bluuebunny/crossref_metadata_2025 huggingface dataset:
Molonglo Deep Survey at 843 MHz
Authors: Subrahmanya C.R. , Mills B.Y.
Published: July 2016

The Molonglo Observatory Synthesis Telescope has been used for a deep survey of 25 southern fields of about 1° diameter. All these fields have been observed on several occasions in 120 × 12-hour sessions during 1983–85. Radio sources have thus been detected down to a few millijansky at 843 MHz in 20 deg2 of sky from these observations and in a few selected fields, it has been possible to reach a detection limit of 1 mJy. The first results on the source counts and optical identifications are presented. By supplementing these data with some existing observations of stronger radio sources, we have been able to obtain source counts at 843 MHz for the entire range of flux densities above 1 mJy.
The Clustering and Evolution of Optically-Selected QSOs
Authors: Boyle B.J. , Shanks T. , Fong R. , Peterson B.A.
Published: July 2016

We are in the process of compiling a large catalogue of faint (B < 20.9 mag), UVX selected QSOs with complete spectroscopic identification using the fibre optic (FOCAP) system at the Anglo-Australian Telescope. From the 220 QSOs thus far identified we find that QSO evolution is most simply parameterised by a uniform increase in luminosity towards higher redshifts. We also find evidence for strong QSO clustering at scales < 10h−1 Mpc.
Determination of “inos” Masses Composing Galactic Halos
Authors: Song D. J. , Ruffini R.
Published: July 2016

One of the most important discoveries in modern cosmology and astrophysics is that the dark matter dominates at every scale of the Universe (Rubin et al., 1978, Forman et al., 1985, Faber and Gallagher, 1979, Sancisi, 1987). The problem that follows is to understand the components of the dark matter and to determine the physical properties of these components.
The “Gravitational Lens” 3C 321: A Remarkable Impostor
Authors: Filippenko Alexei V.
Published: July 2016

Recent observations of the radio galaxy 3C 321 are presented. The optical nucleus consists of two components (A, B), separated by ∼ 4″ (∼ 6 kpc), whose low-resolution spectra strongly resemble those of high-ionization type 2 Seyfert nuclei. The relative intensities of the emission lines differ in A and B by less than 1%, and their profiles are almost identical. 3C 321 appears to be a convincing example of a gravitationally lensed object.

Careful analysis of high-quality radio and optical data, however, reveals that the system is almost certainly not a lens. The equivalent widths of the emission lines are roughly twice as high in B than in A, and there are significant spatial offsets between regions of bright continuum and line emission. A slight, but fundamental, difference is visible in the two Hα emission profiles. The radial velocities of A and B are discrepant by 31 ± 10 km s−1. Finally, component A is nearly coincident with a flat-spectrum radio core, whereas B is next to an extended, steep-spectrum knot of radio emission.

This object should serve as a warning to lens hunters: beware of impostors, whose true properties may be difficult to ascertain without extensive optical and radio observations.
QSO Absorption Lines and Cosmology
Authors: Sargent Wallace L. W.
Published: July 2016

The properties of the different types of QSO absorption systems are briefly summarized. An overview is given of the potential applications of absorption lines in cosmology. Recent work on the cosmological evolution of the different types of absorbers is discussed. The physical properties of the intergalactic medium are discussed in the light of recent work on the “Lyman alpha clouds”. The uses of the lines for studies of the evolution of clustering in the Universe are described. Recent puzzling results on common absorption in pairs of QSOs, particularly Q1037–2704 and Q1038–2712, are summarized.
Clustering of Ly|α Absorbing Clouds at High Redshift
Authors: Webb J.K.
Published: July 2016

High resolution observations of regions in the Lyα forest of QSO spectra have been obtained using the Anglo-Australian Telescope. The amount and quality of the data, and the analysis techniques used, have enabled the clustering properties of these objects to be explored on scales smaller than has previously been possible. The results suggest that the Lyα clouds are weakly clustered with <ξ> = 0.32±0.08 over the velocity range 50–290 km/s.
Quasar Clustering
Authors: Shaver P.A.
Published: July 2016

If quasars are distributed cosmologically according to their red-shifts, then it is expected that their distribution on the sky will be very close to random, because it is in that case an average over an enormous range in distance. Most studies find no significant clustering. It has recently been suggested, however, that there may be a highly significant excess of close pairs of quasars with different redshifts1, although this has been disputed2. The new ROE/ESO quasar survey3provides a very large and deep sample over a connected area of sky, ideal for a more sensitive search for clustering. The result is shown in fig. 1. The observed distributions appear to be random, on all scales from less than an arcmin to tens of degrees.
Infrared Emission from AGN
Authors: B. Sanders D.
Published: July 2016

