bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
Be vs. Li Abundance in Li-Rich Giants: an Evidence of Li Production in Red Giants
Authors: Castilho B. V. 
Published: July 2016

We present Be abundances derived through spectral synthesis for two Li-rich giants and a Li-normal giant, plus α Cen A and B, based on observations of the Be II λ 3130.420 and 3131.066 Å lines obtained with the CASPEC spectrograph at the ESO 3.6m telescope.The values derived for the two Li-rich giants (HD146850, HD787) agree with the one for the Li-normal giant (HD220321), and shows that Be was depleted in these stars (by > 90% i.e. by a factor of 10 or larger from the initial Pop I value (logN(Be)= 1.4)).This result implies that the original Li in these stars was almost completely destroyed, and that Li is most probably produced in red giants.
Radio Continuum Surveys of the Galaxy and Galaxies
Authors: Wielebinski Richard 
Published: July 2016

Radio sky surveys give us basic information about the origin of the radio emission from the Galaxy. By mapping the sky at several radio frequencies a separation of the thermal and non-thermal emission components is possible. The major part of the low-frequency radio emission comes from the synchrotron process, the braking of relativistic electrons in magnetic fields. By mapping the linear polarization at several frequencies (required for the correction of the Faraday rotation) the orientation of the magnetic fields in the emitting regions can be deduced. Older all-sky surveys at 30, 150 and 408 MHz have now been supplemented by new observations of the Galaxy at 45 and 1420 MHz. These surveys, in addition to being important as tracers of the morphology of the magnetic fields in the Galaxy, are also required to correct for the ‘foreground’ features in cosmological studies of the COBE data and the PLANCK surveys in the future. Studies of the Galaxy in polarization have been made some years ago indicating high percentage of linear polarization in various directions. More recent work with good angular resolution has shown spectacular polarized intensity structures in selected regions. Low-frequency data with good angular resolution are urgently required for the interpretation of these features.Observations of nearby galaxies in radio continuum (both total power and polarized intensity) have given us the possibility to study magnetic fields in objects at known distances. Polarization observations of nearby galaxies have confirmed the existence of regular magnetic fields in practically every object so far studied. Originally data were obtained from large single-dish telescopes, notably from Effelsberg and Parkes. These data were greatly enhanced by the addition of higher resolution components from the VLA and ATCA respectively. These results indicate surprisingly homogeneous magnetic fields in most galaxies. High angular resolution observations with the GMRT at lower radio frequencies will add a new dimension to the data on galaxies.
Inverse Energy Cascade in Advanced MHD Turbulence (the RNG Method)
Authors: Kleeorin N. , Rogachevskii I. 
Published: July 2016

The nonlinear (in terms of the large-scale magnetic field) effect of the modification of the magnetic force by an advanced small-scale magnetohydrodynamic (MHD) turbulence is considered. The phenomenon is due to the generation of magnetic fluctuations at the expense of hydrodynamic pulsations. It results in a decrease of the elasticity of the large-scale magnetic field.The renormalization group (RNG) method was employed for the investigation of the MHD turbulence at the large magnetic Reynolds number. It was found that the level of the magnetic fluctuations can exceed that obtained from the equipartition assumption due to the inverse energy cascade in advanced MHD turbulence.This effect can excite an instability of the large-scale magnetic field due to the energy transfer from the small-scale turbulent pulsations. This instability is an example of the inverse energy cascade in advanced MHD turbulence. It may act as a mechanism for the large-scale magnetic ropes formation in the solar convective zone and spiral galaxies.
Galactic Dynamos — a Challenge for Observers
Authors: Beck Rainer 
Published: July 2016

