Angular diameter and effective temperature of a sample of 15 M giants at 2.2 μm from lunar occultation observations

High angular resolution measurements of a sample of 15 M giants at 2.2 μm by the technique of lunar occultation are presented in this paper. We obtain angular diameters for 11 sources of which five are the first diameter measurements. For these resolved sources we have estimated the effective temperatures, which are consistent with previous calibrations. For the other four sources we put the first upper limits on their angular sizes to be 2 mas. Two sources, namely IRC+20090 and IRC+20067, yield appreciably low temperatures, which could point to their possible Mira nature. For sources with Hipparcos parallax measurements, we have calculated the linear radii.     

The fibril structure of prominences

In this paper we present several magneto-hydrostatic equilibrium models for prominences with fibril-like fine structure. For all the models ad hoc temperature profiles are used without discussing the energetics. For our models we assume fine structure to occur either across the prominence axis or along it. This approach is intended as a first step towards more realistic models based upon a series of vertical fibril structures.     

Phobos: Surface density of impact craters

The preliminary conclusion of the Mariner 9 Television Team that the surfaces of Phobos and Deimos are saturated with craters larger than 0.2 km in diameter is reconsidered on the basis of more extensive and uniform crater counts. For Phobos, it is verified that the surface appears saturated with craters larger than 1 km in diameter. For craters smaller than 1 km, the data points fall below the saturation curve, and it is not clear that all the departure can be explained in terms of loss of resolution. For Deimos, because of the paucity of craters visible in the Mariner 9 images, a statistically meaningful crater density curve cannot be constructed. Definitive crater density curves for subkilometer craters can only be established once additional imagery at a resolution of better than 100 m is obtained. Such imagery will be provided by the 1976 Viking Orbiters.     

Television imaging of fast auroral waves

Fast auroral waves have been recorded with an Image Intensifier-TV system and a new characteristic of this phenomenon has been revealed, namely, an abrupt transition from wave motion equatorwards to an E to W motion associated with an auroral band. For equatorward motion speeds ranged from 15 to 150 km/sec which is significantly lower than values previously reported. For the E to W motion speeds ranged from 20 to 90 km/sec.     

An Estimation of the Initial Period of Pulsars

The initial period of a pulsar is an important factor in our understanding of the formation of neutron stars and of the nature of the equation of state of neutron star matter.Up to now this quantity can only be obtained for a few pulsars for which accurate age and braking index are known.Based on the theory of the offcenter dipole emission,in which pulsars obtain theiry high velocities depending on the initial periods,we calculate the initial period using the proper motion data,Because the orbital velocity of the progenitor and asymmetric kick in the supernova explosion may also contribute to the observed velocity of the pusar,the derived values of initial periods are lower limits.For normal pulsars,the initial periods are in the range of 0.6～2.6ms.For the millisecond pulsars,the initial periods are comparable to their current periods,and the ratio between the initial period and the current period increases with the decrease of the current period.For PSR B1937 21 with the shortest period of 1.56ms,the ratio is 0.77.     

恒星自转的引力昏暗效应对谱线的影响

对于快速自转的恒星,谱线的等值宽度（ＥＷ）受引力昏暗效应的影响,即使自转速度达到临界也是很小的;而谱线半宽（ＦＷＨＭ）受引力昏暗效应影响相对较大,在（ω≈０．９９）时,相对变化达到８％．对于光谱型在Ｂ０～Ｂ９范围内的主序星,谱线半宽的相对变化在自转速度较小时（ω＜０．８）与光谱型无关;在自转速度较大时（ω≈０．９９）,谱线半宽的相对变化随光谱次型的增加而下降．     

Photoelectric photometry of 21 asteroids

Photoelectric lightcurves of 21 asteroids are presented. The observations were carried out from 1978 to 1982 at the Astronomical Observatory of Torino (at the Astrophysical Observatory of Catania for 137 Meliboea). For 10 objects a reliable rotation period has been obtained, while for two others a rough estimate is given. In several cases the analysis of the observed amplitudes versus the ecliptic longitudes indicates the most favorable future oppositions for period and/or pole determination. For some asteroids transformations to UBV Standard System were performed.     

First XMM-Newton observations of strongly magnetic cataclysmic variables – II. Timing studies of DP Leo and WW Hor

XMM-Newton was used to observe two eclipsing, magnetic cataclysmic variables, DP Leo and WW Hor, continuously for three orbital cycles each. Both systems were in an intermediate state of accretion. For WW Hor we also obtained optical light curves with the XMM-Newton Optical Monitor and from ground-based observations. Our analysis of the X-ray and optical light curves allows us to constrain physical and geometrical parameters of the accretion regions and derive orbital parameters and eclipse ephemerides of the systems. For WW Hor we directly measure horizontal and vertical temperature variations in the accretion column. From comparisons with previous observations we find that changes in the accretion spot longitude are correlated with the accretion rate. For DP Leo the shape of the hard X-ray light curve is not as expected for optically thin emission, showing the importance of optical depth effects in the post-shock region. We find that the spin period of the white dwarf is slightly shorter than the orbital period and that the orbital period is decreasing faster than expected for energy loss by gravitational radiation alone.     

