bluuebunny/crossref_metadata_2025 huggingface dataset:
The High Resolution Structure of the Centaurus A Nucleus at 2.29 GHz and 8.42 GHz
Authors: Meier D. L. , Jauncey D. L. , Preston R. A. , Tzioumis A. K. , Wehrle A. E. , Batchelor R. A. , Falkner J. , Hamilton P. A. , Harvey B. R. , Haynes R. F. , Johnston B. , Louie A. P. , McCulloch P. , Moorey G. , Morabito D. D. , Nicolson G. D. , Well A. E. , Roberts J. A. , Robertson J. G. , Royle G.W.R. , Skjerve L. J. , Slade M. A. , Slee O. B. , Watkinson A. , Wright A. E.
Published: June 2019

VLBI observations of the nucleus of Centaurus A were made in April, 1982 at two frequencies with an array of five Australian radio antennas as part of the Southern Hemisphere VLBI Experiment (SHEVE). Observations were undertaken at 2.29 GHz with all five antennas, while only two were operational at 8.42 GHz. The 2.29 GHz data yielded significant information on the structure of the nuclear jet. At 8.42 GHz a compact unresolved core was detected as well.
Calculations of the Linear Polarization of Inhomogeneous Relativistic Jets
Authors: Cobb W. K. , Wardle J. F. C. , Roberts D. H.
Published: June 2019

We have performed exact numerical calculations of the Stokes parameters I, Q, and U for optically and Faraday thick inhomogeneous relativistic jets. We consider how changes in Faraday depth, as well as in the observer-jet geometry, change the resolved and unresolved properties of the jet.
VLBI Observations of the 0957+561 Gravitational Lens System
Authors: Gorenstein M. V. , Bonometti R. J. , Cohen N. L. , Falco E. E. , Shapiro I. I. , Bartel N. , Rogers A.E.E. , Marcaide J. M. , Clark T. A.
Published: June 2019

A series of VLBI observations of the gravitational lens system 0957+561 at λ13 cm has yielded the positions of the A and B images, the relative magnification of their largest discernible radio structures, and the time variability of their smallest discernible radio structures. These observations have also allowed upper limits to be placed on the flux density of an expected third image. The positions and relative magnification of the A and B images provide new information with which to constrain models of the lens that forms the images. The detection of variations in the flux densities of the cores of A and B suggests that observations at shorter wavelengths may reveal superluminal motion, which may in turn provide a means to measure the relative time delay.
Observations of Cosmic Masers
Authors: Diamond P. J.
Published: June 2019

A review is presented of recent results from interferometric observations of cosmic masers. Several topics will be discussed, including MERLIN/VLA/VLBI observations of megamasers; recent results on masers in star forming regions and around late-type stars and some new results on the effects of interstellar scattering on maser spot sizes.
First VLBI Observations of 6.3 cm OH Masers in Compact HII Regions
Authors: Baudry A. , Diamond P. J. , Graham D. , Walmsley M. , Booth R. , Brouillet N. , Daigne G.
Published: June 2019

VLBI synthesis observations of the 2Π1/2, J = 1/2 excited-state of OH at 6.3 cm (ΔF = 1–0 = 4765.562 MHz) have been made towards four compact HII regions. Detailed maps have been produced for W3(OH) where three groups of sources are distributed over a region ∼ 0.01 pc in size. The brightest sources are shown to be saturated masers with TB ≳ 109 K. In ONl a weak feature gives fringes with a ∼ 0.05″ lobe spacing.
W43A: A Maverick Maser Source
Authors: Diamond P. J. , Nyman L.-Å.
Published: June 2019

We report here on some preliminary results from a multi-epoch monitoring project of the OH and H2O masers in the source W43A. Our results suggest that W43A is a very young stellar object which has just entered a strong stellar wind stage.
A Search for Very Compact Structure in 17 OH Masers
Authors: Kemball A. J. , Diamond P. J. , Mantovani F.
Published: June 2019

The apparent spot sizes of OH masers appear to be significantly broadened when seen through the inner galaxy or large extents of the galactic disk (Burke 1968). Bowers et al (1980) found evidence of small-scale structure (≲ 50 mas) in OH sources at distances of less than 5 kpc but this was characteristically absent in very distant sources (≳ 8kpc) at galactic longitudes 1 ≲ 40°. This result is typically explained in terms of interstellar scattering (ISS) by intervening diffuse HII regions.
OH Megamasers and Active Galactic Nuclei
Authors: Norris R.P.
Published: June 2019

OH megamasers are believed to be active galaxies in which a substantial fraction of the OH gas in the disk of the galaxy is stimulated by the intense far-infrared flux from the active nucleus. The result is that the galactic disk acts as a maser amplifier, producing in the OH line an amplified image of the radio continuum source in the nucleus. Megamasers promise to be powerful tools for the study of active galaxies, provided we can determine what it is that turns an active galaxy into a megamaser. Here I examine the archetypal megamaser galaxy Arp220 and ask the question: what makes it different from other active galaxies?
Circular Polarization at 1665 and 1667 MHz Towards OH Masers in NGC 6334N, NGC 7538N, NGC 7538S, and G45.07+0.13
Authors: Zheng X. W. , Moran J. M. , Reid M. J. , Schneps M. H. , Garcia-Barreto J. A. , Garay G.
Published: June 2019

VLBI OH maser observations simultaneously in right and left circular polarization at the 1665 and 1667 MHz transitions were conducted by taking advantage of the multichannel capability of the Mk III system. The OH maser maps of the right and left circular polarization at both transitions were obtained toward the OH maser sources NGC 6334N, NGC 7538N, NGC 7538S, and G45.07+0.13.
RS Ophiuchi - A Recurrent Nova with Twin Jets
Authors: Davis R. J. , Taylor A. R. , Bode M. F. , Porcas R. W.
Published: June 2019

