bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Models of Circumstellar Disks
Authors: Aikawa Yuri , Herbst Eric
Published: July 2016

We investigate the evolution of molecular abundances in circumstellar disks around young stars via numerical simulations. The results are compared with the composition of comets and radio observations of protoplanetary disks. First, we consider the molecular evolution in the midplane of the disk. Because of ionization by cosmic-rays or decay of radioactive nuclei, the molecular evolution in the region R ≳ 10 AU bears some similarity to that in molecular clouds. Considerable amounts of CO and N2, which come from the cloud core, are transformed, however, into CO2, CH4, NH3, and HCN. In regions where the temperature is low enough for these products to freeze onto grains, they accumulate in ice mantles. In the inner warmer regions of the disk, these molecules are desorbed from the mantles and transformed by gas-phase reactions into less volatile molecules, such as larger hydrocarbons, which then freeze out. Molecular abundances both in the gas phase and in ice mantles crucially depend on the temperature and thus vary significantly with the distance from the central star. Molecular abundances in ice mantles show reasonable agreement with the composition of comets. Our model suggests that comets formed in different regions of the disk having different molecular compositions.

Secondly, we report two-dimensional (R, Z) distributions of molecules in circumstellar disks. In the Z-direction, which is perpendicular to the midplane, there is a steep gradient of density and radiation field. Since the density is lower in the regions removed from the midplane, there are significant amounts of gas-phase species in these regions, while most species are adsorbed onto grains in the midplane. Chemistry in the surface regions is also affected by the X-rays and UV radiation from the central star, and UV radiation from the interstellar field. The molecular abundances in these regions differ significantly from those in the midplane. Radicals such as CN are especially abundant near the disk surface. We obtain radial distributions of molecular column densities and averaged molecular abundances, which show reasonable agreement with the observational data at millimeter wavelengths.
ISO Observations of Solid-State Features in Circumstellar Disks
Authors: Waelkens C. , Malfait K. , Waters L. B. F. M.
Published: July 2016

ISO has opened new infrared windows for spectroscopy, enabling detailed studies of the composition of the dust particles present in circumstellar disks. For oxygen-rich dust, and in particular for silicates, a forest of new features has been discovered, and comparison with laboratory data has enabled the identification of most of them. Of special relevance is the detection of crystalline silicates, which present themselves as a new diagnostic for studying the formation of comets and planetesimals in the disks surrounding young and, surprisingly, also evolved stars.
The Light Elements: What is Known, What is Controversial
Authors: Spite F.
Published: July 2016

The light elements are essential, because their primordial abundances are linked to the general parameters of the universe (at least in the Big Bang theory). Some of the light elements are fragile, and the interpretation of their abundances in stars requires a good knowledge of the stellar structure. The stellar abundances have to be known with a considerable accuracy, challenging the current level of representation of the stellar atmospheres. It is also difficult to reach accurate abundances in the gas : interstellar, H II regions, PN, intergalactic¨.

On the other hand, the fragile light elements are important probes of the stellar interiors, and their observation helps to the determination of reliable models, which in turn will improve the accuracy of stellar abundances. A part of this symposium is devoted to this probing aspect.

The talks (and many high quality posters) which build this symposium, cover all these aspects. I will try here to point out the controversial points and the reasonably well known facts. We expect from discussions, both formal and informal, a number of (eagerly awaited for) clarifications.
LiBeB Production and Associated Astrophysical Sites
Authors: Vangioni-Flam Elisabeth , Cassé Michel
Published: July 2016

The various modes of spallative LiBeB production are summarized, and classified according to their dependence or independence on the abundance of medium heavy elements (CNO) illustrated by that of oxygen in the interstellar medium. The predictions of the models are confronted to the available observational correlations (Be, B vs O). Clearly, a primary mechanism should lead to a slope one in the lg(Be/H) vs [O/H] plot and a secondary mechanism to a slope two. Due to the ambiguity of the O data, another criterion, based on energetics, can help us to select an adequate model. A purely secondary origin in the very early Galaxy is much more energy demanding than a primary one. Indeed, magnesium seems to be a possible surrogate of oxygen and iron since i) it is spectroscopically more easy to cope with and ii) its nucleosynthetic yield is independent of the mass cut and does not depend on metallicity.
The Recombination in a FRW Universe with a Variable Cosmological Term
Authors: Pires N. , Lima J. A. S.
Published: July 2016

The effects of a time-dependent A term in the recombination epoch are analysed taking into account the main physical processes occurring in the primordial plasma. For a vacuum decaying into photons, we show that the recombination begins when the Universe was smaller and denser, leading to a greater recombination rate. These results may have several implications to the large scale structure. In particular, the earlier recombination means that more time is available to the evolution of density perturbations.
The Deuterium Abundance in QSO Absorption Systems: A Mesoturbulent Approach
Authors: Levshakov Sergei A.
Published: July 2016

A new method, based on simulated annealing technique and aimed at the inverse problem in the analysis of intergalactic or interstellar complex spectra of hydrogen and metal lines, is outlined. We consider the process of line formation in clumpy stochastic media accounting for fluctuating velocity and density fields self-consistently. Two examples of the analysis of ‘H+D’-like absorptions seen at za = 3.514 and 3.378 towards APM 08279+5255 are presented.
Some aspects of the chemical evolution of 4He in the Galaxy: the He/H radial gradient and the ΔY/ΔZ enrichment ratio
Authors: Maciel W. J.
Published: July 2016

