The nature of the 10 and 20 micrometer features in circumstellar dust shells

Photographic reduction techniques are compared using an iris photometer, GALAXY and PDS for measurement of two plates (B andV) of the globular cluster M15. The comparison shows that satisfactory results can be obtained by any of these methods in the outer areas of globular clusters, but in inner regions, due to crowding of stellar images and to the influence of the background density, the most appropriate technique is the procedure applied to PDS scans of the plates.     

Photographic photometry for stellar statistics with Tautenburg Schmidt telescope

Photometric properties of deep Tautenburg Schmidt plates in the UBV system over the whole field and over a wide range of stellar magnitudes are discussed. Different reduction models based on the calibration curve alone and with additional terms containing colour and plate coordinates are considered. With the filter-emulsion combinations used the Johnson UBV system can be reproduced quite well by the Tautenburg telescope. The accuracy of photometric data can be improved if geometrical terms are taken into account. For deep plates with a significant effect of background nebulosity a supplementary term is to be included in the reduction model. The polynomial coefficients vary in dependence on spectral bands and individual properties of each plate.     

A new reduction of digitized photographic plates with selected asteroids obtained with the normal astrograph of the Pulkovo Observatory from 1948 to 1990

The results of a new reduction of 1545 photographic observations of 14 selected asteroids obtained with the Normal Astrograph of the Pulkovo Observatory from 1948 to 1990 are presented. Photographic plates stored in the archive of the observatory were digitized with a general purpose flatbed scanner using a specially developed technique. The accuracy of the reduction of photographic plates is measured. The UCAC3 catalogue has been used as a reference. Residual differences between coordinates of stars in the reference catalogue are used to analyze and tacking into account obtained instrumental systematic errors. Equatorial coordinates of 1378 individual observations of target asteroids are obtained. They are compared with the results of the reduction of the material made earlier. Among the objects of the background, positions of 1475 stars with large proper motions from the LSPM catalogue are measured.     

A fast 2D image reconstruction algorithm from 1D data for the Gaia mission

A fast 2-dimensional image reconstruction method is presented, which takes as input 1-dimensional data acquired from scans across a central source in different orientations. The resultant reconstructed images do not show artefacts due to non-uniform coverage in the orientations of the scans across the central source, and are successful in avoiding a high background due to contamination of the flux from the central source across the reconstructed image. Due to the weighting scheme employed this method is also naturally robust to hot pixels. This method was developed specifically with Gaia data in mind, but should be useful in combining data with mismatched resolutions in different directions.     

Development of technique to detect and classify small-scale magnetic flux cancellation and rapid blue-shifted excursions

We present a set of tools for detecting small-scale solar magnetic cancellations and the disk counterpart of type II spicules(the so-called Rapid Blueshifted Excursions(RBEs)), using line-of-sight photospheric magnetograms and chromospheric spectroscopic observations, respectively. For tracking magnetic cancellation,we improve the Southwest Automatic Magnetic Identification Suite(SWAMIS) so that it is able to detect certain obscure cancellations that can be easily missed. For detecting RBEs, we use a normalized reference profile to reduce false-positive detections caused by the non-uniform background and seeing condition. Similar to the magnetic feature tracking in SWAMIS, we apply a dual-threshold method to enhance the accuracy of RBE detection. These tools are employed to analyze our coordinated observations using the Interferometric BIdimensional Spectrometer at the Dunn Solar Telescope of the National Solar Observatory and Hinode. We present the statistical properties of magnetic cancellations and RBEs, and explore their correlation using this data set.     

The spatial morphology of Europa's near-surface O2 atmosphere

Results from a three-dimensional ballistic model of Europa's O₂ atmosphere are presented. Hubble Space Telescope (HST) ultraviolet observations show spatially non-uniform O₂ airglow from Europa. One explanation for this is that the O₂ atmosphere is spatially non-uniform. We show that non-uniform ejection of O₂ alone cannot reproduce the required morphology, but that a non-uniform distribution of reactive species in Europa's porous regolith can result in a non-uniform O₂ atmosphere. By allowing O₂ molecules to react with Europa's visibly dark surface material, we produced a spatially non-uniform atmosphere which, assuming uniform electron excitation of O₂ over the trailing hemisphere, compares favorably with the morphology suggested by the HST observations. This model, which requires a larger source of O₂ than has previously been estimated, can in principal be tested by the New Horizons observations of Europa's O₂ atmosphere.     

