Multi-anode Microchannel Array Detector Research Articles

Speckle Interferometry of Southern Double Stars. III. Measures from the Cesco Observatory, 1994-1996

Position angle and separation measures of 482 primarily southern binary stars are presented. These were obtained from speckle observations taken at the Carlos U. Cesco Observatory, El Leoncito, Argentina, using a multianode microchannel array detector during the period 1994 July to 1996 July. When comparing our measures to the ephemeris predictions in the case of objects with well-determined orbits, we find that our measures have a precision of approximately 13 mas per observation in separation and 075/ρ in position angle, where ρ is the separation in arcseconds. We briefly discuss the photometric properties of the data and highlight four southern binaries of particular interest that emerge from the list presented.

Design of a multi-anode microchannel array detector system

The Multi-Anode Microchannel Array (MAMA) is a photon counting detector which utilizes a photocathode for photon to electron conversion, a microchannel plate for signal amplification and a proximity focused anode array for position sensitivity. The detector electronics decode the position of an event through coincidence discrimination. These detectors are designed to provide high spatial and temporal resolution for applications in low-light level imaging and spectroscopy at ultraviolet, FUV and EUV wavelengths. Many space ultraviolet astrophysics missions such as STIS are using MAMA detector systems. Several MAMA detectors have been produced by Nanjing Electronic Devices Institute (Nanjing, China). The development of the MAMA systems based on these detectors is performed by Northwest Institute of Nuclear Technology. In this paper, both the design of the MAMA detector system and the progress of the project are presented.

Design of a multi-anode microchannel array detector system

The Multi-Anode Microchannel Array (MAMA) is a photon counting detector which utilizes a photocathode for photon to electron conversion, a microchannel plate for signal amplification and a proximity focused anode array for position sensitivity. The detector electronics decode the position of an event through coincidence discrimination. These detectors are designed to provide high spatial and temporal resolution for applications in low-light level imaging and spectroscopy at ultraviolet, FUV and EUV wavelengths. Many space ultraviolet astrophysics missions such as STIS are using MAMA detector systems. Several MAMA detectors have been produced by Nanjing Electronic Devices Institute (Nanjing, China). The development of the MAMA systems based on these detectors is performed by Northwest Institute of Nuclear Technology. In this paper, both the design of the MAMA detector system and the progress of the project are presented.

AHubble Space TelescopeSearch for Lyman Continuum Emission from Galaxies at 1.1 <z< 1.4

If enough of their Lyman-limit continuum escapes, star-forming galaxies could be significant contributors to the cosmic background of ionizing photons. To investigate this possibility, we obtained the first deep imaging in the far-ultraviolet of 11 bright blue galaxies at intermediate redshift (1.1 < z < 1.4) with the Space Telescope Imaging Spectrograph Far-Ultraviolet Multianode Microchannel Array detector on the Hubble Space Telescope. No continuum emission was detected. Sensitive, model-independent, upper limits of typically less than 10-19 ergs cm-2 s-1 A-1 were obtained for the ionizing flux escaping from these normal galaxies. This corresponds to lower limits on the observed ratio of 1500-700 A flux of 150 up to 1000. On the basis of a wide range of stellar synthesis models, this suggests that less than 6%, down to less than 1%, of the available ionizing flux emitted by hot stars is escaping these galaxies. The magnitude of this spectral at the limit confirms that the basic premise of Lyman break searches for galaxies at high redshift can also be applied at intermediate redshifts. This implies that the integrated contribution of galaxies to the UV cosmic background at z ~ 1.2 is less than 15% and may be less than 2%.

