bluuebunny/crossref_metadata_2025 huggingface dataset:
Equation of State and Ionization of Dense Plasmas
Authors: Ebeling W.
Published: July 2016

In 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

Helioseismology 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

In 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

This 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

In 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 activity

b)

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.
On V603 Aql and Magnetic Novae
Authors: Schwarzenberg-Czerny A. , Udalski A.
Published: July 2016

Our photometry revealed that the old nova V603 Aql has four different coherent periods, including a period present in X-rays and so it is quite unique among all novae. Thus we classify V603 Aql as an intermediate polar (IP) system. Some time ago Hefner and Metz (1985) found that the period of the sinusoidal light variations of V603 Aql is 3.5 hour and thus it is longer by about 5 percent than the spectroscopic orbital period of 3.3 hour. Our observations covering over 30 hours and spanning 30 days confirm their result. However, we discovered also another coherent oscilation with a small amplitude of 0.02 mag and period of 61 min (Udalski and Schwarzenberg-Czerny, 1989). Our analysis of the X-ray observations by Drechsel et al. (1983) revealed 25 percent modulation with the same period and thus confirmed our discovery (Fig. 1). Additionaly we found in our light curves evidence of the 2.5 day beat period of the 3.3 and 3.5 hour periods.
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

Radio 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

We 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

Element 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

Evidence 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.
The Continuum Spectra of Accretion Discs in Novalike Objects
Authors: Shaviv G. , Wehrse R.
Published: July 2016

The exact value of the accretion rate in novae is very important to the theory of thermonuclear runaways and nova statistics. Estimates of the typical accretion rates in nova and novalike objects are 1018g/s (1.6 10−8 M⊙/yr). Patterson (1984) estimated that if the above high accretion rate prevails the expected number of novae according to Bath and Shaviv (1976) exceeds the observed number. Prialnik, Livio, Shaviv and Kovetz (1982) have shown that no thermonuclear runaway can be obtained if the accretion rate is as high as few 10−9 M⊙/yr. Actually, the very strong thermonuclear runaways (TNRs) are obtained only for very low accretion rates namely, 10−10 to 10−11 M⊙/yr. A way out from this inconsistency was suggested by Shara, Livio, Moffat and Orio (1986) in the form of the hibernation model. In this model the high accretion rate is found only shortly before and soon after the nuclear runaway and the nova spends most of the time in a state of very low accretion rate - so low that most novae are not observed at all. The high accretion rate, according to this theory, is a precursor to the runaway. The hibernation model is very attractive in spite of a meager observational proof so far and theoretical justifications. Yet, it is one of the most promising ideas in this field. The hibernation scenario claims that the accretion rate is a function of time. It is high just prior to the runaway and it continues to be high for some time just after the runaway. It then declines to very low values. From the point of the model for the thermonuclear runaway the problem is how the star reacts to a temporary high accretion rate that comes after a long period of low accretion rate (Shaviv and Starrfield, 1987). Thus, even if the accretion rate is low during most of the time the phase of high accretion can still affect the outcome of the thermonuclear runaway.
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.
Spectrophotometry of B and A-Type Supergiants
Authors: Campusano Luis E.
Published: July 2016

Continuum fluxes measured with a two-channel spectrum scanner and a 40 A slit are presented, in a differential manner, for six supergiants over the wavelength range 3390-8090 A. Five of these stars presented variability detectable on a time scale of a few days. The stars with the stronger light changes were HD 148379 and HD 160529, both with Hα-emission, whose maximum observed amplitudes amounted to 0.06 and 0.14 mag. The Ha observations done with a 4 A slit gave no indication of strong intensity variations over the same time interval. Some evidence for the presence of a Balmer continuum emission is presented for HD 160529, and we briefly relate it to a possible origin of its Hα-emission profile.
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.
A Beat Phenomenon in Dwarf Nova Eruptions
Authors: Vogt N.
Published: July 2016

