ALBERT

Description: Three objectives are stated for activities at a proposed manned lunar base. One objective is scientific investigation of the moon and its environment and the application of special properties of the moon to research problems. Another objective would be to produce the capability of using the materials of the moon for beneficial purposes throughout the earth-moon system. The third objective is to conduct research and development leading to a self-sufficient and self-supporting lunar base, the first extraterrestrial human colony. The potential benefits to earth deriving from these moon-based activities, such as technology development and realization, as well as growing industrialization of near-earth space, are addressed.

Description: The evolutionary approach to space development is discussed in the framework of three overall strategies encompassing four case studies. The first strategy, human expeditions, places emphasis on highly visible, near-term manned missions to Mars or to one of the two moons of Mars. These expeditions are similar in scope and objectives to the Apollo program, with infrastructure development only conducted to the degree necessary to support one or two short-duration trips. Two such expeditionary scenarios, one to Phobus and the other to the Mars surface, are discussed. The second strategy involves the construction of science outposts, and emphasizes scientific exploration as well as investigation of technologies and operations needed for permanent habitation. A third strategy, evolutionary expansion, would explore and settle the inner solar system in a series of steps, with continued development of technologies, experience, and infrastructure.

Description: Logistic difficulties associated with the Space Station Freedom are discussed. Proposed ground and on-orbit operations and procedures for supplying the Station are described. The transfer operations of supplies to the modules, the use of expendable launch vehicles for supplying the Station, and the use of EVA suits for assembling and servicing are considered. Ground support activities for resupplying and maintaining the spacecraft are examined.

Description: A technique is described to estimate the area-to-mass ratio of debris fragments using orbital fragments obtained by radar. The area-to-mass ratio of about 2600 fragments arising from the breakup of 24 artificial satellites was determined; an analysis of the data on about 200 objects with known mass, size, and shape has been made, and a calibration of the observed radar cross-section (RCS) to the effective area of these objects has provided a method to estimate the effective area of debris fragments. From the knowledge of the effective area and the estimated area-to-mass ratio, the mass and area distribution of each of the known breakup has been obtained. As a function of time, the orbital elements can be used to invert any propagation algorithm to yield the area-to-mass ratio of an orbiting object.

Description: A catalog of 2678 galaxies within an area of about 40 sq deg centered on the Fornax Cluster has been compiled based on 26 deep large-scale plates obtained with the 2.5-m Las Campanas Observatory reflector. The catalog includes 340 likely cluster members and 2338 likely background galaxies. Radial velocities are given for 89 of the galaxies. The spatial distributions of various types of galaxies have been modeled as the sum of a King (1962) model cluster component superimposed on a uniform background. Using maximum-likelihood fits to these distributions, a core radius of 0.7 deg is found for a King model fit to the cluster, suggesting that there are few cluster members contained in the sample of background galaxies.

Description: Six radio telescopes were operated as the first Southern Hemisphere VLBI array in April and May 1982. Observations were made at 2.3 and 8.4 GHz. This array provided VLBI modeling and hybrid imaging of celestial radio sources in the Southern Hemisphere, high-accuracy VLBI geodesy between Southern Hemisphere sites, and subarcsecond radio astrometry of celestial sources south of declination -45 deg. The goals and implementation of the array are discussed, the methods of modeling and hybrid image production are explained, and the VLBI structure of the sources that were observed is summarized.

Description: Plans for the Comet Rendezvous Asteroid Flyby (CRAF) mission are discussed. The CRAF spacecraft and mission configurations are illustrated and the scientific studies planned for the mission are listed. The scientific benefits of the study of comets and asteroids are reviewed and the characteristics of Comet Kopff are outlined. In addition, the structure, propulsion, attitude and articulation control, radio frequency and antenna, power and pyro, command, and data storage subsystems are described.

Description: Preliminary results from Voyager's encounter with Neptune are reviewed. The major events of the encounter are listed and the data on the atmosphere, magnetosphere, and ring-arc region of Neptune are discussed. The communications and photographical techniques used in the mission are examined. In addition, a search for Neptune satellites is considered.

Description: The NASA Space Shuttle Earth Observations Office conducts astronaut training in earth observations, provides orbital documentation for acquisition of data and catalogs, and analyzes the astronaut handheld photography upon the return of Space Shuttle missions. This paper provides backgrounds on these functions and outlines the data constraints, organization, formats, and modes of access within the public domain.

Description: The old concept of using the wake of a spacecraft to obtain an ultrahigh vacuum is revisited. A wakeshield can be configured so that a surface of interest does not subtend any walls that could become contaminated, thus it should be possible to achieve a contamination-free, ultrahigh vacuum capability with infinite pumping speed even in the presence of high heat loads and moderate gas loads. This papar analyzes the conceptual design for a Space Ultravacuum Research Facility (SURF), both in a shuttle-attached mode and as a free flyer. It is shown that even in the shuttle-attached mode, it should be possible to obtain vacuum levels equivalent to 10 to the -9th to 10 to the -10th Torr with O and N2 as the primary constituents. As a free flyer the SURF will be limited primarily by the gas load from the process being performed. For chemical beam epitaxy it is shown that equivalent vacuum levels of 10 to the -14th Torr should be possible at 300 km.

Description: Results from IRAS and the technical details of the IRAS satellite are reviewed. The IRAS telescope operation is briefly described. The observation of the Vega phenomenon, or the orbiting clouds of dust which encircle main sequence stars, is discussed. Also, the discovery that a large number of solar-type stars have excess IR radiation due to orbiting shells or disks of solid material is examined. In addition, the prospects for future telescopes are considered.

Description: Rendezvous missions to earth-crossing asteroids are of interest to NASA, for scientific purposes as well as for technological applications and ecological implications. To provide a comprehensive data base for planners of such missions, a mission opportunity map (MOM) has been created for eight relatively easy-to-access asteroids. A MOM presents such mission data as launch dates, flight times, and launch and postlaunch delta V requirements for all useful mission opportunities. The merits of a MOM are: (1) searches for all useful mission oportunities are completed in the process of generating a MOM, and (2) a MOM provides a clear view of good and bad opportunities, the extent of performance variations, and the repeatability of the missions.

Description: To attain the fundamental goals of cometary exploration, rendezvous and sample return missions are necessary. This paper investigates various trajectory options and provides a comprehensive set of mission opportunities available for launches in the 1990s. The modes of explorations considered are rendezvous and flybys with atomized-sample-return missions. For each type of exploration, the paper describes various classes and modes of trajectories available, their inherent characteristics, and the techniques of identifying useful trajectories. The energy requirement associated with these missions and the performance possibilities are provided.

Description: An extensive investigation of the ways to rendezvous with diverse groups of asteroids residing between 2.0 and 5.0 AU is made, and the extent of achievable missions using the STS upper-stage launch vehicles (IUS 2-Stage/Star-48 or NASA Centaur) is examined. With judicious use of earth, Mars, and Jupiter gravity assists, rendezvous with some asteroids in all regions of space is possible. It is also shown that the STS upper stages are capable of carrying out missions beyond a single rendezvous, namely with several flybys and/or multiple rendezvous.

Description: Preliminary analysis results have been obtained for tests conducted to ascertain whether a distinctive fragmentation 'signature' allows discrimination between launch vehicle upper stage destructions due to hypervelocity particle impacts and internal explosions. An account is presently given of factors controlling the damage pattern created by hypervelocity impacts, and an evaluation is made of the applicability of the simulation results obtained to actual upper stage destruction characterization.

Description: Thirteen lightcurves of asteroid 3 Juno from three different oppositions are given. The pole of Juno is less than 10 deg from ecliptic longitude 104 deg and latitude + 36 deg (or 316 and + 62 deg). The sidereal period is 0.3003969 + or - 0.0000003 (1 sigma) day and the rotation is prograde. There is little similarity between the Juno lightcurves from 8 oppositions which is unexplained at this time.

