bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared Molecular Absorption Features
Authors: Willner S. P. , Puetter R. C. , Russell Ray W. , Soifer B. T.
Published: July 2016

Spectra of infrared sources associated with molecular clouds have shown absorption features at wavelengths of 6.0 and 6.8 μm. We suggest that the 6.0 μm feature can be identified with the stretching vibration of C=0 and the 6.8 μm feature with the bending vibrations of CH2 and CH3. The amount of carbon in the form of hydrocarbon molecules may be comparable to the amount in CO. This abundance of hydrocarbons is probably too large to be consistent with radio observations if the molecules are gaseous, but large abundances of hydrocarbons on the surfaces of grains may explain the infrared features, yet be unobservable in the radio.
Isotopic Abundance Ratios from Microwave Observations of Formaldehyde
Authors: Wilson T. L. , Henkel C. , Walmsley C. M. , Pauls T.
Published: July 2016

This report is a summary of the determination of the ratio of the column density of H212C16O (hereafter H2CO) or H212C18O (hereafter H2C18O) to that of H213C16O (hereafter H213CO). With one exception, all of the published ratios have been determined from measurements of the 110−111 lines. The exception is the Orion Molecular Cloud (see discussion of Kutner et al. 1976). The most complete surveys of H213CO are those of Wilson et al. (1976) and Gardner and Whiteoak (1979). The ratios obtained from 110−111 data are lower limits because of the effect of photon trapping in H2CO (see the discussion by Henkel et al. 1979b). From measurements of the 110−111 and 211−212 lines and model calculations, Henkel et al. estimate that the corrections for 10 clouds outside the Galactic center region is 1.6±0.7. This correction gives an average (H2CO/H213CO) ratio of 64±17. The models of Henkel et al. also predict the optical depth of the 312−313 line and the brightness temperature of the 212−1 11 line. Preliminary measurements of Wilson et al. (1979) show that the 312−313 results are consistent with the predictions; but more sensitive measurements are required to test the model fully. Unpublished 212− 1 11 emission-line spectra are weaker than predicted by the model, but this might be caused by beam dilution, since the observations were made so as to cover a 1.5′ uniformly weighted aperture. The lineshapes of the 110−111 and 2 11−212 absorption lines agree poorly with the 212−111 emission lines, indicating either that self-absorption in the millimeter lines of H2CO is important, or that there are H2CO clouds behind the continuum sources. Because of their position relative to the continuum sources these clouds would contribute to the millimeter emission lines but not to the centimeter absorption lines.
CO Abundance and Isotopic Fractionation in Dark Clouds
Authors: Goldsmith Paul F. , Langer William D. , Carlson Eric R. , Wilson Robert W.
Published: July 2016

In order to determine molecular fractional abundances, both the molecular density and hydrogen density must be known. In this study we have determined these parameters by fitting the observed intensities of J = 2 → 1 and J = 1 → 0 13CO and C18O transitions using a spherical cloud LVG radiative transfer model. The kinetic temperature is determined by observations of 12CO and is found to be between 9 K and 13 K for our sources. The fractional abundance of CO is expected to rise rapidly between regions of low extinction and those with Av ≥ 4 mag, due primarily to the decrease in photodestruction rates (Langer 1976). The C18O fractional abundance data plotted as function of Av support a nonlinear relationship between X(C18O) and Av for Av ≤ 4 mag, with an indication of an asymptotoic value X(C18O) = 2.2 × 10 (-7) in highly obscured regions. For 16O/18O ratios of 250 (suggested by our data although possible uncorrected saturation of 13CO makes this a lower limit) and 700 (A. Penzias, private communication) the fractions of carbon in CO in well-shielded regions are .08 and .23, respectively.
Interpretation of Isotopic Abundances in Interstellar Clouds
Authors: Guélin Michel , Lequeux James
Published: July 2016

The abundances of elements in the interstellar medium (ISM) result from a complex sequence of nucleosynthetic processes which started some ten billion years ago in the Big Bang and are still going on. Their study and in particular their comparison with the stellar and the solar system abundances may give clues to: i) the properties of the early Universe, ii) the evolution of galaxies (rate of star formation, Initial Mass Function of stars, stellar nucleosynthesis and rate of ejection of matter by stars), and iii) the flux of low-energy cosmic rays. (See e.g. Reeves 1974, Audouze and Tinsley 1976).
Observations of Circumstellar Clouds
Authors: Wannier P. G. , Redman R. O. , Phillips T. G. , Leighton R. B. , Knapp G. R. , Huggins P. J.
Published: July 2016

Observations have been made of J=2-1 CO in eleven circumstellar clouds including seven carbon stars and four oxygen-rich stars. Observations in four sources, including IRC+10216 have already been published (Wannier et al. 1979, henceforth Paper I) and the remaining observations are being prepared for publication (Knapp et al. 1980, henceforth Paper II). Several results are discussed below with special emphasis on the implications for two sources, namely IRC+10216 and Mira (o Ceti). The observations of IRC+10216 show CO emission over a diameter of 6 arcmin (∼ 0.5pc), a result suggesting a very large mass-loss rate. Mira is unique among the objects studied in displaying a small CO opacity and a high CO excitation temperature. It is suggested that this heating results from the orbital velocity of Mira due to its close binary companion.
Infrared Spectroscopy of Molecules in Circumstellar Material
Authors: Hall Donald N. B.
Published: July 2016