The Space Telescope Imaging Spectrograph Design1

ABSTRACTThe Space Telescope Imaging Spectrograph (STIS) instrument was installed on the Hubble Space Telescope (HST) during the second servicing mission, in 1997 February. Four bands cover the wavelength range of 115–1000 nm, with spectral resolving powers between 26 and 200,000. Camera modes are used for target acquisition and deep imaging. Correction for HST's spherical aberration and astigmatism is included. The 115–170 nm range is covered by a CsI MAMA (Multianode Microchannel Array) detector and the 165–310 nm range by a Cs2Te MAMA, each with a format of 2048 × 2048 pixels, while the 305–555 and 550–1000 nm ranges are covered by a single CCD with a format of 1024 × 1024 pixels. The multiplexing advantage of using these two‐dimensional detectors compared with the 1 × 512 pixel detectors of the first‐generation spectrographs is 1 or 2 orders of magnitude, depending on the mode used. The relationship between the scientific goals and the instrument specifications and design is discussed.

Stability coefficients for the multianode microchannel array detector

We conducted a study to estimate the impact that thermal variations and electronic drifts would have on the photometric stability of the multianode microchannel array (MAMA) detectors that are currently flying aboard the space telescope imaging spectrograph (STIS). Included in the present analysis is the expected impact of preferential aging of the microchannel plate due to prolonged concentrations of light in the same location. These data and analyses were used to examine the suitability of specified electronic tolerances to achieve a photometric accuracy of ±1% over a period of 1 week, but may be also useful should the spacecraft environment begin to vary. The original parameter tolerances were found to be adequate in most cases, although a few voltages did require somewhat better tolerance specifications. The present analysis indicates the sensitivity of the STIS MAMA detectors are reproducible over long periods of time to an accuracy of 0.62% (0.33% rms and 0.29% systematic uncertainties) at an arbitrary location in the detector format. This result indicates the detectors are capable of obtaining data with a signal-to-noise ratio (S/N)≳200 in a STIS 2×2 pixel optical resolution element, consistent with observed departures found in high-signal laboratory data. Even higher S/N levels have been demonstrated on orbit using techniques that move the spectral image around on the detector.

SPECKLE IMAGING WITH THE MAMA DETECTOR: PRELIMINARY RESULTS

ABSTRACT We report on the first successful speckle imaging studies using the Stanford University interferometry system, an instrument that uses a multi-anode microchannel array (MAMA) detector as the imaging device. The method of producing high-resolution images is based on the analysis of so-called "near-axis" bispectral subplanes and follows the work of Lohmann, Weigelt, and Wirnitzer (1983). In order to improve the signal-to-noise ratio in the bispectrum, the frame oversampling technique of Nakajima et al. (1989) is also employed. We present speckle imaging results of binary stars and other objects from V magnitude 5.5 to 11, and the quality of these images is studied. While the Stanford system is capable of good speckle imaging results, it is limited by the overall quantum efficiency of the current MAMA detector (which is due to the response of the photocathode at visible wavelengths and other detector properties) and by channel saturation of the microchannel plate. Both affect the signal-to-noise ratio of the power spectrum and bispectrum.

SPECKLE IMAGING WITH THE MULTI-ANODE MICROCHANNEL ARRAY DETECTOR

ABSTRACT This dissertation combines and instrument and a technique that have been studied separately for several years. The instrument is the multi-anode microchannel array (MAMA) detector. This device is a photon-counting imaging system that has been developed primarily for use in ultraviolet astrophysics. Current generation MAMA detectors have the ability to record the arrival time of every detected photon and can distinguish events which arrive only 140 nanoseconds apart in time. The technique is speckle imaging. This is an interferometric method of recovering high-resolution information about astronomical objects from ground-based telescopes, usually carried out in visible or infrared wavelengths. In conventional astronomy, fluctuations in the atmosphere above the telescope blur images so that the resolution is typically 1 to 2 arcseconds, much worse than the theoretical diffraction-limited resolution of large telescopes. Speckle imaging allows for the reconstruction of image features on a much smaller scale by taking many short (typically 0.01 second) exposure images of an object, where over the exposure time the atmospheric fluctuations are effectively frozen. Speckle imaging devices must therefore have the ability to read out images much faster than most other astronomical imaging devices. Since the MAMA detector offers outstanding timing abilities as well as good spatial linearity and is available in a visible light version, it is an excellent choice as the imaging device in a speckle imaging system. A new speckle system based on the MAMA detector has been built at Stanford University and a detailed study of the performance of the system forms a principle part of this work. Under certain observational conditions, the phenonomenon of channel saturation of the MAMA detector can significantly affect the signal-to-noise ratio of the speckle imaging results. In addition, channel saturation leads to a systematic error in the determination of the irradiance ratios (or equivalently, the magnitude differences) of interferometric binary stars. A correction algorithm is described which leads to better estimates of these ratios in simulated data. Four methods of computing the correlation functions necessary for producing high-resolution reconstructed images are compared using MAMA data. Two of these methods explicitly make use of the time-tagging ability of the MAMA detector and have not been previously studied in detail. The highest signal-to-noise ratio in the power spectrum and bispectrum is obtained with a weighted running-window method. Reconstructed images of several objects are presented. The MAMA-based speckle imaging system is shown to determine accurate position angles and separations of sub-arcsecond separation binary stars.

