bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultra Heavy Cosmic Rays
Authors: Fowler P. H. , Masheder M.R.W. , Moses R. T. , Walker R. N. F. , Worley A.
Published: July 2016

The existence in the cosmic rays of ultra-heavy (UH) nuclei with Z ≥ 30 was established by two separate experiments in 1966. Fleischer et al. first demonstrated the fossil tracks of such nuclei in certain meteoritic crystals and shortly afterwards Fowler established their existence in present-day cosmic rays with the detection of their tracks in photographic emulsion which had been exposed during a high altitude balloon flight. The fluxes of such nuclei are very low, only ~ 10−4 of that of iron, and the most suitable method of detection to date has been the analysis of the tracks formed by these particles in very large(several m2) arrays of plastic detector material, notably Lexan polycarbonate. Such exposures on balloons and on Skylab have provided practically all present knowledge of the UH cosmic rays. Unfortunately, the charge resolution obtained was disappointing, even though scrupulous care was taken in the handling and etching of the material, and the charge scale itself of necessity had to be based on a considerable extrapolation from the iron peak and could not be used with great confidence. The situation now, however, is in the process of being transformed. We have two satellite experiments devoted to the study of UH cosmic rays and in operation at the moment. These are the Bristol University experiment on Ariel 6 launched on 3rd June 1979 and the joint group under Israel, Waddington and Stone on HEAO-C launched in September 1979. It is therefore appropriate, I believe, if I devote this review to the new preliminary results and a comparison of this material with the published data.
Nuclei of Galaxies: The Origin of Plasma Beams
Authors: Rees Martin J.
Published: July 2016

The radio structures mapped by aperture-synthesis techniques with the VLA, and discussed earlier at this conference by Fomalont, are energised by activity in galactic nuclei. The compact radio sources resolvable by VLBI techniques (Pauliny-Toth, these proceedings) are on scales ~105 times smaller; but even this still far exceeds the scale where - according to most theoretical ideas - the primary power production is concentrated. This central “core” - involving a large concentrated mass, probably a black hole of ~ 108 M⊙ accreting material from its surroundings - is the primary origin of the power for all categories of activity associated with active galaxies and quasars. In this paper, I shall principally discuss how this “core” could give rise to the fast-moving plasma which emerges in directed beams and energises the radio sources; I shall also comment on some interesting features of radio source structure.
Radio Emission from Nearby Galaxies at High Frequencies
Authors: Beck Rainer , Klein Ulrich
Published: July 2016

High resolution observations of the radio continuum emission from nearby galaxies at several frequencies provide information about the cosmic ray electrons. Optimum results are expected by combining low-frequency synthesis observations with high-frequency single dish data, e.g. Westerbork 610 MHz / Effelsberg 10.7 GHz (1′ resolution) or Cambridge 150 MHz / Effelsberg 2.7 GHz (4′ resolution). Maps of 15 nearby spiral galaxies at 10.7 GHz have been made with the Effelsberg 100-m telescope. Maps of M31 and M33 are available at 2.7 and 4.8 GHz.
Anti-Protons in the Primary Cosmic Radiation
Authors: Szabelski J. , Wdowczyk J. , Wolfendale A. W.
Published: July 2016

A knowledge of the flux of antiprotons is of value in examining the manner in which cosmic rays propagate, assuming, as is conventional, that the antiprotons arise from interactions in the I.S.M. Golden et al. (1979) have recently measured the ratio in the region of 10 GeV and, although confirmatory measurements are needed, it is instructive to compare with expectation. In a recent paper (Szabelski et al., 1980) we presented results of a new calculation of the expected ratio using the standard (equilibrium) ‘leaky box model’.
Dynamical Behaviour of Gaseous Halo in a Disk Galaxy
Authors: Ikeuchi S. , Habe A.
Published: July 2016

Assuming that the gas in the halo of a disk galaxy is supplied from the disk as a hot gas, we have studied its dynamical and thermal behaviour by means of a time dependent, two-dimensional hydrodynamic code.
The Fluctuations of the Cosmic X-Ray Background as a Sensitive Tool to the Universal Source Distribution
Authors: Giommi P. , Bignami G. F.
Published: July 2016

Recent experimental results (Giacconi et al, 79, Tananbaum et al 79) ascribe an increasingly important role to the contribution of discrete sources to the low-energy (few Kev) cosmic X-ray background (CXB). While the astrophysical nature of the objects involved is not yet clear, distant and powerful emitters like QSO play probably an important role (e.g. Setti and Woltjer 1979, Field 1980). For them, often the number-flux curve (LogN-LogS) provides useful hints on such properties as space distribution and/or evolution. For the case of the X-ray sources, moreover, a definite relation exists between their LogN-LogS and the granularity of the sky emission as described by the fluctuations of the X-ray background.
The Gamma-Ray Sky
Authors: Scarsi L. , Buccheri R. , Gerardi G. , Sacco B.
Published: July 2016

When we talk of Gamma-Ray Astronomy we refer in general to celestial photons covering the energy domain from a fraction of MeV up to the highest detected energies at hundreds or thousands of GeV. The six to seven decades altogether spanning the overall energy range constitute a very wide domain to be compared with those of the optical (less than one decade) or of the neighbouring X-Ray Astronomy (about two decades). The observational technique varies widely with changing energy; detector performances and characteristic parameters are not, in general, comparable.
A New Kind of Gamma Ray Burst?
Authors: Pizzichini G.
Published: July 2016

One of the most recently detected (Cline et al., 1980) Gamma Ray Bursts (GRB) appears to have very unusual properties.