Photoelectric observations of the dwarf nova VW Hyi, obtained at the end of the December 1975 supermaximum, are presented. After decline from the outburst, the superhump period (0ḍ07622) combines with the orbital period (0ḍ07427) to a beat phenomenon: the O-C’s and the light curves of the orbital hump vary systematically with the phase of the beat period for at least one week after recovery from the supermaximum. It is suggested that the red secondary component, which rotates non-synchroneously with the superhump period, expands slightly at the beginning of a supermaximum and is heated up asymmetrically, probably due to instabilities in its convection zone. In addition, the increased mass transfer rate may trigger the long eruption in the accretion disc while short eruptions originate in the disc without participation of the secondary.
Is the Close Binary XY Ursae Majoris a Radio Star?
Authors: Geyer E.H.
Published: July 2016

The 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.
Nuclei of Planetary Nebulae in the Pulsation Instability Strip
Authors: Dziembowski W.
Published: July 2016

Pulsation properties of relevant stellar models are investigated with the linear nonadiabatic method. Short-period variability of FG Sge is interpreted as a pulsation phenomenon.
Possible Binary Nature of the Emission-Line Variable Object V 1329 Cygni (= HBV 475)
Authors: Grygar Jiři , Hric Ladislav , Chochol Drahomír
Published: July 2016

The peculiar emission-line object V 1329 Cyg was discovered by Kohoutek (1969), who detected in his objective-prism spectrograms an increasing brightness and the presence of emission lines. High dispersion spectra revealed more than 200 emissions of hydrogen, helium, ionized metals and forbidden lines of oxygen, neon, etc. (Crampton et al., 1970; Andrillat, 1970). The object exhibits the composite spectrum of a hot early-type component and a cold M-type star. Its time evolution in a two-colour diagram is seen in Fig. 1.
1. Orbital Data on the Existence of Oort’s Cloud of Comets
Authors: Marsden B. G.
Published: July 2016

Oort’s work on the cometary cloud is reviewed and extended using new data from 99 comets with high-quality orbits. These data clearly show the pronounced pile-up of the “original” reciprocals of the semi-major axes at values of less than 0.000100 AU-1. This concentration is found to be even more striking for comets of large perihelion distance, and the possible significance of this is discussed. Lyttleton’s criticisms of the concept of the Oort cloud (or, as only he calls it, “shell”) are reviewed and dismissed as largely irrelevant. A set of data on 96 comets with orbits of second-class quality is also considered.
5. Meteoroid Populations and Orbits
Authors: Ceplecha Z.
Published: July 2016

Statistical studies of the photographic data on atmospheric trajectories and orbits of meteors (from 10-4 g to hundreds of tons) point to 5 groups of bodies with different structure and composition. The following classification is proposed: Fireball group I = exceptional cases of so-called “asteroidal” bodies among Super-Schmidt (SS) and small-camera (SC) meteors 5 ordinary chondrites. Fireball group II = group A among SS and SC = carbonaceous chondrites. Group B among SS and SC = dense cometary materials with small perihelion distances (not distinguishable among fireballs). Fireball group IIIa = group C among SS and SC = regular cometary material. Fireball group IIIB = group D (above C) of SS and SC = Draconid-shower type of cometary material. Statistics of the orbits for separate groups is considered and characteristic orbits are given.
4. The Kirkwood Gaps as an Asteroidal Source of Meteorites
Authors: Scholl H. , Froeschle C.
Published: July 2016

Zimmerman and Wetherill’s proposed mechanism for the production of meteorites from asteroids has been explored by numerous numerical computations of orbits. Starting from the vicinity of the 2/1 Kirkwood gap, 30% of our orbits soon have aphelia reaching beyond, but not much beyond 4 A.U.; (3% only exceed 4.3 A.U.). These results suggest that the proposed mechanism might work, although we have not yet checked whether Jupiter’s action will be large enough for those perihelia. Furthermore, our investigation has been extended to the 3/1, 7/3 and 5/2 Kirkwood gaps, and shows that these gaps should also be considered asa possible source of meteorites.
5. Chondrules as Condensation Products
Authors: Wood J. A. , McSween H. Y.
Published: July 2016

