The Multi-spectral Visible Imaging Camera (MVIC) detector is a time-delay and integration (TDI) CCD with 4, 8, 16, 32, and 64 TDI modes. MVIC is scheduled to fly as part of the instrument suite on the Lucy mission to the Trojans launching in 2021. We present here the pre-delivery SwRI Detector Characterization Lab (SDCL) data of the Flight (FM) and Flight Spare (FS) from 370 to 925nm. The MVIC sensor consists of six broad-band top-hat filters on a single sapphire substrate developed by VIAVI Solutions and six CCDs on a single wafer developed by Semiconductor Technology Associates (STA). We have calibrated both the FS and FM for read noise, dark current, linearity, quantum efficiency, and total system throughput. The data were collected using standard Photon Transfer Curve techniques at strategically chosen wavelengths corresponding to center and edge of the bandpass filters. Each system was also calibrated for spuriously operational pixels and cosmetic defects. The pixel response function is mapped on a pixel-by-pixel basis for the 64 TDI mode.
SCORPIO is the next facility instrument for the Gemini South telescope at Cerro Pachon, Chile. SCORPIO’s main science driver is the detection and monitoring of faint time-domain events, in particular the follow-up of discoveries by the Vera C. Rubin Observatory, but it can also carry out with unique efficiency a large variety of astrophysical programs. The instrument has recently passed Critical Design Review and is now in its Assembly, Integration and Verification phase. In this paper we provide an updated overview of the final instrument design and the main performance parameters in light of the science drivers.
The SwRI Detector Characterization Lab (SDCL) was established in order to facilitate the rapid calibration of large numbers of detector arrays for upcoming ground and space missions. The SDCL is equipped with a McPherson monochromator with exchangeable gratings and light sources enabling wavelength coverage from 0.3 to 5.0 micron at sub nanometer resolution. The SDCL also has cryostats capable of maintaining thermal control of detector subassemblies and transfer optics to a precision of 0.1K at 77K and 0.01K at 4K. Using this calibration system, we have calibrated the EEM and ETU detector for read noise, dark current, modulation transfer function, quantum efficiency, cross talk, and total system throughput. The data were collected using standard Photon Transfer Curve techniques at the various wavelengths corresponding to the MVIC filter bandpasses. Here, we will present the data for the engineering unit, the methodology used to perform the calibration, and the steps forward for calibration of the flight unit.
We present the current status of the SCORPIO project, the facility instrument for Gemini South designed to perform follow up studies of transients in the LSST era while carrying out with unique efficiency a great variety of astrophysical programs. SCORPIO operates in the wavelength range 385-2350 nanometers, observing simultaneously in the grizYJHK bands. It can be used both in imaging (seeing limited) and spectroscopic (long-slit) mode, and thanks to the use of frame-transfer CCDs it can monitor variable sources with milli-second time-resolution. The project has recently passed PDR and is on schedule to be commissioned at the time of the LSST first light.
SCORPIO (Spectrograph and Camera for Observation of Rapid Phenomena in the Infrared and Optical) is the new workhorse instrument for the Gemini South Telescope in Chile. Originally proposed in response to the Gen4#3 solicitation, SCORPIO is a unique fast-multicolor imager and ultra-wide band spectrograph capable of rapid exposures for high time-resolution images and spectra. SCORPIO consists of 8 separate channels (corresponding to the standard wavebands g, r, i, z, Y, H, J, K) that can operate with different exposure times. Each channel can be used in imaging or long-slit mode, with independent readout timing. In this report we illustrate the detectors, the control systems, and the observing modes that will be available with SCORPIO.
OCTOCAM is an 8-channel VIS-IR (g to K-band) simultaneous imager and medium-resolution spectrograph proposed as new workhorse instrument for the 8m Gemini telescopes. It also offers additional observing modes of high time resolution, integral-field spectroscopy and spectropolarimetry, making it a very versatile instrument for many science cases in the 2020ies. A special focus of OCTOCAM will be the detection and follow-up of transient sources such as gamma-ray bursts, supernovae, magnetars, active galactic nuclei and yet to be discovered new objects, delivered by large-scale surveys like LSST available in the 2020ies. The diverse nature of transients will require the full range of OCTOCAM capabilities allowing more information in very short time about the source than with any other current instrument and adaptable almost in real time. Another main science topic will be to probe the high redshift Universe and the first stars for which OCTOCAM will be highly suited due to its wide wavelength coverage and high sensitivity. However, OCTOCAM is also suited for a large range of other science cases including transneptunian objects, exoplanets, stellar evolution and supermassive black holes. Our science team comprises more than 50 researchers reflecting the large interest of the Gemini community in the capabilities of OCTOCAM. We will highlight a few important science cases demonstrating the different capabilities of OCTOCAM and their need for the scientific community.
