bluuebunny/crossref_metadata_2025 huggingface dataset:
High Velocity Gas in the Orion Nebula
Authors: Scoville Nicholas Z.
Published: July 2016

Observations at both millimeter and infrared wavelengths reveal energetic activity within the core of the Orion molecular cloud in the vicinity of the KL-BN cluster. New observations of the high velocity CO emission at 2.6-mm with improved angular resolution (HPBW = 44″) show that the source diameter averages 4 × 1017 cm and the center of mass is displaced 10-12″ north of the Kleinmann-Low nebula to a position close to the Becklin-Neugebauer object. The total mass of high velocity gas in the core region is ∼10 M⊙ (assuming 10% of the carbon is in CO); the present kinetic energy is 4 × 1047 ergs. Further evidence that BN may be the ultimate source of this energy is provided by high resolution infrared spectra which show both ionized and high temperature (Tk ≳ 3000 K) neutral gas in this source. CO bandhead emission (v = 2 → 0, 3 → 1, and 4 → 2) seen in BN is thought to arise from collisional excitation at high temperatures in a very dense (nH > 1010 cm−3) region only 1 AU in size. And high spectral resolution profiles of the Br α and γ recombination lines show that the HII region previously detected in BN apparently has motions over 100 km s−1.
High Spatial Resolution Studies of H13CN, H12CN and HCO+ J = 1-0 Emissions in Orion A
Authors: Rydbeck O.E.H. , Hjalmarson Å. , Rydbeck G. , Elldér J. , Sume A. , Lidholm S.
Published: July 2016

The distributions of the H13CN, H12CN and H12CO+ J =1-0 lines have been mapped with 20″ spacing towards the Orion A molecular cloud using the new Onsala 20 m millimeter wave telescope equipped with a room temperature mixer. The aperture and main beam efficiencies are about 49 and 65% and the half power beam width is ∼ 43″. The absolute pointing accuracy is estimated to be better than 5″ rms in the Orion elevation range.
Long Chain Carbon Molecules in the Interstellar Medium
Authors: Avery L. W.
Published: July 2016

The long chain carbon molecules known as the cyanopolyynes (HCnN, n=3,5,7,9) are becoming increasingly more important in astrophysics. At present, the smallest member of the family, cyanoacetylene (HC3N), has been observed in at least 32 sources, and cyanodiacetylene (HC5N) in at least ten. Some 29 transitions of these two molecules have been detected to date, and the number of new sources and new lines is increasing quickly. Although the larger members of the family have not yet been found in sufficient abundance to permit studies in more than a few sources, the fact that they exist at all in detectable amounts is of interest from the standpoint of astrochemistry.
Ammonia Observations of the Molecular Clouds Near S68, S140 and OMC2
Authors: Little L.T. , Brown A.T. , Macdonald G.H. , Riley P.W. , Matheson D.N.
Published: July 2016

Maps of the J=1,K=1 inversion transition of interstellar ammonia are presented and compared with observations of carbon monoxide and formaldehyde.
1.0 mm Continuum Observations of Cool Southern Clouds
Authors: Gezari D. Y. , Cheung L. , Hauser M. G. , Frogel J. A.
Published: July 2016

High surface brightness 1.0 mm continuum emission has been mapped in nine southern hemisphere HII/molecular cloud complexes: NGC 6334, RCW 38, RCW 57, RCW 122, RCW 117, G333.6-0.2, G351.6-1.3, W 33 and W 33A. All of the sources are located in the inner part of the Galaxy near the galactic plane. This paper presents new 1.0 mm continuum mapping results with 65 arc sec resolution. A more detailed discussion of the observations is given by Cheung et al. (1978, 1979).
The Evolution of Giant Molecular Clouds
Authors: Norman Colin , Silk Joseph
Published: July 2016

We discuss the origin, lifetime, destruction, spatial distribution and relation to star formation of giant molecular clouds. A coagulation model including the effects of spiral density wave shocks is described. We explore implications for CO observations of external galaxies. The collective effects of OB star winds and supernova remnants in disrupting clouds are considered.
Atomic Hydrogen in and around the Giant Molecular Cloud Near W3 and W4
Authors: Hasegawa Tetsuo , Sato Fumio , Fukui Yasuo
Published: July 2016

Cold HI gas appears as self-absorption dips in the 21-cm line profiles in and around the giant molecular cloud near W3 and W4. The cold HI cloud is ∼150 pc long and extends along the galactic plane. It consists of several fragments, each of which is typically ∼25 pc in diameter and (1 − 4) × 104 M⊙ in mass. The [H2]/[HI] ratio is estimated to be 15 – 50. The mass of the entire HI cloud amounts to ∼105 M⊙, which is comparable to that observed in CO emission.
Observations of the J=1-0 and J=2-1 Lines of 12CO in L1551: Evidence for Anisotropic Mass Loss
Authors: Snell R. L. , Loren R. B. , Plambeck R. L.
Published: July 2016

Observations of the J=1-0 lines of 12CO have been made to determine the extent and nature of the broad secondary velocity feature in L1551 (S239) first detected by Knapp et al. (1976). L1551 is associated with an extended Herbig-Haro object, HH102 (Strom et al. 1974), and two compact HH objects, HH28 and HH29 (Herbig 1974). Two nearby stars, HL Tau and XZ Tau, show extreme T-Tauri characteristics. The broad CO velocity component is seen toward HH102. Strom et al. (1976) have detected an infrared source near the HH objects which has a luminosity and infrared colors consistent with a late B star reddened by roughly 20 magnitudes of visual extinction (Snell 1979). The infrared source lies in the direction of the core of L1551, which has a density of 105 cm-3 (Loren et al. 1979; Snell 1979). The infrared source is likely to be embedded in this dense core.
Molecular Fan of 360-pc Radius in the Galactic Center Region
Authors: Fukui Yasuo
Published: July 2016