Infrared observations of complete samples of active galactic nuclei (AGN) have shown that a substantial fraction of their bolometric luminosity is emitted at wavelengths ˜8–1000μm. In radio-loud and Blazar-like objects much of this emission appears to be direct non-thermal synchrotron radiation. However, in the much larger numbers of radio-quiet AGN it is now clear that thermal dust emission is responsible for the bulk of radiation from the near-infrared through submillimeter wavelengths. Luminous infrared-selected AGN are often surrounded by powerful nuclear starbursts, both of which appear to be fueled by enormous supplies of molecular gas and dust funneled into the nuclear region during the strong interaction/merger of gas rich disks. All-sky surveys in the infrared show that luminous infrared AGN are at least as numerous as optically-selected AGN of comparable bolometric luminosity, suggesting that AGN may spend a substantial fraction of their lifetime in a dust-enshrouded phase. The space density of luminous infrared AGN at high redshift may be sufficient to account for much of the X-Ray background, and for a substantial fraction of the far-infrared background as well. These objects plausibly represent a major epoch in the formation of spheroids and massive black holes (MBH).
Megamaser Activity in Active Galaxies
Authors: A. Baan Willem
Published: July 2016

Megamaser emission provides an unprecedented view of the inner nuclear regions of active galaxies. The characteristics of OH, H2CO, and H2O sources identify different physical environments in the nuclei of megamaser host galaxies. Various classification schemes suggest a dominant starburst nature for the OH and H2CO sources providing the NIR/FIR radiation field as a pump. The molecular emission originates in a 50–100 parsec disk/torus, which is not yet completely observed. For H2O masers in relatively dust-free LINER/Seyfert 2 sources, the AGN provides the X-ray radiation field for pumping in a compact sub-parsec thin disk.
Are LINERs Starbursts or Mini-quasars? A Comparative Study of their Ultraviolet Spectra
Authors: Koratkar Anuradha
Published: July 2016

Low Ionization Nuclear Emission Line Regions (LINERs) are found in ˜30% of all bright galaxies. The nuclear luminosities in these objects are such that they can be produced by a number of mechanisms and there have been heated debates on the nature of ionizing sources in LINERs. The variety of ionizing mechanisms suggested are low luminosity AGNs, starbursts, shocks, or any combination of these. We have studied Hubble Space Telescope (HST) ultraviolet (UV) spectra of seven LINERs having compact nuclear UV sources.

The picture emerging from this comparison is that the compact source observed in these LINER galaxies, at least in some cases, is a nuclear star cluster rather than a low-luminosity active galactic nucleus (AGN). In these cases, the UV luminosity is driven by tens of thousands of O-type stars, depending on the assumed extinction for these objects. The O-stars could be the high-mass end of a bound stellar population, similar to those seen in super star clusters. Our data do not exclude the possibility that a similar stellar continuum source could dominate in all the LINERs. Alternatively, there may be two types of UV-bright LINERs: those where the UV continuum is produced by a starburst, and those where it is nonstellar.

The “clearly-stellar”, weak [O I] emitters, LINERs have relatively weak X-ray emission, and their stellar populations probably provide enough ionizing photons to explain the observed optical emission-line flux. The other LINERs, strong [O I] emitters, have severe ionizing photon deficits, for reasonable extrapolations of their UV spectra beyond the Lyman limit, but have an X-ray/UV power ratio that is higher by two orders of magnitudes than that of the “clearly-stellar” LINERs. A component which emits primarily in the extreme-UV may be the main photoionizing agent in these objects.

Recent results show that nuclear-starburst and quasar-like activity are often intermingled. Our results extend this result to the lower luminosities of the LINERs.
Blazars: Clues to Jet Physics
Authors: M. Sambruna Rita
Published: July 2016

Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ultimately, how energy is extracted from the central black hole. Crucial information about jet structure is provided by the spectral energy distributions from radio to γ-rays, their trends with luminosity, and correlated multifrequency variability. Since blazar jets have broad implications for all radio-loud (and possibly radio-quiet) AGNs, we also need to understand their circumnuclear structure, especially the details of the physical and dynamical conditions of the highly ionized gas on sub-pc scales, which could be directly related to jet formation and radiative power. Eventually, the bulk of information provided by blazars will help us clarify the origin of the radio-loud/radio-quiet AGN dichotomy, one of the most outstanding open issues of extragalactic astrophysics.
The Second Byurakan Survey: Faint Markarian Galaxies, AGN and QSOs
Authors: Stepanian J. A.
Published: July 2016

On the basis of the Second Byurakan Survey (SBS) we have produced the largest and most homogeneous new complete samples of faint Markarian Galaxies and bright QSOs. The volume of reliable investigation of UVX galaxies reaches to ˜ 200 – 250Mpc,– ten times deeper than the FBS.

New reliable data for the surface density of bright QSOs in mag. range 16.05 < B < 17.45 and redshift 0.3 < z < 2.2 are presented. The complete sample of bright(B < 17m5) SBS QSOs contains 93 QSOs in these ranges. The new data allow us to assume that bright QSOs fast evolution might be perhaps the result of a selection effect.
Galaxies in Selected Fields of the Second Byurakan Survey
Authors: Hakopian S.A. , Balayan S.K.
Published: July 2016

The current state of investigation of galaxies in seven fields of the Second Byurakan Sky Survey (SBS) is presented. These fields have been selected by the results of completeness estimation of the samples of galaxies in 65 fields.

