bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Anti-Tail of Comet Bradfield (1987XXIX)
Authors: Akisawa Hiroki , Oka Takuma , Sugawara Ken 
Published: July 2016

AbstractThe anti-tail of comet Bradfield 1987XXIX (= 1987s) was observed when the earth passed through the orbital plane of this comet on December 20, 1987. The time variation of this phenomenon was monitored continuously by Japanese amateur astronomers. Analyzing these photographs by using the Bessel-Bredkhin theory, we deal with the dust particles in the anti-tail.
Formation Mechanisms of the Split Tail of Comet Bradfield 1987XXIX
Authors: Sugawara Ken , Watanabe Jun-ichi 
Published: July 2016

AbstractComet Bradfield 1987XXIX showed a well-developed split tail, which is a dust tail feature divided into two branches by a dark gap. Similar structures have been observed in several comets. The split tail of comet Seki-Lines is one of them; some authors tried to explain it by rapid dust vaporization or self-regulation model. However, these models can not explain in the case of comet Bradfield 1987s. It was suggested in our previous works that the trend of variation of position angle of the dark gap coincides well with that of the plasma tail or projected radial vector. We discuss the formation mechanisms of the split tail from the view point of dust-plasma interactions.
Lifetime of Meteor Streams Associated with Comet Halley
Authors: Hajdukova M. , Hajduk A. 
Published: July 2016

AbstractCritical examination of the orbital parameters of particles ejected from comet Halley rejects the low age hypotheses for meteor showers associ- ated with the comet. The diffusion of the orbits of large particles is too slow for explaining the observed structural features of the stream. The mass-loss process as derived from space observations compared with the mass of the stream of particles deduced from flux data lead to comet lifetimes of the order of 105years.
Equation of State and Ionization of Dense Plasmas
Authors: Ebeling W. 
Published: July 2016

AbstractIn large regions of densities and temperatures the properties of plasmas are influenced by Coulombic forces. Here especially hydrogen and helium plasmas are studied. The region of nonideality is given and the main effects as screening, quantum corrections, level shifts and the cut off for the sum over states are discussed. Based on methods of classical and quantum statistics corrections to the ideal EOS are calculated. Interpolational expressions covering the whole density-temperature plane are given and phase transitions to highly ionized states are discussed. Level shifts due to nonideality are derived. Finally the ionization equilibrium and kinetics are considered theoretically focussing the attention on nonideality effects.
Networks for Helioseismic Observations
Authors: Hill Frank 
Published: July 2016

AbstractHelioseismology from a single ground-based observatory is severely compromised by the diurnal rising and setting of the Sun. This causes sidelobes to appear in the helioseismic power spectrum at multiples of ± 11.57 μHz from each solar line, contaminating the spectrum and rendering mode identification and frequency measurement extremely difficult. The difficulty can be overcome in three ways — observing from a fully sunlit orbit in space, observing from the Polar regions, or observing with a network of stations placed around the Earth. This paper discusses the networks that are either currently in operation or being planned. These include the Global Oscillation Network Group (GONG) project, the Birmingham network, the IRIS network of the University of Nice, and the SCLERA network of the University of Arizona. The scientific objectives and instrumentation of these networks are briefly described. Theoretical predictions for network performance are compared with actual results. The problem of merging simultaneous data from multiple instruments is discussed, as well as the relationship of the networks with the helioseismology experiments on the SOHO space mission.
Future Prospects of Helioseismology from Space
Authors: Bonnet R.M. 
Published: July 2016

AbstractIn view of their costs, space-borne instruments should be considered only for their exclusive capabilities in helio-and asteroseismology. Space-borne high resolution spectrometers and photometers operate free of atmospheric pertubations, can be put on special orbits offering continuous (uninterrupted) observations and therefore offer the best opportunity for high signal-over-noise ratio. The recent data obtained on board the Phobos-2 mission clearly evidences this fact. The ESA-NASA SOHO observatory will be the first mission of its kind carrying a comprehensive set of instruments to analyse the gravity and acoustic modes of solar oscillations over an uninterrupted period of at least 2 years. Projects also exist to observe oscillations of the solar diameter. Long term observation of the solar constant may provide a clue to the understanding of the origins of the solar cycle. Simultaneous out of eliptic measurements may nicely complement our data set and offer unambiguous views on the asymmetries of the solar interior. Space observations are probably the only means to get access to the deep solar interior through the detections of g modes. They offer the only prospect in the exploitation of asteroseismology over a larger number of stars.
Theory of Transport Processes
Authors: Zahn J.-P. 
Published: July 2016

