Circumstellar dust and circumstellar extinction curves

We have calculated the circumstellar extinction curves produced by dust grains which absorb and scatter the stellar radiation in the shells of pre-main-sequence stars. A Monte Carlo method was used to model the radiative transfer in non-spherical shells. The dependence on the particle size distribution and the dust shell parameters has been examined.The application of the theoretical results to explain the extinction and polarization of the Herbig Be star HD 45677 shows that the dust shell is not disk-like and that very small grains are absent in it.     

Do prominences migrate equatorwards?

The mean latitude of prominence samples referring to one boundary of the polarity division line of the large-scale magnetic field is calculated on the basis of H charts in the period 1955–1982. It is shown that the magnetic field in that period had a latitude zonal structure. The boundaries of the latitude zones of the magnetic field had no regular equatorwards migration. They either oscillated near the mean boundaries at 0°, ±20°, ±40°, or migrated polewards.     

On the excitation of lower levels of singlet helium in quiescent prominences

The paper deals with the excitation of the helium singlet level 2¹ P in the homogeneous and filamentary models of quiescent prominences with following parameters: the optical thickness at the limit of helium Lyman continuum _1c ^M = 0.1–100, T _e = 7000 K, n _e = 5 × 10¹⁰ cm^–3. Assuming a model He atom with seven discrete levels (1¹ S, 2³ S, 2¹ S, 2³ P, 2¹ P, 3³ D, 3¹ D) and the continuum the steady state equations for the levels 2³ S, 2¹ P and the continuum have been solved together with the radiative transfer equations for the line 584 Å and the continuum 504 Å. The variations with depth of the functions n ₂ ³ _S /n ₁ ¹ _S (₁ c), n ₂ ¹ _P /n ₁ ¹ _S (_1c ), and n ⁺ _He n _e /n ₁ ¹ S(_1c ) as well as the intensities of the triplet (D₃, 10830 Å) and singlet (16678, 20581 Å) lines have been calculated. Comparison with observations leads to the following conclusions: (1) The line intensities calculated for filamentary models of prominences agree better with observations than those for homogeneous ones. (2) The helium level 2¹ P is excited by diffuse field 584 Å being formed by recombinations and spontaneous transitions 2¹ P – 1¹ S and escaping from the prominence into the space between the filaments and to the surface. (3) Underpopulation of the singlet level 2¹ P may be explained by combination of weak excitation mechanism (recombinations and formation of the diffuse field 584 Å) and strong deexcitation mechanism (spontaneous transitions into the level 1¹ S).     

The appearance of polarization in radiation from hot stars due to the faraday rotation effect as a possible method of determining stellar magnetic fields

The effect of Faraday rotation is shown to lead to the appearance of linear polarization of stellar radiation scattered in an optically-thin circumstellar electron-magnetized shell, even in the case when the shell is spherical. The spectral dependence of the polarization degree is evaluated for scattering in (i) a spherically-symmetric magnetized shell with a power-law radial dependence of the electron density, and (ii) a non-spherical ellipsoidal uniform envelope. The position of maximum in the polarization spectrum permits us to determine the magnetic field magnitude on a star surface. If the rotational and magnetic axes do not coincide, the periodic variability of the polarization will be observed with the period of stellar rotation. Some Be-stars, such as Cas, 48 Lib, EW Lac, Aqr, HD 45677, X Per, are proposed as candidates to be investigated for magnetic fields, as well as some stars of the T Tau-type. This method may be also applied to supernovae shells.     

Radial velocity and profile variations of the ultraviolet circumstellar lines in ζ tauri

The radial velocity and profile variations of UV lines of the shell star Tau have been examined in the IUE spectra obtained in 1978–1982. The neutral atoms, and once or twice-ionized ions (exceptCii, Aliii, Siiii resonance lines) follow the same velocity variations as in the visual spectra, while the Siiv andCiv resonance lines show a constant negative velocity (–50 km s^–1 at the core). The Aliii,Cii resonance lines and probably Feiii (mult. No. 34) are formed in both regions, i.e., in lowly-ionized and highly-ionized regions and the Siiii resonance line is formed in a highly-ionized region.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.     

Near-infrared observations of the peculiar binary system epsilon Aurigae

Near-infrared photometric and low-resolution spectroscopic observations of Aurigae at two phases during the current eclipse are presented. The eclipse depths are found to be wavelength-independent in the infrared right up to 2.5 m. There is no infrared excess at wavelengths shorter than 2.5 m. The light absorbing particles in the eclipsing body must be larger than 10 m in size.     

