Magnetic field configurations which can produce prominences with inverse polarity

In this Letter several observational aspects of prominences with inverse magnetic polarity are summarised. It is shown that these features can be explained in a natural way if inverse polarity prominences result from the merging of two adjacent bipolar magnetic regions.     

Current sheet models for inverse polarity prominences in twisted flux tubes

This paper treats the prominence model of Low (1993) to examine more complicated sheet currents than those used in the original model. Nonlinear force-free field solutions, in Cartesian coordinates, invariant in a given direction, are presented to show the possibility of an inverse-polarity prominence embedded in a large twisted flux tube. The force-free solution is matched to an external, unsheared, potential coronal magnetic field. These new solutions are mathematically interesting and allow an investigation of different profiles of the current intensity, magnetic field vector and mass density in the sheet. These prominence models show a general increase in magnetic field strength with height in agreement with observations. Other prominence properties are shown to match the observed values.     

Martens-Kuin models of normal and inverse polarity filament eruptions and coronal mass ejections

An analysis is made of the Martens-Kuin filament eruption model in relation to observations of coronal mass ejections (CMEs). The field lines of this model are plotted in the vacuum or infinite resistivity approximation with two background fields. The first is the dipole background field of the model and the second is the potential streamer model of Low. The assumption is made that magnetic field evolution dominates compression or other effects which is appropriate for a low- coronal plasma. The Martens-Kuin model predicts that, as the filament erupts, the overlying coronal magnetic field lines rise in a manner inconsistent with observations of CMEs associated with eruptive filaments. Initially, the bright arc of a CME broadens in time much more slowly than the dark cavity between it and the filament, whereas in the model they broaden at the same rate or the bright arc broadens more rapidly than the dark cavity, depending on the background field. Thus, this model and, by generalization the whole class of so-called Kuperus-Raadu configurations in which a neutral point occurs below the filament, are of questionable utility for CME modeling. An alternate case is considered in which the directions of currents in the Martens-Kuin model are reversed resulting in a so-called normal polarity configuration of the filament magnetic field. In this case, a neutral line occurs above the current-carrying filament. The background field lines now distort to support the filament and help eject it. While the vacuum field results make this configuration appear very promising, a full two- or more-dimensional MHD simulation is required to properly analyze the dynamics resulting from this configuration.Presently NRC Senior Research Associate at NOAA, Space Environment Laboratory, Boulder, Colorado, U.S.A.At the NASA National Space Data Center.     

The Mazapil meteorite: From paradigm to periphery

Abstract— The remarkable fact about the Mazapil meteorite is that it fell on the same night, in 1885, that the Andromedid meteor shower underwent a spectacular outburst. The simultaneity of these two events has driven speculation ever since. From ?1886 to ?1950 the circumstances of the Mazapil fall were taken, by a number of researchers, as the paradigm that demonstrated the fact that comets were actually swarms of meteoritic boulders. Beginning ?1950, however, most researchers began to adopted the stance that the timing of the Mazapil fall was nothing more than pure coincidence. The reason behind this change in interpretation stemmed from, amongst other factors, the fact that none of the prominent annual meteor showers could be clearly shown to deliver meteorites. Also, with the introduction of the icy‐conglomerate model for cometary nuclei, by F. Whipple in the early 1950s, it became increasingly clear that only exceptional circumstances would allow for the presence of large meteoritic bodies in cometary streams. Further, by the mid 1960s it had been shown that meteorites could, in fact, be delivered to the Earth from the main belt asteroid region via gravitational resonances. With the removal of the dynamical “barrier” against the delivery of meteorites from the asteroid region, the idea that the Mazapil meteorite could have been part of the Andromedid stream fell into complete disfavor. This being said, we nonetheless present the results of a study concerning the possible properties of the parent object to the Mazapil meteorite based upon the assumption that it was a member of the Andromedid stream. This study is presented to illustrate the point that while cometary showers do not yield meteorites on the ground, this does not, in fact, substantiate the argument that no meteoritic bodies reside in cometary streams. Indeed, we find no good reason to suppose that an object with the characteristics of the Mazapil meteorite could not have been delivered from the Andromedid stream. However, we argue that upon the basis of the actual reported observations and upon the scientific maxim of minimized hypothesis and least assumption it must be concluded that the timing of the fall of the Mazapil meteorite and the occurrence of the Andromedid outburst were purely coincidental.     