Speckle Observations of Binary Stars with the MAMA Detector

AbstractWe have made two sets of speckle observations of binary stars with the Multi-Anode Microchannel Array (MAMA) detector. Our observing system is a true photon counting imaging device which records the arrival time of every detected photon. We present speckle autocorrelation analyses of five binary systems, two observed with the 3.6-m telescope at the European Southern Observatory and three observed with the 40-in reflector at Lick Observatory. These five systems represent a wide variation in separation and magnitude difference that indicate that the MAMA detector is capable of recording high quality speckle data at extremely low count rates and can recover image features very near the diffraction limit of the telescope. In one case, only 10 photons per frame were recorded for the dim companion of the system, and in another case, a separation of 0″.157±0″.031 was derived for a system observed with the 40-in telescope where the diffraction limit is about 0″.125. Future prospects for this system are discussed.

HIRES: a high-resolution stigmatic extreme ultraviolet spectroheliometer for studies of the fine-scale structure of the solar chromosphere, transition region, and corona

We describe the design of a high-resolution stigmatic extremeultraviolet (EUV) spectroheliometer, configured for flight on a Black Brant sounding rocket, which consists of a 45-cm Gregory telescope coupled to a spectrometer employing a single toroidal diffraction grating in a normalincidence Rowland circle mounting and an imaging pulse-counting multianode microchannel array (MAMA) detector system. The toroidal diffraction grating is fabricated by a technique employing an elastically deformable submaster grating that is replicated in a spherical form and then mechanically distorted to produce the desired aspect ratio of the toroidal surface for stigmatic imaging over the selected wavelength range. The spectroheliometer will produce spatially resolved spectra of the chromosphere, transition region, and corona with an angular resolution of 0.4 arcsec or better, a spectral resolution λ/Δλ of about 10 4 in first order, and a temporal resolution of the order of seconds. Because of the geometric fidelity of the MAMA detector system, the spectroheliometer will be able to determine Doppler shifts to a resolution of at least 2 ma at wavelengths near 600 a (~1.0 km s -1 ), depending on the level of the accumulated signal. The unique characteristics of the spectroheliometer will be used in combination with plasma-diagnostic techniques to study the emperature, density, and velocity structures of specific features in the solar outer atmosphere.

Centroid position measurements and subpixel sensitivity variations with the MAMA detector

Initial measurements of the position sensitivity of a visible-light multi-anode microchannel array (MAMA) detector show that centroid calculations for image spots are accurate to better than 0.04 pixels even with sources that are essentially delta functions at the photocathode. Subpixel sensitivity variations of 10-15% are typically found for pixels in the array. Variations as large as 30% are possible in the worst conditions. These variations limit the photometric accuracy of the detector when very small scale features are observed. The photometric accuracy and the position sensitivity of the detector appear to be limited by cross-coupling effects within the anode array. Initial measurements with more recent designs of the detector show that most or all of this cross-coupling has been eliminated. We will report on the position sensitivity of the newer detectors when they become available for testing.

