bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotation and Stellar Evolution
Authors: Kippenhahn R. , Thomas H.-C.
Published: July 2016

Does rotation influence stellar evolution? Does it cause observational effects other than line broadening? Can rotation be responsible for mixing of chemical elements throughout the star? Do evolved stars have rapidly rotating cores? This, for instance, is of interest if one wants to compute the details of supernova events. We are not sure whether rotation has really important effects on the life of a star. There might be no rapidly rotating cores. If we think that a fossile general magnetic field couples core and envelope of an evolved star, the core will always be slowed down by the big inertial momentum of the outer regions.
The Influence of Rotation on Horizontal Branch Stars and on RR Lyrae Pulsational Properties
Authors: Castellani V.
Published: July 2016

The occurrence of rotation in Globular Cluster stars has been suggested (see e.g. Renzini 1977) as a mechanism producing the observed colour spread in actual Horizontal Branches. If this is the case, canonical results on evolutionary properties of HB stars have to be revisited in order to account for rotation-driven structural variations: faster Main Sequence rotators delay the He flash increasing the mass-size Mc of the He core at the flash and loosing a greater amount of mass during the Red Giant stage.
Viscosity, Thermal and Electrical Conductivities in Turbulent Convection
Authors: Unno Wasaburo , Nakano Tohru , Kondo Masa-aki
Published: July 2016

Turbulent diffusivities are often used for representing nonlinear interactions of turbulent elements on the motion of a larger scale. In turbulent convection, the average life of a representative element is substantially lengthened by bouyancy. Taking this effect into account, we calculate turbulent viscosities, thermal and electrical conductivities for Boussinesq fluids on the basis of a spectral theory of turbulent convection (Nakano, Fukushima, Unno, and Kondo, 1979). The effect of bouyancy results in the increase of turbulent diffusivities, compared with the case without bouyancy. We also propose the generalization of the method such that a stellar convection zone can be theoretically constructed without recourse to the mixing length.
On the Number Ratio of Horizontal Branch Stars to Red Giant Stars in Globular Clusters
Authors: Arimoto N. , Simoda M.
Published: July 2016

The number ratios of horizontal branch stars to red giant stars were obtained for globular clusters and Draco dwarf galaxy and the helium abundance was estimated using model results without semiconvection zone (SCZ) and with fully developed one. The analysis was confined to the four clusters (M4, M5, M13, and 47 Tuc) and the Draco galaxy, for which fairly precise star counts had been carried out. The effect of the difference in radial distribution between horizontal and red giant branch stars were taken into account, if necessary. The statistically significant difference in R exists among these objects. The cause may be the difference in the helium abundance and/or in the development of the SCZ. In the case of the fully developed SCZ, the helium abundance for M5 and Draco is appreciably smaller than the value given by the big-bang cosmology. It may be taken as an evidence against the full development of the SCZ for the horizontal branch stars in these objects.
A New Approach to the Analytic Evaluation of Thermonuclear Reaction Rates
Authors: Haubold H. J. , John R. W.
Published: July 2016

In our paper (Haubold and John 1978) we succeeded in a closed-form evaluation of the reaction rate by means of a special function, known as Meijer's G-function

This representation of the rate is appropriate to perform analytical operations (e.g. for the computation of energy generation in a fusion plasma).
Stellar Collapse and Nascent Neutron Stars
Authors: Mazurek T. J.
Published: July 2016

The collapse of dense cores in massive stars proceeds as follows. Initially, leptons dominate the pressure because neutrinos become trapped at high densities. This results in the formation of a cool inner core that collapses homologously. At around nuclear densities the pressure from nucleons increases rapidly and halts the collapse, giving a core bounce. A shock forms at the surface of the inner core and propagates into the infalling envelope. These basic features have emerged in the hydrodynamic studies of collapse by various researchers. However, the question of final outcome of collapse is unresolved at present. The evolution of the core after the shock has propagated through the envelope has not been addressed in detail. This communication summarizes some current results of the author's ongoing study of stellar collapse.
Stability Against Radial Perturbations of Slowly Rotating Neutron Stars
Authors: Arai Kenzo , Kaminishi Keisuke
Published: July 2016

The dynamical equations governing pulsation in rotating neutron stars are derived in the framework of general relativity. Stellar models are constructed by using a realistic equation of state for cold neutron matter. Small radial displacement and slow rotation are treated as perturbations on spherically symmetric body. In these models the maximum masses are 1.761 M⊙ at the central density 3.461 × 1015 g cm−3 for a sequence of nonrotating configurations and 2.165 M⊙ for rotating models with the critical angular velocity (GM/R3)½.
On the Detection of Heavy Primaries above 1014 EV
Authors: Gaisser T. K. , Stanev Todor , Freier Phyllis , Waddington C. Jake
Published: July 2016

Knowledge of the chemical composition is fundamental to understanding the origin, acceleration and propagation of cosmic rays. At energies much above 1014 eV, however, the detection of single primary cosmic rays is at present impossible because of their low flux, and the only source of information is from the cascades initiated by energetic primary particles in the atmosphere–the extensive air showers (EAS). A similar situation exists for the study of hadronic interactions above 1015 eV. A recent EAS experiment (Goodman et al., 1979) suggests the possibility that the spectrum becomes increasingly rich in heavy nuclei as the total energy per nucleus approaches 1015 eV. Above that energy the overall spectrum steepens and the question of composition is almost completely open.
Interstellar and Intracluster Tunnels and Acceleration of High-Energy Cosmic Rays
Authors: Ferrari A. , Masani A.
Published: July 2016

