bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Resolution Optical and Infrared Observations of Molecules in Comets
Authors: Kim S. J. , Minh Y. C. , Hyung S. , Kim Y. H.
Published: July 2016

Molecules in cometary nuclei are considered to contain information on the constituents in the proto-solar nebula at the time of solar system formation. The composition of cometary nuclei has been indirectly derived from spectroscopic observations of molecules in comae. Ambitious space missions to cometary nuclei for landing and sample return are planned to be realized in 4–7 years. Until then, spectroscopic observations remain a powerful way to remotely investigate molecules and ions in cometary comae. Recent bright comets such as Hale-Bopp (C/1995 O1) and Hyakutake (C/1996 B2) have provided detections of new molecules in comae. Observational results from high-resolution optical and infrared spectroscopy of Hale-Bopp, Hyakutake and recent comets, are presented. In particular, symmetric molecules, which have zero electric dipole moment and are therefore not observable in the radio range, have been detected in several recent comets by infrared observations. The new data can also be used to derive accurate abundances of known molecular species. We present the time-dependent excitation processes of the bands of these molecules and discuss the influence of the fluorescence calculations on the derivations of molecular abundances in comets.
Chemistry in the Outer Solar System
Authors: Owen Tobias C. , Mahaffy Paul , Niemann H. B. , Atreya S. K. , Donahue T. M. , Bar-Nun A. , de Pater I.
Published: July 2016

The discovery by theGalileoProbe Mass Spectrometer that argon is enriched to the same extent as carbon and sulfur on Jupiter requires a revision of models for the formation of this giant planet. Evidently the excess heavy elements were carried to Jupiter in icy planetesimals that formed at temperatures ≤ 30 K. This result indicates that there is no original significance in the present position of Jupiter's orbit.
Constraints on the Origin of the Solar System from Meteorites
Authors: Gilmour J. D.
Published: July 2016

Primitive meteorites have preserved material that was present in the presolar nebula and record processes that occurred as evolution proceeded from the earliest solids. The discovery of isotopic anomalies in these samples led to the isolation of presolar grains and allowed the presence of short-lived radionuclides in the early solar system to be inferred. Isotopic anomalies in oxygen may reflect non-linear chemical fractionation rather than a nuclear effect, but the theory is as yet insufficiently developed to be rigorously assessed.

Analyses of individual SiC and refractory oxide presolar grains reveal that a large number of distinct nucleosynthetic sites contributed material to the solar nebula, and much progress has been made in identifying the various environments in which they formed. Isotopic anomalies associated with nanometre-size diamonds are best explained by supernova nucleosynthesis but it is clear that several sub-populations exist.

The extinct nuclides 26Al, 53Mn and 129I have each been used to establish the relative timing of events in the formation of the solar system. Calibrations of the Mn-Cr and I-Xe systems against the Pb-Pb system (based on decay of uranium isotopes) have been proposed, and Al-Mg data can be included through a calibration with the I-Xe scheme. Assuming these calibrations to be valid allows a tentative chronology of the early solar system to be developed, the plausibility of which can be seen as a test of the calibrations. In this chronology, the first solids to form in the solar system were refractory inclusions. Chondrules (rapidly cooled silicate droplets) appear to have formed later than CAIs over a period of a few million years. Parent body processing began early in solar system history and was ongoing as chondrules formed.
Interstellar Matter in Meteorites and Interplanetary Dust
Authors: Messenger S.
Published: July 2016

Meteorites and interplanetary dust particles (IDPs) are primitive solar system materials which contain preserved nebular condensates, circumstellar dust grains and partially preserved molecular cloud matter. The circumstellar dust grains found in meteorites are direct samples of a variety of stars, and provide detailed constraints on models of stellar nucleosynthesis. Hydrogen and nitrogen isotopic anomalies in organic matter in meteorites and IDPs are thought to originate from chemical processes in a presolar molecular cloud. This material is better preserved, but less well characterized among IDPs.
Alternative Solutions to Big Bang Nucleosynthesis
Authors: Kurki-Suonio Hannu
Published: July 2016

Standard big bang nucleosynthesis (SBBN) has been remarkably successful, and it may well be the correct and sufficient account of what happened. However, interest in variations from the standard picture come from two sources: First, big bang nucleosynthesis can be used to constrain physics of the early universe. Second, there may be some discrepancy between predictions of SBBN and observations of abundances. Various alternatives to SBBN include inhomogeneous nucleosynthesis, nucleosynthesis with antimatter, and nonstandard neutrino physics.
Creation and Destruction of 7Li and 3He in RGB and AGB Stars
Authors: Sackmann I.-Juliana , Boothroyd Arnold I.
Published: July 2016

Early in this decade our theoretical work demonstrated that all AGB stars in the mass range ˜ 4 to ˜ 7 M⊙ pass through a stage when a tremendous amount of lithium [up to log ε(7Li) ˜ 4.5] is created and transported to the surface. These lithium-rich AGB stars are predicted to occupy a narrow luminosity range between Mbol = −6 and −7, in excellent agreement with the observations of Smith & Lambert (1989), and might be useful as approximate standard candles. Recently, we found that even low mass stars (˜ 1 to ˜ 2 M⊙) on the RGB could create a tremendous amount of surface lithium. In both the AGB and RGB cases, it is the Cameron-Fowler mechanism that is responsible for the lithium creation.