AbstractThis review focuses on the transport of matter and angular momentum in the radiative zones of stellar interiors. The two main causes of such transport are the convective overshooting in the vicinity of convection zones, and the slow motions (meridional circulation and turbulence) due to the rotation of the star. In addition, momentum can be transfered through waves (generated by the motions above) and through magnetic stresses. The characteristics of those processes are examined, with special emphasis on turbulent diffusion.
Quasi–periodic Outburst Activity of Novae at Minimum
Authors: Della Valle M. , Calvani M. 
Published: July 2016

AbstractIn this paper we present the statistical analysis of historical light curves of 8 old novae, performed through a Fourier analysis on ~ 1600 no-equispaced (in the time) observations published by Steavenson between 1921 and 1953. The results seems to support the existence of a semiregular variability on typical timescales of 50d ÷ 100d and amplitude of ~ 0.3 ± 0.1 magnitudes.At present the largest body of data concerning the photometric behaviour of novae at minimum, is due to the pioneering works by Steavenson (1920→1950) and also to Robinson’s compilation (1975) of 33 preeruption lightcurves of novae.Besides testing the evolutionary models, such as the Hibernation Scenario (Shara et al. 1986), the importance of very long term observations of novae at minimum, has been recently pointed out by Bianchini (1987) and Warner (1988) in close connection to the possible detection of solar-type cycles of activity of the secondary. In spite of these considerations an interesting body of ~ 1000 homogenous observations of 5 posteruption lightcurves provided by Steavenson between 1920 to 1950 (published on M.N.R.A.S) has been neglected and only recently recovered (Delia Valle 1988).The aim of our analysis is:a)to verify possible presence of Dwarf Nova activityb)to confirm on the basis of a larger sample of objects, the existence of semiregular variability as observed in Q Cyg 1876 (Shugarov 1983) and v841 Oph (Della Valle and Rosino 1987).In this contribute we present only the preliminary results of our Fourier’s analysis, performed by adopting the procedure suggested by Deeming (1975) to analyse data taken at unequally spaced time intervals, whereas a more complete analysis will be presented in a forthcoming paper.
Ultraviolet Observations of Classical Novae in Outburst
Authors: Cassatella Angelo , Gonzalez-Riestra Rosario 
Published: July 2016

More than a dozen classical novae in outburst have been observed with the International Ultraviolet Explorer since its launch in 1978. These data represent a crucial breakthrough in understanding several aspects of the classical novae phenomenon including nucleosynthesis, the energetics of the explosion, the dynamics of the mass ejection, and the processes of dust formation. Also they are important to gain insight on the nature of the white dwarf components and then on the evolutionary scenario of these binary systems.The UV emission lines include important transitions from several species such as He, C, N and O, Ne, Mg, and Al which, whenever symultaneous optical data were available, have lead to a detailed knowledge of the physical conditions in the nebular phases and to the determination, with unprecedented accuracy, of the chemical abundances in the ejecta (see e.g.: Stickland et al. 1981; Williams et al. 1985; Snijders et al. 1987). Precise abundance determinations provide crucial constraints on nucleosinthesis during TNR as well as on the efficiency of diffusion and mixing processes. The ultraviolet range provides also effective means to determine the value of the reddening from the strength of the 2200 A dust feature or from the emission line ratios; an accurate determination of this parameter from the UV is essential, for example, to determine the energy budget of novae and the temperature of the remnants.
Images and Light Curves of the Radio Remnants of Novae
Authors: Hjellming Robert M. 
Published: July 2016

AbstractRadio observations of novae provide direct information about masses, temperatures, and velocities of ejected material, particularly when the radio remnants are resolved or imaged. The radio images of Nova QU Vul 1984 indicate that the mass in its ejecta is 3.6·10−4M⊙, confirming the generally higher masses inferred from radio light curves. All thermally-emitting nova shells that can be observed by the VLA should be resolveable, allowing determination of angular sizes and asymmetries.
Mm CO observation of the old nova NQ Vul
Authors: Albinson J. S. , Evans A. 
Published: July 2016