The rotation of active regions with differing magnetic polarity separations

The separation of the leading and following portions of plages and (multi-spot) sunspot groups is examined as a parameter in the analysis of plage and spot group rotation. The magnetic complexity of plages affects their average properties in such a study because it tends to make the polarity separations of the plages less than they really are (by the definition of polarity separation used here). Correcting for this effect, one finds a clear and very significant dependence of the total magnetic flux of a region on its polarity separation. Extrapolating this relationship to zero total flux leads to an X intercept of about 25 Mm in polarity separation. The average residual rotation rates of regions depend upon the polarity separation in the sense that larger separations correspond to slower rotation rates (except for small values of separation, which are affected by region complexity). In the case of sunspots, the result that smaller individual spots rotate faster than larger spots is confirmed and quantified. It is shown also that smaller spot groups rotate faster than larger groups, but this is a much weaker effect than that for individual spots. It is suggested that the principal effect is for spots, and that this individual spot effect is responsible for much or all of the group effect, including that attributed in the past to group age. Although larger spot groups have larger polarity separations, it is shown that the rotation rate-polarity separation effect is the opposite in groups than one finds in plages: groups with larger polarity separations rotate faster than those with smaller separations. This anomalous effect may be related to the evolution of plages and spot groups, or it may be related to connections with subsurface toroidal flux tubes. It is suggested that the polarity separation is a parameter of solar active regions that may shed some light on their origin and evolution.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.     

The inverse planetary problem: a numerical treatment

The so-called inverse planetary problem can be stated as follows: given the distances from the centre, masses, and radii of (say) three planets of a planetary system, find the optimum polytropic index, mass, and radius of their star, and also other quantities of interest, which depend either explicitly or implicitly on the foregoing ones (e.g., central and mean density, central and mean pressure, central and mean temperature, etc.). It is hereafter tacitly assumed that the system is opaque with respect to observations concerning periods of planetary otbits; hence, we cannot have any relevant estimates due to the well-known period laws. In the present paper, the inverse planetary problem is treated numerically on the basis of the so-called global polytropic model, developed recently by the first author.     

The visual double star data base

Any use of stars for astrometric purposes necessarily involves examination of their duplicity characteristics. The Washington Double Star Catalog (WDS) provides this information in a continuously updated and machine-readable format. This contribution describes the current data base and plans for its future extension.     

The insensitivity of the cosmic ray galactic anisotropy to heliomagnetic polarity reversals

Using the cosmic ray sidereal and anti-sidereal diurnal variations observed underground in London and Hobart during the period 1958–1983, it is demonstrated that: (1) the phase changes of the apparent sidereal diurnal variation observed only in the Northern Hemisphere cannot be attributed to the change of the heliomagnetospheric modulation of galactic cosmic ray anisotropy caused by the polarity reversal of the solar magnetic field, but that they are due to the fluctuation of the spurious sidereal variation produced from the anisotropy responsible for the solar semi-diurnal variation; (2) the spurious sidereal variation can be eliminated from the apparent variation by using the observed anti-sidereal diurnal variation; and (3) after the elimination, the sidereal diurnal variations in the Northern and Southern Hemispheres almost coincide with each other and are stationary throughout the period, regardless of the polarity reversal of the heliomagnetosphere. The origin of the corrected sidereal variation is discussed.     

The excitation of planetary orbits by stellar jet variability and polarity reversal