In the AGB stars, it is hot bottom burning (nuclear burning at the base of the convective envelope) that produces the lithium. In the RGB stars, it is “cool bottom processing” that can lead to either lithium production or destruction. Cool bottom processing results when extra mixing (presumably rotation-induced) transfers material from the cool convective envelope down to the outer wing of the hydrogen-burning shell (where nuclear reactions can take place) and back out to the envelope. If the extra mixing is slow, 7Li is destroyed; if it is fast enough, then 7Li is created - for sufficiently fast and deep extra mixing, log ε(7Li) ˜ 4 is possible.

Unlike 7Li, the 3He abundance is almost independent of the mixing speed, and is constrained by observations of 12C/13C or [C/Fe] on the RGB. Cool bottom processing causes low mass stars of sub-solar metallicity to be net destroyers of 3He, rather than net producers. This is in contrast to previous theoretical predictions, and has a far-reaching effect on our understanding of galactic chemical evolution of 3He.
Improved Use of Inputs to Primordial Nucleosynthesis
Authors: Nollett Kenneth M. , Burles Scott
Published: July 2016

We present a new method to incorporate laboratory nuclear data directly into the standard big-bang nucleosynthesis calculation. Using the quoted uncertainties on the data in a Monte Carlo procedure, we estimate likelihood distributions of the predicted abundances. Our results indicate significantly narrower confidence limits for the predictions than those presently in use. This technique provides error estimates that become smaller as more input data are added, and it allows new nuclear data to be incorporated easily as they become available.
Deuterium Observations in our Galaxy - View A
Authors: Linsky Jeffrey L. , Wood Brian E.
Published: July 2016

Accurate measurements of the D/H ratio in our Galaxy provide critical tests of Galactic chemical evolution and constrain the primordial value of D/H. Very high quality ultraviolet spectra from the GHRS and STIS instruments on HST have been analyzed for lines of sight toward both early and late-type stars and hot white dwarfs. We will summarize the results that are being obtained for D/H along sightlines through the Local Interstellar Cloud (LIC) and other nearby warm clouds. All sightlines through the LIC are consistent with D/H = (1.53 ± 0.18) × 10−5. Whether or not significantly different values of D/H are present in other clouds within 100 pc of the Sun is not yet settled, but there is evidence that D/H is significantly lower in Orion (500 pc). We will describe the likely sources of systematic errors in determining D/H that must be understood and quantified when analyzing such ultraviolet spectra.
Deuterium observation in our Galaxy - View B
Authors: Vidal-Madjar Alfred
Published: July 2016

Galactic D/H evaluations from observations completed in the far UV with first the Copernicus satellite then followed by IUE and the GHRS on the HST studies already suggest that D/H variations may be present in the interstellar medium. More recent IMAPS (the Interstellar Medium Absorption Profile Spectrograph) observations confirm that conclusion while new STIS (which replaced the GHRS on board HST) studies seem to indicate the contrary. The situation is discussed here.

Hopefully FUSE (the Far Ultraviolet Spectroscopic Explorer, launched the 24th of June 1999) will give access to the D/H ratio in many different galactic sites. This will help us reach a better global view of the evolution of that key element, and thus better constrain any evaluation of its primordial abundance.
The D/H Ratio in Interstellar Gas toward the Hot, White Dwarf G191-B2B
Authors: Sahu M. S.
Published: July 2016

Space Telescope Imaging Spectrograph (STIS) observations of the D/H ratio in the two velocity components towards G191-B2B are consistent with 1.5 ± 0.1 × 10−5 and do not agree with the values derived using the Goddard High Resolution Spectrograph (GHRS) data. We present some new work on the G191-B2B sightline, and the results we obtain are consistent with those of Sahu et al. (1999).
The Magellanic Clouds and the Primordial Helium Abundance
Authors: Peimbert Manuel , Peimbert Antonio
Published: July 2016

A new determination of the pregalactic helium abundance based on the Magellanic Clouds H II regions is discussed. This determination amounts to Yp = 0.2345 ± 0.0030 and is compared with those derived from giant extragalactic H II regions in systems with extremely low heavy elements content. It is suggested that the higher primordial value derived by other authors from giant H II region complexes could be due to two systematic effects: the presence of neutral hydrogen inside the helium Strömgren sphere and the presence of temperature variations inside the observed volume.
Observations of 6Li in Metal Poor Stars
Authors: Nissen P. E.
Published: July 2016

Methods and accuracies of determining the lithium isotope ratio in stellar atmospheres from high resolution observations of the profile of the λ6708 Li i doublet are discussed, and recent results for metal-poor disk stars and halo stars are reviewed. The data are compared to models for the Galactic evolution of the 6Li abundance. It is concluded that a much larger data set is needed to understand properly the formation of 6Li in the interstellar medium as well as the depletion in stars.
Li Abundance in Pop I Stars
Authors: Pasquini Luca
Published: July 2016

The study of Li in Pop I stars has focussed in the last years on observations of open clusters, spanning a large range of ages and metallicities. So far the observational picture is quite complex: the data indicate several phenomena which are not well understood, from the 'Li dip', to the scatter in Li abundances found among (otherwise similar) stars both in young and old clusters. Models fail in reproducing most of the observed features; in particular the almost total lack of dependence of Li depletion with metallicity. The comparison between clusters of different ages show that no PMS depletion occurs, and that for a large fraction of old star no additional depletion occurs after the first ˜1.5 Gyrs, while the depletion is strong at earlier ages. These observations are crucial for our understanding of the relationship between the Pop II Li Plateau and the Li primordial abundance.
Lithium in Giant Stars
Authors: de la Reza Ramiro
Published: July 2016

