bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Radio Frequency Interference Survey of Central Ohio
Authors: Dixon Robert S. , Ellingson Steven W. , Koch Ronald J. 
Published: July 2016

ABSTRACTA long-term radio frequency interference monitoring program is now in progress at the Ohio State University Radio Observatory. Current observations encompass the 1-2 GHz band, measuring the signal strength in each 150 KHz subband. Preliminary results show many strong and persistent signals, and wide bands in which no signals are detected. Daily and weekly variations appear to be correlated with periods of maximum human activity such as “rush hours”. It may be that aircraft reflections are causing many of the signals to be received, and that airline schedules correlate with “rush hours”. The program is being upgraded to automatically measure the direction of arrival of each signal, as an aid to further identify it. This directional information will also be used in designing rolled edges and side shields for the co-located OSU Radio Telescope, to further reduce its vulnerability to RFI.
Reduction of Interference in Observations with the Westerbork Synthesis Radio Telescope
Authors: Spoelstra T.A. Th. 
Published: July 2016

ABSTRACTRadio astronomical observations are increasingly affected by man-made interference of various kinds. Sophisticated software tools have to be developed to cope with interference effects in the data. A calibration procedure is described in which the effects of different categories of errors are separated. If this separation can be performed for interference effects.Interference effects remaining in the data are erroneously interpreted as source structure by self-calibration techniques. This is due to the fact that self-calibration alone does not properly take into account this separation. Some results for the Westerbork Synthesis Radio Telescope are given.
The Legal Defense of Radio Astronomy
Authors: Ennis James G. 
Published: July 2016

The purpose of this paper is to describe one program of the National Academy of Sciences’ Committee on Radio Frequencies (“CORF”). This program uses legal means to protect radio astronomy frequencies from radio interference.CORF is composed of eminent scientists from the fields of radio astronomy, space research, remote sensing, meteorology, and wildlife tracking who use radio frequencies in conducting their research. CORF’s primary objective is to limit the level of harmful man-made interference in the bands used by these scientists as much as possible.
Pollution of Geophysical Sites
Authors: Kovalevsky J. 
Published: July 2016

ABSTRACTAstronomy in all wavelengths is not the only science to suffer from various causes of pollution. Sites in which geophysical research is being conducted are also in danger due to a variety of external causes. Among them, the following are described and discussed in addition to electromagnetic nuisances that are common to geophysicists and astronomers: heat production, magnetic disturbances, artificial vibrations in seismic observatories, chemical pollution in atmospheric studies, signal jamming, vandalism and site modifications around automatic stations.
Luminous Blue Variables need not be blue
Authors: de Jager Cornells , van Genderen Arnout M. 
Published: July 2016

AbstractA number of yellow and red super- and hypergiants show phenomena that are similar to those shown by Luminous Blue Variables. The LBV phenomenon may not be restricted to the blue part of the Hertzsprung-Russell diagram and the conventional name ‘S Dor variables’ seems more appropriate.
Atmospheric dynamics of luminous stars
Authors: de Jager Cornells , Carpay Joost , de Koter Alex , Nieuwenhuijzen Hans , Schellekens Erik 
Published: July 2016

AbstractA review is given of data and theories on the motion fields in super and hypergiants with special reference to LBV’s. We show that the radiative momentum flux is incapable of driving the episodical bursts of mass loss of these stars, and that there are several indications that the LBV-phenomenon is hydrodynamically driven. The sum of turbulent and radiative accelerations in the atmospheres of the most luminous stars compensates the gravitational acceleration for stars near the Humphreys-Davidson limit. This explains their atmospheric near-instability. The motion field in the atmosphere of a typical LBV consists mainly of low-order gravity waves, while acoustic waves are rapidly damped. These gravitation waves may be stochastic rather than coherently ordered. These stochastic pulsations are assumed to be responsible for the LBV phenomenon.
P Cygni: The star that started it all
Authors: Groot Mart de 
Published: July 2016