An analysis of European VLBI data of nova RS Ophiuchi shows the presence of a linear jet-like structure which has a brightness temperature of 107K at 1.7 GHz. This ejection is shown to be two sided and the 1.7 GHz emission is non-thermal. The light curves show the presence of a second, thermal component emerging at higher frequencies at a later epoch.
Pulsar Interferometry with Microarcsecond Resolution
Authors: Wolszczan A. , Cordes J. M.
Published: June 2019

An ‘interstellar interferometer’ related to a double imaging of the pulsar PSR 1237+25 by refraction in the interstellar medium has been used to resolve the pulsar magnetosphere for the first time. With an interferometer baseline ∼ 1 AU, we have measured a typical transverse separation between the emitting regions of PSR 1237+25 to be ∼ 108 cm, or an angular separation ∼ 0.02 μas.
The Celestial Reference Frame Defined by VLBI
Authors: Ma C. , Shaffer D. B.
Published: June 2019

VLBI currently produces the most accurate positions of celestial objects. From 1979 to 1987, 114 extragalactic radio sources have been observed with dual-frequency Mark III VLBI as part of the NASA Crustal Dynamics Project and the NGS POLARIS/IRIS program. The formal statistical errors of conventional celestial coordinates are as small as 0.3 milliarcseconds. The fundamental quantity measured by VLBI is the arc length between radio sources. Thus, we suggest that VLBI be used to establish a coordinate reference frame based solely on radio positions, and that this system not necessarily be coupled to right ascension and declination.
Current Plate Motions
Authors: Gordon Richard , Demets Charles , Stein Seth , Argus Don , Woods Dale
Published: June 2019

The standard against which VLBI measurements of continental drift and plate motions are compared are self-consistent global models of “present-day” plate motions determined from geophysical data: marine magnetic anomalies at oceanic spreading centers, azimuths of transform faults, and orientations of earthquake slip vectors on transform faults and at subduction zones. Past global plate motion models have defined regions where the assumption that plates behave rigidly has apparently lead to systematic misfits, sometimes exceeding 10 mm/yr, of plate motion data. Here, we present some of the results from NUVEL-1, a new, self-consistent global model of present-day relative plate motions determined from a compilation and analysis of existing and new geophysical data. These data and new techniques have allowed us to eliminate nearly all statistically significant systematic misfits identified by earlier models, suggesting that the rigid-plate assumption is an excellent approximation when plate motions are averaged over several million years. Beside improving estimates of the motion on previously identified plate boundaries, we have also identified and determined motions on other boundaries whose subtle morphologies, lack of seismicity, and very slow (< 10 mm/yr) relative motions have made them difficult to detect. Here we focus on the application of VLBI measurements to help resolve plate tectonic problems and then briefly outline our results for Pacific-North America motion and plate motions in the Indian Ocean.
NASA/Crustal Dynamics Project Geodetic Data Analysis
Authors: Himwich W. E.
Published: June 2019

The VLBI group in NASA's Crustal Dynamics Project (CDP) maintains an integrated system for analyzing geodetic VLBI data. This system includes: CALC, calibration programs, SOLVE, GLOBL, and the Data Base System. CALC is the program which contains the models used to calculate the theoretical delay. SOLVE is used to analyze single experiments. GLOBL is used to analyze large groups of experiments. The Data Base System is a self-documenting data storage system used to pass data between programs and archive the data. Kalman filtering is being investigated for operational use in geodetic data analysis.
Combining VLBI and GPS to Produce a National Crustal Motion Network in the United States
Authors: Strange W. E. , Mader G. L.
Published: June 2019

A National Crustal Motion Network for the United States using VLBI and GPS technologies is being developed. Implementation of both the VLBI and GPS components of the network is underway.
Properties of the Core-Mantle Boundary
Authors: Hager Bradford H.
Published: June 2019

The core-mantle boundary (CMB), separating the molten metallic core from the overlying solid silicate mantle, marks the largest discontinuity in mechanical properties within the Earth. The ∼ 200 km thick region just above the CMB, named D″ by Bullen (1950), is characterized by an anomalous gradient in seismic velocity versus depth. D″ was originally interpreted as a region with a strong compositional gradient due to the accumulation of dense material at the base of the mantle. Subsequently, the anomalous gradient was interpreted as the result of a strong temperature gradient in a hot thermal boundary layer at the base of the mantle, an interpretation motivated by the requiremnet that heat involved in generating the geodynamo must be transported out of the core and through the mantle by convection.
New Developments in European VLBI
Authors: Schilizzi R. T.
Published: June 2019

Five major areas of development in European VLBI are reviewed: new telescope millimeter-wavelength VLBI; Mk2 and Mk3 correlators, the European Data Processing Facility for the 1990's and a 5 GHz receiver for the RADIOASTRON space VLBI program.
18 cm VLBI Network
Authors: Matveyenko L. I. , Kostenko V. I. , Timofeev V. V. , Kogan L. R. , Kanevskii B. Z. , Moiseev I. G. , Sorotchenko R. L. , Martirosyan R. M. , Golovnya M. V.
Published: June 2019

The Soviet VLBI network includes parabolic 70-m antennas located near Usuriisk and Eupatoria, a 64-m antenna in Bear Lake, 22-m antennas in Pushino and Simeiz, and a 25-m antenna near Ulan-Ude. The maximum baseline length in the E–W direction is equal to about 7000 km, and in the N–S direction is equal to 1300 km. The minimum baseline length is equal to about 100 km.
Japanese VLBI Project - VERA
Authors: Fujishita Mitsumi , Hara Tadayoshi
Published: June 2019

The Japanese VLBI project VERA (VLBI for the Earth Rotation study and Astrometry) is being designed. It will be dedicated to regular monitoring of the Earth's rotation and astrometry. VERA will be composed of two antennas spanning about 2300km and a correlator of multi-station capability. The diameters of the antennas are 35m and 15m.
Performance of the Medicina Radiotelescope and the New S/X Receiver for Geodynamics VLBI
Authors: Grueff G. , Comoretto G. , Mantovani F. , Tomasi P.
Published: June 2019

At the beginning of 1980 the Istituto di Radioastronomia of the Consiglio Nazionale delle Ricerche (C.N.R.) started the Italian VLBI Project.