Results of linear αΩ-dynamo models are confronted with radio polarization observations of spiral galaxies. The general distribution of polarized emission and the magnetic field pitch angle can be described with sufficient accuracy. The occurrance of systematic large-scale variations in Faraday rotation (RM) is the strongest argument in favour of dynamo theory. However, the predominance of axisymmetric SO modes could not be confirmed by observations; S1 modes are about equally frequent. The azimuthal variations of field pitch angles and, in two cases, the phases of the RM variations are inconsistent with a classical αΩ-dynamo. Locally deviating RM values indicate field lines bending out of the plane. There is increasing evidence that galactic fields cannot be described by simple dynamo modes. This calls for more realistic dynamo models, taking into account non-axisymmetric velocity fields and galactic winds.Interpretation of radio observations is difficult because Faraday depolarization can seriously affect the data. Observations of small-scale field structures are summarized which show the path for future research. Instrumental needs for such investigations are discussed.
Nonlinear Dynamo of Magnetic Fluctuations and Flux Tubes Formation in the Ionosphere of Venus
Authors: Kleeorin N. , Rogachevskii I. , Eviatar A. 
Published: July 2016

Magnetic field observations in the dayside ionosphere of Venus revealed the magnetic flux ropes (Russell and Elphic 1979). General properties of these small-scale magnetic field structures can be explained by the theory of magnetic fluctuations excited by random hydrodynamic flows of ionospheric plasma.A nonlinear theory of the flux tubes formation based on the Zeldovich's mechanism of amplification of the magnetic fluctuations is proposed. A nonlinear equation describing the evolution of the correlation function of the magnetic field can be derived from the induction equation, the nonlinearity being connected with the Hall effect. The large magnetic Reynolds number limit allows an asymptotic study by a modified WKB method.On the basis of this theory it is possible to explain why the flux tubes are not observed if there is a strong regular large-scale magnetic field when the ionopause is low. The theory predicts the cross section of the flux ropes in the ionosphere of Venus and the maximum value of the magnetic field inside the flux tube.
Electron Energy Distributions of AGNs in the Thin Synchrotron Limit. II. Peaked Electron Energy Spectra of Blazars and OVV Quasars
Authors: Cruz-González Irene , Salas Luis , Carrasco Luis 
Published: July 2016

We analyse multifrequency quasi-simultaneous observations of AGNs with the Inverse Synchrotron Transform (IST) method described in Salas et al. (1993) and in Paper I (this conference).The observational spectral energy distribution of blazars and OVV quasars used as applications of the IST method were obtained from multifrequency quasi-simultaneous observations of Landau et al. (1986) and Brown et al. (1989). The application of the method requires good spectral coverage, since the presence of gaps larger than ≈ 0.75dex can introduce ficticious peaks. We present the analysis for: 1749+096, 0735+178, 1308+326, 3C273, 3C345, 3C279, OJ287, OJ049, 3C216, 4C39.25.The observed spectra are transformed to the source rest frame, the inverse transform is calculated over the whole spectrum to derive the electron energy spectra, which gives the amount of energy emitted in each characteristic frequency. Our results show that the electron energy spectra, Ψ(vc), of blazars and OVV quasars consists mainly of 4 or 5 well defined peaks superimposed on a down curved continuum. This indicates that the source radiates mainly around certain values of the electron's critical frequency (or energy, since vc ∞ B E2). These peaks are consistent with injection of fresh relativistic particles, occuring in pulses of quasi-monoenergetic groups.The separation between successive peaks (Δp) is ≈ 1.2 dex in critical frequency, and is characteristic for each object. The peaks in the radio region contain approximately the same number of electrons, consistent with evolution given by the continuity equation for constant B. While in the OIR region, the energy radiated increases towards lower frequencies.A comparison of Δp with Lbol and Lradio, and jet parameters such as, jet velocity and B1pc (inferred from the relativistic jet models of Blandford and Königl 1979) given by Cruz-Gonzàlez and Carrillo (1991), shows that Δp increases with jet velocity, stronger B fields imply smaller Δp, and that it is not correlated with Lbol, but is apparently correlated with Lradio.The Inverse Synchrotron Transform method applied in this paper is a powerful tool in the analysis of spectral energy distributions of AGNs.
ROSAT Observations of Einstein EMSS AGNs
Authors: Cappi M. , Palumbo G.G.C. , Della Ceca R. , Maccacaro T. 
Published: July 2016