P Cygni was discovered in 1600 AD during an outburst when it reached 3rd magnitude. After another outburst in 1655 the star is now showing irregular photometric variations with an amplitude inVof ~ 0.2 magnitude. Because of these variations and of its peculiar spectral characteristics, P Cygni has been classified as anything between supernova and W UMa system. However, its light curve is unlike that of any other star and P Cygni could well be considered the first discovered LBV.Over the last three years an accurate photoelectric light curve has been put together.It is based on observations made by a number of amateur and professional observers around the world and shows the following features:+ Variations are irregular with maxima and minima every 1 - 2 months;+ The brightness variations seem to show more scatter when the star is faint.
Dynamics of Groups around Interacting Double Ellipticals: Measuring Dark Matter Haloes
Authors: Quintana H. 
Published: July 2016

Binary galaxies, as binary stars, are important to measure masses, as suggested by Page (1952). Because three orbit parameters are measurable for galaxies at one instant of time, severe uncertainties remain in the orbit and mass determinations. These uncertainties can partly be overcome by statistical studies of selected samples and/or n-body simulations. Close double galaxies (and isolated galaxies) could also be useful to estimate dynamical masses if we can find test particles around them.Interacting elliptical pairs or dumb-bell galaxies are found with a large range, between 0-1200 km s-1, of relative radial velocities. Standard 2-body orbit calculations, highly uncertain due to projection factors, suggest for the largest velocity differences very large galaxy masses, if the systems are bound and stationary. However, recent n-body simulations model these binaries as galaxies captured from hyperbolic orbits, requiring masses of order a few times 1011M⊙) (Borne et al. 1988), but producing systems that are short lived.
Geometrical Parameters of E+S Pairs
Authors: Rampazzo Roberto , Sulentic Jack W. 
Published: July 2016

• Clues Concerning Galaxy Formation. Local environmental conditions (i.e. density and angular momentum properties of protogalactic clouds) are thought to be factors affecting the ultimate morphology of a galaxy. The existence of significant numbers of mixed morphology (E/SO + S) pairs of galaxies would represent a direct challenge to this idea unless all early-type components are formed by mergers. We wish to isolate candidate E+S pairs for detailed study with several questions in mind:a) Are most of the pairs true E+S systems OR, as the theory would suggest more morphologically concordant pairs involving primarily late-type or disky galaxies alone (i.e. misclassified lenticulars)?b) Assuming that many of the pairs are E+S, do their properties differ in any way from E and S galaxies in the field?c) Is their evidence that E galaxies in mixed pairs are preferentially merger products?
Tidal distortions in pairs of early-type galaxies
Authors: Prugniel Ph. , Davoust E. 
Published: July 2016

We are conducting an imaging survey of pairs of elliptical galaxies which has already produced interesting results. Some pairs present a common pattern of distortion interpreted in terms of tidal effects (Davoust and Prugniel, 1988; Prugniel et al., 1989). Other examples drawn from the literature (Borne and Hoessel, 1988; Colina and Pérez-Fournon, 1990) share the same morphology. This Poster presents new cases and lists the characteristics of 24 such systems.Our pairs are drawn from a sample of binary and multiple galaxies which has in turn been extracted from the CGCG, UGC (Nilson, 1973) and VV (Vorontsov-Velyaminov, 1959) catalogues. This sample includes that of Karachentsev (1972). It contains 1800 pairs, among which 700 are S – S or mixed morphology pairs. We are working on the remainder to produce a sample of close physical pairs of elliptical galaxies (we also include bulge dominated S0’s since the morphological discrimination from ellipticals is often ambiguous, in particular for interacting galaxies).
A Spiral-Like Disk of Ionized Gas in IC 1459: Signature of a Merging Collision?
Authors: Goudfrooij Paul , Nørgaard-Nielsen H.U. , Jørgensen H.E. , Hansen L. , de Jong T. 
Published: July 2016

AbstractWe report the discovery of a large (15 kpc diameter) Hα+[NII] emission-line disk in the elliptical galaxy IC 1459, showing weak spiral structure. The line flux peaks strongly at the nucleus and is more concentrated than the stellar continuum. The major axis of the disk of ionized gas coincides with that of the stellar body of the galaxy. The mass of the ionized gas is estimated to be ~ 1 105 M⊙, less than 1% of the total mass of gas present in IC 1459. The total gas mass of 4 107 M⊙ has been estimated from the dust mass derived from a broad-band colour index image and the IRAS data. We speculate that the presence of dust and gas in IC 1459 is a signature of a merger event.
Alignment of cD-Galaxies with their Surroundings
Authors: van Kampen Eelco , Rhee George 
Published: July 2016

