bluuebunny/crossref_metadata_2025 huggingface dataset:
Interstellar D/H on the Sightline of Sirius
Authors: Hébrard G. , Vidal-Madjar A. , Ferlet R. , Mallouris C. , York D. , Lemoine M.
Published: July 2016

We present observations of the binary Sirius A / Sirius B performed with HST-GHRS. Two interstellar clouds are detected on this sightline, one of them being identified as the Local Interstellar Cloud (LIC). Lyman α interstellar lines are also observed, but whereas the deuterium Lyman α line is well detected in the LIC with an abundance in agreement with that obtained by Linsky et al. (1995), no significant D i line is detected in the second cloud. The deuterium abundance which we measured in this cloud is 0 < (D/H)ism < 1-6 × 10−5. Despite the large error bar, this sightline appears consequently as a good candidate for a low (D/H)ism.
In-Orbit Performance of the Far Ultraviolet Spectroscopic Explorer
Authors: Sonneborn G. , Moos H. W. , Sembach K. R.
Published: July 2016

The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched by a Delta II rocket on 24 June 1999 into a ˜768 km, 25° orbit. Following the In-Orbit Checkout phase, FUSE is obtaining high-resoluti
on spectra (λ/Δλ ≳ 20,000) in the spectral range 905 −1187 Å. The sensitivity meets or exceeds the pre-launch predictions. Many QSOs and AGNs have already been observed.
Lithium in the Open Cluster NGC 6475
Authors: Randich S. , Pallavicini R. , Mermilliod J.-C.
Published: July 2016

We present the results of a lithium study of the 220 Myr old cluster NGC 6475. Our data are merged with those from previous Li surveys of this cluster in order to construct a more statistically significant sample. The Li vs. effective temperature distribution of the merged sample is compared with the one of the co-eval, but more metal poor cluster M 34 and with the ones of the younger Pleiades and older Hyades. The results are discussed in the framework of non-standard Li depletion on the main-sequence between the age of the Pleiades (˜ 120 Myr) and that of the Hyades (˜ 600 Myr).
The Properties of the PDS Li-rich Giant Stars
Authors: Torres C. A. O. , Quast G. R. , de la Reza R. , da Silva L.
Published: July 2016

In the Pico dos Dias Survey (PDS), devised to search for young stellar objects, we found also K giants presenting moderate to strong Lithium lines associated with IRAS sources. But there are some gK with weak or absent Li lines too. There is a dichotomy in the distribution of the IRAS spectral indices between both kinds of K stars. A model of an expanding shell with a mass-dependent velocity may explain this behavior, if the photospheric Li depletion takes only ˜2500 yrs.
Be vs. Li Abundance in Li-Rich Giants: an Evidence of Li Production in Red Giants
Authors: Castilho B. V.
Published: July 2016

We present Be abundances derived through spectral synthesis for two Li-rich giants and a Li-normal giant, plus α Cen A and B, based on observations of the Be II λ 3130.420 and 3131.066 Å lines obtained with the CASPEC spectrograph at the ESO 3.6m telescope.

The values derived for the two Li-rich giants (HD146850, HD787) agree with the one for the Li-normal giant (HD220321), and shows that Be was depleted in these stars (by > 90% i.e. by a factor of 10 or larger from the initial Pop I value (logN(Be)= 1.4)).

This result implies that the original Li in these stars was almost completely destroyed, and that Li is most probably produced in red giants.
The Interstellar Lithium Isotope Ratio Toward Per OB2
Authors: Knauth David C. , Federman Steven R. , Lambert David L. , Crane Philippe
Published: July 2016

We are conducting a survey on the 7Li/6Li ratio in interstellar space in order to seek limits on the variation in this ratio. The analysis is based on the technique we adopted in extracting the 11B/10B ratio. This technique uses a line of comparable strength, from a species likely to occupy the same volume of the interstellar cloud, as a template for separating velocity components within the line profile. For our study of the 7Li/6Li ratio, the K I line at 4044 Å serves as the velocity template. Our initial focus is on the variation in the 7Li/6Li ratio around the star-forming region IC 348. Our high-resolution observations of the Li I lines toward o and ζ Per show remarkably different isotope ratios: 7Li/6Li = 2-4 and 11, respectively, where the Solar System ratio is 12.3 and cosmic ray spallation yields a ratio of about 2. The significance of the very low ratio toward o Per is that it is essentially the value predicted for cosmic rays through spallation reactions. The direction to o Per passes closer to IC 348, a site of massive star formation, than does the line of sight to ζ Per. Furthermore, our analysis of OH column densities (Federman, Weber, & Lambert 1996) showed that the cosmic ray flux through o Per's diffuse clouds is higher than average, presumably reflecting the nearby presence of IC 348.
Lithium in Metal Deficient K Giant Stars: The Absence of Dust Signature
Authors: de la Reza Ramiro , da Silva Licio , A. Drake Natalia , A. Terra Marco
Published: July 2016

The 7Li enrichment - mass loss scenario has been constructed using the strong connection found between solar metallicity Li-rich giants and IRAS sources. We show here that the Li-rich metal poor first-ascent red giants are not IRAS sources, although they are loosing Li enriched matter in form of gas.
Detailed Analysis of Li-rich Giants
Authors: Gregorio-Hetem J. , Castilho B.V. , Barbuy B. , Spite F. , Spite M.
Published: July 2016

