bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rotational Splitting of Solar Five-Minute Oscillations of Low Degree
Authors: Claverie A. , Isaak G. R. , McLeod C. P. , van der Raay H. B. , Roca Cortes T. 
Published: July 2016

AbstractAn analysis of 28 contiguous days of whole disk observations of the solar surface by means of optical resonant scattering in the K 769.9 nm line, taken at the Teide Observatory at Izana during July-August 1980, have thus far yielded two significant facts. Firstly when the results of an iterative sine-wave fitting procedure are considered in the period range 2-3 h, although the expected daily harmonics corresponding to 1/8, 1/10, 1/11, and 1/12 of a day are clearly seen the l/9th contribution is significantly absent. It is suggested that this results from an interference between a signal of 160 min (l/9th of a day) with the daily harmonic. It is further pointed out that the observatories at which the 160 min oscillation has been seen, Crimea, Pic du Midi, and Stanford are all separated by integral numbers of 160 min, and thus the phase of the 160 min oscillation relative to the daily observation window is constant. However, the Teide Observatory is situated at a half integral number of 160 min periods relative to the others. Thus when constructive interference exist at the first three sites destructive interference will exist at the latter. It is thus concluded that the non-existence of a peak corresponding to the l/9th harmonic of a day in the sine-wave fit data is strong indirect evidence for the existence of the 160 min signal.An analysis of those same data in the 5 min region has revealed the now well established pattern of discrete frequencies and with the increased resolution obtainable from 28 contiguous days of data, clearly showed the existence of splitting by rotational effects. In all 33 discrete lines were considered in the frequency range 2.4–3.85 mHz, which could be divided up into 3 groups, each of 11 lines, corresponding to the l = 0, l = 1, and l = 2 modes. This definitive classification was possible as the lines are split into (2l + 1) components yielding easily identifiable singlets, triplets and quintuplets. This first observation of the rotational splitting of solar oscillations gave the further information that the splitting of 0.75 ± 0.10 μHz indicated that the solar interior is rotating more rapidly than the observable surface (uniform rotation would yield a splitting of 0.4 μHz). A comparison of the widths of the individual peaks, with the intrinsic resolution of the data string ( ~ 1/T where T = length of the data string), showed that these were consistent with a high Q value oscillation, a fact which is further confirmed by the very existence of singlets triplets and quintuplets in the data.The exact value of the speed of internal rotation of the Sun can only be deduced from these data by a model dependent calculation. The simplest of these would suggest that if the core were almost equal to the solar diameter then it is rotating twice as fast as the surface, whereas if the core were only 15 % of the solar diameter, it would be rotating at 9 times the surface rate.
Variability in the Power Spectrum of Solar Five-Minute Oscillations
Authors: Hill Frank , Toomre Juri , November Laurence J. 
Published: July 2016

AbstractTwo-dimensional power spectra of solar five-minute oscillations display prominent ridge structures in (k, ω) space, where k is the horizontal wavenumber and ω is the temporal frequency. The positions of these ridges in k and ω can be used to probe temperature and velocity structures in the subphotosphere. We have been carrying out a continuing program of observations of five-minute oscillations with the diode array instrument on the vacuum tower telescope at Sacramento Peak Observatory (SPO). We have sought to establish whether power spectra taken on separate days show shifts in ridge locations; these may arise from different velocity and temperature patterns having been brought into our sampling region by solar rotation. Power spectra have been obtained for six days of observations of Doppler velocities using the Mg I λ5173 and Fe I λ5434 spectral lines. Each data set covers 8 to 11 hr in time and samples a region 256″ × 1024″ in spatial extent, with a spatial resolution of 2″ and temporal sampling of 65 s. We have detected shifts in ridge locations between certain data sets which are statistically significant. The character of these displacements when analyzed in terms of eastward and westward propagating waves implies that changes have occurred in both temperature and horizontal velocity fields underlying our observing window. We estimate the magnitude of the velocity changes to be on the order of 100 m s -1; we may be detecting the effects of large-scale convection akin to giant cells.
The Observations of 80-min Oscillations in the Quiescent Prominences
Authors: Bashkirtsev V.S. , Kobanov N.I. , Mashnich G.P. 
Published: July 2016