AbstractFor a sample of 122 rich Abell clusters we find a strong correlation of the position angle (orientation) of the first-ranked galaxy and its parent cluster. This alignment effect is strongest for cD-galaxies. Formation scenarios for cD galaxies, like the merging scenario, must produce such a strong alignment effect. We show some N-body simulations done for this purpose.
Cool Infalling Gas and its Interaction with the Hot Ism of Elliptical Galaxies
Authors: Sparks W.B. , Macchetto F.D. 
Published: July 2016

AbstractWe describe work leading to the suggestion that interaction between infalling cool gas and ambient hot, coronal plasma in elliptical galaxies is responsible for emission filaments, and might remove the need for large mass depositions in cooling flows. A test of the hypothesis is undertaken — the run of surface brightness with radius for the emission lines — and the prediction agrees well with the data.
Energy and Angular Momentum Transfer in Binary Galaxies
Authors: Namboodiri P.M.S. , Kochhar R.K. 
Published: July 2016

AbstractWe have numerically studied tidal effects of a massive perturber on a satellite galaxy. The model consists of a spherical satellite galaxy and a point mass perturber and the encounter is non-penetrating. A wide range of density ratios and eccentricities of the relative orbits have been considered. The disruption of the satellite galaxy has been observed when the numerical value of the fractional change in the energy is greater than two. The changes in the energy and angular momentum show smooth variation in the case of unbound orbits and irregular variation in the bound orbit cases. It is shown that for a constant pericentric distance, increasing the density ratio decreases the tidal effects; and for a given density ratio an increase in the eccentricity decreases the tidal effects.
Simulation of Disk-Disk Encounters with Co-Moving Polar Grids
Authors: Salo Heikki 
Published: July 2016

AbstractTwo-grid simulation method combining advantages of both polar and cartesian mesh-codes is described. In addition to stellar component reacting solely to gravitational forces, gas component is included with dissipatively colliding particles. This allows fairly realistic simulation of planar encounters where both systems contain star+gas disks.
Observations and Models of Star Formation in the Tidal Features of Interacting Galaxies
Authors: Wallin John F. , Schombert James M. , Struck-Marcell Curtis 
Published: July 2016

AbstractMulti-color surface photometry (BVri) is presented for the tidal features in a sample of interacting galaxies. Large color variations are found between the morphological components and within the individual components. The blue colors in the primary and the tidal features are most dramatic in B-V, and not in V- i indicating that star formation instead of metallicity or age dominates the colors. Color variations between components is larger in systems shortly after interaction begins and diminishes to a very low level in systems which are merged. Photometric models for interacting systems are presented which suggest that a weak burst of star formation in the tidal features could cause the observed color distributions. Dynamical models indicate that compression occurs during the development of tidal features causing an increase in the local density by a factor of between 1.5 and 5. Assuming this density increase can be related to the star formation rate by a Schmidt law, the density increases observed in the dynamical models may be responsible for the variations in color seen in some of the interacting systems. Limitations of the dynamical models are also discussed.
Tomographic Separation of Composite Spectra of O-Type Stars
Authors: Bagnuolo W.G. , Gies D.R. 
Published: July 2016

AbstractWe have analyzed UV photospheric lines of three O-type binaries (AO Cas, Plaskett’s Star, and 29 UW CMa) by means of tomographic and cross-correlation analyses, with the goal of estimating the physical properties of the individual stars. The tomographic techniques allowed us to estimate Teff and log g the luminosity ratio, and rotational velocities. The mass ratios were obtained from a cross-correlation technique, applied to spectral regions in which preliminary tomography shows the secondary has strong photospheric line features.
Extracting Velocities for Faint Secondaries
Authors: Cohen D. , Latham D.W. 
Published: July 2016