We have carried out a survey to detect Lithium-rich giants (LRGs). In Castilho et al. (1998) we reported the discovery of five red giants showing a strong Li I (λ670.78 nm) line and six other ones showing a moderate Li I line. In this work we present the main results of a detailed analysis of 10 stars from our survey and 6 LRGs selected from the literature.
The Light Elements Be and B as Stellar Chronometers in the Early Galaxy
Authors: C. Beers Timothy , K. Suzuki Takeru , Yoshii Yuzuru
Published: July 2016

Recent detailed simulations of Galactic Chemical Evolution have shown that the heavy elements, in particular [Fe/H], are expected to exhibit a weak, or absent, correlation with stellar ages in the early Galaxy due to the lack of efficient mixing of interstellar material enriched by individual Type II supernovae. A promising alternative ‘chronometer’ of stellar ages is suggested, based on the expectation that the light elements Be and B are formed primarily as spallation products of Galactic Cosmic Rays.
Effects of Photospheric Temperature Inhomogeneities on Lithium abundance Determinations (2D)
Authors: Cayrel Roger , Steffen Matthias
Published: July 2016

Based on detailed 2D radiation hydrodynamics (RHD) simulations, we have investigated the effects of photospheric temperature inhomogeneities induced by convection on spectroscopic determinations of the lithium abundance. Computations have been performed both for the solar case and for a metal-poor dwarf. NLTE effects are taken into account, using a five-level atomic model for Li I. Comparisons are presented with traditional 1D models having the same effective temperature and gravity. The net result is that, while LTE results differ dramatically between 1D and 2D models, especially in the metal-poor case, this does not remain true when NLTE effects are included: 1D/2D differences in the inferred NLTE Li abundance are always well below 0.1 dex. The present computations still assume LTE in the continuum. New computations removing this assumption are planned for the near future.
AGB Stars Interferometric Signatures: Effects of Possible Li-rich Spots
Authors: de Laverny Patrick , Lopez Bruno
Published: July 2016

We propose to observe Asymptotic Giant Branch stars (AGB) with spectro-differential interferometric techniques in order to find new observational constraints to inner structure and evolutionary models of these stars. We examine the interferometric signatures created by possible heterogeneities on AGB stars surface due to local Li-enrichments or Li-rich spots and find that such heterogeneities, if they exist, could be detected with present or future interferometers.
He Abundance in Planetary Nebulae
Authors: Gruenwald R. , Viegas S. M.
Published: July 2016

Type I planetary nebulae (PNe), defined as those with high He (and N) abundances, generally present bipolar geometries and high stellar temperatures. The main goal of this paper is to check if the empirically derived He overabundance for Type I PNs is real, or if it is a consequence of geometrical effects due to the bipolarity and/or to the ionization stratification due to the high stellar temperature of these objects.
Non-LTE Effects in Berylium Abundances
Authors: Idiart T. P. , Thévenin F
Published: July 2016

In this work we analyze the beryllium-iron chemical diagram from the point of view of non-LTE effects. Be abundances were re-calculated by considering non-LTE corrections in ionization equilibrium (logg) and Fe abundances ([Fe/H]). These corrections seem do not affect the linear relation between Be-Fe for metal-poor stars already found in the literature for LTE derived abundances.
White Dwarf Probes of Interstellar Deuterium
Authors: Landsman Wayne
Published: July 2016

We review the advantages of using hot white dwarfs (WDs) as probes of the deuterium abundance in the local interstellar medium. We then discuss advantages of the Space Telescope Imaging Spectrograph (STIS) for such observations, as compared with earlier observations with the Goddard High Resolution Spectrograph (GHRS). The GHRS Ly α profile of the white dwarf HZ 43 is probably modified by the hot ‘hydrogen wall’ surrounding the Sun; but despite this complication, the sightline remains a promising one for an accurate determination of the deuterium abundance in the local interstellar medium.
Lithium as Probe of the Scenarios of the Chemical Enrichment of the Galaxy
Authors: François P , Hill V. , Spite M. , Spite F.
Published: July 2016

Jehin et al. (1999) find that, in a sample of moderately metal-poor stars, a group is rich in s elements, and they propose an enrichment by accretion of matter by the winds of AGB stars. We tried to check the implications for the lithium abundances.
Implications of Early Cooling Flows and Galactic Winds for the Evolution of Deuterium
Authors: S. Friaça Amancio C.
Published: July 2016

The deuterium abundances in high-redshift QSO absorption-line systems could be an important constraint in models of galaxy formation. Here we investigate the role of galactic winds and massive cooling flows present during the formation of galaxies on the evolution of deuterium abundance. Destruction factors are calculated and the time and spatial scales for the dispersal through galactic winds of the processed deuterium-depleted gas are presented and related to the D/H determinations for QSO absorption-line systems. The calculations are derived from a chemodynamical model within a scenario in which the absorbers are located inside the hot halo of a young galaxy.
Radio Source Surveys
Authors: Condon J. J.
Published: July 2016

