Observed coronal temperatures at 1.37R ⊙ in the region of a helmet structure

During the total solar eclipse, 1965 May 30, a 25 cm aperturef/8.0 telescope and Fabry-Perot interferometer were operated aboard the USAF-AEC aircraft. High resolution spectra of the Fexiv emission line, 530.3 nm, were obtained. Deconvolved intensity vs wavelength profiles of the second order fringe overlay a helmet structure on the NM limb at out to 1.37R . The profiles yield coronal temperatures, absolute intensities and Doppler velocities in regions of apparently open magnetic field structure and within the closed field lines of the helmet. Together with white light intensities the observations are interpreted to provide temperatures and turbulent velocities in and around this coronal structure. Comparison is made with a model by Billings and Roberts. We suggest a model with radial flow (solar wind) velocities of 60 km s^–1 satisfies the observations in the open field line region.Work performed under the auspices of the U.S. Atomic Energy Commission, and portions of the analysis at the National Center for Atmospheric Research, Boulder, Colo.     

The three-dimensional structure of ‘loop-like’ coronal mass ejections

We have measured the brightness and latitudinal extent of the depleted (cavity) region behind the leading edge of three coronal mass ejection (CME) events from the Skylab epoch. The events chosen are among those believed to be typical of non-impulsive, loop-like CMEs (Sime, MacQueen, and Hundhausen, 1984). The pre-event coronal brightness has been matched by a model corona, assuming both a background contribution and a contribution from a range of hypothetical streamer models, distinguished by differing longitudinal extent. Then, assuming that the cavities are voided regions in which the local electron density is negligible, we estimate their minimum line-of-sight extent and find them to be comparable to, or greater than, their measured latitudinal extent. As a result, we suggest this unambiguously demonstrates the three-dimensional nature of these — and likely, this class of — events.     

Joint radio and soft x-ray imaging of an ‘anemone’ active region

The Very Large Array and the Soft X-ray Telescope (SXT) aboard the Yohkoh satellite jointly observed the rapid growth and decay of a so-called anemone active region on 3–6 April, 1992 (AR 7124). The VLA obtained maps of the AR 7124 at 1.5, 4.7, and 8.4 GHz. In general, discrete coronal loop systems are rarely resolved at 1.5 GHz wavelengths because of limited brightness contrast due to optical depth effects and wave scattering. Due to its unusual anemone-like morphology, however, several discrete loops or loop systems are resolved by both the VLA at 1.5 GHz and the SXT in AR 7124.Using extrapolations of the photospheric field and the radio observations at 4.7 and 8.4 GHz, we find that the microwave emission is the result of gyroresonance emission from a hot, rarefied plasma, at the second and/or third harmonic. The decimetric source is complex -1.5 GHz emission from the leading part of AR 7124 is due to free-free emission, while that in the trailing part of the active region is dominated by gyroresonance emission. We also examine an interesting case of a discrete radio loop with no soft X-ray (SXR) emission adjacent to a hot SXR loop. This observation clearly shows the multithermal nature of the solar corona.     

Opening of active region’s large-scale overlying magnetic loops and kinking motion of a magnetic loop triggered by a vicinal small eruption

In this paper, we present a clear case of a small eruption near active region NOAA 10990 leading to opening of active region’s large-scale magnetic loops and kinking motion of a magnetic loop in this active region on April 16, 2008. From a sequence of TRACE 171 ? images, we find that the upper large-scale overlying magnetic loops of the active region expanded upwards from the arcaded configuration to the vertical one accompanying the vicinal small eruption. At the same time, the topology of a magnetic loop inside the active region changed from the inverted “U” shape to the almost vertical one with its two legs intertwining each other. From the temporal analysis of the observations, we find that the opening of the upper large-scale overlying magnetic loops resulted in the instability of the magnetic loop inside the active region. By analyzing the surrounding coronal environment, we suggest that the existence of the lower overlying magnetic loops prevented the magnetic loop from eruption. Generally, the kinking motion of the flux rope is taken as occurrence of kink instability. In this event, the top of the magnetic loop first began the kinking motion and then the two legs intertwined each other. According to our knowledge, the latter process has not been reported. Because there was only one active region on the solar disk on April 16, 2008, it turned out to be a very good candidate for us to investigate the impact of the vicinal eruption on the active region. These findings provide evidence that the active region is very sensitive to the vicinal eruptions.     