We recall here briefly the main features of the time history and of the spectral data, as given by Cline (19 79). The time history has a very fast initial rise, less than 200 usee , a smooth, large but very short initial peak, with a maximum intensity of several × 10−3 ergs cm−2 sec−1 and a 150 msec duration, followed by an oscillating decay phase, with at least 22 compound 8 second pulses. The spectrum of the initial phase of the event; corresponds to a steep power law with possibly a line at 420 keV. The total spectrum of the decay phase is even steeper and shows no lines (Mazets and Golenetskii, 1979), The location of the wait (Evans et al., 1980) corresponds to N49, a supernova remnant in the Large Magellanic Cloud, which gives a total (isotropic) emission of ≈ 1045 erg, one half of it in the initial spike, the rest in the decay phase. Three later events, apparently with no special properties, are attributed to the same source (Mazets and Golenetskii, 1979), with increasing delays (0.6, 29 and 50 days) and decreasing peak intensities (3%, 1% and 0.5% of the first event), because their locations are all consistent with the much smaller March 5 error box.
The Acceleration of Galactic Cosmic Rays
Authors: Axford W. I.
Published: July 2016

Although it is clear that cosmic rays are of considerable astrophysical significance we know surprisingly little about their origin(s), their mode(s) of propagation and escape from the galaxy, and even of their general properties. Practically nothing is known of the composition and energy spectra of different species at energies below about 200 MeV/nucleon as a consequence of solar modulation, which has a significant effect on the observed spectra at energies up to about 10 GeV/ nucleon. The energy spectra of ions (especially protons) appear to be well approximated by a power law (differential spectral index γ ~ 2.6) in the range 1010–1015 eV/nucleon. At higher energies (up to ~ 1020 eV/nucleon) both the spectrum and the composition of the ion component are less well known, however it is significant that the anisotropy, as evidenced from the sidereal diurnal variation, increases substantially, suggesting that perhaps an extragalactic origin must be considered.
Cosmic Ray Acceleration in the Presence of Losses
Authors: Völk H.J. , Morfill G. E. , Forman M.
Published: July 2016

Diffusive Fermi acceleration on hydromagnetic shock fronts is a fairly slow process: most scatterings are energetically neutral, only those across the velocity jump yield a first order acceleration. Thus energy losses of cosmic rays (CR) due to e.g. adiabatic cooling, ionising, Coulomb−, or nuclear collisions, bremsstrahlung, synchrotron radiation, should play a role in limiting the acceleration, since most shocks are coupled with a loss region (HII regions, SNR's, galactic density wave, stellar wind shocks). In addition, for this process to be a local one in the galaxy, the magnetic irregularities must either be excited by the accelerated CR's or produced by a downstream source. This implies a finite wave build-up time during the shock life time. Nevertheless, in the loss free case, the time-asymptotic amplification is independent of the mean free path λ (or the diffusion coefficient κ) which only appears in the spatial scale for the CR intensity. To investigate the effects of losses, the CR diffusion equation is amended by a simple loss term f/τ, with an (energy dependent) loss time τ, f being the CR momentum distribution. For τ spatially homogeneous, a distributed source is required. Then acceleration is only effective if X ≡ 4κ/VS2·τ ≲ 1, i.e. if the acceleration time tacc = 4κ/VS2 is smaller than τ, on either side of the shock. As the Figure shows, also the spatial intensity profile is modified. Wave excitation in dense clouds is prohibitive. Even in a “warm” (T ≃ 104K) intercloud medium shock speeds VS ≳ 3×107 cm/sec are required to accelerate mildly relativistic particles. Waves from an upstream source (star) inside clouds should frictionally dissipate after distances L ≲ 5×1014 cm « λ (10 MeV) if a solar wind scaling is adopted. Thus, presumably in such a case there is no acceleration of stellar or shock-injected particles through a stellar wind shock by scattering within the cloud, but possibly by reflection from beyond the cloud, the condition being 1/τ · VS ≲ 1, where 1 is the linear cloud size. Diffusive approach from outside to a standing shock appears to be very energy-selective, even in a loss free medium.
POLARIMETRY OF INFRARED SOURCES
Authors: Dyck H. M. , Lonsdale Carol J.
Published: July 2016

Polarization at infrared wavelengths has been detected from a number of different objects within the Galaxy. These include young sources associated with molecular clouds and H II regions, cool stars with thick circumstellar shells, bi-polar nebulae, and normal stars suffering interstellar polarization. Typical levels of polarization detected at 2.2 μm are up to 25% for the molecular cloud sources, less than −5% for the cool stars, around 30% for some bi-polar nebulae and less than −2% for interstellar polarization. For the latter three types of source the origin of the polarization is basically understood: it results from scattering of stellar radiation off small particles in the surrounding shell or nebula in the cool stars and bi-polar nebulae and by transfer of flux through a foreground medium of aligned dust grains for the interstellar polarization. The phenomenon of large infrared polarization in the young stellar and pre-stellar sources is less well understood, and it is to this problem that we address ourselves in this review.
THE GALACTIC CENTER
Authors: Gatley Ian , Becklin E. E.
Published: July 2016

Recent infrared and radio observations of the Galactic Center are reviewed. For the region between 1 and 100 pc most of the observed phenomena can be explained by a large density of late-type stars, a ring of molecular material, and a number of regions of active star formation. The central parsec (Sgr A) appears to be a unique region of activity in the Galaxy; this result is based on recent high angular resolution data at 30 to 100 μm and high resolution spectral line observations at 12.8 μm. The observations are discussed in terms of the mass, density structure, and luminosity of the region; the ultimate source of the activity is discussed.
THE INFRARED PROPERTIES OF ACTIVE EXTRAGALACTIC NUCLEI
Authors: Soifer B. T. , Neugebauer G.
Published: July 2016