Observations of the SBS faint candidate galaxies are carried out to complete spectroscopy of galaxies in the selected fields. Currently in one SBS field, with coordinates of center α=15h30m and δ=+59°, the spectra of all galaxies have been obtained and reduced. Besides the redshift and spectral classification, these data allow estimates of the quality of object selection in the Second Byurakan Survey at faint magnitudes.
Active Galaxies and Cosmic Evolution
Authors: S. Longair Malcolm
Published: July 2016

The evolutionary history of active galaxies is surveyed and contrasted with recent observations of the evolution of star and element formation rates with cosmic epoch. The problem of taking proper account of the effects of dust obscuration in optical and ultraviolet observations is reviewed. Recent submillimetre surveys have been used to derive the star formation rate as a function of cosmic epoch independent of dust obscuration. These observations suggest that the star formation rate peaked at redshifts z ˜ 2 – 4, similar to the maximum in the evolution of the populations of active galaxies. The inference of these observations for theories of galaxy formation is discussed.
Estimating the Number of Broad-Line Region Clouds
Authors: Dietrich M.
Published: July 2016

The observed emission-line spectrum of active galactic nuclei is consistent with cold dense gas photoionized by a central continuum source (cf. Ferland & Persson 1989). The estimate of the filling factor of the line-emitting region yields f˜10−6 only (cf. Osterbrock 1993) and motivated the picture of numerous clouds moving around a central black hole. Early estimates of the number of BLR clouds indicated a lower limit of 104 to 105 individual clouds (Capriotti et al. 1981; Atwood et al. 1982). Recently, Arav et al. (1998) estimated the number to be at least of the order of 107 discrete emitters. But the number and the nature of these clouds are still unknown.
General Discussion of Accretion Disks
Authors: Gurzadyan Vahagn G.
Published: July 2016

Even 25 years after the Shakura-Sunyaev seminal paper on the α-disk, we cannot claim that we have a reliable theory of accretion disks in galactic nuclei. Why? Because the problem is extremely complicated, it is essentially nonlinear and contains a number of parameters (i.e. is many-dimensional). The key point is whether it is possible to determine the magneto-hydrodynamical viscosity self-consistently, i.e. as a function of parameters of the disk - the temperature, matter and radiation densities, magnetic field, radius, etc., both in the radiation dominated and matter dominated regions. Another class of fundamental problems concerns the stability of the disk; Krolik mentioned only one instability - in the radiation dominated region, but there are many other types of instabilities which are quite sensitive to the physical conditions in the disk, for example, to the anisotropy of the ion pressure in the outer regions and possible electron-positron pair production near the inner edge of the disk. The other problems include those of the radiative transfer within the disk in various conditions, Comptonization of the outgoing radiation, radiation reflections by the desk, etc. Therefore it is not suprising that one can ‘explain' almost whatever he wants - spectra, variability, jets, wind, etc., by proper fit of the ‘free’ (which are never free) parameters and ignoring the instabilities and so on.
Activity in Interacting and Binary Galaxies
Authors: Terzian Yervant
Published: July 2016

This is a short review of recent studies and reports on interacting galaxies and binary galaxies. Early studies were primarily made at optical wavelengths, but recent ones have concentrated on observing HI at λ21 cm. Application of the Virial Theorem to these observations indicates M/L values of the binary systems of ≲50, suggesting the existence of moderate halos around spiral galaxies.
Supernova Types, Star Formation and AGN
Authors: Turatto Massimo , Cappellaro Enrico , R. Petrosian Artashes
Published: July 2016

New values of the frequencies of SNe are presented and discussed in relation to their use as SF indicators. The rate of core-collapse SNe is correlated to the colors and the FIR excesses of the parent galaxies in the sense that galaxies with blue colors and strong infrared excess have higher occurrence of type II and Ib/c SNe than other galaxies. This is in agreement with the expectation that they contain a higher fraction of massive stars. Instead no correlation is present for SNIa. The SN frequency does not correlate with the galaxy activity probably because searches are unable to discover SNe in the nuclear regions of galaxies.

A number of SNe with spectra similar to those of AGN exist. Their characteristic features are explained with explosion of SNe in dense environments, reminding of cSNR's invoked in the starburst model for AGNs. Some recent, peculiar SNe seem linked to GRB's opening the possibility that at least some GRB's arise from this kind of stellar explosion.
An Analysis of 900 Optical Rotation Curves
Authors: Roscoe D.F.
Published: July 2016

Persic & Salucci (1995; hereafter, PS) reduced raw Hα data from a large sample of southern sky spirals obtained by Mathewson, Ford & Buchhorn (1992), to present 900 Hα, rotation curves. It is found that a power-law, Vrot = A Rα, imposes extremely detailed correlations between the kinematic and the luminous properties of the galaxies through the model parameters (A, α); this law can be inverted to give a form of super Tulley-Fisher relationship for the determination of absolute magnitudes in terms of velocity information. Furthermore, there is very strong evidence suggesting the existence of discrete kinematic states for rotation curves (RCs hereafter) - which ultimately implies the luminosity evolution of galaxies to be similarly constrained to occupy discrete states.
The Orientation of Extragalactic Radiosources Relative to the Optical Axes of their Host Galaxies
Authors: Andreasyan R. , Sol H.
Published: July 2016

The relative orientation of radio and optical axes of radio-galaxies has been analysed for a sample of about 300 sources. Radio major axes have a tendency to align with optical minor axes of the host galaxies for the more elongated radiosources while they appear correlated with optical major axes for the less elongated radiosources.
Flare in the Hydrogen Line Region of the NGC 3227 Nucleus on January 12–15, 1997
Authors: Pronik I. , Metik L. , Merkulova N.
Published: July 2016