Lithium continues to be a surprising element and more than ever the study of its creation, destruction and distribution is giving us tools to understand, not only the chemical evolution of this element, but also the nature of mass loss of evolved giants and nucleosynthesis of other elements in cases of very low-metal giants. It also helps to set constraints for cosmological models. The presence of very strong lithium lines in some giant stars of different spectral types and stages of evolution has been considered up to the end of the nineties as a puzzle. To solve this problem, non standard evolutionary mechanisms must be invoked. We review here all the mechanisms presented in the literature and which are divided into internal and external processes of lithium enrichment. We will also discuss the observational tests which are being performed in order to discard (or not) some of them. In any case, the more realistic values of the lithium abundances in giants are, as we will see, the main test of these proposed scenarios. Because of this importance we discuss here the state of art of the Non-LTE determinations of lithium abundances in strong lithium giants. Evolved giants, with lithium abundances larger than that of the interstellar medium and with their important mass losses can be considered the most realistic sources of lithium in the Galaxy. We believe that a complete physical picture of this problem will give a powerful tool to understand the chemical evolution of a large part of all light elements.
Lithium in Young Open Clusters
Authors: Pallavicini R. , Randich S. , Stauffer J. R. , Balachandran S. C.
Published: July 2016

We present lithium abundances for ∼50 late-type members of the ∼30 — 50 Myr old open clusters IC 2602 and IC 2391 derived from high-resolution spectra obtained at ESO and CTIO. These data enlarge and extend to cooler temperatures previous Li surveys of these clusters by Stauffer et al. (1989) and Randich et al. (1997). We discuss the lithium vs. temperature distribution in the two clusters and we compare our results with those obtained for the Pleiades (∼120 Myr). The results are discussed in the general framework of lithium depletion in young clusters, from the pre-main sequence to the age of the Pleiades.
Li Abundance in Evolved Stars of NGC 6397
Authors: Allen D.M. , Castilho B.V. , Pasquini L. , Barbuy B. , Molaro P.
Published: July 2016

Five giants and 11 subgiants of the metal-poor globular cluster NGC 6397 are analysed. In this Poster we present the lithium abundances derived. The present Li abundances and those of turnoff stars by Pasquini & Molaro (1996) are complementary in terms of stellar evolution stage, and show the Li abundances decreasing off the main sequence along the red giant branch.
Lithium in Cool Stars Detected in EUV Surveys
Authors: Tagliaferri G. , Pastori L. , Cutispoto G. , Pallavicini R.
Published: July 2016

We selected a sample of active cool stars detected in the EUV band by the ROSAT WFC and performed spectroscopic and photometric observations. We inferred spectral type, luminosity class, distance, binary status, rotational velocity. Here we show the results of the Li abundances determination from the Li I 6707.8 Å spectral line.
Lithium Abundance in Late-Type Stars
Authors: Pompéia L , Barbuy B , Grenon M.
Published: July 2016

We have a list of nearby bulge-like turnoff stars with metallicities in the range −0.3 ≤ [Fe/H] ≤ +0.6, for which we have the absolute magnitude from Hipparcos, Geneva photometry (therefore temperature and metallicity), and radial velocity from Coravel (Grenon 1990, 1997). From Hipparcos data, the turnoff of these field stars indicate an age of 10-11 Gyr, which would be the age of the most metal-rich component of the bulge.

We obtained high resolution échelle spectra with FEROS, with the aim to carry out detailed analysis of these stars. In this paper we present the Li abundance for 40 of these metal-rich and old dwarf stars, as a function of their temperatures.
Measurements of Li Abundance in a Sample of T Tauri Stars
Authors: Sartori M. J. , Gregorio-Hetem J. , Castilho B. V. , Lépine J. R. D.
Published: July 2016

In this work we present the stellar parameters and the Li abundances, obtained by spectral synthesis, for a sample of 13 weak-line T Tauri stars.
The Abundance of Boron in Disk-Metallicity Stars
Authors: Cunha Katia
Published: July 2016

Although the behavior of boron versus metallicity has been probed in a fairly large sample of halo dwarfs with HST, it is only very recently that boron abundances have been derived systematically in solar metallicity dwarfs. This effort began with a re-analysis of the solar spectrum with modern atomic data and model atmospheres so that the Sun could be adopted as a standard for the calibration of a line list in the region of the B I transition at 2497 Â. The solar analysis indicates that boron is not depleted in the solar photosphere. From a subsequent study of a sample of 14 field F/G-dwarfs with roughly solar metallicities, it is found that the behavior of boron versus [Fe/H] follows the linear trend that is observed for the halo stars. The average B/Be obtained for solar metallicity stars is 27±5 compared to the solar ratio of 23. The determination of boron abundances in the young B-type and G-type stars of the Orion association reveals a behavior of boron and oxygen in Orion that is opposite of the positive correlation which is observed for the field stars: the boron and oxygen abundances are anticorrelated.
The Light Elements in the Light of 3D Hydrodynamical Model Atmospheres
Authors: Asplund Martin
Published: July 2016

The influence of stellar granulation on the line formation of the light elements in metal-poor stars has been investigated by means of 3D hydrodynamical model atmospheres. Due to a lucky (?) coincidence, the effects due to the lower photospheric temperatures with 3D models compared with classical 1D model atmospheres are almost exactly balanced by a pronounced over-ionization of Li i, as concluded from detailed 3D NLTE calculations. Additionally, the effects of convective line asymmetries on 6Li isotope determinations have been investigated and found to be of minor importance.
Formation of the Optical Spectra of the Coolest M- and L-dwarfs and Lithium Abundances in their Atmospheres
Authors: V. Pavlenko Yakiv
Published: July 2016