Molecular hydrogen of ≳108M⊙ exists in the galactic center region, as has been revealed by recent observations of molecular emission lines (see e.g. Oort 1977). In the inner region of most of the dominant emission features concentrate at and 0 km s-1 ≲v ≲100 km s-1 extremely unevenly with respect to the galactic center (see Fig. 1). As a model of the molecular complex we propose a fan of 360-pc radius whose pivot is at the center. The vertical angle of the fan is about 50° and the central line of the fan makes an angle of about 60° to the line of sight. Molecules in the fan are flowing out radially from the center with a velocity of 110-140 km s-1. The ℓ-v pattern of the fan model is superposed on the CO map in Fig. 1. The model can explain the whole structure of the molecular complex as well as several fine details such as asymmetry in emission line profiles (Fukui et al. 1979). As for Sgr A and Sgr B2, numerical calculations of molecular line profiles have been made by using the large velocity gradient approximation. The calculations show that the broad and asymmetric line profiles in the complex are well reproduced by the fan model. Further, an isotope effect on line shape is predicted, which will be useful as an observational check of the fan model. Additionally, the carbon isotope ratio 12C/13C in HCN and CO was estimated to be 10-20 in the Sgr A +50-km s-1 cloud.
Rotational Fine Structure Lines of Interstellar C2 Toward ζ Persei
Authors: Chaffee Frederic H. , Lutz Barry L. , Black John H. , Vanden Bout Paul A. , Snell Ronald L.
Published: July 2016

We have detected 9 of the rotational fine structure lines of the 2-0 Phillips band of interstellar C2 toward ζ Persei using the Tull spectrograph and Reticon detector on the 2.7 m telescope at the McDonald Observatory. These data yield a total C2 column density of 1.2 × 1013 cm-2 and a rotational temperature of 97 K compared to 1.4 × 1013 cm-2 and 45 K predicted by the detailed model of the cloud by Black, Hartquist and Dalgarno. We suggest that radiative pumping through the Mulliken and Phillips systems has modified the C2 level populations in such a way as to produce an observed rotational temperature which exceeds that arising in pure thermal equilibrium.
The Photodissociation of Interstellar CH+
Authors: Kirby K.
Published: July 2016

Three new excited states of CH+ which can be reached by a dipole transition from the ground state with photon energies less than 13.6 eV have been obtained from accurate theoretical calculations. As these states are unbound with respect to nuclear motion, photon absorption into them results in dissociation of the molecule. Photodissociation cross sections have been calculated, and the CH+ photodissociation rates in the interstellar radiation field as a function of optical depth have been determined. The rates are approximately 500 times larger than previously assumed. We have compared these new photodissociation rates with the rates of other CH+ destruction mechanisms in three different models of the interstellar medium. Photodissociation appears to be a significant destruction mechanism in any model requiring large interstellar radiation fields.
The Formation of Complex Interstellar Molecules by Radiative Association
Authors: Herbst E.
Published: July 2016

A new statistical theory of ion-molecule association reaction rate coefficients has been formulated and found to give good agreement with three-body association rate coefficients studied in the laboratory in the temperature range 100-300 K (Herbst 1979a). The theory indicates that certain radiative association reactions proceed rapidly at low interstellar temperatures to produce complex interstellar molecules, as suggested by Smith and Adams (1978).
On the Formation of Interstellar Linear Molecules
Authors: Sakata Akira
Published: July 2016

A possible mechanism for the formation of interstellar linear molecules is studied experimentally by means of synthesis apparatus. C2 and CN radicals are abundantly formed from plasmas containing C, N and H atoms. The C2 and CN radicals survive electron bombardment. They collide with each other and recombine to form linear molecules.
Laboratory and Modeling Studies of Chemistry in Dense Molecular Clouds
Authors: Huntress W.T. , Prasad S. S. , Mitchell G. F.
Published: July 2016

A chemical evolutionary model with a large number of species and a large chemical library is used to examine the principal chemical processes in interstellar clouds. Simple chemical equilibrium arguments show the potential for synthesis of very complex organic species by ion-molecule radiative association reactions.
Interstellar Molecules on Dust Mantles
Authors: Nakagawa Naoya
Published: July 2016

Condensation temperatures of various interstellar molecules in dark clouds are calculated. Chemical reactions in dust mantles are discussed.
Measurements of Isotopic Abundances in Interstellar Clouds
Authors: Penzias Arno A.
Published: July 2016

While an examination of the available data reveals some seemingly contradictory results, a general framework having the following outlines can be put forward:

1. With the exception of the two galactic center sources SgrA and SgrB, the relative isotopic abundances exhibited by the giant molecular clouds in our Galaxy exhibit few, if any, significant variations from the values obtained by averaging the data from all these sources.

2. The 13C/12C and 14N/15N abundance ratios are ∼130% and ∼150%, respectively, of their terrestrial values throughout the galactic plane and somewhat higher, ∼300%, near the galactic center.

3. The 16O/18O and 17O/18O abundance ratios are ∼130% and ∼160%, respectively, of their terrestrial values throughout the Galaxy, although the former may be somewhat lower near the galactic center.