OCTOCAM has been proposed to the Gemini Observatory as a workhorse imager and spectrograph that will fulfill the needs of a large number of research areas in the 2020s. It is based on the use of high-efficiency dichroics to divide the incoming light in eight different channels, four optical and four infrared, each optimized for its wavelength range. In its imaging mode, it will observe a field of 3'x3' simultaneously in g, r, i, z, Y, J, H, and KS bands. It will obtain long-slit spectroscopy covering the range from 3700 to 23500 Å with a resolution of 4000 and a slit length of 3 arcminutes. To avoid slit losses, the instrument it will be equipped with an atmospheric dispersion corrector for the complete spectral range. Thanks to the use of state of the art detectors, OCTOCAM will allow high time-resolution observations and will have negligible overheads in classical observing modes. It will be equipped with a unique integral field unit that will observe in the complete spectral range with an on-sky coverage of 9.7"x6.8", composed of 17 slitlets, 0.4" wide each. Finally, a state-of-the-art polarimetric unit will allow us to obtain simultaneous full Stokes spectropolarimetry of the range between 3700 and 22000 Å.
Space and launch environments demand robust, low mass, and thermally insensitive mechanisms and optical mount designs. The rotating prism mechanism (RPM), a component of the stabilized dispersive focal plane system (SDFPS), is a spectral disperser mechanism that enables the SDFPS to deliver spectroscopic or direct imaging functionality using only a single optical path. The RPM is a redundant, vacuum-compatible, self-indexing, motorized mechanism that provides robust, athermalized prism mounting for two sets of matching prisms. Each set is composed of a BK7 and a CaF2 prism, both 70 mm in diameter. With the prism sets separated by 1 mm, the RPM rotates the two sets relative to one another over a 180° range, and maintains their alignment over a wide temperature range (190-308K). The RPM design incorporates self-indexing and backlash prevention features as well as redundant motors, bearings, and drive trains. The RPM was functionally tested in a thermal vacuum chamber at 210K and <1.0x10-6 mbar, and employed in the top-level SDFPS system testing. This paper presents the mechanical design, analysis, alignment measurements, and test results from the prototype RPM development effort.
As the costs of space missions continue to rise, the demand for compact, low mass, low-cost technologies that maintain
high reliability and facilitate high performance is increasing. One such technology is the stabilized dispersive focal plane
system (SDFPS). This technology provides image stabilization while simultaneously delivering spectroscopic or direct
imaging functionality using only a single optical path and detector. Typical systems require multiple expensive optical
trains and/or detectors, sometimes at the expense of photon throughput. The SDFPS is ideal for performing wide-field
low-resolution space-based spectroscopic and direct-imaging surveys. In preparation for a suborbital flight, we have
built and ground tested a prototype SDFPS that will concurrently eliminate unwanted image blurring due to the lack of
adequate platform stability, while producing images in both spectroscopic and direct-imaging modes. We present the
overall design, testing results, and potential scientific applications.
The JANUS mission concept is designed to study the high redshift universe using a small, agile Explorer class
observatory. The primary science goals of JANUS are to use high redshift (6<z<12) gamma ray bursts and quasars to
explore the formation history of the first stars in the early universe and to study contributions to reionization. The X-Ray
Coded Aperture Telescope (XCAT) and the Near-IR Telescope (NIRT) are the two primary instruments on JANUS.
XCAT has been designed to detect bright X-ray flashes (XRFs) and gamma ray bursts (GRBs) in the 1-20 keV energy
band over a wide field of view (4 steradians), thus facilitating the detection of z>6 XRFs/GRBs, which can be further
studied by other instruments. XCAT would use a coded mask aperture design with hybrid CMOS Si detectors. It would
be sensitive to XRFs and GRBs with flux in excess of approximately 240 mCrab. In order to obtain redshift
measurements and accurate positions from the NIRT, the spacecraft is designed to rapidly slew to source positions
following a GRB trigger from XCAT. XCAT instrument design parameters and science goals are presented in this paper.
