et al. (2006), the KIII
calibrators have no offset as compared to the AV calibrators, providing a second pillar of the calibration scheme. The
current cryogenic calibration is better than 3% in an absolute sense, with most of the uncertainty still in the knowledge of
the true flux densities of the primary calibrators. We present the final state of the cryogenic IRAC calibration and a
comparison of the IRAC calibration to an independent calibration methodology using the HST primary calibrators.
The Infrared Array Camera (IRAC) is now the only science instrument in operation on the Spitzer Space Telescope. The
3.6 and 4.5 µm channels are temperature-stabilized at ~28.7K, and the sensitivity of IRAC is nearly identical to what it
was in the cryogenic mission. The instrument point response function (PRF) is a set of values from which one can
determine the point spread function (PSF) for a source at any position in the field, and is dependent on the optical
characteristics of the telescope and instrument as well as the detector sampling and pixel response. These data are
necessary when performing PSF-fitting photometry of sources, for deconvolving an IRAC image, subtracting out a
bright source in a field, or for estimating the flux of a source that saturates the detector. Since the telescope and
instrument are operating at a higher temperature in the post-cryogenic mission, we re-derive the PRFs for IRAC from
measurements obtained after the warm mission temperature set point and detector biases were finalized and compare
them to the 3.6 and 4.5 µm PRFs determined during the cryogenic mission to assess any changes.
We present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space
Telescope taken after the depletion of cryogen. The cryogen depleted on 15 May 2009, and shortly afterward a two-month-
long calibration and characterization campaign was conducted. The array temperature and bias setpoints were
revised on 19 September 2009 to take advantage of lower than expected power dissipation by the instrument and to
improve sensitivity. The final operating temperature of the arrays is 28.7 K, the applied bias across each detector is 500
mV and the equilibrium temperature of the instrument chamber is 27.55 K. The final sensitivities are essentially the
same as the cryogenic mission with the 3.6 μm array being slightly less sensitive (10%) and the 4.5 μm array within 5%
of the cryogenic sensitivity. The current absolute photometric uncertainties are 4% at 3.6 and 4.5 μm, and better than
milli-mag photometry is achievable for long-stare photometric observations. With continued analysis, we expect the
absolute calibration to improve to the cryogenic value of 3%. Warm IRAC operations fully support all science that was
conducted in the cryogenic mission and all currently planned warm science projects (including Exploration Science
programs). We expect that IRAC will continue to make ground-breaking discoveries in star formation, the nature of the
early universe, and in our understanding of the properties of exoplanets.
We present an analysis of the stability of the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope over
the first 4.5 years of in-flight operations. IRAC consists of two InSb and two Si:As 256x256 imaging arrays with
passbands centered on 3.6, 4.5. 5.8 and 8.0 microns. Variations in photometric stability, read noise, dark offsets, pixel
responsivity and number of hot and noisy pixels for each detector array are trended with time. To within our
measurement uncertainty, the performance of the IRAC arrays has not changed with time. The most significant variation
is that number of hot pixels in the 8 micron array has increased linearly with time at a rate of 60 pixels per year. We
expect that the 3.6 and 4.5 micron arrays should remain stable during the post-cryogenic phase of the Spitzer mission.
We will briefly discuss some science that is enabled by the excellent stability of IRAC.
The Infrared Array Camera (IRAC) is a four-channel camera on the Spitzer Space Telescope, one of three focal plane science instruments. IRAC uses two pairs of 256×256 pixel InSb and Si:As IBC detectors to provide simultaneous imaging at 3.6, 4.5, 5.8, and 8 μm. IRAC experiences a flux of cosmic rays and solar protons that produce transient effects in science images from each of the arrays, with 4-6 pixels per second being affected during each integration. During extreme solar flares, IRAC experiences a much higher rate of transients which affects the science data quality. We present cosmic ray rates and observed detector characteristics for IRAC during the first two years of science operation, and rates observed in a period of elevated solar proton flux during an intense solar flare in January 2005. We show the changes to the IRAC detectors observed since launch, and assess their impacts to the science data quality.