In this paper we review the observed infrared properties of the general classes of active extragalactic nuclei with the purpose of relating the observations to the mechanisms responsible for the emission processes. We will first give a summary of those observations which define the energy distributions and emission line ratios of broad groups of objects. We will intersperse measurements of specific features throughout the discussion that illustrate definite emission mechanisms.
AN OUTSIDER'S VIEW OF EXTRAGALACTIC INFRARED ASTRONOMY
Authors: Longair M. S.
Published: July 2016

No one could be more of an outsider to infrared astronomy than myself. Like all outsiders, one forms preconceived notions about disciplines outside one's own speciality. In my own case, I can summarise these under three headings.
Simultaneous multi-frequency imaging of the nucleus of NGC 1275
Authors: Romney J.D. , Walker R.C. , Kellermann K.I. , Vermeulen R.C. , Dhawan V.
Published: July 2016

An unusual counterjet feature was discovered in 3C 84, the compact radio nucleus of NGC 1275, in the “First Science” observations on the VLBA at 8.4 GHz (Walker et al., 1994), and simultaneously in Global VLBI observations at 22 GHz (Vermeulen et al., 1994). Comparison of these images indicated a strongly inverted spectrum in this feature, but the interpretation was clouded by the two-year difference between the epochs of observation. To resolve this ambiguity, and to study the spectrum of the counterjet, we exploited the capabilities of the VLBA to make nearly simultaneous observations of 3C 84 at 2.3, 5.0, 8.4, 15.4, 22, and 43 GHz, in four apparitions over a 16-day period in January 1995. These observations also served to continue structural monitoring programs at 15 and 22 GHz. This paper presents preliminary images from those observations. A companion contribution by Walker et al. (1995) discusses the interpretation of the images.
Helical Motion in the BL LAC Object 0J287?
Authors: Vicente L. , Charlot P. , Sol H.
Published: July 2016

The structural evolution of the BL Lac object OJ287 has been studied with milliarcsecond resolution by using 8.4 GHz geodetic VLBI data from the Crustal Dynamics Program. Such data provide valuable maps which are useful to track superluminal components on short time scales (Charlot 1992). We have mapped and model-fitted OJ287 at ten epochs separated by intervals of a few months between 1985.4 and 1988.1 (Fig. 1a). The structure of OJ287 over this time span consists of two components, one of which is the source core, while the other one is identified with the knot K3, ejected during the 1983–1984 optical outburst. Our models indicate that the knot K3 moves along a non-radial path, with evidence for an apparent deceleration by mid-1986 and a reacceleration afterwards (Fig. 1b). We explain this peculiar motion by a projection effect due to a helical morphology of the jet. Our proposed helical model, estimated by considering the sky positions of K3 together with those of the earlier knots K1 and K2 (Roberts et al. 1987, Gabuzda et al. 1989), corresponds to a helix with a pitch angle of 20° on a narrow cone of half opening angle 3.4°, and central axis inclined at 17° relative to the line of sight. Ejection of VLBI components appears to occur simultaneously with optical outbursts and at mid-time between them. This finding is consistent with the supermassive binary black hole model previously proposed to explain those periodical outbursts (Sillanpää et al. 1988). Comparison of our helical fit with hydrodynamical models (Hardee et al. 1994) provides estimates of the radius (R ≃ 0.015 pc at a distance of 5 pc from the core), opening angle (ψ ≃ 0.1°), and Mach number (M ≃ 60) of the jet, and shows that the orbital 9.0 yr period of the binary black hole system is adequate to drive the helical perturbation if the jet propagates in a hot ambient medium with an external sound speed of 5000 km/s.
A VLBI Study of GHz-Peaked-Spectrum Radio Sources
Authors: Stanghellini C. , O'DEA C.P. , Baum S.A. , Dallacasa D. , Fanti R. , Fanti C.
Published: July 2016

The GHz-Peaked-Spectrum (GPS) radio sources are powerful (Lradio ≈ 1045 erg sec–1) and compact (10–100 mas, 10–1000 parsecs) sources characterized by a simple convex spectrum which peaks near 1 GHz (O'Dea et al. 1991 and references therein).

Optical and radio observations lead to the conclusion that GPS sources are formed when the radio source is confined to the narrow line region (or an even smaller scale) by a dense and clumpy medium. This could lead to 2 different evolutionary scenarios: as first suggested by Phillips and Mutel (1982) GPS radio sources could be classical double radio sources at the very first stage of their life, or alternatively they will never become as large as the classical doubles since the dense and turbulent environment is able to confine and trap the radio emitting region on the scale of the NLR (Baum et al. 1990).
Large Rotation Measures in CSS Sources
Authors: Junor W. , Mantovani F. , Peck A. , Saikia D. , Salter C.
Published: July 2016

A majority of compact steep-spectrum (CSS) and GHz-peaked spectrum (GPS) sources show low integrated polarizations (≲ 1%) at or below 5 GHz. To investigate whether this is mostly due to large rotation measures (RMs) arising from their being cocooned in dense gaseous envelopes we have observed 26 CSSs and GPSs at 8 and 15 GHz with the VLA A-array. The sample includes equal numbers whose hosts are galaxies and quasars.
The Evolution of Extragalactic Radio Sources
Authors: Readhead A. C. S. , Pearson T. J. , Taylor G. B. , Wilkinson P. N.
Published: July 2016