AbstractWhen velocities can be determined for both members of a double-lined spectroscopic binary, then the mass ratio can be calculated immediately. With the goal of measuring velocities for faint secondaries in single-lined spectroscopic binaries, we have experimented with a technique of first subtracting the spectrum of the primary using synthetic spectra calculated from Kurucz model stellar atmospheres and then correlating to get the velocity of the secondary. For half a dozen of the single-lined spectroscopic binaries in the Carney-Latham survey of proper-motion stars we have been able to extract velocities for the secondaries and to solve for double-lined orbits.
Colliding Stellar Winds in O-type Close Binary Systems
Authors: Gies D.R. , Wiggs M.S. 
Published: July 2016

In close binary systems of O-type stars, the individual stellar winds will collide between the stars to form shock fronts (Stevens et al. 1992). Binaries with equally luminous stars will have winds of comparable strength, and the shock will occur near the mid-plane between the stars, but in binaries of unequal luminosity, the interaction will occur along a bow shock wrapped around the star with the weaker wind. The presence of the shock region can be detected through excess X-ray emission (Chlebowski & Garmany 1990), and orbital phase-related variations in the UV P Cygni lines (Shore & Brown 1988) and optical emission lines (formed in high density regions of circumstellar gas).We have begun a search for colliding winds through a study of the optical emission lines and UV P Cygni lines in four massive binaries, AO Cas (Gies & Wiggs 1991), Plaskett’s star = HD 47129 (Wiggs & Gies 1992), 29 UW CMa and ι Ori. The optical observations consist of high S/N spectra of the Hα and He I λ6678 region obtained with the University of Texas McDonald Observatory 2.1-m telescope and coudé Reticon system. The UV observations were culled from archival IUE high dispersion spectra of several P Cygni features (N V λ1240, Si IV λ1400, C IV λ1550).
Infrared Spectroscopy of Multiple Star Systems
Authors: Hinkle Kenneth H. , Ridgway Stephen T. , Fekel Francis C. 
Published: July 2016

AbstractUp to this time infrared spectroscopy has been only occasionally used in binary star research due to both the insensitivity of infrared spectrographs and the difficulty of getting observing time on a limited number of spectrographs. However, infrared spectroscopy has a number of interesting applications in binary star research. We present an example of an application to the long-period symbiotic system CH Cyg. Due to the recent development of infrared arrays, infrared spectroscopy (1) is becoming available at a much larger number of telescopes and (2) in the 1.0-2.5 μm region is capable of going to limiting magnitudes nearly as faint as those reached by CCD’s.
Detection of Spectroscopic Triples
Authors: Mazeh Tsevi , Krymolowski Yuval , Latham David W. 
Published: July 2016

Several binary stars detected by the Center for Astrophysics (CfA) radial-velocity surveys were found to be members of triple systems. We present two examples, each requires a different analysis to discover its multiplicity.One example is G176-46, a double-lined halo star of the Carney & Latham (1987) high proper-motion survey. The secondary star (G176-46b) displays large radial velocity variations, in contrast with the primary (G176-46a), which is constant within the error limits. Figure 1 shows two cross correlations of the stellar spectra against the same calculated template taken at different times, which indicate that only the secondary’s peak changes its position. A similar variation was observed previously for ADS 8811 (Mazeh & Latham 1988).We have found the secondary radial velocity to vary with a period of 10.44 days, and therefore conclude that Gl76-46b is a member of a short-period binary system. The orbital solution has an amplitude of 38 km s−1 and eccentricity of 0.05.
Observational Programme for Classical and CCD Photometry of Visual Double and Multiple Systems
Authors: Oblak E. , Lampens P. 
Published: July 2016

Complementary accurate photometric data with astrophysical content are needed for a well-chosen sample of binaries and multiple systems for which good-quality astrometric data already exist or will soon be available. The observational programme, started in the context of the European Network of Laboratories “Visual Double Stars” (Oblak et al. 1992), is therefore based on samples extracted from the “Catalogue des Composantes d’Etoiles Doubles et Multiples” (CCDM, Dommanget, 1989) and reported in Annex 1 (Double and Multiple Systems) of the HIPPARCOS Input Catalogue (C. Turon et al. 1992).Systems with components in the HIPPARCOS Input Catalogue are selected for which the present photometric information is poor, i.e. not all components have been observed or they have colour indices and/or magnitudes of insufficient quality for extraction of astrophysical quantities (Figure 1).Observations, performed in various observatories located in both hemispheres, must yield both classical and CCD photometric campaigns.
UBV CCD Photometry of “Close” Visual Double Stars
Authors: Van Dessel E. , Sinachopoulos D. , Prado P. 
Published: July 2016

