A multiplex imaging spectrometer for low energyX-ray astronomy

A multiplexX-ray image analyser is described. It consists in a time-modulated coded aperture associated with a solid state detector. The system combines the high efficiency and good spectral resolution of solid state spectrometers with the spatial resolution of the coded aperture (200 ).The device can be installed at the focus of a grazing incidence telescope to make images and spectra of faint astronomicalX-ray sources.     

Infrared instruments for the Gemini 8-M telescopes

The Gemini Telescopes are being built to exploit the splendid infrared sites of Mauna Kea in Hawaii and Cerro Pachon in Chile. Both telescopes are being designed to deliver 0.1 arcsecond images at 2.2 m to the focal plane. This image size includes all tracking and enclosure effects. To exploit the superb infrared characteristics of the sites and telescopes we will require a new generation of IR instruments which will challenge both instrument designers and infrared array technologies.     

Extinction and scattering by several types of silicate sphere of radius 0.05–1.0μm,for the wavelength range 0.21–50μm

The exact calculation of scattering and absorption by various sub-micron sized silicate spheres is presented here, using accurately determined optical constants in the wavelength range from 50 m to 0.21 m. The extinction features near 10 m and 20 m for various samples are discussed. It is found that the ratio of peak extinction at 20 m to that at 10 m is constant for small particles up tor=0.4 m, but is less for particles of radius 1 m. The ratio of maximum extinction in the ultraviolet to that at 10 m decreases with increasing particle size.     

Compact Two-Dimensional Array of Stressed GE:GA Detectors

We have developed a 4 × 8 array of stressed Ge:Ga detectors. This array detector has a high density format ofentrance pupils so that we can minimize the size of the cameraoptics. The cutoff wavelength of the detector is about 170 m, and the detector's NEP is better than 10¹⁶ WHz^-1/2. We are going apply this array detector toballoon-borne astronomical observations. Furthermore, we aredeveloping this detector into a 5 × 15 array detector that will be placed onboard the IRIS satellite to be launched in 2003.     

CASPIR: A cryogenic array spectrometer imager for the MSSSO 2.3 m telescope

CASPIR is a near-infrared spectrometer/imager being built for the Mount Stromlo and Siding Spring Observatories' 2.3 m telescope. The instrument is based on a SBRC 256×256 InSb detector array and uses AR-coated Sapphire, MgO, CaF₂, and BaF₂ optics to produce two imaging focal plane scales with 0.5/pixel and 0.25/pixel. Spectral resolving powers of 500 will be achieved through a 1×128 slit with three grisms designed for the J, H, and K bands. IJ, JH, and HK cross-dispersed échelle grisms will achieve resolving powers of 1100 through a 1×15 slit. Coronograph and imaging polarimetry modes will also be available. The various observing configurations are selected via five remotely controlled wheels. The instrument design and system architecture are discussed, and preliminary detector performance figures reported.     

Phase retrieval holography and surface adjustment of SEST using the LES-8 satellite

Phase retrieval holography has been used to determine the surface profile of the Swedish-ESO Sub-millimetre Telescope (SEST). The measurement was performed using a signal transmitted from the geosynchronous LES-8 satellite over a range of elevation angles. The results of the measurements have been used to reset the reflector thus reducing the surface errors from the initial 80 m r.m.s. to 51 m r.m.s. The improvement in the surface accuracy has been confirmed by telescope efficiency measurements at 232–250 GHz.     

LonGSp: A near infra-red spectrometer

We present a new cooled grating near infra-red spectrometer designed to acquire spectra at the TIRGO telescope in the 0.9÷2.5m region with a resolving power of 300÷4000, equipped with a Rockwell NICMOS 3 detector.     

ISOCAM cosmological Surveys

Several deep surveys have been performed at 7 and 15 m by using the mid-infrared camera ISOCAM on board the ISO satellite. We review their first results, emphasizing on the excess detected in the 15 m counts with respect to the predictions of models with a mild evolution that is sufficient to explain the IRAS counts. We point out that a large fraction of the past star formation history is missed when studied using UV/visible data only.     

First experiences with ARNICA,the Arcetri observatory imaging camera

ARNICA (ARcetri Near Infrared CAmera) is the imaging camera for the near infrared bands between 1.0 and 2.5 m that Arcetri Observatory has designed and built as a common use instrument for the TIRGO telescope (1.5 m diameter, f/20) located at Gornergrat (Switzerland). The scale is 1 per pixel, with sky coverage of more than 4×4 on the NICMOS 3 (256×256 pixels, 40 m side) detector array. The optical path is compact enough to be enclosed in a25.4 cm diameter dewar; the working temperature of detector and optics is 76 K. We give an estimate of performance, in terms of sensitivity with an assigned observing time, along with some preliminary considerations on photometric accuracy.     