AbstractOscillations of the line-of-sight velocities with periods were detected in quiescent prominences, with coordinates φ = –75° W and φ = –18° W, respectively.
Quiescent Coronae of Active Chromosphere Stars
Authors: Golub Leon 
Published: July 2016

ABSTRACTThe EINSTEIN Observatory has for the first time provided high sensitivity X-ray measurements of quiescent coronal emission from a large sample of dwarf stars. We now have observed a sufficient number of the nearby M-dwarfs to determine an X-ray luminosity function and we have explored the activity and variability of these stars to the extent of observing, for the first time, X-ray flares with simultaneous groundbased optical and IUE ultraviolet coverage.The M dwarfs are found to have a much higher degree of variability in X-rays than does the Sun; however, in most cases a quiescent level is definable. We will discuss the quiescent emission from these stars and the changes in quiescent level on time scales from hours to ~ 1 year. We have determined coronal temperatures for many of these stars; they are generally hotter than the Solar corona and some of the more active dM stars have Tcor ~ 107 K.Arguments are presented in support of the hypothesis that M-dwarf coronae are magnetically dominated, as is the Solar corona. We then examine the usefulness of loop model atmosphere calculations in elucidating the coronal heating mechanism and the ways in which observations may be used to test competing theories. The X-ray measurements can be used to predict magnetic field strengths on these stars, with testable implications.
Periods of Unevolved Late-Type Close Binaries: Evidence of Magnetic Activity
Authors: Giuricin G. , Catalano S. , Mardirossian F. , Mezzetti M. 
Published: July 2016

ABSTRACTOur study of the period distribution of about 200 FGKM-type unevolved close binaries has revealed a strong deficit of short-period systems.This finding may be connected with the occurrence of a very efficient mechanism of orbital angular momentum loss via magnetic braking by stellar wind, in the earliest evolutionary phases.
Long Periods in the Three-Dimensional Motion of Trojan Asteroids
Authors: Bien R. , Schubart J. 
Published: July 2016

AbstractThe long periods caused by Jupiter, or Jupiter and Saturn in the motion of a Trojan are studied by numerical integration. Orbital inclinations between 0° and 50° are considered. Results on the length of the periods and on their main effects in the osculating elements are presented. It turns out that secular resonances can be important for the evolution of Trojan orbits.
The Mechanism of Branching of Three-Dimensional Periodic Orbits from the Plane
Authors: Robin I.A. , Markellos V.V. 
Published: July 2016

AbstractA linearised treatment is presented of vertical bifurcations of symmetric periodic orbits(bifurcations of plane with three-dimensional orbits) in the circular restricted problem. Recent work on bifurcations from vertical-critical orbits (av = ±1) is extended to deal with the v more general situation of bifurcations from vertical self-resonant orbits (av = cos(2Πn/m) for integer m,n) and it is shown that in this more general case bifurcating families of three-dimensional orbits always occur in pairs, the orbital symmetry properties being governed by the evenness or oddness of the integer m. The applicability of the theory to the elliptic restricted problem is discussed.
Resonant Three-Dimensional Periodic Solutions About the Triangular Equilibrium Points in the Restricted Problem
Authors: Zagouras C.G. , Markellos V.V. 
Published: July 2016

AbstractIn the three-dimensional restricted three-body problem, the existence of resonant periodic solutions about L4 is shown and expansions for them are constructed for special values of the mass parameter, by means of a perturbation method. These solutions form a second family of periodic orbits bifurcating from the triangular equilibrium point. This bifurcation is the evolution, as μ varies continuously, of a regular vertical bifurcation point on the corresponding family of planar periodic solutions emanating from L4.
Characteristics of Periodic Orbits in Elliptical Galaxies
Authors: Caranicolas N. 
Published: July 2016