Two aspects of the chemical evolution of 4He in the Galaxy are considered on the basis of a sample of disk planetary nebulae by the application of corrections due to the contamination of 4He from the progenitor stars. First, the He/H radial gradient is analyzed, and then, the helium to heavy element enrichment ratio is determined for metallicities up to the solar value.
Helium and Oxygen Abundances in SMC Planetary Nebulae
Authors: D. Costa R. D. , de Freitas Pacheco J. A. , Idiart T. P.
Published: July 2016

In this work we report new high quality spectroscopic data for a sample of PNe in the SMC, aiming to derive physical parameters and chemical abundances, in particular to settle the question concerning the oxygen discrepancy found for type I planetaries with respect to stars and HII regions.
Deuterium Balmer Emission from Nebulae
Authors: Hébrard Guillaume , Péquignot Daniel , Vidal-Madjar Alfred , Walsh Jeremy R. , Ferlet Roger
Published: July 2016

We report on the detection and first identification of the deuterium Balmer lines dα and dβ, observed in emission in the Orion Nebula (M 42). The excitation mechanism is UV fluorescence from the Lyman(D i) lines at the interface between the H ii region and the molecular cloud. These lines may open the possibility to measure D/H in galactic H ii regions and, e.g., low-metallicity extragalactic H ii regions, using optical spectroscopy. Fluorescence provides an extremely sensitive way to detect deuterium. Thus, the non-detection of dα and dβ in the planetary nebula NGC 6572 leads to the stringent upper limit (D/H)ngc 6572 less than the order of 1 × 10−7.
Evolution of Lithium Abundance in Pop I Giants
Authors: V. Mallik Sushma
Published: July 2016

Recent observations of cool giants have shown that there exists a large range in their lithium abundances even for apparently similar stars. In order to explore whether this large spread could be interpreted in terms of mass, the Li I line at 6707.8 Å has been observed in more than 100 stars and these data have been combined with the already known lithium abundance data in literature. Absolute magnitudes of these stars have been estimated from the Hipparcos data and an attempt has been made to understand the Li evolution of a star as a function of its mass and the evolutionary status. There are strong evidences for extra-mixing taking place on the red giant branch which explain the unusually low abundances observed.
Lithium in Brown Dwarfs
Authors: Rebolo Rafael
Published: July 2016

Lithium is a key element to establish the substellar nature of brown dwarf candidates. Theoretical calculations show that brown dwarfs with masses below ˜ 0.065 M⊙ preserve a significant fraction of their initial Li content while for higher masses total Li depletion occurs in short timescales. Lithium is preserved at masses well below the hydrogen burning mass. Strong lithium lines have been predicted and discovered in the spectra of brown dwarfs. Most of the bona fide brown dwarfs detected in stellar clusters and in the solar neighborhood have been confirmed to be substellar via detection of the lithium resonance doublet at 670.8 nm. I review these detections and the progress made in understanding the formation of Li lines in very cool high gravity dwarfs.
New Determination Method of Primordial Li Abundance
Authors: Kajino T. , Suzuki T.-K. , Kawanomoto S. , Ando H.
Published: July 2016

We discuss the primordial nucleosynthesis in lepton asymmetric Universe models. In order to better estimate the universal baryon-mass density parameter ωb, we try to remove the uncertainty from the theoretical prediction of primordial 7Li abundance. We propose a new method to determine the primordial 7Li by the use of isotopic abundance ratio 7Li/6Li in the interstellar medium which exhibits the minimum effects of the stellar processes.
The Origin of the Lithium Rich Giants
Authors: Charbonnel Corinne , Balachandran Suchitra
Published: July 2016

We use Hipparcos parallaxes to determine the evolutionary status and the nature of the so-called Li-rich giants. These informations clearly support the hypothesis of internal nuclear lithium enrichment by an extra-mixing process at two distinct evolutionary phases.
Galactic Evolution of Beryllium and Oxygen
Authors: Israelian Garik , J. García López Ramón , Rebolo Rafael
Published: July 2016

We discuss the early evolution of beryllium and oxygen in our Galaxy by comparing abundances of these elements for halo and disk metal-poor stars. Both, O and Be rise as we go progressively to more metal-rich stars, showing a slope 0.41 ± 0.09 ([Be/O] vs [Fe/H]) for stars with [Fe/H]≤ —1. This relationship provides an observational constraint to the actually proposed Galactic Cosmic Ray theories.
Lithium Abundances in Main-Sequence F Stars and Sub-Giants
Authors: Dias do Nascimento Jose , Théado Sylvie , Vauclair Sylvie
Published: July 2016

The application to main-sequence stars of the rotation-induced mixing theory in the presence of μ-gradients leads to partial mixing in the lithium destruction region, not visible in the atmosphere. The induced lithium depletion becomes visible in the sub-giant phase as soon as the convective zone deepens enough. This may explain why the observed ‘lithium dilution’ is smoother and the final dilution factor larger than obtained in standard models, while the lithium abundance variations are very small on the main sequence.
Lithium in Cool Magnetic CP Stars: Some New Results of Observations, Using CAT (ESO) 2.6m (CrAO), (NOT) La Palma Telescopes
Authors: Polosukhina N. , Kurtz D. , Hack M. , North P. , Ilyin I. , Zverko J.
Published: July 2016