Description: In this paper, mission orbit considerations are addressed for using the Space Shuttle as a telescope platform for observing man-made orbital debris. Computer modeling of various electrooptical systems predicts that such a space-borne system will be able to detect particles as small as 1-mm diameter. The research is meant to support the development of debris- collision warning sensors through the acquisition of spatial distribution and spectral characteristics for debris and testing of detector combinations on a shuttle-borne telescopic experiment. The technique can also be applied to low-earth-orbit-debris environment monitoring systems. It is shown how the choice of mission orbit, season of launch, and time of day of launch may be employed to provide extended periods of favorable observing conditions.

Description: The dynamics of the Pluto-Charon system are reviewed from a historical perspective. Although Pluto's orbit crosses Neptune's, an intricate system of nested resonances keeps these planets apart. Pluto's orbit is apparently chaotic as well. Pluto always keeps the same face turned toward Charon, and vice versa. Tides also damp Charon's orbital eccentricity and inclination. Precession of Pluto's orbital plane causes Pluto's obliquity to vary periodically from formally prograde to retrograde. Pluto is probably an original member of the Solar system, but not an escaped satellite of Neptune.

Description: The microspacecraft is defined as a fully functional spacecraft whose mass is on the order of 10 kg or less. The results of a recent microspacecraft workshop are reviewed. The workshop concluded that microspacecraft are feasible and can be enabling for missions that require multiple simultaneous measurements displaced in position or very high mission delta-VSDIO-s. The paper includes discussions of science objectives and instruments as well as potential missions. Potential missions include a very close approach to the sun, determining the origin of gamma ray bursters and a search for gravity waves. Technology for microspacecraft is coming from the 'Lightsat' or small satellite community and developments sponsored by the SDIO. Concepts for microspacecraft power and telecommunications subsystems developed at the JPL are presented. Due to their small size, microspacecraft can be launched by traditional chemical rockets and also unconventional launchers such as electromagnetic launchers.

Description: It is shown that gamma-ray burst detectors on a network of microspacecraft can be used to directly determine burst directions to a few arcsec in both angular coordinates. This level of accuracy is sufficient to conduct searches for the quiescent counterpart of the burster at other wavelengths. It is maintained that the strawman instrument for the microspacecraft network, consisting of two 1 kg Na I detectors on opposite ends of the spacecraft, is capable of providing a nearly omnidirectional FOV with adequate sensitivity to gamma-ray bursts.

Description: An analysis is provided for the capabilities of the Spacewatch Camera operated at Kitt Peak National Observatory by the University of Arizona for the detection of the large flux of small comets in the vicinity of earth that is proposed by Frank et al. (1986). The characteristics of this telescope are used to determine its optimum operational mode for the detection of these small comets. It is concluded that the Spacewatch Camera can detect these small comets near earth if the proposed large fluxes in prograde orbits are present. It is unlikely that previous optical telescope surveys would have detected these objects. A heretofore undetected, large flux of small objects was detected. The characteristics of these objects appear to be in general agreement with those of the comets proposed by Frank et al. (1986). No other known population of objects or other effects that could provide the observed optical signatures has been identified at this time. Because these initial results are of such great importance to our perception of the solar system, they should be conservatively treated as an initial result until confirmation is made with similar observations from other telescopes.

Description: The paper presents launch vehicle and upper-stage options for application to lunar and interplanetary microspacecraft missions. Particular attention is given to the capabilities of Piggyback, small launch vehicles, and large launch vehicles. It is noted that Piggyback options on the Shuttle and expendable launch vehicles enable near-term earth-orbital missions and the potential for lunar and planetary missions if an electric-propulsion upper-stage is developed. Launch systems like the Space Shuttle could be used to launch large members of microspacecraft in 'constellation deployment' and 'shotgun' class missions to a variety of solar-system targets such as the sun, asteroids, comets, the moon, Mars, and Saturn.

Description: The general configuration, development schedule, and capabilities of the NASA International Space Station are reviewed, with an emphasis on the possibilities for long-term measurements of high-energy cosmic and secondary radiation from the main Station spacecraft, coorbiting or polar-orbit platforms, or Station-supported GEO satellites. Also outlined are the organizational structure and the application procedures to be followed by potential users of the Station facilities. Diagrams and drawings are provided.

Description: Plans for space-science experiments on the International Space Station (ISS) are reviewed, with a focus on biological and medical research with implications for manned missions to the moon and planets (in a scenario culminating in the establishment of a space colony by about the year 2018). Both applied biomedical research (determining the limits of human endurance in space and developing CELSS technology to extend them) and basic research (on the physiological response of plants and animals to the space environment) are discussed, and particular attention is given to the design and deployment schedule for the ISS biomedical hardware modules (Life Sciences Module, Centrifuge Module, and Variable-Gravity Research Facility). Also included are diagrams; drawings; photographs; and tables listing the individual experiments, their objectives, and the hardware required.

Description: The IRAS survey detectors show nonlinear characteristics in their gains and baselines. This behavior can be described by an exponentially decaying gain enhancement, dependent on previously observed flux. The baseline behavior has been modeled by a decaying function composed of the sum of two exponential functions. The scale lengths are 10 arcmin and 1.1 deg for 12 microns, and 8 arcmin and 43 arcmin for 25 microns. Amplitude changes due to this type of hysteresis are less than 1 percent. In addition there is a considerable response of all detectors to particles associated with the South Atlantic Anomaly. Attempts to correct for this effect were performed on the 12- , 60- and 100-micron detectors in the form of bias boosts. This note presents a correction procedure for the 25-micron detectors.

Description: New optical spectroscopic and UBV photometric observations of the bright Be/shell star V644 Mon (HD 51480) are presented. The object, which has been described as an interacting binary system, exhibits strong, variable Balmer emission as well as numerous metallic emission features in the blue. No signs of absorption features due to any late-type companion are seen at wavelengths below 6500 A.

Description: NASA has instituted a plan for the definition of activities and resources required over the coming decade for the deepening of current understanding of anthropogenic orbital debris, and its effects on future mission operations. This understanding will be the basis of policy definition and policy implementation efforts. The most immediate requirement is the definition of the debris environment, with emphasis on data for debris sizes smaller than 4 cm. Systems-damage criteria and hypervelocity-impact theory will then be used to define the hazard to specific spacecraft.

Description: The albedo of upper-stage breakup debris is proposed as an accurate discriminator among the various possible causes of breakup, which encompass residual fuel explosions and hypervelocity particle impacts. The fragments from an impact are covered with a thin layer of soot deposited from the destruction of polymeric circuit boards, while pressure vessel explosion fragments can be expected to remain soot-free. Albedo also facilitates the interpretation of small-debris optical telescope measurements.

Description: Earlier airborne studies of the infrared bands between 5 and 8 microns have now been extended to a sample of southern sources selected from the IRAS Low Resolution Spectra (LRS) atlas. The correlation between the strongest bands at 6.2 and 7.7 microns is now based on a total sample of 40 sources and is very strong. A new emission band at 5.2 microns, previously predicted for polycyclic aromatic hydrocarbons (PAHs), is recognized in 27 sources; it too correlates with the dominant 7.7 micron band, showing that the 5.2 micron feature also belongs to the generic spectrum of PAH features at 3.3, 5.6, 6.2, 6.2, 7.7, 8.7, 11.3, and 12.7 microns. Sufficient sources are had now to define the relative strengths of most of these bands in three separate nebular environments: planetaries, H II regions, and reflection nebulae. Significant variations are detected in the generic spectra of PAHs in these different environments which are echoed by variations in the exact wavelength of the strong 7.7 micron peak. The earlier suggestion that, in planetaries, the fraction of total emission observed by IRAS that is carried by the PAH emissions is correlated with nebular gas-phase C/O ratio is supported by the addition of newly-observed southern planetaries, including the unusually carbon-rich (WC10) nebular nuclei. These (WC10) nuclei also exhibit a strong plateau of emission linking the 6.2 and 7.7 micron features.