The primary goal of radio source surveys is to generate flux-limited samples. Sources selected at very low frequencies are dominated by unbeamed emission and give the only unbiased view of the parent populations used by “unification” models to account for the diversity of sources seen at high frequencies. Low-frequency surveys favor sources with exceptionally steep spectra. They include radio galaxies at high redshifts, radio halos of nearby galaxies, relic radio sources, diffuse cluster emission, pulsars that may be missed by traditional pulse searches, and a new class of unidentified compact sources. Flux densities from low-frequency surveys extend the spectra of known source populations to frequencies at which free-free and synchrotron absorption become significant and constrain basic source parameters. Finally, telescope fields-of-view scale ∝ λ2, so gridded surveys can be more efficient than directed observations of individual targets. This review covers recent and proposed low-frequency source surveys and their astronomical uses.
Cambridge Low Frequency Surveys
Authors: Green D.A.
Published: July 2016

Over many years low-frequency radio surveys have been made in Cambridge that cover much of the northern sky at both 38 and 151 MHz. The characteristics of the earlier surveys − 6C (at 151 MHz, δ above +30°) and 8C (at 38 MHz, δ above +60°), both with a resolution of about 4 arcmin — are reviewed, together with the results from more recent surveys made at 151 MHz, with a resolution of about 1·2 arcmin with the Cambridge Low-Frequency Synthesis Telescope (CLFST). These surveys include the 7C survey, which includes low declinations to complement 6C, selected regions at higher declinations, variability studies, and the 7C(G) survey of much of the northern Galactic plane.
WSRT 1.4 GHz Observations of the Hubble Deep Field
Authors: Garrett M.A. , de Bruyn G. , Baan W. , Schilizzi R.T.
Published: July 2016

We present WSRT 1.38 GHz observations of the Hubble Deep Field (and flanking fields). 72 hours of data were combined to produce the WSRT's deepest image yet, reaching an r.m.s. noise level of 8 microJy/beam. We detect radio emission from galaxies both in the HDF and HFF which have not been previously detected by recent MERLIN or VLA studies of the field.
Probing HI in the Universe with SKA
Authors: van der Hulst J.M.
Published: July 2016

This paper briefly describes the capabilities of a new generation large telescope such as the Square Kilometer Array (SKA) for imaging HI in a one degree field out to z ≍ 3
Atomic Hydrogen Gas Images of QSO Host Galaxies
Authors: Lim J. , Ho P.T.P.
Published: July 2016

We present the first neutral atomic hydrogen (HI) gas images of QSO host galaxies. The results come from our ongoing survey of all twenty-three QSOs at redshifts z < 0.07 visible from the VLA. Our images show tidal interactions in all of the QSO host galaxies detected in HI, even when no such interactions are clearly visible in the optical. The results are not consistent with the suggestion by Sanders et al. (1988a, 1988b) that ultraluminous infrared galaxies, the vast majority of which are later-stage mergers, are the parent population of a significant fraction of radio-quiet QSOs. Instead, our results suggest that QSOs reside in a wide variety of interacting environments.
An HI Search for the Host Galaxies of 27 Radio-loud AGN at z ∼ 2.3
Authors: Ghosh T. , Davis M.M. , Salter C.J. , Aller M.C.
Published: July 2016

This project was inspired by optical and IR imaging suggesting that, while most QSO hosts at high z are too faint to detect, radio-loud quasars are hosted by exceptionally luminous galaxies. Thus, a search was undertaken for HI absorption against the continuum emission of strong radio emitters whose redshifts (z ∼ 2.3) bring their HI line into the 430-MHz Arecibo passband2. The aim was to detect, or set useful limits, on the HI in the hosts, say in dust lanes, introduced by mergers, or situated in obscuring circumnuclear tori. At Arecibo there is a choice of, a) the 430-MHz line-feed system, or b) the new 430-MHz Gregorian-dome feed. In practice, most of the data were taken with the Gregorian system, although some line-feed data were also acquired. This represents the first Arecibo line spectroscopy using the 430-MHz Gregorian receiver.
3C Radio Sources as They've Never Been Seen Before
Authors: Blundell K.M. , Kassim N.E. , Perley R.A.
Published: July 2016

Low-radio-frequency observations played a remarkable role in the early days of radio astronomy; however, in the subsequent three or four decades their usefulness has largely been in terms of the finding-frequency of surveys. Recent technical innovation at the VLA has meant that spatially well-resolved imaging at low frequencies is now possible. Such imaging is essential to understanding the relationship between the hotspot and lobe emission in classical double radio sources, for example. We here present new images of 3C radio sources at 74 MHz and 330 MHz and discuss their implications.
Galactic Plane Surveys at Low Frequencies
Authors: Taylor A.R.
Published: July 2016