Theoretical aspects of modeling of spectra of late M- and L-dwarfs are discussed. We show, that the processes of formation of spectra of M- and L-dwarfs are basically different. Instead of the case of M-dwarfs, atoms of Ti and VO should be depleted into grains in the atmospheres of L-dwarfs. Overall shape of the L-dwarf spectra is governed by the K I + Na I resonance line wings of the huge strength. To fit lithium lines observed in spectra of the coolest dwarfs we used two additional suggestions: a) there are some extra depletions of molecular species absorbed in the optical spectra of L-dwarfs; b) there may be (a few?) additional (“dusty”?) opacity sources in their atmospheres. Problems of lithium line formation and the “natural” limitation of their use for the ‘lithium test’ for the case of L-dwarfs are discussed.
Lithium-Rich K Giants with Infrared Excesses: Fundamental Parameters and CNO Abundances
Authors: A. Drake Natalia , de la Reza Ramiro , da Silva Licio
Published: July 2016

We present the results of an analysis of seven faint K giants with strong Li lines, recently discovered during the Picodos Dias urvey, from high-resolution and high signal-to-noise-ratio spectra. The fundamental parameters of these stars, such as effective temperature, surface gravity, metallicity and microturbulence, were determined. We also obtained LTE abundances of Li and CNO elements and measured the 12C/13C ratios by spectral synthesis using the lines of Li I (λ6104Â and λ6708 Â), C2, CN, and [O I]. The studied Li K stars are found to be red giant branch stars with masses around 1M⊙.
The Behavior of the Rotational Velocity in Lithium-Rich Evolved Stars
Authors: Melo C. H. F. , Soares B. B. , Mirandar A. C. , Da Silva J. R. P. , De Medeiros J. R.
Published: July 2016

We analyse the behavior of the projected rotational velocity vsin i for a sample of 20 lithium-rich evolved stars. Most of these stars show normal rotational velocity with respect to the typical lithium-normal evolved stars of the same spectral type. Stars presenting enhanced rotation show also high activity level. No sign of binarity was found for these lithium-rich evolved stars.
Meridional Circulation, Turbulence and Lithium in Sub-Giants Originating from the Hot Side of the Dip
Authors: Talon Suzanne , Charbonnel Corinne
Published: July 2016

We present the impact of meridional circulation and shear turbulence on the evolution of the lithium abundance at the surface of evolved stars originating from the hot side of the Li Dip. We show that our fully consistent treatment of the same hydrodynamical processes which can account for C and N anomalies in B type stars (Talon et al. 1997) and for the shape of the hot side of the Li dip in open clusters (Talon & Charbonnel 1998) also explains Li observations in stars with Teff higher than 7000K on the main sequence as well as in their evolved counterparts (see also Charbonnel & Talon 1999).
Self-regulated hydrodynamical process in halo stars: a possible explanation of the lithium plateau
Authors: Théado Sylvie , Vauclair Sylvie
Published: July 2016

It has been known for a long time (Mestel 1953) that the meridional circulation velocity in stars, in the presence of μ-gradients, is the sum of two terms, one due to the classical thermal imbalance (Ω-currents) and the other one due to the induced horizontal μ-gradients (μ-induced currents, or μ-currents in short). In the most general cases, μ-currents are opposite to Ω-currents. Vauclair (1999) has shown that such processes can, in specific cases, lead to a quasi-equilibrium stage in which both the circulation and the helium settling is frozen. Here we present computations of the circulation currents in halo star models, along the whole evolutionary sequences for four stellar masses with a metallicity of [Fe/H] = −2. We show that such a self-regulated process can account for the constancy of the lithium abundances and the small dispersion in the Spite plateau.
Light Element Evolution at the Solar Neighborhood
Authors: Alibés Andreu , Labay Javier , Canal Ramon
Published: July 2016

We present the Light Element Evolution resulting from our new Chemical Evolution model. The LiBeB evolution is correctly fitted by taking into account several sources: Big Bang, Galactic Cosmic Ray Nucleosynthesis, the ν-process, novae and AGB and C-stars.
Evolution of 6LiBeB in Inhomogeneous Early Galaxy
Authors: Ken Suzuki Takeru , Yoshii Yuzuru , Kajino Toshitaka
Published: July 2016

Results of evolution of light elements (6LiBeB) based on supernova (SN)-induced chemical evolution model are presented. We point out an important property of light elements as a cosmic clock in metal-poor stars.
One Zone Numerical Model for the Galactic Evolution of Lithium
Authors: Terra Marco , I. Arany-Prado Lilia
Published: July 2016

We analyze the evolution of 7Li/H using the basic model for the galactic chemical evolution (GCE) described by Brown (1992) and a numerical procedure which allows to estimate the contribution of the red giants to the enrichment of lithium in the interstellar medium (ISM).
Cosmological Studies from Radio Source Samples
Authors: Rawlings S.
Published: July 2016

