bluuebunny/crossref_metadata_2025 huggingface dataset:
Bridges and Outdoor Lighting
Authors: Upgren Arthur
Published: July 2016

Northeast Utilities, the electric power distributor for Connecticut, has devised a plan to light the Arrigoni Bridge across the Connecticut River at Middletown. This paper descibes the plan and its impact on the surrounding region. The floodlights will affect migratory birds, and teaching and research at the nearby Van Vleck Observatory on Wesleyan Campus. Examples of bridges at other sites are also discussed, including the suspension spans of New York and San Francisco, that bear only tracer lights, or no lights at all.
Observations of Artificial Space Objects in Lviv Astronomical Observatory
Authors: Vovchyk Jeva , Blagodyr Jaroslav , Logvinenko Olexandr
Published: July 2016

Space debris is the price which humankind must pay for entering space. And as this debris is dangerous in different ways, there must be ways to identify, catalogue, and predict the positions of, these cosmic bodies. That is why it is necessary to observe all artificial cosmic objects that are in space. One way of observing debris is by photometry. Photometric observations give light-curves from which one may deduce information about the position in space, the form, size, and other parameters of the object. Since 1975 a research group at Lviv Astronomical Observatory has been working at the problem of recording light-curves of different artificial cosmic objects. Four electrophotometers were constructed and developed. Many light curves of different artificial objects were measured with these electrophotometers. All light curves are collected in the local computer data bank and are available for use by anybody who needs such information.
Radio Astronomy in the European Regulatory Environment
Authors: Cohen R. J.
Published: July 2016

European radio astronomy has major world-class facilites which operate successfully in a hostile electromagnetic and economic environment. In 1988 the Committee on Radio Astronomy Frequencies (CRAF) was established under the auspices of the European Science Foundation, ‘to keep the frequency bands used for radio astronomical observations free from interference’. Coordination of the European efforts through CRAF adds value through the sharing of expertise and information. Having one recognized voice for European radio astronomy also gives us strength. For example, the agreement concluded with Iridium LLC offered radio astronomy significant concessions compared with agreements reached elsewhere in the world. As Europe moves towards harmonized use of the radio spectrum, CRAF members participate in the discussions alongside representatives of governments and industry, to ensure that radio astronomy will have a secure future in Europe. This paper gives an overview of the European regulatory environment and the ways in which CRAF is working to protect radio astronomy.
A Potential Site for the World's Largest Single Dish, FAST
Authors: Peng B. , Strom R. G. , Nan R.
Published: July 2016

We have carried out a series of measurements at some locations in Guizhou Province and one additional site at the Urumqi Astronomical Station in the Xinjiang autonomous region, to check on their suitability, from the point of view of interference, for the construction of a Five-hundred-meter Aperture Spherical Telescope (FAST). This large facility will in some sense act as a prototype for the Square Kilometer Array (SKA). Measurements were made using a commercial receiver in the frequency range 25–1500 MHz. The results in Guizhou look quite promising. A protected radio quiet zone in Guizhou would make it an ideal location for an international radio astronomical facility, and would establish the FAST site as a natural SKA location.
Radio Interference and Ejecting Techniques at Beijing Astronomical Observatory
Authors: Zhang X. , Piao T. , Peng B. , Wang X.
Published: July 2016

In this paper, we first describe the situation of radio interference at the Miyun station in Beijing Astronomical Observatory, and then new developments in both hardware and software techniques of interference rejection for the Miyun Synthesis Radio Telescope (MSRT) are described.
Fixed and Mobile RFI Search Facilities at Medicina
Authors: Montebugnoli S. , Tomassetti G. , Bortolotti C. , Roma M.
Published: July 2016

Fixed and mobile RFI search facilities at the Medicina radio astronomy station are described. A complex system of wide-band antennas that can be steered, has been designed and installed on the top of a 25-m high tower and connected with a wide-band sweeping receiver system. At present it works from 0.08 GHz up to 2.5 GHz in continuous mode. Low-noise front ends are used in the radio astronomy bands. A mobile system, equipped with a similar receiving system, has been designed to facilitate the interfering transmitter's position localization.
Measurements of Radio Interference at Solar Radio Stations in Beijing
Authors: Yan Yihua , Fu Qijun , Liu Yuying , Chen Zhijun
Published: July 2016

Shahe Station of our Solar Radio Group has suffered from radio interference in recent years, so we decided to move our solar radio telescopes to Huairou Station of BAO. We measured radio interference at both sites recently and found that the radio interference is more serious in Shahe than in Huairou. Although the interference is low at the single working frequency, we do find some radio interference within the working band at Shahe. It is comparatively radio quiet at Huairou and suitable for placement of the solar radio instruments there.
Analysis of Solar Radio Observations and the Influence of Interference
Authors: Yan Yihua , Ji Huirong , Fu Qijun , Liu Yuying , Chen Zhijun
Published: July 2016

Based on the data observed by a solar radio spectrometer at 2.6–3.8 GHz and other measurements at Shahe Station, we analyze the radio interference and its influence on observations. We have identified three different types of interference: (a) from antenna; (b) from IFs; and (c) internal signals, etc. Corresponding measures can be taken to reject or correct these errors and to improve the observations.
Saving Our Skies: Communicating the Issues to the Media
Authors: West Richard , Madsen Claus
Published: July 2016