Until recently, high angular resolution and high sensitivity surveys of the radio emission from the plane of our Galaxy were available only at frequencies of several GHz, where large single dish radio telescopes provide arcminute scale angular resolution. At these frequencies thermal radiation from HII regions and diffuse ionized gas comprise a major component of the Galactic emission. Advances in wide field interferometric imaging techniques now make it possible to carry out high sensitivity surveys of the Galaxy with arcminute scale angular resolution at 1.4 GHz and below. Over the past few years initial synthesis surveys have been made. More ambitious surveys that combined sensitive continuum observations with full polarimetry and images of the 3-dimensional structure of atomic hydrogen gas at pc scales are currently underway in the northern (DRAO) and southern (ATNF) hemispheres. The interstellar medium of the Galaxy contains structure on all spatial scales, and these surveys combined data from aperture synthesis telescopes and signal dish antennas to provide full spatial frequency coverage to the resolution limit. Preliminary results reveal wide-spread features and processes in the the interstellar medium that are not readily visible by other means, including, for example, unusual atomic hydrogen structures related to the vertical transfer of matter and radiation between the disk and halo of the Galaxy, Faraday rotation structures that allow study of the magnetic field and diffuse ionized component in the plane of the Galaxy, and a cold atomic phase of the neutral medium that may provide a link between global shock phenomena in the galaxy and the formation of molecular clouds.
Radio Continuum Surveys of the Galaxy and Galaxies
Authors: Wielebinski Richard
Published: July 2016

Radio sky surveys give us basic information about the origin of the radio emission from the Galaxy. By mapping the sky at several radio frequencies a separation of the thermal and non-thermal emission components is possible. The major part of the low-frequency radio emission comes from the synchrotron process, the braking of relativistic electrons in magnetic fields. By mapping the linear polarization at several frequencies (required for the correction of the Faraday rotation) the orientation of the magnetic fields in the emitting regions can be deduced. Older all-sky surveys at 30, 150 and 408 MHz have now been supplemented by new observations of the Galaxy at 45 and 1420 MHz. These surveys, in addition to being important as tracers of the morphology of the magnetic fields in the Galaxy, are also required to correct for the ‘foreground’ features in cosmological studies of the COBE data and the PLANCK surveys in the future. Studies of the Galaxy in polarization have been made some years ago indicating high percentage of linear polarization in various directions. More recent work with good angular resolution has shown spectacular polarized intensity structures in selected regions. Low-frequency data with good angular resolution are urgently required for the interpretation of these features.

Observations of nearby galaxies in radio continuum (both total power and polarized intensity) have given us the possibility to study magnetic fields in objects at known distances. Polarization observations of nearby galaxies have confirmed the existence of regular magnetic fields in practically every object so far studied. Originally data were obtained from large single-dish telescopes, notably from Effelsberg and Parkes. These data were greatly enhanced by the addition of higher resolution components from the VLA and ATCA respectively. These results indicate surprisingly homogeneous magnetic fields in most galaxies. High angular resolution observations with the GMRT at lower radio frequencies will add a new dimension to the data on galaxies.
Low frequency Carbon Recombination Lines
Authors: Konovalenko A. A.
Published: July 2016

Low frequency carbon recombination lines with wavelengths up to twenty five meters became important means of low density interstellar plasma diagnostic. Over the past twenty years impressive amount of information was obtained for Cassiopeia A and other galactic directions.
A Galactic Plane Survey in the CO (2-1) Line with the 60 cm Telescopes to Address Physical Condition of the Interstellar Matter
Authors: Handa T. , Hasegawa T. , Morino J.I. , Sawada T. , Sakamoto S. , Usuda K.S. , Luna A. , Bronfman L. , Hayashi M.
Published: July 2016

To address its temperature and density we made observations of the galactic plane in CO (2-1) line with VST1 and VST2. Using a kinetic model we estimate the volume emissivities and the line intensity ratio as a function of galactocentric radius. Using data in the first and 4th quadrants separately we got shallow gradient in the both quadrants; at the smaller radius is the higher in ratio. The gradient is contributed by less bright pixels in the l-v diagram, suggesting molecular gas in interarm is different along the galactocentric radius but in arm is not.
Orthogonal Polarization Modes from PSR B0301+19 and B0355+54
Authors: Gangadhara R.T.
Published: July 2016

We have analyzed the single pulse data of PSR B0301 + 19 and B0355+54 at 1.41 GHz taken from 100-m Effelsberg radio telescope of MPIfR on 22 and 30 August, 1996. The gray-scale maps are made for the polarization quantities to study the distribution of polarization modes at different pulse longitudes. Circular polarization flips the sign at the pulse center in the case PSR B0355+54 but in the case of PSR B0301 + 19 it is mostly positive throughout the pulse. We find the evidence for depolarization that most of the pulsar radiation depolarizes due to the superposition of orthogonal polarization modes.
Low frequency Observations of Millisecond Pulsars
Authors: Kuzmin Arkady
Published: July 2016

We present results of the first low frequency measurements of integrated profiles and flux densities of a large set of millisecond pulsars at 102 MHz. Combining our observations with data at higher frequencies, borrowed from literature we performed the comparative analysis of the frequency dependence of profile width and spectra of millisecond and normal pulsars, searching for similarities and differences between their properties. Millisecond pulsars are differ to “normal” ones in much weaker frequency dependence of the width of integrated profile and the absence of the low- frequency turn-over in pulsar spectra.
New Radiation Formulae of Relativistic Electrons in Curved Magnetic Field Lines
Authors: Sobolev Ya.M.
Published: July 2016

Radiation mechanism for relativistc charged particles spiraling along curved magnetic field is considered. Emission from many electron revolutions around force line is taken into account.
Frequency Spectra Fluctuations in the Radio Interferometry of Polarized Radiation
Authors: Olyak M.R.
Published: July 2016