The nucleus of NGC 3227 was classified as a Sy2 type before 1974, and a Sy1 type after 1974. The Seyfert type of the nucleus changed corresponding to its brightness: U brightness of the nucleus increased in 1974: ΔU ˜ 1m. Maximum brightness of the nucleus was observed in 1975 – 1977.
NGC 3077: Hα Features and the Young Population
Authors: Abdel-Hamid H. , Notni P.
Published: July 2016

NGC 3077, an Irr II galaxy in the M81/M82 group of galaxies at 3.63 Mpc, suffered a tidal encounter with M81 about 400 Myr ago. Tidal structures of HI in this group of galaxies can best be seen in a VLA image by Yun et al. (1994).
Population Synthesis of Old Neutron Stars in the Galaxy
Authors: Popov S. B. , Colpi M. , Treves A. , Turolla R. , Lipunov V. M. , Prokhorov M. E.
Published: July 2016

The paucity of old, isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of the population is simulated following the paths of a statistical sample of stars for different values of the initial kick velocity, drawn from an isotropic, Gaussian distribution with mean velocity 0 ≤ 〈V〉 ≤ 550 km s−1. The spin-down, induced by dipole losses and the interaction with the ambient medium, is tracked together with the dynamical evolution in the Galactic potential, allowing for the determination of the fraction of stars which are, at present, in each of the four possible stages: Ejector, Propeller, Accretor, and Georotator. Taking from the ROSAT All-Sky Survey an upper limit of ~ 10 accreting neutron stars within ~ 140 pc from the Sun, we infer a lower bound for the mean kick velocity, 〈V〉 ≳ 200–300 km s−1. The same conclusion is reached for both a constant (B ~ 1012 G) and an exponentially decaying magnetic field with a timescale ~ 109 yr. Present results, moreover, constrain the fraction of low-velocity stars which could have escaped pulsar statistics to ≲ 1%.
The Impact of Cooling Flows in Clusters of Galaxies
Authors: Allen S. W.
Published: July 2016

I discuss the impact of cooling flows on the observable X-ray properties of clusters of galaxies. I show that accounting for the effects of cooling flows and subcluster merger events leads to consistent determinations of the distribution of gravitating matter in clusters from X-ray and gravitational lensing studies. Accounting for the effects of cooling flows significantly reduces the scatter in the LBol/TX relation determined for the hottest, most luminous systems and changes the best-fitting slope of the relation to a value close to LBol ∝ T2X, in agreement with theoretical models. A clear segregation between the mean metallicities of cooling-flow and non-cooling-flow clusters is observed, which can be explained by the presence of metallicity gradients in the cooling-flow systems.
The Physics of Soft Gamma Repeaters
Authors: Thompson C.
Published: July 2016

I describe the evidence that Soft Gamma Repeaters are magnetars—neutron stars in which a decaying magnetic field (rather than rotation) is the dominant source of free energy. The focus here is on the bursting emission of these sources and on direct physical diagnostics of very strong magnetic fields (B ≳ 10 BQED = 4.4 × 1014 G). I also summarize the trapped fireball model of SGR outbursts, the influence of QED processes on their spectra and lightcurves, and the genetic connection between neutron star magnetism and the violent fluid motions in a collapsing supernova core.
Particle Acceleration in Solar Flares
Authors: Miller J. A.
Published: July 2016

We review the basic, observationally driven requirements for a successful model of particle acceleration in impulsive solar flares and then evaluate the viability of three classes of acceleration mechanisms. We argue that stochastic resonant acceleration is by far the most promising of the mechanisms.
Radio Evidence for Nonthermal Particle Acceleration in Normal Stars
Authors: Lang K. R.
Published: July 2016

The Very Large Array has been used to detect nonthermal radio emission from nearby stars of late spectral type F, G, K, and M, and has provided unique high-resolution investigations of the Sun's radio emission.
Wave-powered Relativistic Electron Generation in Nonuniform Magnetic Fields
Authors: Leubner M. P.
Published: July 2016

The generation of superthermal electron populations due to resonant energy transfer from Alfvén wave packets can be studied sufficiently well within the Fokker-Planck diffusive formalism, where the particle energization is induced through Landau interaction. From the calculation of the magnetic-field-dependent diffusion operator of an Alfvén wave spectrum, it is demonstrated how resonant energization can be forced in nonuniform magnetic field configurations. On this basis, a mechanism for the acceleration of electrons from thermal to relativistic energies is presented where the specific magnetic field geometry acts as catalyst, providing a highly effective source for synergetic electron energization.
A Model for the Spatial Distribution of Relativistic Electrons in the Crab Nebula
Authors: Amato E.
Published: July 2016

A model for the spatial distribution of relativistic electrons in the Crab Nebula is proposed. Particles injected in the vicinity of the pulsar propagate in a magnetic field of time-dependent but spatially constant intensity. A good description of the nebular synchrotron emission, from radio to X-ray frequencies, is obtained if particle diffusion with respect to the azimuthal field lines is taken into account.
General-Relativistic MHD Simulation of Jets from a Geometrically Thin Accretion Disk Around a Schwarzschild Black Hole
Authors: Aoki S. I. , Koide S. , Shibata K. , Kudoh T.
Published: July 2016