4. The S and Si isotopes have generally terrestrial abundances.
Observations of Shock Waves in Interstellar Clouds
Authors: Beckwith Steven
Published: July 2016

Some techniques for observing shock waves in interstellar clouds are discussed. It is concluded that recent measurements of molecular hydrogen emission provide the best currently available technique for studying shocks. The results of measurements toward the Orion nebula are discussed, and a discussion and summary of the currently known H2 sources is given.
VLBI Observations of the V=1 and V=2 SiO Masers in W Hydra and VX Sagittarius
Authors: Lane A. P. , Ho P. T. P. , Predmore C. R. , Moran J. M. , Genzel R. , Hansen S. S. , Reid M. J.
Published: July 2016

Our previous observations established the small angular size and high brightness temperature of emission from the v=1, J=1-0 transition of SiO from the circumstellar envelopes of the supergiant VX Sgr and the Mira variable R Cas. We performed a second VLBI experiment on the SiO masers in several late type stars on 31 Oct.-2 Nov. 1978 to compare the physical characteristics of the SiO masers in the v=1 and v=2 states. With an energy separation of 1258 cm-1 (an equivalent temperature of 1753 K) between the two vibrational states, differences in excitation and pumping of the maser states may lead to different maser properties.
Absolute Positions of OH Masers Associated with HII Regions
Authors: Booth R. S. , Norris R. P.
Published: July 2016

We have measured the absolute positions of five OH maser sources associated with HII regions, using the Jodrell Bank phase compensated radio linked interferometer (Norris, Booth & Davis, 1980); these are reproduced in Table 1. In addition, we have mapped the relative positions of the features in the OH spectra at 1665 MHz for all of the sources and at 1667 MHz for 3 of them (W30H, NGC 7538 and W49). We are now able to compare the distribution of the OH masers in a given source with its radio continuum map and to investigate the proximity of masers in the 2 main line transitions and the H2O masers.
Further Observations of the H2O Emission from NGC 4945
Authors: Lépine J.R.D. , Santos P. Marques Dos
Published: July 2016

We wish to report briefly here the results of new observations of the H2O maser emission from the galaxy NGC 4945 made in 1979 July with the Itapetinga radio telescope. The H2O emission that we detected in 1978 September, shown in fig. 1, represented an intrinsic intensity about ten times that of W 49, the strongest source in our Galaxy, and raised the question of its nature (Marques dos Santos and Lepine, 1979). The main purpose of the new observations was to obtain a more accurate position for the source and to look for variability.
Detection of Interstellar BS in the Cirrus Dark Cloud of the Numbbum Association: I. An Intuitive Model and Its Subsequent Observation
Authors: Charfman J. J.
Published: July 2016

Previous suspicions of large quantities of BS in large astronomical associations have been confirmed by observation.
Chain-Reacting Thermal Instability and its Implication on Star-Formation in Interstellar CO Clouds
Authors: Sabano Y. , Sofue Y.
Published: July 2016

A new type of non-linear, chain reacting instability is presented that a sequential condensation occurs in a thermally unstable interstellar CO cloud, triggered by a local density perturbation. Non-linear growth of the instability was followed numerically with a one-dimensional and slab symmetric hydrodynamical code. The result shows that a local, small density enhancement onto initial density of n0=510 cm−3around x=0 (x: spatial coordinate) grows to a maximum density of nmax=1300 cm−3in a time scale of 0.6×106y, and at the same time the gas in neighbouring region at x=0.1–0.2 pc shifts into a low-density phase of nmin=200 cm−3. Since we assume a constant heating per particle by photons and cosmic rays, the gas in low density region is relatively more heated so that the pressure therein becomes higher than the background pressure. Then the low density gas pushes its neighbouring gas foward increasing x to lead to a second density enhancement at x=0.2 pc. In this way many further condensations are produced in a sequential manner. The spacings and sizes of condensations are uniquely determined by the characteristic parameters, the growth time of instability and the sound velocity of the background gas alone. The present calculation gives the spacing, 0.24 pc, and the mass of each fragment, 0.2M⊙. This mechanism could be related to sequential formation of less-massive stars in interstellar CO clouds, if the condensations evolve further into star formation sites.
Global Structure of Interstellar Medium and Star Formation Rate
Authors: Ikeuchi S.
Published: July 2016

Assuming that the interstellar medium (ISM) is composed of the hot ionized medium (HIM), the warm ionized medium (WIM) and the cold neutral medium (CNM), we examine the interchange processes among them by supernova remnants. These are the evaporation of CNM, the shock heating of WIM and the cold shell formation at the shock front. Calculating the time variation of each component, the timescale and evolutionary characteristics till attaining a steady state are deduced. Generally speaking, the final steady state is classified to two types.
Age Spread of the Orion Nebular Stars
Authors: Isobe Syuzo , Sasaki Goro
Published: July 2016

The Orion Nebula is a recent star formation place on a sequence of star formation in the Orion Association Ia to Id and further to the Orion Molecular cloud as shown by Kutner, Tucker, Chin, and Thaddeus (1977). From the photoelectric observations, Penston (1973, 1975) obtained the age of the Nebula younger than 3×106 years.
Fragmentation of Collapsing Gas Clouds
Authors: Sørensen S-A. , Narita S. , McNally D.
Published: July 2016

In simulations of the collapse of gas clouds it is usual to start from a uniform sphere the evolution of which is determined by the two energy ratios = Thermal/Gravitational and = Rotational/Gravitational. In numerical calculations the two parameters are unfortunately supplemented by a number of unknown factors related to the exact numerical treatment of the collapse. It is therefore crucial to compare the results of several different methods before any judgement is made concerning the correct evolutionary track of the cloud.
Accumulation of a Rapidly Rotating Protostar and the Formation of an Associated Nebula as a Result of Angular Momentum Transport by Turbulent Friction
Authors: Tscharnuter W. M.
Published: July 2016

