Expected electron and proton environment for the cosmic X-ray experiment aboard the OSO-I and OSO-H satellites
Electron and proton flux densities and spectra from OSO-H and I data
Stassinopoulos, E. G.↗
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An investigation of the structure and composition of the solar atmosphere using X-ray and EUV spectra obtained with the OV1-17 and OSO-4 and OSO-5 satellites
Studies of the structure and composition of the solar corona were undertaken, using a number of satellite observations of the coronal X-ray spectrum. A systematic technique was developed to carry out the required analysis, and the analytical techniques available to calculate the coronal spectrum have been developed and improved. A review of other analyses of solar coronal structure is also included.
Walker, A. B. C., Jr.↗
OSO-7 Orbiting Solar Observatory program
The seventh Orbiting Solar Observatory (OSO-7) in the continuing series designed to gather solar and celestial data that cannot be obtained from the earth's surface is described. OSO-7 was launched September 29, 1971. It has been highly successful in returning scientific data giving new and important information about solar flare development, coronal temperature variations, streamer dynamics of plasma flow, and solar nuclear processes. OSO-7 is expected to have sufficient lifetime to permit data comparisons with the Skylab A mission during 1973. The OSO-7 is a second generation observatory. It is about twice as large and heavy as its predecessors, giving it considerably greater capability for scientific measurements. This report reviews mission objectives, flight history, and scientific experiments; describes the observatory; briefly compares OSO-7 with the first six OSO's; and summarizes the performance of OSO-7.
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Altermagnetic behavior in OsO 2 : Parallels with RuO 2
We investigate and compare the electronic structure of OsO 2 with the extensively studied RuO 2 . Calculations show that OsO 2 exhibits antiferromagnetism and spin splitting driven by crystal symmetry, a characteristic of altermagnetism and similar to RuO 2 . Examination of the Fermi surface, with and without spin-orbit coupling, reveals that OsO 2 has lower Fermi group velocities compared to RuO 2 , suggesting limited charge carrier mobility in OsO 2 . While this characteristic may constrain its performance in high-speed electronic transport applications, it may also enhance stability for spin-based information storage in spintronics. Additionally, comparison of the vibrational properties of these rutile oxide systems demonstrates dynamical stability, typical mass dependent behaviors, and favorable agreement with measured Raman data. The calculated phonon density of states for RuO 2 also agrees with our neutron scattering data. These observations substantiate the implications of the electronic and vibrational behaviors in OsO 2 and RuO 2 , encouraging further investigation of their potential for emerging technological applications.
36 MATERIALS SCIENCE↗
Lattice Structure and Dynamics of Sparse Molecular Crystals: OsO 4 and RuO 4
OsO 4 and RuO 4 are molecular oxides with unique tetrameric structures and rare +8 oxidation states. Accurately modeling their properties remains challenging for density functional theory (DFT) due to weak intertetramer interactions, which standard functionals fail to capture. Here, in this work, we show that the van der Waals (vdW)-corrected density functional (vdW-DF-optB86b) provides structural parameters that are much closer to experimental values than the standard generalized gradient approximation, with volume predictions that fall within the experimentally observed range. Phonon band structure analysis shows that the inclusion of vdW interactions stabilizes soft phonon modes, highlighting the importance of dispersion corrections for accurate predictions of lattice dynamics. Experimental measurements of the phonon density of states for OsO 4 , obtained via inelastic neutron scattering, demonstrate good agreement with our vdW-DF-optB86b calculations. These results validate OsO 4 and RuO 4 as valuable benchmarks for structural and vibrational calculations via vdW-corrected DFT methods and offer insights for studying the broader class of sparse molecular materials.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
OSO-6 Orbiting Solar Observatory
The description, development history, test history, and orbital performance analysis of the OSO-6 Orbiting Solar Observatory are presented. The OSO-6 Orbiting Solar Observatory was the sixth flight model of a series of scientific spacecraft designed to provide a stable platform for experiments engaged in the collection of solar and celestial radiation data. The design objective was 180 days of orbital operation. The OSO-6 has telemetered an enormous amount of very useful experiment and housekeeping data to GSFC ground stations. Observatory operation during the two-year reporting period was very successful except for some experiment instrument problems.