High resolution spectra of red giants and long period variables exhibit lines of infrared CO vibration-rotation bands arising in circumstellar material. In the few such stars so far observed at very high resolution (≲ 1 km/s) the circumstellar material appears localized in 3 distinct regimes with temperatures of 800K, 200K and 75K and expansion velocities of 0, 10 and 16 km/s rather than being uniformly distributed.
Interpretation of Circumstellar Masers
Authors: Goldreich Peter
Published: July 2016

In a short review paper one is often forced to survey the subject in a broad way and to ignore many, perhaps even important, details. Such is the case here. My remarks are intended to indicate how I view the current status of the field. In general, I shall avoid qualifying my statements, even when I am clearly guilty of oversimplification. If someone finds my paper provocative, so much the better.
Λ-Doublet Population Inversion in Collisions of OH, OD, CH, CD and NH+
Authors: Dixon R. N. , Field D.
Published: July 2016

The results of a new approach to the problem of the collisional step in the pumping cycle for OH and CH masers are reported. Rotationally inelastic collisions of OH and CH with both open and closed shell collision partners are considered using an expression derived from scattering theory. It is shown how Λ-doublet population inversion may arise in OH and CH. H-atoms and H2 may show opposite behaviour with CH, one partner cooling where collisions with the other lead to inversion. Implications for maser action are discussed and reveal excellent qualitative agreement with observation. Λ-doublet population inversion in OD, CD and NH+ is also considered.
Collisional Inversion of the Populations of Λ-Doublets in CH and OH: a Critical Study
Authors: Flower D. R.
Published: July 2016

Astronomical studies of the CH and OH masers have been based on the hypotheses of both radiative and collisional pumping. The mechanism of collisional inversion of the ground state Λ-doublets by neutral perturbers was first described by Bertojo et al. (1976) who made a semi-quantitative analysis of the collision process, based on calculations of potential energy curves. More recent work (Kaplan and Shapiro, 1979; Dixon and Field, 1979; Flower, 1980) has, however, been critical of some of the assumptions made by Bertojo et al. Consideration of the symmetry and the form of the interaction of CH and OH with the spherically symmetric perturbers para-H2 and He shows that current knowledge of the interaction potential is insufficient for quantitative results to be obtained.
Maser Amplifiers
Authors: Kollberg E.
Published: July 2016

When the lowest possible noise is required the maser amplifier remains the unquestionable amplifier choice for moderate bandwidth microwave and long wavelength millimeterwave receivers. The reason for the outstanding low noise properties of the maser is partly that it is cooled to a few degrees K (≲ 4 K) but also that the amplification process is the most fundamental one, i.e. amplification takes place when quanta (photons) are added directly to the signal field by stimulated emission of radiation from energetically excited particles.
New Experimental Possibilities and Future Prospects for 1-5μm Infrared Spectroscopy of Interstellar Molecules
Authors: Hall Donald N. B.
Published: July 2016

During the past week we have heard a considerable number of papers dealing with spectroscopic observations in the 1-5μm region of the infrared. I predict that as instruments and detectors continue to improve, such observations will play a major role in the study of interstellar molecules in both molecular clouds and circumstellar clouds around evolved stars. Fourier Transform spectrometers and Fabry Perot interferometers have already yielded spectra of such sources with spectral resolution and radial velocity precision fully comparable to millimeter wave observations. The critical need is to improve the limiting magnitude of such observations by 3-5 stellar magnitudes so that one can study large numbers of sources rather than the few brightest in each class.
Quasistatic Contraction of Magnetic Protostars due to Magnetic Flux Leakage
Authors: Nakano Takenori
Published: July 2016

A protostar with sufficient magnetic flux can be in quasistatic equilibrium. The structure at the time t of such an axisymmetric protostar immersed in a medium of finite pressure is determined when the mass m(ϕ, t) in each axisymmetric magnetic tube with the flux ϕ is given. A new distribution m(ϕ, t+δt) is found by calculating the amount of matter which crosses the surface of the magnetic tube ϕ in a time δt due to plasma drift (ambipolar diffusion), and then the structure at t+δt is determined. By repeating this procedure we can follow the quasistatic contraction of a protostar. Here we take into account the effect of charged grains in addition to ions upon the plasma drift.
Formation of the Giant Planets
Authors: Mizuno Hiroshi
Published: July 2016

The structure of a gaseous envelope surrounding a icy/rocky core is studied in consideration of radiative transfer. It is found that when the core grows beyond a critical core mass, the envelope cannot be in equilibrium and collapses onto the core to form a proto-giant planet. The results are as follows (for details, see Mizuno 1980).

1) The critical core mass is smaller than that estimated by Perri and Cameron (1974) and Mizuno, Nakazawa and Hayashi (1978). 2) When the grain opacity in the envelope varies from 0 to 1 cm2/g, the critical core mass changes from ~2 to ~12 Earth's masses. 3) The critical core mass is independent of the region in the solar nebula.