We have performed a 2.5D, nonsteady, general-relativistic MHD simulation. Initially, we assumed a uniform magnetic field, a geometrically thin accretion disk rotating at Keplerian velocity, and a hydrostatic corona around a Schwarzschild black hole. We have investigated the formation mechanism of gas-pressure driven jets expected by Koide et al. and found the strong dependence of jet velocities Lorentz factor of jets) on the ratio of the density of the accretion disk to that of the corona (ρd/ρc), where γ2j - γj ∝ (ρd/ρc)0.75.
Relativistic Adiabatic Shocks in Accretion Flows
Authors: Caditz D. M. , Tsuruta S.
Published: July 2016

Accretion flows onto compact astronomical sources are likely to be supersonic, and shock waves may therefore be common in such flows. Plasma passing through a shock front will be compressed and heated according to the jump conditions across the shock discontinuity. Shocks in accretion flows may therefore have important consequences for the flow structure and emission characteristics. The equations governing adiabatic (nonradiative) shocks in relativistic plasmas are presented including the effects of radiation pressure and energy density, and pair equilibria in the postshock flow. We find that postshock states for accretion flows within cool, optically thick, accretion-driven sources such as AGN become radiation- or pair-dominated, and the postshock plasma will likely become optically thin before returning to steady-state conditions.
Gyrosynchrotron Emission from Stellar Coronae
Authors: Güdel M. , Zucker A.
Published: July 2016

We analyze quiescent radio spectra of main-sequence cool stars in terms of a simple gyrosynchrotron model. We find that the underlying (assumed) power-law electron distribution is often very hard, with power-law indices (in dN/dE ∝ E−δ) mostly around δ ≍2–3.5.
X-ray Radiation from Flare-heated Coronal Plasma
Authors: Güdel M.
Published: July 2016

We investigate the reaction of a coronal loop in the case of repetitive flares, with a power-law distribution in energy, injected into a rigid magnetic loop. Emission measure distributions and temperature-dependent modulations of the radiation are briefly discussed.
A Scaling Law for Magnetic Flux Tubes on an AGN Accretion Disk
Authors: LeRoux A. M. K. , Longcope D. W. , Tsuruta S.
Published: July 2016

An ASCA observation of Seyfert galaxy NGC 3227 showed flares with a linear increase and exponential decrease similar to that of solar flares. We derive a scaling law relating the loop length of a magnetic flux tube to rise and decay times of the flare using cooling mechanisms suitable for the central engine of a Seyfert galaxy. The predicted loop lengths are consistent with physical constraints on the plasma dynamics, suggesting that the same mechanism which explains solar flares may explain variability in Seyfert galaxies.
Far-ultraviolet Emission from Supernova Remnant Shocks
Authors: Sankrit R. , Blair W. P. , Team Fuse Snr
Published: July 2016

Supernova remnant shocks produce a rich spectrum of lines in the ultraviolet. Among these are important diagnostic resonance lines of O VI, C III, and N III which lie in the bandpass observable with the recently launched Far Ultraviolet Spectroscopic Explorer. We present an overview of a PI program to observe several supernova remnants using this new telescope.
Magnetic Field Effects upon Neutron Star Cooling
Authors: Teter M. A. , Rilett D. , Tsuruta S.
Published: July 2016

The principal mechanism for neutron-star cooling during the early period of its thermal evolution is the emission of neutrinos. Because the neutrino luminosity is very large compared to the photon luminosity, most approximations leave any small effects upon the photon luminosity during the early part of the evolution as ignorable. However, for a field strength of H ~ 1012 gauss, taking those effects into consideration in terms of a decreased photon flux from the surface means that the energy not released from the surface as photons is still trapped within the star. Energy conservation requires that neutrino emission must make up for the difference, thereby modifying the onset of the photon era of cooling. A magnetic field of large magnitude will change the surface temperature. A proper treatment of the neutron-star cooling problem in a large magnetic field requires that tangential heat flow be taken into account. This presentation shows the preliminary results of a study that is leading toward a full two-dimensional calculation of the thermal evolution.
Why Astronomy Needs Low-Pressure Sodium Lighting
Authors: Luginbuhl Christian B.
Published: July 2016

The damage to the dark-sky resource upon which ground-based astronomical observatories depend is substantial and increasing, even at what are considered premier dark-sky sites. Due to its nearly monochromatic output at the Na I resonance doublet near 589 nm, extensive use of low-pressure sodium (LPS) lighting in areas near astronomical observatories offers the potential preservation and even restoration of dark skies at other wavelengths, as well as minimal impact on the lighting needs of surrounding communities. Flagstaff, Arizona, with extensive use of LPS for general area lighting, has shown that this goal can be achieved.
Work for the Reduction of Light Pollution in Turkey
Authors: Asian Z.
Published: July 2016

In recent years Turkey has been losing the beauty of its night sky at a fast rate. The amount of outdoor lighting is increasing every day. University observatories at Ankara and Izmir are already irreversibly affected by light pollution. In this paper, work against light pollution in Turkey is outlined.
Astronomical Sites in the Ukraine: Current Status and Problems of Preservation
Authors: Vavilova I. B. , Karetnikov V. G. , Konovalenko A. A. , Logvinenko O. O. , Pinigin G. I. , Steshenko N. V. , Tarady V. K. , Yatskiv Ya. S.
Published: July 2016

