bluuebunny/crossref_metadata_2025 huggingface dataset:
Superluminal Radio Sources
Authors: Zensus J. A. , Pearson T. J.
Published: June 2019

There are now at least 23 radio sources in which apparent superluminal motion has been found. The effect is not limited to the “classic” examples like 3C 345, but is found in objects with a wide range of characteristic properties. We review the observations of the phenomenon and present an up-to-date list of the known superluminal sources.
Investigations of 3C345
Authors: Biretta J. A. , Cohen M. H.
Published: June 2019

The well known superluminal source 3C345 is associated with a 16th magnitude quasar at z=0.595. The optical continuum is highly polarized and shows violent variations. At x-ray frequencies it is a weak source; while at radio frequencies it is bright and variable. The radio structure consists of a 200 kpc halo, a 20 kpc jet, and a very bright pc scale region which shows superluminal motion. Recent MkII VLBI monitoring (Biretta, Moore, Cohen 1986) at 2, 5, 11, and 22 GHz has provided accurate spectra, sizes, expansion rates, velocities, and trajectories for the superluminal knots and the “core.” Here we consider physical conditions in the emission regions and models for the kinematics.
3C 273 and DA 193 Mapped with Crustal Dynamics VLBI Data
Authors: Charlot Patrick , Lestrade Jean-François , Boucher Claude
Published: June 2019

Hybrid maps of 3C 273 and DA 193 at 2.3 and 8.4 GHz have been produced with VLBI data acquired during a Crustal Dynamics campaign. By comparing to maps at previous epochs, superluminal components of 3C 273 are clearly detected. DA 193 is relatively compact. Structure corrections for the VLBI delay used in astrometry have been estimated from these maps. Some corrections are significant when compared with the precision of models used in astrometry and geodesy.
The Structure of 4C39.25 on Intermediate Scales
Authors: Wu S. Y. , Pauliny-Toth I. I. K. , Porcas R. W.
Published: June 2019

VLBI observations at 18 and 6 cm with European baselines of lengths up to 15 and 23 million wavelengths respectively have been used to search for structure in the quasar 4C39.25 on scales of 10 to 100 milliarcsec. No significant structure on these scales brighter than 5 percent of the peak brightness has been detected. The core itself, however appears to be extended on a scale of 2 to 4 milliarcsec and variable in flux density.
4C39.25 – Superluminal Motion Between Stationary Components
Authors: Shaffer D. B. , Marscher A. P.
Published: June 2019

During the 1970's, the compact radio structure of 4C39.25 consisted of a simple double source, whose separation did not change. A new component, which probably originated in mid-1979, is now seen to be moving superluminally between the original, still stationary, components. It is not clear which component of the source is the core, nor how the moving component will interact with the stationary component that it is now approaching on a collision course.
The Evolution of Compact Double Radio Sources
Authors: Mutel R. L. , Phillips R. B.
Published: June 2019

The evolution of compact double radio sources is discussed using a model due to Carvahlo (1985). We suggest that for doubles associated with active galaxies, there is a plausible evolutionary sequence from compact doubles to steep-spectrum compact sources to extended (D1) doubles.
Tests for a Relativistic Beaming Model Using a VLBI Survey
Authors: Inoue Makoto
Published: June 2019

We have examined a relativistic beaming model using a VLBI survey by Preston et al. (1985). Our statistical study of a ratio R of the flux density for the beamed compact core to that for unbeamed components of a source shows Lorentz factor γ to be ≅ 6 and RT (R at transverse alignment) to be ≅ 10−2 for a sample of 222 QSO's. In addition, we find that a sample of 60 radio galaxies show the beaming effect with γ ≅ 4. It should be emphasized here that the beaming effect strongly affects the source counts (Log N - Log S) especially at high frequencies.
X-Ray Properties of Compact Extragalactic Radio Sources
Authors: Worrall D. M.
Published: June 2019

A good correlation is known to exist between the X-ray and radio luminosity of flat-spectrum, core-dominated radio sources (e.g., Owen, Helfand and Spangler 1981). Worrall (1987) presents a logarithmic plot of spectral luminosity in the source frame at 2 keV versus that at 5 GHz for a variety of QSOs, Highly Polarized QSOs (HPQs), and BL Lac Objects. Friedmann cosmology with Ho = 100h km s−1 Mpc−1, qo = 0 is assumed. Exclusion of objects which are optically or X-ray selected, or in which the radio emission is not dominated by a flat-spectrum compact core, gives a sub-sample consisting of 50 QSOs, 20 HPQs, and 10 BL Lacs, of which 5,4,3, respectively, are known superluminals. The dispersion of these data about the log-log correlation (assuming a Gaussian distribution), is σobs = 0.44 ± 0.06 (90% confidence errors for one interesting parameter).
The Linear Polarization of Extragalactic Radio Sources at Milliarcsecond Resolution
Authors: Wardle J. F. C. , Roberts D. H.
Published: June 2019

We review the polarization sensitive VLBI observations of compact extragalactic radio sources that have been made to date, and discuss some preliminary physical results suggested by the data.
Evolution of the Milliarcsecond Polarization Structure of the BL Lacertae Object OJ287
Authors: Roberts D. H. , Gabuzda D. C. , Wardle J. F. C.
Published: June 2019