These are due to the existence of the radiative region in the envelope.
Contact Binary Evolution and Angular Momentum Loss
Authors: Vilhu Osmi , Rahunen Timo
Published: July 2016

Some fundamental problems connected with the evolution of W UMa stars are considered. While no generally accepted theory for the evolution of these systems exists, different scenarios lead to single stars on a nuclear or thermal time scale, or even to dwarf novae. The cycling and contact discontinuity models for zero age systems have gained much attention during the last few years. The contact discontinuity hypothesis has been heavily criticized on physical grounds, and the cycling at small mass ratios will probably be too violent leading to overcontact. On the other hand, there is increasing evidence of strong magnetic activity in short period solar type binaries, including W UMa stars (spots, flares, strong chromospheres and coronae etc.). This points to enhanced dynamo action inside rapidly rotating components of solar type close binaries. Extrapolating from single stars one finds that this may efficiently brake the orbital rotation. With an angular momentum loss rate of about 1043 g cm2 s−1 per year corresponding to the thermal time scale of the secondary the scenario, where the angular momentum loss controls the zero age contact evolution, seems at least possible. This scenario needs an (hypothetical) equilibrium process between the degree of contact and magnetic activity, damping the angular momentum loss if the contact becomes too thick, so that marginal contact will be preserved. If the angular momentum loss time scale is longer (comparable to the nuclear time scale of the primary), the system is likely to evolve towards more extreme mass ratios and with less violent cycling. (The complete paper will be published elsewhere.)
Blue Stragglers as Long-Lived Stars
Authors: Wheeler J. Craig , Breger Michel
Published: July 2016

The existence of blue stragglers in old open clusters with apparent mass more than twice the mass of the turnoff argues against simple binary mass transfer as the mechanism of their origin. The excess of blue stragglers to the red of the termination of the core hydrogen burning main sequence suggests that blue stragglers are not evolving normally. Stellar evolution models invoking mixing in an extended core region can account for the distribution of blue stragglers in the H-R diagram. Such models live longer, brightening and evolving further to the red before core hydrogen exhaustion than do normal stars. The distribution of blue stragglers in NGC 7789 is consistent with a range of mixed core mass fraction ~30–90 per cent and a narrow range in mass ~1.7–2.1 M⊙. Such evolution will result in a class of helium rich stars which have lived longer than normal and whose total mass exceeds the Chandrasekhar limit.
Effects of Nuclear Burning on X-Ray and UV Emission from Accreting Degenerate Dwarfs
Authors: Weast G. J. , Durisen R. H. , Imamura J. N. , Kylafis N. D. , Lamb D. Q.
Published: July 2016

The energy liberated by nuclear burning of matter accreting onto degenerate dwarfs can be more than an order of magnitude greater than that available from the release of gravitational potential energy. Nuclear burning therefore significantly alters the characteristics of X radiation from such stars. Here we report the results of two-fluid calculations in which steady burning occurs at various rates, and compare them with our earlier calculations which assumed no burning. If the star has a weak or no magnetic field, we find that nuclear burning enhances the soft X-ray flux emitted from the stellar surface, increases Compton cooling of the emission region and therefore reduces the hard X-ray luminosity and softens the hard X-ray spectrum. On the other hand, if the star has a strong magnetic field we find that nuclear burning enhances the soft X-ray flux emitted from the stellar surface but has little effect on the hard X-ray luminosity and spectrum. We apply the results of our calculations to the AM Her sources and to cataclysmic variables such as SS Cyg and U Gem, and discuss the evidence for and against nuclear burning of accreted material in these objects.
Rapidly Rotating and Fully General Relativistic Polytropes
Authors: Eriguchi Yoshiharu
Published: July 2016

A technique used in the numerical computation of Newtonian rotating polytropes has been generalized and applied to the rapidly rotating polytropes in general relativity.
The Neutronization of the Matter and Hydrodynamic Instability at Final Stages of Stellar Evolution
Authors: Chechetkin V. M.
Published: July 2016

In this report I consider dynamic instability when the non-equilibrium neutronization of matter plays the main role. The model of the deflagration supernova has been developed during more than ten year in our group. In 1973 it was shown that thermal flash evolves in the deflagration regime. In our computations the deflagration regime is stipuleted by joint effect of compression of matter and weak shock waves, obtained at the pulsing regime of burning. Fig. 1 shows the graduated growth of entropy in mass zone through passage of weak shock waves.
CR-39 Plastic Track Detector Experiment for Measurement of Charge Composition of Primary Cosmic Rays
Authors: Rao Y. V. , Davis A. , Hagan M. P. , Filz R. C.
Published: July 2016

A study of the relative abundances and energy spectra of heavy cosmic rays and isotopic composition in the region of Fe peak can yield significant information concerning their origin, acceleration and interstellar propagation. In recent years solid state nuclear track detectors have been employed extensively to study heavy primary cosmic rays. Plastic track detectors necessarily have large geometric factors for heavy primaries, and a continuous sensitivity for the duration of an extended exposure. A balloon-borne experiment consisting of 1 m2 passive detector array has been designed in order to obtain charge and energy spectra of primary cosmic rays in the region of Fe peak. Included in the array is a new type of nuclear-track-recording plastic, a polymer made from the monomer allyl diglycol carbonate (commercially known as CR-39). The stack was built as a set of nine modules. Three types of stack assembly was adopted for these modules: one consisting of ‘pure’ CR-39 plastic track detector: the next one, a composite assembly of CR-39 with three layers of 600 micron thick nuclear emulsions: and the last one with CR-39 and Lexan Polycarbonate. The payload was flown successfully in June 1979 from Eielson Air Force Base, Alaska. The flight was aloft for 3 hours 30 min at an average ceiling of 3 gm/cm2 of residual atmosphere. An attempt to stabilize and orient the payload utilizing a biaxial magnetometer combined with and electrical rotator was unsuccessful. The failure to orient the payload in a stable position would prevent us from determining the true direction of each cosmic ray particle and trace it backwards through the earth's magnetic field using a computer tracing program. Recovery of the payload was routine and all materials were in perfect condition.
Supernova and Cosmic Rays
Authors: Wefel John P.
Published: July 2016