Description: High resolution spectra of the 11.3 micron emission band in M82 and NGC 7027 were obtained using the University of Texas IR echelle spectrometer on the IRTF in April 1988. The spectral resolution was 0.004 micron, with coverage from 11.0 to 11.6 microns. Spectra were measured at ten positions along a 10 min. long slit. Analysis of the data is still in progress, but initial results show no clear evidence of narrow structure within the feature. The analysis will involve comparison of the observed spectra to laboratory and predicted spectra of Polycylic Aromatic Hydrocarbons (PAHs) and Quenched Carbonaceous Composite (QCCs) to determine which may be responsible for the emission. The spectra will be examined with a goal of determining whether the emission is caused by molecular or solid state material. The data are also examined for evidence of variations in the shape and strength of the 11.3 micron feature with position on the sky. In NGC 7027 the 10 min. long slit went across the edge of the ionized nebulae, allowing comparison of emission from both ionized and neutral regions.

Description: Images were obtained of the (fluorescent) molecular hydrogen 1-0 S(1) line, and of the 3.3 micron emission feature, in Orion's Bar and three reflection nebulae. The emission from these species appears to come from the same spatial locations in all sources observed. This suggests that the 3.3 micron feature is excited by the same energetic UV-photons which cause the molecular hydrogen to fluoresce.

Description: An interactive, graphical proximity operations planning system was developed which allows on-site design of efficient, complex, multiburn maneuvers in the dynamic multispacecraft environment about the space station. Maneuvering takes place in, as well as out of, the orbital plane. The difficulty in planning such missions results from the unusual and counterintuitive character of relative orbital motion trajectories and complex operational constraints, which are both time varying and highly dependent on the mission scenario. This difficulty is greatly overcome by visualizing the relative trajectories and the relative constraints in an easily interpretable, graphical format, which provides the operator with immediate feedback on design actions. The display shows a perspective bird's-eye view of the space station and co-orbiting spacecraft on the background of the station's orbital plane. The operator has control over two modes of operation: (1) a viewing system mode, which enables him or her to explore the spatial situation about the space station and thus choose and frame in on areas of interest; and (2) a trajectory design mode, which allows the interactive editing of a series of way-points and maneuvering burns to obtain a trajectory which complies with all operational constraints. Through a graphical interactive process, the operator will continue to modify the trajectory design until all operational constraints are met. The effectiveness of this display format in complex trajectory design is presently being evaluated in an ongoing experimental program.

Description: The Office of Exploration has established a process whereby all NASA field centers and other NASA Headquarters offices participate in the formulation and analysis of a wide range of mission strategies. These strategies were manifested into specific scenarios or candidate case studies. The case studies provided a systematic approach into analyzing each mission element. First, each case study must address several major themes and rationale including: national pride and international prestige, advancement of scientific knowledge, a catalyst for technology, economic benefits, space enterprise, international cooperation, and education and excellence. Second, the set of candidate case studies are formulated to encompass the technology requirement limits in the life sciences, launch capabilities, space transfer, automation, and robotics in space operations, power, and propulsion. The first set of reference case studies identify three major strategies: human expeditions, science outposts, and evolutionary expansion. During the past year, four case studies were examined to explore these strategies. The expeditionary missions include the Human Expedition to Phobos and Human Expedition to Mars case studies. The Lunar Observatory and Lunar Outpost to Early Mars Evolution case studies examined the later two strategies. This set of case studies established the framework to perform detailed mission analysis and system engineering to define a host of concepts and requirements for various space systems and advanced technologies. The details of each mission are described and, specifically, the results affecting the advanced technologies required to accomplish each mission scenario are presented.

Description: A recent survey by Roby (1987) discovered that the relatively weak high excitation lines of N 1 near 7468 and 8680 A were undetectable in the majority of HgMn stars, leading to upper limits on the N abundance of roughly ten times below that of the solar N abundance. Standard stars with similar temperatures (10,000 to 13,000 K) did exhibit these same N lines and were found to have roughly solar N abundances. The N abundances were redetermined in two HgMn stars and four standard stars using the strong, low excitation lines of N 1 found in the ultraviolet. The observational data consisted of high quality, high resolution, co-added International Ultraviolet Explorer spectra which was previously collected and reduced. Examination of the spectra plus considerations of signal/noise and severe line blending led to the choice of three promising N 1 lines located at 1742.7, 1745.3 and 1411.9 A. The atomic data for these lines were previously calculated using the best laboratory measurements found in a search of the relevant literature. The chosen N lines turned out to be blended significantly with Fe 2 lines. To obtain the abundances for N synthetic spectra were computed to match the observed spectra. The synthetic spectra were calculated using lie-blanketed model atmospheres, stellar parameters, and abundances for the other elements based upon previous work by S. Adelman. The N abundance was then adjusted to give the best fit of the observed line profiles. In the 2 HgMn stars, the N lines were again found to be undetectable, but the stronger intrinsic strength of the new lines yield more stringent upper limits than those obtained previously. Model atmosphere and abundances were updated in two stars where new results were reported. An additional N 1 line and an additional standard star were added to the program. A line opacity model was developed for a missing feature adjacent to the N 1 line at 1745.2 A, leading to a 25 percent improvement in the determined from this line.

Description: Laboratory experiments were performed to study the temperature dependence of the absorption spectrum of the coronene molecule (C24H12), believed to be representative of the polycyclic aromatic hydrocarbon (PAH) molecules present in the interstellar medium. The main results is that both line positions and total intensities are almost unchanged when varying the temperature so that the spectrum is mostly temperature independent in the explored range, supporting the modeling of the IR emission originally made by Leger and Puget where room temperature was used in the calculations. In the structure of the band shape, small temperature correlated changes are observed. Qualitative arguments are given to interpret them.

Description: Space-based, observational diffuse galactic light (DGL) levels at 4400 A are presented as a function of galactic latitude (b). A peak in the ratio of DGL to direct starlight is apparent at the absolute value of b = 5 to 15 deg, where one third of the celestial brightness is due to scattered light. Another salient feature is the general decrease in the relative contribution of the DGL at intermediate and high galactic latitudes. The relationship DGL (S sub 10(V)sub G2V, 4400 A) = 2.4 x 10 (exp -20 N(sub H I) atoms/sq cm may be used to estimate the brightness of DGL from neutral hydrogen column densities when N(sub H I) is less than 2 x 10(exp 21) atoms/sq cm. The results presented here have been used to characterize the interstellar dust in the general interstellar medium. A galaxy model that reproduces observed brightness levels was used to compare theoretical and observed DGL values. This determines two grain parameters - the albedo and the asymmetry of the scattering phase function (g). The results are albedo = .61 + or - .07, and g = .6 + or - .2.

Description: The Ultraviolet Imaging Telescope (UIT) was designed to be able to obtain deep images of nearby galaxies with a single frame. This ability makes it ideal for many imaging problems of the interstellar dust. The instrument has a forty arc-minute field of view with two arc-second resolution. It has 11 ultraviolet filters and a grating which is used as a grism for full field spectroscopy. In a thirty minute exposure (one orbital night) the limiting magnitude for hot objects is V = 25, or a UV mag of 22 for point sources and a UV mag of 26 for extended sources. Programs are planned for the observation of dust in reflection nebulae H II regions, planetaries, dark nebulae, the diffuse galactic light, and dust in other galaxies are planned. The UIT was integrated into the Astro Spacelab Payload and is scheduled to be launched on the Columbia in Nov. 1989.

