The shape of the small satellites of Saturn: Gravitational equilibrium vs solid-state strength

In the set of small satellites of Saturn recently imaged by the Voyager probes, we can observe the transition from irregularly-shaped, strength-dominated objects to larger, gravity-dominated bodies with shapes roughly fitting the theoretical equilibrium figures. The transition occurs for a radius of 100±50 km, corresponding to a typical material strength of the order of 10⁷ dynes cm^?2. We discuss briefly the cases of Mimas, Enceladus, Hyperion, Phoebe and the small coorbital and F-ring shepherding moons, showing that an analysis of the shape data can often provide interesting results on the physical properties, origin and collisional history of these objects.     

Interpretation of patterns of drifting Zebra stripes

The earlier interpretation of the Zebra patterns by the concept of double resonance is examined for a realistic magneto-hydrostatic model of a coronal condensation over a bipolar spot group. It appears that the frequency drift of the Zebra stripes over a longer time can scarcely be explained by a change of state of the plasma as done till now. The proposed modified mechanism is based on a helical beam of electrons forming fronts that excite radiation at places of double resonance. Considering the field and density configuration conditions are found which produce drifting Zebra stripes. Structures of longer duration and absorptions arise from more or less overlapping stripe segments, which are excited by the fronts following one another in a beam of sufficient great length. The second stripe system of other drift direction found by Slottje (1972a) arises from lateral splitting of the beam.     

On the heat flow of a gravitationally-differentiated moon of fission origin

It is shown that the mean value for the heat flow of a gravitationally-differentiated Moon of fission origin is about 13 erg cm^?2 s^?1 and that the heat flow varies regionally from about 3 erg cm^?2s^?1 to more than 45 erg cm^?2s^?1. These regional variations in the heat flow are caused by a non-uniform distribution of K, U and Th in the KREEP zone at the crust-upper mantle boundary and the redistribution of crustal materials and K, U and Th rich KREEP materials by basin-forming impacts. The scale of these regional variations is hundreds of km. The models presented are in accord with the Apollo 15 and 17 heat flow measurements.     

Photometric and polarimetric studies of three W UMa-type binaries: FZ Ori,V407 Peg and LP UMa

We present analyses of new optical photometric observations of three W UMa-type contact binaries FZ Ori, V407 Peg and LP UMa. Results from the first polarimetric observations of the FZ Ori and V407 Peg are also presented. The periods of FZ Ori, V407 Peg and LP UMa are derived to be 0.399986, 0.636884 and 0.309898 d, respectively. The O?C analyses indicate that the orbital periods of FZ Ori and LP UMa have increased with the rate of 2.28×10^?8 and 1.25×10^?6 d?yr^?1, respectively and which is explained by transfer of mass between the components. In addition to the secularly increasing rate of orbital period, it was found that the period of FZ Ori has varied in sinusoidal way with oscillation period of ～30.1 yr. The period of oscillations are most likely to be explained by the light-time effect due to the presence of a tertiary companion. Small asymmetries have been seen around the primary and secondary maxima of light curves of all three systems, which is probably due to the presence of cool/hot spots on the components. The light curves of all three systems are analysed by using Wilson-Devinney code (WD) and the fundamental parameters of these systems have been derived. The present analyses show that FZ Ori is a W-subtype, and V407 Peg and LP UMa are A-subtype of the W UMa-type contact binary systems. The polarimetric observations in B, V, R and I bands, yield average values of polarization to be 0.26±0.03, 0.22±0.02, 0.22±0.03 and 0.22±0.05 per cent for FZ Ori and 0.21±0.02, 0.29±0.03, 0.31±0.01 and 0.31±0.04 per cent for V407 Peg, respectively.     

A sensor for the spatial registration and measurement of particles parameters in near and deep space—Experimental investigation of SiO2-aerogel characteristics

The paper describes a new sensor for the spatial registration and measurement of particle parameters in near and deep space. The following modern materials are applied in the sensor structure: a PVDF piezoactive film and lightweight heat-shielding high-temperature aerogel. The results from studying the aerogel morphology as well as its thermal conductivity depending on the air temperature are presented. The thermal conductivity of a SiO₂-aerogel is compared with one of foreign aerogels and air. Its elemental quantitative chemical composition is determined.     

A fit to the interstellar extinction curve without graphite

It is shown that interstellar extinction between 1 and 10 μm^?1 can be obtained from a grain mixture containing Fe₃O₄, SiO, MgO, and glassy carbon. MgO produces the 220 nm extinction bump and eliminates the need for graphite as a component of interstellar dust.     