Lithium in cool magnetic CP stars in still poorly studied and estimations of the Li abundance in these stars are scarce. There is some evidence of variability of the LiI 6708 Â line, but this variability has not been studied systematicaly. Even the identification of the 6708 Â line with the LiI resonance doublet is still in doubt. This problem is important in the broader context of the Li abundance in various types of stars, as well as for deeper undersfanding of the magnetic star phonomenon itself. The reason for fhis is that the Li abundance in very sensitive to evolutionary status of the stars and their properties, such as the character and intensity of mixing processes.
On meridional Circulation in Stars
Authors: Talon Suzanne , Michaud Georges , Vincent Alain
Published: July 2016

Even though the existence of meridional currents in stars has been known for quite a long time (Eddington 1925, Vogt 1925), its exact structure as well as its influence on stellar evolution is still unclear. Some authors concentrated on finding the exact shape of meridional circulation in a rotating star, while others tried to model its effect on the chemical distribution in the interior. In all studies performed so far however, meridional circulation is considered in an asymptotic regime in which the advection of entropy by the meridional currents is supposed to balance exactly the source term of the non-zero radiative flux divergence. Other terms could however be added to that asymptotic regime which could turn out to dominate the transport of chemicals. We wish to present here preliminary results of 3D numerical simulation attempted to tackle this problem.
On the Link Between Rotation and Lithium in Giant stars
Authors: De Medeiros J. R. , Nascimento J. D. , Sankarankutty S , Costa J. M. , Da Silva J. R. P. , Maia M. R. G.
Published: July 2016

Late-type evolved stars are well known for the decrease with age of their rotation and lithium abundance. However, the root cause of this property as well as the relationship between rotation and lithium content in these stars are not yet completely established. In the present work, we study the link between rotation and lithium abundances in solar-type giant stars on the basis of a large sample of 380 stars of spectral type F, G and K.
Li in Chromospherically Active Stars with Large Velocity Components
Authors: Rocha-Pinto H. J. , Castilho B. V. , Maciel W. J.
Published: July 2016

We present lithium abundances for nine chromospherically young, kinematically old late-type stars. The data support the interpretation that these objects can be formed during the coalescence of a short-period binary.
Evolution of D and 3He in the Galaxy
Authors: Tosi Monica
Published: July 2016

The predictions of Galactic chemical evolution models for D and 3He are described in connection with those on the other Galactic quantities for which observational constraints are available.

Models in agreement with the largest set of data predict deuterium depletions from the Big Bang to the present epoch smaller than a factor of 3 and do not allow for D/H primordial abundances larger than ∼ 4 × 10—5. Models predicting higher D consumption do not reproduce other observed features of our Galaxy.

If both the primordial D and 3He are low, models assuming that 90% of low-mass stars experience an extra-mixing during the red giant phase reproduce all the 3He observed abundances. The same percentage allows to fit also the observed carbon isotopic ratios, thus supporting the self-consistency of the extra-mixing mechanism.
Signatures of HI in the Early Universe: The End of the Dark Ages
Authors: Meiksin A.
Published: July 2016

Future radio surveys using facilities like the Giant Metre-wave Radio Telescope or a Square Kilometre Array may detect 21-cm radiation from the Intergalactic Medium (IGM) in either emission or absorption against the Cosmic Microwave Background (CMB) at high redshift. Prior to the reionization of the IGM, the first radiation sources would reveal their presence through their effect on the IGM. The signatures include a sharp absorption feature in the radio sky against the CMB resulting from a rapid rise of a Lyman-alpha continuum background shortly after the birth of the first UV sources in the universe, and 21-cm emission and absorption shells created on the several Mpc scale by the first bright QSOs. The detection of these signatures would map the end of the ‘dark ages', the period of transition from the post-recombination universe to one populated by radiation sources.
Associated HI in Absorbers at High Redshift
Authors: Vermeulen R.C.
Published: July 2016

WSRT observations have provided a first inventory of the incidence of HI 21 cm line absorption associated with AGN at redshifts up to z=1.0. There is a large range in line depths, from τ = 0.44 to τ ≤ 0.001, and a substantial variety of line profiles, from Gaussians of less than ten km s−1 to more typically a few hundred km s−1, as well as irregular and multi-peaked absorption, sometimes spanning many hundreds of km s−1. The chance of detecting appreciable HI absorption is greatest in the most compact radio sources, GPSs and CSOs, where it can occur in circumnuclear “disks” or “tori”, as well as in gas enveloping jets and hot spots; inferred densities range at least between 10 cm−3 and 104 cm−3. But HI absorption occurs also in some CSSs, perhaps associated with jet-cloud interaction regions, and in quasars with a large optical reddening. VLBI observations at the unusual UHF frequencies of redshifted HI 21 cm can give unique “sight”lines into the physics and evolution of young radio sources and their inner galactic medium.
A WSRT Survey for HI Absorption at Moderate Redshifts
Authors: Lane W.M. , Briggs F.H.
Published: July 2016

