Showing papers by "Smithsonian Astrophysical Observatory published in 1990"
TL;DR: In this paper, a high-resolution multi-layer-coated X-ray imaging telescope, part of the Normal Incidence Xray Telescope sounding rocket payload, was used to image the peak of a two-ribbon flare.
Abstract: Results from a high-resolution multi-layer-coated X-ray imaging telescope, part of the Normal Incidence X-ray Telescope sounding rocket payload are presented. Images of the peak of a two-ribbon flare showed detailed structure within each ribbon, as well as the expected bright arches of emission connecting the ribbons. The number of X-ray bright points is small, consistent with predictions based on the previous solar cycle. Topology of the magnetic structure is complex and highly tangled, implying that the magnetic complexity of the photosphere is paralleled in the corona.
166 citations
TL;DR: In this article, it was shown that the X-ray-emitting gas in the Hydra A cluster must be condensing out of the intracluster medium at a rate of 600 solar masses/yr. This is the largest mass deposition rate observed in a cluster of galaxies.
Abstract: The Einstein imaging proportional counter observations of the poor cluster of galaxies centered on the radio galaxy Hydra A are examined. From the surface brightness profile, it is found that the X-ray-emitting gas in the Hydra A cluster must be condensing out of the intracluster medium at a rate of 600 solar masses/yr. This is one of the largest mass deposition rates observed in a cluster of galaxies. The ratio of gas mass to stellar mass is compared for a variety of systems, showing that this ratio correlates with the gas temperature.
111 citations
TL;DR: In this paper, the authors used the Arecibo 305 m telescope to observe radio bursts from flare stars at 430 and 1415 MHz, respectively, with bandwidths of 10 MHz and 40 MHz.
Abstract: The Arecibo 305 m telescope has been used to observe radio bursts from flare stars at 430 and 1415 MHz. Dynamic spectra of the emission with bandwidths of 10 MHz in the former case and 40 MHz in the latter are recorded. For AD Leo, the microwave burst emission was 100 percent right circularly polarized, achieved brightness temperatures near 10 to the 16th K, was generally broadband in character, but was superposed with finite structures in both frequency and time. Quasi-periodic pulsations were clearly present as well as a sudden reduction feature. For YZ CMi, the emission was 100 percent left circularly polarized and was relatively broadband with fine structures. Instabilities driven by anisotropies in the electron distribution, particularly the loss-cone distribution, are considered to account for the coherent radiation.
85 citations
TL;DR: In this paper, the depletion of an initially uniform distribution of asteroids extending form Mars to Saturn, caused by the gravitational perturbations of Jupiter and Saturn, is calculated by numerical integration of the asteroid orbits.
83 citations
TL;DR: A nonlinear generalization of quantum mechanics, recently formulated by Weinberg, is extended to systems of composite spin, such as atoms, and used hydrogen (H) masers to set a limit of 3.7 eV (8.9 Hz) on the magnitude of a nonlinear correction to the quantum mechanics of atomic spins.
Abstract: We extend a nonlinear generalization of quantum mechanics, recently formulated by Weinberg, to systems of composite spin, such as atoms. We have used hydrogen (H) masers to set a limit of 3.7\ifmmode\times\else\texttimes\fi{}${10}^{20}$ eV (8.9 \ensuremath{\mu} Hz) on the magnitude of a nonlinear correction to the quantum mechanics of atomic spins. This result is of comparable magnitude to the limit recently set in a single-valued (nuclear) spin system. In the absence of nonlinear effects, the experiment provides a new and stringent test of H-maser clock performance and the applicability of standard maser theory.
55 citations
TL;DR: In this article, the authors describe the instruments and the data reduction and analysis procedures used in each case, together with the sources and estimated magnitudes of associated errors, and make comparisons between different techniques (absorption vs emission) used on the same gondola, as well as between the same technique used on different gondolas.
Abstract: The balloon-borne instruments used in the two Balloon Intercomparison Campaigns in 1982 and 1983 to measure stratospheric HCl included five different IR spectrometers, three of which operated in the solar absorption mode and two in emission mode (at distinctly different wavelengths). This paper describes the instruments and the data reduction and analysis procedures used in each case, together with the sources and estimated magnitudes of associated errors. Comparisons are made between different techniques (absorption vs emission) used on the same gondola, as well as between the same technique used on different gondolas. The final results yield a mean profile of HCl concentration between 18 and 40 km altitude. The absolute accuracy of the final profile is estimated to be no worse than 10 percent.
