Showing papers by "Smithsonian Astrophysical Observatory published in 1983"
TL;DR: In this paper, a test of the Einstein equivalence principle (EEP) was performed by carrying out a 'null' gravitational red-shift experiment, and an upper limit on the relative frequency variation of 1.7 parts in 100 of the external potential was set.
Abstract: A test of the Einstein equivalence principle (EEP) was performed by carrying out a 'null' gravitational red-shift experiment. The experiment compared the rates of a pair of hydrogen maser clocks with those of a set of three superconducting-cavity stabilized oscillator clocks as a function of the solar gravitational potential. If EEP were not valid, the relative rates could vary with potential. During the experiment, the solar potential in the laboratory varied approximately linearly at 3 parts in 10 to the 12th per day because of the earth's orbital motion, and diurnally with an amplitude of 3 parts in 10 to the 13th because of the earth's rotation. An upper limit on the relative frequency variation of 1.7 parts in 100 of the external potential was set. The accuracy was limited by the frequency stability of the clocks and by unmodeled environmental effects. The result is consistent with the EEP at the 2 percent level. The experiment can also be viewed as setting a limit on a possible spatial variation of the fine-structure constant.
121 citations
TL;DR: The inclusions and chondrules of the Mokoia CV3 chondrite are studied systematically and compared with those in the Allende meteorite as mentioned in this paper, and it is concluded that most of the CAIs probably formed during metamorphism, partial melting, and incomplete distillation of primitive dust aggregates heated in the solar nebula.
100 citations
TL;DR: In this paper, multispectral mosaics of the three icy Galilean satellites have been produced from low-to moderate-resolution Voyager images, and the digital image data have been calibrated using preflight and in-flight calibration data, and reduced to normal albedos for four-color band passes, centered at 0.35, 0.41, 0.48, and 0.59 microns.
Abstract: Multispectral mosaics of the three icy Galilean satellites have been produced from low- to moderate-resolution Voyager images. The digital image data have been calibrated using preflight and in-flight calibration data, and reduced to normal albedos for four-color band passes, centered at 0.35, 0.41, 0.48, and 0.59 microns. The individual images have been geometrically corrected, mosaiked, and presented in a normal cylindrical map projection at a uniform scale of 8 km/pixel. Preliminary analysis of the normal albedo data shows that (1) the darkest terrains on the satellites are the dark regions on Callisto, (2) the brightest regions are bright plains regions on Europa and bright, fresh craters on Ganymede, (3) bright craters on Ganymede and its dark, cratered regions are both significantly brighter than comparable terrains on Callisto, and (4) Europa exhibits several distinct spectral units, with regions on the trailing hemisphere having lower relative ultraviolet spectral reflectance than areas on the leading hemisphere. This is consistent with proposals that Io-related plasma impact on Europa's trailing side has altered its optical properties.
97 citations
TL;DR: In this article, the x-ray line emission in the wavelength region was measured from molybdenum in charge states between 28+ and 32+ and the experimental results were compared with calculated line spectra.
Abstract: We report on measurements of the x-ray line emission in the wavelength region $\ensuremath{\lambda}=4.3\ensuremath{-}5.3$ \AA{} from molybdenum in charge states between 28+ and 32+. The experimental results were compared with calculated line spectra (also presented) which facilitated the identification of many of the principal $2p\ensuremath{-}3d$, $2s\ensuremath{-}3p$, and $2p\ensuremath{-}3s$ transitions. Some indications of weaker satellite-line contributions were also found. The principal $2p\ensuremath{-}3d$ transitions were found to be the dominant ones. In particular, ${\mathrm{Mo}}^{32+}$ gave stronger contributions than other charge states for our plasma condition of ${T}_{e}=1.0\ensuremath{-}1.5$ keV while available calculations of relative ion abundances have predicted ${\mathrm{Mo}}^{32+}$ to be relatively strongest at ${T}_{e}=2.5\ensuremath{-}3.0$ keV.
36 citations
TL;DR: In this article, He-like x-ray line spectra for sulfur and chlorine impurity ions in the Alcator-$C$ tokamak plasma are reported and compared with atomic calculations employing accurate atomic data which take into consideration effects on the line ratios due to collisional coupling between the $n=2$ states involved.