The first antenna was completed in October 1983 (see Table 1 for telescope characteristics). The first VLBI Mark2 experiment was performed in March 1984. In December 1984 we had the first Mark3 experiment. From that time our Institute is officially member of the European VLBI Network (EVN) and since January 1986 it is also Associate Member of the US Network.
Mark IIIA and VLBA High-Density Recording
Authors: Webber John C. , Hinteregger Hans F.
Published: June 2019

The wideband Mark III recorder has been improved by the development at Haystack Observatory of a narrow-track recording system. Using 56 MHz bandwidth, more than 3 hours of VLBI data may be recorded on one tape. The same headstacks with new, thinner “digital video” tape allow recording at 128 Mbit/sec for 16 hours on one reel for the VLBA. New electronics for control, signal switching, and record/playback have been designed. Up to 2 Gbit/sec could be recorded by modular expansion.
An Optimal Identification of Clock Behaviour Model for VLBI
Authors: Zheng Dawei , Luo Shifang , Mackay J.R.
Published: June 2019

The accuracy of VLBI measument has reached centimeters (Carter et al., 1985). But in VLBI observation the observable are broken sometimes because of the variations of the clock phases or frequencies. This is the first problem met in VLBI data processing.
Atmospheric Effects on Interferometric Observation
Authors: Wen-jun Han
Published: June 2019

In recent years, the influence of atmospheric irregularities on electronic systems has been recognized. How these irregularities affect electronic systems is related to the propagation environment, the scales of the irregularity, and parameters of the equipment. The phase deviation caused by the atmosphere is important to the interferometer. However, there are some filter effects, namely antenna aperture filter, Fresnel filter, and baseline filter, which must be considered. The first two filter out the effects of small scale irregularities, and the last one filters out larger ones.
Influence of the Ionosphere Model on the Solution of a VLBI Geodetic Experiment
Authors: Petit G. , Lestrade J. F. , Boucher C. , Biraud F. , Rius A. , Nothnagel A. , Kaufmann P.
Published: June 2019

The GRIG-2 geodetic VLBI experiment was conducted in 1985, linking for the first time South America, Europe and Africa. At the single frequency band of 1.66 GHz which was used, the monitoring of the ionosphere is a critical aspect and several predictions of Total Electron Content (TEC) were used. One of them is derived from dual band Doppler observations of TRANSIT satellites, which were simultaneously conducted. The influence of these models on the solution is presented, with comparisons with other VLBI solutions. Decimetric accuracy has been achieved.
4 Years of Radio to X-ray Observations of 3C 273
Authors: Courvoisier T.J.-L. , Robson E. I. , Blecha A. , Bouchet P.
Published: June 2019

The quasar 3C273 has been repeatedly observed at radio, mm, IR, optical, UV and X-ray frequencies since December 1983. A complex pattern of continuum variations has been discovered, which can be used to provide model independent physical parameters, and to constrain different models. The main features revealed by our set of observations are:

(i)

A flux decrease by 40% in the 2–10 kev flux in 20 days in early 1984 (Courvoisier et al. 1987).

(ii)

Differences between the X-ray light curves at 0.5 keV and 2–10 keV.

(iii)

A drop in the mm to mid-IR emission by factors 2–4 in early 1986, while the near infrared flux remained stable (Robson et al. 1986).

(iv)

A decrease in the ultraviolet intensity of ∼40% in about 6 months in 1987 (Ulrich, Courvoisier and Wamsteker 1988).

(v)

Rapid variability in the infrared and optical emission on timescales as short as one day in 1988 (Courvoisier et al. 1988 and Robson, Courvoisier and Bouchet this conference).
Optically Thin Gas in the BLR of Seyfert Galaxies
Authors: Morris Simon L. , Ward Martin J.
Published: June 2019

Evidence has been accumulating that the gas which produces the broad line emission (BLR gas) in active galaxies has a range of physical conditions, and may indeed come from a distribution of spatially distinct regions (Gaskell 1982, Ulrich et al. 1984, Netzer 1987, Collin-Soufrin et al. 1988). In this paper, we try to separate out any contribution to the BLR emission line profiles from optically thin material. We do this by comparing the profiles of OI λ8446 (a flourescence line only produced by clouds very optically thick to Lyman α, Elitzur and Netzer 1985) and Hα (which can be produced by optically thick and optically thin clouds).
Star Clusters in Quasars: Bloated Stars as Broad Emission Line Clouds
Authors: Puetter R. C.
Published: June 2019

Many scenarios of the evolution of star clusters in the centers of galaxies involve the formation of a central supermassive object. Since black hole formation is not 100% efficient in mass usage, stars are left over. This paper investigates the properties of such stars and proposes that their externally heated atmospheres become “bloated” due to radiative forces from trapped line radiation. Such stars would swell to many times their normal diameters and acquire densities, sizes, and mean column masses typical of QSO/AGN emission line clouds (ELCs).
Is There a Scaling Law for the Size of the BELR in AGNs?
Authors: Gondhalekar P M
Published: June 2019