Planets form in active protoplanetary disks that sustain stellar jets. Momentum loss from the jet system may excite the planets’ orbital eccentricity and inclination (Namouni in Astron. J. 130:280, 2005). Evaluating quantitatively the effects of such excitation requires a realistic modeling of the momentum loss profiles associated with stellar jets. In this work, we model linear momentum loss as a time-variable stochastic process that results in a zero mean stellar acceleration. Momentum loss may involve periodic or random polarity reversals. We characterize orbital excitation as a function of the variability timescale and identify a novel excitation resonance between a planet’s orbital period and the jet’s variability timescale where the former equals twice the latter. For constant variability timescales, resonance is efficient for both periodic and random polarity reversals, the latter being stronger than the former. For a time variable variability timescale, resonance crossing is a more efficient excitation mechanism when polarity reversals are periodic. Each polarity reversal type has distinct features that may help constrain the magnetic history of the star through the observation of its planetary companions. For instance, outward planet migration to large distances from parent stars is one of the natural outcomes of periodic polarity reversal excitation if resonance crossing is sufficiently slow. Applying the excitation mechanism to the solar system, we find that the planet-jet variability resonance with periodic polarity reversal momentum loss is a possible origin for the hitherto unexplained inclination of Jupiter’s orbit by 6^° with respect to the Sun’s equator.     

Numerical models of quiescent normal polarity prominences

We present 2-D numerical models of quiescent solar prominences with normal magnetic polarity. These models represent an extension to the classical Kippenhahn-Schlüter model in that the prominence is treated as having finite width and height and the external coronal field is matched smoothly to the internal prominence field so that there are no current sheets at the prominence sides. Using typical prominence and coronal values we find solutions to the generalised Grad-Shafranov equation which illustrate the necessary magnetic support. We also discuss some extensions to the basic model.     

The researches at torino on wide double stars

Summary The present poster shows the main researches conduced at the Astronomical Observatory of Torino during this last decade in the field of the wide double stars. From the observational point of view, two different photographic techniques carried out with our 105 cm astrometric reflector over a selected sample of wide binaries are explained. With reference to the Hipparcos mission, we show two aspects of our collaboration with the INCA and FAST Consortiums. From the statistical point of view, a study concerning the systematic and accidental errors detected in visual double star observations is explained. We conclude the poster with the future foreseen researches concerning new observational techniques and new theoretical statistical studies on these wide objects.     

Low latitude geomagnetic bays and IMF sector polarity

From the examination of IMF data and low latitude positive bays over an interval of 13 years, it is shown that the polarity of the IMF controls seasonal variation in the occurrence of the bays. The study suggests an appreciable contrast between the frequency of bay events during passage of the ‘toward’ and ‘away’ sectors and that this feature is most prominent in summer minimum and autumnal equinoctial maximum. The differences in the frequency of occurrence of low latitude positive bays for the two sectors, as a function of local time, is found to be a feature of the equatorial region only.     

Statistical parameterization of inverse problems

Image restoration, computerized tomography, and other similar problems are considered as a unified class of stochastic inverse problems. The conventional approach to these problems that proceeds from some integral or functional equations suffers from three main shortcomings: (i) subjectivity, (ii) inability to account for the inner (radiational) noise, and (iii) inability to include the fundamental concept of the natural limit of solution accuracy. A general approach is developed, the Statistical Parameterization of Inverse Problems (SPIPR), that takes into account both the inner and external random noise and gives an explicit form of the above-mentioned natural limit. Applications of the SPIPR to various problems show that the maximum likelihood method as the concrete way to obtain an object estimate has practically limiting efficiency.Two new fields of applications of the SPIPR are outlined along with the image restoration problem: the elimination of blurring due to atmosphere turbulence and reconstruction of an object structure in the computerized tomography. The expressions for the main distribution function in all these problems are found. The corresponding real examples and model cases are considered as well.     

Interplanetary magnetic field polarity and low-latitude geomagnetic field

The relationship between the low latitude magnetic field and the polarity of the interplanetary magnetic field, inferred by Svalgaard for a period of about 4 solar cycles, is derived and discussed for low and high solar activity conditions. The field reacts differently during the passage of A (away) and C (toward) sectors and, during the passage of sector boundary, the response is substantially different depending upon the nature of the change, i.e.A to C or C to A; a change of sector from A to C is found to be associated with a large depression in the field. It is also observed that the night-time field in low latitudes is best correlated with the AC index and that the correlation, observed throughout the period of 1929–1957, breaks down after 1962. The results computed from Alibag observations are confirmed by an examination of the data from Hermanus and San Juan.     