The present evidence about the origin of high-energy cosmic rays is that two ranges exist: one below 1018 eV related with galactic sources, and one up to 1020 eV, corresponding to extragalactic processes (Kiràly et al. 1979). However the continuity of the spectrum indicates that the physical mechanisms must be correlated. In the global energetics the spectral range above 1012 eV is irrelevant and the bulk of CR energy is actually provided by supernovae, pulsars, X-ray binaries, etc. in the Galaxy. Nevertheless none of these objects seems capable of producing CR above 1015 eV/nucleon. We have investigated the possibility that the acceleration at higher energies is statistical, taking place over a hierarchy of scales. A model has been developed in terms of the quasi-linear theory of particle acceleration by MHD turbulence. Cosmic rays with ≲1015 eV/nucleon injected by single sources into interstellar space undergo momentum diffusion by stockastic interaction with long wavelength MHD perturbations; small wavelength modes provide pitchangle scatterings. These MHD perturbations, Alfvèn and last magnetosonic waves, are generated by the dynamic interaction of supernova remnants with the interstellar medium. From observations (Jokipii 1977), the range of possible wavelengths extends from the proton gyroradius to the size of the so-called “superbubbles”, up to 100 pc, with a power-law spectrum. Correspondingly acceleration is efficient up to 1018 eV/nucleon; in fact for B 10−3 + 10−5 G, n = 0.01 ÷ 1 cm−3 and L = 0.1 ÷ 100 pc, we find that the acceleration timescale

(ε = eBL is the maximum allowed energy) is always shorter than the time scales of losses and turbulent structure lifetimes; α = 3.5 ÷ 4 is the speciral index of turbulent modes. Contrary to the original Ferm i mechanism, in this theory the time scale for acceleration up to any energy ε is fixed by the final phase, previous steps being negligible.
Compact Radio Sources
Authors: Pauliny-Toth I.I.K.
Published: July 2016

The observational data on the radio properties of compact radio sources are presented, including their radio spectra, their occurence, and their structures, as well as the variations of the structures in the “superluminal” sources.
Neutrino Emission from Galaxies and Mechanisms for Producing Radio Lobes
Authors: Silberberg R. , Shapiro M. M.
Published: July 2016

In the context of the proposed DUMAND-type detector for high-energy neutrinos, it is important to estimate the neutrino fluxes from powerful radio galaxies. This would indicate whether a detectable event rate can be expected, and would help choose among possible mechanisms for generating the radio lobes associated with many such galaxies. Among the models that have been proposed are: (a) a beam from the galactic core that interacts with the extragalactic medium; (b) ejection of clouds of plasma, particles, and magnetic fields into the lobes, either in an explosive burst, or by diffusive escape; (c) black holes or spinars ejected from the galactic nucleus by a gravitational slingshot mechanism.
Cosmic-Ray Self-Confinement in the Hot Phase of the Interstellar Medium
Authors: Cesarsky Catherine J. , Kulsrud Russell M.
Published: July 2016

It is well known that, when cosmic rays stream along the field lines of the galactic magnetic field at a velocity which exceeds the Alfven velocity in the medium, they excite hydromagnetic waves of a wavelength comparable to their Larmor radius. These waves, in turn, scatter the cosmic rays, forcing them to reduce their bulk speed (Wentzel 1974, and references there-in). In a stationary situation, the bulk speed of the cosmic rays will depend on their scale height, and on the strength of the relevant damping mechanisms affecting the waves. Isotope observations imply that cosmic rays of energy ≲ 1 GeV are confined in the galaxy for a time ~ 2.107 yrs (Garcia-Munoz et al. 1977); a simple interpretation of the composition data in the energy range 1–100 GeV implies that the confinement time T decreases as the rigidity ε = cp/eZ increases: Tα ε−a, with a = 0.3 − 0.5. This energy dependence of the confinement time should hold at least up to ε ≃ 3.106 GV, to be consistent with the lack of structure in the cosmic ray spectrum in the range 10–3.106 GV (see Cesarsky 1980 and references therein).
The X-Ray Sky
Authors: Trümper J.
Published: July 2016

Today X-ray astronomy encompasses almost all astronomical objects, from nearby stars to the most distant quasars. We review a few selected recent results obtained by X-ray astronomy on galactic objects like normal stars, supernova remnants, neutron stars and the black hole candidate Cyg X-1.
Quasar Contribution to the X-Ray Background
Authors: Kembhavi Ajit , Fabian A. C.
Published: July 2016

Recent observations by the Einstein Observatory have shown that a majority of known quasars are powerful X-ray emitters. The 107 objects observed as of Feb. 1980 (Zamorani et al. 1980) have X-ray, optical and radio luminosities scattered over a wide range. Until a large enough X-ray selected sample of quasars becomes available, it is necessary to study statistical correlations in the available sample, so that some insight into X-ray production may be obtained, and the contribution of quasars to the X-ray background estimated.
Gamma Rays from Cosmic Rays
Authors: Wolfendale A. W.
Published: July 2016