Abstract: Measurements of He-like x-ray line spectra for sulfur and chlorine impurity ions in the Alcator-$C$ tokamak plasma are reported. Results are presented on the relative line ratios of the resonance (w), intercombination (x and y), and forbidden (z) lines as well as dielectronic satellite lines for plasma conditions of ${T}_{e}=1.0\ensuremath{-}1.8$ keV and ${N}_{e}=(1.5\ensuremath{-}7)\ifmmode\times\else\texttimes\fi{}{10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. The results are compared with atomic calculations employing accurate atomic data which take into consideration effects on the line ratios due to collisional coupling between the $n=2$ states involved.
32 citations
TL;DR: In this paper, a coupled set of rate equations was used along with time and space-resolved measurements of the electron density and temperature to model the plasma light emission and the ionization rates of Kunze were adjusted by multiplying the rate for each ion stage with a constant until the peak intensity of the calculated emission agreed with the time of the observed peak intensity.
Abstract: The ionization rates of Kr(IX), (X), (XI), and (XII) have been measured using a fast 60-kV-60kJ theta pinch as a plasma source. The line emission from each ion stage has been identified and the time evolution observed. A coupled set of rate equations was used along with time- and space-resolved measurements of the electron density and temperature to model the plasma light emission. The ionization rates of Kunze were adjusted by multiplying the rate for each ion stage with a constant until the peak intensity of the calculated emission agreed with the time of the observed peak intensity. The constants required for best fit were 2.5, 0.15, 3.0, and 2.0 for Kr(IX), (X), (XI), and (XII), respectively. Two successive ionization stages, Kr(X) and Kr(XI), have shown the same time dependence and possible reasons for this observation are discussed. During the course of modeling the light emission, we have also found that the rate for the excitation from the 3 d n to the 3 p 5 3 d n +1 level in Kr(X) ( n =9) and Kr(XI) (n=8) is a factor of 5 lower than predicted by the van Regemorter excitation rate equation.
11 citations
TL;DR: A preliminary study of close double comet nuclei as affected by differential nongravitational forces shows that a collision of a cometary satellite with its primary is a likely outcome as mentioned in this paper.
Abstract: A brief summary is given of the current concepts of the icy conglomerate cometary nucleus and of the origin of comets. Evidence that the cores of comets may contain less than average volatile material, whether in formation or by radiative heating, raises the question of why at least two very faint short-period comets suddenly experienced violent outbursts (about 4,000 times in brightness). A preliminary study of close double comet nuclei as affected by differential nongravitational forces shows that a collision of a cometary satellite with its primary is a likely outcome. Thus double nuclei may possibly explain these rare but extreme outbursts. Statistics suggest, however, that most comet splitting and comet outbursts represent intrinsic activities in extremely nonhomogeneous nuclei.
9 citations
Journal Article•
TL;DR: The carbon-14 terrestrial ages of four Yamato meteorites were measured and compared with the C- 14 terrestrial ages for eighteen meteorites from Victoria Land as discussed by the authors, where the Yamato meteorite site is collecting recent falls, less than 25,000 yr, at a more rapid rate than the Victoria Land sites.
Abstract: The carbon-14 terrestrial ages of four Yamato meteorites are measured and compared with the C-14 terrestrial ages of eighteen meteorites from Victoria Land. The youngest Yamato meteorite, Y-75102, is 4300 + or - 1000 yr; the oldest, Y-74459, is 24,000 + or - 2000 yr. The Yamato meteorite site is collecting recent falls, less than 25,000 yr, at a more rapid rate than the Victoria Land sites.
7 citations
TL;DR: The detection of the free radicals ClSO and FSO by the technique of far infrared laser magnetic resonance is reported in this article, where the latter was generated by the reaction of carbon disulphide with the products of a discharge through CF4 + O2.
7 citations
TL;DR: In this article, the contribution of quasifree reactions to the total reaction cross-section is investigated. But the authors focus on the quasi-nucleon absorption reaction and do not consider the free reactions.