The Supernova (SN) is one of the most important and most complex phenomena in astrophysics. Detailed observations of SN require advanced techniques of astronomy and high energy astrophysics, but the theoretical explanation of SN involves virtually every branch of physics. Supernovae, however, offer more than a challenging physics problem because SN are involved in the origin of most of the heavy elements, are the birthplaces of neutron stars, pulsars and probably black holes, control the structure of the interstellar medium, may be responsible for the birth of new stars (and possibly our own solar system), and, of greatest concern in this paper, are involved either directly or indirectly in the origin of the galactic cosmic rays.
The Heavy Nuclei Experiment on HEAO-3
Authors: Binns W. R. , Fickle R. , Garrard T. L. , Israel M. H. , Klarmann J. , Stone E. C. , Waddington C. J.
Published: July 2016

The third High Energy Astronomical Observatory, HEAO-3 was launched on the 20th Sept., 1979 into a 496 km, 43.6° orbit, and has since been successfully returning data from all three experiments on board. One of these experiments, that intended to study the heavy and ultra heavy nuclei in the cosmic radiation, is described here.
Are Stellar Flares and the Galactic Cosmic Rays Related?
Authors: Epstein Richard I.
Published: July 2016

It has been suggested that the Galactic cosmic rays may be accelerated by a two stage process in which one process, such as stellar flares, inject non-relativistic, super-thermal particles which are subsequently boosted to cosmic ray energies by some other mechanism, perhaps related to supernovae (eg. Cassé and Goret, 1978). Two-stage models in which the injection and re-acceleration processes are uncorrelated are apparently untenable because they cannot fit the observed energy dependence of the LiBeBN/CNO ratio. Here it is shown that additional contraints derived by considering the energy losses and nuclear reactions suffered by the super-thermal particles prior to their re-acceleration severely restrict other types of two-stage models.
Central Radio Sources in Galaxies
Authors: Hummel E.
Published: July 2016

From radio continuum observations it is known that the central regions of galaxies can be an important source of cosmic rays, in particular relativistic electrons. In order to get some insight in the properties of the central sources and their dependence on optical properties, especially morphological type, a large sample of galaxies (~ 400) was observed with the Westerbork Synthesis Radio Telescope at 1.4 GHz. The sample definitions, observations, reduction, survey characteristics and the analysis of the data are given in Hummel (1980, 1980a). Here we will concentrate on the results obtained for the central sources (> 20″).
The Large-Scale Distribution of Synchrotron Emissivity in the Galaxy
Authors: Kearsey S. , Osborne J. L. , Phillipps S. , Haslam C.G.T. , Salter C. J. , Stoffel H.
Published: July 2016

The all-sky radio continuum map at 408 MHz presented at this symposium by Haslam et al. can be interpreted in terms of the large-scale 3-dimensional distribution of synchrotron emissivity in the Galaxy when due allowance is made for the thermal emission. Its derivation from a 2-dimensional map must involve a number of assumptions so it is instructive to compare the results of alternative approaches (described in detail in forthcoming papers by the present authors). In both cases the variation of emissivity in the galactic plane is obtained from the observed intensity profile at b=0o and then the z-variation is chosen to give the best fit to the complete map. The observed profile is shown in the figure with and without the contributions of catalogued supernova remnants and HII regions.
The Components of the Galactic γ-Ray Emission
Authors: Salvati M. , Massaro E. , Panagia N.
Published: July 2016

The galactic luminosity for 0.1 < Eγ < 2 GeV can be evaluated directly from observational data and the commonly accepted value is 5 1038 erg s−1. Various contributions to the γ-ray emission can be recognized, namely i) strong sources, ii) pulsars, and iii) diffuse processes. Their relative importance is discussed in the following.
On the Mechanism of Generation of Solar Cosmic Rays Enriched by Helium-3 and Heavy Elements
Authors: Kocharov L. G. , Kocharov G. E.
Published: July 2016

The possible mechanism of helium isotopes separation in the solar atmosphere due to plasma effects have been proposed by G.E. Kocharov (1977), I. Ibragimov and G. Kocharov (1977). The cycle of papers: G. Kocharov and L. Kocharov (1978); L. Kocharov (1979 a,b,c,d, 1980); G. Kocharov, L. Kocharov and Yu. Charikov (1980) is devoted to the development of the theory and to the search of concrete model of corresponding physical processes in the solar plasma. Here we consider briefly the modern state of this problem.
Cosmic Ray Evidence for the Magnetic Configuration of the Heliosphere
Authors: Ahluwalia H. S.
Published: July 2016

Sekido and Murakami (1958) proposed the existence of the heliosphere to explain the scattered component of the solar cosmic rays. The heliosphere of their conception is a spherical shell around the sun. The shell contains a highly-irregular magnetic field and serves to scatter the cosmic rays emitted by the sun. It thereby gives rise to an isotropic component of solar cosmic rays, following the maximum in the ground level enhancement (GLE). Meyer et al. (1956) showed that a similar picture applies to the GLE of 23 February 1956. They conclude that the inner and outer radii of the shell should be 1.4 AU and 5 AU respectively. They suggest that a shell is formed by the “pile-up” of the solar wind under pressure exerted by the interstellar magnetic field, as suggested by Davis (1955).
GLOBULES, DARK CLOUDS, AND LOW MASS PRE-MAIN SEQUENCE STARS
Authors: Hyland A. R.
Published: July 2016

The current observational and theoretical literature on Bok globules and their relationship to star formation is reviewed. Recent observations of globules at optical, infrared, and far infrared wavelengths are shown to provide important constraints on their structure and evolutionary status, and the suggestion that many globules are gravitationally unstable is seriously questioned.