Active Galactic Nuclei (AGN) can be studied in the ROSAT energy band also when serendipitously observed during long pointed observation of unrelated targets. From the available ROSAT database three Extended Medium Sensitivity Survey (EMSS) AGNs, detected with more than 500 counts, have been studied. One AGN (MS 1803.6+6738 = Kaz 102) was observed twice and in one field the target is the BL Lac 0716+714.– Spectral studies reveal that all three AGNs are well described by a single power law. Values of relevance are summarized in the table where they are compared to previous values from Einstein and the ROSAT survey (Walter R. & Fink H.H., 1993, A&A, 274, 105). All four sources have a NH value well below the estimated value given by Stark et al. (1992, ApJS, 79, 77) and Elvis et al. (1989, ApJ, 97, 777). This probably is an indication that a soft excess is present.– Variability studies show flux variations for the BL Lac on time scales of days, while the photon index appears rather constant. The high count rate for this object allows to attribute a probability of variability greater than 99% (running a K-S test against constancy). In the case of Kaz 102, the comparison of previous measurements with the present one does not show evidence of long term (years) variability.
High Resolution NIR Imaging of the Starburst Galaxy NGC 1808
Authors: Tacconi-Garman L.E. , Krabbe A. , Sternberg A. , Genzel R. 
Published: July 2016

We report 0.6″ res. J, H, and K and 1.5″ res. imaging of 2.17 μm HI Brγ and 2.12 μm H2 1-0 S(1) line emission towards the nucleus of the starburst galaxy NGC 1808. In the K-band data we (partially) resolve the nucleus and see several small knots in the circumnuclear region. Further, our JHK continuum images show that a large fraction of the near infrared light in NGC 1808 is produced in young star forming clusters. The Brγ emission originates from a compact nuclear source and from several distinct emission knots in the circumnuclear region. These knots are spatially well correlated with a family of compact radio sources, but uncorrelated with the optical “hot spots”. We propose that the Brγ knots trace the actual sites of starburst activity, while the optical hot spots are just directions of low foreground extinction.We use our data together with radio and far-infrared continuum emission measurements to constrain the parameters of the individual starburst sites in NGC 1808. The data suggest that the starbursts are unsynchronized and prolonged (5 × 106–5 × 107 yrs). The star formation rates in the active sites range from ∼0.1 to ∼0.6 M⊙ yr−1, and the present rapid rate of star-formation in NGC 1808 can be maintained for at most another ∼7 × 107 yrs.Portions of this work are presently in press (Krabbe, Sternberg, and Genzel 1993), and a second paper is in preparation (Tacconi-Garman et al. 1993).
Symposium Sur l'Avenir du Service International des Latitudes — Compte rendu des séances
Authors: Guinot B. , Murray C.A. 
Published: July 2016

Ce symposium a été organisé à la suite de la recommandation de la 10èmeassemblée générale de l'U. A.I. Nous avons essayé d'utiliser le mieux possible le temps écoulé depuis cette assemblée pour effectuer les travaux préparatoires. Je dois exprimer mes remerciements cordiaux à mes collègues, membres du comité d'organisation :Pr. CECCHINI, Dr. MARKOWITZ, Dr. MELCHIOR, Pr. TARDI, pour leur aide efficace dans ce travail. Mr. Sadler, Secrétaire Général de l'U. A.I. a aussi porté son attention sur toutes les étapes de ce travail et son action diligente a contribué à en assurer le succès.
1115 Å far ultraviolet stellar photometry
Authors: Byram E. T. , Chubb T. A. , Werner M. W. 
Published: July 2016