We summarize results from an extensive search for HI 21cm absorption at moderate redshifts. The survey was limited to systems with Mg II absorption at redshifts in the range 0.2 < z < 1.0, which lie in front of bright radio quasars. Narrow band observations centered at the metalline redshifts were made with the UHF-high system and, when possible, the DZB correlator at the WSRT. Three new absorbers have been confirmed and several candidate absorbers identified. Optical depth limits of a few percent at velocity resolutions of about 6 km s−1 are obtained for most of the non-detections. The 21cm search is complementary to similar damped Lyα surveys, and by combining information from both absorption lines we are able to better understand physical conditions in these high neutral column density absorbers. We find that the 21cm objects represent a cold subset of high neutral column density absorbers, but are not necessarily the highest column density systems.
Environmental Effects and the Dynamical State of Coma from a VLA HI Survey
Authors: Bravo-Alfaro H. , van Gorkom J.H. , Cayatte V. , Balkowski C.
Published: July 2016

We present results obtained from our 21cm VLA survey of spirals in Coma. The goal of this HI imaging of galaxies is twofold: first, study the interaction between individual galaxies and the cluster environment, looking for a connection with the starburst and post starburst phenomena. Second, to investigate the dynamical state of the cluster, analyzing the gas content of different groups of galaxies.
Radio-optical Identification of Very-Steep Spectrum Radio Sources from the UTR-2 Catalogue
Authors: Andernach H. , Verkhodanov O.V. , Verkhodanova N.V.
Published: July 2016

We used radio source catalogues accessible from the CATS database to establish radio continuum spectra for decametric radio sources in the UTR-2 catalogue. In an attempt to find further candidates for high-redshift radio galaxies, we searched the FIRST and NVSS surveys for counterparts of a sample of UTR sources with ultra-steep radio spectra (USS, α ≤ −1.2, S ∼ vα). We derived accurate positions and sizes for 23 of these USS sources. The search for optical counterparts from the APM (object) and DSS (image) databases, as well as infrared and X—ray identifications of these UTR sources are in progress.
VLA Observations of the Galactic Centre at 74 MHz
Authors: Anantharamaiah K. R. , E. Kassim Namir , Lazio T.J.W. , Goss W.M. , Falcke H.
Published: July 2016

We present a preliminary image of the Galactic Centre region at 74 MHz made using the Very Large Array (VLA)
Radio Observations of Galactic SNRs
Authors: Green D.A.
Published: July 2016

This paper reviews several aspects of the study of radio emission from Galactic Supernova Remnants (SNRs). The detection of radio emission from SNRs is the most important method for identification of SNRs, and the limitations imposed by selection effects on subsequent statistical studies are discussed. Also discussed are the spectral properties of SNRs, both their integrated spectra, and the evidence for spectral variations across the face of remnants.
Multifrequency GMRT observations of HII regions
Authors: Omar A. , Chengalur J.N. , Roshi D.A.
Published: July 2016

The electron temperatures of the compact cores of the galactic HII regions S206 and S209 have been determined by radio continuum observations near 235, 327 and 610 MHz using the Giant Meterwave Radio Telescope (GMRT). The resolution of our maps are 11″ and 6″ at 327 and 610 MHz respectively. These are the highest resolution low frequency maps of these HII regions.
A Study of Low density Ionized Gas in the Galactic Plane
Authors: Roshi D. Anish , Anantharamaiah K. R.
Published: July 2016

A complete survey of radio recombination lines (RRLs) near 327 MHz from the galactic plane (l = 330° − 0°-89°, b = 0°) was carried out using a section of the Ooty Radio Telescope (ORT) with an angular resolution of 2° × 2°. A subset of regions in the same area was observed using the whole telescope which has a beam of 2° × 6'. Hydrogen RRLs were detected in most of the positions that were observed. The lv diagram and radial distribution computed from the observed spectra and their comparison with other species in the galactic plane indicate that the low density gas detected in the survey is distributed similar to the star forming regions. For an assumed temperature of 7000 K, we estimate that the densities and sizes of the regions are in the range 1 — 10 cm−3 and 20 — 200 pc respectively. Our data suggests that the low density ionized gas is in the form of outer envelopes of normal HII regions.
Galactic Carbon Recombination Lines near 327 MHz
Authors: Roshi D. Anish , Kantharia N.G. , Anantharamaiah K. R.
Published: July 2016

A survey of radio recombination lines (RRLs) in the Galactic plane (l = 332° − 0° − 89°) near 327 MHz made using the Ooty Radio Telescope (ORT) has detected carbon RRLs from all the positions in the longitude range 0° < l < 20° and from a few positions at other longitudes. The carbon lines detected in the survey are, most likely, emission counterparts of the absorption lines observed at frequencies below 150 MHz. Observations towards l = 13°.9, b = 0°.0 indicate that the broader (∼ 38 km s−1) carbon line detected in the lower resolution observation consists of multiple narrow components (∼ 10 km s−1) with different central velocities. The implications of the presence of such narrow components for the modeling of line emission is discussed.
First Results from Simultaneous Dual Frequency Observations of Pulsars
Authors: Gupta Y. , Gothoskar P. , Ramesh Bhat N.D.
Published: July 2016

One of the unique capabilities of the GMRT is the facility for simultaneous multi-frequency observations of pulsars. We have initiated such observations with the aims of (i) studying frequency dependence of pulsar emission, (ii) accurate estimates of pulsar dispersion measure and its variations and (iii) multi-frequency interstellar scintillation studies. Here we present some results from the ongoing dual frequency observations of pulsars.
The NFRA Pulsar Machine PuMA
Authors: G. Strom Richard
Published: July 2016