Current sheet model of a normal prominence in which the background magnetic lines show a ‘dip structure’

We propose a simple 2D current sheet model of a normal prominence, in which the lines of the background magnetic field have the dip structure which seems to be required for such an object to form and to be stably supported.     

On the structure of Saturn's rings and the ‘real’ rotational period for the planet

An analysis of the Lowell Observatory photographic plates of Saturn gave the following results: (1) ring A and B show peculiar brightness distributions around the planet, from which we conclude that both are composed of particles in synchronous rotation. (2) The leading side of the particles in ring A is brighter than the trailing side by about 4%, which may indicate an interaction between such particles and the interplanetary medium. (3) Scans of the rings across the major axis show a small (～0.3″) region of enhanced brightness, from which we derive a value ofT _s =10^h13 _. ^m 8±5 _. ^m 4 for the actual planetary rotational period of Saturn. (4) In order to explain the synchronous rotation, the particles in ring A have to be at least 42 m in diameter.     

The existence of a ‘gap’ in the evolutionary sequence of pulsars

A replot of period derivative against period is done for about 300 pulsars, and the main features of the plot are discussed. The significance of a gap in this plot is reexamined and the existence of pulsars with nulling and subpulse drifting behaviour below this gap is pointed out. The implications of this for pulsar evolution are also discussed.     

Hβ Doppler-velocity fields within sites of flares in a solar active region

In this paper, we analyze the relationship between photospheric magnetic fields and chromospheric velocity fields in a solar active region, especially evolving features of the chromospheric velocity field at preflare sites. It seems that flares are related to unusually distributed velocity field structures, and initial bright kernels and ribbons of the flares appear in the red-shifted areas (i.e., downward flow areas) close to the inversion line of H Dopplergrams with steep gradients of the velocity fields, no matter whether the areas have simple magnetic structure or a weak magnetic field, or strong magnetic shear and complex structure of the magnetic fields. The data show that during several hours prior to the flares, while the velocity field evolves, the sites of the flare kernels (or ribbons) with red-shifted features come close to the inversion line of the velocity field. This result holds regardless of whether or not the flare sites are wholly located in blue-shifted areas (i.e., upward flow areas), or are far from the inversion line of the Doppler velocity field (V = 0 line), or are partly within red-shifted areas. There are two cases favourable for the occurrence of flares, one is that the gulf-like neutral lines of the magnetic field (B = 0 line) occur in the H red-shifted areas, the other is that the gulf-like inversion lines of the H Doppler velocity field (V = 0 line) occur in the unipolar magnetic areas. These observational facts indicate that the velocity field and magnetic field have the same effect on the process of flare energy accumulation and release.     

On the covering of a Hill’s region by solutions in the restricted three-body problem

We consider two classical celestial-mechanical systems: the planar restricted circular three-body problem and its simplification, the Hill’s problem. Numerical and analytical analyses of the covering of a Hill’s region by solutions starting with zero velocity at its boundary are presented. We show that, in all considered cases, there always exists an area inside a Hill’s region that is uncovered by the solutions.     

Low-latitude thermal structure of Jupiter in the region 0.1–5 bars

The radiative heat flux from 0.1 to 10 bars is estimated on the basis of a “two-cloud” scattering model that fits available spectral data and Pioneer photometry. Deeper than a few bars, the flux is 4.5 W m^?2, compared with the 18.8 W m^?2 used in an earlier study by Trafton and Stone. A temperature profile is computed, with the H₂ pressure-induced opacity; the temperature at 1 bar is found to be 156°K, rather than the commonly accepted 170°K. An additional optical depth of unity at the 0.67-bar level could restore the conventional value; otherwise a considerably cooler atmosphere is a serious possibility.     