I review some recent cosmological studies based on redshift surveys of radio sources selected at low frequencies. The accretion rate onto the central black hole is identified as the basis of a crude physical division of the low-frequency population into two sub-populations: the first comprises ‘Eddington-tuned’ (high accretion rate) quasars and their torus-hidden counterparts; the second comprises ‘starved quasars’ like M87. There exist remarkable similarities between the shapes and evolutionary behaviours of the luminosity functions of radio sources and radio-quiet quasars; all luminous AGN are ∼ 300—times rarer at epochs corresponding to z ∼ 0 than at z ∼ 2.5. I argue that any evidence that quasars were intrinsically rarer at z ∼ 5 than at z ∼ 2.5 is as yet both tentative and indirect. A simple calculation suggests that the radio source population has been over-looked as a potentially important contributor to the entropy budget of the Universe. A recent sub-mm survey of radio sources is used to demonstrate a connection between the events which trigger jets and intense bursts of star formation, and a close link between the histories of star formation and AGN activity is proposed. I discuss the aims and methods of future large redshift surveys of radio sources, emphasising the importance of dovetailing these with the development of robust physical models for radio sources and their epoch-dependent environments.
Large Scale Structure Among z ∼ 2 Quasars as a Cosmological Standard Ruler
Authors: Roukema B.F. , Mamon G.A.
Published: July 2016

The peak in the power spectrum at ≈ 130h−1 Mpc at low redshifts provides a standard ruler in comoving space. This scale is shown to be present in the observed quasar distribution at z ∼ 2. This implies strong constraints on the density parameter, Ω0, and weaker constraints on the cosmological constant, λ0. Independently of λ0 (in the range λ0 ∊ [0, 1]), the constraint is 0.1 < Ω0 < 0.45 (68% confidence limit).

Combination of the power spectrum peak method with very independent results from the supernovae Type Ia method yields Ω0 = (0.30 ± 0.11) + (0.57 ± 0.11)(λ0 −0.7), 0.55 < λ0 < 0.95, (68% confidence limits) without assuming Ω0 + λ0 = 1. This supports the almost flat, perturbed Friedmann-Lemaître-Robertson-Walker model, independently of any cosmic microwave background observations.
The Luminosity Periodicity of Galaxies and Quasars in the Decametric Range
Authors: Miroshnichenko A.P.
Published: July 2016

Estimations of the possible activity periods of galaxies and quasars were made from the UTR-2 catalogue samples by two methods.
Absorption Against the Cosmic 2.7 K Background
Authors: Chandra Suresh , Kegel W.H.
Published: July 2016

Observation of an interstellar line in absorption against the cosmic 2.7 K background is an unusual phenomenon. The intensity, Iv, of a line generated in an interstellar cloud, with homogeneous excitation conditions, is given by

where Iv,bg is the intensity of the continuum against which the line is observed, τv the optical depth of the line, and Sv the source function, which is the Planck's function at the excitation temperature Tex, i.e., Sv = Bv(Tex). Observation of an interstellar line in absorption against the cosmic 2.7 K background, obviously, implies 0 K < Tex < 2.7 K, which requires rather peculiar physical conditions in the molecule, generating the line.
A Step to the Reionization Epoch
Authors: Shaver P. A.
Published: July 2016

The reionization epoch may lie not far beyond the most distant known quasars and galaxies, and it might be detectable in a variety of ways. One possibility discussed here is to search for an all-sky spectral step produced by the redshifted HI that was present prior to reionization.
21cm Absorption Lines at High Redshift from Intervening Galaxies
Authors: Briggs F. H.
Published: July 2016

Radio absorption line observations of neutral hydrogen gas against extended radio sources offers the means to measure sizes and kinematics in intervening galaxies at all redshifts up to the maximum redshift where radio galaxies are detected. Such observations can therefore trace the evolution of galaxies at redshifts z ≳ 2 where the damped Lyman — α statistics indicate that the mass in neutral gas exceeded the mass in stars.
Probing Large Scale Structures in HI with GMRT
Authors: Bharadwaj S. , Nath B.B. , Sethi S.K.
Published: July 2016

The redshifted 1420 MHz emission from the HI in unresolved Lyman-α clouds (DLA) at high z will appear as a background radiation in low frequency radio observations. We calculate the brightness temperature and the angular two-point correlation function of the fluctuations of this radiation. This can be an important probe of the large-scale structure at high z.
Extreme Relic Radio Sources in Four Southern Clusters
Authors: Andernach H. , Slee O.B. , Roy A.L. , Ehle M.
Published: July 2016

We describe the highest-resolution radio observations yet made of relic radio sources. These relics have extremely steep (α ≤ −2.5) spectra and are located in four southern Abell clusters (A 13, A 85, A133, A 4038). VLA images at 1.4 GHz and ∼4″ resolution show a remarkable variety of fine structure like arcs, wisps, plumes, and loops. Integrated polarization fractions range from 2.3% to 16.8%. Deep red CCD images do not reveal any optical object with a brightness and/or position typical of a radio host galaxy. The X-ray centroids in ROSAT images tend to be displaced from the cluster potential wells in the direction of the relics in A85, A133 and A4038, suggesting that some of the X-rays may be inverse Compton or excess thermal emission from the relic itself.
Coma Southwest — as seen by the GMRT
Authors: Dwarakanath K. S. , Chengalur J.N.
Published: July 2016

We have imaged in HI a ∼ 25′ field of view in the Coma Southwest region using the Giant Meterwave Radio Telescope. No HI was detected to a 3σ limit of 3 × 108M⊙ in the surveyed volume. Except for NGC 4839, no radio continuum emission was detected from the galaxies in the Coma Southwest to a 3σ limit of 3 × 1020 W Hz−1 of spectral luminosity at 1.4 GHz.
Giant Radio Galaxies and the Inter Galactic Medium
Authors: Schoenmakers Arno P. , de Bruyn A.G. , Röttgering H.J.A. , van der Laan H.
Published: July 2016