AbstractWe have observed the old nova NQ Vul in the J = 2 → 1 rotational transition of 12CO at 230.5 GHz at the University of Texas Millimetre Wave Observatory. The spectrum shows narrow features which clearly arise in the local interstellar medium. However these local features are superimposed on a broad feature which peaks at ~ 63 mK. This feature is centred on velocity VLSR ≃ 26 ± 9 km s−1–consistent with that expected for NQ Vul–and has FWHM 80 ± 20 km s−1. The peak antenna temperature corresponds to an integrated flux of 3.2 × 10−15 erg s−1 cm−2.Assuming LTE and a distance of 1.2 kpc the mass of CO is ~ 10−6M⊙ if the line is optically thin. The CO mass is comparable with the total mass ejected in 1976 (4) so the CO we detect at millimetre wavelengths has nothing to do with the 1976 outburst. If the CO/H ratio in the emitting material is similar to that in the interstellar medium (2), the total mass is ~ 0.6 M⊙.The CO mass rules out an origin both in the 1976 outburst and in the post-outburst phase: the CO must have originated in material ejected by the NQ Vul system prior to the 1976 outburst. There are two possibilities. First, the CO may have formed in material accumulated following a large number of nova outbursts. Second, the CO may have been present, or formed, in material ejected by the NQ Vul system during a previous evolutionary phase. The deduced mass is comparable to the mass of CO seen around planetary nebulae (3); the outflow velocity (~ 40 km s−1) would also be in line with this interpretation.In either case, the above mass estimate of 0.6 M⊙ (based on the interstellar CO/H ratio) is likely to be an upper limit as we would expect an enhancement of heavy elements in any ejected material. A determination of 12C/13C and other isotopic ratios would be valuable to pin down the origin of the CO.
Element Abundances of Nova PW Vulpeculae
Authors: Andreae J. , Drechsel H. 
Published: July 2016

AbstractElement abundances, electron temperatures and densities of the shell ejected during the outburst of the classical nova PW Vulpeculae were determined using ultraviolet (IUE) and optical (ESO 1.52m + B&C + IDS) spectra obtained during the nebular phase (April - July 1985). The C, N, O abundances are enhanced by factor 10 - 100 relative to solar values according to the predictions of the TNR (thermonuclear runaway) theory. The overabundances of Ne, Si, Mg are comparatively small compared with other novae indicating that the outburst of this slow nova occurred on a CO white dwarf.
Effects of the Presence of Supercritical Winds
Authors: Friedjung Michael 
Published: July 2016

AbstractEvidence is given that classical novae have optically thick winds for a certain time after optical maximum. Multifrequency observations especially of FH Ser indicate acceleration of the wind at very large optical depths, probably by radiation pressure of an object above the Eddington limit. This result though fairly convincing needs checking by proper radiative transfer calculations. A way in which it might be produced is mentioned as is the influence of the wind on the structure of the ejected envelope.
Cool Envelopes of Post-Novae Constraints on the Decline of the White Dwarf
Authors: Stasińska Grażyna , Tylenda Romuald 
Published: July 2016

Some post-novae, e.g. DQ Her, CP Pup, T Aur, have cool envelopes, Te < 1000K. As has been shown by Ferland et al. (1984) this effect is primarily due to large overabundances of the CNO elements which at low densities can very effectively cool off the nebular gas through infra-red lines.We have constructed an extensive grid of photoionization models in order to study the exact conditions required for the electron temperature to drop to such low values. As can be seen in Figs. 1 to 4, our results can be summarized as follows.1- The abundance of oxygen which is the dominant coolant in the conditions considered has to be at least 10 times the solar value (with C and N accordingly overabundant).2- The gas density, n, has to be below 1000cm−3.3- The effective temperature of the ionizing source, Teff, has to be below 2 105K.4- The ionization parameter U = QH / (4πr2nc) (QH: number of ionizing photons emitted per second by the central source, r: radius of the envelope) has to be between a certain range, typically 10−2 < U < 10−3, whose exact limits, however, depend on other parameters such as Teff and the abundances.
Spectroscopic Results of the Recurrent Nova RS Ophiuchi
Authors: Anupama G.C. , Prabhu T.P. 
Published: July 2016