A series of VLBI surveys of complete samples of radio sources selected at 5 GHz (Pearson & Readhead 1988, hereafter PR; Xu et al. 1995 and references therein) has revealed that ≃ 10% of the objects are “Compact Symmetric Objects” (CSOs), in which high-luminosity radio emission regions are seen on both sides of the center of activity on scales less than one kiloparsec (Phillips & Mutel 1982; Readhead et al. 1984; Conway et al. 1992; Wilkinson et al. 1994). In order to be sure that an object is a CSO, either the center of activity must be pinpointed (Taylor et al. 1996) or compelling morphological evidence of symmetric structure must be found.
High Radio Frequency Studies of Equatorial and Southern AGN
Authors: Tornikoski M. , Valtaoja E.
Published: July 2016

The Swedish-ESO Submillimetre Telescope (SEST) has been used for the high radio frequency observations of our group's AGN monitoring projects since the end of 1987.

Our SEST results from October 1987 until June 1994 will be published in A&AS (in press); the data will be available electronically. The data set consists of 155 sources with the signal-to-noise -ratio of at least one observation (at 90 or 230 GHz) ≥ 4.
Scintillating Lenses
Authors: Walker M. A.
Published: July 2016

There are now several examples of distant radio sources being gravitationally lensed by foreground galaxies (e.g. PKS1830–211, Jauncey et. al. 1991). In such cases we know that the line of sight must be passing through a substantial amount of ionized material, so it is pertinent to ask whether these free electrons influence the observed properties of the source in any significant way.
PKS 1117+146: Gravitational Lens or Micro lobes
Authors: Bondi M. , Garrett M. , Gurvits L.
Published: July 2016

PKS 1117+146 is a high power radio source (L327MHz=5.4 × 1026 W/Hz) identified with a galaxy of 20.1 red magnitude at z=0.362 (de Vries et al. 1995). At this redshift 1 mas ≃ 2.9 pc (H0 = 100 km/s–1Mpc–1). Based on the properties of the radio spectra, PKS 1117+146 is classified as a GigaHertz Peaked Spectrum source (GPS) (Stanghellini et al. 1990). The GPS are powerful but physically small (sub-galactic sizes) radio sources with turnovers in their radio spectra at v ≃ 1 GHz. They are supposed to be isotropically emitting radio sources confined by exceptional dense circumnuclear gas (O'Dea et al. 1991) or still relatively young (Fanti et al. 1990). PKS 1117+146 is also a low frequency variable (LFV) with no sign of variability at v > 1 GHz (Padrielli et al. 1987, Mitchell et al. 1994). The low frequency variability is caused by propagation effects in the interstellar medium of our Galaxy (Mantovani et al. 1990, Spangler et al. 1993). PKS 1117+146 was observed with VLBI global arrays at 608 MHz (Padrielli et al. 1991), at 327 MHz (Altschuler et al. 1995), and at 1667 MHz (Bondi et al. 1996). All the maps are in agreement showing a compact double structure with components separated by about 70 mas. Flux densities and separation of the two components derived from VLBI and MERLIN (see below) maps are listed in Table 1. The flux ratios of the two components from the VLBI observations are very similar, and the spectral index is relatively flat (α ≃ 0.3–0.4), even if the strong low frequency variability can introduce uncertainties. The similarity of the VLBI morphology and spectral properties of the two components suggested that 1117+146 could be a possible gravitational lens candidate prompting for higher frequency observations. We observed PKS 1117+146 with MERLIN at 22 GHz in March 1993. MERLIN observations reveal for the first time a weak central component with a total flux density of about 20 mJy (Fig.1). From Table 1 we can note that the P.A. between the components is constant at all the frequencies while the separation between the peak flux densities significantly increases at higher frequencies. This is the expected behaviour if the 2 components are 2 lobes with hot-spot at the outer edges. The MERLIN map at 22 GHz seems to rule out the possibility that the morphology of PKS 1117+146 is caused by gravitational lensing.
Cygnus A: Some Topics from the Workshop
Authors: Harris D. E.
Published: July 2016

The international workshop on Cygnus A was held in Green Bank WV, USA and was attended by 45 participants who reported on radio, infrared, optical, UV, X-ray, and theoretical results. Rather than attempt to cover all of the papers presented at the workshop, we have selected 8 topics. We apologize to those whose work is not mentioned here. Because of the limitations of length, we have foregone the luxury of figures and we refer to articles in the Cygnus A book (to be published early in 1996 by Cambridge University Press) by first author only. All references to page and figure numbers refer to the Cygnus A book.
HST Observations of Jets and Radio Lobes
Authors: Crane Philippe
Published: July 2016

The Hubble Space Telescope has proved to be remarkably useful for discovering and for studying the optical counterparts of radio lobes and radio jets. Since much of the structure seen in the radio is found on subarcsecond scales, it is not surprising that HST, with it's improved resolution relative to ground based observations, would be a major contributor to this field of research. This paper reports briefly on some of these successes, and refers to more detailed descriptions in the literature.
Probing AGN with Water Masers
Authors: Moran J. M. , Greenhill L. J. , Herrnstein J. R. , Diamond P. J. , Miyoshi M. , Nakai N. , Inoue M.
Published: July 2016