The Westerbork Telescope has good low-frequency capability, with receivers covering much of the frequency range from 250 to 1800 MHz. For pulsar observations the array elements can be coherently summed to provide the equivalent of a 93 m aperture. To exploit this potential, a new backend, PuMa, has recently been commissioned. It can be configured in various ways, with up to 4096 frequency channels per band, a total bandwidth of 80 MHz, and time resolution of 50 nanoseconds. PuMa can be used in search mode, recording just two polarization channels, or for observations of known pulsars, determining all four Stokes parameters and correcting for dispersion and Faraday rotation. In many of the low-frequency bands (especially 300 — 380 and 800 — 900 MHz) interference-free observing is possible much of the time, enabling wide-band studies of ISS, refraction and the Faraday effect.
GMRT — Current Status
Authors: Rao A. Pramesh
Published: July 2016

The Giant Metrewave Radio Telescope (GMRT) is a major new facility available for observations at metre wavelengths. This paper describes the the GMRT with emphasis on the features that are of relevance to a potential user. The current state of the GMRT is also described.
The 74 MHz System on the VLA
Authors: Perley R.A. , Erickson W.C. , Kassim N.E.
Published: July 2016

The NRL and the NRAO have jointly implemented a low frequency capability on the Very Large Array. Operating at 73.8 MHz, this new frequency band offers unprecedented sensitivity (∼ 25mJy/beam) and resolution (∼ 25″). This paper briefly describes the this new receiving system, and the methodology for using it for astronomy.
The Low-Frequency Array (LOFAR): Opening a New Window on the Universe
Authors: E. Kassim Namir , W. Lazio T. Joseph , C. Erickson William , C. Crane Patrick , Perley R. A. , Hicks B.
Published: July 2016

Decametric wavelength imaging has been largely neglected in the quest for higher angular resolution because ionospheric structure limited interferometric imaging to short (< 5 km) baselines. The long wavelength (LW, 2—20 m or 15—150 MHz) portion of the electromagnetic spectrum thus remains poorly explored. The NRL-NRAO 74 MHz Very Large Array has demonstrated that self-calibration techniques can remove ionospheric distortions over arbitrarily long baselines. This has inspired the Low Frequency Array (LOFAR)—-a fully electronic, broad-band (15—150 MHz)antenna array which will provide an improvement of 2—3 orders of magnitude in resolution and sensitivity over the state of the art.
Geometric Phase in Phasing of Antenna Arrays
Authors: Bhandari Rajendra
Published: July 2016

The response of a pair of differently polarized antennas is determined by their polarization states and a phase between them which has a geometric part which becomes discontinuous at singular points in the parameter space. Some consequences are described.
Solar Coronal Magnetic Fields
Authors: Hildebrandt J. , Kliem B. , Krüger A.
Published: July 2016

A short compilation of various radio methods of the determination of magnetic fields in the solar corona is given which, completed by observations in other spectral ranges (e.g. the optical and X-ray ranges), results in a complex picture of the magnetic field. Some topics of interest are the following:

(1)

Comparison with a standard reference magnetic field in the solar corona,

(2)

Possible evidence of substantial small-scale fluctuations of the magnetic field (e.g. in active regions),

(3)

Indication of magnetic fields substantially in excess of the standard distribution (e.g. in limb flare events).
Magnetic Field and Differential Rotation of the Sun
Authors: Kundt W.
Published: July 2016

The solar magnetized surface reveals a stable spin period — the Carrington period — and a stable oscillation period — the Hale period. The latter is traced by each of the low-order multipole moments, whereby the total magnetic energy (near the surface) is more or less constant. This highly non-stochastic structure is reminiscent of a permanent magnetic flux frozen into the Sun's radiative core, and dragged out into the heliosphere by the solar wind. The radius-dependent torque exerted by this magnetic flux can restore the observed system of torsional oscillations of the convection zone.
An Improved Reynolds Technique for Approximate Solution of Linear Stochastic Differential Equations
Authors: Stahlberg J.
Published: July 2016

Our starting point is a formal linear stochastic differential equation of first order (higher order equations can be transformed to systems of these)

where I, a, W are stochastic functions with and analogously for a and W. I, a, and W are allowed to depend on the element ω of a set Ω in which a probability measure is defined in the usual way (see e.g. Doob, 1953; de Witt-Morette, 1981). To get a solution of eq.(1) for the mean intensity we treat the problem according the Reynolds averaging technique in the usual manner : The stochastic equation is changed into an infinte hierarchical system of equations for the correlations.
Non-Axisymmetric Magnetic Structure Generation in Planets Sun and Galaxies
Authors: Starchenko S.V.
Published: July 2016

The problem of preferential excitation of non-axially symmetric magnetic fields in most of the observed spiral galaxies and in planets as Uranus and Neptune is studied. It is suggested that a dynamo acting in a thin conductive shell is possible in these objects.