Dark clouds associated with T associations are well-known sites of recent and continuing star formation. In recent years molecular observations and far infrared surveys have provided maps of such regions from which possible sites of star formation may be identified. Optical (Hα) and near infrared surveys have enabled a clear identification of pre-main sequence (PMS) objects within the clouds. Methods of distinguishing these from background objects and the nature of their infrared excesses are examined in the light of recent observations in the near and far infrared. The perennial question as to the existence of anomalous reddening within dark clouds is also investigated.
INFRARED SPECTROSCOPY OF PROTOSTELLAR OBJECTS
Authors: Thompson Rodger I.
Published: July 2016

The process of star formation occurs in regions of space not accessible to the traditional techniques of optical spectroscopy and photometry. Star formation begins with a density enhancement in a cold molecular cloud. Stellar gestation then occurs inside an obscuring cocoon of natal gas and dust, which for high mass stars may still be in place when the star reaches the Zero Age Main Sequence (ZAMS). During this time the new star gathers the material which will make up its total mass, solves its angular momentum problem, achieves hydrostatic equilibrium and is making the conversion from gravitational to nuclear energy. The only direct view of this remarkable process is by radio and infrared techniques. Unlike many areas of infrared astronomy, which are extensions of previous optical studies to other wavelengths, information about star formation is primarily gained through infrared and radio studies.
Radio Observations of the γ-Ray Blazar 0528+134
Authors: Pohl M. , Reich W. , Krichbaum T. P. , Standke K. , Britzen S. , Reuter H. P. , Reich P. , Schlickeiser R. , Ungerechts H. , Fiedler R. L. , Waltman E. B. , Johnston K. J. , Ghigo F. D.
Published: July 2016

We report multifrequency observations of the γ-ray blazar 0528+134 with the Effelsberg 100-m telescope, the IRAM 30-m telescope at Pico Veleta and the NRL Green Bank Interferometer. The observing methods are described elsewhere (Reich et al., 1993; Pohl et al., 1995). The radio lightcurves are given in Fig.1 in comparison to the status of 0528+134 in the EGRET energy range. The uncertainties in the flux densities quoted there are less than 5% at 10.55 GHz and lower frequencies, while slightly exceeding this value at 32 GHz and 86 GHz.
A Dramatic (and Invisible!) flare in NRAO 530 3 mm λ VLBI Observations
Authors: Bower Geoffrey C. , Backer Don , Forster Rick , Wright Melvin
Published: July 2016

3 mm λ VLBI observations of the extremely flat spectrum QSO NRAO 530 at the peak of its brightest recorded flare show a resolved core only slightly changed from its pre-outburst state. Observations with Haystack, Kitt Peak and Owens Valley observatories in April 1994, prior to the onset of the flare found a single component with Tb = 8 × 1010 K. One year later, within one week of the peak of flare at 3 mm λ, observations with Haystack, Kitt Peak and Hat Creek observatories revealed a component comparable in size and flux density with Tb = 7 × 1010 K. Table 1 details the source models for the two experiments.
New Results from VLBI Polarization Observations of BL Lacertae Objects
Authors: Gabuzda D.C.
Published: July 2016

The major distinguishing features of BL Lacertae Objects are weak or absent line emission and strong and variable optical, infrared, and radio polarization (Angel and Stockman 1980; Kollgaard 1994). The radio emission and much of the optical emission is believed to be synchrotron radiation. In nearly every BL Lacertae object in which polarization structure has been detected, the polarization position angles χ in knots in the jets are nearly parallel to the VLBI structural axis. Assuming the jet components to be optically thin, the inferred magnetic fields B are nearly perpendicular to the jet direction θ; perhaps the most natural interpretation of this is that the knots are associated with shocks that compress an initially tangled B field as they propagate down the VLBI jet, enhancing B transverse to the compression (Laing 1980; Hughes, Aller, & Aller 1989). The superluminal speeds observed in the jets of BL Lacertae objects are on average lower than those observed in a comparably core-dominated population of quasars (Gabuzda et al. 1994). The distribution of core polarization position angles χcore at λ = 6 cm is bi-modal, suggesting that χcore is roughly perpendicular to θ when the cores are quiescent, and aligns with θ at epochs when polarization from newly emerging shock components is blended with the core polarization (Gabuzda et al. 1994).
3.6 cm VLBI Total Intensity and Polarization Images of BL Lacertae Objects
Authors: Gabuzda D.C. , Pushkarev A.B. , Cawthorne T.V.
Published: July 2016

The major distinguishing features of BL Lacertae Objects are weak or absent line emission and strong and variable optical, infrared, and radio polarization (Angel and Stockman 1980; Kollgaard 1994). The radio emission and much of the optical emission is believed to be synchrotron radiation. There are now some 20 BL Lacertae objects for which VLBI polarization (VLBP) images have been made at λ = 6 cm (Gabuzda et al. 1994 and references therein). In nearly every BL Lacertae object in which polarization structure has been detected, the polarization position angles in knots in the jets are nearly parallel to the VLBI structural axis. Assuming the jet components to be optically thin, the magnetic fields inferred by this orientation are nearly perpendicular to the direction of the jet; perhaps the most natural interpretation of this is that the knots are associated with shocks that compress an initially tangled magnetic field as they propagate down the VLBI jet, enhancing the magnetic field transverse to the compression (Laing 1980; Hughes, Aller, & Aller 1989).
Arcsecond Scale Polarization of BL Lac Objects
Authors: Stanghellini C. , Cassaro P. , Bondi M. , Dallacasa D. , Ceca R. Della , Zappalà R. A.
Published: July 2016

BL Lac objects are an enigmatic class of active galactic nuclei. They are characterized by high luminosity, a flat radio spectrum that steepens at higher energies, relatively high optical and radio polarization, rapid variability and an optical continuum with weak or absent emission lines (see Urry and Padovani, 1995 for a recent review).