Observations of the angular distribution of the water masers in the nucleus of NGC4258 reveal the presence of a thin molecular disk in nearly perfect Keplerian orbit (Miyoshi et al., 1995; Moran et al., 1995). About 300 galaxies have been searched for nuclear water masers to a limiting sensitivity of about 0.1 Jy (e.g., Braatz, 1996); and 16 masers have been detected. The maser imaged by Miyoshi et al. (1995) offers the best example of disk structure. VLA data of NGC1068 shows evidence of disk structure (Gallimore et al., 1996; Greenhill & Gwinn, 1996) and NGC2639 has drifting features, which may be due to centripetal acceleration (Wilson et al., 1995).
Radio Outflows and the Origin of the Narrow Line Region in Seyfert Galaxies
Authors: Capetti A. , Axon D.J. , Macchetto F.D. , Sparks W.B.
Published: July 2016

Seven Seyfert galaxies, Mrk 3, Mrk 78, Mrk 348, Mrk 6, Mrk 573, NGC 3393, IRAS 04210+0400 and IRAS 11058-1131 (all Seyfert galaxies type 2 expect Mrk 6 which is a Seyfert 1.5) were observed with HST. For the first five objects images were taken with the FOC with filters centered on the emission lines [O II] and [O III]. For the remaining three galaxies WFPC2 observations were obtained in the [O III] and Hα lines.
Matter–Bounded Photoionized Clouds
Authors: Binette L. , Wilson A.S. , Storchi-Bergmann T.
Published: July 2016

The extended ionized gas in Seyfert and Radio-Galaxies is characterized by large values of the ratio He ii/Hβ, which exceeds the value predicted by the standard photoionization model in which the ionizing continuum consists of a power-law. This has lead to the suggestion of considering a matter-bounded (MB) component for explaining such extreme values. We now find that it is also possible to resolve the temperature problem if the thickness and the ionization parameter of the MB is appropriately selected. Adopting a canonical power law (α= −1.3) and solar abundances (Z=l), we can account for the observed trends in excitation (represented for example by the ratio [0 ii]/[0 iii] in Fig. 1)) by varying the relative number of MB clouds (which emit the high excitation lines Civ, [Ne v], He ii… and most of [O iii]) versus the number of ionization-bounded (IB) clouds (which emit [N ii],[S ii] [O ii], [O i]…). We obtain a one-parameter sequence (solid line) which is function of the weight AM/I of the MB component relative to the IB component. This AM/I–sequence successfully reproduces the observed range in He ii/Hβ. Note the failure of the traditional U–sequence (long dashed line). Fig. 2 indicates that we can also reproduce the ratio ROIII= [O III]λ4363/[O iii]λ5007 and therefore resolve the temperature problem. Interestingly, our model indicates a temperature difference of 5 000 K between the IB component ([N ii] temperature ≃ 10 000 K) and the MB component ([O iii] temperature ≃ 15 000 K) while the traditional U–sequence predicts a difference of only 1 000 K. Such difference of 5 000 K has been reported in the extended gas of Cygnus A.
Nearly Simultaneous Optical and VLBI Polarization Observations of BL Lac Objects
Authors: Gabuzda D.C. , Kochanev P.Y. , Sitko M.L. , Smith P.S.
Published: July 2016

The continua of BL Lacertae objects and other “blazars” are dominated by nonthermal emission that is variable and highly polarized at UV–radio wavelengths (Angel and Stockman 1980; Kollgaard 1994; Allen et al. 1993). It is believed that this non-thermal emission is associated with the relativistic jets that are known to exist in these sources, but details of the jet structure and physics are still very uncertain. It is usually expected that the polarization behavior at optical and radio wavelengths should show little or no correlation, even if genuinely simultaneous measurements are compared. It is typically thought that the emission in these two wavebands originates in vastly different parts of the source, where the magnetic field geometries are likely to be quite different. In some inhomogeneous synchrotron source models for blazars, however, depending on the model parameters considered, the radio and UV-optical-IR (UVOIR) emission may be co-spatial (Ghisellini, Maraschi & Treves (1985)). It is thus of interest to search for correlations between the emission of blazars in the UVOIR and radio, to test such models. Our approach to doing this has been to compare simultaneous measurements of the optical and VLBI polarization characteristics of compact AGN. The polarization of the radiation is effectively used as a probe of the magnetic field structures in the regions where the emission at the two wavelengths arises.
ROSAT Studies of Extragalactic Radio Sources
Authors: Brinkmann W. , Siebert J. , Yuan W.
Published: July 2016

Complementary information over a large energy range appears to be the best way to study the class properties of Active Galactic Nuclei (AGN). While radio data provide superior spatial resolution required for the analysis of source structures and their morphology, optical data are a necessary ingredient for the classification of the objects and for the determination of their redshifts. Finally, X-ray (and more recently γ-ray) observations give vital information about the energetics of the central engines and on the physical conditions of the ‘heart of the machine’.
The Search for a New BL Lac Sample
Authors: Wolter A. , Caccianiga A. , Maccacaro T. , Ruscica C.
Published: July 2016

The number of BL Lacs discovered in the last 20 years is very small (≃ 200) if compared to that of quasars. Owing to their featureless optical spectrum, BL Lacs have been discovered mainly in radio (RBL) and X-ray surveys (XBL). The limited statistics available prevents a detailed study of the properties of BL Lacs and, in general, all the conclusions based on the present data sets are affected by large uncertainties. Yet, current results are intriguing, for instance RBL and XBL are found to have a cosmological evolution that differs not only in magnitude but most of all in sign (e.g. Stickel et al., 1991 and Wolter et al., 1994 and reference therein). Therefore, we have initiated a project aimed at discovering a significant number of new BL Lac objects (≃ 100), exploiting the fact that they are both radio and X-ray emitters and in particular the fact that they occupy a well defined region in the αox–αro plane. The method we use rests on the expertise grown during the construction of the EMSS sample (Gioia et al. 1990, Stocke et al. 1991) and is described in detail in Wolter et al. (1995).
Radio Structures of the MRC 1-Jy Sources and the Unification of Radio Galaxies and Quasars
Authors: Kapahi V. K. , Athreya R. M. , Subrahmanya C. R. , Mccarthy P. J. , Van BREUGEL W. , Baker J. C. , Hunstead R.W.
Published: July 2016

