bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cepheids in External Galaxies
Authors: Madore Barry F. 
Published: March 2016

The study of Cepheids in external galaxies has been a continuous probing of the near-by distance scale accompanied by a refining and redefining of the Period-Luminosity relation itself. For example, the nearest two late-type galaxies of the Local Group, the Magellanic Clouds have always been the testbed for calibrations, from the pioneering optical studies of Leavitt (1907) to the recent infrared calibration of McGonegal et al. (1982) three quarters of a century later.With time the data have improved in quality and in quantity but the methods of analysis and interpretation have so proliferated that the field might appear to be less well defined than it was at the turn of the century. Discussions of the problems have been so open that many have been driven to the conclusion that it is perhaps better to gauge the distances to galaxies using a variety of indicators, of secondary quality, rather than risk systematic errors at the start, through a complete reliance on one primary distance indicator. That situation, I believe, now has the potential for reversing itself.
Corrections for Velocity Dispersion in the Tully-Fisher Relation
Authors: Bottinelli L. , Gouguenheim L. , Paturel G. , de Vaucouleurs G. 
Published: March 2016

The 21-cm line width is a good indication of the maximum rotational velocity in a galaxy. However, the turbulent motions affect the observed line width and must be corrected. Not taking them into account introduces both accidental and systematic errors.A first example of this effect is the dependence of the slope a of the Tully-Fisher relation:on the level at which the line width ΔVobs. is measured. In their 1977 paper, Tully and Fisher find the following values:A second example is the departure from linearity in the H-band Tully-Fisher relation obtained by Aaronson et al. (1982) (their figure 2): the narrow lines are more strongly affected by these turbulent motions.
Kiloparsec Scale Radio Structure in Active Galaxies
Authors: Wilson A. S. 
Published: March 2016

AbstractA substantial fraction of active galaxies contain linear radio sources with sizes of a few hundreds or thousands of parsecs. Such sources are found in essentially all classes of active galactic nuclei, including Seyfert galaxies of both types, X-ray selected active nuclei, radio galaxies and quasars. The radio emission is clearly energised by the active nucleus, probably in the form of a jet. A number of observable consequences of the interaction of the jet with the interstellar medium of the galaxy are discussed. These processes include jet disruption by instabilities, acceleration of cosmic rays by shocks or turbulence, ionization and radial acceleration of interstellar clouds, creation of a hot thermal component through the agency of shock waves and bending of the jet by the ram pressure of a rotating interstellar medium.
Observations of Mass Flow, Disks, and Accretion Processes in Algol Binary Systems
Authors: Peters Geraldine J. 
Published: March 2016

As part of a multi-faceted study of gas streams, disks, and accretion processes in Algol type binaries, R.S. Polidan and I have obtained high resolution IUE observations of seven systems. Perhaps one of the most interesting results from these observations was the discovery of strong, variable absorption lines of N V, C IV, and Si IV in the spectra of stars whose photospheres are much too cool to form these ions. N V (1239,1243) and C IV (1548,1551) have been observed in AU Mon (B5V, 11ḍ1), CX Dra (B3V, 6ḍ7), and U CrB (B4V, 3ḍ5) while Si IV (1394, 1403) was found in TX UMa (B8V, 3ḍ1). The systems in which these ions have been observed generally contain primaries whose dimensions are greater than the Lubow and Shu (1975) parameter ϖmin.Radial velocity measurements of the N V, C IV, and Si IV features suggest that the line formation region is associated with the primary star and small in size. The strengths of the N V, C IV features appear to be variable on a time scale of several orbital periods and may be determined by the instantaneous rate of mass transfer. However, when the high ionization features are observed, their presence appears to be global and not restricted to the domain of gas stream impact.
Nutation and reference frame
Authors: Capitaine N. 
Published: March 2016

The reference frames are of fundamental importance in all kinds of the precession and nutation studies involving the theory, the coordinate transformation and the observations. The aim of this paper is to review all the frames used in such studies and to lead to a better consistency between them in order that theory and reductions of observations be referred, as close as possible, to the frames to which observables are actually sensitive.The equations of Earth rotation can be expressed either as Euler equations in the Terrestrial Reference System (TRS), or as perturbation theory in the Celestial Reference System (CRS) (Kinoshita 1977). Euler equations are transformed to the CRS in the astronomical approach (Woolard 1953) and solved by the method of variation of the parameters, whereas, in the geophysical approach (Melchior 1971), the solutions, first obtained in the TRS, are transformed to the CRS and then solved by an integration with respect to time.
Hydrogen Line Profiles
Authors: Hubeny I. 
Published: March 2016