On 5694 Å coronal line observations

Coronal yellow line emission was observed by the Lyot coronagraph at the Abastumani Astrophysical Observatory. Line intensity is I = 45 erg cm^?2 s^?1 sr^?1 Å^?1, its half-width Δλ = 1.3 Å, electronconcentration n _e = 7.5 × 10⁹ cm^?3.     

Analysis of the August 7, 1972 white light flare: Light curves and correlation with hard X-rays

Cinematic, photometric observations of the 3B flare of August 7, 1972 are described in detail. The time resolution was 2 s; the spatial resolution was 1–2″. Flare continuum emissivity at 4950 Å and at 5900 Å correlated closely in time with the 60–100 keV non-thermal X-ray burst intensity. The observed peak emissivity was 1.5 × 10¹⁰ erg cm^?2 s^?1 and the total flare energy in the 3900–6900 Å range was ～10³⁰ erg. From the close temporal correspondence and from the small distance (3″) separating the layers where the visible emission and the X-rays arose, it is argued that the hard X-ray source must have had the same silhouette as the white light flare and that the emission patches had cross-sections of 3–5″. There was also a correlation between the location of the most intense visible emissions near sunspots and the intensity and polarization of the 9.4 GHz radio emission. The flare appeared to show at least three distinct particle acceleration phases: one, occurring at a stationary source and associated with proton acceleration gave a very bluish continuum and reached peak intensity at ～ 1522 UT. At 1523 UT, a faint wave spread out at 40 km s^?1 from flare center. The spectrum of the wave was nearly flat in the range 4950–5900 Å. Association of the wave with a slow drift of the microwave emission peak to lower frequencies and with a softening of the X-ray spectrum is interpreted to mean that the particle acceleration process weakened while the region of acceleration expanded. The observations are interpreted with the aid of the flare models of Brown to mean that the same beam of non-thermal electrons that was responsible for the hard X-ray bremsstrahlung also caused the heating of the lower chromosphere that produced the white light flare.     

The quasi-stationary coronal magnetic field and electron density as determined from a Faraday rotation experiment

Pioneer VI was launched into a circumsolar orbit on December 16, 1965, and was occulted by the sun in the latter half of November, 1968. During the occultation period, the 2292-MHz S-band telemetry carrier underwent Faraday rotation due to the interaction of this signal with the plasma and magnetic field in the solar corona. The NASA/JPL 210-ft diameter antenna of the Deep Space Network near Barstow, California, was used for the measurement. The antenna feed was modified for automatic polarization tracking for this experiment. The measurement results are interpreted with a theoretical model of the solar corona. This model consists of a modified Allen-Baumbach electron density and a coronal magnetic field calculated both from Mount Wilson magnetograph observations using a source surface model and field extrapolations from the Explorer 33 satellite magnetometer. The observations and the calculated rotation show general agreement with respect to magnitude, sense, and timing, suggesting the source-surface model and field extrapolations from 1 AU are a valid technique to obtain the magnetic field in the corona from 4 to 12 solar radii. Variations present can easily be ascribed to density enhancements known to be present in the corona. Longitudinal variations of the density in the corona cannot be obtained from coronagraph observations, and thus a purely radial variation was assumed. An improved fit to the Faraday rotation data is obtained with an equatorial electron density $$N = 10^8 \left( {\frac{{6000}}{{R^{10} }} + \frac{{0.002}}{{R^2 }}} \right)...{\text{ cm}}^{{\text{ - 3}}} {\text{ (4 < }}R < 12){\text{ }}...$$ where R is in solar radii. The work of W. V. T. Rusch and J. E. Ohlson was supported in part by research sponsored by the Joint Services Electronics Program through the Air Force Office of Scientific Research under Grant AF-AFOSR 69-1622A at the University of Southern California. The work done by K. H. Schatten was in part supported by the National Academy of Science on a National Research Council postdoctoral fellowship. The work of J. M. Wilcox was supported in part by the Office of Naval Research under Contract Nonr 3656(26), by the National Aeronautics and Space Administration under Grant NGR 05-003-230, and by the National Science Foundation under Grant GA-1319 at the University of California at Berkeley.     

High energy particle acceleration in solar flares — observational evidence

The recent gamma ray and neutron observations made by the SMM Gamma Ray Spectrometer are reviewed. The implication these observations hold for understanding particle acceleration in solar flares are discussed. The data require that both electrons and ions must be accelerated together to relativistic energies and interact with matter in a time scale of seconds.     