27 citations
TL;DR: In this article, the vertical profile of hydrogen fluoride (HF) vapor in the stratosphere and of the vertical column amounts of HF above certain altitudes were made using a variety of spectroscopic instruments in the 1982 and 1983 Balloon Intercomparison Campaigns.
Abstract: Observations of the vertical profile of hydrogen fluoride (HF) vapor in the stratosphere and of the vertical column amounts of HF above certain altitudes were made using a variety of spectroscopic instruments in the 1982 and 1983 Balloon Intercomparison Campaigns. Both emission instruments working in the far-infrared spectral region and absorption instruments using solar occultation in the 2.5-micron region were employed. No systematic differences were seen in results from the two spectral regions. A mean profile from 20 - 45 km is presented, with uncertainties ranging from 20 to 50 percent. Total columns measured from ground and from 12 km are consistent with the profile if the mixing ratio for HF is small in the troposphere and low stratosphere.
21 citations
TL;DR: The combination of low atmospheric water vapor, high altitude, and low temperatures makes the South Pole and other high interior parts of the Antarctic continent particularly suitable locations for certain types of infrared or millimeter-wave astronomy as mentioned in this paper.
Abstract: The combination of low atmospheric water vapor, high altitude, and low temperatures makes the South Pole and other high interior parts of the Antarctic continent particularly suitable locations for certain types of infrared or millimeter-wave astronomy. Information available on the atmospheric column density of water at the South Pole and at Vostok, the Soviet station, are surveyed. To illustrate the usefulness of these areas for infrared astronomy, important astronomical lines in the wavelength region 50 to 200 microns are listed. The atmospheric transmission in this wavelength region is also calculated and plotted for 0.1 mm and 0.3 mm of precipitable water along the line of sight through the atmosphere. Such low values of precipitable water occur frequently enough to allow practical astronomical observations from the ground and, for certain cases, this can provide advantages over observations from high-flying aircraft or satellites.
19 citations
TL;DR: In this paper, Maggio et al. showed that a sharp decrease in maximum activity accompanies the advancing spectral type, with the dividing line corresponding to a steep gradient region, and confirmed the rotation-activity connection for stars in this region of the H-R diagram.
Abstract: Results are presented on an IUE UV survey of 255 late-type G, K, and M stars, complementing the Maggio et al. (1990) Einstein X-ray survey of 380 late-type stars. The large data sample of X-ray and UV detections make it possible to examine the activity relationship between the X-ray and the UV emissions. The results confirm previous finding of a trend involving a steeply-dropping upper envelope of the transition region line fluxes, f(line)/f(V), as the dividing line is approached. This suggests that a sharp decrease in maximum activity accompanies the advancing spectral type, with the dividing line corresponding to this steep gradient region. The results confirm the rotation-activity connection for stars in this region of the H-R diagram.
18 citations
TL;DR: In this paper, the authors compared a wide range of remote sensing techniques involving both emission and absorption in the mid-infrared and emission techniques in the far infrared regions of the spectrum.
Abstract: The Balloon Intercomparison Campaign (BIC) was set up to intercompare remote sensing measurements of a number of compounds other than water vapor; however, water vapor has strong absorption features throughout the infrared and mm wave regions of the spectrum. Therefore many of the investigators involved in BIC have absorption or emission features due to water vapor in the data they obtained during the balloon flights made under the campaign. These features have been used by the investigators to determine the stratospheric water vapor profiles which are compared in this paper. The profiles allow comparison of a wide range of remote sensing techniques involving both emission and absorption in the mid-infrared and emission techniques in the far infrared.
17 citations
01 Jan 1990
TL;DR: The Space Infrared Telescope Facility (SIRTF) is a one-meter class observatory for infrared astronomy that will be launched into high earth orbit by NASA in the late 1990's as discussed by the authors.
Abstract: The Space Infrared Telescope Facility (SIRTF) is a one-meter class observatory for infrared astronomy that will be launched into high earth orbit by NASA in the late 1990's. SIRTF's three focal plane instruments will permit imaging and spectroscopy over most of the infrared spectrum with sensitivities of 100 to 10,000 times their predecessors. This paper briefly reviews SIRTF's capabilities, science objectives, and current status.