The formation of meteoritic chondrules via condensation from the primordial solar nebula is discussed. Chondrule formation in regions where the gas/dust ratio was enhanced, and where transient high energy events heated the gas and temporarily vaporized the dust, is advocated. The observed diversity of chondrule types can be understood as resulting from local variations in the initial gas/dust proportions and other parameters.
1. High-Temperature Condensates in Carbonaceous Chondrites
Authors: Grossman L.
Published: July 2016

Equilibrium thermodynamic calculations of the sequence of condensation of minerals from a cooling gas of solar composition play an important role in explaining the mineralogy and trace element content of different types of inclusions in carbonaceous chondrites. Group IV B iron meteorites and enstatite chondrites may also be direct condensates from the solar nebula. Condensation theory provides a framework within which chemical fractionations between different classes of chondrites may be understood.
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

The 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

To 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

We 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

We 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.
Star Formation in Expanding Shells: When and Where
Authors: Ehlerová S. , Palouš J. , Theis Ch. , Hensler G.
Published: July 2016

The fragmentation of expanding shells and subsequent star formation are analyzed using an analytical model and computer simulations. We discuss the role of the sound speed in the ambient interstellar medium and the influence of the finite thickness of the gaseous disk.
X-ray Emission from G359.1-0.5
Authors: Egger Roland , Sun Xuejun
Published: July 2016

We 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

The 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.
Cloud Formation in a Galactic Fountain Resulting from Rayleigh-Taylor Instabilities
Authors: Berry D.L. , de Avillez M.A. , Kahn F.D.
Published: July 2016

Intermediate and high velocity clouds are produced in a Galactic fountain as a result of Rayleigh-Taylor instabilities that grow at the interface separating the cool descending gas and the hot ascending gas within the fountain flow. It is proposed here that there is no need to introduce any initial perturbation to the system in order to trigger such instabilities. They will arise naturally as a result of the difference in the adiabatic parameters above and below the interface. A three-dimensional study of the unstable layer and the resulting cloud formation is presented.
Radio and Polarization Properties in the Disk and Halo of Edge-On Spirals
Authors: Dumke M. , Krause M.
Published: July 2016

We have observed a small sample of edge-on galaxies in total and linearly polarized radio continuum emission at λ6.2 cm, using the Effelsberg 100m telescope. The resulting maps were combined with available VLA data in order to obtain high-sensitivity radio images which have a sufficient angular resolution and do not suffer from the so-called missing-spacing problem.

From an analysis of these images (together with 2.8cm and 20cm data) we get the following results: 1. The radio emission perpendicular to the plane can be described by a two-component exponential distribution with scale-heights of ~ 300 pc and ~ 1.8 kpc, independently of the star forming activity and interaction state. 2. In the disk of the non-interacting galaxies of our sample the thermal fraction of the emission seems to be higher than usually deduced from observations of face-on galaxies. 3. The fractional polarization p increases with increasing galactic height, reaches a maximum at h ~ 1 – 3 kpc, and decreases again. In general p is lower in actively star forming galaxies.
Anisotropic Outflows from LBVs and Ofpe/WN9 Stars
Authors: Nota Antonella
Published: July 2016

In the past decade, the increasing sophistication of the high resolution techniques from the ground, and the advent of HST have allowed a systematic study of the outflows around evolved massive stars. It has been established (Nota & Clampin 1997) that most LBVs and Ofpe/WN9 stars are surrounded by associated circumstellar nebulae which have been ejected in some previous phase of their evolution. These nebulae are the fossil record of the interactions of previous winds and of the violent ejections in which the stars most likely have shed their outer layers. The study of the morphology, kinematics and chemical composition of the ejected material has allowed us to gain deep insight in the ejection and shaping mechanism.
Extremely Luminous Atmospheres
Authors: Shaviv Nir J.
Published: July 2016