The Spitzer Space Telescope Infrared Array Camera (IRAC) is a four-channel camera that uses two pairs of 256 x 256 pixel InSb and Si:As IBC detectors to provide simultaneous images at 3.6, 4.5, 5.8, and 8 microns. IRAC experiences a flux of cosmic rays that produce transient events in images from each of the arrays, with 5-7 pixels per second being affected in an IRAC integration. The vast majority of these transient events can be adequately characterized so they can be effectively detected and flagged by a pipeline software module. However, because of the nature of the arrays and their arrangement in the camera structure, a small fraction of the cosmic ray hits on IRAC produce transients with unusual morphologies which cannot be characterized in a general way. We present nominal cosmic ray rates observed for IRAC on-orbit and rates observed during a period of elevated solar proton flux following a series of X-class solar flares in late 2003. We also present a guide for observers to help identify unusual transient events in their data. We comment on the physical nature of the production of many o9f these unusual transients and how this mechanism differs from the production of "normal" transient events.
The Infrared Array Camera (IRAC) is one of three focal plane instruments on board the Spitzer Space Telescope. IRAC is a four-channel camera that obtains simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 μm in two nearly adjacent fields of view. We summarize here the in-flight scientific, technical, and operational performance of IRAC.
We describe the process by which the NASA Spitzer Space Telescope (SST) Cryogenic Telescope Assembly (CTA) was brought into focus after arrival of the spacecraft in orbit. The ground rules of the mission did not allow us to make a conventional focus sweep. A strategy was developed to determine the focus position through a program of passive imaging during the observatory cool-down time period. A number of analytical diagnostic tools were developed to facilitate evaluation of the state of the CTA focus. Initially, these tools were used to establish the in-orbit focus position. These tools were then used to evaluate the effects of an initial small exploratory move that verified the health and calibration of the secondary mirror focus mechanism. A second large move of the secondary mirror was then commanded to bring the telescope into focus. We present images that show the CTA Point Spread Function (PSF) at different channel wavelengths and demonstrate that the telescope achieved diffraction limited performance at a wavelength of 5.5 μm, somewhat better than the level-one requirement.
KEYWORDS: Calibration, Infrared telescopes, High dynamic range imaging, Space telescopes, Stray light, Infrared cameras, Stars, Infrared radiation, Space operations, Telescopes
We describe the astronomical observation template (AOT) for the Infrared Array Camera (IRAC) on the Spitzer Space Telescope (formerly SIRTF, hereafter Spitzer). Commissioning of the AOTs was carried out in the first three months of the Spitzer mission. Strategies for observing fixed and moving targets are described, along with the performance of the AOT in flight. We also outline the operation of the IRAC data reduction pipeline at the Spitzer Science Center (SSC) and describe residual effects in the data due to electronic and optical anomalies in the instrument.
The Infrared Array Camera (IRAC) on Spitzer Space Telescope includes four Raytheon Vision Systems focal plane arrays, two with InSb detectors, and two with Si:As detectors. A brief comparison of pre- flight laboratory results vs. in-flight performance is given, including quantum efficiency and noise, as well as a discussion of irregular effects, such as residual image performance, "first frame effect", "banding", "column pull-down" and multiplexer bleed. Anomalies not encountered in pre-flight testing, as well as post-flight laboratory tests on these anomalies at the University of Rochester and at NASA Ames using sister parts to the flight arrays, are emphasized.
Prior to launch, the Spitzer Space Telescope (SST) secondary focus mechanism was set to a predicted desired in-orbit focus value. This predicted setting, determined from double-pass cold chamber measurements and calculated ground-to-orbit corrections, had an uncertainty greater than the required in-orbit focus accuracy. Because of concern about the potential for failure in a cryogenic mechanism affecting all Spitzer instruments, it was required that any focus correction be made in a set of moves directly from the initial to the desired setting. The task of determining the required focus moves fell to IRAC (Infrared Array Camera), the instrument most affected by and sensitive to defocus. To determine the focus directly from examining images at a fixed focus, we developed two methods, "Simfit" and "Focus Diversity" (W. F. Hoffmann, et. al.1). Simfit finds the focus by obtaining the best match between observed images and families of simulated images at a range of focus settings. Focus Diversity utilizes the focal plane curvature to find the best fit of the varied image blur over the focal plane to a model defocus curve. Observations of a single star at many field locations in each of the four IRAC bands were analyzed before and during the refocus activity. The resulting refocus moves brought the focus close to the specified requirement of within 0.3 mm from the desired IRAC optimum focus. This is less than a "Diffraction Focus Unit" (λx(f/2)) of 0.52 mm at the SST focus at the shortest IRAC band (3.58 microns). The improvement in focus is apparent in both the appearance and the calculated noise-pixels of star images.
