The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small (~1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (< 10−3 events per star per year) and short in duration (~200 ms), so many stars must be monitored at a high readout cadence in order to detect events. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astronomico Nacional at San Pedro Martir in Baja California, Mexico. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz. Construction of the site began in the fall of 2013, and the survey will begin by the end of 2018. This paper describes the observing system and provides an update on the status of the survey infrastructure.
The Transneptunian Automated Occultation Survey (TAOS II) is a three robotic telescope project to detect the stellar occultation events generated by TransNeptunian Objects (TNOs). TAOS II project aims to monitor about 10000 stars simultaneously at 20Hz to enable statistically significant event rate. The TAOS II camera is designed to cover the 1.7 degrees diameter field of view of the 1.3m telescope with 10 mosaic 4.5k×2k CMOS sensors. The new CMOS sensor (CIS 113) has a back illumination thinned structure and high sensitivity to provide similar performance to that of the back-illumination thinned CCDs. Due to the requirements of high performance and high speed, the development of the new CMOS sensor is still in progress. Before the science arrays are delivered, a prototype camera is developed to help on the commissioning of the robotic telescope system. The prototype camera uses the small format e2v CIS 107 device but with the same dewar and also the similar control electronics as the TAOS II science camera. The sensors, mounted on a single Invar plate, are cooled to the operation temperature of about 200K as the science array by a cryogenic cooler. The Invar plate is connected to the dewar body through a supporting ring with three G10 bipods. The control electronics consists of analog part and a Xilinx FPGA based digital circuit. One FPGA is needed to control and process the signal from a CMOS sensor for 20Hz region of interests (ROI) readout.
The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small (~1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (< 10−3 events per star per year) and short in duration (~200 ms), so many stars must be monitored at a high readout cadence. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astronómico Nacional at San Pedro Mártir in Baja California, México. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz. Construction of the site began in the fall of 2013, and the survey will begin in the summer of 2017.
The Transneptunian Automated Occultation Survey (TAOS II) is a three robotic telescope project to detect the stellar
occultation events generated by Trans Neptunian Objects (TNOs). TAOS II project aims to monitor about 10000 stars
simultaneously at 20Hz to enable statistically significant event rate. The TAOS II camera is designed to cover the 1.7
degree diameter field of view (FoV) of the 1.3m telescope with 10 mosaic 4.5kx2k CMOS sensors. The new CMOS
sensor has a back illumination thinned structure and high sensitivity to provide similar performance to that of the backillumination thinned CCDs. The sensor provides two parallel and eight serial decoders so the region of interests can be
addressed and read out separately through different output channels efficiently. The pixel scale is about 0.6"/pix with the
16μm pixels. The sensors, mounted on a single Invar plate, are cooled to the operation temperature of about 200K by a
cryogenic cooler. The Invar plate is connected to the dewar body through a supporting ring with three G10 bipods. The
deformation of the cold plate is less than 10μm to ensure the sensor surface is always within ±40μm of focus range. The
control electronics consists of analog part and a Xilinx FPGA based digital circuit. For each field star, 8×8 pixels box
will be readout. The pixel rate for each channel is about 1Mpix/s and the total pixel rate for each camera is about
80Mpix/s. The FPGA module will calculate the total flux and also the centroid coordinates for every field star in each
We report the testing result of e2v CIS 107 CMOS sensor for temperature from 300K to 170K. The CIS 107 sensor is a prototype device with 10 different variations of pixel designs. The sensor has 1500 × 2000, 7 μm pixels with 4 outputs. Each variation covers 1500 × 200 pixels. These are 4T pixels with high resistivity epitaxial silicon and back thinned to 11μm. At room temperature, the several variants of pixels show peak QE higher than 90%, readout noise around 5e- and dark current around 50e-/s/pix. The full well is about 15000 e- due to the limitation of the transfer gate capacitor. The CIS 107 device was further characterized at different device temperatures from 170K to 300K. The readout noise decreases and the full well increases as the device is operated at lower temperature.
The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small (~1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (< 10-3 events per star per year) and short in duration (~200 ms), so many stars must be monitored at a high readout cadence. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astronómico Nacional at San Pedro Mártir in Baja California, México. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz. Construction of the site began in the fall of 2013.
We present the design and lab performance of the Parallel Imager for Southern Cosmology Observations (PISCO), a photometer for the 6.5 m diameter Magellan telescopes that produces gl, rl, il, and zl band images simulta- neously within a 9 arcminute field of view. This design provides efficient follow-up observations of faint sources, particularly galaxy clusters and supernovae. Simultaneous imaging speeds the observing cadence by at a factor
of ~ 3 (including optical losses) compared to other photometric imagers. Also, the determination of color (flux
ratio between bands) is relatively immune to time variations in gray opacity due to clouds, so observations can
proceed in less than optimal conditions. First light is expected in September 2014 2014.