We present the effects that inhomogeneities have on radiating atmospheres. It is shown that nonuniformities in a medium induce a reduction of the effective opacity which subsequently increases the Eddington Luminosity. The most striking effect however that arises from the dependence of the opacity on the inhomogeneities, is the possibility of a phase transition, where the atmosphere energetically favors exciting horizontally propagating waves due to large fluxes.
The Effects of Magnetic Fields on the Winds from Luminous Hot Stars
Authors: Cassinelli Joseph P. , Miller Nathan A.
Published: July 2016

Here we explore three types of models in which the combination of magnetic fields with line driving forces leads to faster winds than line forces alone. The fields can change the flow geometry; they can couple with rotation and transmit angular momentum; and they can carry transverse Alfvén waves. All three can lead to a deposition of momentum beyond the critical point and accelerate winds. Some history of the attempts to use magnetic fields to understand hot star winds is discussed and several new models for magnetic rotator B[e] winds are presented.
O-Star Wind Variability in the Ultraviolet and Optical Range
Authors: Kaper Lex
Published: July 2016

Variability is a fundamental property of O-star winds. One of the major breakthroughs in this field of research has been the recognition that wind variability is cyclical in nature. This suggests that stellar rotation is an important piece in the unsolved puzzle of the wind-variability mechanism. The current idea is that Corotating Interacting Regions (CIRs) are responsible for the observed wind variability. These conclusions are based on detailed and extensive monitoring of ultraviolet resonance lines formed throughout the stellar wind, and subordinate lines like Hα which probe the regions close to the star.
Dusty LBV Nebulae: Tracing the Mass Loss History of the Most Massive Stars
Authors: Waters Laurens B.F.M. , Voors Robert H.M. , Morris Patrick W. , Trams Norman R. , de Koter Alex , Lamers Henny J.G.L.M.
Published: July 2016

We present spectra obtained with the Infared Space Observatory (ISO) of the dust shells surrounding several Luminous Blue Variables (LBVs), both in our galaxy and in the LMC. The 20-45 μm spectra of R71, AG Car and Wra 751 show prominent emission features from crystalline silicates. The composition of the crystalline silicates in LBV dust shells is compared to that found in other types of objects, such as (post)-AGB stars and red supergiants (RSG). Both Wra 751 and AG Car have a high ratio of pyroxenes to olivines. This suggests that the grains in both stars experienced very similar processing, but that this processing has lead to a higher abundance of pyroxenes compared to RSG. The dust composition of the three LBVs discussed here suggests dust formation in a cool outflow not unlike those of RSG.
Wolf-Rayet and LBV Nebulae as the Result of Variable and Non-spherical Stellar Winds
Authors: Mac Low Mordecai-Mark
Published: July 2016

The physical basis for interpreting observations of nebular morphology around massive stars in terms of the evolution of the central stars is reviewed, and examples are discussed, including NGC 6888, OMC-1, and η Carinae.
Do Average Hamiltonians Exist?
Authors: Ferraz-Mello S.
Published: July 2016

The word “average” and its variations became popular in the sixties and implicitly carried the idea that “averaging” methods lead to “average” Hamiltonians. However, given the Hamiltonian H = H0(J) + ϵR(θ,J),(ϵ ≪ 1), the problem of transforming it into a new Hamiltonian H* (J*) (dependent only on the new actions J*), through a canonical transformation given by zero-average trigonometrical series has no general solution at orders higher than the first.
The Separatrix Algorithmic Map: Application to The Spin-Orbit Motion
Authors: Shevchenko Ivan I.
Published: July 2016

The planar rotational motion of a non-symmetric satellite in an elliptic orbit is considered. A two-dimensional map is constructed, describing the motion in a vicinity of the separatrix of the synchronous spin-orbit resonance. This map is a generalization of Chirikov’s separatrix map, in the sense that the asymmetry of perturbation is taken into account. Phase portraits of the generalized map perfectly reproduce well-known examples of surfaces of section (first computed by Wisdom et al. (Wisdom et al., 1984), Wisdom (Wisdom, 1987)) of the phase space of spin-orbit coupling for non-symmetric natural satellites. Moreover, it provides a straightforward analytical description of the phase space: analysis of properties of the map allows one to precalculate, by means of compact analytical relations, the locations of resonances and chaos borders, the emergence of marginal resonances, and even to describe bifurcations of the synchronous resonance’s center, though far from the separatrix.
Mean Motion Resonances in The Asteroid Belt
Authors: Nesvorný D. , Morbidelli A.
Published: July 2016