We discuss possible mechanisms for setting up a global outreach campaign centred on the main theme of this meeting: save our skies! Effective communication of this message to the world's media and the wide public is a prerequisite for successful sensitisation of decision-makers in different countries to the crucial issues at stake. We emphasise the need for careful planning of such a programme, especially in terms of definition of the key issues, the way they are presented, as well as the communication channels to be employed. It is important to differentiate the arguments used in connection with different types of pollution (light, radio, space debris). It will be necessary to identify clear and forceful messages that convincingly stress that these problems are of ultimate concern, not just a small group of astronomers, but to all of humanity. With their extremely sensitive instruments, astronomers constitute an avant-garde that is the first to detect the adverse effects, but as these intensify, increasingly broader sectors of society will be affected. It appears feasible, within the limited means available to the IAU and IDA, to initiate such an outreach effort with a comprehensive web-based campaign that highlights astronomical “pollution”. This may also serve as a useful test-bench for subsequent campaigns based on more communication vehicles and with a wider spectrum of associated activities.
Light Pollution: Education of Students, Teachers and the Public
Authors: Percy John R.
Published: July 2016

The preservation of the astronomical environment is intimately connected to society's understanding and appreciation of astronomy. This requires effective education of students, teachers and the general public. We know how this can be done. It remains for us to become education-active and to convince our colleagues and students to do likewise.
Excitation of H2 and HD in Shocks and PDRs
Authors: Bertoldi F. , Draine B. T. , Rosenthal D. , Timmermann R. , Howat S. K. Ramsay , Geballe T. , Feuchtgruber H. , Drapatz S.
Published: July 2016

Photodissociation regions (PDRs) and shocks give rise to conspicuous emission from rotationally and vibrationally excited molecular hydrogen. This line emission has now been studied with ISO and from the ground in great detail. A remarkable discovery has been that toward the Orion outflow and other shock-excited regions, the H2 level populations show a very high excitation component. We suggest that these high-excitation populations may arise from non-thermal pumping processes, such as H2 formation and high-velocity ion-molecule collision in partially dissociative shocks. In PDRs such as NGC 7023 however, formation pumping is always less important than fluorescent pumping.

We furthermore present two HD emission line detections toward Orion Peak 1. This enables the first comparison of the H2 and the HD excitation, which surprisingly turn out to be identical.
Molecular Data Needs in Astrochemistry
Authors: Millar T. J. , Walmsley C. M. , Rebrion-Rowe C. , d'Hendecourt L. , Saito S. , Rostas F.
Published: July 2016

The development of astrochemistry is inextricably linked to the generation of fundamental data. In this report, we discuss data needs in terms of astrochemical models, gas-phase kinetics, molecular excitation, optical and UV spectroscopy, solid-state chemistry, and millimeter and submillimeter wave spectroscopy.
Interstellar and Circumstellar PAHs
Authors: Tielens A. G. G. M. , van Kerckhoven C. , Peeters E. , Hony S.
Published: July 2016

ISO has shown that the mid–IR spectra of almost all sources are dominated by narrow emission features collectively known as the UIR bands. These bands are carried by a family of polycyclic aromatic hydrocarbon molecules containing about 50 C-atoms. Other classes of molecules such as C-chains as well as non-aromatic groups attached to the PAHs are much less abundant. ISO has revealed that the UIR spectrum is incredibly rich with a large number of weaker features, subfeatures, and shoulders; many of which were not known before. Some examples and the new insights they can provide are described. A systematic study of this spectral structure may well allow us to considerably narrow down the composition of the family of PAHs responsible for the observed emission.
Physical Processes Responsible for the Removal of Circumstellar Disks
Authors: Johnstone Doug
Published: July 2016

The most likely processes responsible for the removal of circumstellar disks around young stars are reviewed with emphasis on the physical state of the disk during the period of destruction and the timescale for disk removal. Four disk dispersal mechanisms are discussed in detail: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, and 4) photoevaporation by ultraviolet radiation. While viscous accretion is shown to be efficient in the inner regions of disks (r < 10 AU), photoevaporation is the principal process of disk dispersal at large radii (r > 10 AU). The commonly held view that stellar winds removed the remnant Solar Nebula is seriously questioned.
Molecules in Comets: An ISM-Solar System Connection?
Authors: Irvine William M. , Bergin Edwin A.
Published: July 2016

Our knowledge of the volatile composition of comets has advanced considerably since the last IAU Astrochemistry Symposium, in large part due to the apparition of comet Hale-Bopp and its study with both new ground-based instruments and from spacecraft. Some 23 or 24 coma molecules are now known which are probably, at least in part, volatile constituents of the nucleus. Relative abundances have been measured for rarer isotopomers of molecules containing 13C, 15N, 34S, and D, and significant isotopic fractionation is observed for D-containing species. There are striking similarities in both relative abundances of molecular constituents and in isotopic fractionation between material in dense interstellar clouds and that in cometary comae. Whether this indicates that cometary nuclei consist of relatively unprocessed interstellar matter is less clear, since the observed coma composition is not simply related to the nuclear composition, and since recent chemical models of the outer solar nebula mimic interstellar chemistry in important respects.
Observations of Gas and Dust in Comets with the Infrared Space Observatory
Authors: Crovisier J.
Published: July 2016