HIGH-RESOLUTION DETECTORS FOR IMAGING AND SPECTROSCOPY AT ULTRAVIOLET AND SOFT X-RAY WAVELENGTHS

The Multi-Anode Microchannel Arrays (MAMAs) are a family of pulse-counting imaging array detectors designed specifically for astrophysical investigations in space. The MAMAs have a number of unique performance characteristics which make them particularly suitable for imaging and spectroscopy at ultraviolet and soft x-ray wavelengths. First, they employ solar blind photocathodes eliminating the red leak problem associated with solid state arrays such as the CCDs. Second, they operate with zero readout noise, yielding photon-statistics limited signals. Third, they utilize a random readout technique and can determine both the location of a detected photon and also its arrival time to an accuracy of the order of 100 ns. This paper will give an overview of the construction, mode-of-operation and performance characteristics of the MAMA detectors and will describe the current status of the development program.

High-Resolution Detectors for Imaging and Spectroscopy at Ultraviolet and Soft X-Ray Wavelengths

AbstractThe Multi-Anode Microchannel Arrays (MAMAs) are a family of pulse-counting imaging array detectors designed specifically for astrophysical investigations in space. The MAMAs have a number of unique performance characteristics which make them particularly suitable for imaging and spectroscopy at ultraviolet and soft x-ray wavelengths. First, they employ “solar blind” photocathodes eliminating the “red leak” problem associated with solid state arrays such as the CCDs. Second, they operate with zero readout noise, yielding photon-statistics limited signals. Third, they utilize a random readout technique and can determine both the location of a detected photon and also its arrival time to an accuracy of the order of 100 ns. This paper will give an overview of the construction, mode-of-operation and performance characteristics of the MAMA detectors and will describe the current status of the development program.

Multianode Microchannel Array Detector Systems: Performance Characteristics

Multianode microchannel array detector systems with formats as large as 256 x 1024 pixels are currently under evaluation in the laboratory. Performance data recorded with sealed ultraviolet and visible-light detector tubes have shown that the detector systems have unique characteristics that make them complementary to photoconductive ar-ray detectors, such as charge-coupled devices, and superior to alter-native pulse-counting detector systems employing high-gain microchannel plates.

Calcium depletion toward moderately reddened stars

Calcium depletions toward five moderately reddened (E/B - V/ greater than 0.35 and less than 0.45) stars and toward HD 147889, a heavily reddened (E/B - V/ = 1.08) member of the Rho Ophiuchi cloud complex is reported. A developmental Multi-Anode Microchannel Array Detector was used to collect the data; its performance is characterized. Comparing the results for calcium from one line of sight to another and to those for other species, it is found that calcium exhibits a depletion pattern remarkably similar to that of silicon. The depletion of iron, on the other hand, has smaller variations and therefore does not correlate as well. Also, the depletion results for manganese and sulfur, both normally undepleted in diffuse clouds, have been included for comparison.

A search for diffuse band profile variations in the rho Ophiuchi cloud

High signal-to-noise profiles of the broad diffuse interstellar band at 4430 A were obtained on the 2.2-m telescope at the Mauna Kea Observatory, using the newly-developed pulse-counting multi-anode microchannel array detector system in an effort to determine whether the band profile varies with mean grain size as expected if the band is produced by absorbers embedded in grain lattices. The lack of profile variability over several lines of sight where independent evidence indicates that the mean grain size varies shows that lambda 4430 is probably not formed by the same grains that are responsible for interstellar extinction at visible wavelengths. The possibility that this band is created by a population of very small ( approximately 100 A) grains is still viable, as is the hypothesis that it has a molecular origin.

Recent Progress with Multi-Anode Microchannel Array Detector Systems

AbstractThe Multi-Anode MicroChannel Arrays (MAMAs) are a family of photoelectric, photon-counting array detectors that are being developed specifically for use in instruments on space-borne and ground-based telescopes. In this paper we review briefly the construction and modes of-operation of the MAMA detectors and describe the current development status of the different detector systems.