It is shown that in this thin shell axisymmetric and non-axisymmetric magnetic field modes can be excited with equal efficiency. The preferential excitation of non-axially symmetric magnetic fields is possible, when the gradient of the angular velocity of rotation is comparatively small and has an essential component perpendicular to the shell.
The Magnetic Field of M 51
Authors: Neininger N. , Horellou C. , Beck R. , Berkhuijsen E.M. , Krause M. , Klein U.
Published: July 2016

We present observations of the polarized emission and the derived magnetic field structure of the spiral galaxy M 51 at different wavelengths: 2.8 cm, 6.2 cm, 18 and 20.5 cm.
Towards the Magnetic Field of M 81
Authors: Moss David , Brandenburg Axel , Donner Karl Johan , Thomasson Magnus
Published: July 2016

We present calculations showing how both transient effects associated with nonaxisymmetric seed fields, and an interaction with a companion, can produce BSS type magnetic structure in a spiral galaxy.
Numerical Models of 3-D Galactic Dynamos
Authors: Panesar J.S. , Moore N. , Nelson A.H.
Published: July 2016

We describe here the results of 3-D numerical simulations of an αω-dynamo in galaxies with differential rotation, small scale turbulence, and a shock wave induced by a stellar density wave. A non-linear quenching mechanism for the dynamo instability is used, and with the model parameters employed the field achieves a steady state which closely resembles observed fields in galaxies. The magnetic field vectors are parallel to the plane in the disc, with the magnetic intensity decreasing away from the plane. The vectors are also nearly parallel to the spiral arms in the disc, and the field direction is axisymmetric about the galactic centre, but with significant increase of intensity in the arms. The magnetic intensity rises steeply towards the centre of the galaxy, where the field becomes dominated by the vertical component. Nowhere in the parameter range covered is the bi-symmetric field mode dominant.
Boundary Layer in Nonlinear Dynamo
Authors: Kuzanyan K.M. , Kvasz L.
Published: July 2016

The solution of the boundary layer problem in a nonlinear galactic dynamo is described.
Basic Properties of Swing-Excitation Mechanism
Authors: Chiba M. , Hanasz M.
Published: July 2016

We describe the basic process of coupling between dynamo and density waves in galaxies. The growth rate of magnetic field as a result of coupling is derived, applying the method of multiple time scales to the marginal state of disk dynamo. It is shown that the 1st-order resonance in a perturbation of density and thus the linear swing excitation, is possible. Moreover, the growth rate of magnetic field is always positive and does not depend on the initial phase difference between the magnetic and density waves. Both the numerical and analytical calculations show that ω = 2ω0 (ω: density-wave freq., ω0: dynamo freq.) is still the best condition for resonance due to the linear effect of swing excitation.
Magnetic Field Generation within Molecular Clouds
Authors: Lazarian A.
Published: July 2016

Magnetic field generation in molecular (atomic) clouds at the early stages of galactic evolution is considered. It is shown that if there is no internal motions immersed the cloud, battery mechanisms (Lazarian 1992a) can account for the generation of thin magnetic shells around clouds insides in plasma with temperature gradients. If turbulent motions are present, the dynamo can be essential. The operation of α — ω, α2 and turbulent dynamos within molecular clouds is discussed. It is shown that the turbulent dynamo leads to generation of magnetic fields in the trace behind the cloud. These magnetic fields within the molecular clouds and in their vicinity are important for the solution of the galactic seed field problem (see Lazarian 1992b) and the formation of structures in clumpy molecular complexes.
The Solar Dynamo and Planetary Dynamo
Authors: Yoshimura Hirokazu
Published: July 2016

A dynamo driven by flows of differential rotation and global convection in a rotating sphere is reviewed as a model of the solar and planetary dynamos. The flows can amplify a magnetic field from an infinitesimal level and thus can generate a magnetic field. The flows periodically reverse the polarity of the field and force the generated field system to propagate along iso-rotation surface in the sphere in form of a wave during the generation process. The flows can also generate the field without reversing its polarity depending on the structure of the flows of the differential rotation. The basic dynamo process with and without polarity reversals is explained in terms of topological deformation of field lines by the flows in the sphere. The oscillatory and steady dynamos are interpreted as corresponding to the solar and planetary dynamos respectively.
Compton Observatory Observations of AGN
Authors: Kurfess J. D.
Published: July 2016

The principal results on active galactic nuclei from the Phase 1 observations by the COMPTON Gamma Ray Observatory are presented. These include the detection of a new class of high-energy gamma ray sources by the EGRET instrument and extensive observations of Seyfert galaxies in low-energy gamma rays by OSSE. The identified EGRET sources are associated with core-dominated radio loud objects, OVV's and BL Lacs. EGRET has not detected any Seyfert galaxies. OSSE observes a thermal-like spectrum from NGC 4151, and the low-energy gamma ray spectra of other Seyferts are significantly softer than the spectra below 50 keV, suggesting that a thermal emission mechanism is characteristic of these objects. OSSE has not detected any positron annihilation radiation from any Seyfert, and neither OSSE nor COMPTEL have detected an MeV excess from these sources.
High-Energy Continuum Variability in Active Galactic Nuclei
Authors: Edelson Rick
Published: July 2016

CGRO and IUE observations suggest that the strong, aperiodic variability seen in the Exosat long-look observations of AGN extends over a much wider energy band. Some BL Lac objects (but no Seyfert 1 galaxies) have shown X-ray variations which were so rapid that they violate the assumptions of isotropy inherent in the Eddington limit. In the ultraviolet, Seyfert 1s as a class show an anti-correlation between the variability amplitude and luminosity, while BL Lacs show a positive correlation. Furthermore, Seyfert 1s show strong flux-correlated spectral variability, while BL Lacs show little or none. All of this suggests that the high-energy continua of BL Lacs are beamed towards us, while the ultraviolet continua of Seyfert 1s are emitted isotropically.