AbstractThe properties of the characteristic curves of several families of periodic orbits, in a conservative dynamical system of two degrees of freedom, symmetric with respect to both axes, are reviewed. The two main types of families are presented. One sees that the pattern of the characteristics in the exact resonance case is similar to that of the near resonance case except for the basic characteristic . The form of the characteristics can be found theoretically by means of the second integral.
Infrared studies of symbiotic stars
Authors: Allen David A. 
Published: July 2016

AbstractInfrared photometry and spectroscopy of symbiotic stars is reviewed. It is shown that at wavelengths beyond lym these systems are generally dominated by the cool star’s photosphere and, indeed, are indistinguishable from ordinary late-type giants. About 25% of symbiotic stars exhibit additional emission due to circumstellar dust. Most of the dusty systems probably involve Mira variables, the dust forming in the atmospheres of the Miras. In a few cases the dust is much cooler and the cool component hotter; the dust must then form in distant gas shielded from the hot component, perhaps by an acccretion disk.Spectroscopy at 2μm can be used to spectral type the cool components, even in the presence of some dust emission. Distances may thereby be estimated, though with some uncertainty.Spectroscopy at longer wavelengths reveals information about the dust itself. In most cases this dust appears to include silicate grains, which form in the oxygen-rich envelope of an M star. In the case of HD 330036, however, different emission features are found which suggest a carbon-rich environment.
X-ray detection of the symbiotic star AG Draconis
Authors: Anderson Christopher M. , Cassinelli Joseph P. , Oliversen Nancy A. , Myers Roy V. , Sanders W.T. 
Published: July 2016

AbstractThe symbiotic star AG Draconis was observed by the HEAO-2 Imaging Proportional Counter (IPC) and found to be an unusually intense source of very soft X-rays.
Spectroscopic observations of AG Dra
Authors: Chang-Chun Huang 
Published: July 2016

AG Dra is an interesting symbiotic star, on account of its very high negative velocity and its earlier spectral type among the symbiotic stars. This star has been classified as dG7 (Wilson,1943), K1 II (Roman,1953) and K3 III (Boyarchuk,1966). It has a variable radial velocity.During summer 1981, spectroscopic observations of AG Dra were performed at the Haute-Provence Observatory using the Marly spectrograph with a dispersion of 80 A mm-1 at the 120 cm telescope and using the Coudé spectrograph of the 193 cm telescope with a dispersion of 40 A mm-1. Professor Ch. Fehrenbach very kindly given me a plate of the star which he had taken in July,1966, using the coudé spectrograph of the 193 cm telescope with a dispersion of 40 A mm-1.
The symbiotics as binary stars
Authors: Plavec Mirek J. 
Published: July 2016

AbstractSymbiotic stars have become an important testing ground of various theories of binary star evolution. Several physically different models can explain them, but in each case certain fairly restrictive conditions must be met, so if we manage to identify a definite object with a model, it will tell us a lot about the structure and evolutionary stage of the stars involved. I envisage at least three models that can give us a symbiotic object: I have called them, respectively, the PN symbiotic, the Algol symbiotic, and the novalike symbiotic. Their properties are briefly discussed. The most promising model is one of a binary system in the second stage of mass transfer, actually at the beginning of it: The cool component is a red giant ascending the asymptotic branch, expanding but not yet filling its critical lobe. The hot star is a subdwarf located in the same region of the Hertzsprung-Russell diagram as the central stars of planetary nebulae. It may be closely related to them, or it may be a helium star, actually a remnant of an Algol primary which underwent the first stage of mass transfer. In these cases, accretion on this star may not play a significant role (PN symbiotic).
Models for symbiotic stars in the light of the data
Authors: Friedjung Michael 
Published: July 2016

AbstractDifferent single and binary models of symbiotic stars are examined. Single star models encounter a number of problems, and binary models are probable. There are however difficulties in the interpretation of radial velocities. Accretion disks play a role in some cases, but winds especially from the cool component must be taken into account in realistic models. There is some evidence of excess heating of the outer layers of the cool component. Outbursts may be related to sudden changes in the characteristics of the cool star wind.
Broadening of the Interplanetary Helium Cone Structure Due to Elastic Collisions of LISM Helium Atoms with Solar Wind Ions
Authors: Fahr Hans J. , Nass Hans U. , Rucinski Daniel 
Published: July 2016