The presence of a longitudinal magnetic field is shown to lead to the appearance of an additional component of the frequency spectrum of the linearly polarized emission. This component is proportional to the spectrum of normal waves phase difference fluctuations. The fluctuations spectra baseline dependence of a linear polarized radiation is periodical near zero frequency, one is absent in the high frequency ranges and such dependence has different character in magnetoactive plasma with electron density irregularities and in plasma with a random magnetic field.
Low Frequency Planetary Radio Astronomy
Authors: Sault R.J.
Published: July 2016

This paper reviews planetary radio astronomy at low frequencies. At least at frequencies observable from the Earth's surface, this field has been almost solely the study of Jovian magnetospheric emissions. With the discovery of extra-solar planets, and the potential for new telescopes with large collecting areas, we may well see more objects and emission mechanisms becoming detectable.
Solar Observation with Miyun Radio Telescope
Authors: Zhang X.Z. , Piao T.Y. , Kang L.S. , Pang L.
Published: July 2016

The Miyun Synthesis Radio Telescope (MSRT), Beijing Astronomical Observatory, has been used in observation of the Sun as an one dimension heliograph. Daily observation with MSRT and other two single dishes for total power measurement have been performed since May,1998.(Zhang, X.Z., 1999)
The Universe at Very Low Radio Frequencies
Authors: Braude S. Ya. , Konovalenko A.A. , Megn A.V.
Published: July 2016

The world biggest decameter wavelength radio telescope UTR-2 and VLBI system URAN, as well as main observational programs carried out with the above mentioned instruments, are described.
High dynamic range, Interferences Tolerant, Digital Receivers for Radioastronomy: Results and Projects at Paris and Nanay Observatory
Authors: Rosolen Carlo , Lecacheux Alain , Gerard Eric , Clerc Vincent , Denis Laurent
Published: July 2016

Radio astronomy in the decameter to centimeter wavelength range is facing new challenges because of man made interferences due to increasing needs in telecommunications. At the Radioastronomy department of Paris Meudon Observatory, we have been working since four years on high dynamic range digital receivers based on Digital Signal Processors (DSP). The first achievement is a digital spectro- polarimeter devoted to spectroscopy of astrophysical radiation in decameter range, now in operation at the Nancay Decameter array. The block diagram of the receiver includes a high dynamic range analogue section followed by a 12 bits analogue to digital converter. The digital part makes use of high power, programmable digital circuits for signal processing, arranged in a dedicated parallel architecture, able to compute in real time the power spectrum and the correlation of the input signals. This receiver was also used, as spectrometer backend, at Nancay decimetric radiotelescope and has performed very well in the presence of very strong interferences. We are presently working on a new digital receiver with broader bandwidth. The objective is 2 × 25 MHz band with at least 60 dB dynamic range. This new receiver will use additional computation power in order to recognise and avoid man made interferences which corrupt the radio astronomical signal. At the Nancay Radioastronomy Observatory, we have started to develop a new digital configurable receiver with 8 times 25 MHz band and ten thousand channels. For low frequency radioastronomy, direct spectrum computation technique is really powerful and offers new capabilities for real time interferences excision. Fig. 1 shows pulsar observations in the presence of interference made with the DSP receiver on the UTR-2 radiotelescope. Fig. 2 shows the effect of satellite interfernce on OH observations made with the Nancay telescope. Fig. 3 shows the block diagram of the DSP system and demonstrates how offline excision of interference in the frequency time-domain enables recovery of the signal. The final spectrum had 960 minutes integration on and off source and took 8045 minutes of procession on a 450 MHz Pentium II.
Flux Tubes and Dynamos
Authors: Schüssler M.
Published: July 2016

The structure of solar surface magnetic fields, the way they erupt from the the convection zone below, and processes like flux expulsion and fragmentation instabilities support the view that magnetic flux in a stellar convection zone is in an intermittent, fragmented state which can be described as an ensemble of magnetic flux tubes. Depending on size and field strength, the dynamics of magnetic flux tubes can strongly differ from the behavior of a passive, diffuse field which is often assumed in conventional mean-field dynamo theory. Observed properties of active regions like emergence in low latitudes, Hale's polarity rules, tilt angles, and the process of sunspot formation from smaller fragments, together with theoretical considerations of the dynamics of buoyant flux tubes indicate that the magnetic structures which erupt in an emerging active region are not passive to convection and originate in a source region (presumably an overshoot layer below the convection zone proper) with a field strength of at least 105 G, far beyond the equipartition field strength with respect to convective flows. We discuss the consequences of such a situation for dynamo theory of the solar cycle and consider the possibility of dynamo models on the basis of flux tubes. A simple, illustrative example of a flux tube dynamo is presented.
Non-Linear Diamagnetic Transport of the Large-Scale Magnetic Field in the Solar Convection Zone
Authors: Krivodubskij V.N.
Published: July 2016

The mean magnetic field transport due to inhomogeneity of the turbulence intensity is considered taking the field back reaction on motion into account. In spite of the magnetic quenching, the downward diamagnetic pumping is still powerful enough to keep the fields of 3 to 4 kG strength near the SCZ base against the magnetic buoyancy.
Bifurcations and Symmetry-Breaking in Simple Models of Nonlinear Dynamos
Authors: Weiss N.O.
Published: July 2016