The November 1991 multi-waveband monitoring of the BL Lac PKS 2155−304 showed strong correlated variability, with the soft X-rays leading the ultraviolet by a few hours, and no measurable lag between the ultraviolet and optical down to a limit of ≲ 1.5 hr. This indicates that the X-rays from this BL Lac are not produced by Compton upscattering, and that the ultraviolet does not come directly from a thermal source such as an accretion disk. This also strongly constrains the relativistic jet model, suggesting that all of the radiation is produced in a flattened region like a shock front.

Low temporal resolution ultraviolet/optical monitoring of the Seyfert 1 NGC 5548 in 1989 yielded a strong correlation with no measurable lag to a limit of ≲4 days, casting some doubt on the standard model of thermal emission from an accretion disk in Seyfert 1s. Upcoming X-ray/ultraviolet/optical monitoring of the Seyfert 1 NGC 4151 in December 1993 will have much faster sampling, to permit a strong test of both this model and the competing reprocessing model.
Contemporaneous Multiwaveband Observations of Blazars
Authors: Marscher Alan P. , Bloom Steven D. , Zhang Yun Fei , Gear Walter K.
Published: July 2016

We have observed a number of blazars at wavebands ranging from radio to γ-ray. We find bright γ-ray emission to be associated with strong synchrotron flares observed at lower frequencies. The X-ray flux and entire radio spectrum of 4C 39.25 have each increased in strength by 30% over a 2-year period, in agreement with the prediction of the bent relativistic jet model.
mm-VLBI: Jets in the Vicinity of Galaxy-Cores
Authors: Krichbaum T.P. , Standke K.J. , Graham D.A. , Witzel A. , Schalinski C.J. , Zensus J.A.
Published: July 2016

Millimeter-VLBI provides an angular resolution of up to a few tens of microarcseconds and allows imaging of compact radio sources, self-absorbed at longer wavelengths, with unsurpassed angular resolution. At 43 GHz the participation of the VLBA and the 30 m-MRT at Pico Veleta (e.g. Krichbaum et al., 1993 a&b), and at 86 GHz the addition of the 100 m-RT at Effelsberg and the 30 m-MRT (Schalinski et al., 1993, and this volume) have improved the imaging capabilities of mm-VLBI observations.

Results: The increased sensitivity of mm-VLBI observations allows the investigation of fainter objects, previously not accessible. As one example we show in Fig.1 the first detection of the compact radio source Sgr A∗ in the Galactic Center with VLBI at 43 GHz in May 1992 (Krichbaum et al., 1993d) and at 86 GHz in April 1993 (Krichbaum et al., 1994). In both observations the size of Sgr A∗ appeared to be larger than its expected scattering size, indicative of intrinsic source structure showing up at mm-wavelengths. Future monitoring with mm-VLBI is necessary to search for (not unexpected) structural variability.

Monitoring of AGN with mm-VLBI reveals in all cases observed in sufficient detail jet curvatures of increasing amplitude towards the self-absorbed VLBI-cores (e.g. in 18034-784: Krichbaum, 1990, OJ 287: Krichbaum et al., 1993c), and sub- or superluminal motion along ‘quasi-helically’ bent trajectories (e.g. 3C 84: Krichbaum et al., 1993b; 3C 273: Krichbaum et al., 1993c), which differ sometimes for adjacent jet components (e.g. 3C 345: Krichbaum & Witzel, 1992, Krichbaum et al., 1992&1993a). In 3C 84, 3C 273 and 3C 345 the apparent velocity of jet components varies systematically along the jet axis, in 4C 39.25 (Alberdi et al., 1993) a moving component decelerates and brightens, all of this suggesting differential Doppler boosting and motion along three-dimensionally curved trajectories. In 3C 345 the complex kinematics of C4 and C5 (Zensus, this volume) has been geometrically modeled by motion along a helical path on the surface of a conical jet (Qian et al., 1992, Steffen et al., 1993, and this volume; see also Camenzind, this volume). As a new example, the oscillations of the inner jet and its velocity variations βapp(r) are shown for the BL Lac object 1803+784 in Fig. 2 (see the maps in: Krichbaum et al., 1993b). The frequent occurence of ‘quasi-sinusoidal’ bends in the inner jets of very different classes of AGN (QSO's, BL Lac's, Seyfert's) suggests that this effect is common in a large fraction of AGN and that the underlying jet-physical process may be fundamental for the understanding of the creation of jets.
Emission Components in Seyfert Galaxies and Quasars
Authors: Courvoisier Thierry J.-L.
Published: July 2016

The continuum emission components of Seyfert galaxies and quasars are reviewed with a particular emphasis on the correlations observed between these components. It is shown that the blue bump emission which is observed in Seyfert galaxies and quasars and not in BL Lac type objects is not hidden in the latter objects by a strong beaming of the jet emission. The shape of the blue bump is described and some consequences of these observations for the interpretation of this component are given. The relationship between the X-ray emission of quasars and the radio beaming properties of the object should be re-visited when the shape of the soft excess emission can be better established.
Structure and Emission of Parsec-Scale Jets in Quasars
Authors: Camenzind Max
Published: July 2016