Differential rotation in a solar-driven quasi-axisymmetric circulation

We consider the concept of a quasi-axisymmetric circulation to explore the global scale dynamics of planetary atmospheres. The momentum and energy transport processes in the smaller scales are formulated in terms of anisotropic eddy diffusion. In the early work of Williams and Robinson (1973) these concepts have been introduced to describe the Jovian circulation. Our study differs in that we adopt a spectral model (with vector spherical harmonics) and consider a linear system; we are also examining a different parameter regime. The troposphere of Jupiter is assumed to be weakly convectively unstable, and the circulation is driven by the fundamental component of solar differential heating with a broad maximum at the equator. Mode coupling arising from the Coriolis action is considered in self consistent form, and momentum and energy are allowed to cascade from lower to higher order modes. With a limited number of spherical harmonics, up to order 40, and with homogeneous boundary conditions, the conservation equations are integrated between the 25 and 10^–5 bar pressure levels. In addition, a simplified single layer model is discussed which, even though heuristic in nature, elucidates and complements the numerical results. Our analysis leads to the following conclusions: (a) For a negative stability, S ₀ = T ₀/r + , the energy transports arising from large scale advection by the meridional circulation can amplify the response to the external heating. This crucially depends on the latitudinal structure of the circulation, so that banded wind fields with equatorial zonal jets are preferentially excited. (b) With a negative stability of order S ₀ ~ – 10^–6 K cm^–1, the computed number of positive (and negative) zonal jets is similar to that observed on Jupiter. (c) The observed magnitudes in the zonal wind velocities require that the vertical eddy diffusion coefficient is of the order K _r ~ 3 × 10⁵ cm² s^–1, which in turn is consistent with the observed outward flux of energy from the planetary interior (F K _r S ₀ ); this diffusion rate is also of the right order of magnitude to obey mixing length theory. (d) The ratio between the horizontal and vertical eddy diffusion coefficients (relative mixing factor) is of critical importance. If it is too large ( 10⁵), differential rotation or alternating zonal jets cannot be maintained; if it is too small ( 10⁴), the equator tends to corotate. The intermediate value of order R ~ 5 × 10⁴ is again consistent with mixing length theory. (e) With the above constraints on the transport coefficients, the flow is quasigeostrophic. (f) The meridional circulation is multicellular and of the Ferrel-Thomson type. It is consistent with the observed cloud striations in the Jovian atmosphere. (g) In the stable stratosphere at higher altitudes the fundamental component, directly driven by the Sun, dominates. The circulation degenerates, and broad, positive zonal jets develop at middle latitudes, resembling the observed wind field in the visible cloud cover of the Venus atmosphere.Applied Research Corporation, Landover, Maryland, U.S.A.     

A quasi-one-dimensional velocity regime of super-thermal electron stream propagation through the solar corona

The propagation of an inhomogeneous-stream of fast electrons through the corona-the type III radio burst source - is considered. It is shown, that the angular spectrum width of plasma waves excited by the stream is defined both by Landau damping by particles of the diffuse component and by damping (in the region of large phase velocities) by particles of the stream itself having large pitch angles. The regime of quasi-one-dimensional diffusion in the velocity space is realized only in the presence of a sufficiently dense diffuse component of super-thermal particles and only for a sufficiently large inhomogeneity scale of the stream. A large scale of the stream space profile is formed, evidently, close to the region of injection of super-thermal particles. It is the result of stripping of part of the electrons from the stream front to its slower part due to essential non-one-dimensionality of the particle diffusion in velocity space.Results obtained may explain, in particular, the evolution of a stream particle angular spectrum in the generation region of type III radio bursts observed by spacecrafts (Lin et al., 1981). For the relatively low energetic part of the stream, the oblique plasma wave stabilization by a diffuse component results in a quasi-one-dimensional regime of diffusion. The latter conserves the beam-like structure of this part of the stream.     

Lifetime migration in Indonesia based on 1971 and 1980 census data

Internal migration trends in Indonesia are reviewed using 1971 and 1980 census data. The author notes that although migration in 1971 was primarily to Jakarta and Lampung, by 1980 it was more diversified, with significant migration to some of the outer islands. The importance of the national transmigration program is noted.     

The acceleration of minor ion species in the solar wind

This paper provides a comprehensive analysis of the dynamics of the flow of minor ion species in the solar wind under the combined influences of gravity, Coulomb friction (with protons), rotational forces (arising from the Sun's rotation and the interplanetary spiral magnetic field) and wave forces (induced in the minor ion flow by Alfvén waves propagating in the solar wind). It is assumed that the solar wind can be considered as a proton-electron plasma which is, to a first approximation, unaffected by the presence of minor ions. In the dense hot region near the Sun Coulomb friction accelerates minor ions outwards against the gravitational force, part of which is cancelled by the charge-separation electric field. Once the initial acceleration has been achieved, wave and rotational forces assist Coulomb friction in further increasing the minor ion speed so that it becomes comparable with, or perhaps even exceeds, the solar wind speed. A characteristic feature of the non-resonant wave force is that it tends to bring the minor ion flow into an equilibrium where the radial speed matches the Alfvén speed relative to the solar wind speed, whereas Coulomb friction and rotational forces tend to bring the flow into an equilibrium where the radial speed of the minor ions equals the solar wind speed. Therefore, provided that there is sufficient wave energy and Coulomb friction is weak, the minor ion speed can be trapped between these two speeds. This inteststing result is in qualitative agreement with observational findings to the effect that the differential flow speed between helium ions and protons is controlled by the ratio of the solar wind expansion time to the ion-proton collision time. If the thermal speeds of the protons and minor ions are small compared to the Alfvén speed, two stable equilibrium speeds can exist because the rapid decrease in the Coulomb cross-section with increasing differential flow speed allows the non-resonant wave force to balance Coulomb friction at more than one ion speed. However, it must be emphasized that resonant wave acceleration and/or strong ion partial pressure gradients are required to achieve radial speeds of minor ions in excess of the proton speed, since, as is shown in Section 4, the non-resonant wave acceleration on protons and minor ions are identical when their radial speeds are the same, with the result that, in the solar wind, non-resonant wave acceleration tends (asymptotically) to equalize minor ion and proton speeds.