The termination of the solar wind

It has previously been suggested that the solar wind might terminate at distances of 5 AU to 20 AU from the Sun, and that the solar wind might be drastically slowed down by charge exchange and photoionization of interstellar hydrogen atoms which approach the Sun. However, recent satellite measurements of resonantly scattered Lyman alpha radiation, together with pulsar dispersion and Faraday rotation measures, imply very small values for the interstellar hydrogen density (0.05 cm⁻³) and magnetic field strength (3 μG). As a result, the solar wind is not expected to be slowed down by more than about 30% inside the termination distance, which is expected to be about 100 AU.     

8–13 μm spectrophotometry of Comet Kohoutek

Spectrophotometry of Comet Kohoutek (1973f) covering the wavelength range 8–13 μm is presented. The spectral shape of the derived flux excess above a blackbody closely resembles that seen in circumstellar and interstellar dust and generally attributed to metallic silicates.     

Solar wind induction in Mercury: Constraints on the formation of a magnetosphere

The discovery of Mercury's magnetosphere by Mariner 10 was surprising since the conventional view of regenerative planetary dynamos had been that the spin requirement would likely have been in excess of the observed spin rate of Mercury. Also internal fluid motions were not expected to be sufficiently large. This paper explores the alternative model of the formation of Mercury's magnetosphere via electromagnetic induction forced by the solar wind. It is shown, however, that the constraints are so severe as to limit severely the applicability of such a model. Although induction is easily observed on the Moon, the modification of the magnetic boundary condition associated with a plasma magnetosphere on Mercury rules out its formation via induction except for interplanetary driving fields which are decreasing in amplitude. That model is explored but retains the difficulty that induced magnetospheres tend to be of small radial and temporal extent compared to that inferred by Ness et al. for Mercury.     

Photometric Inference of the Corotation Radii of Ten Barred Galaxies

We have used photometric images of ten barred galaxies in the B and I bands to infer the geometrical and dynamical parameters of their bars: Their length, (R _bar), their strengths, (S _b), and their corotation radii, (R _CR).These parameters have been obtained studying azimuthal profiles from the B and I band images of the galaxies. We find that R _CR is in all cases slightly larger than R _bar, with mean values close to 1.2 R _bar. We have also found a dependence of the ratio R _CR/R _bar on S _bar. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of Barred Galaxies. VII. Comparative Statistics of SB and SA Galaxies. Near and Mid-IR Regions

The near and mid-IR properties of barred and unbarred spiral galaxies are discussed on the basis of complete samples that were compiled earlier. The two types of spirals are shown not to differ from one another in emission power in the near and mid-IR ranges. Multiple regression and principal component analysis have been applied to investigate near and mid-IR properties of SB and SA galaxies, particularly their relation to X-ray and radio continuum emissions. There are definite differences between SB and SA spirals in the near and mid-IR. In the case of SB galaxies, the compactness of 10 m emission is closely related to the J - H color index, and the redder J - H color corresponds to relatively more extended emission at 10 m. It is assumed that these are caused by the bar itself, which stimulates enhanced star formation in a barred galaxy with respect to unbarred spiral.     

Comparative Analysis of a Transition Region Bright Point with a Blinker and Coronal Bright Point Using Multiple EIS Emission Lines

Since their discovery 20 year ago, transition region bright points have never been observed spectroscopically. Bright point properties have not been compared with similar transition region and coronal structures. In this work we have investigated three transient quiet Sun brightenings including a transition region bright point (TR BP), a coronal bright point (CBP) and a blinker. We use time-series observations of the extreme-ultraviolet emission lines of a wide range of temperature T (logT=5.3?–?6.4) from the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite. We present the EIS temperature maps and Doppler maps, which are compared with magnetograms from the Michelson Doppler Imager (MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker are ≤?25 km?s^?1, which is typical of transient TR phenomena. The Doppler velocities of the CBP were found to be ≤?20 km?s^?1 with exception of those measured at logT=6.2 where a distinct bi-directional jet is observed. From an EM loci analysis we find evidence of single and double isothermal components in the TR BP and CBP, respectively. TR BP and CBP loci curves are characterized by broad distributions suggesting the existence of unresolved structure. By comparing and contrasting the physical characteristics of the events we find that the BP phenomena are an indication of multi-scaled self-similarity, given the similarities in both their underlying magnetic field configuration and evolution in relation to EUV flux changes. In contrast, the blinker phenomena and the TR BP are sufficiently dissimilar in their observed properties as to constitute different event classes. Our work is an indication that the measurement of similar characteristics across multiple event types holds class-predictive power, and is a significant step towards automated solar atmospheric multi-class classification of unresolved transient EUV sources. Finally, the analysis performed here establishes a connection between solar quiet region CBPs and jets.     

Observations of vertical ground accelerations exceeding gravity during the 1997 Umbria-Marche (central Italy) earthquakes

We found extensive evidence that the vertical ground accelerations produced during the largest shock (M = 6.0) of the 1997 Umbria-Marche earthquake sequence exceeded 1g in two areas close to the heavily-damaged villages of Annifo and Colle Croce. This evidence comes from the striking observation of thousands of freshly fractured and broken rocks and stones in these areas. Some of the broken stones lie isolated on soft detritic soil while others had been previously piled up, probably a long time agoto clear the fields for farming. The freshness of the cuts and fractures and the consistency of the observations for thousands of rocks and stones in these areas indicate that these rocks were thrown upwards during the earthquake, with breakage occurring at the time of impact. Ground motion calculations consistent with the static deformation inferred from GPS and interferometry data, show that the broken stones and rocks are found in the zone where the strongest shaking took place during the earthquake and that most of the shaking there was vertical.     

Water relation characteristics ofAlhagi sparsifolia and consequences for a sustainable management

Water relation characteristics of the desert legumeAlhagi sparsifolia were investigated during the vegetation period from April to September 1999 in the foreland of Qira oasis at the southern fringe of the Taklamakan Desert, Xinjiang Uygur Autonomous Region of China. The seasonal variation of predawn water potentials and of diurnal water potential indicated thatAlhagi plants were well water supplied over the entire vegetation period. Decreasing values in the summer months were probably attributed to increasing temperatures and irradiation and therefore a higher evapotranspirative demand. Data from pressure-volume analysis confirmed thatAlhagi plants were not drought stressed and xylem sap flow measurements indicated thatAlhagi plants used large amounts of water during the summer months. Flood irrigation had no influence on water relations inAlhagi probably becauseAlhagi plants produced only few fine roots in the upper soil layers. The data indicate thatAlhagi sparsifolia is a drought-avoiding species that utilizes ground water by a deep roots system, which is the key characteristic to adjust the hyper-arid environment. Because growth and survival ofAlhagi depends on ground water supply, it is important that variations of ground water depth are kept to a minimum. The study will provide a theoretical basis for the restoration and management of natural vegetation around oasis in arid regions.