The spectra of active galactic nuclei (AGNs) are characterised by broad permitted emission lines. The relative intensities of these lines are roughly similar in spectra of galaxies of very different continuum luminosities. The most likely source of energy for the line emitting gas is photoionization by an energetic (non-stellar) radiation field.
The EXOSAT Spectral Survey of Emission Line AGN
Authors: Pounds K. A. , Turner T. J.
Published: June 2019

Results are presented from EXOSAT observations of Seyfert type active galactic nuclei (AGN). The sample chosen for study are 48 hard X-ray selected Seyfert type AGN, including all 30 of the emission line AGN in the Piccinotti sample. Combining EXOSAT LE and ME data has allowed us to obtain broad band X-ray spectra over the range 0.1–10 keV. Spectra in the ∼ 2–10 keV range are found to be well described by a simple power-law. The distribution of spectral indices across the sample can be approximated by a Gaussian distribution of mean energy index ∝ = 0.70 with σ∝ = 0.17 although not all individual spectra are consistent with this mean at the 90% confidence level. EXOSAT has also revealed a substantial number of sources with complex soft X-ray spectra. These include spectra with a second spectral component at soft X-ray energies and sources with “leaky” absorbing columns. Evidence that soft excess components occur in at least 50% of Seyfert type AGN together with detection of rapid variability in the soft component provides quantitative support for an accretion disc model for AGN.
Iron Line Emission from NGC1068
Authors: Koyama Katsuji
Published: June 2019

X-ray emission in the 2–10 keV energy range was observed with the Ginga satellite from the Seyfert 2 galaxy NGC1068. The continuum spectrum can be described by a power-law of photon index about 1.5. An intense iron line at 6.5 keV with an equivalent width of 1.3 keV was clearly noticed. The X-ray flux was about 6 × 10 −12 erg/sec/cm2 or 3 × 1041 erg/sec, assuming a distance of 22 Mpc. The observed spectrum is consistent with the scattering and reprocessing of X-rays by the gas surrounding the central engine. With this picture we estimate that the X-ray flux of the central engine is about 1043 - 1044 erg/sec, a typical value for a Seyfert 1 galaxy.
X-ray Selected AGN from the Extended Medium Sensitivity Survey
Authors: Gioia Isabella M. , Maccacaro T. , Morris S. L. , Schild R. , Stocke J. T. , Wolter A.
Published: June 2019

The spectroscopic identification of the Extended Medium Sensitivity Survey (EMSS) sources now provides ∼350 X-ray selected QSOs and Seyfert galaxies (AGN in our working definition) and 30 BL Lac objects. Almost all of the AGN are spectroscopically similar to AGN found by other means but a few resemble normal galaxies so closely that they would not be identified as AGN easily by any other method.
Spectra of AGN Accretion Disks — Preliminary Results
Authors: Scott H. A. , O'Dell S. L.
Published: June 2019

After the suggestion (Shields 1978) that some AGN emission might arise in an opaque accretion disk around a supermassive compact object, several papers (e.g., Malkan and Sargent 1982; Malkan 1983; Bechtold et al. 1987) have interpreted the flat ultraviolet continuum (“big blue bump”) observed in many AGN spectra, in terms of such a model. The early calculations approximated the radiation locally emergent from the accretion disk as blackbody; the more recent calculations (e.g., Czerny and Elvis 1987; Wandel and Petrosian 1988) have treated this emission as (electron-scattering) modified (possibly comptonized) blackbody.
Some Remarks on Gravitational Micro-Lensing
Authors: Refsdal Sjur , Kayser Rainer
Published: June 2019

Gravitational micro-lensing can be used to obtain information 1) on the inner structure of active galactic nuclei and 2) on the distribution of compact masses in the range 10−4 … 102 solar masses. A regular monitoring of the most promising candidates for micro-lensing should be carried out. The strongest candidate is the macro-lensed quasar 2237+030, for which we expect a change in the luminosity ratio between the images of about 5 per cent per year.
An Optical Imaging Search for Gravitational Lenses
Authors: Djorgovski S. , Meylan G.
Published: June 2019

We are conducting an optical imaging search for gravitational lenses. A sample of known quasars was selected on the basis of high redshifts and apparently large absolute luminosities; these selection criteria significantly enhance the probability that a given QSO is gravitationally magnified. Our search has yielded so far at least one lensed QSO, and several promissing candidates.
TAURUS observations of active galaxies: NGC 1275 and NGC 4151
Authors: Unger S.W. , Taylor K. , Pedlar A. , Ghataure H. , Penston M.V. , Axon D.J.
Published: June 2019

We have used the TAURUS technique to study the morphology and velocity field of spatially extended emission–line gas in a number of active galaxies. This paper describes our results for NGC 1275 and NGC 4151. The emission line maps of NGC 1275 are the first scientific data from the new 4.2-m William Herschel Telescope, and show that the morphology of the foreground galaxy falling into the Perseus cluster bears a close relationship to that of NGC 1275 itself, implying that the two galaxies are physically associated.