The influence of angular momentum transport by turbulent friction on the structure of a rotating protostar has been investigated. Turbulence is characterized by a simple viscosity parameter η = ξ·cs·1, where cs denotes the local speed of sound, 1 the typical length scale of the largest eddies (thickness of the nebula) and ξ the “efficiency” parameter (= 1/10 in our model).
Non-conservative Evolution of Massive O-Type Close Binaries with Galactic and with Magellanic Cloud Chemical Abundances
Authors: Vanbeveren D.
Published: July 2016

The general evolutionary pattern of massive O type close binaries evolving according to a case B mode of mass transfer, including mass loss by stellar wind prior to Roche lobe overflow (RLOF) at rates appropriate for O type stars, only marginally depends on the choice of the initial chemical composition whether the galactic or the MC abundances are used (the difference never exceeds 10%). The theoretical results are compared to the observations, O type binaries describing the evolutionary phase prior to RLOF, WR type binaries describing the helium burning phase after RLOF. The large mass loss by stellar wind in WR stars considerably affects the evolution during the latter phase. The comparison yields the following conclusions:

a) from the ZAMS up to the WR stage, 50%-60% of the initial primary mass is leaving the system corresponding to at least 70%–80% of the total mass lost by the primary due to stellar wind and RLOF;

b) during the WR phase the star is losing approximately half of its mass;

c) the average mass ratio for binaries prior to the supernova explosion equals 3, i.e. the exploding star is 3 times less massive than its companion.
Evolution of Low Mass Binaries under the Influence of Gravitational Radiation
Authors: Massevitch A. G. , Tutukov A. V. , Yungelson L. R.
Published: July 2016

Evolutionary changes of masses and periods under the influence of gravitational radiation (GR) are computed for binaries with main-sequence or degenerate hydrogen-helium (H), helium (He) and carbon (C) secondaries. Tracks in the P-M2 and P-M2 planes are determined. The orbital period of systems P with a non-degenerate dwarf filling its Roche lobe decreases until the time-scale of GR (~ 109−1010yrs) becomes shorter than the thermal time-scale τKH of the mass losing component M2. When M2 becomes ~ 0.1 M⊙, P begins to increase. This could account for the existence of the minimal P ≈ 1.3h and for the accumulation of observed cataclysmic binaries (CB) below P ≤ 2h. The GR can be the driving force for evolution of cataclysmic binaries: TT Ari, OY Car, Z Cha, and WZ Sge as their P, M2 and indicate. The rate of mass exchange driven by GR is ~ 10−9−10−10 M⊙/yrs. It is enough to feed the X-ray bursters and related objects.
Generalized Theory of Shell Flash and Accreting White Dwarfs
Authors: Sugimoto Daiichiro , Miyaji Shigeki
Published: July 2016

Shell flashes take place both in deep interior of red giant stars and near surface of accreting white dwarfs. Theories of shell flashes have been thus far presented piece by piece in different papers. It is the purpose of the present review to construct and generalize them in order to reach better understanding. A non-linear yet almost analytical theory is presented which treats the development of the shell flash in finite amplitude. Recurrence of the shell flashes is also shown to be well understood as a non-linear oscillation in dissipative system which tends to be its limit cycle. As a result strength of the peak energy-generation and recurrence time of the shell flashes are related with mass of the accreting white dwarfs, accretion rate, etc.
Concave Hamburger Equilibrium of Rotating Bodies
Authors: Fukushima T. , Eriguchi Y. , Sugimoto D. , Bisnovatyi-Kogan G.S.
Published: July 2016

Equilibria of rigidly rotating polytropic gas with small compressibilities are computed in order to investigate the relation between the incompressible and compressible equilibria. The equilibrium figure varies from a spheroid-like shape to a concave hamburger as the angular velocity increases. This result is supported by the fact that a concave hamburger equilibrium is obtained even in the complete incompressible case. Thus the Maclaurin spheroid does not represent the incompressible limit of the rotating polytropic gas because of its restriction of the figure. The computed sequence of equilibria clarifies the relation between the Maclaurin spheroid and the Dyson-Wong toroid. Moreover it is the sequence of minimum-energy configuration. These results suggest that our solutions are more physical and probably stabler than any other equilibrium of incompressible fluids.
Supernovae: Progenitor Stars and Mechanisms
Authors: Wheeler J. Craig
Published: July 2016

Type II supernovae probably arise predominantly in stars of 8–15 M⊙ which leave neutron star remnants but accomplish little in the way of nucleosynthesis. Stars in the mass range ~ 15-70 M⊙ may either explode or collapse. Their evolution and final outcome, including their contribution to nucleosynthesis, may depend strongly on processes of mass loss. Type I supernovae probably involve a deflagrative explosion in a carbon-oxygen core surrounded by a distended helium envelope. The evolutionary origin of such a configuration is obscure.
The Common Properties of Plerions and Active Galactic Nuclei
Authors: Panagia N. , Weiler K. W.
Published: July 2016

Plerions, i.e. supernova remnants resembling the Crab Nebula, are characterized at radio wavelengths by having: 1) a centrally peaked brightness distribution, 2) flat radio spectrum (α > −0.3, Sν να), 3) high linear polarization, and 4) a highly ordered magnetic field. At higher frequencies (1011–1013 Hz depending upon the age) the spectrum turns over and attains a slope of α ~ −1. In particular, for the Crab Nebula the turnover frequency occurs at νc ~ 3×1012 Hz (cf. Fig. 1). Moreover, the optical spectrum displays a slope of −0.9 and the radiation is linearly polarized. Nonthermal emission is also detected in the X-ray and γ-ray domains (Fig.1). Similar spectral characteristics are found for other bona fide plerions. As discussed by Weiler and Panagia (1980), the plerion phenomenon is determined by the presence of a highly energetic and active central object (a fast spinning neutron star) which is able to both accelerate and inject continuously relativistic electrons into the remnant with a typically flat energy distribution roughly proportional to E−1.
Distribution of Non-Thermal Emission in Galaxies
Authors: Sancisi R. , van der Kruit P.C.
Published: July 2016