01 Jul 1990
TL;DR: In this paper, a large-format CCD imager is described and tested, which incorporates floating diffusion as well as floating gate amplifiers on a 2048 by 2048 format which was employed as the design base.
Abstract: A large-format CCD imager is described and tested. The CCD imager incorporates floating diffusion as well as floating gate amplifiers on a 2048 by 2048 format which was employed as the design base. The amplifiers are intended to allow repeated nondestructive read operations on individual pixels in the array. The serial register was separated into two independently clocked halves to permit simultaneous readout of all four quadrants of the imager. Extensive schematic layouts of the base model and modification are given. The results of a performance test are presented, showing good results in the cooling curve for average dark current, and for charge transfer characteristics. The amplifiers are intended to reduce net readout noise, and the simultaneous readout capability is intended to reduce total read time, although neither was fully tested. The large-format CCD imager is of interest for astronomical photography and spectroscopic applications.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
01 Jan 1990
TL;DR: POINTS as mentioned in this paper is a space-based optical astrometric interferometer, capable of measuring the angular separation of two stars about 90° apart with 5-microarcsec (μas) nominal accuracy.
Abstract: POINTS is a space-based optical astrometric interferometer, capable of measuring the angular separation of two stars about 90° apart with 5-microarcsec (μas) nominal accuracy. During the intended ten-year mission, a repeated survey of a few hundred targets over the whole sky, including a few bright quasars, will establish a “rigid” reference grid with 0.5 μas position uncertainties. At that level, the grid will be free of regional biases and tied to the extra-Galactic frame that is our present best candidate for an inertial frame. POINTS will also determine parallaxes and annual proper motions at about the same level. Further, the planetary ephemeris frame will be tied through stellar aberration to the grid at about 300 μas. Additional targets of interest, to a limiting magnitude of greater than 20, will be observed relative to the grid, yielding determinations with uncertainties depending on the observing schedule. Measurement at the microarcsec/year level of the apparent relative velocities of quasars that are widely separated on the sky will severely test the assumption of cosmological quasar distances and may also constrain models of the early Universe.
01 Jul 1990
TL;DR: In this paper, the authors present results of charge transfer efficiency and dark current tests for large Reticon and Ford CCDs, as well as a description of some experiments to improve the UV quantum efficiency.
Abstract: Results of charge transfer efficiency and dark current tests for large Reticon and Ford CCDs are given, as well as a description of some experiments to improve the UV quantum efficiency, using a biased flash-gate for thinned CCDs and phosphor overlay for front-illuminated CCDs. The results indicate that large affordable CCDs suitable for astronomical work are now in reach, with excellent charge-handling characteristics, low dark current and readout noise and high quantum efficiency over the 300 nm to 1000 nm wavelength range. With buttable CCDs, whose production is planned for the future, even larger arrays of CCDs will be possible.
01 May 1990
TL;DR: The limitations to frequency stability and accuracy are discussed with emphasis on the problems associated with cavity resonator instability and the lack of reproducibility and stability of the storage volume wall coating frequency shift.
Abstract: The present status of technology development for atomic hydrogen masers (H-masers) is reviewed The limitations to frequency stability and accuracy are discussed with emphasis on the problems associated with cavity resonator instability and the lack of reproducibility and stability of the storage volume wall coating frequency shift New types of coating developed in the Soviet Union and better, cavity resonator materials, are expected to make possible frequency at the 10(exp -16) level at 10(exp 4) sec Better control of systematic effects should extend the long-term stability to levels better than 10(exp -15) for intervals beyond one day Present use of H-masers as flywheel oscillators in timekeeping systems is discussed as is the outlook for the future cryogenic and room temperature H-masers as flywheel oscillators to operate very high resolution frequency discriminators based on the newly evolving technology of trapped and cooled ions and atoms
01 Mar 1990
TL;DR: The Infrared Telescope (IRT) experiment, flown on Spacelab-2, was used to make infrared measurements between 2 and 120 microns as discussed by the authors, which were used for mapping the diffuse cosmic emission and extended infrared sources and technical goals of measuring the induced Shuttle environment.