Description: NGC 2023 is a bright reflection nebula illuminated by the central star HD37903. At 2 microns the nebula is seen solely by reflected light from the central star but in the NIR there is excess radiation that is supposed to arise from thermal emission from a population of small grains (Sellgren, 1984). The unexpectedly high surface brightness at R and I wavelengths has led to the suggestion that even at these wavelengths there is a significant contribution from this thermal emission process (Witt, Schild, and Kraiman, 1984). If the nebula is seen by reflected starlight then this radiation will be linearly polarized. The level of polarization depends on the scattering geometry, grain size distribution, etc., and is typically 20 to 40 percent for nebulae such as NGC 1999 which is morphologically similar to NGC 2023. If, in any waveband, there is a contribution of radiation from emission processes this radiation will be unpolarized and will serve to dilute the scattered radiation to give a lower level of observed polarization. A study of the wavelength dependence of polarization in nebulae in which there may be thermal emission from grains will indicate the contribution from this process to the total luminosity. Polarization maps were produced in BVRI wavebands for the NGC 2023 nebulosity which confirm that at all wavelengths it is a reflection nebula illuminated by a central star. The wavelength dependence of polarization at representative points in the nebula and in a scatter plot of polarization in V and I wavebands at all points at which measurements are given. Results indicate that throughout the nebula there is a general trend for the level of polarization to increase with wavelength and that maximum levels of polarization occur at the longest wavelengths. No evidence is seen in the data for any significant contribution from the thermal emission from grains in the BVRI luminosity of NGC 2023.

Description: The 3 micron spectra is presented for the Orion bar region and the Red Rectangle. In both objects spectra were obtained at more than one location, corresponding to different distances from the excitation source. The well known 3.3 and 3.4 micron emission bands are seen in both objects as well as the recently discovered features at 3.46, 3.51, and 3.57 microns in the Orion bar spectra. The spectra show that the relative strengths of the 3 micron emission features vary within the Orion bar. As distance from the exciting star increases, the 3.4 and 3.51 micron features increase, and the 3.46 micron feature decreases in strength, relative to the strong 3.3 micron feature. These are two possible interpretations which are postulated, each of which involves the breaking of bonds by UV radiation, which removes the modes responsible for the 3.4 micron emission near the star. The two possible bond ruptures are the CH bond in small polycyclic aromatic hydrocarbons (PAHs), or the bond to an aliphatic subgroup. It has to be pointed out that neither interpretation appears entirely satisfactory. The vibrational overtone interpretation cannot explain the presence or behavior of the 3.46 micron feature, whereas the laboratory spectra of aliphatic sidegroups contain many more features in the 3 micron region than are observed in the astronomical sources.

Description: The nation's efforts to expand human presence and activity beyond Earth orbit into the solar system was given renewed emphasis in January of 1988 when the Presidential Directive on National Space Policy was signed into effect. The expansion of human presence into the solar system has particular significance, in that it defines long-range goals for NASA's future missions. To embark and achieve such ambitious ventures is a significant undertaking, particularly compared to past space activities. Missions to Mars, the Moon, and Phobos, as well as an observatory based on the dark side of the Moon are discussed.

Description: The ring-like interstellar visual echoes of radii 33 and 54 arcsec detected around SN 1987A should coincide with infrared echoes (thermal reradiation) from dust at T approximately equal to 15 to 30 K. Whether these infrared echoes are detectable at present is considered. They will be brightest at approximately 100 microns, the range of the Texas infrared photometer. Detectability depends on the ratio zeta congruent to tan(sub a)/tan(sub s)P(theta), where tan(sub a) and tan(sub s) are the visual absorption and scattering optical thicknesses of the echo layer, and P is the phase function function for small-angle scattering (theta approximately equal to 2 to 4 degrees). Zeta approximately greater than 1 is needed for a detectable signal (approximately 0.3 Jy), but zeta cannot be much less than 1; otherwise the visual echoes could not be as bright as they are. Typical dust mixtures of Mathis-Rumpl-Nordsieck type have zeta much less than 1. Zeta remains small even if a population of very small grains with power-law index as steep as approximately 5.5 is added. A population with even more small grains and/or fewer large grains could have a zeta similar to 1 and be detectable at present, but this seems unlikely. The echoes will move, but should remain accessible for many years and should be detected eventually.

Description: The circumstellar grains of two hot evolved post asymptotic giant branch (post AGB) stars, HD 89353 and HD 213985 were examined. From ultraviolet spectra, energy balance of the flux, and Kurucz models, the extinction around 2175 A was derived. With visual spectra, an attempt was made to detect 6614 A diffuse band absorption arising from the circumstellar grains so that we could examine the relationship of these features to the infrared features. For both stars, we did not detect any diffuse band absorption at 6614 A, implying the carrier of this diffuse band is not the carrier of the unidentified infrared features not of the 2175 A bump. The linear ultraviolet extinction of the carbon-rich star HD 89353 was determined to continue across the 2175 A region with no sign of the bump; for HD 213985 it was found to be the reverse: a strong, wide bump in the mid-ultraviolet. The 213985 bump was found to be positioned at 2340 A, longward of its usual position in the interstellar medium. Since HD 213985 was determined to have excess carbon, the bump probably arises from a carbonaceous grain. Thus, in view of the ultraviolet and infrared properties of the two post AGB stars, ubiquitous interstellar infrared emission features do not seem to be associated with the 2175 A bump. Instead, the infrared features seem related to the linear ultraviolet extinction component: hydrocarbon grains of radius less than 300 A are present with the linear HD 89353 extinction; amorphous anhydrous carbonaceous grains of radius less than 50 A might cause the shifted ultraviolet extinction bump of HD 213985.

Description: The reliability of a theoretical model that solves the radiative transfer equation in dust clouds surrounding a central star is checked. In particular, it is found that both classical scattering by dust and the back-heating effects are negligible in the radiative transfer when envelopes similar to IRC+10216 are taken into consideration. In addition, new fits of IRC+10216 spectra are presented which were obtained, when the source is in different luminosity phases, under the assumption that amorphous carbon grains are in the circumstellar envelope. The same model is currently used to simulate the emission from carbon-rich sources showing the silicon carbide feature at 11.3 microns.

Description: The infrared sky is dominated on large scales by emission from interplanetary dust, which produces the zodiacal emission (ZE), and interstellar dust. These two components of the infrared background differ in angular and spectral distribution, allowing the two to be separated easily in some places. A method of determining the emission from interplanetary dust near the Earth's orbit is described, and the results are compared to predictions for realistic materials with the interplanetary size distribution measured in situ.

Description: No single model has been able to account for all of the observed spectroscopic properties of interstellar or circumstellar dust. The reason for this is that, despite the agreement that the grains are composed of silicaceous/metal oxide and carbonaceous material, there is strong disagreement as to their exact structure and composition. This led Draine and Lee (1984) to use interstellar extinction data to define an interstellar graphitic material; new observational findings have made even that identification uncertain. But the great advantage of their approach is that they used observations at all of the wavelengths available to define the material. Here, the authors attempt a variation of that approach. They examine recent UV and IR data and attempt to put constraints on the possible types of interstellar grain composition, and to connect these constraints with grain models. A summary of some of the important constraints imposed by the observations is given.

Description: Among various candidate materials for interstellar dust, amorphous carbon (AC) is playing an increasingly important role (Greenstein, 1981; Hecht et al., 1984; Jura, 1983, 1986). Furthermore, recent in situ measurements have clearly shown the presence of carbonaceous grains in the coma of comet Halley (Kissel et al., 1986). Laboratory investigations on AC grains may be very useful to better interpret observations and to support theoretical elaborations. Recently, the authors started an international research program which also includes UV extinction analyses on AC samples, by using synchrotron light. Preliminary results obtained in a first shift of measurements, last June, are given. At the present stage of the data analysis, the authors can only draw some preliminary considerations. A wide band falling at around 240 nm is detected in all the analyzed samples. It intensity seems to decrease with increasing the dust collecting distance. A peak at 150 nm decreases in intensity with increasing the collecting distance. The band seems absent in the samples characterized by a larger amount of dust. A feature at about 200 nm is detected in some samples. At the moment the authors tend to attribute it to the transmission properties of the LiF substrates at the wavelength and/or to some problems in the experimental setup. It is unclear if a hump at 120 nm is real or due to instrumental effects. The profile of the spectra does not show substantial changes when the samples are cooled down to about 100 K. The present results appear to be in general agreement with previous findings, but their analysis is in progress and the interpretation is still on the way.