Effects of dust charge fluctuations and deviations from isothermality of electrons on nonlinear dust ion-acoustic waves

The effects of dust charge fluctuations and deviations from isothermality of electrons are incorporated in the study of nonlinear dust ion-acoustic waves. Deviations from isothermality of electrons are included in this model as a result of nonlinear resonant interaction of the electrostatic wave potential with electrons during its evolution. The basic properties of stationary structures are studied by employing the reductive perturbation method, and conditions for the formation of small but finite amplitude dust ion-acoustic solitary waves in the space dusty plasma situations are clearly explained. It is shown that a more depletion of the background free electrons owing to the attachment of these electrons to the surface of the dust grains during the charging process can lead to the formation of solitary waves with smaller amplitude. Furthermore, effects of the dust charge fluctuation and deviations from isothermality of electrons show a non-uniform behavior for the amplitude of solitary waves in transition from the Boltzmann electron distribution to a trapped electron one. It is also found that the dust charge fluctuation caused by trapped as well as free electrons is a source of dissipation, and is responsible for the formation of the dust ion-acoustic shock waves.     

Détermination de la position du cratère mösting a À partir de plaques photographiques de la lune sur fond d'étoiles

The reduction of 126 photographic plates from the Moon on stellar background, gives a new determination from the Mösting A coordinates with respect to the Lunar inertial system. This determination is based on: the Eckhardt theory for the physical libration, and the ephemeride (j = 2) derived from Brown's theory. The S.A.O. star catalog for the star positions, is used for this reduction.     

Similarity solution of the propagation of spherical shock waves in a magnetogasdynamic self-gravitating system

The self-similar model of propagation of spherical strong shock waves into non-uniform stellar atmosphere under self-gravitation and non-uniform magnetic field is investigated. The disturbances are headed by a shock surface of variable strength. Gas is assumed to be grey and opaque and the shock tobe transparent.     

Cosmic microwave background power spectrum estimation with non-circular beam and incomplete sky coverage

Over the last decade, measurements of the cosmic microwave background (CMB) anisotropy have spearheaded the remarkable transition of cosmology into a precision science. However, addressing the systematic effects in the increasingly sensitive, high-resolution, 'full' sky measurements from different CMB experiments poses a stiff challenge. The analysis techniques must not only be computationally fast to contend with the huge size of the data, but the higher sensitivity also limits the simplifying assumptions which can then be invoked to achieve the desired speed without compromising the final precision goals. While maximum likelihood is desirable, the enormous computational cost makes the suboptimal method of power spectrum estimation using pseudo-C _l unavoidable for high-resolution data. The debiasing of the pseudo-C _l needs account for non-circular beams, together with non-uniform sky coverage. We provide a (semi)analytic framework to estimate bias in the power spectrum due to the effect of beam non-circularity and non-uniform sky coverage, including incomplete/masked sky maps and scan strategy. The approach is perturbative in the distortion of the beam from non-circularity, allowing for rapid computations when the beam is mildly non-circular. We advocate that it is computationally advantageous to employ 'soft' azimuthally apodized masks whose spherical harmonic transform die down fast with m . We numerically implement our method for non-rotating beams . We present preliminary estimates of the computational cost to evaluate the bias for the upcoming CMB anisotropy probes  ( l _max∼ 3000)  , with angular resolution comparable to the Planck surveyor mission. We further show that this implementation and estimate are applicable for rotating beams on equal declination scans, and can possibly be extended to simple approximations to other scan strategies.     

On the gravitational instability of a medium in non-uniform rotation and magnetic field

The effect of a non-uniform magnetic field on the gravitational instability for a non-uniformly rotating, infinitely extending axisymmetric cylinder in a homogeneous medium has been studied. The Bel and Schatzman criterion of gravitational instability for a non-uniformly rotating medium is modified under the effect of a non-uniform/uniform magnetic field acting along the tangential and axial directions. As a consequence the stabilizing and destabilizing effect of the non-uniform magnetic field is obtained, a new criterion for the magneto-gravitational instability is deduced in terms of Alfven’s wave velocity; and it is also found that the Jeans criterion determines the gravitational instability in the absence of rotation and when the non-uniform/uniform magnetic field acts along the axis of the cylinder.     

Studies on some properties of coronal mass ejections based on angular width

The paper investigates the effects of thermal conductivity and non-uniform magnetic field on the gravitational instability of a non-uniformly rotating infinitely extending axisymmetric cylinder in a homogeneous heat conducting medium. The non-uniform rotation and magnetic field are supposed to act along θ and z directions of the cylinder. It is found that the gravitational instability of this general problem is determined by the same criterion as obtained by Dhiman and Dadwal (Astrophys. Space Sci. 325(2):195–200, 2010) for the self-gravitating isothermal medium in the presence of non-uniform rotation and magnetic field with the only difference that adiabatic sound velocity is now replaced by the isothermal sound velocity. It is found that the thermal conductivity has stabilizing effect on the onset of gravitational instability. Further, the stabilizing/destabilizing effect of the non-uniform magnetic field on the gravitational instability of heat conducting medium has been discussed and is illustrated by considering some special forms of the basic magnetic fields.     