Abstract: The Infrared Telescope (IRT) experiment, flown on Spacelab-2, was used to make infrared measurements between 2 and 120 microns. The objectives were multidisciplinary in nature with astrophysical goals of mapping the diffuse cosmic emission and extended infrared sources and technical goals of measuring the induced Shuttle environment, studying properties of superfluid helium in space, and testing various infrared telescope system designs. Astrophysically, new data were obtained on the structure of the Galaxy at near-infrared wavelengths. A summary of the large scale diffuse near-infrared observations of the Galaxy by the IRT is presented, as well as a summary of the preliminary results obtained from this data on the structure of the galactic disk and bulge. The importance of combining CO and near-infrared maps of similar resolution to determine a 3-D model of galactic extinction is demonstrated. The IRT data are used, in conjunction with a proposed galactic model, to make preliminary measurements of the global scale parameters of the Galaxy. During the mission substantial amounts of data were obtained concerning the induced Shuttle environment. An experiment was also performed to measure spacecraft glow in the IR.
TL;DR: A simple model is developed that yields an approximate analytical expression for the Coulomb-barrier penetration factor in terms of the reduced mass of the nucleon pair, the mass that binds together the nuclei, the inner turning point for the state under consideration, and the variation in the electronic or muonic contribution.
Abstract: We have developed a simple model that yields an approximate analytical expression for the Coulomb-barrier penetration factor in terms of the reduced mass M of the nucleon pair, the mass m of the particle that binds together the nuclei, the inner turning point ${\mathit{r}}_{\mathit{i}}$ for the state under consideration, and the variation in the electronic or muonic contribution ${\mathit{E}}_{\mathit{e}}$(r) to the total energy between r=0 and ${\mathit{r}}_{\mathit{i}}$. In the case of muon-catalyzed d+t\ensuremath{\rightarrow}\ensuremath{\alpha}+n fusion, our model yields fusion rates within 25% of those obtained from much more elaborate calculations. The remarkable accuracy of our simple model results from the fact that it is highly accurate for small r, the region that we demonstrate makes the predominant contribution to Coulomb-barrier penetration factors. Furthermore, we use this observation to explain the old puzzle of why the adiabatic approximation yields such accurate fusion rates.
01 Aug 1990
TL;DR: In this article, the designs of the delay lines constructed for the Mark III Optical Interferometer (M3OI) currently operating on Mt. Wilson and for the Infrared Optical Telescope Array (IOTA) to be constructed for Mt. Hopkins are described.
Abstract: This paper describes the designs of the delay lines constructed for the Mark III Optical Interferometer (M3OI) currently operating on Mt. Wilson and for the Infrared Optical Telescope Array (IOTA) to be constructed for Mt. Hopkins. Special attention is given to experience with M3OI which was used to improve the design of the IOTA system. Schematics are presented for the IOTA instrument layout, the IOTA coarse delay line, and the IOTA long delay line.
01 Oct 1990
TL;DR: In this paper, nonlinear effects of parametric and of heating, produced in a plasma under the action of an electric field E(sub 0)(e exp i(omega)t), are considered in connection with the tethered magnetospheric cloud (TMC) accompanying the Tether Satellite System (TSS).
Abstract: Nonlinear effects of parametric and of heating type, produced in a plasma under the action of an electric field E(sub 0)(e exp i(omega)t), are considered in this work in connection with the Tethered Magnetospheric Cloud (TMC) accompanying the Tether Satellite System (TSS). The theoretical results show that these phenomena should appear in the ionosphere at high altitudes Z greater than or = (150-200) km, particularly, at Z approximately = 300 km of the TSS system orbit. Therefore, it is of a special interest to search these phenomena by such a unique experiment as the forthcoming first TSS-I and by the future, perhaps modified TSS missions. Because of the parametric decay instability, new branches of wave may be excited both around the electron and ion Lengmuir frequencies Omega (sub 0) = 2(pi)f(sub 0) and Omega (sub 0) = 2(pi)f(sub 0) under the influence of high frequency (HF), (f less than or = 10(exp 6) to few 10(exp 6) Hz), strong electric waves. The heating of all the kinds of particles is growing up very quickly in the ionosphere with altitude in the extra low and very low frequency ranges, F approximately = (1 to 10(exp 4) Hz, discussed below. The temperatures (energies), for example, of the electrons accelerated by the electric field become larger than the ionization potential in this frequency range already at altitudes Z greater than or = (150 - 200) km when the amplitude of the electric field is the absolute value of E(sub 0) approximately = (1-2) mV/m. The sources of these electric fields may be in the TSS-I mission, that so called Phantom Loop (PL) - the Tethered Electrodynamic Tail (TET), and the different kind of electromagnetic oscillations produced by different kinds of instabilities in the TMC plasma. The growth rates of these instabilities will become very high in the TSS surrounding magnetoplasma. However, in the future TSS missions, special artificial sources (generators) of electric fields should be used for these investigations.