Using the WENSS survey, we have selected a complete sample of 26 Giant Radio Galaxies. We have investigated the properties of their radio structures using multifrequency radio observations. A spectral ageing analisys reveals that, among other things, that these sources are typically 50 — 100 Myr old and that their lobes have higher advance velocities than smaller sources of similar radio power. Further, we find pressure gradients in their radio lobes, suggesting that the lobes are still overpressured with respect to the environment. We find no evidence for a cosmological evolution of the radio lobe pressures with increasing redshift, at least up to z ∼ 0.3, other than that caused by our selection technique. A faint, higher redshift sample of giant sources is needed to constrain the pressure in their environments, the IGM. We are well underway with selecting such a sample, and the GMRT can play an important role in studying the radio properties of these sources.
Statistical Study on Large Samples of Radio Sources
Authors: Zhang X.Z. , Peng B. , Chen P.C.
Published: July 2016

We present some statistical results on a large sample of radio sources selected from the most important catalogs. Instrument selection effects on this sample are discussed for the first time. Our analysis suggests that the slope of the median spectral index becomes flatter with decreasing flux density. But the slope is rather small.
Compact Steep Spectrum Radio Sources
Authors: Jeyakumar S. , Saikia D. J.
Published: July 2016

We suggest that most compact radio sources are young objects advancing outwards through a dense environment which is asymmetric on opposite sides of the nucleus. This gas might be intimately related to the supply of fuel for the young radio source.
Interferometer Observations of Extragalactic Radio Sources at Decameter Wavelengths
Authors: Megn A.V. , Braude S. Ya. , Rashkovsky S.L. , Shepelev V.A. , Sharykin N.K. , Inyutin G.A.
Published: July 2016

The angular structure of extragalactic radio sources was studied at decameter wavelengths with resolution up to 1 arcsec using the URAN interferometer network. A extended low frequency halo with steep spectrum is detected for some of them and the known components of others become, as a rule, bigger at these wavelengths.
BVRI-Photometry of Distant Radio Galaxies from RC Catalogue in SAO RAS
Authors: Parijskij Yu.N. , Goss W.M. , Kopylov A.I. , Soboleva N.S. , Verkhodanov O.V. , Temirova A.V. , Zhelenkova O.P.
Published: July 2016

With the aim to extend a sample of the distant radio objects, about 100 steep spectrum FRII radio galaxies (SS FRII RG) from the RATAN—600 RC catalog were mapped by the VLA1 and identified with optical objects down to R = 24m − 25m with the 6 m telescope. The mean estimated redshift of SS FRII RGs from the RC list happened to be greater than 1.5. BV RI photometry was made, and by standard model fitting we have estimated “colour” redshift and the age of stellar population of the parent gE galaxy in 50 cases. Several objects were found in which active star formation began in the first billion of years after the Big Bang.
Effects of Synchrotron Loss on the Low-Frequency Spectra of Extragalactic Radio Sources with Inhomogeneities
Authors: Tsvyk N.
Published: July 2016

In this work we explain the integrated spectrum measurements (Braude et.al.,1978—1995) in terms of the synchrotron theory and the the recent measurements of radio fine structure in different classes of sources (Carilli et.al.,1991). This provides a new method of investigating extragalactic radio sources
GMRT Observations of M 82 and NGC 3079
Authors: A. Irwin Judith , Saikia D. J.
Published: July 2016

We present preliminary GMRT maps of M 82 and NGC 3079 at 327 MHz and 610 MHz.
Low Frequency Catalogues of the CATS Database
Authors: Verkhodanov O.V. , Trushkin S.A. , Andernach H.
Published: July 2016

We describe the most complete, publicly accessible database of radio sources, CATS (“astrophysical CATalogues Support system”). It contains more than 300 catalogues of objects detected in various (mostly radio) wavelength ranges. Apart from catalogues drawn from the most important existing surveys and compilations (e.g. NVSS, FIRST, GB6, IRAS, ROSAT, PGC, MCG), CATS includes the largest low-frequency catalogues published so far: UTR, Culgoora, Cambridge, Miyun, WENSS, TXS, Bologna and Molonglo etc., CATS allows one to operate with these, and to draw samples of objects for the study of a large variety of astrophysical problems. Some modes of access are described here.
On the Association of G343.1-2.3 and PSR 1706-44
Authors: Dodson R. , Golap K. , Osborne J. , UdayaShankar N.
Published: July 2016

The observations of the supernova remnant G343.1—2.3 with the Mauritius Radio Telescope, the Australia Compact Array, and the Hobart Single dish are presented. With these more sensitive measurements the association with the pulsar PSR1706-44 becomes much more likely. The major points from the observations are presented.
A Multifrequency Radio Spectral Study of SNR HB21
Authors: Zhang X.Z. , Higgs L.A. , Landecker T.L. , Qian S.J. , Wu X.J.
Published: July 2016

Radio observational results at 232 MHz and multifrequency studies of supernova remnant (SNR) HB21 are presented in this paper. Both the integrated spectral index and the spatial variations of spectral index of the remnant were calculated by combining the new map at 232 MHz with previously published maps made at 408, 1420, 2695, and 4750 MHz.
Supernova Remnant G11.2—0.3 and the ISM
Authors: Seth A.C.
Published: July 2016

We present 610 and 235 MHz GMRT observations of the supernova remnant (SNR) G11.2—0.3 which shows a very large roation measure gradient (ΔRM∼1600 rad m−2) across it. The GMRT observations are the first high-resolution observations of this object at low frequencies. There are differences between the structure observed at 610 and at 235 MHz only some of which can be explained by free-free absorption.
Anisotropy of Hectometric Cosmic Background
Authors: Tokarev Y.V. , Kaiser M.L. , Boiko G.N. , Gustov P.V.
Published: July 2016