The Kirkwood gaps in the main asteroidal belt (2 – 3.5 AU) coincide with the mean motion resonances with Jupiter (4/1, 3/1, 5/2, 7/3, 2/1). Similarly, several narrower gaps are observed in the outer asteroid belt (3.5 – 4 AU) at places of 11/6, 9/5, 7/4 and 5/3 Jovian resonances (Holman and Murray 1996). As it is now generally accepted, the formation and preservation of these gaps is due to the chaos of the resonant space and efficient ejection of the primordial and collisionaly injected bodies towards high eccentricities and planet-crossing orbits.

The Jovian mean motion resonances are not the most important in what concerns the chaos of the observed (i.e. remaining) asteroid population. It was estimated by Šidlichovský and Nesvorný (1998) that about 40% of known objects have the Lyapunov time less than 105 years. It was later found (Nesvorný and Morbidelli 1998, 1999; Morbidelli and Nesvorný 1999) that the resonances responsible for this chaos are, in decreasing order of importance: 1) three-body resonances with Jupiter and Saturn, 2) exterior resonances with Mars, 3) moderate order Jovian resonances, and 4) three-body resonances with Mars and Jupiter.
A Necessary Condition to the Simultaneous Correction of Celestial Reference Frames and Minor Planets Orbital Elements
Authors: Martínez Usó M.J. , Marco Castillo F. , López Ortí J.A.
Published: July 2016

In order to obtain corrections to orbital elements of minor planets and to determine parameters of rotation of a reference frame, a geometrical model with restrictions in the declination, longitude of the ascending node and argument of the perihelion to minimize a residual function involving all named parameters was presented (Marco et al., 1996, 1997). On the other hand, such rotational model of correction should not modify the semiaxis, eccentricity nor the mean anomaly, so new restrictions on these parameters seem to be necessary. These conditions should reflect the invariability in the size of the orbit and they should be included in the model to complete a consistent set of restrictions.
Observations and Interpretation of Cataclysmic Variables
Authors: Warner Brian
Published: July 2016

Recent observations pertaining to the structure of cataclysmic variables (CVs) are reviewed. Detection of X-rays from CVs, and their behaviour during outbursts, has opened new possibilities of studying the innermost regions of accretion discs. Studies of rapid oscillations continue to be an important source of information (and problems) on the white dwarf and accretion disc.

Several major reviews of the properties of cataclysmic variables have appeared in recent years (Gorbatsky 1975; Warner 1976; Robinson 1976; Wolf 1977; Payne-Gaposchkin 1977a, b; Mallama and Trimble 1978; Gallagher and Starrfield 1978) so there would be no justification at this date in another survey of the entire field of CVs. This review is therefore confined to a discussion of some of the recent observations and their relevance to the problems of understanding the structure and mechanisms in novae and related stars. I have omitted AM Herculis stars as they are discussed by Tapia later in this Conference.
Recent Photometric and Spectroscopic Observations of Southern Dwarf Novae
Authors: Vogt N.
Published: July 2016

This contribution concerns three dwarf novae of special interest: one of them has the longest known orbital period of all dwarf novae (BV Cen); the remaining two variables (Z Cha and EX Hya) belong to the group of the ultra-short periodic cataclysmic binaries. Here only short summaries are given. The detailed results will be published elsewhere, in the case of BV Cen together with J. Breysacher, and in the case of EX Hya together with D. Comte, C. Sterken and W. Krzeminski.
VW Hydri: Photo-Electric Observations during the 1977 May Supermaximum
Authors: Marino B. F. , Walker W.S.G.
Published: July 2016

Photo-electric observations of VW Hydri during the 1977 May supermaximum are presented in the context of an observational model in which supermaxima are triggered by a normal outburst. Two new hump features are identified. A possible explanation of the various superhump types is suggested.
Spectroscopic Observations of Dwarf Novae
Authors: Whelan J.A.J. , Rayne M.W. , Brunt C.C.
Published: July 2016