In the case of NGC 4151, we find the emission line region is elongated along the same axis as the nuclear radio source. This cannot be due to emission-line gas being accelerated by radio ejecta, since the emission-line gas rotates with the galactic disk. We suggest that the emission-line gas is being ionized by a highly anisotropic nuclear continuum source, UV photons escaping from the nucleus preferentially along the radio axis.
First Results with HIFI: Studies of Extended Anomalous Emission Regions with an Imaging Fabry-Perot
Authors: Tully R. Brent , Bland Jonathan , Cecil Gerald
Published: June 2019

The new imaging Fabry-Perot interferometer at the University of Hawaii is especially suited for studying extended emission regions in the vicinity of active nuclei. Dramatic results have been obtained for the objects observed so far: M51, M82, NGC 1068, NGC 4151, and NGC 4258.
The Large-Scale Activity in NGC 1068
Authors: Bland J. , Cecil G. N.
Published: June 2019

While NGC 1068 has received much attention in recent years, little is known of the large-scale dynamics and physical state of the ionized gas in this nearby Seyfert galaxy and, in particular, its connection with the nuclear activity. We have used the Hawaii Imaging Fabry-Perot Interferometer (HIFI) at the CFHT to obtain detailed spectrophotometry at 65 kms−1 resolution (FWHM) over the Hα and neighbouring [N II] lines. The final maps are derived from 100 000 fits to spectra taken at 0.4″ increments over a 200″ field-of-view. (A higher resolution study which concentrates on the circumnuclear, optical emission and its relation to the radio jet is presented at this conference by Cecil & Bland.)
Emission-Line Asymmetries and the Kinematics of the Narrow-Line Region in AGNs
Authors: Shaw Richard A. , De Robertis Michael M.
Published: June 2019

We have obtained high signal-to-noise ratio CCD spectra at ≤ 150 km/s resolution for 6 high-ionization Seyfert galaxies. We analyzed the profiles of the emission-lines over a wide range in both ionization potential (IP) and critical density (Ncr) in order to study the fundamental problem of cloud motion in the narrow-line region (NLR). Using the known correlations between FWHM and IP and/or Ncr for these galaxies, and assuming that the blueward profile asymmetries result from the combined effects of radially infalling or outflowing clouds and extinction within or between them, we deconvolve these effects by analyzing the correlation between emission-line asymmetries and both IP and Ncr. We find fair to good correlations in the sense that lines with high IP and Ncr also tend to have high asymmetry, while lines with low IP and Ncr have low but usually non-zero asymmetry. Simulated emission-line profiles generated with a spherically-symmetric model of a NLR suggest that the extinction arises primarily within radially infalling clouds.
Optical & Near Infrared Imaging of NGC1275
Authors: Hughes D. H. , Robson E. I. , Ward M. J.
Published: June 2019

We are currently studying a selection of active galaxies using the new IR array camera IRCAM on UKIRT. Our aim is to seperate the underlying stellar emission from that of the active galactic nucleus. Although the optical is the best wavelength region to discriminate between the different populations in the underlying spiral and elliptical galaxies, it is in the infrared that the contrast between the non-thermal central core and the surrounding galaxy is increased. We present reduced data from infrared images taken at 1.25, 1.65 and 2.2 μm with an image scale of 0.6 arcsec/pixel together with optical 0.44 and 0.55 μm CCD images of the Seyfert galaxy NGC1275.
Optical-Infrared Continuum Spectra and Polarization of Quasars: An Outburst in 3C 279 During 1987–88
Authors: Balonek Thomas J. , Heckert Paul A. , Elston Richard , Smith Paul S. , Sitko Michael L.
Published: June 2019

We have observed a period of rapid and intense optical-infrared brightness and polarization variability in the quasar 3C 279. The observations were obtained as part of an ongoing study of the optical-infrared continuum evolution in a sample of optically violent variable (OVV) quasars and BL Lacertae objects. Simultaneous broadband UBVRI photometric and polarimetric observations are used to study the optical continuum spectral evolution and wavelength dependent linear polarization and to search for broad near-ultraviolet continuum spectral components.
Hot Dust on the Outskirts of the BLR in Fairall 9
Authors: Clavel J. , Wamsteker W. , Glass I.
Published: June 2019

Since 1978, the Seyfert I galaxy F9 (z = 0.0461) has been observed at 54 epochs in the far ultraviolet and optical range with the IUE (Boggess et al 1978), and 27 times in the near IR from SAAO. The IUE provided spectrophotometric low resolution (900 km.s−1) datá over the 1200–3200 Å range as well as simultaneous broad band optical photometry at an effective wavelength of 5200 Å. SAAO data consist of photometric measurements in the J, H, K and L bands. From the IUE data, we obtained the light-curves of the continuum at 1328 Å and 1826 Å (rest wavelengths), as well as those of the Lyα1216, CIV1550 and MgII2800 emission lines. More details can be found in Clavel, Wamsteker and Glass (1989).
Millimeter Observations of Optically Selected Quasars
Authors: Keene J. , Neugebauer G. , Carico D. , Sanders D. , Soifer T.
Published: June 2019

We have observed a group of optically selected quasars at a wavelength of 1.25mm with the Caltech Submillimeter Observatory in 1988 May. Except for Mrk 231, they were chosen from the PG sample of quasars (Schmidt and Green 1983) and are thus UV bright objects. All of them, except for PG 2209+184, were also detected at 60μm by IRAS.
Submillimeter Observations of NGC 4151: Evidence for Thermal Dust Emission
Authors: Malkan M. A. , Gear W. K. P. , Edelson R. A. , Robson E. I.
Published: June 2019

Observations of NGC 4151 were made with the JCMT on UT 20 April 1988. The detector was the UKT14 system, a dual-beam, 3He cooled, composite doped Germanium bolometer. A bandpass filter was used to define a central wavelength of 438 μm (685 GHz) with a bandwidth of 84 GHz. The beam was approximately Gaussian, with a FWHM of 11′, and the pointing was good to A very significant 5σ upper limit of 200 mJy was obtained. The Figure shows the continuum energy distribution for NGC 4151, made without correcting for beam size. When combined with the measured 155 μm flux density of 4.8 Jy, a lower limit on the spectral index of α155–438μm ≥ +3.06 is derived. Since the steepest cut off allowed by synchrotron self-absorption is α = +2.5, these observations can place an upper limit on the flux at 155 μm arising from a synchrotron self-absorbed source, with the rest arising from a thermal dust source.
Morphological Properties of Unusually Warm IRAS Galaxies
Authors: Heisler Charlene Anne , Vader J. Patricia
Published: June 2019