Description: Visual extinction of distant clusters seen through the Coma cluster seem to suggest that dust may be present in the hot x ray emitting intracluster gas. However, the Infrared Astronomy Satellite (IRAS) failed to detect any infrared emission from the cluster at the level expected from the extinction measurements. Researchers carried out a detailed analysis of the properties of intracluster dust in the context of a model which includes continuous injection of dust by the cluster galaxies, grain destruction by sputtering, and transient grain heating by the hot plasma. Computed infrared fluxes are in agreement with the upper limit obtained from the IRAS. The calculations, and the constraint implied by the IRAS observations, suggest that the intracluster dust must be significantly depleted compared to interstellar abundances. Researchers discuss possible explanations for the discrepancy between the observed visual extinction and the IRAS upper limit.

Description: First results of an on-going program to determine the wavelength dependence of the interstellar optical polarization of reddened stars in the Small Magellanic Cloud (SMC) are presented. IUE observations of reddened stars in the SMC (Bouchet et al. 1985) generally show marked differences in the extinction law as compared to both the Galaxy and the Large Megallanic Cloud. The aim here is to determine the wavelength dependence of the optical linear polarization in the direction of several such stars in the SMC in order to further constrain the dust composition and size distribution in that galaxy.

Description: Near-IR absorption features produced by core-mantle dust grains are observed in many protostellar objects. The high spatial resolution observations (less or equal to 3 in.) could be helpful to monitor the expected changes of the features. Cep A/IRS 6 is a suitable candidate to carry out such a kind of study. It is located in an active star formation region and consists of a young object associated with an extended reflection nebula. The ice feature was observed in four positions of Cep A/IRS 6 with a 2.7 in. aperture. The observations were carried out at the IRTF using the cooled grating array spectrometer CGAS. The 2.4 to 3.8 micron spectra of two positions are presented.

Description: Survey observations were conducted for H alpha-emission stars in the Orion region using the Kiso Schmidt telescope and partly the CTIO Curtis Schmidt telescope. In the area of about 25 square degrees, a total of 236 H alpha-emission objects, mostly supposed to be T Tau type stars, have been detected among which 155 are new ones including 6 non-stellar objects. Celestial coordinates and V-magnitude are measured for the detected objects. Eye estimation of the H alpha-emission intensity is also made at three epochs in a time span of about two years, where notable variation of H alpha intensity was found in 68 out of 236 objects. Besides a remarkable concentration along the northern dark cloud complex, a loose concentration is noticed near the Orion Belt region, fairly well coinciding with the distribution of the Orion OBIb association members. A comparison with the Av-map is also made to see the relationship between the distribution of emission-line objects and that of interstellar dust.

Description: Based on the idea that star formation goes on progressively in molecular clouds, a search was conducted for protostars by mapping compact H II regions at a frequency of 250 GHz. The IRAM 30 m radio telescope was used with a (3)He cooled bolometer. Twenty compact H II regions usually obtaining twice the expected free-free flux density, positionally coincident with the H II region, were observed. Even fine structure within the H II regions can be traced in the maps as in the case of G75.84+0.40 near ON-2. The high degree of coincidence between the 250 and 5 GHz map of Harris shows that the excess flux density observed must come from dust mixed with the ionized gas. Part of the dust must however be accumulated in the outer part of the H II region, since in some cases the contours are shifted outwards relative to the radio maps. This is consistent with the fact that in those cases where enough information is available to make a model fit, temperatures were derived of 80 + or - 30 K.

Description: An infrared defined (60 micron) sample of IRAS sources were systematically studied in order to investigate star formation in the outer Galaxy. Five percent of the sample are point sources with IRAS spectra that suggest the emission is from a dust shell surrounding a mature star. Ninety five percent have spectra where flux density strictly rises with wavelength. The sources are extended, and it is shown that Point Source Catalog fluxes seriously underestimate total fluxes. CO kinematic distances were reliably assigned to two thirds of the sources. Most of the infrared luminosities correspond to B spectral types. Six cm continuum emission were detected from all sources inferred to have spectral type B1 or earlier. The combined IRAS/CO/6 cm data show these sources are young, moderately massive stars that are embedded in interstellar clouds. The young embedded sources define a distinct band in an IRAS color-colar diagram. Normal IRAS galaxies fall in the same band, consistent with the interpretation that their infrared emission is due to star formation.

Description: A near infrared (2.2 micron) polarization survey of about 190 sources was conducted toward nearby dark clouds. The sample includes both background field stars and embedded young stellar objects. The aim is to determine the magnetic field structure in the densest regions of the dark clouds and study the role of magnetic fields in various phases of star formation processes, and to study the grain alignment efficiency in the dark cloud cores. From the polarization of background field stars and intrinsically unpolarized embedded sources, the magnetic field structure was determined in these clouds. From the intrinsic polarization of young stellar objects, the spatial distribution was determined of circumstellar dust around young stars. Combining the perpendicularity between the disks and magnetic fields with perpendicularity between the cloud elongation and magnetic fields, it is concluded that the magnetic fields might have dominated nearly all aspects of cloud dynamics, from the initial collapse of the clouds right through to the formation of disks/tori around young stars in these low to intermediate mass star forming clouds of the Taurus, Ophiuchus, and Perseus.

Description: Several new red and reddened stars are detected in the most heavily reddened associations Cyg OB2. About 47 IRAS sources are detected in Cyg OB2. Their flux distributions, and colors, suggest that they are young stellar objects embedded in dust envelopes or disks (some of them may be proto stars) and are most likely members of the Cyg OB2 association. The large values of the flux ratio L sub IR/L sub VIS suggests that the central objects are obscured because of very large extinction.

Description: Observations are presented of the H II region complex in W51 made with a mm interferometer. W51 is a region of massive star formation approx. 7 kpc distant from the sun. This region has been well studied in both the IR and submillimeter, the radio, as well as the maser transitions. These previous observations have revealed three regions of interest: (1) W51MAIN, a know of bright maser emission near two compact H II regions W51e1 and W51e2 (W51MAIN is also the peak of the 400 micron emission indicating that the bulk of the mass is centered there; (2) W51IRS1 is a long curving structure seen at 20 micron and at 2 and 6 cm but not at 400 micron; (3) W51IRS2 (also known as W51NORTH) is another compact H II region slightly offset from an 8 and a 20 micron peak and a collection of masers. Some conclusions are as follows: (1) SO and H(13)CN emission are similar and coincide with outflow activity; (2) HCO+ spectra show evidence for overall collapse of the W51 cloud toward W51MAIN; (3) A previously undetected continuum peak, W51DUST, coincides with the molecular peak H(13)CN-4; and (4) Dust emission at 3.4 mm reveals that about half of the 400 micron emission comes from the ultracompact H II region e2, and the rest from W51e1 and W51DUST.

Description: Two of the most promising explanations for the origin of the interstellar emission features observed at 3.29, 3.4, 6.2, 7.7, 8.6, and 11.3 microns are: quenched carbonaceous composite (QCC) and polycyclic aromatic hydrocarbons (PAHs). High resolution spectra are given of the 3.29 micron emission feature which were taken with the Cooled Grating Array Spectrometer at the NASA Infrared Telescope Facility and previously published. These spectra show that the peak wavelength of the 3.29 micron feature is located at 3.295 + or - 0.005 micron and that it is coincident with the peak absorbance of QCC. The peak wavelength of the 3.29 micron feature appears to be the same in all of the sources observed thus far. However, the width of the feature in HD 44179 and Elias 1 is only 0.023 micron, which is smaller than the 0.043 micron width in NGC 7027, IRAS 21282+5050, the Orion nebula, and BD+30 deg 3639. Spectra of NGC 7027, QCC, and PAHs is shown. QCC matches the 3.29 micron interstellar emission feature very closely in the wavelength of the peak, and it produces a single feature. On the other hand, PAHs rarely match the peak of the interstellar emission feature, and characteristically produce multiple features.

Description: A statistical examination of 126 extinction curves has revealed the presence of a second broad absorption feature similar in nature to the 2200 A feature. The feature is centered on wavelength 1706 A, has a full half-width of 350 A, and a mean central height of 0.21 magnitudes. The strength of the feature increases with E(B-V) supporting an interstellar origin, and on average it is 18 times weaker than the 2200 A feature.