The current status of optical and radio astronomical sites in the Ukraine and the problems of preservation are briefly reviewed. The problems of light pollution and the influence of technology can be solved using scientific and engineering methods. However the main problem of preservation is the economic one of maintaining infrastructure.
The Space Debris Environment - Past and Present
Authors: Flury W.
Published: July 2016

The mass and number of Earth-orbiting human-generated space debris have increased steadily since the beginning of space flight. Recent voluntary measures for debris mitigation applied by space operators have not stemmed the increase. The debris hazard for manned and unmanned missions is still low, but rising. More effective but also more costly measures, such as selective deorbiting of used stages, will be necessary to avoid a run-away situation. Internationally agreed codes for debris management and control are needed to solve this global space environment problem.
World Radio Conference WRC-2000
Authors: Ruf Klaus
Published: July 2016

The World Radio Conference 2000 must be considered the most important one for radio astronomy since WARC-79. The conference agenda contains about 30 topics of substance, and more than 10 of these have direct impact on radio astronomy frequency allocations. From the perspective of radio astronomy the most important items are: “Allocation of Frequency Bands above 71 GHz to the Earth-Exploration Satellite Service (passive) and Radio Astronomy Service” and the agenda items dealing with Recommendation 66 (Unwanted Emissions). A review of the status of preparations is given.
Steps to Establish International Radio Quiet Zones
Authors: Butcher Harvey
Published: July 2016

Future radio telescopes will feature large increases in sensitivity, not only to celestial sources but also to man-made interference. In addition, they will need to measure spectral lines as a function of redshift and hence observe at arbitrary frequencies. Current international regulations governing the use of the radio spectrum are in principle inappropriate to these science-driven needs. There are still a few places on Earth that are relatively interference-free, but the coming generation of telecommunications satellites in low orbit will compromise even those sites. The Organization for Economic Cooperation and Development (OECD) has recently sponsored a working group on the future of radio astronomy, which recommended that the possibility of establishing one or more formally recognized International Radio Quiet Zones (IRQZ) be studied seriously. First results of that effort will be discussed.
Techniques for Coping with Radio Frequency Interference
Authors: Fisher J. R.
Published: July 2016

As a complement to spectrum management efforts by radio astronomers a number of observatories and research groups around the world have begun looking into technical solutions to the problem of separating weak cosmic radiation from man-made radio signals. Some of the technical research now getting underway includes: high dynamic range receivers, low-noise superconducting filters, passive digital filtering, adaptive filters, adaptive sidelobe nulling, multi-feed correlation of RFI, and various techniques for signal blanking.

Increased technical support to spectrum management can also be provided in the form of accurate and statistically significant characterization of the radio environment, empirical and theoretical improvement of over-the-horizon propagation models, and timely measurements of spurious radiation falling in the protected radio astronomy bands.

Finally, credibility of our spectrum management effort can only be maintained by making sure that local radiation under the control of our radio observatories is in compliance with the field strength limits of Recommendation ITU-R R.A.769. This requires sensitive radiation measurements and often shielding of digital equipment, microwave ovens, test equipment, local oscillators, etc.
Protecting Space-Based Radio Astronomy
Authors: Altunin V.
Published: July 2016

This paper outlines some of the radio frequency interference issues related to radio astronomy performed with space-based radio telescopes. Radio frequency interference that threatens radio astronomy observations from the surface of Earth will also degrade observations with space-based radio telescopes. However, any resulting interference could be different than for ground-based telescopes due to several factors. Space radio astronomy observations significantly enhance studies in different areas of astronomy. Several space radio astronomy experiments for studies in low-frequency radio astronomy, space VLBI, the cosmic microwave background and the submillimetre wavelengths have flown already. The first results from these missions have provided significant breakthroughs in our understanding of the nature of celestial radio radiation. Radio astronomers plan to deploy more radio telescopes in Earth orbit, in the vicinity of the L2 Sun-Earth Lagrangian point, and, in the more distant future, in the shielded zone of the Moon.
Radio Workshop Report: Public Awareness of Radio Interference
Authors: Finley David G.
Published: July 2016

This, the final radio workshop session, covered the vital topic of public outreach. A number of valuable ideas emerged, with at least one specific goal to be achieved in a relatively short amount of time.
Chemistry and Depletion in Pre-Stellar Cores
Authors: Rawlings J. M. C.
Published: July 2016

The star-formation history of molecular cores is largely determined by gas phase chemical processes that are greatly modified by gas-dust interactions. Substantial elemental depletions may result from the efficient formation of refractory grain material. The depletion of carbon and of refractory elements such as S, Si, Mg, etc. in molecular clouds is well known, but is very poorly constrained. Star forming regions are cold, dark and chemically quiescent, so that in addition to the initial elemental depletions, an ongoing dynamical depletion of molecular material occurs as gas-phase material freezes out onto the surface of dust grains. Observational evidence for anomalous depletions in low mass star forming clumps became apparent in the early 1980s when the narrowness of molecular emission lines (especially those of NH3) suggested that high velocity infalling material is being depleted from the gas phase. This prompted further studies into the chemical effects of differential depletion and together with radiative transfer models has established molecular diagnostics of infall/depletion sources. Recent observations at high spatial resolution show direct evidence for gas-phase depletions in the central regions of protostellar cores.