It is shown that there is evidence favouring molecular clouds being sources of γ-rays, the fluxes being consistent with expectation for ambient cosmic rays interacting with the gas in the clouds for the clouds considered. An estimate is made of the fraction of the apparently diffuse γ-ray flux which comes from cosmic ray interactions in the I.S.M. as distinct from unresolved discrete sources. Finally, an examination is made of the possibility of gradients of cosmic ray intensity in the Galaxy.
High Energy γ-Rays from the Direction of the Crab Pulsar
Authors: Dzikowski T. , Grochalska B. , Gawin J. , Wdowczyk J.
Published: July 2016

A search has been made for very high energy photons from the direction of the Crab Pulsar using the Lodz extensive air shower array. This device is particularly suitable for such a study because it consists of a large muon detector which can be used to search for the characteristic muon poor showers.
High Energy Gamma Rays from Accretion Disc
Authors: Giovannelli F. , Karakula S. , Tkaczyk W.
Published: July 2016

In the case of spherical symmetric accretion into a black hole, the matter may be heated up to the temperature KT = 0.1 mpc2 (Kolykhalov and Sunyaev, 1979). In such a hot plasma inelastic collisions of protons may produce Π° which is the gamma quantum source.

In this work we determined γ-rays production spectrum in the comoving plasma reference frame, expected γ-rays spectrum for the case of spherica symmetric accretion of matter into a black hole and the upper limit to the number of black holes in Galaxy is evaluated.
High Energy Phenomena in the Sun
Authors: Chiuderi Claudio
Published: July 2016

High energy phenomena in the solar physics context, simply means solar flares. To be sure, the energies attained during flares are certainly not very impressive on a cosmic-ray scale. The most energetic particles belong the GeV range, the highest temperatures are of the order of 107 K, γ-ray emission is occasional and the total energy emitted remains below 1033 ergs for all the flares so far observed. Apart from an absolute energy scale, flares are also energetically irrelevant on a solar scale. In fact in a large flare a few units in 1032 ergs are emitted, with a total duration of about one hour and a total surface area involved of a few units in 10−4 of the solar surface. Recalling the values of the luminosity, L⊙ ≃ 4 × 1033 erg s−1 and the solar flux F⊙6.3 × 1010 erg cm−2s−1, we see that
On 3-He Rich Solar Particle Events
Authors: Möbius E. , Hovestadt D.
Published: July 2016

Extensive measurements of the composition of energetic solar flare particles have revealed the frequent occurrence of solar flares with large enrichments of 3He and heavy ions compared to the composition of the solar atmosphere. The basic characteristics of these events can be summarized as follows:

–

3He/4He-ratios up to more than 1 are observed

–

the 3He/4He-ratio increases with energy

–

no comparable enhancement of 2H or 3H is found

–

there is a strong correlation of 3He and heavy ion enrichment.
ATMOSPHERIC STRUCTURE OF THE OUTER PLANETS FROM THERMAL EMISSION DATA
Authors: Orton Glenn S.
Published: July 2016

Determination of atmospheric temperature structure is of paramount importance to the understanding of planetary atmospheric structure. The most powerful methods for determining atmospheric structure exploit the opacities provided by the collision induced H2 dipole and the ν4 fundamental of CH4. In addition to earth-based observations, useful measurements of thermal emission from Jupiter and Saturn have been or soon will be made by several spacecraft, with results cross-checked with independent radio occultation results. For Uranus and Neptune, only a limited set of whole-disk earth-based data exists. All the outer planets show evidence for stratospheric temperature inversions; temperature minima range from about 105 K for Jupiter and 87 K for Saturn, to roughly 55 K for Uranus and Neptune. In addition to better data, remaining problems may be resolved by better quantitative understanding of gas and aerosol absorption and scattering properties, chemical composition, and non-LTE source functions. Ultimately, temperature structure results must be supplemented by quantitative energy equilibrium models which will allow some meaning to be given to the relationships between such characteristics as temperature, clouds, incident solar and planetary radiation, and chemical composition.
EMISSION LINE OBSERVATIONS OF H II REGIONS
Authors: Lacy J. H.
Published: July 2016

Optical observations provide a wealth of information on atomic abundances, the excitation (level of ionization), the kinetic temperature, and the density of the gas in H II regions. However, obscuration by dust limits optical observations of galactic H II regions to those which are nearby (within a few kpc) and which are unobscured by the molecular clouds out of which they are formed (and so generally evolved). Radio observations are unhampered by extinction but provide much more limited information. The abundance of H+, He+ and occasionally C+ can be determined as well as the kinetic temperature of the gas, but no direct information on the abundance of other species or the excitation is available.
INTERPRETATION OF THE LARGE-SCALE EMISSION FROM THE GALACTIC PLANE
Authors: Drapatz S.
Published: July 2016

To obtain information on the large-scale structure of our Galaxy, one has to investigate the radiation in the short-wavelength and long-wavelength portion of the electromagnetic spectrum where attenuation throughout the whole galactic disk is very low: gamma-radiation on the one-hand side and infrared and radio radiation on the other side. But since most of the different modes of radiation are generated by interaction of two or more basic galactic constituents one derives only indirect information on a specific component. To come as close to a unique solution as possible the results of as many different spectral regions as possible should be combined. From this point of view it is very encouraging that infrared astronomy has been entering the field and will continue to contribute in the years to come. While gamma-radiation presents mainly information about the cosmic rays and the interstellar gas and radio astronomy about early-type stars and the interstellar gas, infrared astronomy has opened a new way to investigate a major fraction of the stellar population and the interstellar dust. The information is contained in the diffuse galactic emission, which is observed at low galactic latitudes with a field of view large enough to discriminate against point sources, i.e. the emission is averaged over typical dimensions of some 100 pc.
RAPID STAR FORMATION IN GALACTIC NUCLEI
Authors: Rieke G. H.
Published: July 2016