The properties of the radio continuum emission from spiral galaxies have been reviewed by Van der Kruit and Allen (1976) and by Van der Kruit (1978). In more recent years the major developments in the understanding of the radio continuum properties and the underlying physical conditions of galaxies have come from a number of surveys of large samples of objects. Some of these surveys (e.g. Hummel, 1980a) have good sensitivity and sufficiently high angular resolution to allow for the first time a clear separation of central sources and disk emission and a study of the properties of these components in a large number of galaxies. As a consequence some results already found, suggested or only suspected in previous detailed investigations of a limited number of objects are put on a firmer basis or entirely new aspects are revealed.
SPECTROPHOTOMETRIC REMOTE SENSING OF PLANETS AND SATELLITES
Authors: McCord T. B. , Cruikshank D. P.
Published: July 2016

Near infrared spectrophotometry has vastly increased our knowledge of the composition and structure of asteroids, satellites and planetary surfaces over the past ten years. In this article we will attempt to summarize the most recent comprehensive results. We will emphasize the interpretations and present only examples of the data.
INFRARED SOURCES IN DENSE MOLECULAR CLOUDS
Authors: Evans Neal J.
Published: July 2016

The study of infrared sources in molecular clouds necessarily places the practitioner at the interface between two rapidly evolving fields of study. In such a situation, yesterday's heresy often becomes today's dogma. Since it is hard enough to keep up with even one field of study, I thought it might be helpful to recount a bit of history regarding molecular clouds. The objective is to put various notions about molecular clouds into proper context.
SPECTROSCOPY OF THE ORION MOLECULAR CLOUD CORE
Authors: Scoville N. Z.
Published: July 2016

Recent infrared and radio spectroscopic data pertaining to the Orion BN-KL infrared cluster are reviewed. A new, high resolution CO map shows that the thermal structure over the central 10′(1.5 pc) in the Orion molecular cloud is dominated by energy sources in the infrared cluster and M42. Peak CO brightness temperatures of 90 K occur on KL and near the bar at the southern edge of M42.

Within the central 45″ of the infrared cluster, both radio and IR data reveal a highly energetic environment. Millimeter lines of several molecules (e.g. CO, HCN, and SiO) show emission over a full velocity range of 100 km s−1. These supersonic flows can be modeled as a differentially expanding envelope containing a total of ~5 M⊙ of gas within an outer radius of r ≃ 1.3 × 1017 cm. Over the same area emission is seen from vibrationally excited molecular hydrogen at an excitation temperature of 2000 K. The high velocity mm-line emission and the NIR H2 lines are clearly related since they exhibit similar spatial extents and line widths. Comparison of the total cooling rate for all the H2 lines with the estimated kinetic energy and expansion time for the mm-emission region indicates that the H2 emission probably arises from shock fronts where the expanding envelope impinges on the outer cloud.

Near IR spectroscopy also probes ionized and neutral gas closely associated with BN. Br α and Br γ emission is detected from an ultracompact HII region of mass MHII ≲ 10−4 M⊙. Full widths for the HII lines are ~400 km s−1. CO bandhead emission detected in BN at λ ≃ 2.3 μm is probably collisionally pumped in a high excitation zone (nH+H2 > 1010 cm−3 and TK ≃ 3000 K) at only a few AU from the star. The velocity of both the HII and CO emission is VLSR ≃ + 20 km s−1; thus BN appears to be redshifted by 11 km s−1 with respect to OMC-1.
SPECTROPHOTOMETRY OF DUST
Authors: Aitken D. K.
Published: July 2016

In recent years there have been a number of extensive review papers and books on interstellar dust (e.g. Savage and Mathis, 1979, and references therein). This short review deals only with the spectral properties of dust within the wavelength range 3–25μm, with particular emphasis on recent results.
Continuum VLBI Polarimetry of 3C454.3 at 43 GHz
Authors: Kemball A. J. , Diamond P. J.
Published: July 2016

Polarization VLBI calibration at high frequencies has traditionally been difficult due to poor sensitivity and high antenna instrumental polarization across inhomogeneous networks. The higher observing frequency and increased spatial resolution diminishes the chances of finding ideal VLBI polarization calibrators. The advent of the Very Long Baseline Array (VLBA), which has standardized feeds with low instrumental polarization, has minimized these observational difficulties. Recent work in polarization calibration has suggested that somewhat resolved sources may be used in an iterative polarization calibration scheme (Cotton 1993). A full generalization of this method has been developed by Leppanen, Zensus and Diamond (1995) in calibrating 22 GHz polarization observations with the VLBA.
Structural Changes in CTA102
Authors: Rantakyrö F.T. , Bååth L.B.
Published: July 2016

A study over several epochs and frequencies has demonstrated that the variability in CTA 102 (QSO 2230+114, z = 1.037) at λ<32 cm is mainly due to intrinsic processes (Rantakyrö et al. 1995, A&A, in press, hereafter R1995). Observations of CTA 102 with the EGRET telescope at the high-energy γ-ray waveband have shown that the source exhibits a strong γ-ray luminosity, Lγ = 5 × 1047 ergs s–1 (Nolan, P.L., et al. 1993, ApJ, 414, 82). This luminosity dominates the emission seen at all other wavebands, a common feature among BLAZARs. The common explanation for the high Lγ is that the emission is the result of a beamed jet with a high Lorentz factor.
VLBA Studies of BL Lac
Authors: Denn G. , Mutel R.
Published: July 2016