Stellar brightness measurements in the far ultraviolet at wavelengths above Lyman α have been obtained from several experiments beginning in 1960. The 1960 data were obtained using mirror telescopes and gas gain ion chambers. They indicated far ultraviolet stellar brightness about 1 magnitude lower than predicted by theory. Subsequent Geiger counter data appear to support this conclusion. The reliability of rocket far ultraviolet stellar photometry, however, is still insufficient, to place great confidence in the above conclusions.Stellar brightness measurements in the band 1150–1180 Å indicate that there may be a considerably greater deficiency in far ultraviolet stellar emission at wavelengths below Lyman α than above.
High energy cosmic photons and neutrinos
Authors: Gould R. J. , Burbidge G. R. 
Published: July 2016

This review concentrates primarily on the problem of interpreting the recent X-ray and γ-ray observations of celestial sources. The expected fluxes of hard radiation from various processes are estimated (when possible) and are compared with the observations. We compute the synchrotron, bremsstrahlung, and (inverse) Compton spectra originating from relativistic electrons produced (via meson production) in the galaxy and intergalactic medium by cosmic ray nuclear collisions; the spectra from π°-decay are also computed. Neutron stars, stellar coronae, and supernova remnants are reviewed as possible X-ray sources. Special consideration is given to the processes in the Crab Nebula. Extragalactic objects as discrete sources of energetic photons are considered on the basis of energy requirements; special emphasis is given to the strong radio sources and the possibility of the emission of hard radiation during their formation. The problem of the detection of cosmic neutrinos is reviewed.As yet, no definite process can be identified with any of the observed fluxes of hard radiation, although a number of relevant conclusions can be drawn on the basis of the available preliminary observational results. In particular, some cosmogonical theories can be tested.
The mass distribution in early type disk galaxies
Authors: Noordermeer Edo , Van Der Hulst Thijs , Sancisi Renzo , Swaters Rob 
Published: July 2016

We are studying the mass distribution in a sample of 50 early type spiral galaxies, with morphological type betweens SO and Sab and absolute magnitudes Mb between −18 and −22; they form the massive and high-surface brightness extreme of the disk galaxy population. Our study is designed to investigate the relation between dark and luminous matter in these systems, of which very little yet is known.From a combination of WSRT Hi observations and long-slit optical spectra, we have obtained high-quality rotation curves. the rotation velocities always rise very fast in the center; in the outer regions, they are often declining, with the outermost measured velocity 10-25% lower than the maximum.We decompose the rotation curves into contributions from the luminous (stellar and gaseous) and dark matter. the stellar disks and bulges always dominate the rotation curves within the inner few disk scale lengths, and are responsible for the decline in the outer parts. As an example, we present here the decompositions for UGC 9133. We are able to put tight upper and lower limits on the stellar mass-to-light ratios.
Properties of galaxy dark matter halos from weak lensing
Authors: Hoekstra Henk , Yee Howard K.C. , Gladders Michael D. 
Published: July 2016

We present the results of a study of the average mass profile around galaxies using weak gravitational lensing. We use 45.5 deg2 of RC band imaging data from the Red-Sequence Cluster Survey (RCS) and define a sample of ~ 1.2 × 105 lenses with 19.5 < RC < 21, and a sample of ~ 1.5 × 106 background galaxies with 21.5 < R < 24.We constrain the power law scaling relations between the B-band luminosity and the mass and size of the halo, and find that the results are in excellent agreement with observed luminosity–line-width relations. Under the assumption that the luminosity does not evolve with redshift, the best fit NFW model yields a mass M200 = (8.8±0.7) × 1011h–1M⊙ and a scale radius rs = I6.7+3.7–3.0h–1 kpc for a galaxy with a fiducial luminosity of Lb = 1010h–2LB⊙. the latter result is in excellent agreement with predictions from numerical simulations for a halo of this mass. We also observe a signficant anisotropy of the lensing signal around the lenses, implying that the halos are flattened and aligned with the light distribution. We find an average (projected) halo ellipticity of 〈ehalo〉 = 0.20+0.04–0.05, in fair agreement with results from numerical simulations of CDM. Alternative theories of gravity (without dark matter) predict an isotropic lensing signal, which is excluded with 99.5% confidence. Hence, our results provide strong support for the existence of dark matter.