Observed hydrogen line profiles are an enormously important source of diagnostic information about virtually all kinds of astronomical bodies. Therefore, it is important to understand the hydrogen line formation in sufficient detail to be able to achieve a high degree of reliability by analyzing observed hydrogen line profiles.Calculation of the predicted hydrogen line profiles involves two basic ingredients, (i) intrinsic line profiles, or line broadening - ”atomic physics” part, and (ii) the radiative transfer problem - ”astrophysics” part. There is not enough space to discuss here the current status of the astrophysical part of the problem. Fortunately, this topic is covered by many reviews. There are two major problems here, (a) departures from local thermodynamic equilibrium (LTE) - the so-called non-LTE description (e.g. Mihalas 1978; Hubenyet al.1994); and (b) departures from complete frequency redistribution (Cooperet al.1989; Hubeny and Lites 1994).
Lithium-6 Nucleosynthesis in the ISM
Authors: Malaney Robert A. 
Published: March 2016

The nucleosynthesis of 6Li in the galaxy has become of considerable interest in the past year. This is largely because of the exciting developments relating to the first detection of this isotope outside of our own solar system. Not only has 6Li been recently detected in the atmospheres of halo dwarfs [1-2], but also in the local interstellar medium (ISM) [3-4].It is well known that knowledge of the primordial abundance of the lithium isotopes has important ramifications for cosmology, through the constraints they impose on standard big bang nucleosynthesis (SBBN) [5], and those imposed on non-standard primordial nucleosynthesis models. Since a complete understanding of the galactic evolution of the lithium isotopes is a prerequisite to unambiguously determining their primordial abundance, a thorough interpretation of the new 6Li data in the context of chemical evolution models cannot be overstated.
How Massive is the Black Hole in M87?
Authors: Chakrabarti S.K. 
Published: March 2016

Using the Faint Object Spectrograph (FOS) on Hubble Space Telescope (HST), Harms et al. (1994, H94) have recently reported the spectroscopy of central region of the elliptical galaxy M87. Ford et al. 1994 (hereafter F94), using Wide Field Planetary Camera-2 have imaged the region around the nucleus in Hα+[NII] and find an ionized disk with spiral structures of mainly two arms. From the kinematical argument, based on the Doppler shifts of several lines emitted from the disk, and assuming a Keplerian motion of the emitting gas, they conclude that the mass of the disk plus the nucleus: Mc(R < 18pc) = (2.4± 0.7)× 109M⊙ and the inclination angle of the disk with the line of sight is i = (42±5)°. However, if the bright spiral structures are real, and represent shocked region in the disk, we expect that the disk is strongly non-Keplerian and therefore the mass of the black hole must be higher than above estimation.In the present contribution, we provide a complete description of the velocity field of the ionized disk and compute the shape of typical line profiles expected from various parts of the disk. Our analysis is based on the solution of a non-axisymmetric disk which includes two armed spiral density waves. We find a very good agreement between the theoretical and observed line profiles as regards to the Doppler shifts, line widths and the intensity ratios and estimate the mass of the black hole to be (4 ± 0.2) × 109M⊙. Details of this work will be published elsewhere (Chakrabarti, 1995).In a binary system with a thin accretion disk, the binary companion can induce two armed spiral shocks in the disk (e.g., Matsuda et al. 1987, Spruit 1987, Chakrabarti & Matsuda, 1992). In the case of active galaxies, a passing companion (or a globular cluster or a dwarf galaxy) which is more massive than the disk can induce the same effect.
High-Redshift Radio Galaxies
Authors: Miley George 
Published: March 2016