The λ6 cm total intensity and polarization structures of OJ287 have been determined at two epochs a year apart. At each epoch the source can be modeled as a linear structure consisting of a core and two knots at position angle PA ≃ −115°. This structure expanded slightly over a year, each knot increasing its separation from the core by ≃ 0.3 mas, suggesting an apparent superluminal velocity of ≃ 3.3h−1c for each.
Evidence for a Radio Brightening Zone Around SS433
Authors: Vermeulen R. C. , Schilizzi R. T. , Icke V. , Fejes I. , Spencer R. E.
Published: June 2019

SS433 is thought to be a binary system from which two antiparallel beams are ejected at 0.26c. An excellent review of this peculiar object has been given by Margon (1984). The so-called “kinematic model” describes the precessing motion of the beams. They can be obcervef over at least 8 orders of magnitude in distance: from 1012 cm to 1020 cm.
Using the Hubble Space Telescope to Relate the HIPPARCOS and Extragalactic Reference Frames
Authors: Hemenway P. D. , Duncombe R. L.
Published: June 2019

The HIPPARCOS satellite will produce positions, motions and parallaxes of celestial objects with previously unattained accuracy. This HIPPARCOS Instrumental System, however, will have an unknown solid body rotation with respect to an inertial reference frame. One aspect of our program of astrometric observations with the Hubble Space Telescope is to determine the rotation of the HIPPARCOS reference frame with respect to an extragalactic reference system.
Beyond Plate Tectonics: Looking at Plate Deformation with Space Geodesy
Authors: Jordan Thomas H. , Minster J. Bernard
Published: June 2019

We address the requirements that must be met by space-geodetic systems to place useful, new constraints on horizontal secular motions associated with the geological deformation of the earth's surface. Plate motions with characteristic speeds of about 50 mm/yr give rise to displacements that are easily observed by space geodesy. However, in order to improve the existing plate-motion models, the tangential components of relative velocities on interplate baselines must be resolved to an accuracy of < 3 mm/yr. Because motions considered small from a geodetic point of view have rather dramatic geological effects, especially when taken up as compression or extension of continental crust, detecting plate deformation by space-geodetic methods at a level that is geologically unresolvable places rather stringent requirements on the precision of the measurement systems: the tangential components on intraplate baselines must be observed with an accuracy of < 1 mm/yr. Among the measurements of horizontal secular motions that can be made by space geodesy, those pertaining to the rates within the broad zones of deformation characterizing the active continental plate boundaries are the most difficult to obtain by conventional ground-based geodetic and geological techniques. Measuring the velocities between crustal blocks to ± 5 mm/yr on 100-km to 1000-km length scales can yield geologically significant constraints on the integrated deformation rates across continental plate-boundary zones such as the western United States. However, baseline measurements in geologically complicated zones of deformation are useful only to the extent that the endpoints can be fixed in a local kinematical frame that includes major crustal blocks. For this purpose, the establishment of local geodetic networks around major VLBI and SLR sites in active areas should receive high priority.
VLBI studies of the nutations of the earth
Authors: Herring T. A.
Published: June 2019

The application of very–long–baseline interferometry (VLBI) to the study of the nutations of the earth has yielded unprecedented accuracy for the experimental determination of the coefficients of the nutation series. The analysis of six years of VLBI data has yielded corrections to the coefficients of the seven largest terms in the IAU 1980 nutation series with periods of one year or less, with accuracies approaching the truncation error of this nutation series (0.1 mas). The nutation series coefficients computed from the VLBI data, and those obtained from theoretical considerations (the IAU 1980 nutation series), are in excellent agreement. The largest corrections are to the coefficients of the retrograde annual nutation [2.0 ± 0.1 mas], the prograde semiannual nutation [(0.5 -ι0.4) ±0.1 mas], and the prograde 13.7 day nutation [−0.4 ± 0.1 mas]. (The imaginary term for the semiannual nutation represents a term 90° out–of–phase with the arguments of the nutation series.) The geophysical implications of these results are currently under active investigation. We discuss the methods used to extract the nutation information from the VLBI data, the calculations of the uncertainties of the resultant corrections to the coefficients of the nutation series, and the current research into the nutations of the earth.
Analysis of the Offset QUASAT Antenna
Authors: Catarzi M. , Tofani G.
Published: June 2019

In the ESA phase A of the Quasat project the use of a 10 m offset antenna, has been suggested (1). In the present work the use of the multifrequency coaxial feed, developed by ESA for the symmetric configuration, is analyzed with a multireflector configuration. The coaxial feed has the advantage of a more compact configuration. However reduced efficiency and higher cross polarization are expected at the lower frequency, due to the scattering on the subreflector surfaces.
Chinese Dual Frequency Water Vapor Radiometer for VLBI
Authors: Pei-yuan Xu
Published: June 2019

A Chinese VLBI Network Project is under construction in China. The first 25-m antenna and associated VLBI system have just been completed at the She-Shan Station of the Shanghai Observatory. Both geodetic and astrophysical VLBI programs will be undertaken with the Network. A dual frequency water vapor radiometer is being developed to determine the tropospheric path delay correction.
The Destruction of Quasars Clustering at z > 2
Authors: Chu Yaoquan , Zhu Xingfen
Published: June 2019

The study of quasars clustering could become an important discriminant among different scenarios of the formation of large scale structure. The quasar clustering has now been confirmed and measured (Chu and Fang, 1986; Shaver, 1988) and the evolution of quasar clustering has been reported (Fang, Chu and Zhu, 1985; Chu and Fang, 1986). In the present work a large sample of about 3600 quasars in Hewitt-Burbidge catalog is employed and it is divided into several subsamples with different redshift ranges, a comparison of the correlation function in different subsamples provides then a mean of studying the evolution of the clustering with cosmology time.
“On the Broad Hα Component of IC 5063, IC 5135 and NGC 2992”
Authors: Busko I. C. , Steiner J. E.
Published: June 2019