Description: An analysis is presented for the variability of absolute IR, optical, and UV extinction, A(sub lambda), derived through the ratio of total-to-selective extinction, R, for 31 lines of sight for which reliable UV extinction parameters were derived. These data sample a wide range of environments and are characterized by 2.5 is less than or equal to R is less than or equal to 6.0. It was found that there is a strong linear dependence between extinction expressed as A(sub lambda)/A(sub V) and 1/R for 1.25 micron is less than or equal to lambda is less than or equal to 0.12 micron. Differences in the general shape of extinction curves are largely due to variations in shape of optical/near-UV extinction corresponding to changes in R, with A(sub lambda)/A(sub V) decreasing for increasing R. From a least-squares fit of the observed R-dependence as a function of wavelength for 0.8/micron is less than or greater than 1/lambda is less than or equal to 8.3/micron, an analytic expression was generated from which IR, optical, and UV extinction curves of the form A(sub lambda)/A(sub V) can be reproduced with reasonable accuracy from a knowledge of R. It was also found that the absolute bump strength normalized to A(sub V) shows a general decrease with increasing R, suggesting that some fraction of bump grains may be selectively incorporated into coagulated grains. Finally, it was found that absolute extinction normalized by suitably chosen color indices results in a minimization of the R-dependence of portions of the UV curve, allowing A(sub lambda) to be estimated for these wavelengths independent of R.

Description: The soft X-ray excess component is studied for a signal to noise limited subsample of 14 quasars from the WE87 sample observed with the Einstein Imaging Proportional Counter (IPC). Detailed analysis of the IPC data, combined with Einstein Monitor Proportional Counter (MPC) data where possible, and use of accurate galactic N sub H values allows estimation of the strength of any excess and improvement of constraints on the spectral slope at higher X-ray energies. A significant excess in 9 of the 14 objects is found. It is confined in all but one case to below 0.6 keV and variable in the two cases where there are multiple observations. The relation of the soft excess to other continuum properties of the quasars is investigated.

Description: A survey of the diffuse soft X-ray background as seen directly by the Einstein Observatory Imaging Proportional Counter (IPC) is presented. A source free region of the detector 1 by 1 degree field is used. The background in the 0.16 to 3.5 keV spectral region is viewed. The data covers roughly 5 percent of the sky, with some bias in coverage towards the galactic plane. The moderate energy resolution of the IPC enables the characterization and the production of maps of the background as a function of energy within the Einstein passband. The results are compared with previous observations of the diffuse X-ray background. The implications for galactic structure and for the soft component of the extragalactic X-ray background are discussed.

Description: The X-ray spectra of 27 Seyfert galaxies measured with the Solid State Spectrometer (SSS) onboard the Einstein Observatory is investigated. This new investigation features the utilization of simultaneous data from the Monitor Proportional Counter (MPC) and automatic correction for systematic effects in the SSS. The new results are that the best-fit single power law indices agree with those previously reported, but that soft excesses are inferred for at least 20 percent of the measured spectra. The soft excesses are consistent with either an approximately 0.25 keV black body or Fe-L line emission.

Description: The results of the search for iron features performed on 40 of the 48 EXOSAT spectral survey sources are discussed. In thrirteen of the sources the spectral fit was improved by the inclusion of an iron emission line at approximately 6.5 keV. In three of these, an ionized absorption edge improved the spectral fit. In one source, the spectral fit was improved by the addition of a cold iron absorption edge at approximately 7.1 keV. Line equivalent widths are not well determined. A statistical analysis of the line fits suggest an inverse correlation between line equivalent width and intrinsic source luminosity. Comparison of the host galaxy axial ratio with the line equivalent width suggests that larger equivalent widths occur in sources with more nearly face on host galaxies.

Description: Massive X ray binaries consist of an early type primary lossing mass via a strong stellar wind driven by the stars radiation field, and an accreting neutron star companion. The X rays from the neutron star affect the wind dynamics by changing the temperature and ionization structure. The effect of the accretion powered X rays on the radiative line force that drives the stellar wind is calculated. The consequences of these calculations for the wind dynamics in massive X ray binaries is discussed.

Description: The stability properties of radiative shocks in spherically symmetric accretion flows onto white dwarfs is discussed. Accretion rates that result in shock thicknesses ranging from thin to settling solutions are investigated. Models for white dwarf masses from 0.3 to 1.2 of the solar mass are presented. The effects of unequal ion and electron temperatures, electron thermal conduction, bremsstrahlung, and Compton cooling are included. It is shown that thick two-temperature shocks are unstable to oscillations in the fundamental mode for white dwarf mass up to and including 1.0 of the solar mass. The possibility that the 0.3 to 1.0 Hz optical Quasi-Periodic Oscillations (QPOs) observed in four AM Her type cataclysmic binaries are due to the first overtone instability. Low accretion rate shock instabilities may be responsible for the tens of seconds to several minute X-ray QPOs observed in some AM Her objects.

Description: Timing analysis of the pointed observations of 5 selected binary X ray pulsars, in two categories of disk-fed and wind-fed sources, by HEAO 1 A-2 is reported. The power spectral analysis was performed on the data in the frequency range from approx. 1 MHz to 6.25 Hz. The coherent signal of the pulsation, the continuum of the power spectrum, varies in time and differs among sources. Quasi-Periodic Oscillation (QPO) is probably related to a fast spinning but weakly magnetized neutron star in the low mass X ray binaries. QPO was searched for in this frequency range to see if scaling laws exist among these two systems which may have possessed different order of magnitude of magnetic field strengths and the inner disk radii. One possible QPO is found centering at 0.062 Hz in 4U0115+63 during a flare.

Description: Ginga observations of several low mass X ray binaries displaying pronounced dips of variable depth and duration in their X ray light curves are analyzed. The periodic occultation of the central X ray source by azimuthal accretion disk structure is considered. A series of spectra selected by intensity from the dip data from XB1916-053, are presented. The effects of a rapidly changing column density upon the spectral fitting results are modeled. EXO0748-676 was observed in March 1989 for three days. The source was found to be in a bright state with a 1 to 20 keV flux of 8.8 x 10 (exp -10) erg/sqcms. The data include two eclipses, observed with high time resolution.

Description: The Broad Band X Ray Telescope (BBXRT) is a new X ray spectrophotometer scheduled for launch Apr. 26, 1990, for a 10 day mission aboard the Space Shuttle Columbia. High quality spectra between 0.3 and 12 keV of about 100 different sources are expected. BBXRT has the best energy resolution for examining features due to the K-shell of Fe, seen in the spectra of X ray binaries. The resolution is sufficient to make sensitive searches for broadened emission lines, to resolve multiple features, and to determine the ionization state of the emitting plasma by measuring line energies. Simulated spectra of several sources are presented.

Description: The results of timing and spectral analyses of the X-ray sources Aql X-1 (X1908+005) and 4U1820-30 (NGC6624) are reported using data obtained with the Einstein SSS (Solid State Spectrometer) and MPC (Monitor Proportional Counter) instruments. A classic type I burst was observed from Aql X-1 in both detectors and a coherent modulation with a period of 131.66 + or - 0.02 ms and a pulsed fraction of 10 percent was detected in the SSS data. There is no evidence for a loss of coherance during the approximately 80 sec when the burst is observable. The 2 sigma upper limit on the rate of change of the pulse period is 0.00005s/s. It is argued that an asymmetrical burst occurring on a neutron star rotating at 7.6 Hz offers a plausible explanation for the oscillation. The data from 4U1820-30 show that the amplitude of the 685 sec modulation, identified as the orbital period, is independent of energy down to 0.6 keV. The SSS data show that the light curve in the 0.6 to 4.5 keV band is smoother than at higher energies.