A large percentage of spiral galaxies are forming stars at a very high rate in their nuclei. There are indications that the process of star formation is modified significantly in these regions, compared with the solar neighborhood. The star formation may be fueled by interstellar material that is captured by the nucleus. Further work is needed to explore these possibilities and to establish the evolutionary connections among galactic nuclei, various types of which can be distinguished by their radically different infrared properties.
Guglielmo Marconi and Radioastronomy
Authors: Setti Giancarlo
Published: July 2016

The decision to hold this IAU Symposium at Bologna on the occasion of the 100th anniversary of the discovery of the wireless telegraphy represents in itself a recognition of the widespread feeling of a historical link between the great discovery of Guglielmo Marconi and the birth of radioastronomy. Obviously, it is not a direct link. We all well know that the birth of radioastronomy must be traced back to the year 1932 when Karl Jansky recognized for the first time the existence of a radio signal probably associated with a celestial source. This a classical example of a ‘serendipitous’ discovery made while Jansky was investigating for the Bell Telephone Laboratories the sources of radio interferences with a rotating antenna array operating at about 14 m wavelength. The study of local disturbances was of primary importance in the rapid development of radio communications which had been geared by the Marconi's discovery.
Extended Emission in BL Lac Objects
Authors: Bondi M. , Dallacasa D. , Stanghellini C. , Ceca R. Della
Published: July 2016

The study of the extended emission and polarization properties of BL Lacs is an important step for the identification of their parent population. FRI radio sources, the supposed parent population of BL Lacs, have weaker extended radio luminosity and a dominant inferred magnetic field perpendicular to the jet, while FRII radio sources, the supposed parent population of quasars, have stronger extended radio power and an inferred magnetic field parallel to the jet. The only complete sample of radio selected BL Lacs (1 Jy sample, Stickel et al. 1991, ApJ, 374, 431) contains 34 objects. Unfortunately, about half of 1 Jy BL Lacs do not have very high dynamic range images, necessary to detect the low emissivity radio emission surrounding the bright compact source, either because the object was never observed, or because the observation was carried out at the beginning of 1980s with low sensitivity. In 1994 we started a programme using the VLA (A, B, and D configuration, see Table 1) and the WSRT (W in Table 1) to complete the high sensitivity radio imaging of the 1 Jy sample. We aim to investigate morphology and polarization properties, as well as the luminosity of the extended emission. This contribution presents the L band observations. The results are very preliminary, some of the data reduction is still in progress as well as the statistical analysis. The sources in Table 1 have been roughly classified as extended (E), or point-like (P) if no extended feature was detected. Among the 15 sources observed at the highest resolution 13 were classified as extended. In many sources we detect significantly much more extended flux than previously reported from earlier observations. Almost all the BL Lac objects we observed at the highest resolution show some extended features; furthermore, in a few cases, we detected emission on the arcminute scale. The power of the extended luminosity covers 3 orders of magnitude, 3 objects (0537–441, 0820+225, and 2240–260) have values typical of a FRII radio source. These new data will be used for an updated statistical analysis of the properties of the extended emission in the 1 Jy sample of BL Lac objects.
Superluminal motions: the first 100 sources
Authors: Vermeulen R.C.
Published: July 2016

First results from a large homogeneous superluminal motion survey are presented. The data do not show compelling evidence for the existence of intrinsically different populations of galaxies, BL Lac objects, or quasars. βapp in the range 1–5 h–1 occur with roughly equal frequency; higher values, up to βapp = 10 h–1, are rather more scarce than appeared to be the case from earlier work, which evidently concentrated on sources which are not representative of the general population. The βapp distribution suggests that there might be a skewed distribution of Lorentz factors over the sample, with a peak at γb ≈ 2 h–1 and a tail up to at least γb ≈ 10 h–1. There appears to be a clearly rising upper envelope to the βapp distribution when plotted as a function of observed 5 GHz luminosity; a combination of source counts and the apparent velocity statistics in a larger sample could provide much insight into the properties of radio jet sources.
High-Resolution Structure of Southern Compact Steep Spectrum Sources
Authors: Tzioumis A. , Morganti R. , Tadhunter C. , Dickson R. , Fanti C. , Dallacasa D. , Reynolds J. , Jauncey D. , Preston R. , Mcculloch P. , King E. , Tingay S. , Edwards P. , Costa M. , Jones D. , Lovell J. , Clay R. , Meier D. , Murphy D. , Gough R. , Ferris R. , White G. , Jones P.
Published: July 2016

Two important factors for understanding the physical nature of compact steep spectrum (CSS) radio sources are determining the correct radio morphological classification of these objects together with their characteristics in wavebands different from the radio (Fanti et al. 1995, A&A, 302, 317). Seven CSS sources (linear dimensions < 30kpc for Ho = 50 kms–1Mpc–1 and α > 0.5, S ≃ v–α) have been found in a complete sample of strong southern radio sources. This group of CSS sources is particularly interesting because some optical and X-ray information is already available as part of a more general study of southern radio sources (Morganti et al. & Siebert et al. these Proceedings). The spectra of all the sources were presented in Tadhunter et al. (1993, MNRAS, 263, 999.) Here we present VLBI observations for three of these sources (0252-71, 1306-09 and 1814-63). The remaining four have already been imaged with VLBI (King et al. these Proceedings).
Extreme Depolarization in Compact Steep Spectrum sources
Authors: Garrington S.T. , Akujor C.E.
Published: July 2016