A sample of unusually warm IRAS galaxies with spectral energy distributions peaking at 60μm is studied. The complete sample consisting of 21 known galaxies and 40 previously unidentified galaxies is selected according to the following criteria: all galaxies in IRAS Point Source Catalogue with high quality detections at 25μm and 60μm, FIR fluxes such that 4>f60/f25>1 and f60/f100>1, and a galactic latitude of |b|>10°. The colour ctireria select against galaxies with a significant cool dust component and the hotter dust present is presumably circumnuclear (Vader et al., 1988). CCD imaging reveals a morphological dichotomy in our sample - the galaxies are either relaxed systems (E/S0) or interacting (double nuclei, tidal features etc.). The relatively fast process of merging may link these two types of systems.
IRAS Galaxies: Near-Infrared Colours and Starformation
Authors: van den Broek Albertus C.
Published: June 2019

IRAS made it possible for the first time to study infrared complete samples of galaxies. On the average these galaxies appear to emit most of their energy in the infrared in contrast to optical selected galaxies. The so-called minisurvey is the first infrared completem sample studied and additional observations in the optical, near-infrared and radio have already been done for these galaxies. The interpretation of these observations has not yet led to a clear and uniform picture of the astrophysical processes in these galaxies. The question whether these galaxies are highly obscured by dust or whether these galaxies experience starbursts is not yet satisfactory answered.
Interaction of the Beams of Active Galactic Nuclei with Their Environment at High Redshifts
Authors: Gopal-Krishna  , Wiita P. J.
Published: June 2019

Aiming at a physical interpretation of the cosmological evolution of radio galaxies, we extend to a high redshift our analytical model for the propagation of relativistic beams first through a hot gaseous halo of the parent elliptical galaxy and then through an even hotter, but less dense, diffuse IGM, after crossing a pressure-matched interface between the two media1–5. This model, verified by quasi-hydrodynamical numerical simulations5 has earlier explained: (1) the current mean size of classical double radio sources (D ∼350 kpc), (2) their steep linear-size evolution with redshift, z: D α (1+z)−3, (3). The correlation between size and radio luminosity (at fixed z): D α P0.3, (4) the number and  of giant radio galaxies, and (5) the break in the local radio luminosity function (LRLF), occurring near P ∼1024W.Hz−1 at 1 GHz (Ho = 50 kms−1 Mpc−1). Inputs to the model are observationally based average parameters of the halo1 {kTh∼1 keV, n(r) ∼10−2cm−3[1+(r/2kpc)2]−3/4}, IGM7 {kTIGM ∼18 keV (1+z)2, nIGM ∼7.10−7cm−3(1+z)3} and the beam4 {opening angle θ (radian) = 0.02 + 0.03 [29 - log P(t=0)]}. We assume a reasonable value of ∊ = 0.1 for the initial efficiency of conversion of the beam power, Lb (Watts) into (total) radio output Pt ∼1010. P(W.Hz−1). A gradual weakening of magnetic field within the expanding source raises the significance of inverse Compton losses against the Cosmic Microwave Background (CMB), leading to a reduced radio efficiency (RRE)3,2.
X-ray Constraints on AGN Clustering
Authors: De Zotti G. , Persic M. , Franceschini A. , Danese L. , Palumbo G.G.C. , Boldt E. A. , Marshall F. E.
Published: June 2019

Studies of the HEAO–1 A2 all–sky survey data have established that the level of anisotropy of the extragalactic X–ray background (XRB) is relatively low:

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The cell–to–cell XRB intensity variations can be entirely accounted for by Poisson fluctuations in the space distribution of known classes of sources; the 90% confidence upper limit to any additional contribution on a scale of 26 square degrees is 2.3% (Shafer and Fabian 1983).

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No significant correlations of XRB intensity fluctuations appear to be present; the formal 90% confidence upper limit on the amplitude of autocorrelations, relative to the mean background intensity, for an angular scale of 3° is Γ(3°) ≤ 1.9 × 10−2 (Persic et al. 1988).
Compact Radio Components in Seyfert Nuclei
Authors: Taylor D. , Dyson J.E. , Pedlar A. , Axon D.J. , Unger S.W.
Published: June 2019

Although initial, low resolution radio measurements by deBruyn and Wilson (1978), suggested that the radio emission in Seyfert nuclei was in approximate pressure equilibrium with thermal gas in the Narrow Line Region (NLR), higher resolution radio measurements using the VLA and MERLIN (eg Unger et al. 1985) showed that the radio components were at significantly higher pressures than the NLR thermal gas. This is even more apparent in the very long baseline interferometry (VLBI) observations using the European Network (EVN). Observations of NGC4151 (Harrison et al.1986) and NGC7674 (Unger et al. 1988) have already been described, together with a summary of work in progress by Pedlar et al. 1987. Several Seyfert nuclei have components in which relativistic particle/magnetic field pressures as high as 10−7 dynes/cm2 are infered. These observations are also consistent with the collimated ejection of either radio emitting ‘plasmons’ or beams from the optical nucleus.
Monitoring of Southern QSOs at 843 MHz
Authors: McAdam W.B.
Published: June 2019