The recurrent nova RS Ophiuchi has had five outbursts in 1898, 1933, 1958, 1967 and 1985. We present here in brief the spectroscopic results of the 1985 outburst and subsequent quiescence, based on data obtained at the Vainu Bappu Observatory (VBO), Kavalur. Detailed results of the 1985 outburst appear in Anupama & Prabhu (1989).Spectra were recorded in the range 6200-8900 A at dispersion of 194 A mm−1 at four epochs: 32, 59 & 60; 89 & 91 and 108 days since the 1985 outburst maximum on January 27.5. In addition, spectra were recorded in the range 4300-5600 and 5000-7600 A at dispersion of 132 A mm−1 on day 60, and in the range 5700-8000 A, at dispersion of 194 A mm−1, on days 89, 91 and 108.
The Light Curve of the Symbiotic Nova HM Sagittae
Authors: Arkhipova V.P. , Belyakina T.S. , Dokuchaeva O.D. , Noskova R.I. 
Published: July 2016

The light curve of the symbiotic nova HM Sge in 1960–1988 derived from 260 photographic and 243 photoelectric observations (Arkhipova et al. 1989) in presented in Fig. 1.The rate of nova-like brightness increase in 1975 was about 0.04 mag/day. The maximum duration was about 4 years, with brightness oscillations of up to 1 mag. After 1981 the star brightness decreased slowly (at the rate of ~ 0.08 mag/yr) with small oscillations of 0.2 mag in the B band.Fourteen years before the outburst of HM Sge a preoutburst phase with a light amplitude of 1 mag and a duration of about two years was observed, but its reality is rather doubtful. Similar features can also be seen in the light curves of the symbiotic novae V1016 Cyg and V1329 Cyg, 15 and 12 years before their outbursts, respectively.
Spectroscopic and Photometric Observations of YY Orionis
Authors: Walker Merle F. 
Published: July 2016

Three observational studies of YY Ori, the apparently brightest of the YY Ori-type variables in the Orion nebula cluster (Walker 1972), have been carried out. These are:
1. A program of simultaneous spectroscopic and photometric observations. In this program, spectra were obtained on 14 nights at a dispersion of 115 A/mm using a Spectracon image converter mounted at the focus of the Bowen f/1 camera of the coudé spectrograph of the 120-inch reflector (Walker 1966, 1969a). The simultaneous photoelectric observations, on the U B V system, were obtained using the 24-inch Lick reflector.2. In collaboration with D. Burstein, higher dispersion (0.625 A/channel) observations were obtained on two nights using the Robinson-Wampler scanner at the Cassegrain focus of the 120-inch reflector to investigate in greater detail the structure of the emission and inverse P Cyg absorption features in the spectrum.3. Spectrophotometry observations were obtained using the instrumentation described in (1) above with a wide slit (4” in width) to investigate the form of the energy distribution in the region from 3200A - 5100A.
The Variable Shell Star HR 5999
Authors: Thé P.S. , Tjin A Djie H.R.E. 
Published: July 2016

From spectroscopic observations Bessell and Eggen (1972) (hereafter called BE) have detected that HR 5999 (erroneously named HR 6000 by BE) is a shell star of spectral type A7 III-IV with hydrogen lines in emission. Photometric observations show subsequently that HR 5999 varies in brightness up to about 1 mag semiregularly with a period of about 1 month. Eggen (1975) believes that HR 5999 forms a pre-main sequence object.With HR 6000, the star HR 5999 forms a visual double star system named Δ199; HR 5999 is the southern component. The angular separation is about 45”. BE show that these stars have a common proper motion, and are, therefore, believed to form a physical pair.
Is the Close Binary XY Ursae Majoris a Radio Star?
Authors: Geyer E.H. 
Published: July 2016

AbstractThe optical position of the short period eclipsing binary XY UMa, which shows large scale star spot activities, coincides within 2 minutes of arc with a radio source, listed in the 4C-, 4CP-, OK-catalogues, and the position obtained with the Effelsberg radio telescope. A fainter star, centered on the radio source position, is according its U-, B-, V-values a K main sequence star. The radio source is non-thermal, and has a spectral index α ~-0.85. If the radio source is identical with the binary, it would imply important consequences about the extragalactic nature of high latitude 4C-sources, the radio background and the high radio luminosity of the binary.
Low Energy Cosmic Rays Emitted by the Orion Complex into the Local Medium
Authors: Schönfelder V. , Dogiel V.A. , Freyberg M.J. , Morfill G.E. 
Published: July 2016