Abstract: Proton spectra of /sup 3,4/He(..pi../sup + -/,p) and /sup 27/Al(..pi../sup + -/,p) have been measured at theta/sub p/ = 20/sup 0/ for T/sub ..pi../ = 50, 100, 150, 200, and 250 MeV, and at theta/sub p/ = 20/sup 0/ and 40/sup 0/ for T/sub ..pi../ = 295 MeV. A small contributor to these spectra is the exclusive pion absorption reaction for which the cross section of /sup 4/He(..pi../sup +/,p)/sup 3/He is reported. Major contributions are identified to come from quasifree ..pi..N..--> pi..p scattering and ..pi..NN..-->..Np absorption for which cross sections are also reported. The quasifree cross sections are compared with those of the free reactions ..pi..N..--> pi..p and ..pi..d..-->..pp. We use these results to assess the contribution of quasifree reactions to the total reaction cross section. The comparison of the quasifree ..pi..NN..-->..Np reaction relative to ..pi..d..-->..pp is discussed in terms of differences in the attenuation and the dynamics of the reactions. This information is of interest for the phenomenological interpretation of complex reactions such as the two-nucleon absorption model of /sup 3/He(..pi../sup -/, n)/sup 2/H, /sup 4/He(..pi../sup -/, n)/sup 3/H, and /sup 4/He(..pi../sup +/, p)/sup 3/He in which ..pi..d..-->..pp is assumed to be an elementary process. This experiment also providesmore » information on the cross section of ..pi../sup -/pp..-->..pn from which we determine the dependence of pion absorption on the isospin of the initial NN state.« less
6 citations
TL;DR: In this article, a simple model for the optical and X-ray luminosities of QSOs is proposed, which shows that a thick accretion disk around a black hole is consistent with the observed dependence of the X ray luminosity on the optical luminosity to the bth power, with b roughly in the range 0.5-0.8.
Abstract: A study of simple models for the optical and X-ray luminosities of QSOs shows that a thick accretion disk around a black hole is consistent with the observed dependence of the X-ray luminosity L(x) on the optical luminosity L(opt) to the bth power, with b roughly in the range 0.5-0.8. The disk is expected to be thick since the sources are accreting at rates near the Edington limit. Using the model of McMillan, Lightman, and Cohn (1981) for the gas supply rate, the evolution of L(opt) is predicted to be proportional to t/t(0) to the -8/3 and that of L(x) is predicted to be proportional to t/t(0) to the -2.
01 Jan 1983
TL;DR: In this paper, the origins and uses of scaling laws in studies of stellar outer atmospheres are reviewed with particular emphasis on the properties of coronal loops, and the applicability of single loop models is examined.
Abstract: The origins and uses of scaling laws in studies of stellar outer atmospheres are reviewed with particular emphasis on the properties of coronal loops. Some evidence is presented for a fundamental structuring of the solar corona and the thermodynamics of scaling laws are discussed. It is found that magnetic field-related scaling laws can be obtained by relating coronal pressure, temperature, and magnetic field strength. Available data validate this method. Some parameters of the theory, however, must be treated as adjustable, and it is considered necessary to examine data from other stars in order to determine the validity of the parameters. Using detailed observational data, the applicability of single loop models is examined.
TL;DR: In this article, the rotational spectrum of HOCl from 70-263/cm has been obtained and statistical strengths for the Q branches have been calculated and mu sub b, the component of dipole moment that allows Q branch transitions, has been determined from P and R branch line intensities.
Abstract: The far IR rotational spectrum of HOCl from 70-263/cm have been obtained. The most prominent features of the rotational spectrum are the Q branches, for which positions have been measured. Statistical strengths for the Q branches have been calculated and mu sub b, the component of the dipole moment that allows Q branch transitions, has been determined from P and R branch line intensities. It is found that mu sub b = 1.4 + or - 0.2 D. Q branch strengths and shifts at stratospheric temperature are calculated.
01 Feb 1983
TL;DR: In this article, a concept for a phase-coherent optical telescope array which may be deployed by the Space Shuttle in the 1990's is presented, where the system would start as a four-element linear array with a 12 m baseline.