As part of a high resolution (0.55Å) spectroscopic survey of southern Seyfert galaxies, we observed a number of objects in the Hα region. The main goal of this survey is to study the profiles of the narrow lines in Seyfert 1 and Seyfert 2 galaxies. As a by-product, one can search for and analyse weak broad components in Ha that sometimes show up when Seyfert 2 galaxies are observed with high resolution and high signal to noise. Such objects are usually classified as Seyfert 1.8 or 1.9. The search and detailed study of these objects is of great importance for characterizing the weak end of the luminosity function of active galactic nuclei (AGN). The observations were made with a two channel intensified Reticon at the Coude spectrograph of the 1.6m telescope at the Laboratorio Nacional de Astrofisica (CNPq/LNA).
The Discrete Correlation Function: A New Method for Analyzing Unevenly Sampled Variability Data
Authors: Edelson R. A. , Krolik J. H.
Published: June 2019

A method of measuring correlation functions without interpolating in the temporal domain, the Discrete Correlation Function, is introduced. It provides an assumption-free representation of the correlation measured in the data, and allows meaningful error estimates. This method does not produce spurious correlations at zero lag due to correlated errors. It is shown that physical interpretation of the cross-correlation function of two series believed to be related by a convolution requires knowledge of the input function's fluctuation power spectrum. In the case of AGN line-continuum cross-correlation functions, the interpretation also involves model-dependence in the form of symmetry assumptions, and must take into account intrinsic scale bias. Application to published data for Akn 120 and NGC 4151 illustrates this method's capabilities. No correlation was found for the optical data for Akn 120, but the ultraviolet NGC 4151 data show a strong correlation, indicating that the broad C IV feature emanates from a region whose size is greater than 1.2 and less than 20 light days. These bounds on the size of the line-emitting region in NGC 4151 are in good agreement with the predictions of photoionization models.
The X-ray Spectra of High Redshift Quasars
Authors: Canizares Claude R. , White Julia L.
Published: June 2019

We present mean spectral parameters for various ensembles of quasars observed with the Einstein Observatory Imaging Proportional Counter (IPC). Our sample contains 71 optically or radio selected quasars with 0.1 < z < 3.5, Galactic NH < 1021 cm−2, total counts of 30 −500, and IPC gain < 19. Quasars are grouped into ensembles according to radio properties (Flat Radio Spectrum [FRS], Steep Radio Spectrum [SRS] or Radio Quiet [RQ]), and either redshift or X-ray luminosity, lx. We find a clear correlation between radio properties and α. FRS quasars have α∼0.4, SRS quasars have α∼0.7 and RQ quasars have α ∼1–1.4. There is no evidence for a dependence of α on z nor, for the FRS and SRS ensembles, on lx over nearly three decades. FRS quasars with 2.0 < z < 3.5 have just as flat mean spectra as those with low z, implying that a single power law, which is flatter than the canonical one with α ∼ 0.65, continues into the 1–10 keV band (in which the observed softer X-rays were emitted). Unfortunately, the results for high redshift and high lx RQ quasars are ambiguous because of systematic uncertainties in the ensemble means. Thus we cannot test the two-component spectral hypothesis of Wilkes and Elvis for these objects. SRS X-ray spectra could be steeper than FRS spectra because of the mixing of two components, although a single intrinsically steeper spectrum is easier to reconcile with the absence of z dependence. The uncertainty in a for RQ quasars with high z leaves open the important question of their contribution to the cosmic X-ray background.
EXOSAT Observations of Flux and Spectral Variability in the Seyfert Galaxy NGC5548
Authors: Branduardi-Raymont G.
Published: June 2019

The Seyfert galaxy NGC5548 was observed with EXOSAT 12 times between February 1984 and March 1986. The bottom panel of Fig. 1 shows the lightcurves obtained with the Low Energy telescope and CMA detector and the Medium Energy proportional counters. The CMA flux doubled in a month at the beginning of the EXOSAT coverage, and was down by more than an order of magnitude 15 months later; the source was again in a high state in January and March 1986. The ME lightcurve mirrors that of the CMA, with L2–6 keV varying between 1 and 5 × 1043 erg s−1.
Variable X-ray Absorption in NGC 4151
Authors: Warwick R. S. , Yaqoob T. , Pounds K. A.
Published: June 2019

The medium energy X-ray spectrum of the Seyfert galaxy NGC 4151 is characterised by a hard power-law continuum, a variable low-energy cut-off and iron line and edge features. Holt et al. (1980) found the spectral form below 4 keV to be incompatible with absorption in a uniform screen of cold gas and interpreted the apparent soft X-ray excess in terms of a partial covering model. However, recent observations point to a somewhat different description of the X-ray absorbing medium present in the nucleus of this galaxy.
Pair Production in AGN
Authors: Done C. , Fabian A. C.
Published: June 2019