The radio core of BL Lac has been monitored with VLBI techniques since 1980. At least seven superluminal events have been seen, usually associated with flux outbursts. The components have been interpreted as weak relativistic shocks associated with opposed jets. Recent dramatic changes in the nucleus of BL Lac have been seen: optical spectra (Lawrence et al. 1995) show the presence of broad-line Hα and [NII] emission lines. The single-dish radio flux has also increased by 3 times in the past year. Often in BL Lac's past, a flux outburst immediately precedes the ejection of a new superluminal component.
A Circumnuclear HI Disk in the Compact Symmetric Object 4C31.04?
Authors: Conway J.E.
Published: July 2016

Compact Symmetric Objects (CSO's) are strong, compact (< lkpc) objects with radio structure and luminosity similar to classical double radio sources (i.e. two lobes and a weak core), but thousands of times smaller (Wilkinson et al 1994). It has been proposed that CSO's are either young radio sources which will later evolve into classical sources, or sources whose growth is ‘frustrated’ by dense surrounding gas. In a recent survey of z < 0.1 CSO's searching for HI absorption, approximately 50% were detected (see Conway et al 1996), a much higher percentage than found in surveys of general radio loud ellipticals with similar sensitivity (see van Gorkom et al 1989).
Multifrequency Study of VLBI–Compact Sources: 1–22 Ghz Spectra Observations and Model Fits
Authors: Kovalev Yu.A. , Berlin A.B. , Nizelskij N.A. , Kovalev Y.Y. , Babak S.V.
Published: July 2016

Results of instantaneous (with accuracy of a minute) spectra observations for a sample of 113 compact objects, selected from the VLBI survey, are presented. Measurements have been made in 1989.9 at the RATAN–600 at 7 wavelengths of 31, 13, 8.2, 7.6, 3.9, 2.7 and 1.4 cm as a set of our spectra monitoring program.
VLBI Observations of Low-Redshift Radio Galaxies
Authors: Tingay S.J. , Jauncey D.L. , Preston R.A. , Meier D.L. , Reynolds J.E. , Tzioumis A.K. , Lovell J. , Jones D.L. , Mcculloch P.M. , Murphy D.W. , Nicolson G.D.
Published: July 2016

Here we will describe briefly some of the VLBI observations we are making of low-redshift, compact radio sources in the southern hemisphere, using the Southern Hemisphere VLBI Experiment (SHEVE) array of telescopes (Jauncey et al., 1994).
Low Luminosity Radio Galaxies
Authors: Parma P. , DE RUITER H.R. , Fanti R.
Published: July 2016

This review talk will deal almost exclusively with the radio aspects of low luminosity radio galaxies, as the other wavelength bands (optical, X, IR) are covered by others during this conference. By low radio luminosity we mean a radio power at 20 cm in the range 1019 to 1024,5 W Hz–1 (Hubble constant of 100, as throughout this talk). At the upper limit occurs the “break” in the radio luminosity (RLF) (Auriemma et al 1977) as well as the transition from Fanaroff -Riley type I to type II (Fanaroff & Riley, 1974). This limitation to weak radio powers does not necessarily imply that such radio sources constitute a homogeneous class of objects; it has been shown by Wrobel & Heeschen (1991) that a number of radio galaxies of very low luminosity have a ratio between far-infrared and radio emission similar to spiral galaxies and this might suggest that these objects are powered by star formation phenomena. Long baseline interferometry is able to pinpoint compact radio nuclei and therefore can distinguish starburst related radio sources from those powered by nuclear activity (see Slee et al 1994).
Radio Polarisation Studies of Galaxies at z > 2
Authors: Athreya R.M. , Kapahi V.K. , Mccarthy P.J. , Van Breugel W.
Published: July 2016

We present some interesting results from a radio study of 17 radio galaxies at z >2, selected from a complete sample of Molonglo sources with S408 > 0.95 Jy for which optical identifications and spectroscopic redshifts are being obtained in a major observational programme (Kapahi et al. 1995).

Observations and results : The 17 galaxies were mapped using the VLA at 1.4, 4.8 and 8.3 GHz with the highest resolution of ≃ 0.3″ at 8.3 GHz. The integrated spectra are generally quite steep and convex in many sources, steepening to α ≥ 1.2 (S ∝ v–α) at the highest frequency. Most of the sources have a double structure with sizes ranging up to 22″. Unresolved radio cores, coincident with the optical galaxies, are detected at the mJy or sub-mJy level in most cases. Several sources also show one-sided jetlike features. Surprisingly, most of the cores appear to have steep spectra between 5 and 8.3 GHz!
Analysis of VLBI Spot Map of H20 Masers for the HII Region Complex IC133 of Spiral Galaxy M33
Authors: Zhi-Yao Yu
Published: July 2016

Interstellar H2O masers in the Galaxy occur in active star forming regions. The spectrum often shows multiple distinct features. The VLBI maps reveal that each spectral feature corresponds to emission of spatially distinct maser sources (maser spots), whose sizes are ≈ 1013cm. The maser in M33 is associated with the HII region complex IC133, which has been studied optically by Boulesteix et al. (1974) and Kiwitter and Aller (1981). This maser is the nearest (≤ 1Mpc) extragalactic H2O source visible in the northern sky, although it is not the strongest. It is known to have persisted for over a decade, and its spectra consistently show peak flux densities of ≈ 1.5 Jy and at least 10 features spread over ≈ 50 km s–1 (Huchtmeier, Eckart and Zensus 1988). Using VLBI Greehill et al. (1990) have obtained the positions of 14 H2O maser spots.
Optical Properties of FRI Radio Galaxies
Authors: Ledlow Michael J. , Owen Frazer N.
Published: July 2016