MIRSI (Mid-InfraRed Spectrometer and Imager) is a mid-infrared camera system recently completed at Boston University that has both spectroscopic and imaging capabilities. MIRSI is uniquely suited for studies of young stellar objects and star formation, planetary and protoplanetary nebulae, starburst galaxies, and solar system objects such as planets, asteroids, and comets. The camera utilizes a 320 x 240 Si:As Impurity Band Conduction (IBC) array developed for ground-based astronomy by Raytheon/SBRC. For observations at the Infrared Telescope Facility (IRTF), MIRSI offers a large field of view (1.6 arcmin x 1.2 arcmin) with a pixel scale of 0.3 arcsec, diffraction-limited spatial resolution, complete spectral coverage over the 8-14 μm and 17-26 μm atmospheric windows for both imaging (discrete filters and circular variable filter) and spectroscopy (10 and 20 μm grisms), and high sensitivity (expected one-sigma point source sensitivities of 5 and 20 mJy at 10 and 20 μm, respectively, for on-source integration time of 30 seconds). MIRSI successfully achieved first light at the Mt. Lemmon Observing Facility (MLOF) in December 2001, and will have its first observing run at the IRTF in November 2002. We present details of the system hardware and software and results from first light observations.
Because of concern over possible failure of the SIRTF cryogenic focus mechanism in space, the SIRTF Project Office has directed that the focus should be set before launch so that the telescope arrives in orbit as close to optimum focus as possible. Then focus evaluation and determination of any required focus change to achieve best focus must be carried out without the conventional approach of a focus slew. For these tasks we have created two methods: Simfit and Focus Diversity. Simfit is a procedure for comparing an observed stellar image with a family of simulated point-source images with a range of focus settings. With a sufficiently accurate as-built telescope model for creating the simulated images, the focus offset and direction can be accurately and unambiguously determined because of the change in image appearance with defocus. Focus diversity takes advantage of the variation of best-focus setting over the instrument's focal plane due to focal plane curvature and tilt and offsets between different instrument channels. By plotting an image quality parameter, such as noise-pixels, for observed stars at several positions on the focal plane versus a defocus variable, the focus error and direction can be determined. We have developed an efficient program for carrying out these procedures. The validity of this program has been successfully confirmed using point-source images observed with three bands of the IRAC camera during a double-pass optical test of SIRTF in a Ball Aerospace cryogenic test chamber. The two procedures are described and are illustrated with these results
The Infrared Array Camera (IRAC) is one of three major scientific instruments to be launched aboard the Space Infrared Telescope Facility (SIRTF). This document briefly describes the features, usage, and limitations of the IRAC Science Data Simulator (ISDS) that can be used to generate simulated data to anticipate data quality and reduction issues for mission operations. The software is a combination of C++ and IRAF SPP routines that implement the features already characterized during the integration and test phase of IRAC's
development. While no guarantee of accuracy is made, the intention is to replicate as faithfully as possible known characteristics and artifacts of the IRAC instrument. The many beneficial applications of the ISDS include facilitating planning of the IRAC pipeline by the SIRTF Science Center (SSC), and validating observing strategies for SIRTF Guaranteed Time Observers and Legacy teams. The simulator has already been used by mission planners to demonstrate the relative effectiveness of different approaches to data reduction. It will also be of great value in demonstrating IRAC's capabilities for mapping and source detection, and in testing post-pipeline software currently being developed for these purposes.
The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12x5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detector arrays in the camera are 256x256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functional and calibration tests completed at Ball Aerospace during the integration with the cryogenic telescope assembly, and provide updated estimates of the in-flight sensitivity and performance of IRAC in SIRTF.
This paper describes the principal optical results of the "End to End" test conducted on the SIRTF Cryogenic Telescope Assembly. Test system focus was located using images from the shortest wavelength science instrument, IRAC, much as it will be on-orbit. Deep out-of-focus images were used to determine the system wavefront by Phase Retrieval methods with heritage to Hubble Space Telescope work. This work has been used to update the SIRTF optical models and aid in predicting the on-orbit performance of the observatory. Images made with other assemblies able to observe in the test (IRS, PCRS) were used to verify their function and co-focus to the IRAC established position. Image jitter was analyzed warm and cold, with visible images captured by the PCRS instrument and cold, with images captured by the IRAC instrument.