The results of investigation of the low-frequency cosmic background by the WIND spacecraft near the L1 point during the deepest phase of the last solar activity minimum are presented. The antenna temperature modulation index and the ecliptic longitude of the primary area of radiation for frequencies 260, 516, 772, and 1028 kHz were measured by means of a dipole on the spacecraft which is rotated in ecliptic plane. Our results correct and complement the conclusions of the previous measurements made with IMP-6.
HI 21cm-line Observations with the GMRT Towards Interstellar Clouds Previously Seen in Optical Absorption
Authors: Mohan R. , Dwarakanath K.S. , Srinivasan G. , Chengalur J.N.
Published: July 2016

We have made HI 21cm-line absorption measurements using the GMRT towards 15 directions in the Galaxy which are known to have high random velocity clouds as seen in the optical absorption lines of CaII and NaI. For the first time, in 6 out of these 15 directions we detect HI absorption features corresponding to the high random velocity optical absorption lines. The mean optical depth of these detections is ∼ 0.08.
Preliminary Results of Galactic Radio Recombination Line Observations using the GMRT
Authors: Kantharia N.G. , Roshi D. Anish
Published: July 2016

A pilot project to observe recombination lines of hydrogen and carbon from Galactic HII regions near 20cm (n = 168) and 49cm (n = 220) using the 30-station correlator at the Giant Metre-wave Radio Telescope was undertaken. The preliminary results from observations of the HII regions W3 and S106 are presented here.
Recombination Radio Lines at Very Low Frequencies
Authors: Konovalenko A.A. , Stepkin S.V. , Shalunov D.V.
Published: July 2016

Investigations of carbon low frequency radio recombination lines measured with the world biggest decameter wavelength array UTR-2 are described.
A VLA search for the Geminga Pulsar at 74 and 326 MHz
Authors: W. Lazio T. Joseph , E. Kassim Namir
Published: July 2016

We have used the VLA to image the location of the gamma-ray pulsar Geminga at 74 and 326 MHz. Upper limits to the pulse-averaged flux density, taking diffractive scintillation (DISS) into account, are S < 56 mJy (2σ; DISS quenched) at 74 MHz and S < 5 mJy (95% confidence) at 326 MHz. Intrinsic variability appears to be required in order to reconcile our upper limits with previous low-frequency detections.
Radio Variability of the Galactic X-ray Binaries with Relativistic Jets
Authors: A. Trushkin Sergei , N. Bursov Nikolai
Published: July 2016

Variable non-thermal radio emission from Galactic X-ray binaries is a trace of relativistic jets, created near accretion disks. The spectral characteristics of a lot of radio flares in the X-ray binaries with jets (RJXB) is discussed in this report. We carried out several long daily monitoring programs with the RATAN-600 radio telescope of the sources: SS433, Cyg X-3, LSI +61°303, GRS 1915+10 and some others.

Many flaring RJXB show, exponential and power laws of flare decay. Moreover, these different laws could be present in one or several flares and commonly flare decays are faster at a higher frequency. The decay law seems to change because of geometric form of the conical hollow jets. The synchrotron and inverse Compton losses could explain general frequency dependences in flare evolution.
Radio Astronomical Scintillation in the Solar Wind Plasma: Imaging Interplanetary Disturbances
Authors: Manoharan P.K. , Pick M. , Consortium Lasco
Published: July 2016

When radio waves propagate through a irregular medium, scattering by the random refractive index inhomogeneities can lead to a wide variety of phenomena, which include intensity scintillation. The observed scattering can be interpreted to gain information about the random medium and such inversion studies are valuable when the accessibility of the medium becomes difficult. This paper briefly describes the intensity scintillation of celestial radio sources caused by the turbulence in the solar wind and summarizes the salient features of the method employed in mapping the structure of disturbances leaving the Sun out to ∼1 AU.
Observations of Solar Bursts Using the New Radio Spectrograph
Authors: Shanmugaraju A. , Umapathy S. , Balasubramanian V.
Published: July 2016

This paper presents a detailed analysis of 80 type III radio bursts, two noise storms and 10 type II radio bursts observed in the 30-80 MHz range with the new radio spectrograph (Madurai Solar Radio Spectrograph) when it was operated on a daily basis during the periods December 1997 — April 1998 and August 1998. Results from statistical analysis of type III bursts are in agreement with earlier results. Employing a technique of separating the background continuum of noise storms show that the continuum is produced by electron accumulated from the preceding bursts. Also it is seen that the number of occurrences of type I bursts is maximum during the maximum of the background continuum. Comparison of records of type II bursts from MSRS with other spectrographs (Culgoora & Hiraiso) for the same bursts indicate that the sensitivity of the MSRS at low frequencies is much better than the other spectrographs.
Concepts and Technical Studies of the Square Kilometre Array
Authors: van Ardenne Arnold
Published: July 2016

We present the concepts and their unique features presently being studied for the Square Kilometer Array expected to be operational between 2010 and 2015. A comparison is made between telescopes in operation to day and SKA ambitious set of requirements is presented. The framework for coordinating the studies of various countries aiming to conclude on a concept choice in 5 years is introduced. As a desirable side effect, efforts relevant for SKA, will result in new albeit smaller telescopes coming into operation at earlier stages.
The Development of the FAST Project in China
Authors: Nan R. , Peng B. , Qiu Y. , Zhu L. , Su Y. , Zhu W.
Published: July 2016