The Infrared Space Observatory (ISO) offered us the opportunity to observe celestial bodies from 2.4 to 196 μm, which is of particular interest for comets. We present here spectroscopic observations with ISO of comets C/1995 O1 (Hale-Bopp) and 103P/Hartley 2. Fluorescence emissions of H2O, CO2 and (for comet Hale-Bopp only) CO and CH4 are observed, yielding the production rates of these species. High-resolution spectra of water permit the study of the rotational and spin temperatures of this molecule. In comet Hale-Bopp, the thermal infrared region of the spectra shows specifically, in addition to continuum-like emission, the signatures of crystalline, Mg-rich olivine (forsterite), and signs of crystalline pyroxenes, amorphous silicates and water ice. The presence of crystalline silicates is also suggested in the Jupiter-family comet P/Hartley 2.
The Atmospheres of Substellar-Mass Objects
Authors: Burrows Adam
Published: July 2016

Between the masses of the Jovian planets and the stars, a new population of exotic substellar-mass objects (SMOs) is now being discovered in profusion, that are challenging our notions of what a planet, brown dwarf, or star can be. I focus on some exotic and distinctive aspects of the compositions of SMO atmospheres. In particular, I review the formation of silicate, water, and ammonia clouds, the role of rainout in altering the abundance of the alkali metals, and the suppression by atomic potassium of the optical fluxes of a methane dwarf such as Gliese 229B. Furthermore, I discuss the order in which various molecular, atomic, and condensed species might dominate or influence SMO atmospheres, with an eye to anchoring new spectral classes from Teff ~ 2000 K to ~ 100 K.
Astrochemistry: From Molecular Clouds to Planetary Systems; Conference Summary
Authors: Williams D. A.
Published: July 2016

Some thoughts on the state of our subject, as described in the presentations at the Symposium, are given here.
Primordial Nucleosynthesis For The New Millennium
Authors: Steigman G.
Published: July 2016

The physics of the standard hot big bang cosmology ensures that the early Universe was a primordial nuclear reactor, synthesizing the light nuclides (D, 3He, 4He, and 7Li) in the first 20 minutes of its evolution. After an overview of nucleosynthesis in the standard model (SBBN), the primordial abundance yields will be presented, followed by a status report (intended to stimulate further discussion during this symposium) on the progress along the road from observational data to inferred primordial abundances. Theory will be confronted with observations to assess the consistency of SBBN and to constrain cosmology and particle physics. Some of the issues/problems key to SBBN in the new millenium will be highlighted, along with a wish list to challenge theorists and observers alike.
LiBeB Evolution: Three Models
Authors: Ramaty Reuven , Lingenfelter Richard E. , Kozlovsky Benzion
Published: July 2016

We consider the three principal LiBeB evolutionary models, CRI in which the cosmic-ray source at all epochs of Galactic evolution is the average ISM, CRI+LECR in which metal enriched low energy cosmic rays (LECRs) are superimposed onto the CRI cosmic rays, and CRS in which the cosmic-ray source, accelerated in superbubbles, is constant, independent of the ISM metallicity. By considering the evolutionary trend of log(Be/H) vs. both [Fe/H] and [O/H], we demonstrate that the CRI model is energetically untenable. We present evolutionary trends for 11B/10B and B/Be which, combined with future precision measurements, could distinguish between the CRS and CRI+LECR models. We show that delayed LiBeB synthesis in the CRS model, due to the transport of the cosmic rays, could explain why log(Be/H) is steeper vs. [O/H] than vs. [Fe/H]. We also show that delayed deposition of Fe into star forming regions, due to its incorporation into high velocity dust, could provide an explanation for the possible rise of [O/Fe] with decreasing [Fe/H]. Observations of refractory and volatile α-elements could test this scenario. There seems to be a need for pregalactic or extragalactic 6Li sources.
Photon Creation in the Universe and Primordial Nucleosynthesis
Authors: Lima J.A. S. , S. Alcaniz J. , Santos J. , Silva R.
Published: July 2016

In hot big bang cosmologies, the irreversible process of continous photon creation may phenomenologically be described through a thermodynamic approach. In these models, the radiation temperature law depends on a phenomenological parameter β which is closely related to the photon creation rate. It is shown that a stringent constraint on the value of this parameter is imposed from primordial nucleosynthesis.
Measurements of The Primordial D/H Abundance Towards Quasars
Authors: Tytler David , O'Meara John M. , Suzuki Nao , Lubin Dan , Burles Scott , Kirkman David
Published: July 2016

Big Bang Nucleosynthesis (BBN) is the synthesis of the light nuclei, Deuterium (D or 2H), 3He, 4He and 7Li during the first few minutes of the universe. In this review we concentrate on recent data which give the primordial deuterium (D) abundance.

We have measured the primordial D/H in gas with very nearly primordial abundances. We use the Lyman series absorption lines seen in the spectra of quasars. We have measured D/H towards three QSOs, while a fourth gives a consistent upper limit. All QSO spectra are consistent with a single value for D/H: 3.325+0.22−0.25X10−5. From about 1994 − 1996, there was much discussion of the possibility that some QSOs show much higher D/H, but the best such example was shown to be contaminated by H, and no other no convincing examples have been found. Since high D/H should be much easier to detect, and hence it must be extremely rare or non-existent.