NIRMOS (Near-Infrared Multiple Object Spectrograph) is a 0.9 to 2.5 μm imager/spectrograph concept proposed for the
Giant Magellan Telescope1 (GMT). Near-infrared observations will play a central role in the ELT era, allowing us to
trace the birth and evolution of galaxies through the era of peak star formation. NIRMOS' large field of view, 6.5′ by
6.5′, will be unique among imaging spectrographs developed for ELTs. NIRMOS will operate in Las Campanas' superb
natural seeing and is also designed to take advantage of GMT's ground-layer adaptive optics system. We describe
NIRMOS' high-performance optical and mechanical design.
We have found a commercially-available ethernet interface module with sufficient on-board resources to largely handle
all timing generation tasks required by digital imaging systems found in astronomy. In addition to providing a high-bandwidth
ethernet interface to the controller, it can largely replace the need for special-purpose timing circuitry.
Examples for use with both CCD and CMOS imagers are provided.
The TAOS II Project requires high-speed differential photometry of 10-20 thousand stars over a telescope field of
154mm diameter with 16-micron spatial resolution and good noise performance. We are developing a custom CMOS
imager array to accomplish this task.
The f/5 instrumentation suite for the Clay telescope was developed to provide the Magellan Consortium observer community with wide field optical imaging and multislit NIR spectroscopy capability. The instrument suite consists of several major subsystems including two focal plane instruments. These instruments are Megacam and MMIRS. Megacam is a panoramic, square format CCD mosaic imager, 0.4° on a side. It is instrumented with a full set of Sloan filters. MMIRS is a multislit NIR spectrograph that operates in Y through K band and has long slit and imaging capability as well. These two instruments can operate both at Magellan and the MMT. Megacam requires a wide field refractive corrector and a Topbox to support shutter and filter selection functions, as well as to perform wavefront sensing for primary mirror figure correction. Both the corrector and Topbox designs were modeled on previous designs for MMT, however features of the Magellan telescope required considerable revision of these designs. In this paper we discuss the optomechanical, electrical, software and structural design of these subsystems, as well as operational considerations that attended delivery of the instrument suite to first light.
The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small ( 1 km diameter) objects in the Solar System and beyond. Such events are very rare (< 10−3 events per star per year) and short in duration ( 200 ms), so many stars must be monitored at a high readout cadence. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astron´omico Nacional at San Pedro Martir in Baja California, Mexico. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz.
The Kepler Mission is designed to detect the 80 parts per million (ppm) signal from an Earth-Sun equivalent
transit. Such precision requires superb instrument stability on time scales up to 2 days and systematic error
removal to better than 20 ppm. The sole scientific instrument is the Photometer, a 0.95 m aperture Schmidt
telescope that feeds the 94.6 million pixel CCD detector array, which contains both Science and Fine Guidance
Sensor (FGS) CCDs. Since Kepler's launch in March 2009, we have been using the commissioning and science
operations data to characterize the instrument and monitor its performance. We find that the in-flight detector
properties of the focal plane, including bias levels, read noise, gain, linearity, saturation, FGS to Science crosstalk,
and video crosstalk between Science CCDs, are essentially unchanged from their pre-launch values. Kepler's
unprecedented sensitivity and stability in space have allowed us to measure both short- and long- term effects from
cosmic rays, see interactions of previously known image artifacts with starlight, and uncover several unexpected
systematics that affect photometric precision. Based on these results, we expect to attain Kepler's planned
photometric precision over 90% of the field of view.
We present characterization methods and results on a number of new devices produced specifically to address LSST's
performance goals, including flatness, QE, PSF, dark current, read noise, CTE, cosmetics, and crosstalk. The results
indicate that commercially produced, thick n-channel over-depleted CCDs with excellent red response can achieve tight
PSF at moderate applied substrate bias with no evidence of persistent image artifacts. We will also report ongoing
studies of mosaic assembly techniques to achieve chip-to-chip
co-planarity, high fill factor, and thermal stability.
The Smithsonian Widefield Infrared Camera (SWIRC) is a Y -, J-, and H-band imager for the f/5 MMT.
Proposed in May 2003 and commissioned in June 2004, the goal of the instrument was to deliver quickly a wide
field-of-view instrument with minimal optical elements and hence high throughput. The trade-off; was to sacrifice
K-band capability by not having an internal, cold Lyot stop. We describe SWIRC's design and capabilities, and
discuss lessons learned from the thermal design and the detector mount, all of which have been incorporated into
the upcoming MMT & Magellan Infrared Spectrograph.