This paper describes the "End to End" optical test conducted on the Space InfraRed Telescope Facility (SIRTF) Cryogenic Telescope Assembly (CTA) in 2001. It was critical to verify SIRTF's optical functionality and quality under optical and thermal conditions that as much as possible simulated the flight environment. The Liquid Nitrogen cooled "Brutus" chamber at Ball Aerospace was the test facility. Flight-like self cooling, thermal blanketing, and auxiliary cooling loops allowed the assembly to reach temperatures close to orbital conditions. (25-5K) Introducing optical sources at the SIRTF focal plane allowed the telescope to perform as the collimating source. A motorized and cryogenically characterized reflection flat was used to direct the refocused images of test sources to visible and IR focal planes in SIRTF's Multi-Instrument Chamber. A sequence of tests was performed to gather data on system focus position, image stability, telescope wavefront and instrument assembly confocality.
The Infrared Array Camera (IRAC) is one of three science instruments that will fly aboard the Space Infrared Telescope Facility mission scheduled for launch in December, 2001. This paper summarizes the `as built' design of IRAC along with important integration and testing results.
The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12 X 5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detectors arrays in the camera are 256 X 256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functionality and calibration tests completed at Goddard Space Flight Center, and provide estimates of the in-flight sensitivity and performance of IRAC in SIRTF.
The NIRI for the Gemini North telescope is now undergoing acceptance testing. NIRI is the main near-IR facility camera on the Gemini North telescope and is designed to fully exploit the excellent characteristics of the site and the expected high performance o the telescope. NIRI offers 3 different pixel scales for wide-field, tip-tilt corrected and diffraction-limited imaging. It is equipped with a pupil imaging system to evaluate the telescope emissivity and to optimize the alignment of the instrument with the telescope. NIRI has an IR wavefront sensor so that tip-tilt and focus corrections can be obtained even in dark cloud regions or during daytime observing.
A 1-5 micrometers IR camera and spectrograph (IRCS) is described. The IRCS will be a facility instrument for the 8.2 m Subaru Telescope at Mauna Kea. It consists of two sections, a spectrograph and a camera section. The spectrograph is a cross-dispersed echelle that will provide a resolving power of 20,000 with a slit width of 0.15 arcsec and two-pixel sampling. The camera section serves as a slit viewer and as a camera with two pixel scales, 0.022 arcsec/pixel and 0.060 arcsec/pixel. Grisms providing 400-1400 resolving power will be available. Each section will utilize an ALADDIN II 1024 X 1024 InSb array. The instrument specifications are optimized for 2.2 micrometers using the adaptive optics and the tip-tilt secondary systems of the Subaru Telescope.
We discuss the main design features of the Gemini Near-IR Imager (NIRI) and its scientific capabilities. NIRI is designed to fully exploit the excellent image quality and low telescope emissivity expected from the Gemini telescope on Mauna Kea. It offers a range of pixel scales matched to different scientific objectives and has spectroscopic as well as polarimetric capabilities. One of its main design features is the use of a near-IR 2 X 2 Shack-Hartmann wavefront sensor for tip-tilt and focus control.
The Space IR Telescope Facility (SIRTF) contains three focal plane instruments, one of which is the IR Array Camera (IRAC). IRAC is a four-channel camera that provides simultaneous 5.12 X 5.12 arcmin images at 3.6, 4.5, 5.8 and 8 microns. The pixel size is 1.2 arcsec in all bands. Two adjacent fields of view in the SIRTF focal plane are viewed by the four channels in pairs. All four detector arrays in the camera are 256 by 256 pixels in size, with the two short wavelength channels using InSb and the two longer wavelength channels using Si:As IBS detectors. The IRAC sensitivities at 3.6, 4.5, 5.8, and 8.0 microns are 6, 7, 36, and 54 microJanskys, respectively. Two of the most important scientific objectives of IRAC will be to carry out surveys to study galaxy formation and evolution during the early stage of the Universe, and to search for brown dwarfs and superplanets.