Description: Emission lines are probes of the conditions in the accretion flows associated with binary X-ray sources. The hard X-ray iron K line, soft X-ray lines, and UV lines, and what they indicate about the conditions in binary X-ray sources are discussed. These lines are interpreted using an X-ray illuminated accretion disk model. The structure and dynamics of the heated disk, its spectral signatures, and the major unsolved theoretical issues surrounding them are investigated.

Description: The observations of the M giant star, IRAS 09371+1212, in the 40 to 70 microns emission bands, are reported. This star has a circumstellar CO envelope, and a unique infrared color, attributed to ice emission bands. The observations performed in February 1988, using grating spectrometer, showed that the far infrared bands of ice are the strongest known in the sky, and that its dust temperature (50K) is the lowest known for a circumstellar envelope. The 43 microns band of ice is also detected in several very cold circumstellar envelopes.

Description: The data concerning low resolution airborne spectra from 5 to 8 microns available for a sample of 40 sources selected from the Infrared Astronomy Satellite low resolution spectral Atlas with polycyclic aromatic hydrocarbon (PAH) emission features, are discussed. A new emission band at 5.2 microns, previously predicted for PAHs, was found in 33 sources; it also correlates with the 7.7 microns band. This extends the spectrum of narrow observed PAH features to 3.3, 5.2, 5.6, 6.2, 6.9, 7.7, 8.7, 11.3, and 12.7 microns. From the data the relative strengths of most of these bands are defined in three separate nebular environments: planetaries, H II regions, and reflection nebulae. The differences in the PAHs spectra in those environments are analyzed.

Description: The infrared spectrum emitted by nebular dust, heated by the ionizing stars in H II blisters and spherical H II regions, is calculated for various model parameters. Absorption of the non-ionizing radiation in a neutral layer is included. Heating by the Lyman alpha photon field is taken into account. The dust is composed of silicate and graphite grains, and evaporation of the grains in the inner region is considered. The models are presented with a view to interpretation of infrared observations of dusty H II regions and can be applied directly to the infrared astronomy satellite survey data. The continuum emission is compared with calculated fine structure line emission.

Description: The major scientific issues raised in this meeting about Active Galactic Nuclei (AGN) are summarized. The X-ray background and the capabilities of missions to be launched in the next 5 years (GRANAT, ROSAT, BBXRT, GRO, Astro-D, SAX, Spectrum-X-gamma, XTE) are discussed. Each one of these missions is considerably more powerful than its predecessor and will add to the knowledge of AGN and the X-ray background. By the end of the 1990's both of the X-ray astronomy Great Observatories, Advanced X-ray Astrophysics Facility (AXAF) and X-ray Multi mirror Mission (XMM), should be flying, each one of them more powerful than the intermediate scale missions of the early 1990's.

Description: The principal sources of the cosmic X-ray background (CXB) can be objects indicative of a physically early stage of active galactic nuclei (AGN) evolution. Such an evolutionary scenario is examined by using the HEAO-1 A2 X-ray selected sample of bright AGN as a diagnostic of anisotropies in the unresolved background. The observed limit on CXB global anisotropy is used to place an upper bound on the present-epoch volume emissivity of unresolved X-ray sources. Considering the A2 AGN count, CXB surface brightness fluctuations observed at higher energies (via HEAO-1 A4) suggest that present-epoch AGN could have the broadband spectral structure needed for the redshifted contributions of more luminous AGN with this same spectrum to account for the entire CXB.

Description: X-ray spectral surveys of large samples of Seyfert galaxies are discussed. The spectral shape in the 0.1 to 20 keV energy range is considered. Two new spectral survey are undertaken, one involving 105 Imaging Proportional Counter (IPC) observations of 75 Seyfert galaxies, the other using IPC and Monitor Proportional Counter (MPC) data from 28 observations of 23 Seyfert galaxies. The X-ray spectra of active galactic nuclei (AGN) are complex, with in most cases considerable steepening at the lowest energies. At higher energies (2 to 20 keV), the existence of a universal, canonical power law is confirmed, independent of X-ray luminosity over four orders of magnitude.

Description: SOFIA will be a three meter class telescope operating in a Boeing 747, offering astronomers routine access to infrared wavelengths unavailable from the ground, and with the means to observe transient astronomical events from anywhere in the world. The concept is based on 15 years of experience with NASA's Kuiper Airborne Observatory (KAO), which SOFIA will replace in the mid 1990's. SOFIA's wavelength range covers nearly four decades of the electromagnetic spectrum: from the visible, throughout the infrared and submillimeter, to the microwave region. Relative to the KAO, SOFIA will be roughly ten times more sensitive for compact sources, enabling observations of fainter objects and measurements at higher spectral resolution. Also, it will have three times the angular resolving power for wavelengths greater than 30 microns, permitting more detailed imaging at far infrared wavelengths.

Description: The Infrared Space Observatory (ISO) is an astronomical satellite, which will operate at infrared wavelengths (2.5 to 200 microns) for a period of at least 18 months. Imaging, spectroscopic, photometric and polarimetric observations will be obtained by four scientific instruments in the focal plane of its 60-cm diameter, cryogenically-cooled telescope. Two-thirds of ISO's observing time will be available to the astronomical community. ISO is a fully approved and funded project of the European Space Agency (ESA) with a foreseen launch date of May 1993.

Description: Large area focal plane arrays of unprecedented performance were developed for use in Near Infrared Camera and Multi-Object Spectrometer (NICMOS), a proposed Hubble Space Telescope refurbishment instrument. These FPAs are 128x128-element, HgCdTe hybrid arrays with a cutoff wavelength of 2.5 microns. The multiplexer consists of a CMOS field effect transistor switch array with a typical mean readout noise of less than 30 electrons. The detectors typically have a mean dark current of less than 10 electrons/s at 77 K, with currents below 2 electrons measured at 60 K (both at 0.5 V reverse bias). The mean quantum efficiency is 40 to 60 percent at 77 K for 1.0 to 2.4 microns. Functional pixel yield is typically greater than 99 percent, and the power consumption is approximately 0.2 mW (during readout only).

Description: Preliminary two-dimensional speckle interferometry results of HL Tau were found to be qualitatively similar to those found with one-dimensional slit scanning techniques; results consist of a resolved component (approximately 0.7 arcsec in size) and an unresolved component. Researchers are currently reducing the rest of the data (taken on three different telescopes and at three different wavelengths) and are also exploring other high resolution methods like the shift and add technique and selecting only the very best images for processing. The availability of even better two-dimensional arrays within the next couple of years promises to make speckle interferometry and other high resolution techniques very powerful and exiting tools for probing a variety of objects in the subarcsec regime.

Description: The development of stressed Ge:Ga detector arrays for far-infrared astronomy from the Kuiper Airborne Observatory (KAO) is discussed. Researchers successfully constructed and used a three channel detector array on five flights from the KAO, and have conducted laboratory tests of a two-dimensional, 25 elements (5x5) detector array. Each element of the three element array performs as well as the researchers' best single channel detector, as do the tested elements of the 25 channel system. Some of the exciting new science possible with far-infrared detector arrays is also discussed.

Description: It is shown that large format PtSi Schottky diode infrared arrays, the Hughes 256 X 256 hybrid Schottky array in particular, are competitive alternatives to the smaller format photovoltaic arrays for ground-based astronomy. The modest quantum efficiency of the PtSi compared to the photovoltaic devices is more than compensated for by the larger format. The use of hybrid technology yields effective fill factors of nearly 100 percent, and the low dark current, noise, excellent imaging characteristics, cost, and solid nitrogen operating temperature add to the effectiveness of this array for ground-based imaging. In addition to discussing the characteristics of this array, researchers present laboratory test data and astronomical results achieved at Kitt Peak.

Description: The University of Hawaii operates an infrared camera with a 128x128 HgCdTe detector array on loan from JPL's High Resolution Imaging Spectrometer (HIRIS) project. The characteristics of this camera system are discussed. The infrared camera was used to obtain images of the night side of Venus prior to and after inferior conjunction in 1988. The images confirm Allen and Crawford's (1984) discovery of bright features on the dark hemisphere of Venus visible in the H and K bands. Our images of these features are the best obtained to date. Researchers derive a pseudo rotation period of 6.5 days for these features and 1.74 microns brightness temperatures between 425 K and 480 K. The features are produced by nonuniform absorption in the middle cloud layer (47 to 57 Km altitude) of thermal radiation from the lower Venus atmosphere (20 to 30 Km altitude). A more detailed analysis of the data is in progress.