The X-ray luminosity and variability of many AGN are sufficiently extreme that any hard γ-rays produced in the source will collide with the X-rays and create electron-positron pairs, rather than escape. A small region where vast amounts of energy are produced, such as an AGN, is an ideal place to accelerate particles to relativistic energies and so produce γ-rays by Compton scattering. The observed X-ray spectra of AGN are hard and indicate that most of the luminosity is at the highest energies so that absorption of the γ-rays represents a large fraction of the energy flux, which can then be re-radiated at lower energies. Pairs can thus effectively reprocess much of the radiant power in an AGN.
Relativistic Beaming of X-rays from Quasars
Authors: Kembhavi Ajit , Wagh Sanjay , Narasimha D.
Published: June 2019

A method is suggested for estimating the beamed and unbeamed components of the X-ray emission from quasars. It is shown that the beamed component correlates well with the core radio luminosity, while the unbeamed component shows no such correlation.
New Evidence for Accretion Disks in AGNs
Authors: Halpern Jules P. , Chen Kaiyou
Published: June 2019

We have refined our calculation of the line profile of a relativistic, Keplerian disk by incorporating a variety of emissivity laws, as well as broadening due to turbulence or electron scattering. The significant improvement in the fit to the double-peaked Ha line profile of the elliptical radio galaxy Arp 102B provides the most convincing direct evidence for an accretion disk in any AGN. Arp 102B appears to be a low-luminosity analog of 3C 390.3, and several lines of evidence point to the existence of small, hot ion tori illuminating an outer thin disk in both of these galaxies. The rarity of these emission-line profiles might be understood if this particular combination of ion torus/thin disk occurs only for a narrow range of ṁ(= Ṁ/ṀEdd).
The Spectrum of Massive Thin Accretion Disks: Theory and Observations
Authors: Laor Ari
Published: June 2019

We have made detailed calculations of the structure and the spectrum of massive, geometrically thin “bare” accretion disks. The calculations are for an α-disk with various assumptions on the viscosity law. The radiative transfer was treated with the Eddington approximation for an atmosphere with a vertical temperature gradient. All significant sources of opacity, for T>104K, are included, and all models are found to be optically thick throughout. Spectral modifications due to electron scattering (modified blackbody and comptonization) are not significant in most cases. The requirement of a geometrically thin accretion disk forces a limit of L<0.3Led on the accretion rate. Several previous disk calculations violate this limit (Malkan 1983, Czerny & Elvis 1987, Bechtold et al. 1987) and their results are questionable. The surface temperature is close to the effective temperature, even for regions where electron scattering effects are significant. This is due to the vertical temperature gradient and is in contradiction to earlier findings. The angular distribution of the ionizing flux is strongly influenced by general relativistic effects, and can be very different for various disks.
Near-Infrared Emission-Line Spectra of the Orion Nebula, NGC 4151, and Other Seyfert Galaxies
Authors: Osterbrock D. E. , Shaw R. A. , Veilleux S.
Published: June 2019

CCDs make the near-infrared spectral region out to about 1.1 μ observable. A good deal of information on the spectra of AGNs in this range has been published, which we are trying to systematize and extend at Lick. Our original lens-grism spectrograph camera is opaque over the region λ8600-λ10250, no doubt as a result of a coating on one of the elements of the Nikon lens, making this program impossible with it. However our newer “UV-Schmidt” camera is quite effective in this region. With it we have obtained well exposed spectra at moderate resolution (FWHM ≈ 7 Å) of NGC 4151 in three overlapping segments covering the region 7000–11000 Å. Also, for comparison we obtained similar spectra of NGC 1976, the Orion Nebula. The wavelengths and relative line fluxes were measured, and most of the lines were identified. The strongest three lines in both objects are, in order, [S III] λ9532, He I λ10830, and [S III] λ9069. The Orion Nebula spectrum is very helpful for identifying lines in NGC 4151, and for comparison with it. Among the lines identified in NGC 1976, many of them previously known, are [O II], [S II], [Ar III], [Fe II], [Ni II], [Ni III], [Cl II], [C I], in addition to O I λ8446, many H I Paschen lines and He I.
Using Narrow Emission Lines to Test Physical Models Unifying AGNs
Authors: Rawlings Steve , Saunders Richard
Published: June 2019

We contend that quantitative measurements of nuclear narrow emission line strength can strongly constrain models that unify AGNs. The reasons for the importance of narrow-line luminosity LNLR are:

a)

The lines normally arise via photoionisation by the integrated UV/soft X-ray luminosity LPHOT of the central source. Thus LNLR is directly linked to a physical quantity intimately connected with the central engine but not observable from the ground. For constant covering factor we expect an approximate proportionality between LNLR and LPHOT; this has been confirmed observationally for AGNs by estimating LPHOT from either optical non-stellar luminosity or effective ionisation parameter.

b)

NLRs are far enough from the photoionising source to avoid the excessive obscuration that appears able to attenuate broad-line and continuum emission. Narrow-lines are radiated isotropically unlike, eg, the radio core which may be Doppler boosted. Their variability timescale of 103–4 years is intermediate between those of LPHOT and any large-scale radio emission.
Composite Models: A Tool for Interpreting the Emission-Line Spectra of Active Galactic Nuclei
Authors: Viegas-Aldrovandi S.M. , Contini M.
Published: June 2019