The new D/H measurements give the most accurate value for the baryon to photon ratio, η, and hence the cosmological baryon density: ωb = 0.0190 ± 0.0009 (1σ) A similar density is required to explain the amount of Lyα absorption from neutral Hydrogen in the intergalactic medium (IGM) at redshift z ≃ 3, and to explain the fraction of baryons in local clusters of galaxies. The D/H measurements lead to predictions for the abundances of the other light nuclei, which generally agree with measurements. The remaining differences with some measurements can be explained by a combination of measurement and analysis errors or changes in the abundances after BBN. The measurements do not require physics beyond the standard BBN model. Instead, the agreement between the abundances is used to limit the non-standard physics.
Inhomogeneous H II Regions and the Helium Abundance
Authors: Viegas S. M. , Gruenwald R.
Published: July 2016

When calculating the helium (4He) abundance in low metallicity H ii regions, the ionization correction factor (icf) for unseen neutral helium (and hydrogen) is usually assumed to be unity. In this paper, we explore this factor for H ii regions ionized by young stellar clusters. Our main result is that icf < 1 for homogeneous H ii regions and, that the effect of density condensations in the H ii regions is to further reduce the icf. For icf < 1, the primordial helium abundance inferred from observations of low-metallicity, extragalactic H ii regions is decreased.
Deuterium and Helium-3 in the Protosolar Cloud
Authors: Gloeckler George , Geiss Johannes
Published: July 2016

New measurements of the isotopic composition of helium in the solar wind obtained from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses are presented and compared with earlier SWICS results and previous mass spectrometric determinations of this ratio with the Apollo Solar Wind Composition (SWC) experiment and the Ion Composition Instrument (ICI) on the International Sun Earth Explorer 3 (ISEE 3). The new SWICS data from both the fast and slow solar wind are extrapolated to the photosphere to obtain a representative value of the present-day ratio of3He/4He = (3.75 ± 0.27) × 10−4in the Outer Convective Zone (OCZ) of the Sun. After corrections of this ratio for secular changes caused by diffusion, mixing and3He production by incomplete H-burning (Vauclair 1998), we obtain (D +3He)/H = (3.6 ± 0.38) × 10−5for the Protosolar Cloud (PSC). Adopting the Jovian3He/4He ratio = (1.66 ±0.05) × 10−4measured by the Galileo Probe mass spectrometer (Mahaffy et al. 1998) as representative for the PSC, we obtain (D/H)protosolar= (1.94 ±0.39) × 10−5. Using results of galactic evolution studies (Tosi 1998, 2000) and the D and3He abundances in the Protosolar Cloud and the Local Interstellar Cloud (Linsky 1998; Gloeckler &Geiss 1998), we estimate (D/H)primordial= (2.4 − 4.2) × 10−5. This range corresponds to a universal baryon/photon ratio of (5.9−4.2) × 10−10.
FUSE Spectra of Sk 80, an 07 Supergiant in the Small Magellanic Cloud
Authors: Iping R. C. , Sonneborn G. , Massa D. , Fullerton A. W. , Hutchings J. B.
Published: July 2016

We present far-UV spectra (910-1190Å) of Sk 80, an 07 supergiant in the Small Magellanic Cloud, observed by the FUSE satellite during its In-Orbit Checkout phase. The spectra reveal many interstellar absorption lines, including H2, and O VI, and several key stellar wind features.
7Li in Metal-Poor Stars: The Spread of the Li Plateau
Authors: Ryan Sean G.
Published: July 2016

A highly homogeneous study of 23 halo field dwarf stars has achieved a Li abundance accuracy of 0.033 dex per star. The work shows that the intrinsic spread of the Li abundances of these stars at a given metallicity is < 0.02 dex, and consistent with zero. That is, the Spite Li plateau for halo field dwarfs is incredibly thin. The thinness rules out depletion by more than 0.1 dex by a rotational-induced extra-mixing mechanism. Despite the thinness of the plateau, an increase of Li with [Fe/H] is seen, interpreted as evidence of Galactic chemical evolution (GCE) of Li, primarily due to Galactic cosmic ray (GCR) spallation reactions in the era of halo formation. The rate of Li evolution is concordant with: (1) observations of spallative 6Li in halo dwarfs; (2) GCE models; and (3) data on Li in higher metallicity halo stars. New data have also revealed four new ultra-Li-deficient halo dwarfs, doubling the number known. Based on their propensity to cluster at the halo main sequence turnoff and also to exist redward of the turnoff, we hypothesise that they are the products of binary mergers that ultimately will become blue stragglers. We explain their low Li abundances by normal pre-main-sequence (and possibly main-sequence) destruction in the low mass stars prior to their merging. If this explanation is correct, then such stars need no longer be considered an embarrassment to the existence of negligible Li destruction in the majority of field halo dwarfs.
Search for Lithium-Rich Stars Among G-K Giants with IR-excess
Authors: Jasniewicz G. , Parthasarathy M. , de Laverny P. , Thévenin F. , Mauron N. , Chadid M.
Published: July 2016

We report here new results about a search for Li-rich stars among 52 G-K giant stars which are known to have near IR excess. Eleven giants have been found to have log ∊(Li) ≥ 1.0. Five are new Li-rich stars. We suspect circumstellar shells around one of them, HD 219025. There is no clear correlation between Li-richness and rotation, or with binarity.
Lithium Depletion in a [Fe/H]= —3.4 star?
Authors: Spite M. , Spite F. , Cayrel R. , Hill V. , Depagne E. , Nordström B. , Beers T.C.
Published: July 2016

We present a determination of the lithium abundance from high quality spectra in an extremely metal poor star where the lithium line had not been detected.
Understanding the Li Production in AGB stars: the J-type Stars
Authors: Abia Carlos , Isern Jordi
Published: July 2016