Radio galaxies are unique cosmological probes. As with radio-loud quasars, the presence of luminous radio continuum and optical line emission enable radio galaxies to be observed and recognized at large distances, up to z = 4.2. However, unlike the situation for most quasars, their optical emission can be spatially resolved from the ground and studied in detail.Progress in detecting distant radio galaxies has been rapid in recent years due to the use of CCDs and the exploitation of new selection criteria. Now, more than 60 radio galaxies are known with z > 2. More than half of these have been found by our group by concentrating on radio sources with the steepest spectra, most of these in a “Key Programme” of the European Southern Observatory. Although several people contributed to this Key Programme, most of the work was done by Huub Röttgering, who presented his Ph.D thesis in January and Rob van Ojik, who succeededhim. Redshifts of 1.5 to 4 correspond to a time when the Universe was 10% -20% of its present age. This was a crucial period in history when galaxy formation must have been rampant. It corresponds to the AGN era, a two-billion year “delta function” in the population evolution of luminous quasars and radio galaxies, when their space-density rose to a value several hundred times larger than the present density before the species mysteriously and suddenly became almost extinct.
Summary of the IRON and OPACITY Projects
Authors: Berrington Keith A. 
Published: March 2016

Considerable effort has been made recently by international collaborations, exploiting advances in atomic physics and in supercomputing, to compute complete sets of accurate data for astrophysically important processes; in particular, the Opacity Project and the IRON Project.The Opacity Project computed atomic data for opacity calculations• for H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe.• energies of terms having effective quantum numbers v≤10 and total angular momentum L≤3 or 4, all spin and parity combinations;• gƒ-values for all dipole transitions between these bound terms;• total cross sections for photoionizaion from all calculated bound terms, tabulated on a grid of photon energies suitable to describe the resonance structure in sufficient detail to calculate reliable opacities;• line broadening parameters.28 key research papers arising from the Project, together with calculated energies and oscillator strengths for light ions, are reprinted in ‘The Opacity Project Volume 1’ (Opacity Project Team, 1994, IOP Publ. ISBN 0 7503 0288 7). All data are available from TOPbase, an on-line database at the CDS (Cunto et al. 1993, A&A 275, L5).The IRON Project aims to systematically compute electron excitation cross sections for the iron group of elements. Particular attention is given to requirements for the interpretation of data from specific space observations.In the first stage of the Project excitation cross sections have been computed for fine-structure transitions in the ground configuration of all ions of astrophysical interest. These data are essential for the interpretation of IR lines to be observed by ISO, as well as for coronal spectra.
Jupiter’s Synchrotron Radiation Throughout the Comet P/Shoemaker-Levy 9 Impact Period
Authors: de Pater I. , Heiles C. , Wong M. , Maddalena R.J. , Bird M.K. , Funke O. , Neidhoefer J. , Price R.M. , Kesteven M. , Calabretta M. , Klein M.J. , Gulkis S. , Bolton S.J. , Strom R.G. , LePoole R.S. , Spoelstra T. , Robison M. 
Published: March 2016

Jupiter’s microwave emission was observed throughout the SL9 impact period by many different telescopes, among which the NRAO 140-foot telescope in Green Bank (21 cm), Westerbork (92 cm), Effelsberg (6, 11 cm), Parkes (21 cm), NASA DSN (13 cm), and the Very Large Array (22, 90 cm). We determined the “average” total nonthermal flux density from the planet after having subtracted the thermal contribution, following the formulation by de Pater and Klein, (1989) and Klein et al., (1989). The flux density increased typically by 40-50% at 6 cm wavelength, 27% at 11-13 cm, 22%at 21 cm and 10-15% at 90 cm. Thus the radio spectrum hardened considerably during the week of cometary impacts. Following the week of cometary impacts, the flux density began to subside at all wavelength.VLA images show the brightness distribution of the planet; a comparison of images taken before and during the week of impacts show marked changes in the brightness distribution. At a central meridian longitude λIII≈ 110°, the left side of the belts increased considerably and moved inwards by ~ 0.2 RJ. This suggests that the increase in flux density is caused by energization of the resident particle population.
The Three-Dimensional Structure of Our Galaxy
Authors: Perryman M.A.C. 
Published: March 2016