A theoretical study of downward H+ field-aligned velocities at mid-latitudes

This paper examines the magnitude of downward H⁺ field-aligned velocities at mid-latitudes. For the isothermal, collisionless, steady-state case an analytical form is derived for the critical temperature, below which the plasma temperature must lie for there to be a possibility of supersonic H⁺ flow. Some simple equations are presented which yield velocity profiles and an aid to the understanding of energy distribution in the H⁺ gas. Very little gravitational potential energy is converted to kinetic energy. For the general case the situation is far more complicated, but we note in particular the importance of the O⁺ contribution to the electrostatic field. For the simpler case the flow is always subsonic regardless of the plasma temperature and it appears unlikely that supersonic flow will occur in the more general case.     

Mapping monthly quantiles of ionospheric electron content and foF2

Monthly quantiles of ionization parameters are important information for system planning and to assess one aspect of ionospheric variability. For ionosonde parameters the data base is probably large enough to allow mapping of deciles. For electron content the situation is not so good: at least for Europe the data base only allows to construct maps for the upper and and the lower monthly quartiles.We present mapping procedures and maps for monthly quartiles of electron content and of foF2 based on experiences with mapping procedures for monthly medians. It turned out that for the lower quartiles it is necessary to to use more coefficients for the quartile maps than for the median maps.We discuss possibilities to gain decile information for electron content from foF2. For a few selected months and locations deciles can be gained from the Faraday effect on the signals of geostationary satellites. These selected cases are used to check on procedures to use foF2 experience to construct electron content deciles.     

截短后平衡的扩频码搜索方法

为了能够高效地找出平衡的扩频码(平衡性的扩频码有较好地抑制载波的性能),研究了一种不交叠平衡性扩频码字的搜索方法。在这种方法中,首先生成母码,然后计算、查找平衡不交叠的子码。该方法在计算平衡码时与其它方法有相同的时间复杂度。计算机仿真表明,该母码生成方法较为高效。在采用分割方法后,搜索过程得到了进一步的优化。     

Numerical simulation of comet nuclei I. Water-ice comets

A one-dimensional simulation of pure water-ice cometary nuclei is presented, and the effect of the nucleus as a heat reservoir is considered. The phase transition from amorphous to crystalline ice is studied for two cases: (1) where the released latent heat goes entirely into heating adjacent layers and (2) where the released latent heat goes entirely into sublimation. For a Halley-like orbit it was found that for case 1 the phase boundary penetrates about 15 m on the first orbit and does not advance until sublimation brings the surface to some 10 m from the phase boundary. For case 2 the phase boundary penetrates about 1 m below the surface and remains at this depth as the surface sublimates. For an orbit like that of Schwassmann-Wachmann 1 the phase boundary penetrates about 50 m initially for case 1 and about 1 m for case 2. There is no further transformation until the entire comet is heated slowly to near the transition temperature, after which the entire nucleus is converted to crystalline ice. For an Encke-type orbit case 1 gives a nearly continuous transition of the entire nucleus to crystalline ice, while for case 2 the initial penetration is about 8 m and remains at this depth relative to the surface as sublimation decreases the cometary radius. Thus the entire comet is converted to crystalline ice just before it is completely dissipated.     

The gravity-perturbed Lambert problem: A KS variation of parameters approach

A new formulation is presented for the perturbed Lambert problem. The formulation employs the variation-of-parameters method in the KS transformed state space to determine perturbations of a Keplerian Lambert solution. The approach is universal (in that its validity is not restricted to a particular energy domain). For the case of the second zonal harmonic (oblateness) perturbation, first order perturbations are carried out entirely analytically; non-iterative corrections are determined through solution of a pair of algebraic equations. For more general perturbations, numerical quadratures are required.     

Nonlinear Force-Free Magnetic Field Extrapolations: Comparison of the Grad Rubin and Wheatland Sturrock Roumeliotis Algorithm

We compare the performance of two alternative algorithms which aim to construct a force-free magnetic field given suitable boundary conditions. For this comparison, we have implemented both algorithms on the same finite element grid which uses Whitney forms to describe the fields within the grid cells. The additional use of conjugate gradient and multigrid iterations result in quite effective codes. The Grad Rubin and Wheatland Sturrock Roumeliotis algorithms both perform well for the reconstruction of a known analytic force-free field. For more arbitrary boundary conditions the Wheatland Sturrock Roumeliotis approach has some difficulties because it requires overdetermined boundary information which may include inconsistencies. The Grad Rubin code on the other hand loses convergence for strong current densities. For the example we have investigated, however, the maximum possible current density seems to be not far from the limit beyond which a force-free field cannot exist anymore for a given normal magnetic field intensity on the boundary.     