The moving knots observed in VLBI of compact quasars are due to off-axis substructures in the parsec-scale jets which are dragged along by the underlying plasma flow. This is suggested by detailed MHD models for the structure of relativistic jets on the parsec–scale that are based on exact solutions of the nonlinear Grad–Schlüter–Shafranov equation in the asymptotic domain. These jet models are characterized by a current–carrying core and a current–free envelope. The corresponding core–radius Rc = upRL is related to the poloidal jet velocity up and the light cylinder radius RL generated by the rotation of the magnetic surfaces. The Poynting flux, which has an inhomogeneous distribution in the jet, provides an off–axis energy reservoir that could be tapped and converted into particle acceleration by non-axisymmetric instabilities in the core–jet structure. Evidence is presented that quasi-periodic synchrotron emission (in the IR–optical) and inverse Compton emission (in X– and γ–rays) from freshly accelerated electrons are due to a lighthouse effect of the rotating knots.
Emission of Accretion Disks
Authors: Czerny B.
Published: July 2016

Accretion disks surrounding massive black hole is an attractive scenario of nuclear activity. A number of arguments support it although there is no unquestionable proof of the existence of accretion disks in active galactic nuclei. Meaningful comparison of the disk model prediction with the data can only be made if emission of accretion disks is calculated taking into account the existence of optically thin parts responsible for the emission of x-ray radiation. Nonlocal reprocessing phenomena have to be also included. Since we have no real understanding of the viscous processes operating in accretion disks some ad hoc parameterization of these processes has to be used and its applicability should be checked by broad band comparison of predictions for continuum emission and spectral features with available data.
Spectra of Quasars with Extreme Continuum Properties
Authors: Mathur Smita
Published: July 2016

The quasar population as a whole covers a wide range of continuum properties; sufficient to cause a marked difference in the physical conditions of the gas in the nuclear region of a quasar. In this paper we will discuss our results on 3C351, an X-ray “quiet” quasar; and 3C212, a “red” quasar. We identify the “warm absorber” observed in the ROSAT observations of 3C351 to be the UV absorber observed by HST.
The Palomar Observatory Dwarf Seyfert Survey
Authors: Ho Luis C. , Filippenko Alexei V. , Sargent Wallace L. W.
Published: July 2016

We describe an optical, spectroscopic survey of the nuclei of the 500 brightest galaxies in the northern sky. The primary goal is to search for low-luminosity active galactic nuclei (LLAGNs) in the centers of nearby galaxies. The results of this survey will have many astrophysical applications, including quantifying the faint end of the local AGN luminosity function and estimating the contribution of LLAGNs to the X-ray background. We summarize the statistical properties of the survey, describe our methods of analysis, and present some preliminary results based on ∼ 60% of the sample.
Quasar Formation in Hierarchical Structure Formation Models
Authors: Haehnelt M.G.
Published: July 2016

Hierarchical cosmogonies can consistently explain the evolution of the quasar population if quasars are short-lived and supermassive black holes form fast in the newly-formed nuclei of dark-matter haloes. Here we investigate the relevant physical processes and show that such a fast formation is plausible. The angular-momentum and the gas-supply problem for the formation/feeding of a supermassive black hole are strongly alleviated compared to a scenario in which gas is transported to the centre by tidal interaction of ready-assembled galaxies. The baryonic component of the newly-formed nucleus will cool catastrophically and settle into a self-gravitating angular momentum-supported disc of radius ∼ 100 pc. Gravitational instabilities and/or supernovae-induced turbulence will transport the gas further to the centre within less than 108 yr. In nuclei of very massive dark matter haloes with sufficiently deep potential well to retain the gas against feedback processes from massive stars and supernovae, concentration of a major fraction of the gas component of the nucleus within the central 1 pc and subsequent formation of a black hole seem unavoidable. A coeval short phase of efficient star formation could explain the observed high metallicities of quasars.
Hubble Space Telescope Observations of NGC 4151: Implications for the Unified Model of AGN
Authors: Tsvetanov Z. , Evans I.N. , Kriss G.A. , Ford H.C.
Published: July 2016

HST Planetary Camera narrow band emission-line and continuum images are used to study the nuclear region of NGC 4151 at the highest possible spatial resolution. The [O III] λ5007 image reveals a striking biconical structure with a projected opening angle of 75° ±10°, and whose apex coincides with the bright, unresolved central source. The projected axis is oriented along PA 60°/240° ± 5°, and is aligned with the extension of the nuclear VLBI radio source. Analysis of the geometry of the narrow-line region places our line of sight well outside the ionization cones, and yet we see nearly unobscured optical and near-UV continuum and broad lines. In addition, material with significantly different column densities is required to explain the numerous optical and UV absorption lines and the soft X-ray absorption. We conclude from these data that the simplest version of the obscuring torus unification model is inconsistent with the observations and some modifications are required. We discuss some alternative collimation mechanisms that are compatible with our observations.
Quasi-Steady State Cosmology
Authors: Burbidge G. , Hoyle F. , Narlikar J.V.
Published: July 2016

The standard big bang cosmology has the universe created out of a primeval explosion that not only created matter and radiation but also spacetime itself. The big bang event itself cannot be discussed within the framework of a physical theory but the events following it are in principle considered within the scope of science. The recent developments on the frontier between particle physics and cosmology highlight the attempts to chart the history of the very early universe.
HST, IUE and ROSAT Observations of High Z QSOs
Authors: Band D. L. , Cohen R. D. , Blanco P. R. , Junkkarinen V. T. , Burbidge E. M. , Rothschild R. E. , Reichert G. A.
Published: July 2016

The optical through X-ray spectra of 3 QSOs between z = 1.32 and 3.53 show these objects to be very similar to low z AGN.