AbstractNeutral interstellar particles penetrating into the heliosphere, besides being subject there to specific loss processes, suffer elastic collisions with KeV-solar wind ions. The momentum transfer to the neutrals connected with these collisions leads to a loss of angular momentum with respect to the sun and to a fractional compensation of the effective solar gravity. The dynamical particle trajectories hence are changed into non-Keplerians leading to density and temperature distributions differing from those calculated in the past. This is found from a solution of the Boltzmann equation that linearizes the effect of this additional force. It is shown here that the HeI-584A resonance glow of the heliospheric helium cone lead to substantially lower interstellar helium temperatures if re-interpreted on the basis of this revised theory. These temperatures now seem to be in accordance with the derived temperatures for interstellar hydrogen.
Deuterium Abundance in the Local Interstellar Medium
Authors: Ferlet R. , Gry C. , Vidal-Madjar A. 
Published: July 2016

AbstractWe underline the present situation of deuterium abundance evaluation in interstellar space and show that it should be < 10-5. Studiing in more detail the λ Sco line of sight and having observed two Nal interstellar components toward that star, we can show that the D/H evaluation made toward λ Sco is in fact related to the local interstellar medium (less than 10 pc from the sun). Because this evaluation is also < 10-5 it is in stricking contrast with the one made toward α Aur (D/H > 1.8 10-5 ) confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.
Voyager EUV and FUV Observations
Authors: Holberg J.B. 
Published: July 2016

AbstractThe Voyager 1 and 2 ultraviolet spectrometers are sensitive over the wavelength range 500 to 1700 A. In the EUV, at wavelengths shortward of the Lyman limit (912 A), Voyager observations have detected emission from three out of a sample of 11 nearby hot DA white dwarfs. These observations imply very low HI column densities in the directions of the three stars detected. In the FUV, at wavelengths between 912 and 1200 A, Voyager observations of O and B stars can be used to study interstellar reddening at the shortest wavelengths and to provide useful estimates of interstellar H2 column densities.
Detection of Narrow C IV and Si IV Absorption Features in Spectra of Stars within 200 pc of The Sun
Authors: Molaro P. , Beckman J.E. , Franco M. , Morossi C. , Ramella M. 
Published: July 2016

AbstractDetection of narrow ( δλ< 0.5 A ) absorption features in C IV at λ λ 1548 and 1550 have been made in the spectra of 4 late B dwarfs within 200 pc of the sun; the Si IV doublet at λ λ 1393 and 1403 shows up in two of them. We argue that it is difficult to account for the strengths, widths, shapes , and C IV/Si IV ratios in terms consistent with a circumstellar origin except possibly for an asymmetric C IV component in one star (HD 135037). The most probable source is “semi-torrid” gas (cf. Bruhweiler et al. 1980) in the 50,000 K range forming the interfaces between cooler H I clouds and the ambient medium at coronal temperatures. Our technique, using late B rapid rotators, is useful for LISM probing of this kind.
Molecular Clouds Within 100 pc
Authors: Blitz Leo , Magnani Loris , Mundy Lee 
Published: July 2016

AbstractObservations at the 2.6 mm line of CO reveal the presence of a large number of molecular clouds at high galactic latitude. If the velocity dispersion of the clouds is a measure of their scale height, the mean distance of the ensemble we have detected is 100 pc. The clouds are unusual in that either they are not gravitationally bound or they are very deficient in CO relative to molecular hydrogen. These clouds represent a heretofore unrecognized component of the local interstellar medium. If they are pervasive in the Milky Way, they probably represent the small molecular cloud component of the interstellar medium.
Stromgren Trails of Hot White Dwarfs
Authors: Raymond John C. 
Published: July 2016

