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Astronomical models of galactic nuclei emission spectra are reassessed in light of ultraviolet and X-ray spectroscopic observations. Spectral analysis of BL Lacertae objects using data collected by the International Ultraviolet Explorer (IUE) and other astronomical observatories is presented.
High speed photometric observations obtained with a single channel photometer on the South African Astronomical Observatory 0.5-m and 1.9-m telescopes are presented. It is argued that the dominant source of noise at periods near 5 minutes is sky transparency variation rather than scintillation. For bright stars this means that, at this period, increased telescope aperture does not improve photometric accuracy. It is claimed that ground based photometric observations cannot reach accuracies sufficient to study solar-type oscillations in other stars. Such observations must be made from space. Recommendations for improving ground based observations are made.
The NASA Office of Space Sciences and Applications is sponsoring a series of Space Shuttle missions named Astro-n which are dedicated to a variety of astronomical projects. These missions will be the first in which the Space Shuttle crew will be interactively operating an astronomical observatory which is fixed in the payload bay. The operation of an instrument in such an environment requires a considerable amount of software both on board and on the ground. The Spacelab Experiment Computer provides generalized interactive telemetry display and command processing services through the Experiment Computer Operating System. The experimenter must then design a software package for his Dedicated Experiment Processor which can provide complete control of his instrument as well as communicate with the Experiment Computer. This paper describes the design considerations and operational features of the Ultraviolet Imaging Telescope Dedicated Experiment Processor and Instrument Ground Support Equipment software.
The International Ultraviolet Explorer (IUE) is a large astronomical observatory which was launched on January 26, 1978. The observatory was placed into a three-axis stabilized, eccentric synchronous orbit with an inclination of about 29 degrees. It was designed for a three year lifetime, but is currently still operational. This paper will briefly review the thermal design which consists of multilayer insulation, ammonia-filled grooved heat pipes, bimetallic actuated louvers, and assorted commandable heaters. It will then discuss the seven years of thermal data and compare the results with prelaunch predictions. Finally an attempt will be made to explain the unexpected and continuing rise in temperature of the hydrazine auxiliary propulsion system which has increased over twenty degrees centigrade since launch.
A report of 20 stars to be occulted by Neptune and 46 stars to be occulted by Uranus during the period 1986-1990 has been provided by Mink and Klemola (1985). This paper has the objective to present J, H, and K magnitudes for most of these stars. It is pointed out that Uranus and Neptune occultation events observed in the K band give optimal signal-to-noise ratios due to the planets' strong methane absorption at 2.2 microns. Program stars and standards were observed over six nights with the aid of the 30- and 74-in telescopes at the South African Astronomical Observatory in Sutherland. The obtained results show that several bright candidates exist for both planets. The brightest are N55 for Neptune and U37, U41, and U65 for Uranus.
Data were obtained on stellar occultations by Neptune on June 7 and 25, 1985 in an attempt to validate previous data which supported the presence of a ring-like 'arc' near the planet. The data were taken with an IR photometer at the South African Astronomical Observatory using continuous measurements at 2.2 microns. One dip was observed in the light curve of an occulted binary star. The dip was similar to a previously observed dip and, because no dip was seen for the companion star, indicated a discontinuous structure. Two estimates, around 62,600 and 63,760 km, are made for the equatorial radius of the potential arc structure, which may be discontinuous on a scale of a few thousand kilometers.
The main characteristics of meteor showers associated with Comet Halley were derived from the most recent radar observations carried out at the Ondrejov Astronomical Observatory during the periods of May 1 to 10 and October 15 to 30. The activity variations, the positions of activity maxima, the size distribution of particles, the particle flux variation within the stream and other characteristics were determined and compared with other results.
Three broad goals were presented by NASA as a guide to meet the challenges of the future: to advance scientific knowledge of the planet Earth, the solar system, and the universe; to expand human presence beyond the Earth into the solar system; and to strengthen aeronautics research and technology. Near-term and new-generation space transportation and propulsion systems are being analyzed that will assure the nation access to and presence in space. Other key advanced studies include large astronomical observatories, space platforms, scientific and commercial payloads, and systems to enhance operations in Earth orbit. Longer-range studies include systems that would allow humans to explore the Moon and Mars during the next century. Research programs, both to support the many space missions studied or managed by the Center and to advance scientific knowledge in selected areas, involve work in the areas of atmospheric science, earth science, space science (including astrophysics and solar, magnetospheric, and atomic physics), and low-gravity science. Programs and experiment design for flights on the Space Station, free-flying satellites, and the Space Shuttle are being planned. To maintain a leadership position in technology, continued advances in liquid and solid propellant engines, materials and processes; electronic, structural, and thermal investigations; and environmental control are required. Progress during the fiscal year 1987 is discussed.
The program history, scientific aims, design, and projected performance of the LDR, a 20-m-primary two-stage four-mirror orbiting sub-mm/FIR astronomical observatory under NASA development, are reviewed. It is shown that the LDR would provide capabilities complementary to those of IRAS, the Kuiper Airborne Observatory, the IRTF, the Hubble Space Telescope, and the planned Space IR Telescope Facility for observations of small-scale background anisotropies, high-redshift galaxies, and objects at temperatures of a few times 10 K or lower. The current design concept is illustrated with extensive drawings, diagrams, and tables of instrument parameters. Particular attention is given to the graphite-epoxy facing and Al-honeycomb core of the primary structure, the focal-plane instruments, and outstanding technological problems.