The IR Camera and Spectrograph for the Subaru telescope uses a series of reflective and transmissive slits. The width of the slits ranges from 48 micrometers to 440 micrometers . The requirements for both types of slits include sharp edge definition, good surface figure at cryogenic temperature and high reflectivity. Several different substrate materials and fabrication methods were investigated. The substrate materials considered include aluminum, copper, tungsten carbide, chromium carbide, and sapphire. The fabrication methods investigated include photo-etching micro machining using UV laser, electroforming, diamond turning, conventional polishing and electrical-discharge-machining. The pros and cons of each material and fabrication method will be described.
KEYWORDS: Signal processing, Sensors, Digital signal processing, Cameras, Electrons, Field effect transistors, Telescopes, Clocks, Filtering (signal processing), Astronomy
MIRAC2 was built for ground-based astronomy at Steward Observatory, University of Arizona and Harvard-Smithsonian Center for Astrophysics. It utilizes a Rockwell HF-16 128 X 128 arsenic-doped silicon blocked-impurity-band hybrid array with a wavelength range of 2 to 28 micrometers operating in a liquid helium-cooled cryostat at 5K. Reflective optics, and externally actuated detector and pupil slides provide a variety of magnification and focal ratio settings without opening the cryostat. Nominal settings at the NASA IRTF and UKIRT give diffraction-limited imaging with .34 and .27 arcsec/pixel, respectively. The sensitivity on the IRTF at 11.7 micrometers , 10 percent bandwidth filter, chop-nod, source in one beam, 1 sigma, one minute total time is 25 mJ/arcsec surface brightness and 43 mJy point source.
We have successfully used nulling interferometry at 10 μm wavelength to interferometrically suppress a star's radiation. This technique was first proposed by Bracewell 20 years ago to image extra-solar planets and is now the basis for proposed space-borne instruments to search for Earth-like extra-solar planets and their spectroscopic signatures of habitability and life. In our experiment, the beams from two 1.8 m telescopes of the Multiple Mirror Telescope were brought into registration at a semi-transparent beamsplitter, and the images made coincident on an infrared array detector capable of taking rapid short exposure images. The atmospheric fluctuations caused the phase difference between the beams to fluctuate, changing the total flux of the star seen in the image plane. When the atmosphere caused the wavefronts to be exactly out of phase the entire stellar Airy pattern disappeared. For the unresolved star α Tauri the cancellation was such that a companion only 0.2 arcsec from the star and 25 times fainter would appear equal in intensity to the nulled star. The residual flux was spread into a wide halo suggesting the cause of this flux was imperfect cancellation of the aberrated wavefronts. To increase the precision of nulling beyond this first step several sources of error need to be addressed. We discuss the control of errors due to amplitude, polarization, chromatic differences, stellar leak, and sampling time. Improvements such as active phase tracking, adaptive optics, and cooled optics will increase the achievable gain of nulling interferometry and allow it to be used on fainter objects.
The infrared instrumentation plan for the Subaru telescope is described. Four approved infrared instruments and one test observation system are now in the construction phase. They are coronagraph imager using adaptive optics (CIAO), cooled mid- infrared camera and spectrograph (COMICS), infrared camera and spectrograph (IRCS), OH-airglow suppressor spectrograph (OHS) and mid-infrared test observation system (MIRTOS). Their performance goals and construction schedules are summarized. The plan for procurement and evaluation of infrared arrays required by these instruments is briefly described.
The first prototype of a HgCdTe infrared detector array with 1024 X 1024 pixels developed by the Rockwell International Science Center has been tested in a new infrared camera at the UH 2.2 m telescope, the 0.6 m telescope, and the CFHT. At the 2.2 m tests were conducted both at f/31, where images of very high resolution were obtained using tip-tilt correction, and at f/10 for a wide field of view. At the CFHT both wide field imaging (f/8) and adaptive optics work was done. The HAWAII (HgCdTe astronomical wide area infrared imager) prototype device achieved very good performance. In the camera system, a double correlated readnoise of 15 e- rms was achieved. The dark current at 1 V bias could be confirmed to be below 1 e-, even though the device was operated above 77 K. The quantum efficiency is slightly below 50% and shows the wavy pattern characteristic of LPE-grown HgCdTe. The full well capacity is above 105 e- at 1 V bias, limited in our system by the dynamic range of the A/D converter. Data reduction is practically identical to what is used for NICMOS3 256 X 256 devices. Combined integration times of more than 1 hour have been used and demonstrate that the HAWAII devices are suitable for very deep imaging. The residual excess dark current problem known from NICMOS3 devices is not fully resolved. However, it appears less serious in our first HAWAII prototype device.
