bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Timescales of Variations in Continuum and Hydrogen Lines During Stellar Flares
Authors: Pettersen B.R. 
Published: July 2016

AbstractLight curves of major stellar flares have been used to study the behavior of U-B, B-V, and V-R. The majority of the flux transmitted through these filters is continuum radiation, but U and B are affected by emission lines. The variability of Ha and H$ emission lines were monitored through narrow band filters. The timescales of emission line variability are considerably longer than those for the continuum, and the emission line flare peak occurs a few minutes after the continuum flare maximum. No variability in lines at a timescale of seconds is detected in our data.
Flares on the Sun: Selected Results from HINOTORI
Authors: Tanaka Katsuo 
Published: July 2016

ABSTRACTThe X-ray observations of solar flares by Japanese astronomy satellite Hinotori (ASTRO-A) are reviewed. Detailed results from the X-ray telescope and the soft X-ray spectrometers are given. The hard X-ray images in the 17-40 keV range show a wide variety of source structures. Examples of compact single source, stationary coronal source, and double sources are presented. High resolution spectra in the range 1.7-2.0A indicate strong turbulence and blue-shifted components in the beginning of flares. From the FeXXV and FeXXVI spectra two kinds of thermal plasma are shown to appear. The cooler component of Te=15-20xl06K, which increases in the impulsive phase of the hard X-ray burst, is suggested to be produced by the dissipation of the electron beams. The hotter component of Te=30-50xl06K and Ne=1011-1012 increases towards the flare maximum. This component is also responsible for emitting 17-40keV continuum, and emitted from a very compact source. The results are discussed in comparison with flare loop models. It is shown that evolutionary changes in the loop density realize various source structures in the hard X-ray under the unitary electron beam hypothesis.
Doppler Imaging of Starspots
Authors: Vogt Steven S. , Penrod G. Donald 
Published: July 2016

ABSTRACTWe discuss a newly-developed technique for spatially resolving starspots on some of the more rapidly rotating RS CVn stars. Basically, the method uses high resolution, very high signal-to-noise spectral line profiles and exploits the Doppler velocity correspondence between position across the stellar disk and wavelength position across a rotationally broadened line profile to synthesize an image of the star, showing the location, sizes, and shapes of its starspots. Though still in a developmental stage, the technique is already yielding information about the structure and general appearance of starspots. Examples of Doppler Imaging observations of HR 1099 will be presented, along with a movie showing the behavior of synthetic line profiles generated from a computer spot model.
Contact Binary Stars
Authors: Dupree A.K. 
Published: July 2016

Abstract:Ultraviolet and X-ray surveys of the W Ursae Majoris type stars are reviewed. These systems exhibit extended coronas and transition regions that are confined close to the optically determined surfaces. Correlations of X-ray activity with period or rotational velocity indicate a turn-over or saturation of emission at the short periods or high velocities found in the W UMa-type systems. For a number of systems, ultraviolet emission appears to be anti-correlated with the strength of X-ray emission. These observations are discussed in terms of solar structures, activity, and evolution.
Photospheric Sources of Magnetic Field Aligned Currents
Authors: Nordlund Ake 
Published: July 2016

Possible (small-scale) photospheric sources of coronal magnetic field aligned currents are discussed. Such currents are equivalent to local (small-scale) twists of the coronal magnetic field, and may cause field topologies that are (MHD or resistively) unstable, and thus contribute to the (small-scale) coronal activity.One electro-motive force associated with photospheric magnetic fields is due to the asymmetry between ions and electrons as agents of conductivity and as agents of momentum transfer to the (dominant) neutral gas component. In the solar photosphere, where only some of the easily ionized heavier elements (Mg, Si, Fe, ...) are significantly ionized, the ratio of number density of electrons and ions to neutrals is very small, of the order of the total abundance of these elements, which is of the order 10-4, by number. Due to the larger electron than ion mobility, electric currents are mainly carried by the electron component of the plasma whereas, because of the ions greater momentum transfer to the neutrals in collisions, the friction between the charged and the neutral components of the plasma is mainly due to the ions. Thus, the Lorenz force i x B acts mainly on the electron component of the plasma, whereas the balancing gas pressure gradient and gravity terms act mainly on the neutral component.
Asymmetric Periodic Orbits in the Three-Body Problem and Their Stability
Authors: Tsouroplis A. , Zagouras C.G. 
Published: July 2016