Abstract: Numerical methods of image construction which can be used to produce very high angular resolution images at optical wavelengths of astronomical objects from an orbiting array of telescopes are discussed and a concept is presented for a phase-coherent optical telescope array which may be deployed by space shuttle in the 1990's The system would start as a four-element linear array with a 12 m baseline The initial module is a minimum redundant array with a photon-counting collecting area three times larger than space telescope and a one dimensional resolution of better than 001 arc seconds in the visible range Later additions to the array would build up facility capability The advantages of a VLBI observatory in space are considered as well as apertures for the telescopes
01 Jan 1983
TL;DR: In this article, the authors developed a workable pre-release maneuver with particular emphasis on accounting for propagation delay and the dynamics of the tether itself in order to release the payload with no loss of tension along the wire.
Abstract: The algorithm used in the reel maneuver was refined so as to develop a workable pre-release maneuver with particular emphasis on accounting for propagation delay and the dynamics of the tether itself in order to release the payload with no loss of tension along the wire.
01 Mar 1983
TL;DR: In this paper, the effect of reeling operations on the orbital altitude of the tether system and the development of control laws to minimize tether rebound upon payload release were studied, and it was concluded that reeling operations contribute a significant amount of energy to the orbit of the system and should be considered in orbit calculations and predictions.
Abstract: The effect of reeling operations on the orbital altitude of the tether system and the development of control laws to minimize tether rebound upon payload release were studied. The use of the tether for LEO/GEO payload orbital transfer was also investigated. It was concluded that (1) reeling operations can contribute a significant amount of energy to the orbit of the system and should be considered in orbit calculations and predictions, (2) deployment of payloads, even very large payloads, using tethers is a practical and fully stable operation, (3) tether augmented LEO/GEO transfer operations yield useful payload gains under the practical constraint of fixed size OTV's, and (4) orbit to orbit satellite retrieval is limited by useful revisit times to orbital inclinations of less than forty-five degrees.
08 Nov 1983
TL;DR: A balloon-borne three-meter telescope for far-infrared and sub-millimeter astronomy has been proposed jointly by the University of Arizona, the Smithsonian Astrophysical Observatory, and University of Chicago as discussed by the authors.
Abstract: A balloon-borne three-meter telescope for far-infrared and submillimeter astronomy has been proposed jointly by the University of Arizona, the Smithsonian Astrophysical Observatory, and the University of Chicago. The purpose of this project is to provide a facility for photometry, spectroscopy, and imaging in the spectral region 30 micrometers to 1 millimeter, which is largely inaccessible with ground-based telescopes. The three-meter telescope will provide a much needed gain in sensitivity and spatial resolution compared with present approximately one-meter sized balloon and aircraft telescopes. The telescope is to be a Cassegrain design with an angular resolution diffraction limited to a wavelength of 30 microns. It will be supported on a three axis, gyroscopically-stabilized system with a pointing stability of one arcsecond rms. The overall weight of telescope and gondola is expected to be approximately 2800 kg, assuming a lightweight mirror formed as a welded structure of Pyrex or fused silica. We are also studying the possibility of using a carbon fiber reinforced plastic sandwich panel for the primary and secondary mirrors and carbon fiber reinforced plastic members for the telescope structure. The intended operation is approximately five 8 to 10 hour flights per year carrying two instruments at a time.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, the EINSTEIN objective grating spectrometer was used to obtain high-resolution spectra of the bright cosmic x-ray source Scorpius X-1, which revealed absorption features due to intervening helium, nitrogen, and oxygen.
TL;DR: In this article, the implications of the X-ray observations for the classification of clusters, the formation of SO galaxies, and the interaction of the galaxies with the intracluster gas are reviewed.
09 Aug 1983
TL;DR: In this article, the authors describe the operation of a very sensitive focal plane array in the space environment, in particular its sensitivity to the contamination environment, and the performance of the Spacelab IRT.