The possible use of optical fibers to remotely couple photometers to telescopes is considered. Such an application offers the apparent prospect of enhancing photometric stability as a consequence of the benefits of remote operation and decreased sensitivity to image details. A properly designed fiber optic coupler will probably show no significant changes in optical transmisssion due to normal variations in the fiber configuration. It may be more difficult to eliminate configuration-dependent effects on the pupil of the transmitted beam, and thus achieve photometric stability to guiding and seeing errors. In addition, there is some evidence for significant changes in the optical throughputs of fibers over the temperature range normally encountered in astronomical observatories.
The opportunities along with the advantages and disadvantages of the Moon for astronomical observatories are carefully and methodically considered. Taking a relatively unbiased approach, it was concluded that lunar observatories will clearly be a major factor in the future of astronomy in the next century. He concludes that ground based work will continue because of its accessibility and that Earth orbital work will remain useful, primarily for convenience of access in constructing and operating very large space systems. Deep space studies will feature not only probes but extensive systems for extremely long baseline studies at wavelengths from gamma rays through visible and IR out to radio is also a conclusion drawn, along with the consideration that lunar astronomy will have found important permanent applications along lines such as are discussed at the present symposium and others quite unsuspected today.
Occultations of stars by planets, satellites, planetary ring systems, asteroids, and comets provide valuable opportunities to probe the Solar System in ways otherwise impossible from the surface of the earth. For example, one can precisely measure the size and shape of objects which are much too small to be resolved directly, accurately map the structure and transparency of ring systems, and detect the faintest trace of an atmosphere. In this investigation, researchers identify upcoming occultations through wide-ranging computer searches, provide accurate predictions for the more important events, and observe selected occultations with our specially designed portable photometric equipment. During the past year, researchers produced accurate predictions for an occultation of AG+40 degrees 0783 by 324 Bamberga on 8 December 1987 and coordinated efforts to observe this event. The occultation was successfully observed at 13 sites including two manned by Lowell Observatory astronomers.
The conclusions and recommendations of the workshop held to study technology development issues critical to the Large Deployable Reflector (LDR) are summarized. LDR is to be a dedicated, orbiting, astronomical observatory, operating at wavelengths from 30 to 1000 microns, a spectral region where the Earth's atmosphere is almost completely opaque. Because it will have a large, segmented, passively cooled aperture, LDR addresses a wide range of technology areas. These include lightweight, low cost, structural composite reflector panels, primary support structures, wavefront sensing and adaptive optics, thermal background management, and integrated vibration and pointing control systems. The science objectives for LDR present instrument development challenges for coherent and direct arrayed detectors which can operate effectively at far infrared and submillimeter wavelengths, and for sub-Kelvin cryogenic systems.
The Large Deployable Reflector (LDR) is a system concept for a dedicated, orbiting, submillimeter, far infrared, astronomical observatory. The purpose of the 3rd conference was to review the latest system concepts for LDR, update the science requirements, and assess the status of the technology development that was recommended at Asilomar 2. The technology development assessment included ongoing work within NASA, the DOD, and various universities. Problem areas and technologies not being adequately addressed were to be identified and prioritized. In particular, the CSTI program in Sensors and Precision Segmented Reflectors was reviewed for appropriateness and progress relative to LDR technology needs.
ROSAT was designed specifically to detect high energy radiation, by using its telescopes to study x ray and ultraviolet emissions, regions of the electromagnetic spectrum that cannot be seen and that cannot penetrate the Earth's atmosphere. ROSAT is an international astronomical observatory project. ROSAT's science mission is divided into two phases. With its in-orbit checkout period complete, ROSAT has begun phase one of its mission, an all sky survey to map the heavens. When the 6 month mapping survey is complete, the satellite will begin phase two and be pointed at selected objects, studying individual targets, for the remainder of its mission.
A list of 1186 ultraviolet-excess objects (designated KUV) was compiled as a result of a search conducted with the 105-cm Schmidt telescope of the Kiso station of the Tokyo Astronomical Observatory. This document describes the machine readable version of the KUV survey list and presents a sample listing showing the logical records as they are recorded in the machine readable catalog. The KUV data include equatorial coordinates, magnitudes, color indices, and identifications for previously cataloged objects.
The transfer of diffuse city light from a localized source through a dust-laden atmosphere with optical depth less than 0.5 has been analyzed in the source-observer plane on the basis of an approximate treatment. The effect on several types of astronomical observation at night has been studied, considering different size distributions and amounts as well as particle shapes of the aerosols. The analysis is made in terms of the signal-to-noise ratios for a given amount of aerosol. The model is applied to conditions at the Wise Astronomical Observatory in the Negev desert, and limiting backgrounds for spectroscopy, photometry, and photography of stars and extended objects have been calculated for a variety of signal-to-noise ratios. Applications to observations with different equipment at various distances from an urban area of any size are possible. Due to the use of signal-to-noise ratios, the conclusions are different for the different experimental techniques used in astronomy.
The Hubble Space Telescope was designed to be an orbiting astronomical observatory which could be operated in the same manner as ground based observatories. The design drivers for the pointing control system's hardware and software were the requirements of an absolute pointing accuracy of 4.8E-8 radians and pointing stability (jitter) of 3.4E-8 radians. Of comparable importance was the objective of providing a flexible command methodology and structure to enable seven day operational planning employing stored program command and real time command capability. The pointing control system hardware, software, safemode control schemes, ground system monitoring capability, and in-orbit results are reviewed.