AbstractAn algorithm for the numerical determination of asymmetric periodic solutions of the planar general three body problem is described. The elements of the “variational” matrix which are used in this algorithm are computed by numerical integration of the corresponding “variational” equations. These elements are also used in the study of the linear isoenergetic stability. A number of asymmetric periodic orbits are presented and their stability parameters are given.
New Results for the Linear Stability of the Triangular Points in the Elliptic Restricted Problem
Authors: Meire R. 
Published: July 2016

AbstractNew results are obtained for the linear stability of the triangular points in the elliptic restricted problem using the Hill equations which describe the infinitesimal motion around L4,L5. Also the shape of the 4Π-periodic solutions along the transition curves in the μ-e plane is investigated .
The Planar Inverse Problem for Autonomous Systems
Authors: Xanthopoulos Basilis C. , Bozis George 
Published: July 2016

AbstractWe study the general version of the inverse problem for planar trajectories and for autonomous dynamical systems possessing three integrals, i.e., for a given three-parametric family of curves f(x,y,a,b)=c we find the potential V(x,y) for which these curves are orbits of a unit mass. All possible cases, depending on the preassigned function f, are classified and in each case the necessary and sufficient conditions for the.existence of a solution are established. Among the examples is the case of the Keplerian conic sections which is studied in detail.
Trapping Time of Resonant Orbits in Presence of Poynting - Robertson Drag
Authors: Gonczi R. , Froeschlé Ch. , Froeschlé C. 
Published: July 2016

AbstractWe study numerically the competition between the Poynting-Robertson drag and the gravitational interaction of grains with Jupiter near orbital resonances. The computations are based on the plane elliptic restricted three body problem. Numerical investigations show that the grains always cross the resonance region without any oscillation, except in the special case where the grains were initially inside the resonance. Such grains are temporarily trapped, then due to the drag they are ejected out of the resonance. The trapping time of a particle turns out to be much more important in the 3/2 and 2/1 commensurabilities than in the others.A numerical exploration of numerous orbits for different initial conditions and different sizes of grains has been performed. The trapping time appears to be closely connected to the size of the librator-type orbits regions; it increases with the initial eccentricity of the orbit, and is also proportional to the radius and the density of the particle.
IUE observations of CI Cygni during 1979–1981
Authors: Baratta G.B. , Altamore A. , Cassatella A. , Friedjung M. , Ponz D. , Ricciardi O. 
Published: July 2016

High and low resolution IUE spectra of CI Cyg were obtained at VTLSPA during 1979-81 allowing for an analysis of the spectral variations related to the decreasing activity of the star, and to the eclipse (June 1980).In the high resolution spectra the emission lines have a width slightly larger than the instrumental one. This fact is particularly evident in the HeII 1640 A line and could be related to the peculiar behaviour of this line at low resolution as reported by Michalitsianos et al. (this volume). A systematic radial velocity difference between permitted and intercombination lines was found; this difference should be connected with the structure of the emitting region(s). “Secular” and eclipse varia tion was found in particular in the intercombination line intensities (Viotti et al. 1980). An electron density of ∼ 0.3–1.5×1010 cm–3 was evaluated from the intensity ratios of the NIII] emission lines. No significant difference in these ratios and in the CIII]/NIII] ratio as well was found,during 1979, 1980 (eclipse) and 1981 suggesting no large Ne variation with both the activity phase and eclipse of the star. This result should imply a low density gradient in the partially eclipsed NIII] and CIII] regions. A more detailed analysis of the high resolution data is in course to better clearfy these points, and their implications on the possible models for CI Cyg.
Variability of HBV 475 in the near infrared
Authors: Andrillat Y. 
Published: July 2016