In addition to the diagnostic and purely chemical implications for collapsing cores, depletion plays a very active role in the physical evolution of star-forming regions. Most gravitationally unstable low mass cores are believed to be magnetically sub-critical. Recent polarimetric studies of elongated cores are also providing evidence of magnetic alignment, giving strong support to the idea that magnetic fields play a dominant role in core evolution. The relaxation of magnetic pressure (whether through ambipolar diffusion, or by the damping of MHD waves) is critically dependent on the ionization structure which, in turn, is highly sensitive to the elemental and molecular depletions.
Translucent Clouds as Testbeds of Basic Chemical Networks
Authors: Turner B. E.
Published: July 2016

We have developed comprehensive models, based on the New Standard Model reaction dataset, for the gas-phase chemistry of translucent clouds. These models predict satisfactorily the abundances of 34 of the 38 molecular species observed in both translucent and cold dense clouds. With 3 additional reactions, the models also appear able to explain diffuse cloud abundances.
The Fractional Ionization in Molecular Cloud Cores
Authors: Caselli Paola
Published: July 2016

Ions and electrons play a key role in the chemical and dynamical evolution of interstellar clouds. Gas phase ion–molecule reactions are major chemical routes to the formation of interstellar molecules. The ionization degree determines the coupling between the magnetic field and the molecular gas through ion–neutral collisions, and thus regulates the rate of star formation. In the theoretical determination of the degree of ionization we run into several sources of uncertainty, including the poorly known cosmic ray flux and metal depletion within the cores, the penetration of UV radiation deep into regions of high visual extinction due to cloud inhomogeneities, and the ionization rate increase in the proximity of young stellar objects which may be strong X–ray emitters. Observational estimates of electron (or ion) fractionsx(e) (≡n(e)/n(H2), wheren(e) andn(H2) are the electron and molecular hydrogen number densities, respectively) in dense cloud cores are thus of considerable interest. In this paper, I will review recent improvements in the estimates of the ion fraction in dense cores and point out the difficulties in determiningx(e).
Molecular Excitation and Radiative Transfer: Current Results and Future Prospects
Authors: Black John H.
Published: July 2016

The spectra of dilute molecular gases in astrophysics arise in material far out of thermodynamical equilibrium (non-LTE), often in inhomogeneous atmospheres where Doppler motions from kinematical gradients and turbulence are large compared with thermal motions. Thus line intensities contain information about density and temperature as well as abundances, and line profiles probe the structure of the atmosphere. However, the theoretical description of the atmosphere can be extremely complicated and can make enormous demands for molecular data. Improvements in angular resolution and the possibility to make sensitive spectroscopic measurements at mid-infrared and submillimeter wavelengths pose new challenges for theoretical models.
Infrared Observations of Interstellar Ices
Authors: Ehrenfreund P. , Schutte W. A.
Published: July 2016

In the recent years revolutionary results concerning the nature of icy dust particles have been obtained with the help of the Infrared Space Observatory (ISO) and ground based observations. To date interstellar ice features of H2O, CO, CO2, CH3OH, CH4, H2CO, OCS and HCOOH as well as other minor species are observed. Interstellar grains act as important catalysts in the interstellar medium. Processes such as UV irradiation, cosmic ray processing and temperature variations determine the grain mantle growth and chemical evolution. ISO has revealed that ice segregation is an important and ubiquitous process in the vicinity of massive protostars and reflects the extensive thermal processing of grains in such environments.

In this paper a recent view on the inventory of interstellar ices is presented. Constraints on the reservoirs of oxygen in dense clouds are discussed, taking into account recent measurements of oxygen-bearing species. Large abundances of CO2 and CH3OH in dense molecular clouds provide challenging perspectives to investigate the differences of ice chemistry in the vicinity of high and low-mass protostars. Accurate abundances of ice species and knowledge on the ice distribution in the protostellar regions are an important tool to define the environmental conditions in molecular clouds. A global understanding of interstellar ice chemistry also allows monitoring the incorporation and evolution of volatiles in planetesimals and comets and to reveal processes predominant in the early Solar System.
Observations of Molecular Hydrogen in Shocks and PDRs with the Infrared Space Observatory
Authors: Wright Christopher M.
Published: July 2016

A review is presented of ISO observations of molecular hydrogen and its isotopic species, HD, toward various Galactic source types, such as shocks (Orion, DR 21, Cep A), photon dominated regions (IC 1396A, S140, Orion Bar) and putative X-ray excited sources (RCW 103, SS 433). In so doing I examine the similarities and differences in the H2 spectrum found under these different excitation conditions and mechanisms, and how the observations impact on some of the latest shock and PDR models. For instance, in addition to the ubiquitous ~ 2000 K component in shocks, seen using ground-based instrumentation, ISO reveals the existence of gas with both lower (150–800 K) and higher (≥ 3000 K) excitation temperatures. Further, ISO allows for the first time a measure of the bulk gas temperature toward PDRs (100–700 K), and H2 is also detected where X-ray emission is observed, providing at least circumstantial evidence of X-ray heating.
Optical and Near-Infrared Imaging of Jets and Outflows
Authors: Yang Ji , Yao Yongqiang
Published: July 2016

Jets and outflows are typical manifestations of the stellar mass loss process during the early stage of star formation. Optical and near-infrared (NIR) imaging of jets and outflows has become extremely popular recently, especially concerning large-scale surveys of Herbig-Haro (HH) objects, NIR imaging of jets and outflows driven by both low- and high-mass stars, and detailed imaging of jets and bow shocks at sub-arcsec resolution.