The LSST camera focal plane array will consist of individual Si sensor modules, each 42×42mm2 in size, that are
assembled into 3×3 "raft" structures, which are then assembled into the final focal plane array. It is our responsibility at
Brookhaven National Lab (BNL) to insure that the individual sensors provided by the manufacturer meet the flatness
requirement of 5 μm PV and that the assembled raft structure be within the 6.5 μm PV flatness tolerance. These
tolerances must be measured with the detectors operating in a cryogenic environment at -100C in a face-down
configuration. Conventional interferometric techniques for flatness testing are inadequate to insure that edge
discontinuities between detector elements are within the tolerances because of the quarter-wave phase ambiguity
problem. For this reason we have chosen a combination of metrology techniques to solve the discontinuity ambiguity
problem that include both a full aperture interferometer and a scanning confocal distance microscope. We will discuss
concepts for performing flatness metrology testing with these instruments under these conditions and will present
preliminary results of measurement sensitivity and repeatability from tests performed on step height artifacts.
Science studies made by the Large Synoptic Survey Telescope will reach systematic limits in nearly all cases. Requirements for accurate photometric measurements are particularly challenging. Advantage will be taken of the rapid cadence and pace of the LSST survey to use celestial sources to monitor stability and uniformity of photometric data. A new technique using a tunable laser is being developed to calibrate the wavelength dependence of the total telescope and camera system throughput. Spectroscopic measurements of atmospheric extinction and emission will be made continuously to allow the broad-band optical flux observed in the instrument to be corrected to flux at the top of the atmosphere. Calibrations with celestial sources will be compared to instrumental and atmospheric calibrations.
Sensors for the LSST camera require high quantum efficiency (QE) extending into the near-infrared. A relatively large thickness of silicon is needed to achieve this extended red response. However, thick sensors degrade the point spread function (PSF) due to diffusion and to the divergence of the fast f/1.25 beam. In this study we examine the tradeoff of QE and PSF as a function of thickness, wavelength, temperature, and applied electric field for fully-depleted sensors. In addition we show that for weakly absorbed long-wavelength light, optimum focus is achieved when the beam waist is positioned slightly inside the silicon.
The LSST project has embarked on an aggressive new program to develop the next generation of silicon imagers for the visible and near-IR spectral regions. In order to better understand and solve some of the technology issues prior to development and mass-production for the huge LSST focal plane, a number of contracts have been written to imager firms to explore specific areas of technology uncertainty. We expect that these study contracts will do much toward reducing risk and uncertainty going into the next phase of development, the prototype production of the final large LSST imager.
The Kepler Mission is a search for terrestrial planets specifically designed to detect Earth-size planets in the habitable zones of solar-like stars. In addition, the mission has a broad detection capability for a wide range of planetary sizes, planetary orbits and spectral types of stars. The mission is in the midst of the developmental phase with good progress leading to the preliminary design review later this year. Long lead procurements are well under way. An overview in all areas is presented including both the flight system (photometer and spacecraft) and the ground system. Launch is on target for 2007 on a Delta II.
We present the preliminary design for the MMT and Magellan Infrared
Spectrograph (MMIRS). MMIRS is a fully refractive imager and multi-object spectrograph that uses a 2048x2048 pixel Hawaii2 HgCdTe array. It offers a 7'x7' imaging field of view and a 4'x7' field of view for multi-object spectroscopy. Dispersion is provided by a set of 5 grisms providing R=3000 at J, H, or K, or R=1300 in J+H or H+K.
In 2003, the converted MMT’s wide-field f/5 focus was commissioned. A 1.7-m diameter secondary and a large refractive corrector offer a 1° diameter field of view for spectroscopy and a 0.5° diameter field of view for imaging. Stellar images during excellent seeing are smaller than 0.5" FWHM across the spectroscopic field of view, and smaller than 0.4" across the imaging field of view. Three wide-field f/5 instruments are now in routine operation: Hectospec (an R~1000 optical spectrograph fed by 300 robotically-positioned optical fibers), Hectochelle (an R~40,000 optical spectrograph fed by the same fibers), and Megacam (a 340 megapixel, 36 CCD optical imager covering a 25' by 25' format).