A sample of more than 100 southern QSOs is being monitored for flux density variations by the Molonglo Observatory Synthesis Telescope (MOST). Provisional results for an interval of 4 years shows that the variability at 843 MHz is less than at 408 MHz. There seems to be a real ‘mid-frequency gap’ with little variability near 1 GHz.
Optical Properties of High Redshift Radio Galaxies
Authors: McCarthy Patrick J. , Spinrad Hyron , van Breugel Wil
Published: June 2019

The 3CR catalogue of extragalactic radio sources is now completely identified for b > 15° and redshifts have been determined for > 98% of them (see Djorgovski et al. 1988 for the latest update). The radio galaxies in this catalogue span the redshift range from 0 to 2.48. This sample provides us with a unique opportunity to examine the optical and radio properties of a complete sample over a look-back time comparable to the Hubble time.
Statistical Properties of the Lyman α Forest
Authors: Bechtold Jill , Shectman Stephen A.
Published: June 2019

We have observed two high-redshift quasars with the echelle spectrograph and 2D-Frutti Photon Counter at Las Campanas, in order to investigate the statistical properties of the Lyman-α forest. The two-point correlation function for the Lyman-α forest lines at z ≈ 3 is consistent with zero, for all velocity splittings Δv > 50 km/sec. When Lyman-α lines and other metal lines from known metal-line systems are included, the correlation function shows a weak non-zero signal at small Δv. We suggest that the weak clustering of the Lyman-α forest detected by other workers may be the result of contamination by a small number of metal-line systems and their associated Lyman-α lines.
The Ejection of QSOs from Galaxies
Authors: Burbidge G. , Hewitt A.
Published: June 2019

In the 1950s, V.A. Ambartsumian (1958) proposed that galaxies result from explosive processes in galactic centers. Soon after the discovery of powerful radio galaxies in this same period, it became clear that explosive ejection of gas and relativistic particles was a common feature of active galaxies (Burbidge, Burbidge and Sandage 1963).
On the Number of Galactic Planetary Systems
Authors: Beckwith Steven
Published: June 2019

The discoveries of small particulate clouds surrounding several young stellar objects may be the first direct indications of ongoing planet formation in the Galaxy. If these clouds are indeed the initial stages of new planetary systems around the stars, then planetary systems are probably not rare occurrences around stars and may even be quite common. The evidence for these clouds and their interpretation as young planetary systems is reviewed and discussed in the context of estimating the probability for planet formation around solar-mass stars.
Prebiotic Matter in Interstellar Molecules
Authors: Brown Ronald D.
Published: June 2019

With the discovery of the first polyatomic molecules, NH3, H2O and H2CO in 1968/9 there was immediate speculation as to how far biological chemical evolution - from atoms to small carbon compounds of biological significance - could have occurred in the Galaxy. There was also potential conflict with the canonical scientific view of the origin of life, traceable to the production of simple bio-molecules from the influence of energetic atmospheric events on the simple gaseous mixture (CH4, H2, H2O and NH3) presumed to compose the atmosphere of the very young Earth.
Molecular Replication
Authors: Orgel Leslie E.
Published: June 2019

The replication of DNA is the process by means of which genetic information is passed from one generation to the next in all living organisms. It is widely believed that a similar process must have become important early in the development of life on the Earth, either before or at the same time as the evolution of protein synthesis. The evolution of any life-form based on familiar chemistry would seem to require the early appearance of some type of residue-by-residue replication, although it might be very different in detail from the one we know.
The Precambrian Evolution of Terrestrial Life
Authors: Knoll A. H.
Published: June 2019

Paleontological evidence indicates that terrestrial life existed at least 3500 Ma ago, and it is quite possible that the earliest cells arose well before that time. The early appearance of life on Earth suggests that under appropriate environmental conditions the probability of chemical evolution proceeding to the point of biogenesis may be reasonably high. Most of biological history has been the history of microorganisms, with tissue-grade plants and animals characterizing only the most recent 15% or so of the fossil record. Intelligent life has occupied only the latest instant in geological time. The time table of terrestrial evolution is governed more by the particulars of our planet's physical and biological history than by some universal tempo of evolutionary change. One aspect of terrestrial life that is likely to be universal is the organization of populations into efficient biogeochemical systems.
Some Implications of Mass Extinction for the Evolution of Complex Life
Authors: Sepkoski J. John
Published: June 2019

Extinction has the destructive effect of eliminating established lineages from an evolutionary system and the constructive effect of vacating ecospace into which new lineages can evolve. Mass extinctions, which are times of unusually intense extinction, have been consistently followed by major radiations of new lineages. Extraterrestrial impacts associated with extinction events and a periodic recurrence of these events implicates an extraterrestrial forcing mechanism as the ultimate cause of mass extinction. This suggests that the extraplanetary environment has played an important, active role in the development of complex life on Earth.
Project Sentinel: Ultra-Narrowband SETI at Harvard/Smithsonian
Authors: Horowitz Paul , Forster John
Published: June 2019

We have been searching the northern sky for ultra-narrowband carriers of intelligent extraterrestrial origin at 21cm wavelength. The dual-polarization 65,536-channel receiver has a resolution bandwidth of 0.03Hz, matched to the Drake-Helou spreading of the interstellar medium. This maximizes signal/noise ratio, and simultaneously rejects carriers of terrestrial origin. The results of 15 months of observation are summarized.
A Milky Way Search Strategy for Extraterrestrial Intelligence
Authors: Sullivan Woodruff T. , Mighell Kenneth J.
Published: June 2019

