An imaging telescope for high energy gamma-ray astronomy

Recent tests of a γ-ray imaging telescope, which incorporated a coded aperture mask and multi-wire proportional counter system produced good images of a tritium target source which was used to generate the 20 MeV protons at a proton Van de Graaff accelerator. This paper indicates what performance one might expect if a large area drift chamber were used in conjunction with a coded aperture mask. The prospects for achieving significant scientific results if such a system were flown on a variety of space vehicles are discussed.     

An imaging telescope for soft gamma ray astronomy

A telescope capable of producing images of the gamma ray sky in the energy range 0.2–20 MeV with an angular resolution of a few tenths of a degree is presented. This capability is achieved by means of a large array of Sodium Iodide position sensitive elements together with a coded imaging mask. The expected performance, derived from calculations and preliminary laboratory tests, is described.     

The gamma-ray observatory mission objectives and its significance for gamma-ray astronomy

The Gamma Ray Observatory (GRO) is an approved NASA mission, programmed for launch in 1988. Its complement of four detectors has established goals: 1) to study the nature of compact γ-ray sources such as neutron stars and black holes, or objects whose nature is yet to be understood; 2) to search for evidence of nucleosynthesis especially in the regions of supernovae; 3) to study structural features and dynamical properties of our galaxy; 4) to explore other galaxies, especially the extraordinary types such as radio, Seyferts, and quasars; and 5) to study cosmological effects by examining the diffuse radiation in detail. This paper discusses the design, objectives, and expected scientific results of each of the GRO instruments in view of the GRO mission goals.     

Current wisdom and future possibilities for gamma-ray sources within high-energy astronomy

The current knowledge on celestial high-energy gamma-ray sources is reviewed on the occasion of the end of the COS-B satellite. The breakthroughs of such a mission are outlined together with its limitations. Future experimental possibilities are presented in the context of planned missions.     

Design study for a three-meter balloon-borne telescope for far infrared and submillimeter astronomy

A NASA supported design study is being carried out for a three-meter balloon-borne far infrared and submillimeter telescope. The goal of this project is to provide a facility for frequent flights for photometry, spectroscopy, and imaging in the spectral region 30 micrometers to 1 millimeter. It is intended to provide a scientific and technical step on the way to a large submillimeter telescope in space in the future. The study is concentrating on areas where technical advances are required: materials and fabrication techniques for lightweight primary mirrors, telescope and gondola structure, and pointing and stabilization. We are carrying out a design optimization and environmental test program of state-of-the-art carbon fiber reinforced plastic sandwich panels in collaboration with Dornier Systems. Similar efforts are being pursued for very lightweight molded glass mirrors. Innovative approaches to the telescope support and stabilization are being explored for achieving the required 1 arcsecond pointing stability.     

The observation of the galactic anticenter region by the balloon borne gamma-ray telescope Natalya-I

This paper presents the results of measurements of gamma radiation with energies above 5 MeV, from the galactic anticenter region. The balloon-borne gamma ray telescope “Natalya-I”, was launched on 6 November, 1980 from the Tata Institute of Fundamental Research's Balloon Facility (Hyderabad, India) and reached ceiling altitude of 35 km. The results on the accelerator calibration of the telescope, using a “tagged” gamma ray beam are also presented.     

EUVITA — An extreme UV imaging telescope array with spectral capability

EUVITA is a set of 8 extreme UV normal incidence imaging telescopes, each of them sensitive in a narrow band (λ/Δλ = 15 to 80), centered at wavelengths between 50 and 175 Å. Each telescope has an effective area of a few cm²; a field of view of 1.2° and a spatial resolution of 10 arcsec.

EUVITA will be flown on the Russian mission SPECTRUM X-G. This satellite will be launched in a highly eccentric orbit with a period of 4 days, allowing long, uninterrupted observations (e.g. 10⁵ seconds). EUVITA's narrow spectral bands allow the measurement of source parameters such as temperature or power law index as well as interstellar absorption, and will resolve groups of strong lines emitted by optically thin hot plasmas.     

An automatic navigation and aspect sensing system for X-ray astronomy

An automatic navigation and aspect sensing system is being developed for use in trans-Australia and possible globe circling balloon flights by the University of Tasmania stabilised platform for X-ray astronomy. This system comprises an Omega receiver, three axis magnetometer, alt-az. mounted CID camera and an on-board computer. The computer uses the Omega receiver output or other dead reckoning information together with the magnetometer data to calculate the approximate position of selected bright stars. It then drives the camera to each of these positions in turn and determines from the camera output the precise coordinates relative to the platform of each of these stars. From this information it will fix the geographic coordinates of the platform to within a few nautical miles and will determine the true platform azimuth with a precision of approximately 0.1°. These data will be passed to the platform aspect control computer via a serial link.     