AbstractThe excess of γ-ray emission in the energy range 3–7 MeV discovered by COMPTEL in the direction of the Orion complex may imply that there is a powerful source of low energy cosmic rays in the local galactic medium. Several interpretations of the excess have been suggested. One of them assumes that the emission is identified with nuclear de-excitation lines of excited 16O and 14C. To provide the excess the energy deposit in these nuclei should be as large as ~ 1039 erg s−1. If a comparable part of these nuclei escape into the local galactic medium they can play a significant role in the energy balance there.If the excess is interpreted as continuous it can be produced by bremsstrahlung emission of fast 10 MeV electrons. Much less energy deposit in these electrons is necessary (~ 1036 erg s−1) to generate the observed Orion flux. The intensity of these electrons even near Earth can be higher than that of the galactic cosmic ray electrons.
Small-Scale ¼ keV Fluctuations Due to the Local Hot Bubble
Authors: Kuntz K.D. , Snowden S.L. , Warwick R.S. 
Published: July 2016

AbstractTo determine fluctuations in the ¼ keV emission due to the LHB, without contamination due to sources within the galactic disk, the Galactic halo or the extragalactic background, we have formed a mosaic of PSPC observations towards the Hyades, a direction where distant emission is effectively blocked by a Galactic column of many optical depths. After removing the point sources from this image, we find the ¼ keV emission to be smooth on scales from 6′ to a few degrees.
The Radiation Transfer of Soft X-rays
Authors: Kerp Jürgen , Pietz Jochen 
Published: July 2016

AbstractWe discuss the link between the halo plasma temperature and the power-law spectral index of the extragalactic background radiation. This link is of strong influence for the derivation of the Galactic halo intensity distribution. In principal, we can distinguish between two combinations of Galactic halo plasma temperature and power-law slope. The first combination consists of a halo plasma of Thalo = 106 K and an E−2 approximation of the extragalactic background radiation. The second combination is Thalo = 106.2 K and an E−1.5. Both combinations are in agreement with recent observational results, thus it is not feasible to discriminate between both models on the basis of X-ray data available. But, the soft X-ray background intensity distribution in the ¼ keV and ¾ keV ROSAT energy bands differs significantly. The Thalo = 106 K and an E−2 allows a patchy ¼ keV intensity distribution while the Thalo = 106.2 K and an E−1.5 predicts a much smoother intensity variation since the hotter halo plasma accounts for a significant fraction of the ¾ keV background radiation.
In Situ Measurements of Interstellar Dust
Authors: Landgraf M. , Grün E. 
Published: July 2016

AbstractWe present the mass distribution of interstellar grains measured in situ by the Galileo and Ulysses space probes as cumulative flux. The derived in situ mass distribution per logarithmic size interval is compared to the distribution determined by fitting extinction measurements. Large grains measured in situ contribute significantly to the overall mass of dust in the local interstellar cloud. The problem of a dust-to-gas mass ratio that contradicts cosmic abundances is discussed.
X-ray Emission from G359.1-0.5
Authors: Egger Roland , Sun Xuejun 
Published: July 2016

AbstractWe report on the detection of X-ray emission from the supernova remnant (SNR) G359.1-0.5 in a deep ROSAT PSPC pointed observation. The diffuse emission is well confined within the radio shell of the SNR. Its spectrum can be represented by a thermal plasma model at T ~ 1 keV and Fx ~ 2×10−11 erg cm−2 s−1 (0.1–2.0 keV) modified by the column absorption of NH ~ 3 × 1022 cm−2. This result supports the view that the source is at a large distance consistent with that from radio observation, and helps to resolve a puzzle about the SNR in previous observations.
The Role of Magnetic Reconnection in the Interaction of High-Velocity Clouds and the Galactic Disk
Authors: Lesch Harald , Birk Guido T. 
Published: July 2016

AbstractThe boundaries of high-velocity-clouds that hit the Galactic plane are sources of strong X-ray emission indicating gas temperatures of a few million Kelvin. We show that numerous individual magnetic reconnection processes in the interaction region between an HVC and the ionized Reynolds layer may cause the gas heating via dynamical Ohmic dissipation. We present results of numerical plasmaneutral gas fluid simulations performed to study the dynamical reconnection process and to calculate the conversion of magnetic energy into heat.