In the last decade, emission-lines from a large number of active galactic nuclei (AGN) have been observed. Most of the models built to explain the observed narrow emission-lines are based on photoionization. Although these photoionization models account for the observed general features, many points remain unexplained and several authors suggest an additional energy source (Ferland and Mushotzky 1984, Ferland and Osterbrock 1986, Stasinska 1984, Viegas-Aldrovandi and Gruenwald 1988). Another possible explanation is suggested by the emitting cloud motions, which account for the observed line widths. If the clouds are moving throughout a dilute gas (n0 ≃ 300 cm−3), a shock can develop. Then, the physical conditions in the cloud are determined by the coupled effect of photoionization and shock hydrodynamics.
High Optical Polarization in Flat-Spectrum Radio Sources
Authors: Wills D. , Wills Beverley J. , Antonucci R.R.J. , Barvainis Richard , Breger Michel , Bailey J. A. , Hough J. H. , Ballard K.
Published: June 2019

We have made a polarimetric survey of 84 quasi-stellar objects, to supplement published polarization measurements for two samples of quasars identified with flat-spectrum (core-dominant) radio sources in 5 GHz surveys made at Bonn (Kühr 1980) and at the VLA (Perley 1982). The observations were made using the McDonald 2.1m Struve reflector and the polarimeter described by Breger (1979); the typical accuracy is 0.5% for an 18 mag object after half an hour. Earlier surveys, such as those by Stockman, Moore and Angel (1984), included objects of various radio spectral types, and only a small fraction of the objects showed high polarization (> 3%), but our sample of flat-spectrum quasars reveals many more (about half) of the objects to be highly polarized. Some of them are, expectedly, of the BL Lac class, but many of them have strong broad emission lines. There are two striking correlations among the results:

(1)

The degree of polarization is strongly correlated with the dominance of the radio core - specifically, with the ratio, R, of core to lobe luminosity (Fig. 1). For example, about 75% of the objects with log R > 1.25 and redshift z < 1 have p > 3%. This relation implies that if the radio core radiation is beamed, as seems likely, then so is the optical synchrotron component.

(2)

The fraction of objects with p > 3% is inversely correlated with redshift (e.g. Fig. 2). The most likely interpretation of this result is that quasars' degree of polarization decreases with decreasing rest wavelength, and the shorter wavelengths are shifted into our wide observational passband at higher redshifts.
Gravitational Acceleration and Forbidden Line Widths in Seyfert Galaxies
Authors: Whittle Mark
Published: June 2019

There now exists extensive data on the forbidden line widths in Seyfert galaxies. While a few Seyferts have anomalously broad lines with FWHM ∼ 500 - 1000 km s−1 (e.g. NGC 1068, MKN 3, MKN 78), the majority have narrower lines with FWHM ∼ 200 - 400 km s−1. Although these line widths are well known to be of Doppler origin, the physical processes responsible for accelerating the gas have yet to be clearly identified. Processes associated with the activity itself are suggested by the large linewidths of the broadest profiles as well as by the presence of a correlation between [OIII] FWHM and steep spectrum radio luminosity. On the other hand, the prevelence of narrower lines and total absence of correlation between [OIII] FWHM and overall level of activity (Seyfert 2s, Seyfert 1s, and QSOs) suggests that more normal, possibly gravitational, processes are important. To test this latter possibility, it is necessary to look for explicit correlations between [OIII] FWHM and diagnostics of galactic gravitational potential.
CO in Seyfert Galaxies
Authors: Heckman Timothy M.
Published: June 2019

We present data for Seyfert and normal galaxies in the Revised Shapley-Ames Catalog. The type 2 Seyferts are stronger CO and Far-IR emitters (by factors of 2–4) than either normal galaxies or type 1 Seyferts. The Seyfert CO line-widths correlate with both the 21cm HI and [OIII]5007 line-widths. Interferometer maps show that in many Seyferts the CO emission is strongly concentrated within radii of 100–1000pc of the nucleus. The implications of these results are briefly discussed.
Infrared-Selected “Warm” Galaxies Observed in X-rays
Authors: Green Paul J. , Ward Martin , Anderson Scott F. , Margon Bruce , Degrijp M. H. K. , Miley George K.
Published: June 2019

The Infrared Astronomical Satellite (IRAS) has detected many galaxies in the infrared (IR), most of which have fairly steep 25μ to 60μ spectra. Many quasars and active galaxies exhibit a significantly flatter spectrum in the infrared. Several studies, for example, DeGrijp et al. (1985) used this characteristic to select a subsample of “warm” objects from the IRAS PSC (1985).
The New Double Nuclei Markarian Galaxies
Authors: Petrosian A.R. , Sahakian K.A. , Khachikian E. Ye.
Published: June 2019

In the course of morphological survey of Markarian galaxies on 2.6 m telescope of the Byurakan Observatory four new double nuclei objects were discovered. The results of morphological investigation of these galaxies are given and some parameters of the objects and their nuclei are estimated.
Optical Nuclear Activity in Radio Galaxies in Clusters
Authors: Yee H. K. C. , De Robertis M. M.
Published: June 2019

It has traditionally been accepted that quasars and strong emission-line radio galaxies, although situated in regions of enhanced galaxy density, are rarely found within rich clusters (Yee and Green 1984; Longair and Seldner 1978). The recent finding by Yee and Green (1987) that at z ≳0.5 a substantial fraction of optically bright radio-loud quasars are found in galaxy clusters as rich as Abell class 1, suggests that a substantial evolution of the environments of rich clusters has taken place over this short time period. Similar results for radio galaxies have also been obtained by Hill and Lilly (1988, private communication). If this is an evolutionary effect, then at least some first-rank elliptical galaxies in low-redshift rich clusters must contain remnants of active galactic nuclei (AGN). Motivated by this, we attempted to find traces of AGN-like activity in a sample of FR class I radio galaxies which are known to be “quiescent” absorption-line systems situated in low-redshift clusters.
Interactions of Jets with Interstellar and Intergalactic Media
Authors: Wiita Paul J. , Rosen Alexander
Published: June 2019