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Analysis of time dependent phenomena observed with the LPSP OSO-8 instrument
The dynamics of the solar photosphere and chromosphere are studied. Observations obtained by the Laboratorie de Physique Stellaire et Planetaire's (LPSP) ultraviolet spectrometer onboard the OSO-8 spacecraft are analyzed, and dynamic models of the chromosphere and the emitted resonance line spectrum are calculated. Some of the unpublished data analysis and theoretical modeling which are being prepared for publication are discussed. A discussion of the state of the theory of velocity fields in the solar atmosphere is also presented. An invited review presented at the OSO-8 Workshop on the topic of oscillatory motions in the quiet sun is included. The results of the OSO-8 data analysis prepared in close collaboration with LPSP scientists are presented. Material for two articles is also presented.
Leibacher, J. W.↗
X-ray observations of AM Herculis from OSO 8
X-ray observations of the white dwarf binary system AM Herculis in the range 2 to 250 keV, taken by OSO 8, are presented and compared with balloon and Ariel 5 measurements. The composite spectrum of the 2 to 40 and 20 to 250 keV fluxes determined by the proportional counter and the high energy scintillation spectrometer, respectively, on board the satellite is shown averaged over the entire binary cycle. Variations in spectral shape and intensity between the OSO 8 results and balloon measurements taken 10 to 20 days apart are observed. Results indicate the presence of a spectral break at about 15 keV on some occasions, similar to that seen in Her X-1, however presumably caused by a different mechanism than in the neutron star. It is also considered unlikely that the gamma-ray tail observed by Ariel 5 existed during OSO 8 observations.
Coe, M. J.↗
Equatorial ozone profile comparisons using OSO-8 UVMCS and Nimbus 4 BUV data
A comparison is made of equatorial ozone altitude profiles derived from data taken during near-coincident passes of the French solar occultation experiment on OSO-8 and the BUV instrument on Nimbus 4. The period of observation is August through October 1975. OSO-8 data are confined to sunset and the BUV measures ozone during the day for a range of solar zenith angles. Good agreement is found between ozone concentrations from OSO-8 and Nimbus 4 in the region of near overlap, 0.7 mb (52 km). Data indicate that the diurnal variation in ozone below 55 km is less than 20 percent in agreement with current models. The equatorial ozone profile can be described frequently by a single scale height from 34 to 60 km.
Aikin, A. C.↗
Two OSO's scheduled in series
Orbiting Solar Observatories OSO-E and OSO-D for studying Sun influence on Earth atmosphere
EARTH ATMOSPHERE↗
Models of the quiet and active solar atmosphere from Harvard OSO data.
Review of some Harvard Observatory programs aimed at defining the physical conditions in quiet and active solar regions on the basis of data obtained from the OSO-IV and OSO-VI spacecraft. The spectral range covered is from 300 A to 1400 A. This spectral range consists of emission lines and continua from abundant elements such as hydrogen, helium, carbon, nitrogen, oxygen, silicon, magnesium, aluminum, neon, iron, and calcium in various ionization states ranging from neutral to 15 times ionized. The structure is discussed of the quiet solar atmosphere as deduced from center-to-limb behavior of spectral lines and continua formed in the chromosphere and corona. In reviewing investigations of solar active regions, it is shown that the structure of these regions varies in a complicated manner from point to point. The local structure is influenced by factors such as the magnetic field configuration within the active region and the age or evolutionary state of the region.
Noyes, R. W.↗
The diffuse X-ray spectrum from 14-200 keV as measured on OSO-5
The measurement of energy spectrum of the diffuse component of cosmic X-ray flux made on the OSO-5 spacecraft is described. The contributions to the total counting rate of the actively shielded X-ray detector are considered in some detail and the techniques used to eliminate the non-cosmic components are described. Positive values for the cosmic flux are obtained in seven energy channels between 14 and 200 keV and two upper limits are obtained between 200 and 254 keV. The results can be fitted by a power law spectrum. A critical comparison is made with the OSO-3 results. Conclusions show that the reported break in the energy spectrum at 40 keV is probably produced by an erroneous correction for the radioactivity induced in the detector on each passage through the intense charged particle fluxes in the South Atlantic anomaly.