The Zadko telescope: A resource for science education enrichment

This paper describes plans for employing a new fully robotic optical telescope in Western Australia, the Zadko telescope, for evaluating education-outreach. A key feature of the telescope is the optimized observation-scheduling program, developed by our French collaborators who operate the TAROT robotic telescope network. It provides a simple interface for requesting observation time remotely, and has the potential for school students to participate in real astronomical research. The University of Western Australia and Curtin University are commencing a study for evaluating changes in student perceptions of science by participation in our astronomy research. Other areas of interest include broadening the program to include access of students from European countries, and exploring how remote access astronomy can be used to encourage awareness between different cultures.     

The oriented scintillation spectrometer experiment for the gamma-ray observatory

The Oriented Scintillation Spectrometer Experiment (OSSE) for the Gamma Ray Observatory is described. OSSE uses four identical NaI(T1)-CsI(Na) phoswich detectors to provide gamma-ray line and continuum detection capability in the 0.05–10 MeV energy range. Additional gamma-ray and neutron detection capability is achieved above 10 MeV. Each detector has a CsI annular shield and a tungsten alloy collimator which define a 5° × 11° (FWHM) field-of-view. The detectors have independent, single-axis orientation systems which permit offset pointing to provide source-background subtraction. The sensitivity for line gamma rays in the 0.05–10 MeV region will be 2–3 × 10^?5 photons/cm²-s for a 10⁶-second observation period. The several modes of data acquisition and the emphases for the planned observational program are discussed.     

Teaching astronomy for pre-service elementary teachers: A comparison of methods

This study investigates the effect of text structure and “hands-on” methods in the acquisition of the concepts of moon phases and seasons for pre-service elementary teachers. The goal is to evaluate the most appropriate method for facilitating conceptual change. The presentation of two main misconceptions associated with each concept (moon phases and seasons) is tested. Sixty pre-service elementary teachers are divided into three same size experimental groups after a pre-test on their knowledge about astronomy: one group read a simple expository text that presents factual information about seasons and moon phases, another group read a refutation text that moreover presents explicitly two main and usual misconceptions about each concept and arguments to refute them; the last group participates to a refutation modelling activity by testing, for each concept, three hypothesis: the scientific explanation and the two common misconceptions. The hands-on method is used as a way to refute the pre-conceptions thanks to a collaborative activity in small groups.     

SIGMA observations of two new hard X-ray and soft gamma-ray transients: GX 354-0 and Nova Persei

We report the first detection of two soft gamma ray transients GX 354-0 and Nova Persei (GRO J0422+32) by the coded-mask telescope SIGMA. Only preliminary results are presented with regard to Nova Persei while special emphasis is given to the data on GX 354-0 which has been monitored during the 1992 February–April survey of the Galactic Center. GX 354-0 underwent two flares of about two week duration and its average spectrum is well described by a thermal Bremsstrahlung model or a broken power law whereas the Nova Persei spectrum seems to be similar to the one observed for GRS 1124-684 in Musca.     

Long duration balloon flights: A probe for deep hard X-ray astronomy investigation

In this note the state of the art of our knowledge of the high energy sky will be reviewed, with particular regard to the hard X-ray range.The use of more complex and sophisticated payloads that is necessary to obtain up-to-date results mandatory to achieve a better understanding of the actual scenario in the range 15–300 keV, causes new continuous requirements for long duration balloon flights.The needs for astronomy oriented scientific ballooning will be considered and discussed.     

Sigma: A new gamma-ray space observatory with high angular resolution for 1985 and beyond

The SIGMA mission is designed to obtain images of the sky in the hard X-ray/low energy gamma-ray domain 30 keV - 2 MeV, with an angular accuracy a few arc min., and a sensitivity for point sources down to a level of a few UFU. The principal scientific objectives of the SIGMA mission are described, as well as the anticipated performance of the instrument.     

The soft X-ray superoutburst of VW hydri: 14 second periodicity

EXOSAT observations of the dwarf nova VW Hydri reveal a strong soft X-ray flux during optical superoutburst. The onset of the X-ray outburst was delayed by 2.5 days compared to the optical outburst. A modulation of the extreme soft X-ray flux was detected, consistent with a coherent (0 >x 10⁷) pulsation with a period of 14.07 seconds, probably reflecting the rotation period of the white dwarf.IIf this is indeed the case, VW Hydri is the fastest rotating white dwarf detected so far.     