Low-order models of nonlinear dynamos can be used to investigate generic properties of more realistic mean field dynamos. Reducing the partial differential equations to a set of ordinary differential equations makes it possible to explore the bifurcation structure in considerable detail and to compute unstable solutions as well as ones that are stable. Complicated time-dependent behaviour is typically associated with a homoclinic or heteroclinic bifurcation. Destruction of periodic orbits at saddles or saddle-foci gives rise to Lorenz-like or Shil'nikov-like chaotic oscillations, while destruction of a quasiperiodic orbit leads to aperiodically modulated cycles. Changes in spatial symmetry can also be investigated. The interaction between solutions (steady or periodic) with dipole and quadrupole symmetry gives rise to a complicated bifurcation structure, with several recognizably different mixed-mode solutions; similar behaviour has also been found in spherical dynamo models. These results have implications for the expected behaviour of stellar dynamos.
Stationary Turbulent Dynamo as Spontaneous Symmetry Breaking
Authors: Hnatich M.
Published: July 2016

The large-scale magnetic field generation by the turbulent motion energy, known as turbulent dynamo [1], is perspective candidate to explain the observed stationary magnetic fields of cosmic objects.
Inverse Energy Cascade in Advanced MHD Turbulence (the RNG Method)
Authors: Kleeorin N. , Rogachevskii I.
Published: July 2016

The nonlinear (in terms of the large-scale magnetic field) effect of the modification of the magnetic force by an advanced small-scale magnetohydrodynamic (MHD) turbulence is considered. The phenomenon is due to the generation of magnetic fluctuations at the expense of hydrodynamic pulsations. It results in a decrease of the elasticity of the large-scale magnetic field.

The renormalization group (RNG) method was employed for the investigation of the MHD turbulence at the large magnetic Reynolds number. It was found that the level of the magnetic fluctuations can exceed that obtained from the equipartition assumption due to the inverse energy cascade in advanced MHD turbulence.

This effect can excite an instability of the large-scale magnetic field due to the energy transfer from the small-scale turbulent pulsations. This instability is an example of the inverse energy cascade in advanced MHD turbulence. It may act as a mechanism for the large-scale magnetic ropes formation in the solar convective zone and spiral galaxies.
Galactic Dynamos — a Challenge for Observers
Authors: Beck Rainer
Published: July 2016

Results of linear αΩ-dynamo models are confronted with radio polarization observations of spiral galaxies. The general distribution of polarized emission and the magnetic field pitch angle can be described with sufficient accuracy. The occurrance of systematic large-scale variations in Faraday rotation (RM) is the strongest argument in favour of dynamo theory. However, the predominance of axisymmetric SO modes could not be confirmed by observations; S1 modes are about equally frequent. The azimuthal variations of field pitch angles and, in two cases, the phases of the RM variations are inconsistent with a classical αΩ-dynamo. Locally deviating RM values indicate field lines bending out of the plane. There is increasing evidence that galactic fields cannot be described by simple dynamo modes. This calls for more realistic dynamo models, taking into account non-axisymmetric velocity fields and galactic winds.

Interpretation of radio observations is difficult because Faraday depolarization can seriously affect the data. Observations of small-scale field structures are summarized which show the path for future research. Instrumental needs for such investigations are discussed.
The Magnetic Field of M 83
Authors: Neininger N. , Klein U. , Beck R. , Wielebinski R.
Published: July 2016

This southern galaxy with its fairly regular pattern is well suited to study the influence of a bar onto the magnetic field in a galaxy. With its low inclination of 24° it provides a geometry similar to M 51. Also the magnetic field strength of 11±2 μG is in the same range.
On the Parametric Resonance in Thin Disk Galactic Dynamo
Authors: Kuzanyan K.M. , Sokoloff D.D.
Published: July 2016

The absence of parametric resonance by generation of the large-scale bisymmetric magnetic field in the framework of the simplest thin disk galactic dynamo model is shown.
Observational Properties of Helical Magnetic Fields
Authors: Urbanik M. , Otmianowska-Mazur K.
Published: July 2016

The model of the polarized emission from a spiral galaxy similar to M31, containing helically twisted magnetic field has been constructed. Helical magnetic field was found to cause a specific asymmetry of the distribution of the polarized brightness of the galactic disk.
Dynamical Galactic Halos
Authors: Breitschwerdt D. , Völk H.J. , Ptuskin V. , Zirakashvili V.
Published: July 2016

It is argued that the description of the magnetic field in halos of galaxies should take into account its dynamical coupling to the other major components of the interstellar medium, namely thermal plasma and cosmic rays (CR's). It is then inevitable to have some loss of gas and CR's (galactic wind) provided that there exist some “open” magnetic field lines, facilitating their escape, and a sufficient level of self-generated waves which couple the particles to the gas. We discuss qualitatively the topology of the magnetic field in the halo and show how galactic rotation and magnetic forces can be included in such an outflow picture.
Generation of the Seed Magnetic Field
Authors: Lazarian A.
Published: July 2016