Dennis, B. R.↗
Stellar X-ray polarimetry on OSO-1
The importance of stellar X-ray polarimetry is reviewed. A graphite crystal polarimeter sensitive near 2.6 and 5.2 keV which was designed for the OSO-1 satellite is described. The instrument's predicted performance for many stellar X-ray sources is presented, and the fundamental questions that can be resolved with the OSO-1 polarimeter are considered. The sensitivity of the instrument is such that, during an observation time of 24 hours, the polarization of the Crab nebula can be measured with an accuracy of 0.6 percent.
Landecker, P. B.↗
The OSO-7 mission
Addition of a gyro and star sensor to the wheel section of OSO-G provided nighttime pointing capability and functional redundancy in correcting an anomaly that put the combined OSO spacecraft and launch vehicle into a flat spin.
Thole, J. M.↗
The OSO-7 year of discovery.
The OSO 7 scientific findings reveal hitherto unknown processes in solar flares and some remarkable properties of the corona. Gamma-ray emission lines provide evidence of nuclear reactions in solar flares. The measurements were made during the large flares of Aug. 4 and 7, 1972. The data clearly show line emission at energies of about 0.5 MeV (million electron volts) and 2.2 MeV, with weaker enhancements at 4.4 MeV and 6.1 MeV. It appears that the nuclear processes in flares as revealed by OSO 7 are probably thermal reactions. Some flare electron streams also produce bursts of hard X rays. Holes and poles in the corona, and coronal streams and the interplanetary blast were studied.
Maran, S. P.↗
The extreme ultraviolet emissions of solar flares - A comparison between OSO-6 spectroheliograph observations and SFDs.
The time structure and intensity of OSO-6 observations of EUV bursts were studied in relation to the corresponding 10-1030 A enhancements deduced from SFD data. Impulsive EUV emissions from lines normally emitted from either the chromosphere or from the chromosphere-corona transition region rise simultaneously with the 10-1030 A flash, to within the time resolution of the OSO-6 observations. Mg X 625 A also showed concurrent impulsive emissions and a close intensity relation to the 10-1030 A enhancement. The observational results are consistent with the hypothesis that most of the EUV radiation is being produced thermally in a region of chromospheric density, which is being heated by collisional losses of nonthermal electrons.
Donnelly, R. F.↗
The diffuse X-ray spectrum from 14 to 200 keV as measured on OSO-5
Evaluation of OSO-5 measurements of the energy spectrum of the diffuse component of the cosmic X-ray flux in the energy range from 14 to 200 keV. A detailed description is given of the X-ray detector employed and of the method of selection and pulse-height analysis of X-ray events. The method employed in eliminating noncosmic X-ray contributions to the total counting rate is discussed. The final energy spectrum is found to be best fitted by a power law which is in essential agreement with that obtained from OSO-3 by Schwartz et al. (1970), in spite of what is regarded as an erroneous correction procedure used by them. In particular, it is suggested that the break in the energy spectrum at 40 keV which they reported may have been produced by an erroneous correction for the radioactivity induced in the detector during each passage through the intense charged-particle fluxes in the South Atlantic Anomaly.
Dennis, B. R.↗
Analysis of OSO data to determine the structure and energy balance of the solar chromosphere
A detailed reexamination of the temperature-density structure of the photosphere and low chromosphere shows that the middle and upper chromosphere, which directly emits most of the OSO spectrum, is sensitive to conditions in this underlying region of the atmosphere. A model of this region is based on a unified compilation of all recently published broadband flux and central intensity observations of the solar spectrum from 500 microns in the far infrared to 1220 A in the far ultraviolet. This extensive compilation includes the OSO 4 and 6 observations in the wavelength range 1400 to 1220 A. A model is presented of the quiet solar atmosphere in the height range between the temperature minimum and the upper part of the chromosphere-corona transition region. This model is based on statistical equilibrium calculations of H, He 1, He 2, Si 1, C 1, and other ions.
Avrett, E. H.↗