Further seasonal changes in Uranus’ cloud structure observed by Gemini-North and UKIRT

Near-infrared observations of Uranus were made in October/November 2010 with the Gemini-North telescope in Hawaii, using NIFS, an integral field spectrograph, and the NIRI instrument in imaging mode. Observations were acquired using adaptive optics and have a spatial resolution of approximately 0.1–0.2″.The observed spectra along Uranus’ central meridian were analysed using a multiple-scattering retrieval algorithm to infer the vertical/latitudinal variation in cloud optical depth, which we compare with previous observations made by Gemini-North/NIFS in 2009 and UKIRT/UIST observations made between 2006 and 2008. Assuming a continuous distribution of small particles (r ～ 1 μm, and refractive index of 1.4 + 0i) with the single scattering albedo set to 0.75 and using a Henyey–Greenstein phase function with asymmetry parameter set to 0.7 at all wavelengths and latitudes, the retrieved cloud density profiles show that the north polar zone at 45°N has continued to steadily brighten while the south polar zone at 45°S has continued to fade. As with our previous analyses we find that, assuming that the methane vertical profile is the same at all latitudes, the clouds forming these polar zones at 45°N and 45°S lie at slightly lower pressures than the clouds at more equatorial latitudes. However, we also find that the Gemini data can be reproduced by assuming that the main cloud remains fixed at ～2 bar at all latitudes and adjusting the relative humidity of methane instead. In this case we find that the deep cloud is still more opaque at the equator and at the zones at 45°N and 45°S and shows the same seasonal trends as when the methane humidity remain fixed. However, with this approach the relative humidity of methane is seen to rise sharply from approximately 20% at polar latitudes to values closer to 80% for latitudes equatorward of 45°S and 45°N, consistent with the analysis of 2002 HST observations by Karkoschka and Tomasko (Karkoschka, E., Tomasko, M. [2009]. Icarus 202, 287–302), with a possible indication of seasonal variability. Overall, Uranus appeared to be less convectively active in 2010 than in the previous 4 years, supporting the conclusion that now the northern spring equinox (which occurred in 2007) has passed, the atmosphere is settling back into the more quiescent state seen by Voyager 2 in 1986.     

On the fine structure of the Fe I λ532.4185-nm line profile in the spectrum of the solar disk center

Based on the digital spectra taken with double monochromators of high spectral resolution, we have constructed the profile of the Fe I λ532.4185-nm line in the spectrum of the solar disk center. Basic spectrophotometric characteristics of the line profile have been determined with a high accuracy. The fine structure of the line profile is studied in detail. The profile asymmetry parameters have been determined.     

Possible radio precursors/signatures of the CMEs onset:radio type Ⅲ bursts and fine structures in the centimeter-metric wavelength region

Seventy-one occurrences of coronal mass ejections(CMEs) associated with radio bursts,seemingly associated with type Ⅲ bursts/fine structures(FSs),in the centimeter-metric frequency range during 2003-2005,were obtained with the spectrometers at the National Astronomical Observatories,Chinese Academy of Sciences(NAOC) and the Culgoora radio spectrometer and are presented.The statistical results of 68 out of 71 events associated with the radio type III bursts or FSs during the initiation or early stages of the...     

A ‘magnetospheric’ scenario of the solar flare in a quadrupole magnetic configuration

An attempt is made to impart a constructive character to the concept of the solar flaremagnetospheric substorm analogy. An idealized scheme for a two-ribbon solar flare in the originally closed magnetosphere of the active region is discussed. The basis is formed by a terrestrial substorm scenario with two active phases (Mishin et al., 1992). While a quadrupole magnetic configuration turns out to be a solar analog of the Earth's magnetosphere. A physical mechanism that sustains the preflare storage phase, is provided by an instability like a stretching instability of the closed geomagnetotail. The storage process is attributed to the emergence into the corona of closed magnetic flux lines in adjacent (to the location of the would-be flare) regions. The flare flash-phase is determined by the change-over of the stretching instability to a disruption instability of a nonstationary (not neutral) current sheet inside the storage zone. The final recovery phase corresponds to the wellknown Pneuman-Kopp model.     