AbstractThis presentation has the following goals: (i) to explain, within a historical context, some of the difficulties in disentangling our Galaxy’s three-dimensional structure; (ii) to summarise in broad terms what we presently know of this structure, concentrating on those features inferred from accurate distance measurements; (iii) to illustrate selected aspects in a visually stimulating manner; and (iv) to give a foretaste of the exciting results that lie ahead with future space astrometric experiments.
Rationale for the Joint Discussion
Authors: Conti Peter S. , Churchwell Edwin B. 
Published: March 2016

AbstractThis Joint Discussion (JD) will consider the birth processes of massive stars. While similar phenomena (e.g., accretion discs, outflows, etc.) are found in low mass star formation, additional physics must be considered given the ionization of the interstellar environment by Lyman continuum photons, stellar winds from the hot star(s), and their deeper gravitational potentials. This JD will bring together experts from several disparate astronomical communities: stellar astrophysics, interstellar medium, radio astronomy, and stellar dynamics. The concept is to contrast observations of very young stars and star formation regions over various wavelengths with theoretical expectations.
The Supernebula and Protoglobular Cluster in NGC 5253
Authors: Turner Jean L. 
Published: March 2016

AbstractA compact and bright radio and infrared source within the starburst center of the dwarf galaxy NGC 5253 appears to be an extremely large compact HII region. The high density (ne ~ few xlO4 cm-3) and size (∼1-2 pc) of the nebula require the ionization equivalent of at least 4000 O7 stars. We suggest that this optically obscured nebula is a forming super star cluster, or protoglobular cluster, with an age of a few hundred thousand years.
Evolution of the Kuiper Belt during the Accretion of the Outer Planets
Authors: Brunini A. , Melita M.D. 
Published: March 2016

AbstractA set of self-consistent simulations of the formation of Uranus and Neptune are performed to study the evolution of the native KBOs in the process. Our main goal is to have a deeper understanding of the impact of the formation of the outer planets on the present orbital structure of the trans-neptunian region. We aim to understand if resonance capture driven by the outward migration of Neptune can actually occur and its interplay with the invasion of massive planetesimals expelled from the Uranus-Neptune region as a byproduct of their formation. Also the putative present existence in the Oort reservoir of a population of objects originated in the Kuiper belt is analyzed.
Collisional Evolution of the Edgeworth-Kuiper Belt: Implications for the Origin and Evolution of Small Body Populations
Authors: Davis Donald R. , Farinella Paolo 
Published: March 2016

AbstractCollisions have been a major process that shaped the Kuiper Belt that we see today. Collisional grinding likely played a significant role in removing mass from the trans-neptunian region and collisions are a mechanism for injecting fragments into resonances to start their journey to become short period comets. The Kuiper Belt preserves the accretional size distribution in bodies ≳ 100 km while the size distribution of smaller bodies is the result of collisional evolution. Observational confirmation of the transition size between these different regimes will constrain our understanding of the origin and evolution of the Kuiper Belt.
Horizontal Branch Models as a Test of Mixing on the RGB
Authors: Sweigart Allen V. 
Published: March 2016

AbstractWe discuss the impact of mixing and rotation along the red-giant branch (RGB) on the properties of horizontal-branch (HB) stars with emphasis on two problems: the nature of the unexpected blue HB population in the metal-rich globular clusters (GCs) NGC 6388 and NGC 6441 and the cause of the low gravities in the blue HB stars. New stellar models indicate that the sloped HBs in NGC 6388 and NGC 6441 might arise from a spread in metallicity, implying that these GCs may be metal-rich analogues of ω Cen. The low gravity problem can be largely explained by the radiative levitation of Fe in the atmospheres of the blue HB stars. We show that the onset of radiative levitation and the drop in HB rotation velocities at Teff ≈ 11,000 K coincide with the disappearance of surface convection. The low rotation velocities of the hotter HB stars may be due to the spin down of the surface layers by a weak stellar wind induced by the radiative levitation of Fe. We conclude that the impact of mixing and rotation on the HB remains to be clearly established.
Solar Eruptions - the Effects on the Earth’s Environment
Authors: Brekke P. 
Published: March 2016