We assume that the density of sites of technical civilizations emitting suitable signals (whether purposeful or unintentional) is proportional to the stellar density at any location in our Galaxy, as modelled by Bahcall and Soneira (1980). A wide variety of possible radio luminosity functions Ø(L) for these civilizations is then assumed and for each the number of detectable signals per square degree over the sky is calculated. We find that most detectable signals occur at galactic latitudes of 10° or less and longitudes within 90° of the galactic center, a region which covers only 9 per cent of the entire sky. This result holds for a wide range of Ø(L) types, including Gaussian distributions and power law functions with slopes less than 2.5, or any combination of these. The Milky Way is much less preferred, but still advantageous, for cases of steep power law functions (slopes greater than 2.5) or Gaussian functions with mean luminosities so low that any existing civilizations can only be detected at distances less than 0.5 kpc. The only cases where low galactic latitudes are not advantageous are (1) for frequencies of operation less than 600 MHz where the deleterious effects on signal-to-noise ratios of the natural galactic background emission become dominant, and (2) in searches for narrowband (⩽ 1 Hz) signals at frequencies less than 2 GHz where significant interstellar broadening of signals occurs over distances of ≳10 kpc. Furthermore, all of the above results have broader applicability: they are equally valid for searches for any type of natural radio phenomenon if its probability of occurrence is proportional to stellar density.
New 45M Radio Telescope and Fourier-Transform Type Spectrometer at Nobeyama Radio Observatory
Authors: Hirabayashi Hisashi
Published: June 2019

The 45m radiotelescope of Nobeyama Radio Observatory (NRO) is now in operation. It has a surface accuracy of 0.2 mm (rms) and a pointing accuracy of 0.001 degrees. Two types of spectrometers were designed for the telescope. One type is an Acousto-Optical-Spectrometer (AOS) with a 16,384 channel, 2000 MHz full-bandwidth spectrometer, and a 8192 channel, 160 MHz full-bandwidth spectrometer. The other type is a direct Fourier transform type spectrometer called “FX”. One FX is designed for a 10 meter, 5 element supersynthesis interferometer and another for the 45m radio telescope. The “interferometer FX” is a spectro-correlator that processes 5 inputs of 320 MHz bandwidth signals into correlations with 1024 frequency channels. The “45m FX” has 4 sets of 10 MHz bandwidth, 1024 channel spectrometers.

It has been pointed out by Morimoto, Hirabayashi, and Jugaku (1978) that formaldehyde anti-maser absorption lines in the direction of dark clouds would be suitable for SETI (Search for Extra-Terrestrial Intelligence). The Nobeyama 45m radiotelescope is suited for such targeted deep SETI.
A Comparative Analysis of Space Colonization Enterprises
Authors: Drake Frank D.
Published: June 2019

It is shown that the energy requirements for interstellar colonization exceed that for intraplanetary colonization by a factor of ten million or perhaps much more. This is offered as an argument against extensive interstellar colonization as a means of dealing with population expansion, and as a possible explanation of the Fermi paradox.
Galactic Colonization and Competition in a Young Galactic Disk
Authors: Turner Edwin L.
Published: June 2019

Even if long-lived advanced technical civilizations arise very frequently and interstellar colonization is possible and common among them, it is argued that this colonization process is unlikely to fully occupy the Galaxy (i.e., saturate it) due to interactions between the colonizing civilizations. This argument is supported by the analysis of population dynamics equations based upon those of theoretical ecology which are believed to be applicable to an extremely wide range of behavior patterns. It is also pointed out that recent astronomical evidence suggests that the disk of our Galaxy may be substantially younger than previously thought, thus making a non-saturated colonization model more plausible.
Radial Velocities and Proper Motions of Globular Cluster Stars
Authors: Lupton Robert , Gunn James E. , Griffin Roger F.
Published: June 2019

We describe techniques and results for obtaining radial velocities and proper motions for individual stars in globular clusters. One set of these results for the nearby northern clusters M92 and M13 are discussed in terms of new dynamical models and distance estimators.
Rotational Field and Velocity Dispersion in Globular Clusters: ω CEN and 47 TUC
Authors: Meylan G. , Mayor M.
Published: June 2019

Thanks to numerous and accurate radial velocity measurements obtained with CORAVEL, the rotational velocity fields, the spatial velocity dispersions from the centre to the edge and the ordered to random motions ratios are deduced for two globular clusters: ω Cen and 47 Tuc. Masses through virial theorem and M/L ratios are also given. A more comprehensive study will be published in Astron. & Astrophys.
Possible Characteristics of Supernova Induced Enrichment of Globular Clusters
Authors: Smith Graeme H.
Published: June 2019

Within globular clusters, stars of similar temperatures and gravities commonly exhibit differences in the strength of the λ3883 CN band, the distribution of which is often bimodal. An archetype example of this phenomenon is NGC 6752 (Norris et al. 1981). As documented by Da Costa and Cottrell (1980), and Norris et al. (1981), the CN-rich giants in this cluster possess enhancements in nitrogen abundance by factors of 7–8 relative to the CN-poor giants. This may indicate that chemical enrichment of proto-cluster gas clouds took place as a result of the activity of massive stars, which manufactured nitrogen within their interiors and ejected it into the cluster gas while low mass stars were forming. The aim of this paper is to investigate whether the properties of NGC 6752 mentioned above might be consistent with supernova enrichment. Both the free and adiabatic expansion phases of supernova shells (Spitzer 1968) will be discussed in this context.
Gaseous Models
Authors: Sugimoto Daiichiro
Published: June 2019

We can understand physics of self-gravitating system in terms of gaseous models in so far that their global natures and effects of self-gravity are concerned. Here summarized what are known in idealized gaseous models. They include gravothermal collapse/expansion in linear and non-linear regimes, and post-collapse evolution with gravothermal oscillation. Also discussed are their relations with discrete system and with treatment in statistical mechanics.