In the spectral range λλ5800-8750, HBV 475 shows important spectral variations between 1969 and 1974. Sometimes the “hot component” spectrum dominates (many emission lines), sometimes the “cool component” is preponderent (many molecular absorption Ti0 bands) (Andrillat 1973 – Andrillat, Houziaux 1976).On August 4 1974, June 6 1975 and August 9 1981, we have extended the observations up to l.lμ (fig.l) (Haute Provence Observatory 193 Telescope – Spectro ROUCAS + Image tube – dispersion 230 A.mm-1).
Determination of the term Symbiotic Star
Authors: Boyarchuk A. A. 
Published: July 2016

Symbiotic stars have been studied for many years. But the common determination of the term “symbiotic star” does not exist even now. Merrill (1958) introduced this term in order to emphasize unusual spectral features – absorption TiO bands and emission lines belonging to highly ionized ions.If we look on the eruptive stars spectra we well see absorption and emission features in the spectra of many stars which we cannot certainly consider as symbiotic stars. For example the U Gem type stars have absorption and emission features in their spectra. A similar situation exists in the case of the old novae. The T Tau type stars have many emission lines, and their spectral type corresponds to G-K. Even the long period variables have some emission lines though their spectral type is M. On the other hand, there are also the BQ[]type stars which are characterized by the presence in their optical spectrum of forbidden emission lines and of a rather hot absorption spectrum.
IUE Observations of the Gaseous Component of the Local Interstellar Medium
Authors: Gilra Daya P. 
Published: July 2016

AbstractDiscovery of interstellar Ge, Ga, and Kr is reported. Several intercombination lines of Fe II are detected. The depletion is most pronounced in Ca, Ti, and V. The highly ionized gas C IV and Si IV is not coextensive with the Si II and C II gas nor with the 0 VI gas. The molecular gas (CO) shows very small velocity dispersion (b~l km/sec).
The Soft X-Ray Diffuse Background: Implications for the Nature of the Local Interstellar Medium
Authors: McCammon Dan 
Published: July 2016

AbstractObservations of the diffuse X-ray background in the B and C bands (130-188 eV and 160-284 eV, respectively) provide convincing evidence for the existence of high-temperature interstellar gas. Since the opacity of normal interstellar material is very high, we must assume that the soft X-ray flux observed in the galactic plane originates within a few hundred parsecs of the Sun. The intensity and B/C ratio of this low-latitude flux can be provided by emission from an equilibrium plasma with normal abundances, T = 106.0 K, and 0.0019 cm-6 pc emission measure. More sophisticated nonequilibrium models of material heated by a supernova blast wave would reduce the required emission measure somewhat, but not by so much as a factor of two. Arbitrarily limiting the pressure to 104 cm-3 K gives a maximum density of 0.005 cm-3 and a minimum radius for the emitting region of 75 pc. This fits in well with UV interstellar absorption measurements which indicate that the ISM is very deficient in neutral hydrogen out to ~100 pc from the Sun.The constancy of the observed B/C ratio implies that there are less than 5x1019 cm-2 variations in any cooler material lying between us and the bulk of the emission. This is consistent with the much smaller column densities of neutral or partially ionized material detected in the solar neighborhood through UV absorption measurements, but the organization of the cooler gas and its interaction with the coronal material require further investigation.X-ray intensities at high latitudes are larger than those in the plane by as much as a factor of three. The fluctuations show a global anti-correlation with H I column density which suggests that they might be caused by variations in the transmission of X-rays from an extragalactic source, such as a galactic halo or corona. Such models are very difficult to reconcile quantitatively with existing H I measurements, however, and it seems more likely that the bulk of the high-latitude excess is produced by an extension of the unabsorbed interstellar emission in those directions with the remaining fluctuations produced by a combination of absorption and displacement by embedded cooler material, or possibly by transmission of flux from a hot halo.While it would be most interesting to resolve this point because of its impact on the nature of the galactic halo and the high-latitude H I distribution, it does not greatly affect the amount of hot gas which apparently exists in the solar neighborhood: an isotropic emitting region with only the emission measure required by the average intensity near the galactic plane would account for about two-thirds of the integrated B and C band flux observed at the Earth. The total energy flux is ~1x10-6 ergs cm-2 s-1 if we assume a thermal equilibrium spectrum.
The Nature of the Soft X-Ray Emitting Region in the Direction of the North Polar Spur
Authors: Morrison James P. , Sanders Wilton T. 
Published: July 2016