Description: In infrared (2.2 micron, K-band) search of small regions (25 in square) near 26 members of the Taurus star-forming association has revealed 20 dim (K = 13-16 mag) stellar objects near 13 of them. Of these 20 objects, 9 are exceptionally red. It is argued that these 9 are probably also Taurus members. From the luminosities (0.4 to 4 times 10 the -3 power luminosity) and ages (estimated at 10(exp 6) years), masses can be determined by reference to theoretical low-mass cooling curves. The masses are in the range 0.005 to 0.015 solar mass, i.e., low-mass brown dwarfs. Proper motion studies of 7 of the objects visible on the POSS plates conducted by Burton Jones establish that 4 are highly probable Taurus members while 1 is a possible member.

Description: An introduction to a series of infrared detector technology workshops is given. The establishment of goals and new requirements is addressed in a general way. The Shuttle Infrared telescope Facility (SIRIF) goals are listed. Given that the wavelength coverage is established at 2 to 750 microns and the unvignetted field of view is 7 arcmin, the field should be fully utilized at each wavelength, diffraction should be critically sampled, and each detector should be background limited.

Description: The instrumental background of X-ray astronomy with an emphasis on high resolution imagery is outlined. Optical and system performance, in terms of resolution, are compared and methods for improving the latter in finite length instruments described. The method of analysis of broadband images to obtain diagnostic information is described and is applied to the analysis of coronal structures.

Description: The principal features of the CRAF (Comet Rendezvous/Asteroid Flyby) mission are briefly reviewed. The mission profile is summarized and the CRAF trajectory is shown. The investigations tentatively selected for CRAF are listed and described. The planned approach and observations of the asteroid 449 Hamburga are outlined, and the spacecraft itself is depicted and briefly described.

Description: The life expectancy of the Voyager spacecraft as they enter interstellar space, and what they will find along the way, are examined. The range of options available to mission planners as to which instruments to keep alive and which to shut off for the interstellar voyage is addressed. The way that the spacecraft will be operated in interstellar space is described.

Description: The Ulysses mission will, for the first time, explore the heliosphere within a few astronomical units of the sun over the full range of heliographic latitudes, thereby providing the first characterization of the uncharted third dimension. Highly sophisticated scientific instrumentation carried on board the spacecraft is designed to measure the properties of the solar wind, the sun/wind interface, the heliospheric magnetic field, solar radio bursts and plasma waves, solar X-rays, solar and galactic cosmic rays, and interplanetary/interstellar neutral gas and dust. This collaborative ESA/NASA mission, scheduled for launch in October 1990, will use a Jupiter gravity-assist to achieve a trajectory extending to high solar latitudes /1,2/.

Description: Direct exploration of the heliosphere out to distances of about 40 AU has been carried out with Pioneer 10, 11 and Voyager 1, 2 while making use of supplementary observations by various spacecraft near 1 AU. In the past, these heliospheric observations have involved at least three divisions in the NASA Office of Space Science and Applications: Solar System Exploration, Astrophysics and Earth Observations. Consideration is now being given to combining the various missions into a single coordinated heliospheric program. A committee has been formed, the Heliospheric Science Working Group, consisting of the project scientists of the ongoing as well as future missions. The HSWG has drawn on appropriate members of the scientific community to assist in the development of a plan and in documenting it in a report. The highlights of the plan, with emphasis on both short range and long range scientific objectives, are described.

Description: This article describes the reduced astrometric observations of Phobos and Deimos derived from Mariner 9 imaging data. This data set spans 11 months from 1971 and 1972, contains 82 sets of spacecraft-centered right ascension and declination observations, and has an accuracy of 3 to 10 km (1-sigma) in orbital position. The details of the observation formulation and its use for ephemeris improvement are given.

Description: Microwave observations of Pallas, Vesta, and Hygiea at 2 and 6 cm wavelength yield brightness temperatures that are much lower than would be expected for a rapidly rotating blackbody. An analysis of the wavelength dependence of the observed brightness temperatures shows that, as was found for Ceres, these asteroids may be covered by a layer of material with the physical properties of finely divided dust. Models with layer depths of greater than 6 cm (Pallas), 6 cm (Vesta), and 8 cm (Hygiea) were found to represent well the variation in emissivity at radio wavelengths. The properties of the underlying layer are not well constrained by the microwave observations. It does appear that the real part of the dielectric vector for the substrate is similar to that of basaltic rock. Major compositional changes, if any, must take place at depths greater than about 10 cm. No evidence for water ice was found. Disk-resolved observations of the 2-cm emission of Vesta yield physical dimensions consistent with the recently published speckle-interferometry results.

Description: Far-infrared observations of chromospherically active, spotted, and plage stars in the dF7-dk7 spectral range are examined. Most (75 percent) of the stars have detectable 12-micron fluxes, and 50 percent of them have 25-micron emission. The 12-micron luminosity, L(12), is found to be in the range of 1.5-13 x 10 to the 30th ergs/s and to comprise only 0.2-0.5 percent of the star's total luminosity, L(bol). The present work extends to earlier spectral types and higher stellar luminosities the L(12) vs L(bol) relationship noted previously for late-type active dwarfs (K5-M5).

Description: Optical identifications are presented for 158 radio sources, mostly from the Southern Hemisphere, based on the coincidence between the position of the optical object and the compact milliarcsecond radio nucleus. Radio positions with an accuracy of typically 0.3 arcsec rms were measured from the observed delay and fringe rate of VLBI observations at 2.29 GHz on an Australia-to-South Africa baseline. Optical identifications and positions were measured from the UK Schmidt Telescope deep IIIa-J Southern Sky Survey plates, where available.

Description: Cousins (1980) data for 54 of the standard stars of Neckel and Chini (1980) and published measurements are used to investigate the properties of the Neckel-Chini VRI system. For red stars, this system diverges from the Johnson (1962) system, despite frequent claims of identity between the two. The Neckel-Chini and Cousins systems, however, are closely comparable. Both of these conclusions were previously reached in a paper by Bessell (1983); fair to good quantitative agreement with his results are obtained. Reddening ratios, the scatter in the Neckel-Chini standard-star data, and the effect of this scatter on published measurements for program stars, are discussed. Transformations from the Neckel-Chini system to the Cousins system are given.

Description: The H-II region W51 has been mapped in the near-infrared H and K wavebands with a resolution of about 6 arcsec over an area of about 14 sq arcsec. The W51 IRS 1 source has been resolved into six components, and an arc-like extension of small H-II regions is found that seems to parallel the edge of the molecular cloud. Measurements of the fluxes and extinctions of these sources are presented. A close correspondence is noted between the present K maps and the radio maps of Scott (1978).

Description: Results are presented from a study to determine the visibility of the crescent moon on July 14, 1988. About 2,000 observations from the U.S. and Canada are used to produce a visibility map. The factors affecting visibility are analyzed, including clouds, haze, and humidity.

Description: Numerical integrations are used here to show that small dust grains can be temporarily captured into exterior orbit-orbit resonances with the earth, lasting from less than 10,000 years to more than 100,000 years. Grains with radii of 30-100 microns, orbiting in planes less than 10 deg from the plane of the solar system and with orbital eccentricities of less than 0.3, are captured most easily. It is argued that there should be an approximately toroidal cloud of particles, derived mostly from the asteroid belt, trapped into a variety of these exterior resonances. The cloud is mostly beyond the earth's orbit, but includes it.

Description: The possibility of using aperture synthesis to image other planetary systems at submillimeter wavelengths is considered. The approach requires only a small increase in dynamic range over that already demonstrated by the VLA at longer wavelengths. The values of the relevant parameters are calculated and presented.