NASA's Kepler Mission is designed to determine the frequency of Earth-size and larger planets in the habitable zone of solar-like stars. It uses transit photometry from space to determine planet size relative to its star and orbital period. From these measurements, and those of complementary ground-based observations of planet-hosting stars, and from Kepler's third law, the actual size of the planet, its position relative to the habitable zone, and the presence of other planets can be deduced. The Kepler photometer is designed around a 0.95 m aperture wide field-of-view (FOV) Schmidt type telescope with a large array of CCD detectors to continuously monitor 100,000 stars in a single FOV for four years. To detect terrestrial planets, the photometer uses differential relative photometry to obtain a precision of 20 ppm for 12th magnitude stars. The combination of the number of stars that must be monitored to get a statistically significant estimate of the frequency of Earth-size planets, the size of Earth with respect to the Sun, the minimum number of photoelectrons required to recognize the transit signal while maintaining a low false-alarm rate, and the areal density of target stars of differing brightness are all critical to the photometer design.
The primary goal of Kepler, a recently selected Discovery mission, is to search for terrestrial size planets orbiting other stars using the transit method. To accomplish this goal, a space-based photometer is being developed that employs a 0.95-meter Schmidt camera incorporating a large focal plane array (FPA). The FPA is populated with 42 large format custom CCD detectors with integral field flattening optics covering a 100 square degree field of view. The FPA will measure the precise relative intensity of approximately 100,000 main sequence stars nearly continuously over the mission's 4-year lifetime to search for the small changes caused by planetary transits. All critical electronics are housed immediately behind the FPA, which yields a low noise compact design that is both robust and fault tolerant. The design and development of the FPA, its detectors, its main systems issues, and their relationship to photometric precision will be discussed along with results from detailed performance models.
The Hectochelle will be a fiber-fed, multi-object spectrograph for the post-conversion MMT which will take 255 simultaneous spectra at a resolution of 32,000 - 40,000. The absolute efficiency, including optical fiber losses, is predicted to be 6% - 10%, depending on the position of a line within a diffractive order. In one hour, features with 60 mangstrom should be resolved in mR equals 18 stars with a signal to noise of 10.
The S.A.O. Megacam focal plane will consist of 36 large CCDs (2 K X 4.5 K format), each with 2 output ports running at pixel rates up to 200 kHz. The unbinned data field is thus as large as 324 megawords and is presented at a sustained data rate during readout approaching 28 megabytes/sec. We have developed a simple camera controller to deal with the problem of handling so many channels and their digitized outputs at fairly high speeds. We also present some results from ongoing efforts to optimize the 200 kHz signal processing chain for low noise and low crosstalk.
Megacam is a 36 CCD mosaic camera that will cover a 24' X 24' field of view at the f/5 wide-field focus of the converted 6.5 m Multiple Mirror Telescope. The mosaic is a 9 X 4 array of thinned 2048 X 4068 pixel CCDs with 13.5 micrometer pixels. The CCDs are dual-output EEV devices in a custom package to allow the devices to be closely butted on all four sides. The dewar will be mounted to a 2 m diameter assembly that contains the filter wheels (for 30 X 30 cm filters) and the shutter. Telescope guiding will be accomplished with two additional CCDs mounted at the edges of the focal plane. The guider CCDs will be operated slightly defocused, one on either side of focus, to allow simultaneous focusing and guiding. Guide stars will be selected by reading out the full guider frame, after which only a small area surrounding the guide star will be read out. Our simulations show that the defocused guide star images will also be useful for low order wavefront sensing, allowing corrections to the telescope collimation. We are developing a new CCD controller capable of reading the full Megacam in 24 seconds. This controller will also be used to operate the guide chips.
The conversion of the Multiple Mirror Telescope from six 1.8 m primary mirrors to a single 6.5 m primary will significantly increase its capability for imaging. The f/5 configuration will provide a corrected field of view for imaging that is flat and 30 arcminutes in diameter. The image quality in the absence of atmospheric seeing is 0'.1 over the full field. We are currently designing a camera system to take advantage of this large field. The proposed direct imaging system will be located at the Cassegrain focus of the telescope, behind a three-element refractive corrector. We will use an array of 8 X 4 three-edge-buttable CCDs, each with 2048 X 4096 pixels and two output amplifiers. This will provide a field of view of 24' X 24'. With a new packaging scheme we will reduce the gap along the readout edge to a few millimeters. The pixel size is 15 microns, or 0'.09, well sampling the point-spread- function. In many applications it will be possible to bin the pixels, thus reducing the amount of data (500 Mb per read at full resolution). The back-illuminated CCDs will be thinned and anti- reflection coated to provide high quantum efficiency from 320 to 1000 nm. The camera system will be useful for many studies requiring both a large collecting area and large area coverage on the sky. Planned projects include redshift and photometric surveys of faint galaxies, searches for high-redshift quasars and searches for objects in the outer solar system.