The viewing angle of ≃45° (between the jet axis and the line of sight) dividing quasars and radio galaxies in the orientation-based unified scheme (Barthel 1989) is based largely on the observation that in the redshift range of 0.5 < z < 1.0 in the low-frequency 3CRR sample, there are about twice as many radio galaxies than quasars and the median linear size of galaxies is about twice that of the quasars. The relative numbers and sizes of quasars in other redshift ranges in the 3CRR are however in conflict with the simple unified scheme even if the opening angle is considered to evolve with epoch or radio luminosity (Kapahi 1990; Singal 1993). Larger sources samples, preferably selected at low radio frequencies, are clearly important in such statistical studies.
Depolarization Studies of Radio Sources and the Unified Scheme
Authors: Garrington S.T. , Holmes G.F. , Saikia D.J.
Published: July 2016

In powerful FRII radio galaxies and quasars the polarization of the two radio lobes is often very asymmetric and strongly correlated with jet sidedness. These sources usually have one-sided jets and the lobe on the jet side depolarizes more slowly than the one on the counter-jet side (Laing 1988; Garrington et al. 1988). This correlation can be interpreted in terms of depolarization of the receding lobe by a halo of hot gas surrounding the radio source and is in the expected sense if the jet asymmetry is due to Doppler boosting.
KECK Spectropolarimetry of High Redshift Radio Galaxies
Authors: Cimatti A. , Dey A. , Van BREUGEL W. , Antonucci R. , Spinrad H.
Published: July 2016

High redshift radio galaxies (HzRGs) are observable up to cosmological distances competitive with the most distant quasars. However, before using them as probes of galaxy evolution, it is crucial to separate the stellar and non-stellar components. One of the most striking properties of HzRGs is the alignment of the UV continuum with the axis of the radio source (alignment effect; McCarthy et al. 1987). However, the relative importance of the stellar and non-stellar radiation to the alignment effect is still unknown, although a significant fraction is recognized to come from scattering of anisotropic radiation emitted by the obscured nucleus, as expected in the unified model of powerful radio sources (di Serego Alighieri, Cimatti & Fosbury 1994). Spectropolarimetry is the most powerful technique to observe at the same time different radiation components, but the 4m class telescopes can reach a sufficient S/N ratio only on the few brightest objects. Therefore, in order to investigate the origin of the alignment effect and to test the validity of the unified model of powerful radio-loud AGN, we have started a program of optical spectropolarimetry of HzRGs with the W.M. Keck 10m telescope equipped with the Low Resolution Imaging Spectrometer (LRIS) in polarimetric mode.
High-Energy Gamma and Radio Variability of Blazars in the Model of Non-Stationary Jets
Authors: Romanova M.M. , Lovelace R.V.E.
Published: July 2016

A model has been developed for impulsive VLBI jet formation and gamma ray outbursts of Blazars. Propagation of newly expelled matter in the old channel of a jet is calculated supposing that the main driving force is the electromagnetic field. The new outflowing matter overtakes the old matter and forms double, fast or slow magnetosonic shock fronts. In the region of the fronts, the number of particles and their energy increase continuously with propagation time from the central object (Romanova and Lovelace, 1995). Accelerated electrons and positrons in the front interact with a diffuse field of UV photons (inverse Compton scattering), with the magnetic field (synchrotron radiation), and with synchrotron photons (SSC processes), thus creating radiation in a very wide range of bands. The self-consistent relativistic equations for the number of particles, the momentum, energy, and magnetic flux in the front are derived and solved numerically (Lovelace and Romanova, 1995). The time-dependent apparent luminosities in the radio to gamma ray bands are calculated taking into account the Doppler boost of the photons. The model predicts a short outburst of radiation in gamma rays (weeks or so) connected with Compton processes, a sharp (less than a day) outburst in the X-rays with a smooth decrease of the luminosity connected with SSC processes, and synchrotron radiation changing from infrared to radio bands (Fig. 1A). The lepton distribution function was taken as fl = K1/γ2 in the main energy containing range, γ1 ≤ γ ≤ γ2, steeper distribution fl = K2/γ3 for γ2 ≤ γ ≤ γ3, and even steeper for γ ≥ γ3. For γ < γ1, fl is assumed negligible as a result of synchrotron self-absorption. The lowest frequency f(syn1), determined by self-absorption, corresponds initially to the infrared band, and later - to the radio band. From Fig.1B, one can see that radio at 3 mm may start to appear after 2 weeks after outburst. But its maximum may correspond to much later times (months), because f(syn1) decreases slowly with time. The appearance of the new VLBI component in QSO 0528+134, which approximately coincides with the strong gamma-ray flash and with the beginning of the strong mm radio outburst (Krichbaum, et al. 1995; Pohl, et al. 1995), supports the proposed model.