A 256×256 pixel InSb FPA for SIRTF and other astronomical applications

As part of the NASA Space Infrared telescope Facility (SIRTF), a low noise multiplexer has been developed. The hybridization of this multiplexer to a high indium antimonide (InSb) photodiode array has resulted in a MWIR detector of outstanding performance. The multiplexer is made of a 256×256 array of source follower amplifiers on a 30 m square pitch. Random access binary decoders are used to access each pixel of the array, allowing any read-out scheme to be implemented. Dark current has been measured at temperatures ranging from 4K to 77K. Generation recombination currents dominate above 45K. With 100mV of reverse bias applied, less than 3×10^-17 A is typical below 50K with 8×10^-19 A (5 e^-/s) at 4K. Under the same conditions 0.25 pA was measured at 77K. Read noise has been measured as low as 186 e^- using non-correlated techniques. Detector QE is 50 to 80 % through the entire 1 to 5 m band.     

The future of large-format InSb arrays for astronomy

Introduced to astronomy less than a decade ago, infrared detector arrays have radically and forever changed astronomer's observational techniques, instruments, and telescope designs. This paper first examines the array technology development that caused this change, with emphasis on the 1- to 5-m band. Technology trends and projections for further development within the infrared industry are analyzed to assist astronomers in planning future instruments. This technology development is predicted to result in arrays with lower noise, greater well depth, response to a wider band of wavelengths, and, above all, much larger formats than arrays currently in use.     

New 8–13 μm Si:Ga/DRO hybrid arrays for very large telescopes

Since 1984, the CEA-LETI-LIR (Infrared Laboratory) has been involved in development of Si:Ga/DRO hybrid detector arrays dedicated to imaging of astronomical sources in the 8–13 m range. Successively, 32×32 element arrays were successfully manufactured for the ISOCAM camera and 64×64 arrays were fabricated for ground-based imaging. The latter detectors have been integrated in 3 cameras (C10, CAMIRAS and TIMMI for ESO) and have led to excellent astrophysical results since 1990.To equip instruments to be mounted on very large telescopes such as the European VLT at ESO, manufacture of new arrays has been undertaken and is currently under way at CEA-LETI-LIR. These new arrays will have a 128×192 format and will present the outstanding essential feature that their storage capacity will be able to be changed according to observation conditions (2 capacities will be implemented in the pixel).The main characteristics of these new detectors will be presented in this paper.     

A high resolution mid-infrared image of the Starburst Galaxy M82

We have produced high-resolution images of the nuclear region of M82 with SpectroCam-10, a mid-infrared instrument at the Palomar 5 m telescope. These images were taken at 11.7 m and 9.8 m with a 1m filter bandpass at the diffraction limit of 0.6 arcsec, making them the highest resolution maps yet available of M82. In addition, we have obtained high-resolution (/=2000) maps of the velocity field of the nuclear disk of M82 in the 12.81 m line emission of [NeII]. In these proceedings we present the 11.7 m image, which will appear together with the 9.8 m map and the [Ne II] spectra in a subsequent paper, now in preparation. This image shows very clearly a bridge structure joining the eastern and western clusters.     

Nifte: The near infrared faint-object telescope experiment

The high sensitivity of large format InSb arrays can be used to obtain deep images of the sky at 3–5 m. In this spectral range cool or highly redshifted objects (e.g. brown dwarfs and protogalaxies) which are not visible at shorter wavelengths may be observed. Sensitivity at these wavelengths in ground-based observations is severely limited by the thermal flux from the telescope and from the earth's atmosphere. The Near Infrared Faint-Object Telescope Experiment (NIFTE), a 50 cm cooled rocket-borne telescope combined with large format, high performance InSb arrays, can reach a limiting flux < 1 Jy (1) over a large field-of-view in a single flight. In comparison, ISO will require days of observation to reach a sensitivity more than one order of magnitude worse over a similar area of the sky. The deep 3–5 m images obtained by the rocket-borne telescope will assist in determining the nature of faint red objects detected by ground-based telescopes at 2 m, and by ISO at wavelengths longer than 5 m.     