Jets emanating from AGN propagate first through an isothermal, but roughly power-law in density, galactic halo and then into a hotter, less dense, and uniform intergalactic medium (IGM) or intracluster medium (ICM). We use a three-dimensional boundary-following code (Mitteldorf & Wiita 1988), altered to allow for a two-phase external medium. We vary the beam power, P, the redshift, z, the radius of the galactic halo/IGM interface, Rh, the steepness of the power-law fall-off within the halo, n, and the temperature ratio of the IGM (or ICM) to the halo, Tr to estimate the average linear sizes of extragalactic radio galaxies (RGs). Good agreement is obtained with regard to the relationships between the overall linear size of such radio sources and both the total radio power (at fixed redshift) and the cosmological redshift (at fixed power). These numerical models tend to support recent analytical models (Gopal–Krishna & Wiita [GW] 1987, 1988).
Formation of Bi-Polar Spiral Features in Galactic Nuclei
Authors: Pişmiş Paris , Moreno Edmundo
Published: June 2019

In earlier communications we have called attention to the existence of very tight spiral formations in the nuclei of some galaxies, particularly of the early type barred spirals, proposing a mechanism for their formation (Pişmiş and Moreno 1984). These kiloparsec-scale structures are loosely termed “rings” but their overall morphology suggests strongly that the image is a tightly wound double spiral usually delineated by knots of emitting material, “hot-spots”. A striking characteristic of these spirals is their very high luminosity compared to the outer regions of the galaxy. 26 galaxies with “nuclear” spirals are listed by Buta, thesis. A systematic search with short exposure high resolution imagery may reveal many more nuclear spirals. NGC 4736 (Sb) though not a barred spiral has a well defined inner spiral delineated by very luminous H II regions.
Low-Power Radio Sources in the Nuclei of Nearby E/S0 Galaxies: Evidence for Active Nuclei and for Current Star Formation
Authors: Wrobel J. M.
Published: June 2019

Galaxies were selected from the CfA redshift survey (Huchra et al. 1983, Ap.J.Suppl., 52, 189; Tonry 1984, private communication) according to: Decl.(1950) ≥ 0°; photographic or B(0) magnitude ≤ 14 mag; heliocentric velocity ≤ 3000 km s−1; and de Vaucouleurs morphological type T ≤ −1. The third criterion roughly corresponds to a distance limit of 40 Mpc for H0 = 75 km s−1 Mpc−1. The fourth criterion is equivalent to a Hubble morphological type of elliptical (E) or lenticular (S0), collectively referred to as E/S0 galaxies hereafter. 213 galaxies satisfy the above selection criteria, after 3 Local Group dwarf spheroidals are excluded. Various galaxy catalogs and the recent literature were consulted to check the CfA morphological classifications and to divide the galaxies into Es and S0s. These galaxies comprise a volume– and optical–magnitude–limited sample that is ideally suited to systematic searches in all spectral domains for low-power nuclear activity (Wrobel 1988, A.J., in press).
Radio-Optical Correlations in Distant Radio Galaxies
Authors: van Breugel Wil , McCarthy Patrick J.
Published: June 2019

Optical identifications and redshifts are now available for nearly all 3CR radio galaxies (Spinrad et al. 1985; Djorgovski et al. 1988). Using new radio and optical observations, supplemented with data from the literature, we are conducting a systematic comparison of their radio and optical (emission-line and galaxy) properties, and their dependence on redshift. Here we present new results on the alignments of galaxies and their associated radio sources, and radio source asymmetries.
Lyman α Emission from Disk Absorption Systems in QSOs: Star Formation in Young Galaxy Disks
Authors: Smith Harding E. , Cohen Ross D. , Burns Joseph E. , Moore David J. , Uchida Barbara
Published: June 2019

The strong self-damped Lyman α absorption systems present in the spectra of high redshift QSOs represent a unique population of absorber which has recently been associated with the precursors of current disk galaxies. In a low resolution survey for what we have come to call “Lyman α disk systems” performed at Lick Observatory (Wolfe, et al. 1986, Ap. J. Suppl. 61, 249) approximately 18 systems with confirmed damped Lyman α profiles and rest frame equivalent widths greater than 5 Å were detected in a sample of 68 high redshift QSOs (Smith, Cohen and Bradley 1986, Ap. J. 310, 583). Subsequent higher resolution study has shown these systems to have the following properties (Turnshek, et al. 1988, Ap. J., in press):

1.

Neutral hydrogen column densities, 2 × 1020 ≤ NHI ≤ 8 × 1021 cm−2.

2.

Low-mixed ionization state. Typically the low ionization states dominate the high ionization states (e.g. CII ≫ CIV). Some enrichment has occurred, −2≲[X/H]⊙ ≲0.

3.

Gas density, n ≲ 1 cm−3.

4.

The gas shows two components, a quiescent (disk) component, σν ≲ 10 km s−1, and a turbulent (halo) component, σν ≲ 20 km s−1. Some systems show only the low velocity dispersion component.

5.

At least one system intervening toward a radio QSO (Pks 0458-020) shows 21-cm absorption. The system shows multiple cloud structure with σν ≈ 6 km s−1, Ts ≈ 100 K, and structure extended over several kpc on the sky.

6.