Both authors were supported in part by NSF grant AST-9320068. MMR is grateful to RFBR and Organizers of the Symposium for the partial support.
The Production of Jets from Magnetized Accretion Disks: Simulation of the Blandford-Payne Mechanism
Authors: Meier D.L. , Payne D.G. , Lind K.R.
Published: July 2016

We have used massively parallel supercomputer simulations to perform an extensive study of a plausible mechanism for producing the jets seen in extragalactic radio sources - acceleration and collimation by coronal magnetic fields in an accretion disk orbiting a central black hole. We find that such disks can propel jets for a wide range of coronal conditions. The terminal jet velocity is a strong function of the magnetic field equatorial component. Acceleration and collimation are produced by a tight azimuthal field coil generated in the corona, rather than by a stiff poloidal field extending to large distances. The jets are pressure-confined when the external medium pressure is high, but magnetically-confined when it is low.
Simulations of Superluminal Radio Sources
Authors: Komissarov S.S. , Falle S.A.E.G.
Published: July 2016

The superluminal knots of VLBI-sources are widely believed to be shocks travelling along relativistic jets. So far only very simple quasi-one dimensional models have been used to study this phenomenon. Recent progress in numerical methods for relativistic fluid dynamics (Falle & Komissarov 1995) make it possible to carry out much more realistic simulations of such flows.
A New Analytical Jet Model
Authors: Kaiser C.R. , Alexander P.
Published: July 2016

We present a self-consistent, self-similar model for classical radio double sources (FRIIs). This model depends only on quantities which can in principle be measured.
Distortion Effects in BL Lac Radio Jets
Authors: Sol H. , Appl S. , Vicente L.
Published: July 2016

BL Lac objects often show a quite distorted radio morphology. Almost 75% of the BL Lacs for which the information is available show an apparent misalignment angle ΔPA between the VLBI jet and the large scale radio structure larger than 45 degrees. This can be explained by strong enhancement of slight bending due to projection effects, especially if BL Lacs are the most highly beamed sources. However we recently performed a statistical analysis of misalignment angle histograms for 155 extragalactic radio sources of different types and found that the intrinsic distortion is significantly more important in BL Lacs than in quasars and even CSS sources. Indeed the best fits of the δPA histograms by a simple bend model correspond to γɸ = 123° for BL Lacs, 37° for quasars and 36° for CSS sources, where ɸ and γ are the jet typical intrinsic bend and Lorentz factor within a given class of sources (Appl et al, 1995). If, as currently thought, jets in BL Lacs have smaller Lorentz factors than in quasars, high intrinsic bending and misalignment appear to be the rule in BL Lac sources.
How Radio Sources Stay Young
Authors: Eilek J.A.
Published: July 2016

In studying the dynamical evolution of radio galaxies, I find that the dynamical ages of the sources are older than the ages inferred from spectral breaks, typically by a factor ≃ 10. This suggests to me that the spectral ages are misleading.
2-Jy Sample of Southern Radio Sources
Authors: Morganti R. , Tadhunter C.N. , Dickson R. , Shaw M. , Oosterloo T.A. , Reynolds J.E.
Published: July 2016

We have collected multi-waveband (radio, optical and X-ray) data for a complete sample of southern radio sources. The sample includes 88 objects selected from the Wall & Peacock (1985) catalogue that is complete down to S2.7GHz = 2 Jy, δ < 10° and the z < 0.7. This database (Tadhunter et al. (1993), Morganti et ai. (1993), and Siebert et al. these Proceedings) provides an important tool for investigating the nature of anisotropies and orientation effects in AGN and the physical causes of the correlation between their emission at different frequencies.
The MRC 1-Jy Sample of Radio Galaxies
Authors: Kapahi V. K. , Mccarthy P. J. , Athreya R. M. , Van BREUGEL W. , Subrahmanya C. R.
Published: July 2016

Most known galaxies at high redshifts have been found by concentrating on ultra steep spectrum (α≳l) sources in low frequency radio surveys (eg. Rottgering et al., 1994; McCarthy et al., 1990). We have been carrying out a systematic study of a large and complete sample from the 408 MHz Molonglo Reference Catalogue which is not biased by any spectral index criterion. Containing 558 sources, defined by S408 ≥ 0.95 Jy; −30° < δ < −20° and the RA ranges of 20h 20m to 06h00m and 09h20m to 14h00m, our sample is about 3 times larger in size and 5 times deeper in flux density than the well studied 3CRR sample.
Radio Observations of the Marano Field: Sub-Millijansky Source Counts and Spectral Index Studies
Authors: Gruppioni C. , Parma P. , De Ruiter H.R. , Zamorani G.
Published: July 2016

The Marano Field (centered at α(2000)=03h15m09sδ(2000)= −55° 13′ 57″) is a deep ROSAT field (flux limit ≃ 4 × 10–15erg cm–2s–1), which has been entirely covered by ESO 3.6 m plates and in the inner part by deep CCD exposures. In order to follow up these data in other wavelength regions, deep radio observations of this field have been carried out with the Australia Telescope Compact Array (ATCA) at 1.370 and 2.378 GHz. The minimum reached rms noise value is ≃42 μJy at both frequencies. 80 and 45 sources form complete samples above 5.5 σlocallevel at 1.370 and 2.378 GHz respectively, in a square area of ≃0.34 sq. deg. Almost all of the sources detected at 2.378 GHz have been detected also at 1.370 GHz.
The VLBA Calibrator Survey
Authors: Beasley A.J. , Dhawan V. , Fomalont E.B. , Walker R.C. , Wrobel J.M.
Published: July 2016

Using phase-referencing, the coherent integration time of VLBI observations can be substantially increased, permitting observations of weaker (≃mJy) target sources (see e.g. Beasley & Conway 1995). The position of a source can also be accurately measured relative to a reference source, allowing absolute and proper-motion measurements, optical-radio image alignment, and alignment of images made at different frequencies.
VLA Observations of the Cambridge-Cambridge Rosat Survey
Authors: Ciliegi P. , Elvis M. , Wilkes B.J. , Boyle B.J. , Mcmahon R.G. , Maccacaro T.
Published: July 2016