These properties have been interpreted in terms of a relativistic jet closely aligned to the line of sight (Blandford and Rees, 1978, Ghisellini et al., 1993). This model, known as the beaming model, implies that there must be a so called “parent population” of radio sources intrinsically identical to BL Lac objects, but with the jets oriented at large angles to the line of sight. Browne (1983) was the first to propose the low luminosity FR I radio galaxies as the most likely candidates for the “parent population” of the core dominated BL Lac objects. An outcome of the beaming model is that all the properties not depending on orientation should be shared by the BL Lac objects and the FR I radio galaxies.
Large Bent Jets in the Inner Region of CSS
Authors: Mantovani F. , Junor W. , Bondi M. , Padrielli L. , Cotton W. , Salerno E.
Published: July 2016

Recently we focussed our attention on a sample of Compact Steep-spectrum Sources (CSSs) selected because of the large bent radio jets seen in the inner region of emission. The largest distortions are often seen in sources dominated by jets, and there are suggestions that this might to some extent be due to projection effects. However, superluminal motion is rare in CSSs. The only case we know of so far is 3C147 (Alef at al. 1990) with a mildly superluminal speed of ≃ 1.3v/c. Moreover, the core fractional luminosity in CSSs is ≃ 3% and ≤ 0.4% for quasars and radio galaxies respectively. Similar values are found for large size radio sources i.e. both boosting and orientations in the sky are similar for the two classes of objects. An alternative possibility is that these bent-jet sources might also be brightened by interactions with the ambient media. There are clear indications that intrinsic distortions due to interactions with a dense inhomogeneous gaseous environment play an important role. Observational support comes from the large RMs found in CSSs (Taylor et al. 1992; Mantovani et al. 1994; Junor et al. these proc.) and often associated with strong depolarization (Garrington & Akujor, t.p.). The CSSs also have very luminous Narrow Line Regions emission, with exceptional velocity structure (Gelderman, t.p.).
A World Array VLBI Image of 3C216 at 1.6GHz
Authors: Akujor C.E. , Porcas R.W. , Fejes I.
Published: July 2016

The quasar 3C216 has the distinction of being classified as a blazar as well as a compact steep-spectrum radio source (Akujor et al, 1993). It has a grossly mis-aligned large-scale radio structure. Previous VLBI images include those of the core region (Barthel et al 1988; Venturi et al 1993) with 1 mas resolution, and the sub-kpc scale core-jet with resolution ca. 25 mas (Fejes et al, 1992; Akujor et al, 1993). In order to investigate the connection between these structures seen on different scales, we have made a 1.6 GHz observation of the core-jet region with a “World Array” VLBI network. This consisted of 20 antennas, at Effelsberg (Germany), Jodrell “Lovell” (UK), Westerbork (Netherlands), Medicina and Noto (Italy), Onsala-26m (Sweden), Torun-15m (Poland), Simeiz (Ukraine), Bear Lakes (Russia), Seshan (China), Hartebeesthoek (S. Africa), Green Bank-43m, VLA and the VLBA antennas at HN, NL, PT, KP, LA, BR, OV (USA). The observations were made on 18 November, 1992, using the Mk2 recording system, and these were amongst the last to be correlated using the JPL-Caltech Block2 processor. The NRAO AIPS package was used for the data analysis.
Extreme Rotation Measure Radio Galaxies Measuring Cluster Magnetic Fields
Authors: Carilli C.L. , Perley R.A. , Miley G. , Röttgering H. , Van OJIK R.
Published: July 2016

Slysh (1966) first pointed out the bizarre properties of the polarized emission from Cygnus A: a strong wavelength dependence on fractional polarization, and a large difference in rotation measures (RMs) for the (integrated) emission from each lobe. These properties were confirmed, but not resolved, in the work of Mitton (1971) and Alexander et al., (1984).
Unusual Radio Structures in Markarian 6
Authors: Kukula M.J. , Pedlar A. , Baum S.A. , Holloway A.J.
Published: July 2016

Markarian 6, a Seyfert Galaxy of type 1.5, is one of several Seyfert nuclei to be observed with MERLIN at 6 and 18 cm as part of a project to investigate the radio structures of these objects on sub–arcsecond scales (corresponding to scales of a few tens of parsecs at typical distances). The angular resolution of MERLIN at 6 cm is equivalent to that of the HST, making the radio images ideal for comparison with HST images of the optical Narrow–Line Region (NLR). In this paper we briefly discuss the results of our MERLIN observations of Markarian 6, along with a 6–cm Westerbork Synthesis Radio Telescope (WSRT) map of the arcsecond (kpc) scale radio emission. The data is discussed in more detail by Kukula et al. (1996) and Baum et al. (1993).
A Search for HI in Strong Radio Galaxies
Authors: Simkin S. M. , Callcut J.
Published: July 2016