Two mechanisms of the galactic seed field generation are discussed. One of the mechanisms implies a direct generation of the seed magnetic field through a battery process (Lazarian 1992a). The other accounts for the possibility of the preliminary amplification of the magnetic field on a scale of molecular clouds (Lazarian 1992b). This means that the galactic dynamo can feed on the non-zero average value of the magnetic field amplified by such a small-scale dynamo. It is shown that both mechanisms can generate an adequate seed field. These two scenarios of the seed magnetic field generation can be distinguished by an analysis of the present day galactic magnetic structure.
A New Numerical Scheme in the Solution of the Geodynamo Z-Model
Authors: Hejda Pavel , Anufrijev Alexander P.
Published: July 2016

The hydromagnetic dynamo Z-model represents a nonlinear dynamic system. Its steady-state solution is derived by step-by-step integration of parabolic partial differential equations of the second order with the use of the finite difference method. Until now, two methods have been used: the semi-implicit method in which the θ-diffusion was carried out implicitly while the r-diffusion explicitly, and the implicit method in which the complete diffusion was carried out implicitly. In the present contribution, a combined semi-implicit method is suggested which reflects not only the singularity at the coordinate system origin but also the decreasing mesh size near the core-mantle boundary. This procedure preserves the advantage of semi-implicit methods and, simultaneously, increases the stability in the most critical boundary layer.
Ekman-Hartmann Boundary Layers and the Length of Day Variations
Authors: Kleeorin N. , Rogachevskii I. , Ruzmaikin A.
Published: July 2016

In the first issue of Journal of Fluid Mechanics Ian Proudman published a paper on the dynamical properties of a fluid between two concentric rotating spheres (Proudman, 1956). The angular velocities of the spheres were assumed only slightly different and the Reynolds number of the flow was large. It was found under non-slip boundary conditions that the cylindrical surface that touches the inner sphere and parallel to the axis of rotation is a singular surface in which velocity gradients are very large. Outside the cylinder the fluid rotates as a rigid body with the same angular velocity as the outer sphere. Inside the cylinder the fluid rotates with an angular velocity intermediate to the angular velocities of the spheres and there is also a meridional circulation. Later Stewartson (1966) presented a detailed investigation of structure of the shear layer near the cylindrical surface. One of the present authors (Ruzmaikin, 1989) pointed out a possible geophysical importance of these solutions. The liquid part of the Earth core occupying a shell between the inner solid core and the rock mantle can be considered as the fluid between two rotating spheres.
Nonlinear Dynamo of Magnetic Fluctuations and Flux Tubes Formation in the Ionosphere of Venus
Authors: Kleeorin N. , Rogachevskii I. , Eviatar A.
Published: July 2016

Magnetic field observations in the dayside ionosphere of Venus revealed the magnetic flux ropes (Russell and Elphic 1979). General properties of these small-scale magnetic field structures can be explained by the theory of magnetic fluctuations excited by random hydrodynamic flows of ionospheric plasma.

A nonlinear theory of the flux tubes formation based on the Zeldovich's mechanism of amplification of the magnetic fluctuations is proposed. A nonlinear equation describing the evolution of the correlation function of the magnetic field can be derived from the induction equation, the nonlinearity being connected with the Hall effect. The large magnetic Reynolds number limit allows an asymptotic study by a modified WKB method.

On the basis of this theory it is possible to explain why the flux tubes are not observed if there is a strong regular large-scale magnetic field when the ionopause is low. The theory predicts the cross section of the flux ropes in the ionosphere of Venus and the maximum value of the magnetic field inside the flux tube.
Solving the Mystery of the Periodicity in the Seyfert Galaxy NGC 6814
Authors: Madejski Greg M. , Done Chris , Turner T. Jane , Mushotzky Richard F. , Serlemitsos Peter , Fiore Fabrizio , Sikora Marek , Begelman Mitchell C.
Published: July 2016

The reports of periodic X–ray emission from the Seyfert galaxy NGC 6814 have motivated a number of exotic models for the active nucleus. Our ROSAT observation shows that while the nucleus of NGC 6814 is indeed an X–ray emitter, the periodicity is due to another source, most likely a Galactic accreting binary system, ∼ 37 arc min away.
Variability in the Millimeter and Radio Domains
Authors: Valtaoja Esko
Published: July 2016

The radio domain spans only a small fraction of the total electromagnetic spectrum, and is for most active galaxies energetically insignificant in comparison with higher frequencies. However, only in the radio regime can we obtain continuous fluxcurves and be certain that we are not missing anything. We also believe we know where the radiation comes from, and by which mechanisms it is produced. Furthermore, since VLBI generally cannot resolve the smallest core components, multifrequency continuum monitoring remains our only way to study the innermost radio cores of AGN. Finally, continuum monitoring is cheap (although time-consuming) in comparison with most other methods, and therefore we can observe many more sources and with far better time coverage.
Multiwavelength Experiments on AGN: Reverberation Experiments
Authors: Wamsteker W. , Vio R.
Published: July 2016

The nature of the successful reverberation campaigns on variable active galaxies is summarized. A general summary of the completed campaigns is given. A discussion of the results of the first order (CCF) analysis is given and some comments are made on the directions needed to obtain more physcally meaningful solutions to the inversion problem presented by such observations of the sources of activity in the centers of active galaxies
The Structure of the Broad Emission Line Region as Shown by Variability Monitoring
Authors: Krolik Julian H.
Published: July 2016