A full abundance analysis have been carried out in 12 galactic J-stars. The analysis shows: a) 12C/13C ratios are low, b) the abundance of s-process and rare-earth elements with respect to the stellar metallicity is nearly-solar, [< heavy > /Fe] = 0.10 ± 0.11 c) Tc is not present in most of the stars although upper limits are placed in WZ Cas and WX Cyg, probably two SC-type stars, and d) all the stars are Li-rich, log ∈(Li)> 1. The location of J-stars in an empirical H-R diagram when compared with that of the normal N-type carbon stars, suggests that J-stars may be in the early-AGB phase. The different mechanism proposed to be responsible of this Li production are briefly discussed.
The Lithium Abundance and Mass Loss Rate in Galactic Super-Li-Rich Carbon and S Stars
Authors: Lubowich D. A. , V. Smith Verne , Turner B. E. , Sahai R.
Published: July 2016

The super-Li-rich (SLR) stars are rare AGB stars containing enhanced Li/H ≈ 2000 times the ISM Li/H. In order to determine if mass loss from SLR stars is a significant source of ISM Li, we measured their Li/H and the mass loss rate. From the weak Li I 8126 Â line in 2/4 SLR C stars and 6/8 SLR S stars we obtained Li/H = (0.2 — 5) x 10—6 for SLR C stars and Li/H = (0.2 — 5) x 10—7 for the SLR S stars. We determined dM/dt from the expansion velocity and line profiles of the circumstellar CO. The dM/dt = 1.3 × 10—5M⊙/yr, 2.6 × 10—7M⊙/yr, and 2.6 × 10—8M⊙/yr for the C stars IY Hya, T Ara, and WZ Cas; and average dM/dt = 5.5 × 10—7M⊙/yr for the S stars. Thus mass loss from SLR stars is a significant source of Galactic Li.
Transport Phenomena and Light Element Abundances in the Sun and Solar Type Stars
Authors: Vauclair Sylvie
Published: July 2016

The observations of light elements in the Sun and Solar type stars give special clues for understanding the hydrodynamical processes at work in stellar interiors. In the Sun 7Li is depleted by 140 while 3He has not increased by more than ≅ 10% in 3 Gyrs. Meanwhile the inversion of helioseismic modes lead to a precision on the sound velocity of about 1%. The mixing processes below the solar convection zone are constrained by these observations. Lithium is depleted in most Pop I solar type stars. In halo stars however, the lithium abundance seems constant in the “spite plateau” with no observed dispersion, which is difficult to reconcile with the theory of diffusion processes. In the present paper, the various relevant observations will be discussed. It will be shown that the μ-gradients induced by element settling may help solving the ‘lithium paradox’.
Peculiar J-type Carbon Stars and Li
Authors: Lorenz-Martins S. , Drake N. A.
Published: July 2016

We determined the carbon and lithium abundances and carbon isotopic ratios for 4 peculiar carbon stars by means of spectral synthesis method. Li abundances were derived using Li resonance line at λ6707.8 Â. For carbon abundance determinations we used the lines of the red system of CN molecule. Spectral region of λλ7994 — 8030 Â containing the lines of molecules 12CN and 13CN was used also for 12C/13C ratio measuring. The high-resolution spectra were obtained on the 1.52m telescope of ESO with the Fiber-fed Extended Range Optical Spectrograph (FEROS). These observations were obtained under the agreement between the CNPq-Observatório Nacional, Brazil, and ESO.
The Evolution of 3He, 4He and D in the Galaxy
Authors: Chiappini Cristina , Matteucci Francesca
Published: July 2016

In this work we present the predictions of a modified version of the ‘two-infall model’ (Chiappini et al. 1997 - CMG) for the evolution of 3He, 4He and D in the solar vicinity, as well as their distributions along the Galactic disk. In particular, we show that when allowing for extra-mixing process in low mass stars (M < 2.5 M⊙), as predicted by Charbonnel and do Nascimento (1998), a long standing problem in chemical evolution is solved, namely: the overproduction of 3He by the chemical evolution models as compared to the observed values in the sun and in the interstellar medium. Moreover, we show that chemical evolution models can constrain the primordial value of the deuterium abundance and that a value of (D/H)p < 3 × 10—5 is suggested by the present model. Finally, adopting the primordial 4He abundance suggested by Viegas et al. (1999), we obtain a value for ΔY/ΔZ ≃ 2 and a better agreement with the solar 4He abundance.
Stellar and GCR Production of Lithium in the Milky Way
Authors: Matteucci F. , Romano D.
Published: July 2016

Lithium production from several stellar sources (C-stars, massive AGB stars, Type II supernovae and novae) as well as from galactic cosmic rays (GCR) is included in a succesfull model for the chemical evolution of the Milky Way in order to predict the evolution of the 7Li abundance (A(Li) = log(7Li/H) + 12) as a function of [Fe/H]. From comparison with the oservational data we infer the following conclusions: 1) Li production from novae seems to be necessary to explain the steep rise of the Li abundance for metallicities larger than [Fe/H] = — 1.0 dex, 2) Li production from SNe II should be less than assumed before in order to reproduce the long plateau observed for A(Li) for low metallicities, 3) Li production from C-stars is negligible relative to Li production from massive AGB stars which is instead a necessary Li- source, 4) Li production from GCR should contribute by no more than 20% to the solar Li abundance.
The Sydney University Molonglo Sky Survey (SUMSS) and Optical Redshift Surveys of the Southern Sky
Authors: M. Sadler Elaine , Hunstead R.W.
Published: July 2016