Interpretation of vector magnetograph data including magneto-optic effects

In this paper, the presence of Faraday rotation in measurements of the orientation of a sunspot's transverse magnetic field is investigated. Using observations obtained with the Marshall Space Flight Center's (MSFC) vector magnetograph, the derived vector magnetic field of a simple, symmetric sunspot is used to calculate the degree of Faraday rotation in the azimuth of the transverse field as a function of wavelength from analytical expressions for the Stokes parameters. These results are then compared with the observed rotation of the field's azimuth which is derived from observations at different wavelengths within the Fei 5250 Å spectral line. From these comparisons, we find: the observed rotation of the azimuth is simulated to a reasonable degree by the theoretical formulations if the line-formation parameter η _o is varied over the sunspot; these variations in η _o are substantiated by the line-intensity data; for the MSFC system, Faraday rotation can be neglected for field strengths less than 1800 G and field inclinations greater than 45°; to minimize the effects of Faraday rotation in sunspot umbrae, MSFC magnetograph measurements must be made in the far wings of the Zeeman-sensitive spectral line.     

The cooling of a sunspot

This paper considers the recent criticism by Mullan (1973) of sunspot models and the cooling mechanism which I have proposed in Papers I, II and III of this series. The discussion of the cooling produced by an idealized flow cycle has been extended to include vertical temperature gradients which are consistent with a convectively unstable atmosphere. This leads to an expression for Mullan's parameter f (the ratio in which estimates of the energy flux based on an idealized Carnot cycle should be reduced) which is appropriate to this situation. It is shown that, for a cycle similar to that of Paper III, f = 0.82, while for one which has a vertical extent of order 5 Mm, f= 0.4. Hence the energy flux which, in principle, can be transported away from a sunspot by such a cycle is conservatively estimated to be 1.1 × 10²⁹ erg s^?1 compared with a typical sunspot energy deficit of 2.2 × 10²⁹ erg s^?1. Other criticisms relating to the magnetic field amplification and the ‘cool one’ model are discussed. It is concluded that the essential features of these models remain valid and that the modifications suggested by Mullan's criticism greatly increase their applicability to the sunspot problem.     

Results of a long-term monitoring of the 1.35-cm water-vapor maser source ON 1 (1981–2013)

We present the results of our long-term monitoring of the 1.35-cm water-vapor maser source ON 1 performed at the 22-m radio telescope of the Pushchino Radio Astronomy Observatory from 1981 to 2013. Maser emissionwas observed in a wide range of radial velocities, from ?60 to +60 km s^?1. Variability of the integrated flux with a period of ～9 years was detected. We show that the stable emission at radial velocities of 10.3, 14.7, and 16.5 km s^?1 belongs to compact structures that are composed of maser spots with close radial velocities and that are members of two water-maser clusters, WMC 1 and WMC 2. The detected short-lived emission features in the velocity ranges from ?30 to 0 and from 35 to 40 km s^?1 as well as the high-velocity ones are most likely associated with a bipolar molecular outflow observed in the CO line.     

Imaging of impulsive solar flare phenomena

We review some recent advances in our understanding of impulsive solar flare phenomena obtained through new hard X-ray and radio imaging instruments (the Solar Maximum Mission and Hinotori satellites, the VLA and VLBI).     

The absorption of soft X-rays from the Crab nebula

The X-ray spectrum of the Crab nebula has been determined in the energy range 0.5 10 keV using thin window proportional counters carried aboard a Centaur IIA rocket launched from TERLS, India. The spectrum can be well represented by a power law with an exponent?2.1 beyond 2 keV. The absorption of the soft X-ray component below 2 keV is clearly seen in the experiment. Attempts to understand quantitatively the spectral features in terms of interstellar absorption lead to a column density of hydrogen in the iirection of the Crab nebula of 3.5×10²¹ H atoms cm^?2, if we adopt a revised version of the interstellar absorption coefficients of Brown and Gould to include the contributions of heavier elements, especially of iron. This value of density is a factor of 2 higher than the density obtained from 21 cm radio observations, but falls well within the range of values for atomic and total hydrogen deducible from UV measurements with satellites and the measured visual extinction coefficients for the Crab nebula. It is concluded that it is not necessary to consider anomalous abundance of elements like carbon or neon either in the source or in the interstellar medium as suggested by some authors. The absorption of X-rays in the interstellar dust in the light of current dust models is presented.     