Optical and IR observations of jets and outflows have revealed (1) cavities evacuated by the outflow motion; (2) bow shocks inside and near the surface of the jets and outflows; (3) exciting sources; (4) circumstellar disks responsible for collimating the jets and outflows; (5) sometimes a cluster instead of a single source from which the jets and outflows initiate; (6) bursts of jets and outflows in some regions. Large-scale surveys of HH objects and outflows have been done in a number of nearby regions including Taurus, Orion, and Perseus. The prominent results of these studies range from the discovery of parsec-scale jets and outflows to their large-scale distribution. These studies also begin to reveal the relation between outflow activity and the large-scale distribution of young stellar objects.
Laboratory Simulation of Chemical Reactions in Interstellar Ices
Authors: Hiraoka K. , Sato T. , Takayama T.
Published: July 2016

The reactions of H atoms with solid thin films at 10 K were studied by using thermal desorption mass spectrometry and FT-IR spectroscopy. The N, C, and O atoms trapped in solid matrices were converted efficiently to fully hydrogenated compounds. In the reaction of H atoms with a solid CO film, the formation of formaldehyde and methanol were confirmed. The relatively low yield of the reaction products suggests either the smaller rate constants of the H atom addition reactions to CO and/or the occurrence of the hydrogen abstraction reaction H + HCO → H2+ CO. The reactions of H atoms with thin films of acetone and 2-propanol were also studied. The major products from acetone were found to be methane and alcohols but 2-propanol was not detected as a reaction product. The reaction of H with 2-propanol led to the formation of methane, alcohols, and acetone as major products.

In the reaction of H with C2H2, C2H6was found to be the major product but C2H4could not be detected. This is due to the fact that the first-step addition reaction H + C2H2→ C2H3is the rate-controlling process and the following reactions to form the final product C2H6proceed much faster than the initial one. This finding is in accord with the observation of comets Hyakutake and Hale-Bopp, i.e., C2H2and C2H6but not C2H4were detected in the coma of these comets. In the reactions of H with C2H2and C2H4, the C2H6product yields increased drastically with decrease of temperature from 50 to 10 K. This is most likely due to the increase of the sticking probability of H atoms on the solid films at lower temperature. These findings led us to conclude that the chemical evolution taking place on the dust grains via H-atom tunneling reactions becomes efficient only at cryogenic temperatures, i.e., ~ 10 K.
Sinks of Light Elements in Stars - Part I
Authors: Deliyannis Constantine P. , Pinsonneault Marc H. , Charbonnel Corinne
Published: July 2016

The fragile light elements lithium, beryllium, and boron (Li, Be, B) are easily destroyed in stellar interiors, and are thus superb probes of physical processes occuring in the outer stellar layers. The light elements are also excellent tracers of the chemical evolution of the Galaxy, and can test big bang nucleosynthesis (BBN). These inter-related topics are reviewed with an emphasis on stellar physics.

In Part I (presented by CPD), an overview is given of the physical processes which can modify the surface abundances of the light elements, with emphasis on Population I dwarfs - convection; gravitational settling, thermal diffusion, and radiative levitation; slow mixing induced by gravity waves or rotation. We will discuss the increasingly large body of data which begin to enable us to discern the relative importance of these mechanisms in Population I main sequence stars. In Part II (presented by MHP), discussion is extended to the issue of whether or not the halo Li plateau is depleted, and includes the following topics: Li dispersion in field and globular cluster stars, Li production vs. destruction in Li-rich halo stars, and constraints from 6Li. Also discussed are trends with metal abundance and Teff and implications for chemical evolution and BBN. In Part III (presented by CC), evidence is reviewed that suggests that in situ mixing occurs in evolved low mass Population I and Population II stars. Theoretical mechanisms that can create such mixing are discussed, as well as their implications in stellar yields.
Cosmological Gravitons Back Reaction and the Primordial Nucleosynthesis
Authors: Maia M. R. G. , Carvalho J. C. , Alcaniz J. S. , Maia J. M. F.
Published: July 2016

The back reaction of effective gravitons created during noninflationary epochs due to the inequivalence of vacuum states at different eras is examined in the context of primordial nucleosynthesis. Our final purpose is to obtain limits on the model employed to study such a process.
Change in Primordial Abundances Due to a Change in the Primordial Plasma Energy Density
Authors: Opher M. , Opher R.
Published: July 2016

We recently showed that the energy density of a plasma is appreciably different than previously thought when high frequency plasma fluctuations, ω ≥ kB/ħ, are taken into account (M. Opher &R. Opher, 1999). A change in the primordial plasma energy density changes the primordial expansion rate of the universe, the neutron temperature freeze-out, and the primordial nucleosythesis abundances. The change in the primordial abundances due to the change in the primordial plasma energy density is evaluated, taking into account the high frequency, as well as the low frequency fluctuations of the plasma.