A sample collector for robotic sample return missions II: Radiation tests

Sample return from small solar system objects is playing an increasingly important part in solar system exploration. Critical to such missions is a robust, simple, and economic sample collector. We have developed a collector such as this for near-Earth asteroid sample return missions that we have termed the Touch-and-Go Impregnable Pad (TGIP). The collector utilizes a silicone substrate that is pushed into the dust and gravel surface layer of the asteroid. As part of a systematic evaluation of the TGIP, we have investigated the resilience of this substrate to ionizing radiations. Several miniature versions of the collector, containing typically ∼3 g of the collection substrate, were exposed to 0.564 MeV beta particles from a ⁹⁰Sr source and a 6 MeV electron beam in a linear accelerator to simulate the wide range of energies of solar and galactic ionizing radiation. Various radiation levels up to eight times greater than expected on a six-year asteroid mission (in the case of beta radiation) and 50 times greater than expected (in the case of the 6 MeV electron radiation) were administered to the substrate. After irradiation, the efficiency of the substrate in collecting samples of mock regolith was compared with that of collectors that had not been irradiated. No difference beyond experimental uncertainty was observed and we suggest that the operational TGIP will not be affected adversely by radiation doses expected during a typical six-year inner solar system mission.     

The Antaeus project: An orbital quarantine facility for analysis of planetary return samples

A systems design study group jointly sponsored by the American Society for Engineering Education, Stanford University and NASA's Ames Research Center, was requested to develop a design for an orbiting quarantine facility. The proposed facility is constructed of Spacelab shells formed into five modules of different sizes, each compatible with missions of other objectives. Once placed in a low Earth orbit by the Space Shuttle, each component is linked via the international docking system. Radiating from the docking module are a replaceable logistics module which stores a thirty day supply of consumables and waste, a module providing living quarters for five crew members, a power system module, and a quarantine testing laboratory. Within the laboratory module is a primary barrier system of sealed cabinets in which the sample is assessed for life forms. These chambers isolate the sample from terrestrial contamination and protect the researchers. A combination of procedures and mechanisms separates the laboratory module from the remainder of the facility and provides a secondary barrier. The conditions of space provide a tertiary barrier protecting the Earth's biosphere.     

An imaging gas scintillation proportional counter coupled to a channel multiplier array for application in cosmic X-ray spectroscopy

The development of an imaging gas scintillation proportional counter which utilises a channel multiplier array as the readout element is discussed. Preliminary experimental results and theoretical considerations indicate that spatial and energy resolutions of below 500 μm and 8% respectively should be achievable at an X-ray energy of 6 keV.     

The infrared imaging channel of the IKS instrument for detection of Comet Halley nucleus

The imaging Channel of the IKS Instrument placed on board the Vega fly-by probes will perform measurements of the infrared emission of the central region of Comet Halley at distances in the 10⁴ ? 10⁵ km range. An encoding wheel analyses one spatial frequency of the infrared image during the whole fly-by. Inversion of this measurement will give low resolution brightness profiles of the nucleus and its immediate surroundings, in two wave-length bandpasses and in two directions of analysis.     

The ultraviolet sky: An overview from the GALEX surveys

The Galaxy Evolution Explorer (GALEX) has performed the first surveys of the sky in the ultraviolet (UV). Its legacy is an unprecedented database with more than 200 million source measurements in far-UV (FUV) and near-UV (NUV), as well as wide-field imaging of extended objects, filling an important gap in our view of the sky across the electromagnetic spectrum. The UV surveys offer unique sensitivity for identifying and studying selected classes of astrophysical objects, both stellar and extra-galactic. We examine the overall content and distribution of UV sources over the sky, and with magnitude and color. For this purpose, we have constructed final catalogs of UV sources with homogeneous quality, eliminating duplicate measurements of the same source. Such catalogs can facilitate a variety of investigations on UV-selected samples, as well as planning of observations with future missions. We describe the criteria used to build the catalogs, their coverage and completeness. We included observations in which both the far-UV and near-UV detectors were exposed; 28,707 fields from the All-Sky Imaging survey (AIS) cover a unique area of 22,080 square degrees (after we restrict the catalogues to the central 1° diameter of the field), with a typical depth of ∼20/21mag (FUV/NUV, in the AB mag system), and 3008 fields from the Medium-depth Imaging Survey (MIS) cover a total of 2251 square degrees at a depth of ∼22.7mag. The catalogs contain ∼71 and ∼16.6 million sources, respectively. The density of hot stars reflects the Galactic structure, and the number counts of both Galactic and extra-galactic sources are modulated by the Milky Way dust extinction, to which the UV data are very sensitive.