AbstractWe use the CCD cameras of the 61-cm UTSO and the 90-cm Dutch telescopes of the Las Campanas and European Southern Observatories respectively in order to perform UBV photometry of visual double stars.Our sample contains southern visual binaries with A–type (470 pairs) and G–type primaries (170 pairs), which have angular separations mainly between 1″.5 and 5″. The double stars of our sample have been selected from the WDS according to their astrophysical interest and the technological limits of contemporary CCDs.
Stellar Masses from Double Star Observations with the Mark III Interferometer
Authors: Armstrong J.T. 
Published: July 2016

AbstractBy improving on the angular resolution possible with conventional telescopes, speckle interferometry has been adding to the list of known masses, resolving binaries with separations of 30 mas. Interferometry with separate apertures offers the possibility of going to much higher resolution.The Mark III Optical Interferometer on Mt. Wilson has been used for astrometry, for stellar diameter measurements, and for binary observations since routine operations began in late 1988. The fringe visibilty calibration uncertainty is ~1% for m < 4m at λ800 nm with good seeing, so that both binary components can be detected when the magnitude difference is 3.5m to 4m.From Mark III data, masses of eight stars have been determined. The most precise determination is for the components of the ϕ Cygni system: 2.545 ± 0.085 and 2.445 ± 0.081 M⊙. To improve on this measurement, more precise spectroscopic data are needed, as is the case for most of the systems for which we have orbits or preliminary orbits.The NRL/USNO Optical Interferometer Project is currently designing two more capable instruments: a four–element system for astrometric observations, and a six–element system for imaging. The ultimate 430-m maximum baseline and 35-cm apertures of the imaging interferometer will allow observations to 8th to 10th mag and resolution of binary components separated by as little as ≈ 200 µas.
Simultaneous Spectroscopic and Interferometric Measurements of Binaries with the GI2T
Authors: Mourard D. , Bonneau D. , Blazit A. , Labeyrie A. , Morand F. , Percheron I. , Tallon–Bosc I. , Vakili F. 
Published: July 2016

The “Grand Interféromètre à deux Télescopes” (GI2T) is presently the largest operational interferometer operating at visible wavelengths (Labeyrie et al. 1986, Mourard et al. 1991). With two telescopes of 1.5-m aperture and baselines reaching 65 m in the North–South direction, it gives stellar spectra containing interference fringes, which provide high angular resolution measurements in the range of one milliarcsecond.The GI2T optical combination follows the Michelson principle of output pupil remapping to preserve a constant fringe spacing on the detector for stable and economical spatial sampling. The stellar light is dispersed in order to study the fringes parameters simultaneously with the spectral information. The direction of dispersion is perpendicular to that of the recombined pupils. Due to atmospheric turbulence the instantaneous images contain about 100 speckles. To freeze the atmospheric turbulence a temporal resolution of at least 10 milliseconds is needed.
Interferometric Imaging of Nearby Low–Mass Spectroscopic Binaries. I. KPNO Observations
Authors: Duquennoy A. , Christou J. , Mariotti J.-M. , Mayor M. , Morbey C. , Perrier C. , Probst R. , Tessier E. , Ridgway S. 
Published: July 2016

AbstractWe present a preliminary report on radial–velocity and infrared interferometric observations, with emphasis on the newly resolved nearby sources Gl 609.2 and Gl 804. We briefly discuss their low–mass companions, their luminosities, and their individual masses inferred from the combined solution of their spectroscopic and visual orbits.
A Four Star Photometer
Authors: Valtier J.C. , Contel J.M. Le , Antonelli P. , Michel P. , Sareyan J.P. 
Published: July 2016

AbstractA new photometer is presently being developed at the O.C.A. Observatory. It consists of four arms and a CCD camera situated in the focal plane of the telescope. Each arm can move in both directions and support a diaphragm and a liquid optic guide that directs the light to a photomultiplier. The simultaneous acquisition of the four signals enables to obtain magnitude differences between the objects in real time. A typical use of this photometer is to observe at the same time one or two variables, comparison stars and the sky background.