The Sydney University Molonglo Sky Survey (SUMSS) is a radio imaging survey at 843 MHz of the whole sky south of declination −30°. With a resolution of 43″ × 43″ cosec |δ| and an rms noise level of ∼ 1 mJy/beam, SUMSS has similar sensitivity and resolution to the northern NRAO VLA Sky Survey (NVSS). Here, we present some results from the first two years of SUMSS and also show what can be done by combining radio data from SUMSS and NVSS with the new generation of large optical redshift surveys (including the 2dF Galaxy Redshift Survey and 6dF Galaxy Survey) now becoming available in the southern hemisphere.
HI with the GMRT
Authors: Chengalur J. N.
Published: July 2016

The Giant Metrewave Radio Telescope (GMRT) has recently come into operation. This paper reports on observations of the HI line made using the GMRT during its commissioning phase. These include observations of the nearby Low Surface brightness galaxy Cepheus 1, as well as of a number of low and medium redshift damped Ly-α systems. The derived spin temperatures for these systems is typically higher than that characteristic of the gas in the disk of the Galaxy. Higher spin temperatures were known to be characteristic of high redshift damped Ly-α absorbers, and had been earlier attributed to evolutionary effects. Our observations suggest that high spin temperatures are not a consequence of evolutionary effects since the look back time to these low z absorbers is modest. We also report on the short time scale (days) variability of the absorption profile of the z = 0.3127 system in front of B1127-145. This is the second damped Ly-α system to show such variation (the other being the z = 0.524 absorber in front of AO 0235+164).
Diffuse Sources in Clusters: What Turns them on?
Authors: Murphy Tara , Hunstead R.W.
Published: July 2016

To investigate the rate of occurrence and possible triggering mechanisms for diffuse radio sources, we have carried out a statistical study of a volume-limited sample of 92 clusters of galaxies.
A Large Diffuse Radio Source in a Cluster of Galaxies at z = 0.13
Authors: Krishna Gopal , Kulkarni V.K. , Bagchi J. , Melnick J.
Published: July 2016

Discovery of a diffuse ultra-steep spectrum radio source of size ∼ 0.3 Mpc, possibly a radio halo, in a cluster of galaxies at z = 0.13 is reported hilighting the presence of a giant radio spiral within the halo.
VLA Images of Two Extended Radio Galaxies
Authors: Junor W. , Mantovani F. , Morganti R. , Padrielli L.
Published: July 2016

There is some evidence from earlier studies that the two sources 0235 — 197 and 1203 + 043 exhibit low frequency (< 1 GHz) variability. This work shows that both sources have linear polarizations, if any, below the detection limits at 320 MHz, so we cannot explain the variability as being due to instrumental polarization effects as has been suggested for 3C159. Refractive scintillation may be the cause of the variability in 0235—197. The radio source 1203+043 lacks any bright compact component thereby ruling out a refractive scintillation mechanism for its variability. Consequently, it is possible that claims of variability in this source are spurious. However, the 320 MHz VLA observations show that 1203+043 has an ‘X'-shaped radio structure.
Radio Recombination Lines from Starburst Galaxies: High and Low Density Ionized Gas
Authors: Mohan N.R. , Anantharamaiah K.R. , Goss W.M.
Published: July 2016

Radio recombination lines (RRL) at 8 GHz and 15 GHz detected from four starburst galaxies are shown to arise in compact high density HII regions, which are undetectable below ∼4 GHz. Detection of an RRL at 1.4 GHz towards one galaxy and upper limits in the other three are consistent with the presence of an equal amount of low density diffuse gas. Continuum flux density measurements using the GMRT will be important in constraining the properties of the diffuse gas.
GMRT Observations of the Galactic Centre region
Authors: Roy Subhashis , Rao A. Pramesh
Published: July 2016

We have started a project to study the Galactic Centre region using the GMRT in all it's frequency bands. For the first time, Galactic Centre have been imaged with high resolution at 610 MHz. Also, at 325 MHz, we have observed a few of the suspected supernovae remnants (SNRs) close to the Galactic Centre. Here we present some of the preliminary results of our 610 and 325 MHz observations.
Radio Observations of Supernova Remnants and the Surrounding Interstellar Medium
Authors: Dubner Gloria
Published: July 2016

Supernova Remnants (SNRs) play essential roles in the dynamics of galaxies by injecting large amounts of energy which can accelerate particles generating cosmic radiation, create large, hot, low density bubbles, and maintain turbulent cloud motions. SNRs shock waves can also compress nearby dense clouds, inducing fragmentation and perhaps collapse into protostars, thus joining the extremes in the life-cycle of stars. The present review illustrates how high quality low frequencies radio observations of galactic SNRs and the surrounding interstellar medium (ISM), can help in the understanding of the many aspects of the nature of the remnants, as well as the consequences of their interaction with the ambient gas.
Low Frequency Insights into Supernova Remnants
Authors: Dyer K.K. , Reynolds S.P. , Borkowski K.J. , Kassim N.E. , Lacey C.K.
Published: July 2016