Abstract: The small helium-cooled infrared telescope (Spacelab IRT) is a multiband instrument capable of highly sensitive observations from space. The experiment consists of a cryogenically cooled, very well baffled telescope with a ten channel focal plane array. During the Spacelab 2 flight of the Space Shuttle, this instrument will make observations between 5 and 120 micron wavelength that will be background limited by the expected zodiacal emission. Design considerations necessitated by this level of performance are discussed in this paper. In particular, the operation of a very sensitive focal plane array in the space environment is described. The Spacelab IRT will be used to map the extended, low-surface brightness celestial emission. During the seven day length of the mission better than 70 percent sky coverage is expected. The instrument will also be used to measure the infrared contamination environment of the Space Shuttle. This information will be important in the development of the next generation of infrared astronomical instruments. The performance of the Spacelab IRT, in particular its sensitivity to the contamination environment is detailed.
TL;DR: In this paper, the contribution of X-ray data and magnetic fields in the formation of coronal structures in late-type stars is discussed. And the relationship between surface magnetic fields and chromospheric emission in the chromosphere is briefly reviewed.
Journal Article•
TL;DR: The Smithsonian Astrophysical Observatory (SAO) was given responsibility for optical tracking of satellites during the International Geophysical Year (IGY) of 1957-1958 as mentioned in this paper.
Abstract: When Fred L. Whipple of Harvard University assumed the directorship of the Smithsonian Astrophysical Observatory (SAO) in mid-1955, he proposed to the National Academy of Sciences and the National Science Foundation that the observatory be given responsibility for optical tracking of satellites during the IGY of 1957–1958. Several countries had expressed their intentions to launch satellites during the 18-month period to support research in ionospheric and upper atmospheric physics, including the effects of solar flares and solar radiation, and in geodesy and geophysics. On the basis of his experience at the Harvard College observatory with the Super-Schmidt cameras for meteor photography, Whipple was confident that optical tracking could provide a powerful means of monitoring satellite positions. The proposal was accepted in late 1955, and it was assumed that the total observing program would last only 18 months and would involve only a few satellites.
01 Sep 1983
TL;DR: In this article, the cosmic-ray, solar-flare, and solar-wind bombardments of lunar rocks and soils and meteorites were studied by measurements of tritium, carbon-14 and argon radioactivity.
Abstract: The cosmic-ray, solar-flare, and solar-wind bombardments of lunar rocks and soils and meteorites were studied by measurements of tritium, carbon-14 and argon radioactivity. The radioactivity integrates the bombardment for a time period equal to several half-lines. H-3, Ar-37, Ar-39, C-14. For the interior samples of lunar rocks and for deep lunar soil samples, the amounts of the radioactivities were equal to those calculated for galactic cosmic-ray interactions. The top near-surface samples of lunar rocks and the shallow lunar soil samples show excess amounts of the radioactivities attributable to solar flares. Lunar soil fines contain a large amount of hydrogen due to implanted solar wind. Studies of the H-3 in lunar soils and in recovered Surveyor-3 materials gave an upper limit for the H-3/H ratio in the solar wind of 10 to the -11th power. Solar wind carbon is also implanted on lunar soil fines. Lunar soils collected on the surface contained a 0.14 component attributable to implanted solar wind C-14. The C-14/H ratio attributed to the solar wind from this C-14 excess is approximately 4 x 10 to the -11th power.
01 Jan 1983
TL;DR: A preliminary study of close double comet nuclei as affected by differential nongravitational forces shows that a collision of a cometary satellite with its primary is a likely outcome as mentioned in this paper.
Abstract: A brief summary is given of the current concepts of the icy conglomerate cometary nucleus and of the origin of comets. Evidence that the cores of comets may contain less than average volatile material, wheter in formation or by radiative heating, raises the question of why at least two very faint short-period comets suddenly experienced violent outbursts (~4000 times in brightness). A preliminary study of close double comet nuclei as affected by differential nongravitational forces shows that a collision of a cometary satellite with its primary is a likely outcome. Thus double nuclei may possibly explain these rare but extreme outbrusts. Statistics suggest, however that most comet splitting and comet outbursts represent instrinsic activities in extremely non-homogeneous nuclei.