Compact steep spectrum (CSS) sources show all the features of the powerful extended radio galaxies and quasars but on a scale at least ten times smaller. The debate continues over whether this is primarily due to a difference in age or the result of denser gas surrounding CSS sources (Fanti et al. 1990); although two of the most recent investigations favour the view that CSS sources are young (Readhead et al. and Fanti et al., these proceedings)
PKS 1413+135: A Very Young Radio Galaxy
Authors: Perlman Eric S. , Carilli Chris L. , Stocke John T. , Conway John
Published: July 2016

PKS 1413+135 is an enigma: while classified as a BL Lac due to its polarized near-IR continuum (Stocke et al. 1992) and optical spectrum (Beichmann et al. 1981), it appears to lie within a spiral host (McHardy et al. 1991, Stocke et al. 1992). In addition, the AGN is highly obscured (Beichmann et al. 1981, Carilli et al. 1992, Stocke et al. 1992, Wiklind & Combes 1994, 1995). Yet there is no evidence that the absorbing gas is being heated and re-emitting the AGN radiation in the form of thermal IR or emission lines (as in, e.g., Sey 2s). This led Stocke et al. (1992) to suggest that the AGN might be background to the optical galaxy.
Long-term Variability of Extragalactic Sources at 843 MHz
Authors: Hunstead R. W. , Gaensler B. M.
Published: July 2016

Time variability is commonly observed in the most compact extragalactic radio sources. Low-frequency variability (LFV)—at frequencies <1 GHz—is thought to arise through two different mechanisms, intrinsic and extrinsic. The former is just an extension of the often rapid high-frequency variations, delayed and reduced in amplitude. The latter is usually attributed to refractive interstellar scintillation (RISS; Rickett et al. 1984), whereby the variations in intensity are the result of wavefront distortions caused by transverse gradients in electron density. If RISS arises predominantly along the signal path through our Galaxy, we might expect to find evidence for a dependence on Galactic coordinates.
High Precision Astrometry over Large Angular Scales with Closure Constraints: the Triplet 1803+784/1928+738/2007+777
Authors: Ros E. , Marcaide J.M. , Guirado J.C. , Krichbaum T.P. , Preston R.A. , Ratner M.I. , Shapiro I.I. , Witzel A.
Published: July 2016

The technique of differential astrometry using the phase-delay VLBI observable promises fractional precisions of ≃2 × 10–9 in the determination of the separation of sources 5° or 6° apart on the sky (Guirado et al. 1995a; Lara et al. 1996). In our present research we seek further improvement in this technique through using triplets of radio sources, which provide a closure constraint in the determination of relative angular positions. This constraint not only eases the resolution of the phase-cycle ambiguities (a major problem in the least-squares approach to astrometry with phase delays), but it also strongly constrains the space of allowable parameter values.
VLBI Observations of FRI Radio Galaxies
Authors: Venturi T. , Cotton W.D. , Feretti L. , Giovannini G. , Lara L. , Marcaide J.M.
Published: July 2016

The Fanaroff-Riley type I radio galaxies (Fanaroff & Riley, 1974) presented in this paper belong to the complete sample of low-intermediate luminosity radio galaxies published in Giovannini, Feretti & Comoretto (1990). This sample includes radio galaxies with different morphologies on the arcsecond scale, such as compact sources, core-halos, FRIs and FRIIs.
Parsec Scale Properties of Low Power Radio Galaxies
Authors: Giovannini G. , Cotton W.D. , Lara L. , Venturi T.
Published: July 2016

We shortly discuss here the parsec scale information presently available on the extended low power radio galaxy (FR I, Fanaroff and Riley, 1974) NGC6251 (Jones and Wehrle, 1994) and on 11 radio galaxies from the sample presented in Giovannini et al. (1990).
Low-Luminosity Radio QSOs: the B2 sample
Authors: González-Serrano J.I. , Pérez-Fournon I. , Gregorini L. , Padrielli L. , DE RUITER H.R.
Published: July 2016

We present preliminary results from imaging and spectroscopy of a complete sample of radio quasars selected from the B2 survey. The optical data, which provide us information on the environment around the quasars, as well as the redshifts, allow us to address several questions related to the origin and evolution of the radio quasars population. Using VLA observations of the sources we investigate the radio morphology and distortions of these low-luminosity radio quasars. We compare these properties with those of powerful radio quasars.
IRAS 0421+0400: A Curious Spiral with Flaring Jets
Authors: Steffen W. , Holloway A.J. , Pedlar A. , Axon D.J.
Published: July 2016

We present new VLA observations of IRAS 0421+0400 at 1.4 and 5 GHz, providing dual frequency information and higher resolution than previously available. We find extremely accurate alignment of the central double with the closest (though not brightest) feature in the southern kiloparsec hotspot region. There is a tight relation between the symmetric radio structure and emission line gas in the hotspot regions of this Seyfert 2 type galaxy.
A Powerful Jet/Cloud Interaction in the Radio Galaxy PKS 2250-41
Authors: Morganti R. , Tadhunter C.N. , Clark N. , Killeen N.
Published: July 2016