The various methods used to infer the physical conditions and location of the material responsible for broad line emission in AGN are reviewed. Recent efforts have focussed on reverberation mapping, whose basic concepts and experimental constraints are discussed. A new method for analyzing the results of monitoring experiments, regularized linear inversion, is presented. This method is then applied to published data from the 1989 IUE campaign on NGC 5548, and the results found contrasted with those obtained by the previous standard method, maximum entropy.
Models for Variability in AGNs
Authors: Rees Martin J.
Published: July 2016

In this talk I shall address three different processes relevant to continuum variability in AGNs. The first two refer to the physical conditions in the regions responsible for the non-thermal emission, and the implications of high brightness temperatures. The third is the distinctive type of flare that results when a star is tidally disrupted by a massive black hole; this process, which merits much further study, it likely to be specially important as a diagnostic of physical conditions in low-luminosity nearby nuclei.
Variability and Slim Accretion Disks
Authors: Wallinder F.H.
Published: July 2016

Many compact galactic and extra-galactic sources have a luminosity in the slim accretion disk regime, i.e. L/LE ∼ 1, where LE is the Eddington luminosity. The correspondingly large accretion rates diminish the relevance of variability interpretations based on the thin disk model. This paper explores the possible connection between variability in AGN and local instabilities in slim disks, and points out some relevant areas of future research.
Unified Models: Religion and Science
Authors: Antonucci Robert
Published: July 2016

The Unified Model states that the classification of individual AGN is a function of orientation, and that orientation effects are key to understanding the different classes. In its most extreme form, it states that every AGN has a featureless continuum (FC) source and a broad line region (BLR), both enclosed in an opaque torus. The torus is perpendicular to the associated radio structure axis. For the powerful radio sources (in Elliptical galaxy hosts), the jets undergo bulk relativistic motion, giving rise to phenomena such as superluminal motion associated with the blazar class. All strong radio sources have diffuse double radio lobes, although in the blazars one is sometimes seen projected onto the other. To take this to the extreme, we can suppose that all opaque tori are made of dust and have the same opening angle and that the radio jets are all narrow and have the same bulk-motion Γ factor.
X-ray Luminous Non-Seyfert Galaxies
Authors: Ward M.J. , Hughes D.H. , Dunlop J.S. , Appleton P.N.
Published: July 2016

There are now well established classes of X-ray emitting galaxies, which exhibit characteristic ranges of luminosity, for example Green et al. (1992). The ROSAT all sky survey, has detected a relatively small number of galaxies whose overall properties do not appear consistent with any of these classes. We discuss whether these X-ray luminous galaxies (XLGs) are the extreme end of the luminosity range of starburst galaxies, or whether they represent a new X-ray class of AGN.
Electron Energy Distributions of AGNs in the Thin Synchrotron Limit. II. Peaked Electron Energy Spectra of Blazars and OVV Quasars
Authors: Cruz-González Irene , Salas Luis , Carrasco Luis
Published: July 2016

We analyse multifrequency quasi-simultaneous observations of AGNs with the Inverse Synchrotron Transform (IST) method described in Salas et al. (1993) and in Paper I (this conference).

The observational spectral energy distribution of blazars and OVV quasars used as applications of the IST method were obtained from multifrequency quasi-simultaneous observations of Landau et al. (1986) and Brown et al. (1989). The application of the method requires good spectral coverage, since the presence of gaps larger than ≈ 0.75dex can introduce ficticious peaks. We present the analysis for: 1749+096, 0735+178, 1308+326, 3C273, 3C345, 3C279, OJ287, OJ049, 3C216, 4C39.25.

The observed spectra are transformed to the source rest frame, the inverse transform is calculated over the whole spectrum to derive the electron energy spectra, which gives the amount of energy emitted in each characteristic frequency. Our results show that the electron energy spectra, Ψ(vc), of blazars and OVV quasars consists mainly of 4 or 5 well defined peaks superimposed on a down curved continuum. This indicates that the source radiates mainly around certain values of the electron's critical frequency (or energy, since vc ∞ B E2). These peaks are consistent with injection of fresh relativistic particles, occuring in pulses of quasi-monoenergetic groups.

The separation between successive peaks (Δp) is ≈ 1.2 dex in critical frequency, and is characteristic for each object. The peaks in the radio region contain approximately the same number of electrons, consistent with evolution given by the continuity equation for constant B. While in the OIR region, the energy radiated increases towards lower frequencies.

A comparison of Δp with Lbol and Lradio, and jet parameters such as, jet velocity and B1pc (inferred from the relativistic jet models of Blandford and Königl 1979) given by Cruz-Gonzàlez and Carrillo (1991), shows that Δp increases with jet velocity, stronger B fields imply smaller Δp, and that it is not correlated with Lbol, but is apparently correlated with Lradio.

The Inverse Synchrotron Transform method applied in this paper is a powerful tool in the analysis of spectral energy distributions of AGNs.
Simultaneous Optical to Near-IR Observations of Blazars
Authors: Falomo R. , Bersanelli M.
Published: July 2016

We obtained simultaneous optical spectrophotometry (4000-8000 Å) and near-IR photometry (JHKL) for 34 blazars, with repeated observations for 21 of them. All the data were taken at ESO and cover a period of 3 years with a typical time interval of 6 months. The observations were corrected for interstellar extinction and analyzed using a uniform procedure. This allows to form a large and homogeneous data set of optical-near-IR measurements of blazars emission.