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.     

UV observations of macrospicules at the solar limb

During the Spacelab 2 mission, the NRL High Resolution Telescope and Spectrograph (HRTS) obtained a time-series of broad-band ultraviolet images of macrospicules at the solar limb inside a polar coronal hole with a temporal resolution of 20 and 60 s. The properties of the macrospicules observed in the Spacelab data are measured and compared with the properties reported for EUV macrospicules observed during Skylab (Bohlin et al., 1975; Withbroe et al., 1976). There is a general agreement between the data sets but several differences. Because of the higher temporal resolution of the Spacelab data, it is possible to see macrospicules with shorter lifetimes than seen during Skylab, as well as variations on faster timescales. The largest (30–60) and fastest (150 km s ^-1) macrospicules seen during Skylab were not found in the Spacelab observations. The Spacelab data support the conclusion that many macrospicules decay by simply fading away.     

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.     

Cosmogenic Isotope Variability During the Maunder Minimum: Normal 11-year Cycles Are Expected

The amplitude of the 11-year cycle measured in the cosmogenic isotope ¹⁰Be during the Maunder Minimum is comparable to that during the recent epoch of high solar activity. Because of the virtual absence of the cyclic variability of sunspot activity during the Maunder Minimum this seemingly contradicts an intuitive expectation that lower activity would result in smaller solar-cycle variations in cosmogenic radio-isotope data, or in none, leading to confusing and misleading conclusions. It is shown here that large 11-year solar cycles in cosmogenic data observed during periods of suppressed sunspot activity do not necessarily imply strong heliospheric fields. Normal-amplitude cycles in the cosmogenic radio-isotopes observed during the Maunder Minimum are consistent with theoretical expectations because of the nonlinear relation between solar activity and isotope production. Thus, cosmogenic-isotope data provide a good tool to study solar-cycle variability even during grand minima of solar activity.     

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.     

Adaptive optics at short wavelengths

The First Light Adaptive Optics (FLAO) system has been successfully commissioned at the Large Binocular Telescope. It delivers extreme adaptive optics performance using bright natural guide stars reaching 90 % Strehl Ratios in H-band. Observations with current adaptive optics systems are limited to the near infrared wavelengths, in these bands the diffraction limited resolution of the largest ground-based telescopes (8–10 meter class) is comparable to the one of the much smaller Hubble Space Telescope that observes in the visible bands. This study aims to demonstrate the feasibility of an adaptive optics system designed to achieve very high order correction at visible wavelengths (0.5 to 0.8 μ m) with significant sky coverage. Upgrading the FLAO design with a low noise CCD relaxes the reference magnitude limit needed to achieve greater performance. In particular, we demonstrate that a gain of 1–2 magnitudes is possible by upgrading the wavefront sensor with a very low read out noise CCD. For future AO systems, in addition to low noise CCDs, deformable (secondary) mirrors with a higher actuator density will be able to move the high order correction capability from the near infrared to the visible wavelengths (Strehl Ratio of 80 % in R (0.7 μ m), 60 % in V (0.5 μ m)). We investigate, by means of numerical simulation, the gain in imaging performance obtained at Near Infrared, Visible, and UV wavelengths. The results of these simulations have been used to derive the empirical relation between Strehl Ratio and magnitude of the reference star and we then use this relationship to perform a detailed sky coverage analysis based on astronomical catalog data. The detailed simulations of the Point Spread Functions allow us to compute Ensquared Energy and Strehl Ratio for the magnitude working range of such an Adaptive Optics system. We present the results of the instrumental isoplanatic angle determination. We then used these values to compute the relationship between correction level and the off-axis angle from the reference star. The Strehl Ratio relationship with the reference magnitude and the angular distance provides the information needed to perform the sky-coverage analysis, which demonstrates that the designed system is able to provide V and R bands correction on a not negligible few percent of the sky.     

A second fundamental model for resonance

We analyse a simple one degree of freedom Hamiltonian system depending upon a parameter \(H = - 3(\delta + 1)R + R^2 - 2\sqrt {2R} \cos r\) . This model is much closer to resonance problems arising in Celestial Mechanics than the pendulum. We deduce from it the conditions of capture into resonance or escape from resonance for systems drifting slowly. We apply this analysis to the Enceladus-Dione resonance.     

Cosmic ray exposure ages of features and events at the apollo landing sites

Cosmic ray exposure ages of lunar samples have been used to date surface features related to impact cratering and downslope movement of material. Only when multiple samples related to a feature have the same rare gas exposure age, or when a single sample has the same⁸¹Kr-Kr and track exposure age can a feature be considered reliably dated. Because any single lunar sample is likely to have had a complex exposure history, assignment of ages to features based upon only one determination by any method should be avoided. Based on the above criteria, there are only five well-dated lunar features: Cone Crater (Apollo 14) 26 m.y., North Ray Crater (Apollo 16) 50 m.y., South Ray Crater (Apollo 16) 2 m.y., the emplacement of the Station 6 boulders (Apollo 17) 22 m.y., and the emplacement of the Station 7 boulder (Apollo 17) 28 m.y. Other features are tentatively dated or have limits set on their ages: Bench Crater (Apollo 12) ?99 m.y., Baby Ray Crater (Apollo 16) ?2 m.y., Shorty Crater (Apollo 17) ≈ 30 m.y., Camelot Crater (Apollo 17) ?140 m.y., the emplacement of the Station 2 boulder 1 (Apollo 17) 45–55 m.y., and the slide which generated the light mantle (Apollo 17) ?50 m.y.     