Properties of Ion-Cyclotron Waves in the Open Solar Corona

Remote observations of coronal holes have strongly suggested the resonant interactions of ion-cyclotron waves with ions as a principal mechanism for plasma heating and acceleration of the fast solar wind. In order to study these waves, a WKB (Wentzel?CKramers?CBrillouin) linear perturbation analysis is used in the frame work of a collisionless multi-fluid model where we consider in addition to protons a second ion component made of alpha particles. We consider a non-uniform background plasma describing a funnel region in the open coronal holes and we use the ray tracing Hamiltonian-type equations to compute the ray path of the waves and the spatial variation of their properties. At low frequency (smaller than the proton cyclotron frequency), the results showed a distinct behavior of the two ion-cyclotron modes found in our calculations, namely the first one propagates anisotropically guided along the magnetic field lines while the second one propagates isotropically with no preferred direction.     

A new method for simulation of atmospheric effect on the emergent radiation over non-uniform terrain

For a precise atmospheric correction over the non-uniform terrain in satellite imageries, a numerical method for evaluating the upwelling radiation at the top of the atmosphere bounded by the non-uniform surface is developed as an extended doubling-adding method. The present method enable us to treat quantitatively the case of hazy atmosphere and (or) large albedo of the surface.     

On the Jeans Criterion of a Stratified Heat Conducting Gaseous Medium in the Presence of Non-uniform Rotation and Magnetic Field

The problem of self-gravitational instability of an infinite, homogeneous stratified gaseous medium with finite thermal conductivity and infinite electrical conductivity, in the presence of non-uniform rotation and magnetic field in the Chandrasekhar’s frame of reference, is studied. It is found that the magnetic field, whether uniform or non-uniform, has no effect on the Jeans’ criterion for gravitational instability and remains essentially unaffected. However, the thermal conductivity has the usual stabilizing effect on the criterion that the adiabatic sound velocity occurring in the Jeans criterion is replaced by the isothermal sound velocity. Thus, the present analysis extends the results of Chandrasekhar for the case of heat conducting medium and for non-uniform rotation and magnetic field.     

The contribution of faint active galactic nuclei to the hard X-ray background

Hard X-ray selection is the most efficient way to discriminate between accretion-powered sources, such as active galactic nuclei (AGN), and sources dominated by starlight. Hard X-rays are also less affected than other bands by obscuration. We have therefore carried out the BeppoSAX High Energy Large Area Survey (HELLAS) in the largely unexplored 5–10 keV band, finding 180 sources in ∼50 deg² of sky with flux≳5×10⁻¹⁴ erg cm⁻² s⁻¹. After correction for the non-uniform sky coverage this corresponds to resolving about 30 per cent of the hard cosmic X-ray background (XRB). Here we report on a first optical spectroscopic identification campaign, finding 12 AGN out of 14 X-ray error boxes studied. Seven AGN show evidence for obscuration in X-ray and optical bands, a fraction higher than in previous ROSAT or ASCA – ROSAT surveys (at 95–99 and 90 per cent confidence levels respectively), thus supporting the scenario in which a significant fraction of the XRB is created by obscured AGN.     

Detecting Sunyaev–Zel'dovich clusters with Planck– II. Foreground components and optimized filtering schemes

The Planck mission is the most sensitive all-sky cosmic microwave background (CMB) experiment currently planned. The High-Frequency Instrument (HFI) will be especially suited for observing clusters of galaxies by their thermal Sunyaev–Zel'dovich (SZ) effect. In order to assess Planck 's SZ capabilities in the presence of spurious signals, a simulation is presented that combines maps of the thermal and kinetic SZ effects with a realization of the CMB, in addition to Galactic foregrounds (synchrotron emission, free–free emission, thermal emission from dust, CO-line radiation) as well as the submillimetric emission from celestial bodies of our Solar system. Additionally, observational issues such as the finite angular resolution and spatially non-uniform instrumental noise of Planck 's sky maps are taken into account, yielding a set of all-sky flux maps, the autocorrelation and cross-correlation properties of which are examined in detail. In the second part of the paper, filtering schemes based on scale-adaptive and matched filtering are extended to spherical data sets, that enable the amplification of the weak SZ signal in the presence of all contaminations stated above. The theory of scale-adaptive and matched filtering in the framework of spherical maps is developed, the resulting filter kernel shapes are discussed and their functionality is verified.     

Similarity solutions for a stellar line explosion

Similarity solutions for line explosion in a non-uniform self-gravitating medium including the effects of magnetic field radiation flux and neglecting the radiation pressure and energy are investigated. Gas is assumed to be grey and opaque and the shock to be transparent and isothermal.     

Some developments of the magnetic beam absorption filter

In the present paper some experimental arrangements are shown which utilize the magnetic filter described by Cimino et al. (1968). For a single cell we have elaborated an elementary theory in the following cases: (i) absorption by an atomic beam in a uniform magnetic field (i.e. pure damping profile); (ii) atomic beam in a non-uniform magnetic field; (iii) vapours in a uniform magnetic field (i.e. gaussian distribution); (iv) vapours in a non-uniform magnetic field.