AbstractThe response of our space environment to the constantly changing Sun is known as ”Space Weather”. The Solar and Heliospheric Observatory (SOHO) has obtained significant new information about coronal mass ejections (CMEs), the source of the most severe disturbances in the Earth’s environment. Most of the time space weather is of little concern in our everyday lives. However, when the space environment is disturbed by the variable outputs of the Sun, technologies that we depend on both in orbit and on the ground can be affected. The increasing deployment of radiation-, current-, and field-sensitive technological systems over the last few decades and the increasing presence of complex systems in space combine to make society more vulnerable to solar-terrestrial disturbances. Thus, our society is much more sensitive to space weather activity today compared to the last solar maximum. By observing the Sun 24 hours per day, SOHO has proved to be an important “space weather watchdog”. The importance of real-time monitoring of the Sun will be pointed out and a number of enterprises affected by space weather will be discussed.
Mechanism of Coronal Mass Ejections Triggered by Emerging Flux
Authors: Chen P.F. , Fang C. , Shibata K. 
Published: March 2016

The origin of coronal mass ejections (CMEs) is an interesting, while still mysterious, subject in solar physics. As well, the relationship between CMEs and solar flares is poorly understood. This paper attempts to provide answers to these questions on the base of the flux rope model, and put forward a trigger mechanism for CMEs. The work is motivated by an interesting discovery of the relation between reconnection-favored emerging flux and CMEs (Feynman and Martin 1995), i.e., such emerging flux, either within the filament channel or on the outer edge of the channel, can trigger CMEs.In the consideration of Aly’s constraint, a detached flux rope model was proposed for the pre-CME configuration. A quadrupolar magnetic field with a flux rope is introduced as the initial magnetic configuration in current research. Since our trigger mechanism is magnetic in nature, gravity is omitted. Emerging flux is simulated by changing the local magnetic flux at the bottom boundary.
Oxygen Abundances Derived from UV OH and O I IR Lines in Very Metal-Poor Stars
Authors: López Ramón J. García , Israelian Garik , Rebolo Rafael , Bonifacio Piercarlo , Molaro Paolo , Basri Gibor , Shchukina Natalya 
Published: March 2016

AbstractOxygen abundances have been derived in a sample of very metal-poor stars using the O I triplet at λλ 7771-5 Å and OH lines in the near UV. A detailed NLTE analysis of iron lines has been carried out for one of the observed stars, BD +23° 3130, providing consistent values of effective temperature and surface gravity that are in very good agreement with independent estimates from the infrared flux method and Hipparcos parallaxes, respectively. These parameters, especially the higher gravity obtained with respect to previous analyses, reduce the discrepancies claimed between the oxygen abundances determined from OH, O I triplet and [O I] λ 6300 Å lines, and give consistent abundances to within 0.16 dex for BD +23° 3130 ([Fe/H]NLTE = −2.43). The oxygen abundances derived for this new sample confirm previous findings for a progressive linear increase in the oxygen-to-iron ratio with a slope −0.33 ± 0.02 (including NLTE corrections to the iron abundances for all the stars considered) from solar metallicity to [Fe/H]∼ −3, and [O/Fe] values as high as ∼ 1.1 for stars with [Fe/H]≾ −2.5. These results can be interpreted as evidence for oxygen overproduction in the very early epoch of the formation of the Galactic halo, possibly associated with supernova events with very massive progenitor stars.
Lithium-Beryllium-Boron and Oxygen in the Early Galaxy
Authors: Vangioni-Flam Elisabeth , Cassé Michel 
Published: March 2016

AbstractOxygen is a much better evolutionary index than iron to follow the history of Lithium-Beryllium-Boron (LiBeB) since it is the main producer of these light elements at least in the early Galaxy. The O-Fe relation is crucial to the determination of the exact physical process responsible for the LiBeB production. Calculated nucleosynthetic yields of massive stars, estimates of the energy cost of Be production, and above all recent observations reported in this meeting seem to favor a mechanism in which fast nuclei enriched in He, C and O arising from supernovae are accelerated in superbubbles and fragment on H and He in the interstellar medium.
The Dawn of Galaxies: Deep MAMBO Imaging Surveys
Authors: Bertoldi F. , Menten K.M. , Kreysa E. , Carilli C.L. , Owen F. 
Published: March 2016

AbstractWe discuss results from sensitive, wide-field imaging of the millimeter extragalactic background using the Max-Planck Millimeter Bolometer array (MAMBO) at the IRAM 30 m telescope.