Fragmentation of the universe

We have tested the hypothesis that the universe underwent a single fragmentation event, separating into protogalactic volumes at a relatively early stage after the Big Bang. Assuming that the present total luminosity of each galaxy is proportional to its mass, we plotted the number and mass distribution of a thousand nearby galaxies just as we would in an analysis of fragments from a laboratory high-explosive experiment. The results are consistent with the single-fragmentation hypothesis.     

The alignment of the Crab pulsar magnetic axis

The magnetic distortion is estimated for neutron stars in which the matter in the interior consists of superfluid neutrons and superconducting protons. For type II proton superconductivity, the arrangement of magnetic flux in a two-dimensional lattice of quantized fluxoids and the kinetic energy of the supercurrent carriers cause some components of the spatially averaged stress tensor for field and superconductor to be several orders of magnitude greater than the components of the Max-well stress tensor for a uniform distribution of the same magnetic flux. It is shown that for the Crab pulsar PSR 0531+21, which is considered to have the greater part of its mass in the form of superfluid neutrons and superconducting protons, the magnetic distortion is almost certainly more important than the clastic energy of the outer shell in determining the departure of the inertia tensor from its spherically symmetric form. With the assumption that internal and external magnetic fields have the same symmetry axis, the external field dipole moment of the Crab pulsar is predicted to be approximately perpendicular to the spin direction, in agreement with a number of published interpretations of observational data.     

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.     

STE-QUEST mission and system design

STE-QUEST is a fundamental science mission which is considered for launch within the Cosmic Vision programme of the European Space Agency (ESA). Its main scientific objectives relate to probing various aspects of Einstein’s theory of general relativity by measuring the gravitational red-shift of the earth, the moon and the sun as well as testing the weak equivalence principle to unprecedented accuracy. In order to perform the measurements, the system features a spacecraft equipped with two complex instruments, an atomic clock and an atom interferometer, a ground-segment encompassing several ground-terminals collocated with the best available ground atomic clocks, and clock comparison between space and ground via microwave and optical links. The baseline orbit is highly eccentric and exhibits strong variations of incident solar flux, which poses challenges for thermal and power subsystems in addition to the difficulties encountered by precise-orbit-determination at high altitudes. The mission assessment and definition phase (Phase-A) has recently been completed and this paper gives a concise overview over some system level results.     

Areas of Polar Coronal Holes from 1996 Through 2010

Polar coronal holes (PCHs) trace the magnetic variability of the Sun throughout the solar cycle. Their size and evolution have been studied as proxies for the global magnetic field. We present measurements of the PCH areas from 1996 through 2010, derived from an updated perimeter-tracing method and two synoptic-map methods. The perimeter-tracing method detects PCH boundaries along the solar limb, using full-disk images from the SOlar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT). One synoptic-map method uses the line-of-sight magnetic field from the SOHO/Michelson Doppler Imager (MDI) to determine the unipolarity boundaries near the poles. The other method applies thresholding techniques to synoptic maps created from EUV image data from EIT. The results from all three methods suggest that the solar maxima and minima of the two hemispheres are out of phase. The maximum PCH area, averaged over the methods in each hemisphere, is approximately 6 % during both solar minima spanned by the data (between Solar Cycles 22/23 and 23/24). The northern PCH area began a declining trend in 2010, suggesting a downturn toward the maximum of Solar Cycle 24 in that hemisphere, while the southern hole remained large throughout 2010.     

The symbiotic binary system EG Andromedae

Photometric observations of the symbiotic star EG and confirm that the binary system is eclipsing. The epoch of primary minimum is computed. The new period 474 days instead of 470 days is estimated by a comparison of line profiles of Balmer lines taken in 1967–69 and 1982–84. The new ephemeris is 1 $$JD_{min.} = 2 446 336.7 + 474 E.$$      

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.     

Isovortical orbits of autonomous,conservative, two degree-of-freedom dynamical systems

For an autonomous, conservative, two degree-of-freedom dynamical system, vorticity (the curl of velocity) is constant along the orbit if the velocity field is divergence-free such that: $$u\left( {x, v} \right) - \psi _y , v\left( {x, y} \right) = - \psi _x .$$ Isovortical orbits in configuration space are level curves of a scalar autonomous function Ψ (x, v) satisfying a second-order, non-linear partial differential equation of the Monge-Ampere type: $$2\left( {\psi _{xx} \psi _{yy} - \psi _{xy}^2 } \right) + U_{xx} + U_{yy} = 0,$$ where U(x. y) is the autonomous potential function. The solution Soc the time variable is reduced to a quadrature following determinatio of Ψ. Self-similar solutions of the Monge-Ampere equation under Birkhoff's one-parameter transformation group are derived for homogeneous (power-law) potential functions. It is shown that Keplerian orbits belong to the class of planar isovortical flows.     

Soft X-ray reflectivity measurements of the mirrors flown on the Ariel-6 satellite

This paper describes the detailed calibration at soft X-ray energies (0.1–2.0 keV; 125 Å-6 Å) of gold coated, paraboloidal X-ray mirrors, four of which were subsequently flow on the Ariel-6 satellite. Uncertainties in the attitude of the satellite together with an apparent reduction in sensitivity of the soft X-ray experiment necessitated observations using the Crab Nebula as a reference. These showed that a dramatic reduction in the reflection efficiencies of all four mirrors had occurred, almost certainly after or during launch. An initial recalibration of the mirrors using the Crab observation is described.