Acting as a pilot of the Square Kilometer Array (SKA), the Five hundred meter Aperture Spherical Telescope (FAST) has been proposed for construction in the unique karst area of southwest China. FAST is of Arecibo-type with rather a number of innovations, among which the active main spherical reflector shows fascinating. Furthermore, the feed cabin is supported and moved by cables controlled by computer, which avoids a heavy and expensive focal pointing system. With the effective aperture of 300 m, a large sky coverage, and a broad bandwidth (200 to 2000 MHz), possible capability up to 5 ∼8 GHz, FAST will be the world's largest single dish and perform markedly role in radio astronomy.
Radio Frequency Interference
Authors: Ekers R.D. , Bell J.F.
Published: July 2016

We describe the nature of the interference challenges facing radio astronomy in the next decade. These challenges will not be solved by regulation only, negotiation and mitigation will become vital. There is no silver bullet for mitigating against interference. A successful mitigation approach is most likely to be a hierarchical or progressive approach throughout the telescope and signal conditioning and processing systems. We summarise some of the approaches, including adaptive systems.
The Solar Dynamo
Authors: Schmitt D.
Published: July 2016

The generation of the solar magnetic field is generally ascribed to dynamo processes in the convection zone. The dynamo effects, differential rotation (ω–effect) and helical turbulence (α–effect) are explained, and the basic properties of the mean–field dynamo equations are discussed in close comparison with the observed solar cycle.

Especially the question of the seat of the dynamo is addressed. Problems of a dynamo in the convection zone proper could be magnetic buoyancy, the nearly strict observance of the polarity rules and the migration pattern of the magnetic fields which are difficult to understand in the light of recent studies of the field structure in the convection zone and by observations of the solar acoustic oscillations. To overcome some of these problems it has been suggested that the solar dynamo operates in the thin overshoot region at the base of the convection zone instead. Some aspects of such an interface dynamo are discussed. As an alternative to the turbulent α–effect a dynamic α-effect based on magnetostrophic waves driven by a magnetic buoyancy instability of a magnetic flux layer is introduced. Model calculations for both pictures, a convection zone and an interface dynamo, are presented which use the internal rotation of the sun as deduced from helioseismology. Solutions with solar cycle behaviour are only obtained if the magnetic flux is bounded in the lower convection zone and the α–effect is concentrated near the equator.

Another aspect briefly addressed is the nonlinear saturation of the magnetic field. The necessity of the dynamic nature of the dynamo processes is emphasized, and different processes, e.g. magnetic buoyancy and α-quenching, are mentioned.
Nonlinear Coupling Between the 110-Year Periodic Modulations of Solar Differential Rotation and Solar Cycle
Authors: Yoshimura Hirokazu
Published: July 2016

An observational example of nonlinear coupling between flows and magnetic field generated by dynamo action of the flows is found in the 110-year periodic modulations of the solar differential rotation and the solar cycle.
Can Mean Helicity Fluctuations Explain the Variability of the Solar Cycle ?
Authors: Hoyng P.
Published: July 2016

I consider the effect of rapid fluctuations in the mean helicity on a plane dynamo wave in the αω-approximation and in the weak forcing limit. The phase shift and the logarithmic amplitude of the wave exhibit a correlated random walk, so that weaker (stronger) cycles last longer (shorter). The solar cycle data follow this prediction rather well. Mean helicity fluctuations are concluded to be an important source of solar cycle variability.
Chaos in Nonlinear Dynamo Models
Authors: Kurths J. , Brandenburg A. , Feudel U. , Jansen W.
Published: July 2016

Two nonlinear dynamos have been analyzed by numerical means: 3D-simulation of the magneto-hydrodynamic equations and qualitative analysis of a simplified low-dimensional mean field model. It turns out that both are capable of deterministic chaos in a certain parameter range. As the basic tool the calculation of Lyapunov exponents has been used.
On the Dimension of the Solar Activity Attractor
Authors: Orzaru C.M.
Published: July 2016

The correlation dimension D(2) as a characteristic measure of the regular or chaotic behaviour of the solar dynamical system has been calculated. The algorithm suggested by Grassberger and Procaccia (1983) has been applied to time series of relative sunspot numbers and of areas of sunspots and faculae. In the first case, a correlation dimension D(2) ≃ 1.5 has been found; in the other two cases, the algorithm was not convergent, the results obtained being not relevant, due to the too short series of data available.
Dipole Field, Sunspot Cycle and Solar Dynamo
Authors: Simon P.A. , Legrand J.P.
Published: July 2016

From the analysis of a series of data concerning phenomena taking place in the high corona, in the interplanetary medium and in the magnetosphere, we came to the conclusion that we have to take into consideration a two-component solar cycle in which, with a 5–6 yr delay, the cycle of the dipole component of the solar magnetic field and the following sunspot cycle are closely correlated. In order to show the new mechanisms to incorporate into a model of a two-component solar cycle, we discuss several other relevant solar data.
Alpha-Quenched Alpha-Lambda Dynamos and the Excitation of Nonaxisymmetric Magnetic Fields
Authors: Barker Dale M. , Moss David
Published: July 2016

We present calculations showing how stable nonaxisymmetric magnetic fields may be excited in an alpha-quenched mean field dynamo in a deep spherical shell. The large scale velocity fields (differential rotation, meridional circulation) are determined by solving the axisymmetric Navier-Stokes equation, neglecting the Lorentz force but including a term parameterizing the turbulent Reynolds stresses.