Gamma-ray bursts (GRBs) provide extremely luminous background light sources that can be used to study the
high redshift universe out to z ~ 12. Identification of high-z GRBs has been difficult to date because no good
high-z indicators have been found in the prompt or afterglow emission of GRBs, so ground-based spectroscopic
observations are required. JANUS is an Explorer mission that incorporates a GRB locator and a near-IR
telescope with low resolution spectroscopic capability so that it can measure the redshifts of GRBs immediately
after their discovery. It is expected to discover 50 GRBs with z > 5 as well as hundreds of high redshift quasars.
JANUS will facilitate study of the reionization phase, star formation, and galaxy formation in the very early
universe. Here we discuss the mission design and status.
JANUS is a NASA small explorer class mission which just completed phase A and was intended for a 2013 launch date.
The primary science goals of JANUS are to use high redshift (6<z<12) gamma ray bursts and quasars to explore the
formation history of the first stars in the early universe and to study contributions to reionization. The X-Ray Flash
Monitor (XRFM) and the Near-IR Telescope (NIRT) are the two primary instruments on JANUS. XRFM has been
designed to detect bright X-ray flashes (XRFs) and gamma ray bursts (GRBs) in the 1-20 keV energy band over a wide
field of view (4 steradians), thus facilitating the detection of z>6 XRFs/GRBs, which can be further studied by other
instruments. XRFM would use a coded mask aperture design with hybrid CMOS Si detectors. It would be sensitive to
XRFs/GRBs with flux in excess of approximately 240 mCrab. The spacecraft is designed to rapidly slew to source
positions following a GRB trigger from XRFM. XRFM instrument design parameters and science goals are presented in
The Ultraviolet and Optical telescope (UVOT) on board the SWIFT observatory, plays an important part in the quest to understand gamma-ray bursts. As its name suggests, the UVOT obtains ultraviolet and optical data at high time resolution, with 7 broad band filters and 2 low resolution grisms. This paper forms the second of a pair of papers presenting the initial on-board calibration of the UVOT. The first one (Part 1) deals with distortion, large and small scale sensitivity variations and the telescope point spread function. In this paper we cover the following topics: the photometry of the broadband filters including colour transformations and linearity; the wavelength calibration and sensitivities of the grisms; time resolution and red leak.
The Ultraviolet and Optical telescope (UVOT) is one of the three instruments on board of the SWIFT observatory. UVOT is on the cutting edge of our ability to observe and eventually help scientists to understand gamma-ray bursts. As any space-based telescope it requires both pre-flight and on-orbit calibrations. This paper is the first of a pair of papers presenting the initial on-board calibration of the UVOT. In particular, we'll discuss distortion, large and small scale sensitivity variations and the telescope point spread function.
The Swift Gamma Ray Burst Explorer, chosen in October 1999 as NASA's next MIDEX mission, is now scheduled for launch in October 2004. SWIFT carries three complementary instruments. The Burst Alert Telescope (BAT) identifies gamma-ray bursts (GRBs) and determines their location on the sky to within a few arc-minutes. Rapid slew by the fast-acting SWIFT spacecraft points the two narrow field instruments, an X-ray Telescope (XRT) and an Ultraviolet/Optical Telescope (UVOT), to within the BAT error circle within 70 seconds of a BAT detection. The XRT can determine burst locations to within 5 arc-seconds and measure X-ray spectra and photon flux, whilst the UVOT has a sensitivity down to 24th magnitude and sub arc-second positional accuracy in the optical/uv band. The three instruments combine to make a powerful multi-wavelength observatory with the capability for rapid determination of GRB positions to arc-second accuracy within a minute or so of their discovery, and the ability to measure light-curves and red-shifts of the bursts and after-glows. The paper summarises the mission's readiness for October's launch and operations.
The Swift/UVOT is a 30-cm aperture imaging telescope that is sensitive to photons in the wavelength range 170nm-600nm and is designed to provide near-ultraviolet and optical measurements of γ-ray bursts and other targets that the Swift observatory observes. The performance of the telescope and its photon counting detectors has been assessed in a series of calibration measurements made under vacuum conditions in a test facility at the Goddard Space Flight Center. We describe some of the results of this campaign, including measurements of the instrument throughput, image quality and distortion, and linearity of response. We also describe the spectroscopic capability of the instrument, which is enabled by the use of two grisms operating in the UV and optical bands respectively. The results from the ground calibration activities will form the basis for establishing the full calibration matrix of the instrument once on orbit.