The spatial structure of the X-ray sky in the direction of the North Polar Spur was examined in two energy bands, the B band (0.10 - 0.18 keV) and the C band (0.15 - 0.28 keV). A model with two emitting regions, one local with unabsorbed emission, and the other more distant with emission partially absorbed by spatially varying amounts was investigated.Using the distribution of atomic hydrogen as a measure of absorbing material, this model was used to predict the flux in the direction of the North Polar Spur. The predicted flux was compared to the data obtained from several sounding rocket flights. The derived flux was found to correlate well with the observed data.
The z-dependence of the Spin Temperature of HI
Authors: Kulkarni Shrinivas R. , Heiles Carl , Van Gorkom J. , Dickey John M. 
Published: July 2016

In 1981 we conducted an extensive, low-latitutde, HI 21-cm absorption survey from the VLA. The goal of the survey was to answer the following questions:(a) What is the vertical distribution of the cold HI clouds?(b) Do HI clouds get systematically warmer at high |z|?(c) Does the fraction of warm intercloud medium HI increase with high |z|?(d) How much HI has been missed in previous HI emission surveys because of optical depth effects?(e) What is the galactic distribution of cool HI clouds?
Future Studies of the Local Interstellar Medium With Space Telescope and Columbus
Authors: Savage Blair D. 
Published: July 2016

AbstractThe spectrographs aboard Space Telescope and Columbus will provide important new information about the interstellar medium in the immediate vicinity of the sun. The Space Telescope high resolution spectrograph (HRS) will produce resolutions, λ/Δλ, of about 18,000 and 70,000 with high sensitivity between 1200 and 3200 A and greatly reduced sensitivity between 1060 and 1200 A. The highest resolution is adequate to define the multicomponent nature of interstellar absorption lines and to measure thermal line widths exceeding 3 km s-1 . The Columbus mission is in the planning stages. However, it is likely that the spacecraft will contain spectrographs capable of resolutions of 3 x 104 between 912 and 1200 A and 500 between 100 and 900 A. In the longer wavelength region, the very important lines of 0 VI, S VI, H2, H I , and D I are available for study. In the short wavelength region, lines of He I and II, are observable. If the 3x104 resolution spectrograph can provide extended wavelength coverage to 770 A, lines of Ne VIII which are expected from 8x105 K gas are accessible. Astronomers using the ST HRS and Columbus spectrographs will be able to study a wide range of problems relating to cold, warm, and hot gas in the local ISM. Some of the most important observing projects are described.
Observations of Local ISM Emission With the Berkeley EUV/FUV Shuttle Telescope
Authors: Martin Christopher , Bowyer Stuart 
Published: July 2016

AbstractThe Berkeley Extreme Ultraviolet/Far Ultraviolet Shuttle Telescope (BEST) will be launched on the Space Shuttle in November, 1984, as part of the NASA UVX project. The Berkeley spectrometer will make observations of the cosmic diffuse background in the 600-1900 Å band, with a spectral resolution of 10 Å. The sensitivity and spectral resolution of the instrument make it ideal for the study of components of the interstellar medium in the 104 - 106K range.
The LPL Radial Accelerometer
Authors: McMillan R.S. , Smith P.H. , Frecker J.E. , Merline W.J. , Perry M.L. 
Published: July 2016