THz photometers for solar flare observations from space

The search for the still unrevealed spectral shape of the mysterious THz solar flare emissions is one of the current most challenging research issues. The concept, fabrication and performance of a double THz photometer system, named SOLAR-T, is presented. Its innovative optical setup allows observations of the full solar disk and the detection of small burst transients at the same time. The detecting system was constructed to observe solar flare THz emissions on board of stratospheric balloons. The system has been integrated to data acquisition and telemetry modules for this application. SOLAR-T uses two Golay cell detectors preceded by low-pass filters made of rough surface primary mirrors and membranes, 3 and 7 THz band-pass filters, and choppers. Its photometers can detect small solar bursts (tens of solar flux units) with sub second time resolution. Tests have been conducted to confirm the entire system performance, on ambient and low pressure and temperature conditions. An artificial Sun setup was developed to simulate performance on actual observations. The experiment is planned to be on board of two long-duration stratospheric balloon flights over Antarctica and Russia in 2014–2016.     

X-ray nova flares

In order to find out the physical nature of galactic X-ray sources, data on variability of 24 sources during 1964–1971 have been investigated. The fluxes of 9 sources are found to be increasing to the maximum value (for several months) and then slowly decreasing (for }3 yr). These 9 sources have been related by us to the class of X-ray novae. The X-ray nova synthetic light curve has been drawn from data on the fluxes of 9 discovered novae. Assumptions have been made on the physical nature of the X-ray novae. Between the flares the X-ray novae may be weak X-ray sources with luminosity about 10³⁴ erg s^?1. During the flares the luminosity increases to about 10³⁸ erg s^?1. The number of X-ray sources in the Galaxy is about 10⁴–10⁵, the average distance between them about 0.5 kpc. The object of the optical identification may be a dwarf star of no earlier spectral class than F.     

A dynamo theory of solar flares

It is proposed that the solar flare phenomenon can be understood as a manifestation of the electrodynamic coupling process of the photosphere-chromosphere-corona system as a whole. The system is coupled by electric currents, flowing along (both upward and downward) and across the magnetic field lines, powered by the dynamo process driven by the neutral wind in the photosphere and the lower chromosphere. A self-consistent formulation of the proposed coupling system is given. It is shown in particular that the coupling system can generate and dissipate the power of 10²⁹ erg s^#X2212;1 and the total energy of 10³² erg during a typical life time (10³ s) of solar flares. The energy consumptions include Joule heat production, acceleration of current-carrying particles along field lines, magnetic energy storage and kinetic energy of plasma convection. The particle acceleration arises from the development of field-aligned potential drops of 10–150 kV due to the loss-cone constriction effect along the upward field-aligned currents, causing optical, X-ray and radio emissions. The total number of precipitating electrons during a flare is shown to be of order 10³⁷–10³⁸.     

Energetic lunar nighttime ion events

The Rice University Suprathermal Ion Detector Experiment regularly observes ion events normally ranging from 250 eV q^?1 to 1000 eV q^?1 all through the lunar night. These ion events occur most often 2 to 3 days prior to the sunrise terminator. There is also a secondary activity peak 3 to 4 days after local sunset on the Moon. The events are normally of 4 hr or less in duration and the integral flux is 10⁶ ions cm^?2 s^?1 ster^?1. This article discusses the character of these events and presents the preliminary findings of a detailed study begun on this subject.     

A coordinated effort for observations and theories of the natural satellites

It was recognized over a year ago that a requirement to improve the ephemerides of the natural satellites existed and that it might be satisfied by a coordinated effort. Both the national ephemeris offices, which publish the satellite ephemerides, and NASA, which plans to send spacecraft to observe the satellites, require improved ephemerides of the natural satellites, but individually none of the organizations has the personnel or finances to undertake the task alone. At that time a few people and institutions had become interested in or were beginning to work on the theories and to make observations of the satellites. It was apparent that if the efforts of the various people and institutions were coordinated and others were encouraged to contribute, it might be possible in the next five years to satisfy the requirement for improved ephemerides. The coordinated effort includes personnel from the University of Texas, Smithsonian Astrophysical Center, University of Cincinnati, Bureau des Longitudes, Jet Propulsion Laboratory, University of Virginia, Vanderbilt University, Lowell Observatory, NASA Headquarters, and the U.S. Naval Observatory, with the latter institution serving as the coordinator.