The origin of the ‘FUN’ anomalies and the high temperature inclusions in the allende meteorite

The discovery of isotopic anomalies in white inclusions of the meteorite Allende has led to fundamental questions concerning the origin of these anomalies and of the white inclusions themselves. An analysis of the FUN anomalies in the inclusions C1 and EK1-4-1 demonstrates that these isotopic anomalies may be decomposed into individual nucleosynthetic components, which have been subjected to separate mass and component fractionations. There is no evidence that any freshlysynthesized material injected into the primitive solar nebula was of abnormal isotopic composition, or that the FUN anomalies were due to an injection of unusual material. Rather, they show the effects of form of interstellar grains whose size or chemistry served as a memory for the nucleosynthetic origins of their constituent atoms. Giant gaseous protoplanets, as described for the early solar nebula by Cameron (1978), are a potential site for achieving both mass and component fractionations, and for producing white inclusions in general.     

On the origin of energetic particles in the foreshock region of the Earth’s bow shock

We consider the processes related to the formation of the so-called foreshock region upstream of the Earth’s bow shock. We suggest a model based on the surfing of pick-up ions in the bow shock front in terms of which the ion acceleration mechanism in the front can be explained. We ascertain the physical conditions under which the accelerated ions lie upstream of the shock front and determine the direction of motion of the energetic ions. We conclude that it is this population of energetic ions (longitudinal beams) that plays a major role in forming the ion foreshock boundary.     

Non-thermal processes during the ‘build-up’ phase of solar flares and in absence of flares

Hard X-ray and radio observations lead to the conclusion that production of non-thermal electrons is a common phenomenon of the active Sun. A preliminary analysis of three hard X-ray bursts observed with the OGO-5 satellite and the radio observations reported in the literature indicates that non-thermal particles are present in the flare region prior to the impulsive (flash) phase and also during the gradual rise and fall (GRF) bursts which are usually explained in terms of purely thermal radiation. The principal difference between the non-thermal electrons observed before the flash phase and during the flash phase appears to be in their total number rather than in the hardness of their energy spectrum. This indicates that the basic characteristics of the two acceleration processes are probably similar although the total energy converted into non-thermal electrons is considerably larger in the flash phase than in the build-up phase. Transient absorbing H features and filament activations are discussed in terms of their ability to produce energetic particle events and magnetic energy release.Presently at the Space Sciences Laboratory, University of California, Berkeley and Institute of Plasma Research, Stanford University, Stanford, California.     

An explanation of the ‘granulation boundary’ in the HR diagram

The granulation boundary is a line running in the HR diagram from about F0V stars to G1Ib. It divides the HR diagram in two regions in which the spectral line bisector behaves differently. To the right (cooler stars) the Fraunhofer lines in stellar spectra show the characteristics typical for convective motions. For hot stars it indicates the presence of large velocities involving a large part of the line-forming region. We give evidence that the opposite behaviour shown by spectra of hotter stars can be explained by gravity waves.     

Polarization properties of a ‘Zeiss-type’ coelostat: The case of the solar tower in Arcetri

A theoretical model of the polarization properties of a Zeiss-type coelostat is presented and discussed in detail. The Muller matrix describing the modification of the Stokes vector of the incident radiation as a result of the multiple reflections on the coelostat mirrors is derived as a function of the solar coordinates, the geometrical configuration of the coelostat, and the parameters defining the optical properties of the mirrors. These parameters, or more particularly, the index of refraction n and the extinction coefficient k, have been evaluated by means of laboratory measurements performed on a series of specimens having characteristics similar to those of the coelostat mirrors. The geometry of the coelostat configuration is described in full detail. The theoretical model has been then particularized to the case of the Donati Solar Tower in Arcetri, and some experimental measurements have been performed to check the correctness of the model. These measurements show the basic adequacy of the mathematical model, although some offset terms are found in the Stokes parameters U and V.