The UV/optical telescope (UVOT) is one of three instruments flying aboard the Swift Gamma-ray Observatory. It is designed to capture the early (~1 minute) UV and optical photons from the afterglow of gamma-ray bursts as well as long term observations of these afterglows. This is accomplished through the use of UV and optical broadband filters and grisms. The UVOT has a modified Ritchey-Chretien design with micro-channel plate intensified charged-coupled device detectors that provide sub-arcsecond imaging. Unlike most UV/optical telescopes the UVOT can operate in a photon-counting mode as well as an imaging mode. We discuss some of the science to be pursued by the UVOT and the overall design of the instrument.
We have been working on the design of a wide-field, short focal length, grazing incidence mirror shell set with a desired rms image spot size of 15 arcsec. The baseline design consists of Wolter I type mirror shells with polynomial perturbations applied to the baseline design. The overall optimization technique is to efficiently optimize the polynomial coefficients that directly influence the angular resolution without stepping through the entire multi-dimensional coefficient space. We have previously investigated the use of Response Surface Designs and Artificial Neural Networks as a means for optimizing the polynomial coefficients. The results have been published elsewhere. Here we have investigated Markov chain Monte Carlo (MCMC) algorithms as a method for optimizing the multi-dimensional coefficient space. Although MCMC algorithms are traditionally used to explore probability densities that result from a particular model specification, they can be used to create irreducible algorithms for optimizing arbitrary, bounded functions. In situations where very little is known, a priori, about a function and where the function may have multiple minimums, the irreducible nature of the MCMC algorithm combined with the ability to adapt MCMC algorithms offers a promising framework for optimizing this multi-dimensional complex function.
The Swift MIDEX mission is the first-of-its-kind observatory for multi-wavelength transient astronomy. The goal of the mission is to ascertain the origin of gamma-ray bursts and to utilize these bursts to probe the early universe. The Ultra- Violet/Optical Telescope (UVOT) is one of three telescopes flying aboard Swift. The UVOT is a working 'copy' of the Optical Monitor on the X-ray Multi-mirror Mission (XMM- Newton). It is a Ritchey-Chretien telescope with microchannel plate intensified charged-coupled devices (MICs) that provide sub-arcsecond imaging. These MICs are photon counting devices, capable of detecting very low signal levels. When flown above the atmosphere, the UVOT will have the equivalent sensitivity of a 4 m telescope on the ground, reaching a limiting magnitude of 24 for a 1000 second observation in the white light filter. A rotating filter wheel contains sensitive photometric broadband UV and visual filters for determining photometric redshifts. The filter wheel also contains UV and visual grisms for performing low-resolution spectroscopy.
The energy resolution degradation of the ACIS CCDs on board the Chandra X-ray Observatory has been under investigation since the effect was first recognized two months after launch. A series of laboratory CCD irradiations with electrons and protons have taken place, leading to the belief that low energy protons are responsible for the damage. In order to confirm this, an experiment has been devised to represent the flight experience of the ACIS CCDs, and the results to date are shown here.
Discussions of optimizing wide-field x-ray optics, with field-of-view less-than 1.1 degree-squared, have been made previously in the literature. However, very little has been published about the optimization of wide-field x-ray optics with larger field-of-views, which technology could greatly enhanced x-ray surveys. We have been working on the design of a wide-field (3.1 degree-squared field-of-view), short focal length (190.5 cm), grazing incidence mirror shell set, with a desired rms image spot size of 15 arcsec. The baseline design consists of Wolter 1 type mirror shells with polynomial perturbations applied to the baseline design. The overall optimization technique is to efficiently optimize the polynomial coefficients that directly influence the angular resolution, without stepping through the entire multi-dimensional coefficient space. We have investigated optimization techniques such as the downhill simplex method, fractional factorial, and response surface (including Box- Behnken and central composite) design. We have also investigated the use of neural networks, such as backpropagation, general regression, and group method of data handling neural networks. We report our findings to date.
The GoldHelox Solar X-ray Telescope underwent several tests during the years of 1997 - 1999, and continues through the testing phase of the project. The instrument itself, a solar telescope to ride on board the Space Shuttle, is designed to photograph the sun in soft x-ray wavelengths between 171 angstroms to 181 angstroms. Critical to its success, many tests are required to insure safety, robustness, and overall accuracy of the telescope during its mission. Among these are shake table tests, optical tests, vacuum integrity, and thermal analysis. This paper describes the GoldHelox project including its current status as a mission, the tests performed on the instrument to date, and the tests pending.