In the past decade it has become clear that many classical, double radio galaxies have hosts with extensive ionized gas inside the body of the optical galaxy (Hansen et al., 1987) (Baum et al., 1988). We have observed three such sources (PKS349-27, PKS634-20, and Pictor A) in both Hα and HI (with the VLA).
Merlin and HST Observations of the Jet in 3C273
Authors: Conway R.G. , Garrington S.T. , Muxlow T.W.B. , Davis R.J.
Published: July 2016

The jet of 3C273 is the only quasar jet visible at both radio and optical wavelengths. Investigations using ground-based observations suggest that the optical emission, like the radio, is produced by the synchrotron process. We present here a new radio map at 18 cm wavelength made with the improved MERLIN array (Fig. 1b) and compare it with a new optical image obtained with WFPC2 on the Hubble Space Telescope (Fig. 1a) This work has been carried out in collaboration with colleagues from Princeton, Pennsylvania State University and Caltech and is being published by Bancall et al. (1995).
Optical Polarization of 3C 265
Authors: Cohen M.H. , Tran H.D. , Ogle P.M. , Goodrich R.W.
Published: July 2016

3C 265 is a high-redshift (z=0.811) radio galaxy showing extended emission line regions (EELR) to 50 kpc from the nucleus (McCarthy et al 1995). However, it does not show the alignment effect (McCarthy 1993) that is common in distant galaxies: the EELR is not extended along the radio axis.
The Big Picture from Radio Waves to Gamma Rays
Authors: Impey C.D.
Published: July 2016

The conventional paradigm of active galactic nuclei (AGN) holds that they are powered by accretion onto a gravitational engine. In addition, the presence of Doopler-boosted radiation from jets and anisotropic obscuration can create large differences between the observed and intrinsic properties of AGN (Antonucci 1994). The “big picture” of extragalactic radio sources must include observations across the electromagnetic spectrum. Relativistic processes produce radiation with a very wide bandwidth. In addition, much of the energy from AGN is reprocessed, and the opacity is a function of wavelength. Finally, it turns out that only a small fraction of the bolometric luminosity of most AGN is emitted in the traditional radio and optical bands.
General Properties of Giant Radio Galaxies
Authors: Klein U. , Mack K.-H. , Saripalli L.
Published: July 2016

So far, the number of so-called giant radio galaxies (GRGs) is small. We define them as radio sources with linear sizes larger than 1 Mpc (H0 = 75 km s–1 Mpc–1). On-going low-frequency surveys may come up with many more candidates for this species. Their very existence may ultimately be connected with their environment. For instance, for a source like 3C236, which exhibits a linear and undisturbed structure over some 4 Mpc, the surrounding medium must have a low density. GRGs may thus serve to probe large volumes of the most tenuous intergalactic medium (IGM), e.g. via depolarization studies.
The Relic Radio Source B2 0924+30
Authors: Klein U. , Mack K.-H. , Gregorini L. , Parma P.
Published: July 2016

The double radio source B2 0924+30, associated with the luminous E/S0 galaxy IC2476, may be considered a prototypical genuine relic of a ‘dead’ radio galaxy as it seems to perfectly fulfill the following criteria: It has a rather steep overall radio spectrum (Ekers et al., 1981; Cordey, 1987). Its core luminosity is by far the lowest known so far (Giovannini et al., 1988). No coherent jet structure or other signs of activity are visible. Since only four possibly genuine relics of radio galaxies are known so far (Harris et al., 1993), a study of the archetypical source B2 0924+30 is of eminent importance for the understanding of this rare species of radio galaxies.
Radio Spectra and Particle Ages of the Head-Tail Radio Galaxy NGC1265
Authors: Feretti L. , Giovannini G. , Klein U. , Mack K.-H. , Sijbring L.G.
Published: July 2016

We have performed sensitive observations of three classical head-tail radio galaxies at λ11.1, 6.3, and 2.8 cm using the Effelsberg 100-m telescope (Zech, 1994). Complete maps of the sources 3C129, NGC1265, and 3C465 were obtained, including the distributions of the linearly polarized intensity. Together with the low-frequency interferometric maps these allow a comprehensive study of their radio spectra and, based on models of particle losses, the derivations of particle ages across these sources. The highest frequency involved allows an unambiguous derivation of the projected magnetic field structure, unimpeded by Faraday effects. Here we focus on NGC1265, which is located in the Perseus Cluster.
ATCA 13 and 20 cm Observations of A3556
Authors: Bardelli S. , Morganti R. , Venturi T. , Hunstead R.W.
Published: July 2016

We observed the cluster of galaxies A3556 (< v > = 14300 km/sec), belonging to the supercluster of galaxies known as the Shapley Concentration (Bardelli et al., 1994, MNRAS 267, 255, and references therein), with the Australia Telescope Compact Array. Our observations took place in the continuum band at 20 cm with the configurations 1.5D and 6C, and at 20 cm and 13 cm in the configuration 6A, for a total of 12×3 hours, with a resolution ranging from ≃ 6″ to ≃ 40″. We observed a sky region of ≃ 2° × 1° around the cluster center taking advance of the mosaicing technique developed ATNF.
The X-ray Intracluster Medium
Authors: Böhringer H.
Published: July 2016