We report the result of the VLA observations of all the 80 AGN in the Cambridge-Cambridge ROSAT Serendipity Survey (CRSS, Boyle et al. 1995), a new well defined sample of 80 X-ray selected AGN with fx(0.5-2.0keV)≥ 2 × 10–14 erg s–1 cm–2. Our aim was to obtain a complete classification of the sample members as Radio-loud (RL) or Radio-quiet (RQ) in order to determine well-constrained X-ray luminosity function (XLF) for X-ray selected RQ and RL AGN separately.
Doppler images of HR 1099 from 1981–1993
Authors: Vogt S. S. , Hatzes A. P.
Published: July 2016

We present 23 Doppler images of the spotted RS CVn star HR 1099 (V711 Tau) from 1981 to 1993. All of the images show a large variable-shape cool spot straddling the pole. Many of the images also show a number of isolated low-latitude spots. This image set has been used to track the emergence and evolution of spots on this star over the 12-year interval. The Doppler images are compared to previous ‘few-circular-spot’ photometric model solutions when available. These photometric solutions do not well-represent the spot distribution. We discuss, among other things: the location on the stellar surface where spots first appear, their subsequent movement with time, differential rotation from spot motions, and spot cycles and dynamos within HR 1099.
Stellar plages
Authors: Walter F. M.
Published: July 2016

The solar surface contains of bright regions (plages) and dark regions (sunspots) superposed on the photosphere. If the solar analogy is valid, then active late-type stars should also exhibit bright, spatially distinct plages. These plages can be detected by rotational modulation of chromospheric flux, or by Doppler imaging in chromospheric/transition region lines. I review the evidence for the existence of plages, with particular emphasis on two very active systems: AR Lacertae, for which we have sequences of Doppler imaging observations since 1984, and AB Doradus, which we observed extensively in 1994. I conclude that we need to be cautious when relying on the solar analogy to interpret observations of the most active late-type stars.
Chromospheric variation in cool supergiant stars
Authors: Eaton J. A. , Henry G. W.
Published: July 2016

Stars close to the main sequence, if they rotate rapidly enough, show magnetic activity in the form of spots, active regions, and strong chromospheres. With the exception of the hybrid stars, stars cooler and more luminous than the so-called Linsky-Haisch dividing line, in contrast, are not known to have any of these phenomena. In fact, it is not clear such stars, even though rotating and convective, show any magnetic phenomena at all. We discuss (1) photometry used to search for spots in the hybrid stars, which we have not found, and (2) evidence for chromospheric variation in K supergiants that takes the form of enhanced winds, but which may be analogous to the activity of stars closer to the main sequence.
Are there prominences around binary systems?
Authors: Jeffries R. D.
Published: July 2016

I examine the possibility that large, cool prominences can be formed in close binary systems, when coronal structures grow beyond the point where centrifugal force balances gravitational attraction. X-ray light curves of the eclipsing binary XY UMa indicate that an extended corona is probably present and this is likely to reach heights > 1.5 R⊙, where centrifugal compression may render plasma in the coronal loop apexes unstable to thermal perturbations. Cool condensations could form, explaining features such as the dips in the X-ray light curves of V471 Tau, and the circumstellar material deduced to be present in several close binary systems.
Imaging stellar coronae from eclipsing binary X-ray light curves
Authors: Siarkowski M.
Published: July 2016

The Sun is the only star whose X-ray emitting, strongly inhomogenous corona can be spatially resolved via direct observations. For other late type-stars it is known that coronae do exist, but the spatial distribution of their emission is largely unknown. However in the case of eclipsing binaries this spatial structure can be potentially deduced from the orbital modulation of the observed X-ray light curve. The best candidates for this kind of analysis are RS CVn binaries, the most active and luminous late-type X-ray coronal sources. These are detached binaries with periods typically between 0.5 and 20 days, in which one or both stars have evolved into subgiant or giant of spectral type G or K. For short orbital periods (< 14 days) the tidal forces lead to synchronization of the orbital and rotational periods, so these systems rotate rigidly.
Doppler tomography of chromospheres and accretion regions in Algol binaries
Authors: Richards Mercedes T. , Albright Geary E.
Published: July 2016

The technique of back-projection Doppler tomography has been used to produce the first set of reconstructed images of chromospheric emission sources in the class of Algol-type binaries. The Hα emission sources in the Doppler tomograms include the gas stream, a sub-Keplerian accretion annulus, a quasi-stable accretion disk, and the chromosphere of the cool secondary star. The chromospheric images of several Algol secondaries (e.g., RS Vul, β Per, TX UMa, RW Tau) are consistent with that of the RS CVn binary V711 Tau.
Observed and computed spectral line profiles
Authors: Dravins Dainis
Published: July 2016

For the diagnostics of stellar surface structure, studies of “ordinary” line profiles may prove inadequate. However, hydrodynamic models may be constrained by second-order quantities, such as line asymmetries and wavelength shifts (and especially the differential behavior between lines of different excitation potential, ionization stage, and height of formation, as well as by the time dependence).
Progress in semi-empirical modelling of main-sequence stellar chromospheres
Authors: Houdebine E.R.
Published: July 2016

We present the results of a long term research programme on the outer atmospheres of main-sequence dwarfs. Combining NLTE-radiation transfer calculations with high resolution spectroscopic observations have led to significant progress in understanding chromospheric physical properties and spectral signatures. We emphasize that in order to unravel the extremely complex physics of the outer atmosphere and its energy source, magnetic field and acoustic wave dissipation, one must isolate the influence of all stellar parameters.