The mass/eccentricity limit in double star astronomy

A research that we conducted in 1963 on the evolution of the binaries based on the available orbital data to obtain a philosophical degree, led to the establishment of an interesting and new diagram between the logarithm of the total mass and a particular parameterX, bound to the areal constant. This appeared to have a real physical significance but the basic observational material was insufficiently extended to assure its undeniable existence. In 1981, a new research based on a more extended orbital material, has confirmed this diagram. Presently, another important increase in the orbital material and the availability of highly accurate trigonometric parallaxes produced by the Hipparcos satellite, gave us the opportunity to confirm once more the stability of this diagram. This last research is here described.     

The fraction of double degenerates among DA white dwarfs

We present the results of a radial velocity survey designed to measure the fraction of double degenerates among DA white dwarfs. The narrow core of the H line was observed twice or more for 46 white dwarfs yielding radial velocities accurate to a few km s¹. This makes our survey the most sensitive to the detection of double degenerates undertaken to date. We found no new double degenerates in our sample, though H emission from distant companions is seen in two systems. Two stars known to be double degenerates prior to our observations are included in the analysis. We find a 95 per cent probability that the fraction of double degenerates among DA white dwarfs lies in the range [0.017, 0.19].     

The stellar content of a prototype double barred galaxy

High spatial resolution visible and NIR observations of the bar of NGC 5850, a prototype of double barred spirals, together with visible intermediate and high dispersion spectra along the primary bar, are being used, with the aid of simple stellar population synthesis models, to investigate the mean age and metallicity of the different stellar components of the central part of the galaxy. The determination of stellar ages and metallicities would constrain theoretical scenarios for secondary bar formation and the evolution of barred spirals. Unfortunately, we cannot obtain a good fit with simple stellar populations (SSPs) to the spectral indices, so it can not give us, by now, insight into the mean stellar age and metallicity of the real populations in the central region of the galaxy. These preliminary results show a relatively old primary bar with metallicity about solar, although absolute values must be taken with care. The nucleus has a young stellar component, and is very dusty. This revised version was published online in August 2006 with corrections to the Cover Date.     

The mass ratio distribution of short-period double degenerate stars

Short-period double degenerates (DDs) are close white dwarf–white dwarf binary stars which are the result of the evolution of interacting binary stars. We present the first definitive measurements of the mass ratio for two DDs, WD 0136+768 and WD 1204+450, and an improved measurement of the mass ratio for WD 0957−666. We compare the properties of the six known DDs with measured mass ratios to the predictions of various theoretical models. We confirm the result that standard models for the formation of DDs do not predict sufficient DDs with mass ratios close to 1. We also show that the observed difference in cooling ages between white dwarfs in DDs is a useful constraint on the initial mass ratio of the binary. A more careful analysis of the properties of the white dwarf pair WD 1704+481.2 leads us to conclude that the brighter white dwarf is older than its fainter companion. This is the opposite of the usual case for DDs and is caused by the more massive white dwarf being smaller and cooling faster. The mass ratio in the sense (mass of younger star)/(mass of older star) is then  1.43±0.06  rather than the value of  0.70±0.03  given previously.     

The gravitational wave emission of double white dwarf coalescences

Type Ia Supernovae(SNe Ia) are widely used as standard candles to probe the Universe. However,how these fierce explosions are produced itself is still a highly debated issue. There are mainly two popular models for SNe Ia: the double-degenerate scenario and the single-degenerate scenario. The doubledegenerate scenario suggests that SNe Ia are produced by the coalescence of two degenerate white dwarfs,while the single-degenerate scenario suggests that the continuous accretion of a single degenerate white dwarf from its normal stellar companion will finally lead to a disastrous explosion when it is over-massive,resulting in an SN Ia. The rapid development of the gravitational wave astronomy sheds new light on the nature of SNe Ia. In this study, we calculate the gravitational wave emissions of double white dwarf coalescences and compare them with the sensitivities of several upcoming detectors. It is found that the gravitational wave emissions from double white dwarf mergers in the local universe are strong enough to be detected by LISA. We argue that LISA-like gravitational wave detectors sensitive in the frequency range of 0.01 — 0.1 Hz will be a powerful tool to test the double-degenerate model of SNe Ia, and also to probe the Universe.