Low frequency observations at 330 and 74 MHz can provide new insights into supernova remnants (SNR). We can test theoretical predictions for spectral index variations. Nonlinear models of shock acceleration predict that the spectra from young SNR should be slightly concave rather than power laws — flattening toward higher energies. However, few SNR are bright and compact enough to be studied at millimeter wavelengths, restricting studies to the small range from 6 to 20 cm (a factor of 1.7 in electron energies). Observations at 330 MHz increase the electron energy baseline to a factor of 4, while providing sensitivity to larger spatial scales that are resolved out by centimeter-wavelength interferometers. Such observations can also separate thermal from nonthermal emission and detect excess free-free absorption associated with cool gas in remnants. Wide field images also provide an efficient census of both thermal and nonthermal sources over a large region.
The Radio Spectral Index of 3C58
Authors: Bietenholz M. F. , Kassim N. , Weiler K.
Published: July 2016

We report on 74 MHz and 330 MHz VLA observations of the plerionic supernova remnant 3C58. The radio spectral index, α, is uniform across the remnant to within 0.18, indicating a single source for the accelerated electrons. We find no emission from any shell surrounding the remnant. Our 3σ brightness limit on shell emission surrounding 3C58 is < 1.3×10−21 W m−2 Hz−1 sr−1 at 330 MHz.
Low frequency Recombination Lines of Hydrogen
Authors: Anantharamaiah K. R.
Published: July 2016

A brief review of Galactic and extragalactic recombination lines of hydrogen at frequencies ≤ 1.4 GHz is presented.
Populations of Hydrogen-like Atoms or Ions and Radio Recombination Lines (RRL's) Interpretation
Authors: Rovenskaya N.I.
Published: July 2016

The problem of non-LTE populations has been considered in terms of the departure coefficients ∂bn/∂n as functions of the kinetic temperature Te, the electron density Ne, the continuum radiation flow Ic and the ratios of IHnα, IHnβ, IHnδ and IHnε (the line radiation flows). The ratio of IHnα/IHnβ are sensitive to the thermal radiation from HII regions. Characterized by the relation of ∂2bn/∂n2 > 0, the populations are shown to be inhabited radiatively.
Low Frequency Emission Regions in Pulsars
Authors: Kijak Jaroslaw
Published: July 2016

The systematic increase of component separation and profile widths with decreasing frequency in pulsars suggests that the radiation at different frequencies is emitted from different altitudes above the polar cap. This concept is known as the radius-to-frequency mapping. According to RFM the observed low-frequency radiation should be generated farther from the neutron star than higher-frequency radiation. We discuss radial locations of the pulsar emission regions using a geometrical method for the estimation of emission altitudes. It is argued that the emission altitude at a given frequency is slightly different for young and old pulsars.
Unique Radio Pulsar Geminga
Authors: Malofeev V.M. , Malov O.I.
Published: July 2016

This pulsar has unique properties of radio emission, the most steep spectrum, the largest changes of pulse widths and phases and the presence of giant pulses.
Towards a Concept Design for a LOFAR
Authors: D. Bregman Jaap
Published: July 2016

The LOw Frequency ARray is a Digital Software Radio Telescope under study by the NFRA and the NRL. A scaleable architecture is proposed for the antenna stations of an aperture synthesis array operating in the 10 — 160 MHz frequency band. The use of advanced phased array technology with digital beamforming results in a multi-beam capability of up to 64 beams, which cover together about a steradian on the sky, and can be placed such that all relevant science objects are covered simultaneously. Based on the fast expansion of high performance processing technology, it is just after 2003 that signal and data processing will no longer dominate the cost of LOFAR in producing a confusion limited sky survey at the mJy level.
ALOFT: A Potential Low Frequency Space VLBI Mission
Authors: Hirabayashi Hisashi , Avruch Ian M. , W. Murphy David
Published: July 2016

We present a preliminary study of A LOw Frequency Orbiting Telescope (ALOFT) which co-observes with ground radio telescopes, in a similar fashion to the current VSOP mission. Our current straw-man ALOFT mission has a spacecraft operating at three frequency bands (0.33, 0.6, and 1.4—1.6 GHz) in an orbit with a 10,000 km apogee height. It should be relatively low cost as the lower frequencies less stringently constrain the design, for example uncooled receivers, narrower bandwidth, and simple antennae. The major science goal to be addressed by this mission is to examine scattering phenomena through the technique of space VLBI, although other problems, such as AGN physics, can of course also be addressed.
Low Frequency VLBI Project
Authors: Molotov I.E. , Likhachev S.F. , Chuprikov A.A. , Dementiev A. , Lipatov B. , Nechaeva M. , Snegirev S. , Dugin N. , Ananthakrishnan S. , Balasubramanian V. , Benz A. , Mantovani F. , Liu X. , Hong X. , Kus A. , Molotov E.P. , Ignatov S.P. , Poperechenko B.A. , Gorshenkov Y.N. , Konovalenko A.A.
Published: July 2016

An international Low Frequency VLBI Network (LFVN) has been organized for observations at 327 MHz and 1665 MHz frequencies with MARK-II and S2 recording terminals. Data on the interplanetary medium and spike-like solar bursts were obtained in first preliminary experiments.
Wide Field Imaging at Low Frequencies
Authors: Sault R.J.
Published: July 2016

Despite seemingly being poles apart, the two techniques of mosaicing and “polyhedron imaging” in radio interferometer do share some common aspects. This note shows some of these similarities. In particular, a simple method for producing geometrically correct images of large fields is described.
Filter CLEAN — An Improved Method for CLEANing Images
Authors: McPhail Alan
Published: July 2016