Extended emission line regions aligned with the radio axis are a common feature of powerful radio galaxies and there is much interest in the origin of the extended gas and excitation mechanism. One model that can produce this alignment is photoionization by anisotropic nuclear continuum radiation. However, strong evidence exists, especially in high redshift radio galaxies, for powerful interactions between the relativistic radio jets and the ISM/IGM. Here we present the results of our study of the southern radio galaxy PKS 2250–41 (z = 0.308). This object is the most spectacular found in a sample of southern radio sources studied by Tadhunter et al. (1993) and it displays particularly clear evidence for such an interaction (Tadhunter et al. 1994; Dickson et al. 1995).
Is the UV Alignment Effect Present in Low Redshift Radio Galaxies?
Authors: Cimatti Andrea , Alighieri Sperello Di Serego
Published: July 2016

When a FRII radio galaxy at z > 0.7 is observed in the optical, its continuum appears extended and aligned with the radio axis. This phenomenon occurs actually when the optical bands start to sample the rest-frame UV, and it was called alignment effect (McCarthy et al. 1987). The UV continuum of high z radio galaxies shows also strong linear polarization due to scattering of anisotropic radiation escaping from the obscured quasar nucleus (di Serego Alighieri, Cimatti & Fosbury 1994). However, the observations of the UV continuum have been concentrated mostly on high z radio galaxies, leaving open a main question : is the alignment effect an evolutionary phenomenon present only at high z, or is it simply a selection effect due to the K-correction ? In order to investigate the origin and evolution of the UV alignment effect, we have started a ground-based imaging and polarimetric survey for studying the UV continuum in FR II radio galaxies with 0.1 < z < 0.5. Depending on the redshift, the filters U and B can be used to sample the UV continuum free from strong emission lines, and in the same rest-frame spectral region observed in radio galaxies at higher redshift. The survey is in progress and here we present only our first results.
Optical Properties of B2 Radio Galaxies
Authors: González-Serrano J.I. , Carballo R.
Published: July 2016

We present a large program of CCD imaging of low-luminosity radio galaxies selected from the B2 survey of radio sources. We aim to study their optical properties: brightness profiles, isophotal distortions, morphological peculiarities. As the sample contains jet and no-jet sources, this investigation will allow us to compare both populations of low-luminosity radio galaxies. In particular, we will study the local environment and test whether the galaxy density around radio sources plays an important role on the presence of jets or not. The analysis of morphological distortions on the host galaxies will provide us with detailed information on past or recent galaxy encounters.
Intraday Variability Statistics in Radio-Selected and X-Ray Selected BL Lac Objects Implications for Unified schemes
Authors: Heidt J.
Published: July 2016

BL Lac objects, characterized by their high variability across the electromagnetic spectrum, strong and variable polarization in the radio and optical domain and a (nearly) featureless continuum can in general be divided into the radio-selected (RBL) and X-ray selected BL Lac objects (XBL) according to their αro – αox spectral indices (Stocke et al., 1985). Attempts to unify both classes within a single model have been suggested e.g. by Ghisellini et al. (1993) or Giommi et al. (1994).
Host Galaxies of Radio-Loud & Radio-Quiet AGN
Authors: Kukula M.J. , Dunlop J.S. , Taylor G.L. , Hughes D.H.
Published: July 2016

A clear understanding of both the differences and similarities between the host galaxies of the three main classes of powerful active galaxy – radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and radio galaxies (RGs) – is vital in any attempt to unify or relate the various manifestations of the AGN phenomenon. The unification of RLQs and RGs via orientation effects requires that the hosts of the two types be derived from the same population of galaxies. Meanwhile, the correlation between radio power and host morphology in nearby AGN, with radio-quiet objects (Seyferts) occurring in disc systems and radio-loud sources in ellipticals, is generally assumed to persist at higher redshifts and nuclear luminosities. However, in both cases the evidence remains ambiguous and, moreover, many previous studies have been based on poorly selected samples.
Optical Properties of the Radio Source B2 0828+32
Authors: Ulrich-Demoulin M.-H. , Rönnback J.
Published: July 2016

A small number of radio galaxies have two sets of classical double radio lobes with the radio axes aligned in different directions. Furthermore differences in the properties of the radio lobes such as the surface brightness and spectral index indicate that the two sets of double radio structure have different ages. The radio ejection axis has therefore changed direction with time. In the first two known radio galaxies of this type, 3C 315 and B2 0055+26, the host galaxy is a member of a close pair of ellipticals in a common optical envelope suggesting that the complex radio structure is caused by gravitational interaction.
X-Ray Spectra of BL Lacertae Objects from the ROSAT Archive
Authors: Lamer G. , Brunner H. , Staubert R.
Published: July 2016

Our sample comprises all BL Lac objects listed in the catalogue of Véron-Cetty & Véron (1993) and which are detected in a ROSAT PSPC observation with at least 50 source counts: 74 objects in total. We reduced the data from the ROSAT archives at MPE and GSFC and fitted single power-law models with photoelectric absorption to the spectra. We calculated the broad band spectral indices αrx, αro, and αox from the ROSAT 1 keV fluxes, 5 GHz radio, and optical V band fluxes (Véron-Cetty & Véron 1993).
The Rosat X-Ray Spectra of BL Lacertae Objects
Authors: Padovani Paolo , Giommi Paolo
Published: July 2016