The Gemini Infrared Imager is a 1 - 5.5 micrometers general purpose camera to be built by the Institute for Astronomy for the Gemini Telescope on Mauna Kea, Hawaii. The camera will provide both high spatial resolution and wide field modes, and support spectroscopic, coronographic, and polarimetric capabilities. The camera project is currently in its preliminary design phase. We present the results of the conceptual design study.
The MegaCam is a multi-purpose, wide-field, two-color camera being designed for use at the UH 2.2m telescope. The camera will utilize a Rockwell 1024 x 1024 HgCdTe detector array for 1-2.5 micrometers imaging, and a 2048 x 4096 frame-store CCD (2048 x 2048 active area) for optical imaging. The optics are based on a modified Offner relay design with additional lenses to give a 2:1 magnification in the infrared channel for a field of view of 5'.8 x 5'.8 (0.34 arcsec/pixel) using the f/10 telescope secondary, or a scale of 1'.9 x 1'.9 (0.15 arcsec/pixel) at f/31. This design provides a simple, high-throughput, and compact optical layout. A beamsplitter is placed in front of the IR optics at a low angle of incidence to form the optical image at 1:1 magnification on the CCD, for a field of view of 4'.7 x 4'.7 and 1'.5 x 1'.5 at f/10 and f/31, respectively. The optics and filters are to be housed in a LN2-cooled dewar. The CCD and IR arrays will be operated with modified SDSU-design controllers. The user interface will have several modes to make simultaneous optical/IR imaging simple to configure and perform at the telescope.
The optical design of a general-purpose 1 to 5 micrometers cryogenic IR camera and spectrograph (IRCS) for the 8.2-m Subaru telescope is described. The camera section serves the essential purpose of a slit-viewer in order to permit efficient use of the spectrograph on faint objects. It will also serve as a multipurpose IR camera. The spectrograph section will have a resolving power of (lambda) /(Delta) (lambda) equals 660 to 1600. 1 to 2.5 micrometers or 3 to 5 micrometers will be observed in a single exposure by using gratings and cross-dispersing prism combinations. The slit length will be 3 to 5'. The camera section will have 3 pixel scales (0'.030, 0'.056, and 0'.125) that provide high spatial imaging, 1:1 imaging (high throughput), and `wide-field' (about 2' X 2'). The spectrograph section will have 2 pixel scales: 0'.05/pixel and 0'.125/pixel. The important features of the IRCS are: (1) Two pixel scales are available, one matched to the tip-tilt secondary and the other matched to the adaptive optics system. (2) Switching between imaging and spectroscopic modes is possible. Therefore observational programs can be optimized for the seeing, availability of guide stars, and weather conditions. (3) In some cases deep imaging can be undertaken while long exposures are made in the spectroscopic mode.
KEYWORDS: Sensors, Signal processing, Telescopes, Cameras, Optical filters, Space telescopes, Infrared detectors, Digital signal processing, Electronics, Signal detection
MIRAC is a Mid InfraRed Array Camera built for ground-based astronomy by Steward Observatory at the University of Arizona, Harvard Smithsonian Center for Astrophysics, and the Center for Advanced Space Sensing at the Naval Research Laboratory. It utilizes a Hughes Aircraft Co. 20 X 64 pixel arsenic-doped silicon impurity band conduction hybrid array with a capacitance transimpedance amplifier readout (CRC 444A) operating at 10 K in a liquid helium-cooled cryostat. It has an operating wavelength range of 2 to 26 micrometers . Using 20 parallel readout lines and frame rate of 10 KHz, the array exhibits both low noise and good linearity at high background flux, which is essential for 10 and 20 micrometers ground-based observing conditions. It has a peak quantum efficiency of 0.42 at 22 micrometers , and a well size of 120,000 electrons. MIRAC has been operated on the Steward Observatory 2.3-meter and NASA 3-meter IRTF telescopes a number of times for observing a variety of objects including infrared-luminous galaxies, planetary nebulae, star forming regions, and young stellar objects. The NEFD of MIRAC on the IRTF at 11.7 micrometers is 0.1 Jy/square-arcsec in one second of integration on-source, four seconds total time, including nodding and chopping off-source.
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