Dwarf novae spectroscopic work is briefly reviewed and the radiation emitted by the components of the system is discussed. The reasons why the broad, shallow absorption lines arise in the disc, and not in the white dwarf, are assembled. Results are presented for: (a) outburst and quiescent spectra of V436 Cen and VW Hyi; and (b) Z Cha throughout its binary orbit.
Stellar Magnetism: Some Observable, Expected and Suggested Effects of Magnetic Field in Eruptive Varaibles
Authors: Gershberg R.E.
Published: July 2016

Consideration of main stellar-statistical and astrophysical features of th UV Cet-type flare stars leads to a conclusion that the evolution of these variables, as well as other stars, is determined by their masses and chemical composition; a third essential evolution factor is the magnetic field which is responsible for all manifestations of flare activity.

The main physical features of the T Tau-type stars can be understood in the framework of a hypothesis that these stars have large scale magnetic fields. Their strengths are close to a critical level at which the magnetic field and subphotospheric convection begin to interact strongly causing a significant decrease of the photospheric brightness, as in sunspots. Physical and genetic similarities of the UV Cet and T Tau stars are discussed withinth the framework of the idea of the essential role of stellar magnetism.
A Search for TcO in S-Type Long Period Variables
Authors: Davis-Locanthi D.
Published: July 2016

There are still several unidentified bands in S -star spectra, especially at minimum light. Since most S spectra exhibit strong Tel lines, compounds with 0, N, and H might be expected to form in-S star atmospheres. Although much oxygen is already bound with carbon, titanium, and zirconium, to mention a few known compounds, there might also be enough TcO to produce visible absorption.

The spectrum of TcO was, however, unknown until recently (Cherniawsky, 1977). After considerable experimentation with the related spectra of MnO and ReO, Tatum and Cherniawsky succeeded in producing from ammonium pertechnate, NH4TcO4, a molecular spectrum in the 500-720 nm. region. which they believe is due to TcO. Unfortunately, like ReO, this spectrum has a strong continuum. Still, more than a dozen bandheads show on their plates.
Hα Observations of Southern Beat Cepheids
Authors: Barrell Susan L.
Published: July 2016

Recent Ha observations of 10 beat Cepheids have revealed an unexpected degree of Ha emission in several of these stars. An attempt is made to relate the emission feature to the various periodicities associated with beat Cepheids and the possible cause and implications are discussed.
A New Approach to the Determination of the Intrintic Colours of the Cepheid Variable Stars
Authors: Kron Gerald E. , Roach Franklin E.
Published: July 2016

Intrinsic colours have been determined for 247 of the 275 variable stars listed in the “Catalogue of the Light and Colour Curves of Cepheids in the UBV System” by N. Nikolov. Algorithms for computing intrinsic colour are derived from 59 standard stars. The intrinsic colours of the standards were derived from four sets of data from colour excesses deemed reliable in four references. The colours of the standard stars indicate a need for revival of Eggen’s concept of discretee classes of Cepheid Variables. A new principle of least reddening is used to improve the accuracy of the intrinsic colours of normal supergiants, where these are needed, and to test our derived colour excesses for the 247 Cepheids.
Production of New and Revised A.A.V.S.O. Charts
Authors: Ford Clinton B.
Published: July 2016

A “new charts program” for the Americal Association of Variable Star Observers was instigated in 1966 via the gift to the Association of the complete variable star observing records, charts, photographs, etc. of the late Prof. Charles P. Olivier of the University of Pennsylvania (USA). Adequate material covering about 60 variables, not previously charted by the AAVSO, was included in this original data, and was suitably charted in reproducible standard format.

Since 1966, much additional information has been assembled from other sources, three Catalogs have been issued which list the new or revised charts produced, and which specify how copies of same may be obtained. The latest such Catalog is dated June 1978, and lists 670 different charts covering a total of 611 variables none of which was charted in reproducible standard form previous to 1966.