We have analyzed the X-ray spectra of all BL Lacs observed (as pointed or serendipitous sources) by ROSAT. Spectral indices were obtained from the hardness ratios given in the WGA catalogue, a large list of X-ray sources generated from all the ROSAT PSPC pointed observations. The selection of the objects was done by cross-correlating the first revision of the WGA catalogue with our recent catalogue of BL Lacs. This resulted in 163 observations of 85 distinct BL Lacs, which correspond to about half the confirmed BL Lacs presently known. This represents the largest number of BL Lacs for which homogeneous X-ray spectral information is available and the largest BL Lac sample ever studied at X-ray frequencies.
Quasar Radio Morphology and Environment at z ≃ 1/2
Authors: Rector Travis A. , Stocke John , Ellingson Erica
Published: July 2016

The radio morphology of thirty radio-loud quasars atz≃ 1/2 is studied as a function of cluster galaxy density using data available in the literature. While correlations between several morphological parameters of the radio emission are consistent with interactions with an intracluster medium (ICM), we do not see the correlation between galaxy density and quasar radio morphology expected from ICM interaction. Therefore, distorted radio morphology isnotan indicator for the presence of a distant cluster as previously suggested. Because such correlations are found atz≃ 0, these results are suggestive that the rich clusters containing quasars atz≃ 1/2 have not yet developed a dense ICM. An inelastic collision with neighboring galaxies and intergalactic clouds can account for the morphology of several of the sources in this sample and is a viable alternative explanation.
The Radio Lobes of Virgo A
Authors: Rottmann H. , Mack K.-H. , Klein U. , Wielebinski R. , Kassim N. , Perley R.
Published: July 2016

In the framework of our multi-frequency study of Virgo A we have performed observations of Vir A at 10.55 GHz with the Effelsberg 100-m telescope. Using our improved CLEAN procedure for single dish data we have increased the dynamic range to some 40 dB.

By applying our newly developed polarization CLEANing technique we are able to diminish instrumental polarization effects. Since Faraday rotation is negligible at λ2.8 cm the measured linear polarization is a direct trace of the projected magnetic field in Vir A. In combination with low-frequency data obtained with the VLA it is possible to determine parameters like spectral indices, break frequencies, and spectral ages.
Observations of Straight-angle Tailed Radio Galaxies in Rich Clusters of Galaxies
Authors: O'Donoghue Aileen A. , Eilek Jean A. , Owen Frazer N.
Published: July 2016

We have begun VLA observations of straight-angle tailed radio sources (SATs) at 1.5 and 4.8 GHz (L and C band) to achieve one arcsecond resolution at each frequency. This will provide a SAT data set similar to the O'Donoghue, Owen, and Eilek (1990) WAT data set with both total intensity and spectral index information. We will use these data to examine morphological and dynamical properties of straight-tailed radio sources in clusters of galaxies.
The Nature of Flat Spectrum Sources
Authors: Melrose D.B.
Published: July 2016

Nonthermal radio sources near the Galactic Center with flat or weakly inverted spectra (S((ω) ∝ ωα with α ≳ 0) are attributed to optically thin synchrotron emission from a hard electron energy spectrum, N(ε) ∝ ε–α with a = 1 – 2α ≲ 1, produced by Fermi acceleration or diffusive shock acceleration at multiple shocks combined with a synchrotron pile up. This basic mechanism is also plausible for flat-spectrum AGN.
Physics of the M87 Jet
Authors: Begelman Mitchell C. , Bicknell Geoffrey V.
Published: July 2016

Motivated by the recent determination of proper motions of knots in the M87 jet by Biretta, Zhou, & Owen (1995), we have investigated the relationship between the dynamics of the jet and the kpc-scale radio and optical structure. We interpret the knots as internal shocks in the jet, and find that relativistic effects play an important role in their appearance. In particular, knot A, which appears to be almost transverse to the flow and seems to be viewed nearly edge-on, is in fact a highly oblique shock. The direction of its normal with respect to the flow lies within about 10° of the Mach angle, i.e., the angle of obliquity beyond which no shock is possible. In a frame comoving with the shock front, the incident streamlines make an angle of about 40° – 60° with respect to the shock normal. Knot A has a proper motion corresponding to only 0.51c, and the relativistic effects are modest. Its edge-on appearance is largely fortuitous. We have found, however, that relativistic effects would create a strong bias for shocks with apparent superluminal speeds to appear nearly edge-on.
Relativistic Electron-Positron Clouds in VLBI Jets
Authors: Despringre V. , Fraix-Burnet D.
Published: July 2016

Extragalactic jets have always had two characteristics : the presence of knots and the requirement for particle acceleration. Shock fronts provide an explanation for both. However, the knotty appearance is less obvious at kp-scale on very high resolution observations from the VLA and the HST. The evidence for shock fronts is therefore weakened. At the pc-scale (or VLBI scale), a lot of these blobs are moving superluminally and they have been interpreted and modelled as shock fronts in a relativistic jet.
The Cosmic Nozzle
Authors: Konjukov M.V.
Published: July 2016

The cosmic nozzle is a channel with flowing hot gas in a system containing the following components: stars, a hydrostatic gaseous corona and a cavity with hot gas in the central part of the system. In the quasi one-dimension approximation, the following solution of the cosmic nozzle problem about cosmic nozzle was obtained Here (ν,ω, T, σ) are the dimensionless density, hydro dynamical velocity, temperature and cross section of the channel (η0, ω0, T0 σ0 are these values at ζ = 1), φ(ζ), πg(ζ) are the gravitational potential and the pressure in the gaseous corona. For a polytropic state equation of the gas in the gaseous corona
Intrinsic Kinematics of Moving Components in Curved Relativistic Jets
Authors: Lara L. , Alberdi A.
Published: July 2016