From the VLA 20cm survey of ≃ 500 Abell clusters reported by (Ledlow and Owen, 1995), we have obtained optical R-Band CCD observations and optical spectra for 265 radio galaxies. The survey is complete for 20cm flux density greater than 10 mJy within 0.3 corrected Abell radii of the cluster center. All Abell clusters with measured z < 0.09 were surveyed. This statistically complete sample was supplemented by ≃ 200 clusters with 0.09 < z < 0.25 including sources with flux density > 200 mJy. Only 6% of the sample consists of FR II radio sources, the remainder are twin-jets, tailed, or compact sources associated with the FR I class.
The Highest Energy Cosmic Rays
Authors: Norman Colin A.
Published: July 2016

The current data on the highest energy cosmic rays (UHECRs) is discussed and an understanding of the origin of these particles is reviewed. New and proposed facilities for measurement of UHECRs, neutrinos and γ-rays can interestingly and significantly constrain the physics of the source origin. Cosmic magnetic field strengths are the most uncertain physical parameter.
Spectral Indices and Particle Ageing Studies on the Giant Radio Galaxy NGC6251
Authors: Mack K.-H. , Klein U. , Saripalli L. , Willis A. G. , O'DEA C. P.
Published: July 2016

In the framework of our high-frequency survey of giant radio galaxies with the Effelsberg 100-m telescope (Klein et al., 1994; Saripalli et al., 1995) we have obtained radio continuum maps of NGC6251, a source of 1.5 Mpc size (H0 = 75km s–1Mpc–1). Together with low-frequency WSRT observations (Willis & O'Dea, 1990), these measurements form a unique data base which for the first time allows thorough studies of the spectral index over a large frequency range. Theoretical models of particle ageing have been fitted to the spectrum to determine particle ages and other relevant physical parameters. Because of the immense size of NGC6251 these numbers provide information about the physics of the surrounding intergalactic medium.
Clusters of Galaxies at Intermediate Redshifts: a Sample Selected at Radio Wavelenghts
Authors: Zanichelli A. , Scaramella R. , Vigotti M. , Vettolani G. , Grueff G.
Published: July 2016

In order to gather a sample of intermediate redshifts (z ≃ 0.1 ÷ 0.2) clusters avoiding evolutionary effects or biases induced by limited sensitivity of instruments and optical plates that affect samples selected through inspection of optical plates, color diagrams or X-ray emission properties, we plan to use radio galaxies as suitable tracers of dense environments (e.g. Allington-Smith et al., 1993). This would allow us to effectively test different environments and population properties, and would also give valuable information on the effect of environment on the radioemission phenomena. Moreover, it would not impact on the X–ray or optical properties of clusters, since there is no significant correlation between the radio properties of galaxies within a cluster with its LX (Feigelson, Maccacaro and Zamorani, 1982), or with richness of the cluster (Zhao, Burns, and Owen, 1989).
Quasar Radio Structure in Cluster Environments
Authors: Hutchings J.B. , Gower A.C. , Ryneveld S. , Dewey A.
Published: July 2016

We have VLA snapshots at 6cm and 20cm of ≃50 QSOs of redshift ≤0.7 with a range of known optical galaxy environments. The radio sources were characterised by measures of flux, size, and shape. The cluster density of the QSOs is given by the Bgq number from galaxy companion data largely published by Yee and Ellingson (e.g. ApJ 411, 43, 1993).
Multi-Wavelength Study of Rosat Clusters of Galaxies
Authors: Reid A. D. , Hunstead R. W. , Pierre M. M.
Published: July 2016

We are engaged in a radio–IR-optical–X-ray study of two flux-limited samples of ROSAT clusters of galaxies south of declination −20° (Pierre et al., 1994a). One sample covers an area of 1750 deg2 in Hydra (Pierre et al., 1994b) and includes some distant (z ≈ 0.3) and X-ray luminous (LX ≈ 1045 ergs–1) clusters. The other sample derives from a volume-limited subset (nominally z ≤ 0.1) of southern X-ray clusters, which are the focus of an ESO Key Program (Guzzo et al., 1995).
Spectral Index Asymmetries in Low-z Radio Galaxies
Authors: Dennett-Thorpe J. , Bridle A.H. , Laing R.A. , Scheuer P.A.G.
Published: July 2016

In recent years a number of correlations have been observed between the large-scale properties of FRII radio galaxies and quasars. Some correlations find their simplest explanations in terms of environmental effects, others in terms of beaming/orientation effects. The problem, however, is that there is an implied correlation between these different types of effects. This is a report on work underway to investigate this directly and exclude the confusion introduced by use of different samples.
X-Ray and Gamma–Ray Emission in Blazars
Authors: Ghisellini Gabriele
Published: July 2016

More than 50 sources have been detected by EGRET in 4 years of operations (e.g. von Montigny et al. 1995). Almost all of them show the violent characteristics typical of blazars, such as superluminal motions, strong radio emission mainly produced in a flat spectrum core and large amplitude variability at all frequencies. Interestingly, optical polarization does not seem to be required, since more than 1/3 of the detected sources are less than 3% polarized.
Shock Excitation of Emission Lines and the Relation to GPS Sources
Authors: Bicknell G.V. , Dopita M.A. , O'DEA C.P.
Published: July 2016

Gigahertz Peak Spectrum (GPS) and Compact Steep Spectrum (CSS) sources have attracted a large amount of attention in recent years since they occupy a surprisingly large fraction of the extragalactic radio source population. In this paper we summarise a theory which attempts to unify the optical emission line and radio properties of these sources. In outline the theory is as follows: The bow shock preceding the radio lobe driven into the ISM by a powerful radio jet ionizes the ISM producing both optical line emission and a free-free absorbing screen. The free-free absorption can explain the relationship between size and turnover frequency (Stanghellini et al., 1995) and the prediction of the line emission is in accord with the observation for a small sample of sources for which optical data are available.
Shock Excitation of Emission Lines in Radio Galaxies
Authors: Koekemoer A. M. , Bicknell G. V.
Published: July 2016