AbstractHigh resolution IUE spectra of Feige 24 reveal sharp C IV absorption features at both the stellar velocity and the velocity of the interstellar lines. Dupree and Raymond have shown that the ionization zone created by Feige 24 itself accounts for the interstellar components of C IV and Si IV, and that the density of hot white dwarfs in the galaxy implies that similar ionized zones around hot white dwarfs make a significant contribution to the C IV column densities observed toward distant O and B stars. Typical white dwarf velocities of around 30 km/s and C IV ionization zone diameters less than 1 pc imply that the crossing time is comparable to the ionization time, so that non-equilibrium ionization models are required. Models of the resulting elongated trails are presented.
Measuring EUV Line Emission from the Hot Interstellar Medium
Authors: Labov Simon , Martin Christopher , Bowyer Stuart 
Published: July 2016

AbstractIn the local interstellar medium, the presence of hot gas (log T ~ 5 to 6) has been inferred from measurements of oxygen VI absorption in the ultraviolet, and from diffuse emission in the extreme ultraviolet (EUV) and soft X-ray regions. Here we describe a spectrometer that is very sensitive to gas in this temperature range. The spectrometer uses an array of plane-ruled gratings at grazing incidence in the extreme off plane mount. A set of Kirkpatrick-Baez mirrors focuses the conically diffracted light on to one of two microchannel plate detectors. The field of view of the instrument is 0.2° by 12°. The predicted sensitivity ranges from 50 to 200 ph/(cm2 sec str) with a resolving power (λ/Δλ) of 15 to 50 over the 50 to 700A wavelength band. The instrument is currently under construction for a sounding rocket flight.
The McDonald Observatory High Precision Radial Velocity Spectrometer
Authors: Cochran William D. , Young Brenda W. 
Published: July 2016

AbstractWe are developing a prototype instrument for McDonald Observatory designed to measure stellar radial velocity variations to a precision of a few meters per second. The instrument will be used to study low amplitude stellar oscillations, to search for binary stellar systems with large mass ratios, and possibly to search for extra-solar planetary systems. A fixed gap Fabry-Perot etalon, used in reflection, imposes a set of fixed reference absorption lines on the stellar spectrum before it enters the McDonald Observatory 2.7m coudé spectrograph. The spectrum, covering 1500 Å at 0.13 Å resolution, is recorded on a set of eight Reticon arrays, placed end-to-end. Doppler shifts of the stellar spectral lines with respect to the fixed Fabry-Perot orders are measured by cross-correlation techniques. Calibration methods have been developed to measure any long-term drifts within the system.
Absolute Astronomical Accelerometry
Authors: Connes Pierre 
Published: July 2016

AbstractA new technique is proposed, leading to two closely related instruments, the solar and stellar accelerometers. The principal fields of application are solar/stellar seismology and the search for extrasolar planets. The technique is fully specific: it cannot give the velocities themselves. The results are absolute : the measured accelerations are directly related to primary length and frequency standards. Essentially one makes use of a variable path Fabry-Pérot interferometer whose channelled spectrum is constrained by a servo loop to track the Doppler shifted astronomical spectrum. Then a tunable laser tracks the interferometer. The ultimately measured quantity is the beat frequency between the tunable laser and a stabilized one.A fundamental limit to the precision of radial velocity measurements, set by photon counts and the spectral profile itself, is established, and it is shown that the proposed technique closely approaches that limit. Hence it is considerably more sensitive than any other used so far, and holds the promise of making both planetary searches and the study of oscillations practical for a large number of stars.
Current Programs of Local Galactic Structure and Evolution
Authors: Andersen J. , Nordström B. 
Published: July 2016

AbstractWe present a progress report on some current radial-velocity observing programs aiming to provide complete data for selected samples of stars covering the whole sky. The velocities are based on ESO coudé spectra as well as CORAVEL observations obtained in both hemispheres. As a first step, the Bright Star Catalogue has been completed in radial velocities ( ~1500 stars or ~l/3 of the southern BS stars). Currently, we are approaching completion of some 4000 dwarf F stars from Olsen’s (1983) uvbyß photometric survey. The data will be used to study the velocity dispersion of these stars as a function of age and metal abundance from a kinematically unbiased sample. They will also provide a basis for an improved determination of Kz. Extension of the program to the G dwarfs is planned for the near future.