Fluid dynamics of local martian magma oceans

The evolution of a melt region produced by a large impact during Mars formation is addressed. While some impact induced melt is redistributed during crater excavation, sufficiently large impacts (much larger than basin forming impacts) generate an intact melt region which is retained beneath the excavation zone, i.e., a local magma ocean. Local magma ocean evolution depends on the effective rheology controlling large scale deformation of the solid part of the planet, mechanism of crystallization, and melt region size. Within the uncertainties of various parameters, two scenarios are possible. For sufficiently weak rheology or large melt region size, evolution is characterized by rapid extrusion and formation of a global magma ocean. For sufficiently strong rheology or small melt region size, in situ crystallization to a partially molten solid state occurs prior to isostatic adjustment. Subsequent to in situ crystallization, local magma ocean evolution depends on melt region size and efficiency of lateral redistribution compared to bulk conductive cooling. For large melt regions, lateral spreading occurs via plastic deformation and results in an asymmetric, global, partial melt layer. For small melt region size, viscous spreading viscous can result in bulk cooling below the solidus prior to formation of a global layer. A hypothesis for the origin of the hemispherical crustal dichotomy and Tharsis rise is suggested. The dichotomy is associated with a global partial melt layer produced by evolution of a large, local magma ocean. After dichotomy formation, evolution of a second, smaller, local magma ocean is related to Tharsis development.     

Symplectic methods and their application to the motion of small bodies in the Solar System

Symplectic methods have been widely used in Solar System dynamics. This paper discusses both single step and multistep symplectic methods. For single step methods we point out that the modified algorithm (Wisdom et al., 1991, Kinoshita et. al., 1991) can be executed in the mass center coordinate system and in the Jacobian coordinate system. For multistep methods we describe the connections between symmetric and symplectic methods.     

East-west asymmetry of Saturn's rings

The energy distribution curves of eleven Ap stars, three Am stars, four normal A stars and one F0 V magnetic star have been obtained between 478 nm and 680 nm. For four of the Ap stars, two Am stars and all the four normal A stars, the effective temperatures are believed to have been estimated for the first time. For the rest, these estimates are expected to be an improvement over previously available values.It is concluded that the Ap and Am stars are not much different from the normal A stars in so far as their temperatures are concerned.     

On the r-mode spectrum of relativistic stars in the low-frequency approximation

The axial modes for non-barotropic relativistic rotating neutron stars with uniform angular velocity are studied, using the slow-rotation formalism together with the low-frequency approximation, first investigated by Kojima. The time-independent form of the equations leads to a singular eigenvalue problem, which admits a continuous spectrum. We show that for     , it is nevertheless also possible to find discrete mode solutions (the r modes). However, under certain conditions related to the equation of state and the compactness of the stellar model, the eigenfrequency lies inside the continuous band and the associated velocity perturbation is divergent; hence these solutions have to be discarded as being unphysical. We corroborate our results by explicitly integrating the time-dependent equations. For stellar models admitting a physical r-mode solution, it can indeed be excited by arbitrary initial data. For models admitting only an unphysical mode solution, the evolutions do not show any tendency to oscillate with the respective frequency. For higher values of l it seems that in certain cases there are no mode solutions at all.     

Symplectic methods and their application to the motion of small bodies in the Solar System

Symplectic methods have been widely used in Solar System dynamics. This paper discusses both single step and multistep symplectic methods. For single step methods we point out that the modified algorithm (Wisdom et al., 1991, Kinoshita et. al., 1991) can be executed in the mass center coordinate system and in the Jacobian coordinate system. For multistep methods we describe the connections between symmetric and symplectic methods.     

An Analytical Solution of the Lagrange Equations Valid also for Very Low Eccentricities: Influence of a Central Potential

This paper presents an analytic solution of the equations of motion of an artificial satellite, obtained using non singular elements for eccentricity. The satellite is under the influence of the gravity field of a central body, expanded in spherical harmonics up to an arbitrary degree and order. We discuss in details the solution we give for the components of the eccentricity vector. For each element, we have divided the Lagrange equations into two parts: the first part is integrated exactly, and the second part is integrated with a perturbation method. The complete solution is the sum of the so-called “main” solution and of the so-called “complementary” solution. To test the accuracy of our method, we compare it to numerical integration and to the method developed in Kaula (Theory of Satellite Geodesy, Blaisdell publ. Co., New York. 1966), expressed in classical orbital elements. For eccentricities which are not very small, the two analytical methods are almost equivalent. For low eccentricities, our method is much more accurate.