There is evidence that these systems may be self gravitating with scale height of the order of 300 pc.

7.

These systems represent a unique population of absorber (distinct from the ‘Lyman a forest’ and heavy element systems) covering approximately 20% of the sky to z ≈ 3 and accounting for all of the baryonic matter at that redshift.
Twenty-Five Years of the Search for Extraterrestrial Communications
Authors: Morrison P.
Published: June 2019

On this silver anniversary of the first published proposal for a search of the skies to seek communications over interstellar distances, I present a rather personal account of the origins of the proposal, and an appraisal of the new and hopeful status of the search worldwide.
SETI is Coming of Age
Authors: Cocconi G.
Published: June 2019

If asked to assess the evolution of SETI in the quarter of a century which has elapsed since its proposal, I would say that it parallels that of most novel and challenging human endeavours; a mixture of technical and cultural progresses and set-backs.
Welcoming Address
Authors: Metcalf Arthur G. B.
Published: June 2019

This Welcoming Address on behalf of Boston University, the host institution for IAU Symposium 112, was given at the Symposium Banquet, which was held at the new hall of flags of Boston University in the evening of June 19, 1984.
Invocation
Authors: Trakatellis Demetrios
Published: June 2019

This invocation was offered at the Banquet of IAU Symposium 112 in the evening of June 19, 1984.
A Review of the Scientific Rationale and Methods Used in the Search for other Planetary Systems
Authors: Black David C.
Published: June 2019

Planetary systems appear to be one of the crucial links in the chain leading from simple molecules to living systems, particularly complex (intelligent?) living systems. Although there is currently no observational proof of the existence of any planetary system other than our own, techniques are now being developed which will permit a comprehensive search for other planetary systems. The scientific rationale for and methods used in such a search effort are reviewed here.
Assisting Extrasolar Planetary Detection Through the Determination of Stellar Space Orientations
Authors: Doyle Laurance R.
Published: June 2019

Various methods outlined for indirect planetary detection would greatly benefit (in some cases require) the determination of the planetary orbital plane, which is theoretically equivalent to the stellar equatorial plane. Determining the stellar space orientation, therefore, would greatly benefit extrasolar planetary detection.

We utilize stellar rotation periods determined from short-term variations in Call H&K sunspot emission combined with both stellar radii measurements and Doppler broadened spectral line profiles to get the stellar inclination to the line of sight.

The clocklike, on the plane-of-the-sky component determination utilizes the concentration of sunspot associated plage areas at central stellar latitudes when viewed in Call H or K emission. One can perform Call H&K emission speckle interferometry to measure the clocklike angle of this stellar Call H&K emission band, modeling it as an elliptical intensity distribution. Both components should be determinable to within ten degrees for at least resolvable fifth magnitude stars.
SETI: A More Eclectic Approach
Authors: Oliver Bernard M.
Published: June 2019

Three groups, one at Ames Research Center, one at the Jet Propulsion Laboratory, and one at Stanford University are currently engaged in the research and development phase of the NASA SETI program Other papers in this session will describe in greater detail some of the work going on at each of these centers. It is my intent here to give an overall picture of the program so that the other papers may be viewed in context.
Extraterrestrial Intelligence: Where is Everybody?
Authors: Ball John A.
Published: June 2019

Why are we unaware of extraterrestrial intelligence?
Dynamical Instabilities in Spherical Stellar Systems
Authors: Barnes Joshua
Published: June 2019

Equlibrium spherical stellar systems exhibiting instabilities on a dynamical timescale were first studied by Henon (1973), using a spherically symmetric N-body code. We have re-examined Henon's models using an improved code which includes non-radial forces to quadrupole order. In addition to the radial instability reported by Henon, two new non-radial instabilities are also observed. In one, found in models with highly circular orbits, the mass distribution exhibits quadrupole-mode oscillations. In the other, seen in models with highly radial orbits, the system spontaneously breaks spherical symmetry and settles into a tri-axial ellipsoid. These instabilities, which are driven by fluctuations of the mean field, offer some analogies to the well-known dynamical instabilities of a cold disk of stars. While our models are rather artificial, they indicate that dynamical instabilities may be more common in spherical systems than had been thought.
Tidal Effects on Globular Clusters
Authors: Seitzer P.
Published: June 2019

It was von Hoerner (1957) who pointed out that the tidal field of the Galaxy imposed a boundary condition on the size of globular clusters, a fact that had observational consequences when the first deep star counts became available (King 1962). More recently, though, dispute (cf Innanen, et al. 1983) has arisen over the identification of the observed limiting radius from star counts with that predicted by simple dynamical theory (King 1962, 1966; Szebehely 1967). Straightforward application of the classical three body problem seemed to imply that no stable stellar orbits would be found beyond the collinear Lagrangian points. Thus, to first order, the observed limiting radius would be just the radius of the inner Langrangian point L2 from the cluster center. For clusters in eccentric orbits, the tidal radius would be set at perigalacticon, where the tidal force is strongest. Numerical models of stellar orbits about a cluster in a realistic galactic potential by several authors (Jefferys 1976; Keenan and Innanen 1975; Keenan 1981) showed that stable orbits can exist with apocluster distances greater than rL2, due to the presence of non algebraic integrals of the motion that constrained the stars to move in a restricted region about the cluster rather than escaping.
The Structure and Internal Kinematics of Open Clusters
Authors: Mathieu Robert D.
Published: June 2019

Open clusters provide an opportunity for observational study of several important facets of stellar dynamics which cannot easily be addressed in globular clusters for either fundamental or practical reasons. In particular, open clusters are case studies for:

1)

The dynamics of small-N stellar systems. This aspect of open clusters has been excellently reviewed by King (1980), to which the reader is referred. The work of Retterer (1979) and Goodman (this volume) suggests that any differences in the velocity distributions of small-N systems as compared to large-N systems due to the increased importance of close stellar encounters will appear primarily in the high-energy tails of the distributions. This will be reflected in the structure of the cluster halos, where quality data are difficult to obtain. In order to guide observational study, more theoretical work is needed regarding the expected nature and magnitude of any observable deviations from large-N theory.