The Italian Astrophysical Observatory in Antarctica: OASI

OASI (Infrared and Sub-mm Antarctic Observatory) is the first large telescope permanently installed in Antarctica. It is located close to the Italian Base in Antarctica (Terra Nova Bay Station, latitude: 74.39 S, longitude: 164.09 E). The OASI first light was received in December 1990 when the wobbling secondary mirror was mounted. The telescope is planned to be an open facility which can operate in the wavelengths range between 350 m and 3mm. The sky coverage from OASI goes down to a declination of about-35° for a 24 hours/day observing time.     

The ESA project for a Grazing Incidence Solar Telescope (GRIST)

The Grazing Incidence Solar Telescope (GRIST) as it is being studied by the European Space Agency (ESA) is described: A soft X-ray and extreme-ultraviolet (XUV) facility for solar observations with 1 arc sec spatial resolution in a wavelength range extending from 9 to beyond 100 nm. The telescope, a 35° sector of a Wolter, type-II, configuration, will have a focal length of 4 m and a collection area of 280 cm².It is planned that GRIST be flown on joint Spacelab flights with the Solar Optical Telescope (SOT), a NASA facility for the wavelength range, 110 nm to 1 m, which affords a 0.1 arc sec spatial resolution. This would render possible synoptic observations of the solar atmosphere with the highest ever achieved spatial resolution at wavelengths between 9 nm and 1 m.Possible focal-plane instruments and the most important research goals are briefly described.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.On behalf of the ESA Consultants for the Phase-A Study of GRIST: A. H. Gabriel, U. Grossmann-Doerth, M.C.E.H., M. Malinovsky-Arduini, G. Tondello, and H. F. van Beek.     

The near infrared spectrophotometer for the 182 cm Asiago telescope

A new near infrared spectrophotometer has been built for the Asiago 182 cm telescope. The instrument performs both large band JHKLM photometry and 1–5 spectrophotometry; a tracking system on a field star allows closed loop mapping. The design and performances are discussed.     

A new method for determining the internal rotational angular velocity of the stars

Infrared spectra of submicrometre-sized particles of several protosilicates have been used to derive mass absorption coefficients. These data have been applied in order to describe the infrared radiation from the source OH 26.5+0.6 in terms of a simple model. A good fit of the 10 m absorption feature could be achieved, but some discrepancies remain in the 20 m region. The reasons for the weakness of the 20 m band in infrared sources are discussed.The laboratory spectra revealed that the samples contained a small admixture of carbonates. Thus, some statements about the infrared spectrum of submicrometre-sized carbonate particles could also be made.     

Summary of ISO Detector Workshop

The Infrared Space Observatory successfullycarried out a wide range of astronomical observations in thewavelength range 2.4 m to nearly 200 m. To coverthis extremely broad range, a variety of detector technologies wereused by the instruments teams. As such ISO also proved to bean important test bed for the operation of these detectors ina low-background space environment. Over the two year mission,all the detector types have proven to be quite stable, withonly the Si:As IBC showing any long term degradation.Significant effort has been expended to cope with thebehaviour of the detectors under the space conditions bothoperationally and in ground processing. The main undesirableeffect can be classified as either transient responseanomalies or radiation effects. Overall sensitivity of theISO detectors was generally worse than predicted fromground-based measurements due to combinations of these twoclasses of phenomena. Splinter meetings were held to exchangespecific strategies for dealing with glitches, radiation curing,and transient effects. Plans for future actions were initiated.     

Optical characteristics of the whipple observatory TeV gamma-ray imaging telescope

In TeV -ray astronomy, large mirrors are used to collect erenkov light from electromagnetic cascades in the atmosphere in order to obtain low energy thresholds. The flux sensitivity of TeV -ray detectors is limited by background due to erenkov light bursts from isotropic, cosmic-ray showers which are much more numerous than -ray showers. It has recently been established that most of this background can be eliminated on the basis of the shapes of erenkov light images on the focal plane of a telescope. In order for this technique to work, the light collector must have adequate resolution over a relatively wide field of view. In this paper, the optical characteristics of the 10 m reflector used in the imaging detection of the Crab Nebula are examined and contrasted with those of a standard parabolic design. This 10 m reflector has a unique (Davies-Cotton) design with small spherical facet mirrors placed on spherical support structure with radius equal to exactly 1/2 the curvature radius of the facet mirrors. The off-axis focusing properties of this type of telescope have not been examined previously.