Clusters of galaxies are the largest aggregates of matter that have decoupled from the universal expansion and have approximately evolved to a proper dynamical equilibrium configuration. While in the optical they are just observed as dense concentrations of galaxies, they are seen in X-rays as continuously connected entities through the emission of the X-ray luminous intracluster plasma (e.g. Sarazin 1986). Relativistic particles and magnetic fields are observed in clusters in radio halos, in regions around radio galaxies and through Faraday rotation of the radiation from background radio sources (see contribution by L. Feretti and e.g. Kronberg, 1994). Thus Clusters of galaxies are the largest, well characterized astrophysical laboratories in which plasma physical processes of diffuse media can be studied. In this brief summary the bulk properties of the intracluster medium (ICM) are discussed and two studies of the interaction of galactic radio lobes with the intracluster plasma are presented (related topics are discussed by F. Owen and L. Feretti in this volume).
Orientation Effects and Seyfert Cores
Authors: Norris R. P. , Roy A. L.
Published: July 2016

Activity in galaxies takes on a bewildering array of guises. Not all of this diversity comes from fundamentally diverse physics, but if we can understand the relationships between different types of galaxy then we may be able to perceive the underlying physics. This taxonomic approach aims to determine which properties are common to several types of galaxy, and which properties differ. The danger in this process is that it is easy to invent spurious relationships between similar, but quite distinct, types of object.
New Observations of BL Lacertae Objects
Authors: Stocke John T.
Published: July 2016

This contribution is divided into three parts: 1. A summary of mostly published work that describes the new type of BL Lac Objects discovered with X-ray satellites, “X-ray Bright BL Lacs (XBLs)”, and their relationship to the previously known “radio bright BL Lacs (RBLs).” Most (but not all?) of the differences between XBLs and RBLs are explicable using a “viewing angle” model in which the soft X-ray emission emanates into a much wider cone (23-30°) than the radio emission (8-10°). 2. New ROSAT PSPC soft X-ray observations are presented for complete samples of XBLs and RBLs which may explain the absence of luminous optical emission lines in BL Lacs. 3. A deep, subarcsec optical imaging survey of a large (50) sample of both XBLs and RBLs conducted at the Canada-France-Hawaii 3.6m Telescope (CFHT), whose purpose was to characterize the host galaxies and clustering environment of BL Lacs. This work defines more precisely the “parent population” of BL Lacs and identifies a small number of discrepant objects which may not be “beamed FR 1s”.
The UV/Radio Correlation of Quasars and its Implications for Unified Schemes
Authors: Falcke Heino
Published: July 2016

What causes the differences in the central engines of AGN? Are they intrinsically different or are the differences entirely due to environment and orientation? We have postulated that there is basically only one engine, consisting of a black hole and a closely coupled (even symbiotic) jet/disk system with very similar parameters in all AGN. This has lead to interesting results concerning the modelling of the UV/radio correlations of quasars and the difference between FRI and FRII radio galaxies.
Cooling-Flow Models of the X-Ray Emission and Temperature Profiles of Elliptical Galaxies
Authors: Bertin Giuseppe , Toniazzo Thomas
Published: July 2016

We compare the results of a spherical, steady-state cooling-flow model with gas loss with the observed X-ray emission profiles and temperatures for five bright elliptical galaxies in Virgo and Fornax. We adopt a “thermal-instability” mass-loss prescription (following Sarazin & Ashe 1989) and refer to galaxy models constrained by radially extended stellar dynamical data (Saglia et al. 1992). Our cooling-flow models are specified by three free parameters: the mass accretion rate and the pressure pext at some external radius rext, and a dimensionless constant q, which regulates the mass deposition rate along the flow. We find that models with confining pressures of pext ≃ 4 ÷ 14 × 103K cm–3 and significant accretion rates of external material, up to 4M⊙/yr, provide emission and temperature profiles in good agreement with present-day data. The trend shown in the right frame of the lower panel in the Figure suggests a possible correlation between LX/LB and the iron abundance in the gas inside ellipticals. A full account of this work, together with all the relevant references, is given in Bertin & Toniazzo (1995); here below, we add a comparison of the models with some recent ASCA data (Loewenstein et al. 1994; Mushotzky et al. 1994).

This work was partially supported by ASI (under contract 94RS94-202/3 FAE) of Italy.
3-D Simulations of Kelvin-Helmholtz Instabilities in Supersonic Jets
Authors: Rossi P. , Bodo G. , Massaglia S. , Ferrari A. , Malagoli A.
Published: July 2016

One of the key processes governing the structure and evolution of astrophysical jets is their interaction with the surrounding medium. A jet can deposit momentum and energy in the ambient medium, and entrain external material. The main physical process responsible for mixing between a jet flow and the ambient medium is the Kelvin-Helmholtz (KH) instability. We have previously analysed the 2D evolution of the axisymmetric modes of a cylindrical jet (Bodo et al 1994) and of the antisymmetric modes of a planar slab jet (Bodo et al 1995). These last are thought to give indications of the 3D evolution of the helical modes of a cylinder, since the linear behavior is very similar. In this contribution we present some preliminary results of fully 3D simulations comparing them with the mentioned 2D results.
Dynamical Models of Emission-Line Gas in Radio Galaxies
Authors: Koekemoer A. M. , Bicknell G. V.
Published: July 2016

Extended emission-line regions (EELRs) in radio ellipticals are generally thought to trace gas acquired externally, eg. through interaction with a gas-rich disk galaxy (Athanassoula and Bosma 1985, Barnes and Hernquist 1992, Hernquist and Mihos 1995). We examine here the dynamical evolution of gas in mergers, focussing on the conditions required for collisions between streams of gas. We find that such collisions can occur over a relatively wide range of encounter geometries, producing large-velocity-amplitude kinematic signatures characteristic of those observed in EELRs. This is relevant to the formation of shocks, which can account for the ionization properties of EELRs (Koekemoer and Bicknell, this conference).