AbstractWe have begun to observe radial velocities of stars with an optical spectrometer designed for unusually high accuracy. Light from a star image in the focal plane of a telescope is fed to the entrance aperture of the spectrometer by a single optical fiber. Wavelengths are calibrated by transmission of collimated light through a tilt-tunable Fabry-Perot interferometer. The scrambling of incident light rays by the optical fiber and the intrinsic stability of the Fabry-Perot etalon provide immunity to the sources of systematic errors that plague conventional radial velocity meters. The spectrum is dispersed by an echelle grating crossed with another plane reflection grating. Several echelle orders in the vicinity of 4250-4600 Å are imaged in a two-dimensional format on a charge-coupled (CCD) array of detectors. About 350 distinct points on the profile of the stellar spectrum are sampled by successive orders of interferometrie transmission through the etalon. In the vicinity of 4300 Å each interference order is 47 milliangstroms wide and the sample points are 0.64 Å apart, resulting in distinct , widely-spaced monochromatic images of the entrance aperture to be formed in the focal plane of the camera. Changes in Doppler shift cause changes in the relative intensities of these images, according to the slope of the spectral profile at each point sampled. The instrument is being operated as a null-measurement accelerometer, sensitive only to changes in radial velocity, which simplifies operation and enhances sensitivity. With an argon-filled, iron hollow cathode emission line lamp, the interferometer can be calibrated to two parts in 100 million; this corresponds to ± 6 meters/sec in Doppler shift. Calibrations of the interferometer show variations of ± 27 meters/sec on a time scale of months; observations of stars are corrected for such changes. The internal repeatability of observations of the differential Doppler shift of light from the integrated disk of the Sun is ± 6 meters/sec. The corresponding result from about 70 observations of Arcturus (Kl IIIb; B=1.19) is ± 40 meters/sec internal repeatability for each exposure of 20 square-meter seconds. The external repeatability (day-to-day differential accuracy) of nightly averages of stellar observations is ± 20 meters/second. Since the internal precision on the sun and the argon lamp is much better than it is with short exposures on Arcturus, the quality of our observations of stars is limited by the rate of detected photons. This justifies averaging a number of short exposures of a star to approach “laboratory” precision.
The Local Galactic Escape Velocity
Authors: Carney Bruce W. , Latham David W. , Peterson Ruth C. 
Published: July 2016

AbstractWe discuss the corrections to the perceived motions of stars due to the disk’s circular velocity, which we determine to be 220 km sec . This implies a Keplerian escape velocity of 310 km sec−1. We discuss upper limits to the rest-frame space velocities of stars from four sources: the summary of Saio and Yoshii (1979); the large new survey of proper motion stars of Carney and Latham (1985); a study of 27 faint proper motion stars near the South Galactic Pole by Carney and Peterson (1984a); and observations by Carney and Peterson (1984b) of stars with possibly extreme velocities identified by Eggen (1969). We find the maximum velocities are near 500 km secc−1, which is likely to be the local value of the escape velocity. This implies a large amount of gravitating matter outside the solar galactic orbit.
Vitesses Radiales Pour Le Programme Hipparcos
Authors: Duflot M. 
Published: July 2016

L’étude faite par Ch. Fehrenbach prouve que les Prismes-Objectifs à champ normal (PO) sont les instruments parfaitement adaptés a une étude statistique des mouvements stellaires dans la galaxie.Les PO souffraient jusqu’à ces dernières années, d’un dépouillement laborieux, inadapté à leur capacité. Les moyens informatisés actuels donnent la possibilité de les utiliser avec le rendement voulu.Au début de 1982, le groupe du satellite Hipparcos a fait une demande de mesures de vitesses radiales (VR) pour compléter les informations que donnera le satellite. Depuis cette date, nous nous sommes engagés dans la mesure des VR des étoiles brillantes (mg < 9,0) qui sont une partie essentielle du programme Hipparcos. En particulier, nous avons choisi des champs où se groupaient des étoiles des premiers types spectraux (≤ F5) dont la VR était inconnue. Les étoiles des types plus avancés (> F5) peuvent en effet être mesurées, avec plus de précision, avec la méthode de spectrocorrelation directe sur le ciel. Signalons que nous mesurons cependant, dans les champs choisis, les étoiles de tous les types spectraux
Metallic-Line Binaries
Authors: Abt Helmut A. 
Published: July 2016

AbstractA new radial-velocity study of 55 Am stars reveals 16 SB2s, 20 SBls, and 22 visual or occultation companions for a total of more than one companion per primary. Only about 75% of the primaries are in binaries with periods less than 100 days, even if we allow for unobservable small inclinations and low-mass secondaries. Therefore it may not be true that tidal interactions in close binaries is the only mechanism necessary to produce the low rotational velocities that allow diffusion to act, unless small reductions (factor of 1.4) in rotational velocities occur in binaries of longer periods. The binary frequency of the combined Am plus normal A stars is normal.