The Filter CLEAN algorithm has been developed for CLEANing images containing a mixture of extended and fine-scale sources. Filter CLEAN requires fewer iterations and the residual rms is much lower than results from Högbom CLEAN. Filter CLEAN is particularly good at recovering extended sources while maintaining good resolution on fine-scale sources. The Filter CLEAN algorithm is described and results presented.
MHD Turbulence in the Solar Wind and Interplanetary Dynamo Effects
Authors: Marsch E. , Tu C.-Y.
Published: July 2016

From the fluctuations of the velocity and magnetic field observed in different kinds of solar wind the fluctuating electric fields are derived, and their power spectra are constructed and analysed. The mean electromotive force ɛ generated by the turbulent motions depends upon the nature of the fluctuations. Simple dynamo theory predicts a linear relationship between ɛ and the mean magnetic field B0. Correlation studies carried out to establish the alpha effect in the solar wind have given negative results.
Simulating the Solar Dynamo
Authors: Brandenburg Axel
Published: July 2016

Mean-field and direct simulations of the hydrodynamics and hydromagnetics of the solar convection zone are discussed with the ultimate aim to understand the generation of differential rotation and magnetic fields. Various arguments constraining the values of the various turbulent diffusion coefficients are presented. It is suggested that the turbulent magnetic diffusivity is much smaller than the eddy viscosity which, in turn, is by up to a factor of ten smaller than the eddy conductivity. The magnetic field obtained from direct simulations is highly intermittent, and there is no clear systematic orientation of bipolar regions emerging from the convection zone. Various mechanisms that might cause such a field orientation are considered. Finally, the application of direct simulations to the determination of mean-field transport coefficients is emphasised.
Reynolds Stresses Derived from Simulations
Authors: Pulkkinen P. , Tuominen I. , Brandenburg A. , Nordlund Å. , Stein R.F.
Published: July 2016

Three-dimensional simulations of convection are studied with specific attention to the effects of rotation and latitude on different quantities. The latitude-dependence of the strength of convection is found to decrease with increasing strength of the turbulence. The λ-effect is, however, still present also in a more turbulent case.
A Numerical Approach to Dynamically Consistent Spherical Dynamo Models
Authors: Fuchs H. , Rädler K.-H. , Schüler M.
Published: July 2016

Models of spherical dynamos are considered which involve the full interaction between the magnetic field and the motion of an incompressible conducting fluid. In the basic equations magnetic field and fluid velocity are expanded in series of certain decay modes. In this way these equations are reduced to an infinite set of ordinary first-order differential equations for the coefficients of these expansions. The behaviour of dynamos can then be studied by integrating a finite set of these equations numerically. Some first results obtained in this way are presented for mean-field models in which the growth of the magnetic field due to the α–effect is limited by large-scale motions generated by Lorentz forces.
Asymptotic Model for Large-Scale Quasiheliostrophic Flow
Authors: Ghizaru Mihai
Published: July 2016

Starting from the ideal MHD equations written in spherical coordinates, using the regular perturbation method, quasiheliostrophic equations are derived as generalisation of quasigeostrophic models for atmospheric flow. From the fourth order momentum and induction equations, two prognostic equations for the stream function and magnetic flux function are derived. The magnetohydrodynamic model based on these equations is a suitable framework for describing the interaction between large-scale dynamic and magnetic features and the presence of specific patterns like active longitudes in the solar activity cycle.
Magnetic Braking of Late-Type Stars
Authors: Mestel L.
Published: July 2016

This report deals with the rotational history of late-type stars subsequent to their reaching the main sequence. The question of relevance to this Symposium is whether detailed comparison of magnetic braking theory with observations of young stellar clusters will yield any constraints on dynamo activity, in particular on the relation between the surface field strength Bs and the angular velocity ω.
Emission Regions on the Flare Star EV Lac in 1989
Authors: Pustil'Nik L.A. , Panferova I.P. , Gershberg R.E. , Shakhovskaya N.I.
Published: July 2016

Emission spectra of the flare star EV Lac in several nights of September 1989 are studied. Their variations due to the stellar rotational modulation are found and permit to define the most active longitudes on the stellar surface.
Bipolar Flows During Early and Late Phases of Star Evolution
Authors: Volkamer Klaus , Streicher Christoph
Published: July 2016

A mechanism for bipolar flows during early and late phases of star evolution is given, based on recently detected cold dark matter.
Generation of Magnetic Fields in Accreting Systems as a Basis of Nonthermal Mode of Energy Release
Authors: Pustil'Nik L.A. , Ikhsanov N.R.
Published: July 2016

Generation of the magnetic field during procces of disc accretion onto black hole or magnetize neutrin star may form current structures in a polar region. The instability and disruption of this currents must lead to effective acceleration of the particles to ultra high energy as it observe by GRO and UHE-astronomy experiments.
Dynamo Action in Accretion Disks
Authors: Torkelsson Ulf
Published: July 2016

Employing the standard theory for thin accretion disks I estimate the relevant parameters for a dynamo in an accretion disk. These estimates could then be compared to the results of numerical simulations. Some preliminary results of such simulations (Torkelsson & Brandenburg 1992) are presented too.
Magnetic Fields in the Irregular Galaxy LMC
Authors: Wielebinski Richard
Published: July 2016

New radio continuum surveys allowed the determination of the magnetic field in the Large Magellanic Cloud. The magnetic field is filamentary, extending to the south of the 30 Doradus nebula. Some possible explanations for this unusual morphology are discussed.