2)

The effects of a large stellar-mass spectrum. While globular clusters probably also have a spectrum of masses spanning an order of magnitude or more, the extension of the mass spectrum to higher masses in open clusters permits the dynamical consequences of a mass spectrum to be more easily studied. In addition, many studies have pointed out the significance of stellar mass lośs in massive stars for the evolution of clusters (e.g., Terlevich 1983). However, as yet the theory regarding the effects of such mass loss has not provided unique observational predictions which might act as critical tests, so this important issue will not be discussed further here.

3)

A spectrum of cluster ages. Open clusters span the complete spectrum of age from birth to dissolution. Except for the classic work of Wielen (1971 and this volume) in which he analyses the observed distribution of cluster ages, this feature of open clusters has been little exploited. Yet by mapping appropriate diagnostics with cluster age open clusters have the potential to provide empirical measures of the fundamental dynamical time-scales, e.g. the relaxation time, equipartition time and mixing time. Also, study of the very youngest clusters provides appropriate initial conditions for evolutionary models as well as insight into star- and cluster-formation processes.

4)

The effect of the external environment. Open cluster halos are molded by the galactic tidal field. In addition, open clusters are subject to Impulsive encounters with clouds in the interstellar medium. The effects of these environmental influences can be examined in numerous ways, including detailed analyses of the structure of cluster halos and observations of the variation with radius of anisotropy in the cluster velocity distributions.
N-Body Simulations of Realistic Open Clusters
Authors: Terlevich Elena
Published: June 2019

N-body simulations of dynamical evolution of open clusters have been computed with the purpose of comparing them with observations. Special effort has been put into reproducing conditions present in galactic clusters. Most of the models contain 1000 bodies with masses following a power-law mass function of slope a = −2.75 and mean mass 0.5M⊙. Neutron stars or white dwarfs (depending on the initial stellar mass) are generated by instantaneous changes in individual masses, when stars reach the end of their main sequence life. Close approaches between particles are treated by a two-body regularization technique that allows to follow binary evolution in detail. Two types of tidal perturbation are considered: a smooth linearized galactic tidal field is simulated assuming that the clusters move in a circular orbit at 10kpc from the galactic centre; transient shocks are simulated by encounters with extended interstellar clouds of different mass-spectrum, densities and space concentration. It is found that the combined action of evolutionary mass loss and binaries (when the cluster has a realistic mass function) is enough to arrest the core collapse. Tidal heating shapes the halo of the cluster. There is good agreement with the observed density and velocity distribution of open clusters and with reported changes in their mass function.
Structure Parameters of Galactic Globular Clusters
Authors: Webbink R. F.
Published: June 2019

Observed and derived structure parameters are tabulated for 154 galactic globular clusters, 7 dwarf spheroidal satellites of the Galaxy, and 6 globular clusters in the Fornax dwarf spheroidal. Observational parameters listed include equatorial coordinates, apparent level of the horizontal branch, reddening, subgiant branch color at the horizontal branch level, limiting and core angular radii, integrated magnitudes, and central surface brightnesses. Derived parameters include galactic coordinates, heliocentric and galactocentric distance, metallicity, limiting and core radii, central relaxation time scale, central mass density, central velocity dispersion, and central escape velocity.
On the dominant relativistic terms in the lunar theory
Authors: Soffel M. , Ruder H. , Schneider M.
Published: June 2019

For a simplified 3-body (Earth, Moon, Sun) problem it is shown how the usual Einstein-Infeld-Hoffmann equations for the lunar motion reduce to the Jacobi-equations after the transformation to the proper reference frame. The dominant relativistic contributions to the lunar laser ranging observables are then obtained in a Hill-Brown calculation. It is argued that in the proper reference frame all post-Newtonian variational terms are proportional to m = n′/(n-n′) [n(n′) = mean motion of Moon (Sun)].
Relativity in astrometry
Authors: Murray C A
Published: June 2019

The coordinate dependence of the definition of light deflexion is discussed and the concepts of “natural” and “proper” reference frame are introduced in order to derive astrometric observables from coordinate quantities. Confusion in published formulations of VLBI data analysis is discussed in the context of the IAU definition of the coordinate time scale TDB. It is pointed out that with this definition, the unit of TDB differs from that of TDT and it is suggested that the speed of light in barycentric units be adopted as a defining constant in the system of astronomical constants.
The relativistic effects in localization of gamma-burst sources
Authors: Mersov G. A.
Published: June 2019

The paper discusses influence of relativistic effects in gamma-burst propagation and the time sync. It is shown that the phenomenon of gamma-source aberration, while using the localization algorithm based on the estimates of gamma-burst arrival time instants should be regarded as relativistic effect. Criterions are derived which determine whether it is necessary to account for the relativistic effects, depending on the localization accuracy.