01 Jul 1990
TL;DR: The project to enlarge the MMT to a 6.5 m single primary mirror telescope is described in this paper, which has more than twice the light gathering power and 15 times the angular field of view.
Abstract: The project to enlarge the Multiple Mirror Telescope (MMT) to a 6.5 m single primary mirror telescope is described. The goal is to provide a telescope which is competitive with the existing MMT in tracking and pointing performance (0.2 and 1.0 arcseconds, respectively) but has more than twice the light gathering power and 15 times the angular field of view. The existing mount and building will be used with minor modifications so that the cost of the project is relatively modest. Casting of the 6.5 m mirror is scheculed in early 1991 and first light in late 1993.
01 Jan 1990
TL;DR: The well determined distance to M31 provides a unique opportunity to study galactic x-ray sources in a spiral system at a well known distance, without the uncertainty on the luminosity inherent to the study of xray sources as discussed by the authors.
Abstract: The well determined distance to M31 provides a unique opportunity to study galactic x-ray sources in a spiral system at a well known distance, without the uncertainty on the luminosity inherent to the study of x-ray sources in our own Galaxy M31 was extensively mapped with both imaging instruments on board the Einstein satellite Preliminary results were presented earlier (cf Long and Van Speybroeck 1983, and references therein), and a list of possible identifications of sources outside the very confused region around the nucleus was given by Crampton et al (1984) I am reporting the main results obtained so far from the ongoing careful analysis of the x-ray observations
01 Jun 1990
TL;DR: In this paper, a preliminary status report is given on studies using the Einstein x ray observations of distant clusters of galaxies that are also candidates for gravitational lensing, where the location and surface brightness distribution of the x ray emission from clusters associated with selected gravitational lenses are determined.
Abstract: A preliminary status report is given on studies using the Einstein x ray observations of distant clusters of galaxies that are also candidates for gravitational lenses The studies will determine the location and surface brightness distribution of the x ray emission from clusters associated with selected gravitational lenses The x ray emission comes from hot gas that traces out the total gravitational potential in the cluster, so its distribution is approximately the same as the mass distribution causing gravitational lensing Core radii and x ray virial masses can be computed for several of the brighter Einstein sources, and preliminary results are presented on A2218 Preliminary status is also reported on a study of the optical data from 0024+16 A provisional value of 1800 to 2200 km/s for the equivalent velocity dispersion is obtained The ultimate objective is to extract the mass of the gravitational lens, and perhaps more detailed information on the distribution of matter as warranted A survey of the Einstein archive shows that the clusters A520, A1704, 3C295, A2397, A1722, SC5029-247, A3186 and A370 have enough x ray counts observed to warrant more detailed optical observations of arcs for comparison Mass estimates for these clusters can therefore be obtained from three independent sources: the length scale (core radius) that characterizes the density dropoff of the x ray emitting hot gas away from its center, the velocity dispersion of the galaxies moving in the cluster potential, and gravitational bending of light by the total cluster mass This study will allow the comparison of these three techniques and ultimately improve the knowledge of cluster masses
01 Jan 1990
TL;DR: The potential implications of future measurements of the heavy-element abundances in intracluster gas are considered in the framework of the cold-dark-matter scenario of structure formation in the early universe (Blumenthal et al., 1984).
Abstract: The potential implications of future measurements of the heavy-element abundances in intracluster gas are considered in the framework of the cold-dark-matter scenario of structure formation in the early universe (Blumenthal et al., 1984). Particular attention is given to the correlation between the M(gas)/M(stellar) ratio and the gas temperature in groups and clusters of galaxies found by Jones et al. (1989) and its relationship to the efficiency of galaxy formation. Quantitative predictions for the correlation between Fe abundance and gas temperature are presented in graphs and discussed in detail.