We describe the design of an ultra-format, 8192 x 8192 pixel CCD mosaic imager under construction for the Mauna Kea Observatory. The mosaic will be built from a 4 x 2 array of 3-edge-buttable 2048 x 4096 15 micrometers pixel CCDs fabricated by Loral Fairchild. We outline the scientific justification for such a mosaic and the technical details of the 3-edge-buttable 2048 x 4096 CCD design. We also present our strategy for imager packaging and subsequent mosaic construction which will result in a mosaic with individual elements that can easily be installed and removed. This particular CCD mosaic is intended for two existing MKO telescopes: the UH 2.2 m and the CFHT 3.6m. In either configuration, the imager will offer an enormous field of view with excellent spatial sampling.
A series of small rapid-framing CCD designs have been designed, fabricated, and tested for use as adaptive optics sensors for laser guide star image correction. To reduce video bandwidth and thus minimize readout noise, these CCD's employ 16 output amplifiers. Designs with 2 different formats (64 X 64 and 128 X 128) and with three different output amplifiers structures have been produced.
CCDs having circular rather than rectilinear symmetry offer some advantages for low-order wavefront sensing. A series of imagers having 24 sectors and 12 radial zones (plus frame store) has been developed. Three different output structures have been utilized in order to investigate low-noise operational limits.
Several large-format CCDs have been designed and are in process at the Loral Aeronutronics fabrication plant. One is an edge-buttable 2048 X 2048 device that will allow a 2 X 2 array to be formed with an imaging area measuring more than 61 mm on a side and with only 400 microns dead space between arrays. Another is a 3072 X 1024 CCD with both floating diffusion and non-destructive read floating gate amplifiers. Also included are smaller arrays of 2688 X 512 and 1200 X 800 in the chords of the wafers. All of these designs were accomplished by a non-specialist scientist using AutoCAD on an inexpensive PC, a level of customer interaction with CCD manufacturing not previously available.
Results obtained in fabricating and testing of large CCD image sensors are reported. The emphasis is on high quantum efficiency, excellent charge transfer efficiency at low signal level, large pixel count, low readout noise, and very low dark current. The focus is on the use of the devices for optical astronomy where these parameters are most important. Test results for CCDs fabricated by Ford Aerospace and by EG Experiments to demonstrate the feasibility of a reproducible biased-gate using transparent indium tin oxide as a conducting layer over a silicon oxide insulating layer are discussed. Quantum efficiency of bias-gate thinned CCDs is compared with results obtained from a phosphor-coated front- illuminated CCD.
A large-format CCD imager to be used in a 2 X 2 mosaic array has been designed and fabricated. Each quadrant is an independent imager of 2048 X 2048 15 micrometers pixels, designed to be edge-butted on two sides. After sawing and mounting the individual dice in custom, buttable packages, the authors assembled a 4096 X 4096 mosaic array measuring more than 61 mm on a side with just 400 microns dead space between imaging areas. With this buttable package design, each quadrant of the mosaic can be separately tested, optimized, and, if necessary, replaced. Also described are smaller 2688 X 512 15 micrometers pixel CCD imagers designed for spectrographic applications that were fabricated using space in the chords of the same 100 mm silicon wafer containing the 2048 X 2048 edge-buttable devices.
A large-format CCD imager is described and tested. The CCD imager incorporates floating diffusion as well as floating gate amplifiers on a 2048 by 2048 format which was employed as the design base. The amplifiers are intended to allow repeated nondestructive read operations on individual pixels in the array. The serial register was separated into two independently clocked halves to permit simultaneous readout of all four quadrants of the imager. Extensive schematic layouts of the base model and modification are given. The results of a performance test are presented, showing good results in the cooling curve for average dark current, and for charge transfer characteristics. The amplifiers are intended to reduce net readout noise, and the simultaneous readout capability is intended to reduce total read time, although neither was fully tested. The large-format CCD imager is of interest for astronomical photography and spectroscopic applications.
Results of charge transfer efficiency and dark current tests for large Reticon and Ford CCDs are given, as well as a description of some experiments to improve the UV quantum efficiency, using a biased flash-gate for thinned CCDs and phosphor overlay for front-illuminated CCDs. The results indicate that large affordable CCDs suitable for astronomical work are now in reach, with excellent charge-handling characteristics, low dark current and readout noise and high quantum efficiency over the 300 nm to 1000 nm wavelength range. With buttable CCDs, whose production is planned for the future, even larger arrays of CCDs will be possible.