Superluminal motion in extragalactic jets is successfully explained assuming a relativistic flow of material in a direction close to the observer's line of sight. In rectilinear jets, the apparent velocity measured by the observer (βapp) is related with the intrinsic velocity of the moving component (β) and the angle between the jet direction and the observer's line of sight (θ) through the equation (eg. Rees 1966, Nature 211, p.468):
Boundary Layers in Extragalactic Jets
Authors: DE YOUNG DAVID S.
Published: July 2016

The radio morphology of extragalactic radio sources, in particular the FR I objects, has long been recognized to be suggestive of an outflow which is undergoing a strong interaction with the surrounding medium. Two essential elements must be noted in considering this interaction. First, it is inevitable. Second, the interaction will always provide mass and energy transfer from the jet to the ambient medium, and thus it is a loss term in the overall energy balance of the radio source. As will be seen, these losses can be comparable to the overall radio luminosity and hence are a nontrivial constraint on the energy requirements placed on the central engine.
ISM / Radio Material Interaction Modeling
Authors: Ferruit P. , Binette L. , Pecontal E.
Published: July 2016

With the outcoming of high angular resolution imaging and 3D spectrographic facilities (HST, TIGER-OASIS at the CFH Telescope…), the need of spatially resolved theoretical models of the kinematic interaction of radio material with the ISM (or the IGM for radio-galaxies) is increasing dramatically. In order to fill the gap between pure hydro dynamical models (3D approach, but very poor atomic physic) and photoionisation/shocks ones (planar description, full account for atomic physic processes), we have started to develop 2D or 3D hydro dynamical models including a good description of atomic physic processes (using photoionisation routines from the code MAPPINGS).
Describing the Asymmetries in Extragalactic Radio Sources
Authors: Ryś STANISLAW
Published: July 2016

As an ideally symmetrical regime we assume that central engine ejects the same volumes of radio emitting matter – hereafter called ‘plasmons’ – into two opposite directions. The plasmons have the identical velocities and evolution and are small. We assume that each plasmon on one side has its corresponding twin on the opposite side of the structure. Since in fact observations do not reveal any symmetrical structures we must include into our model some mechanism to reproduce an asymmetry. It is our assumption that such asymmetry is due to the fact that the observer sees the plasmons at their different evolutionary ages and that their velocity vectors have different directions. We are looking for the functions which describe differences between the twins. These functions give us differences in brightness and expected positions of the twins and may be used for interchanging their elements. This exchange leads to obtaining new structure. If this new structure is identical to the original one, then the functions correctly describe the differences between the two sides of the structure (Paper 1).
The Parkes-MIT-NRAO Radio Surveys
Authors: Wright Alan E. , Tasker Niven J. , Savage Ann , Vaughan Alan E.
Published: July 2016

During 1990, the Parkes radio telescope made a new, deep survey of the southern sky at 4850 MHz (the PMN Survey: see e.g. Griffith and Wright, 1993; Wright et al., 1994). The declination coverage of the survey was from δ = −87° to +10°. The flux limit of the survey was around 30 mJy, although dependent on declination. This survey increased the number of known, southern radio sources by a factor of about 6 to over 65,000.
A Deep 20 cm Radio Mosaic of the ESO Key-project Galaxy Redshift Survey
Authors: Prandoni I. , Gregorini L. , Parma P. , De Ruiter H.R. , Vettolani G. , Wieringa M.H. , Ekers R.D.
Published: July 2016

In two strips of 22° × 1° and 5° × 1° near the SGP Vettolani et al. (1993, IA U Symposium 161, “Astronomy from Wide Field Imaging”, H.T. MacGillivray ed., Reidel, in press) have made a deep redshift survey as an ESO Key Project. All the galaxies down to bJ ≃ 19.4 were observed with the OPTO-PUS multi-fiber spectrograph on the 3.6 m telescope in La Silla, yielding 3348 redshifts. The survey has a typical depth of z = 0.1. It fully samples the optical luminosity function down to B = −15 and various galaxy populations (e.g. normal galaxies, LSBDs and BCDs) are present. Interestingly, emission lines (OII, Hβ, OIII) have been found in a large fraction of the galaxy spectra (≃ 40%), suggesting strong evolution of the galaxy population in terms of enhanced star formation.
Space Distribution of Radio-Source Populations
Authors: Wall J.V.
Published: July 2016

This paper sets out the status of data determining the space distribution of extragalactic radio-source populations, describes some recent results from analyses of the data, and indicates why and how the analyses need revision in the light of unified models. It concludes by emphasizing the severity of the effects of large-scale structure on modern survey data.
The Space Density of High-Redshift Quasars
Authors: Shaver P.A. , Wall J.V. , Kellermann K.I. , Jackson C. , Hawkins M.R.
Published: July 2016

An upper limit on the space density of quasars at z > 5 is obtained independent of any optical magnitude limit, from the complete identification of a large sample of flat-spectrum radio sources. This upper limit is below the observed space density at z ≃ 2 − 3, showing that the turnover in space density is real and not merely due to obscuration.