We present evidence for the viability of “auto-ionizing” shocks as the dominant ionization mechanism in extended emission-line regions (EELRs) in two radio galaxies, PKS 0349–27 and PKS 2356–61. The application of this model, rather than the nuclear photoionization hypothesis of unified schemes (Barthel 1989), is motivated by observed EELR properties: large line-of-sight velocity widths (up to δv ≃ 500 km s–1 for nearby objects and ≳ 1000kms–1 at higher z); kinematics/excitation relationships (Baum et al. 1992); the EELR/radio axis alignment (Chambers et al. 1987, McCarthy et al. 1987); and the correspondence between the brighter EELR and the shorter radio lobe (McCarthy et al. 1991), suggestive of jet/gas interactions. We show that the flux, excitation and kinematics across the gas is self-consistently accounted for in terms of shocks as a single physical mechanism, requiring fewer unknown parameters than nuclear photoionization.
The B3-VLA Sample
Authors: Vigotti M. , Djorgovski S.G. , Gregorini L. , Klein U. , Mack K.H. , Maxfield L. , Reuter H.P. , Thompson D.
Published: July 2016

The use of radio sources to identify the most distant object in the Universe has been proved to be a very successful approach in observational cosmology. Studies of high flux, powerful 3CR and 1-Jy galaxies show dramatic evidence for color and luminosity evolution, reaching to look-back times 80% of the Hubble time. In order to disentangle the selection effect, correlation with redshift, and correlation with radio power, it is necessary to obtain well defined, complete samples of radio galaxies at a large range of redshifts, and with a wide baseline of radio power. We need the identifications of complete samples in the flux range of a factor 10 smaller than 3CR sample. The B3VLA sample (Vigotti et al. 1989) is a subset of 1050 sources selected in restricted areas at high galactic latitudes from the B3 survey, which is complete down to S(408 MHz) = 100 mJy. For the B3VLA sample detailed VLA maps were obtained at 1.4 GHz using A, C and D arrays. We are conducting a long-term effort to provide optical ID's and redshifts for well-defined, complete subsamples of the B3VLA survey (Djorgovski et al. 1990, Vigotti et al. 1990, Thompson et al., 1994), a similar effort is being conducted independently by others. We present here the “status of the art” for the B3VLA sample: a new low flux sample of 124 QSS selected at meter wavelenghts, a sample of 194 radio galaxies (77 with measured redshift) and a sample of 732 Empty Fields (EF : no optical counterpart on POSS I plate).
Space Densities for Powerful Radio Sources in the Light of Unification
Authors: Jackson C.A. , Wall J.V.
Published: July 2016

As radio survey frequency is raised the proportion of flat-spectrum sources increases in bright flux-limited samples (eg Wall 1994, Aust J Phys47, 625). Differential source counts show a corresponding broadening of the central maximum due to the increasing proportion of flat-spectrum sources. Orr & Browne (1982, MNRAS200, 1067) modelled this change in shape of the source count by proposing a unifying scheme which states that the core-dominated, flat-spectrum radio sources are the steep-spectrum sources with their cores Doppler-boosted due to the alignment of the jets with the line of sight.
Cosmological Size Evolution of Extragalactic Radio Sources
Authors: Singal Ashok K.
Published: July 2016

The study of cosmological evolution of the sizes of extragalactic radio sources started about a quarter century back. From the very first angular size-redshift (θ-z) plots (Miley 1968, 1971; Legg 1970) and angular size-flux density (θ-S) plots (Swarup 1975; Kapahi 1975) it became evident that some sort of cosmic epoch-dependent evolution in the size distribution for the population of extragalactic radio source needs to be proposed; the sources at earlier epochs appeared on the average to have smaller physical sizes. However, a suitable luminosity-linear size (P-l) correlation among the radio source population could also explain the observations, without invoking a size evolution with redshift. The only reliable way to disentangle these two separate effects is to investigate the size distribution in the luminosity-redshift plane, where one could examine not only the l-z relation for a given luminosity class, but could also check for a P-l correlation in a given redshift bin.
Spectral Index - Redshift Relation for Radio Galaxies and Quasars
Authors: Dagkesamanskii R.D.
Published: July 2016

Cosmological evolution of synchrotron spectra of the powerful extragalactic radio sources was studied by many authors. Some indications of such an evolution had been found firstly by analysis of ‘spectral index - flux density’ (α – S) relation for the sample of relatively strong radio sources. Later Gopal-Krishna and Steppe extended the analysis to weaker sources and found that the slope of αmed(S) curve changes dramatically at intermediate flux densities. Gopal-Krishna and Steppe pointed out that the maxima of the αmed(S) curve and of differential source counts are at almost the same flux density ranges (see, Fig. 2). It has to be noticed that the all mentioned results were obtained using the low-frequency spectral indices and on the basis of low frequency samples.
HST and KECK Observations of High Redshift Radio Galaxies
Authors: Van Breugel W.J.M.
Published: July 2016

Together with several of my colleagues I have embarked on a comprehensive program to study the radio–aligned restframe UV structures in high redshift radio galaxies (HzRGs) using some of the world's premier optical telescopes: the Hubble Space Telescope for high spatial resolution imaging, and the Keck 10m telescope for high S/N spectropolarimetry. I will discuss some of our latest results from these observations which elucidate, and at the same time obscure, our evolving understanding of HzRGs.