bluuebunny/crossref_metadata_2025 huggingface dataset:
H-Alpha Emission in Hot Degenerates and OB Subdwarfs
Authors: Reid Neill , Wegner Gary
Published: July 2016

Based on observations obtained using the 60-inch telescope at Palomar Observatory which is jointly owned by the California Institute of Technology and the Carnegie Institution of Washington and on observations obtained with the 200-inch Hale telescope which is owned by the California Institute of Technology.

The intial observations of white dwarf stars and their immediate precursors, the hot subdwarfs, suggested that these stars possess the simplest (and, aesthetically, the most pleasing) spectra of any astronomical object. The high gravity leads to the spectrum being dominated, in the most stars, by broad lines of either hydrogen or helium, depending on the composition of the photospheric layers, with a few stars exhibiting lines from both species. However, the more detailed observations of recent years have revealed a higher degree of complexity. In particular, absorption lines of high excitation species (N V, C IV, etc.) have been detected in the ultraviolet spectra of several hot white dwarfs (Bruhweiler & Kondo, 1982) and, most recently, high resolution optical spectra have shown that one of the latter stars, the hottest known DA, G191-B2B, exhibits significant emission in the core of the H-alpha absorption line (Reid &: Wegner, 1988). Following up the latter observation, we have obtained high resolution spectra of a number of hot subdwarfs, with temperatures ranging from ~ 20,000K to more than 60,000 K. Most of these stars also exhibit Baimer emission, at Hβ as well as Hα in at least one case. We suggest the temperature reversal in the stellar atmosphere may be a function of the He/H ratio at the level of the photosphere.
Gravitational Redshifts and the Mass-Radius Relation
Authors: Wegner Gary
Published: July 2016

The gravitational redshift is one of Einstein’s three original tests of General Relativity and derives from time’s slowing near a massive body. For velocities well below c, this is represented with sufficient accuracy by:

As detailed by Will (1981), Schiff’s conjecture argues that the gravitational redshift actually tests the principle of equivalence rather than the gravitational field equations. For low redshifts, solar system tests give highest accuracy. LoPresto & Pierce (1986) have shown that the redshift at the Sun’s limb is good to about ±3%. Rocket experiments produce an accuracy of ±0.02% (Vessot et al. 1980), while for 40 Eri B the best white dwarf, the observed and predicted VRS agree to only about ±_5% (Wegner 1980).
Critical Mass for Merging in Double White Dwarfs
Authors: Hachisu Izumi , Kato Mariko
Published: July 2016

We examine whether or not double white dwarfs are ultimately merging into one body. It has been argued that such a double white dwarf system forms from some intermediate-mass binary stars and will merge due to the gravitational radiation which decreases the separation of binary. After filling the inner critical Roche lobe, the less massive component begins to transfer its mass to the more massive one. When the mass transfer rate exceeds a some critical value, a common envelope is formed. If the common envelope is hydrostatic, the mass transfer is tuned up to be a some value which depends only on the white dwarf mass, radius, and the Roche lobe size. The mass transfer from the less massive to the more massive components leads the separation to increase. On the other hand, the gravitational radiation effect reduces the separation. Which effect wins determines the fate of double white dwarfs, that is, whether merging or not merging. Since the formula of the gravitational radiation effect is well known, we have studied the mass accretion rate in common envelope phase of double white dwarfs assuming the Roche lobe size is as small as 0.03 R⊙ or 0.1 R⊙.
Evolution of Low-Mass Helium Dwarfs in Interacting Binaries: Application to 4U1820-30
Authors: Nelson Lorne A. , Joss Paul C. , Rappaport Saul
Published: July 2016

A number of evolutionary scenarios have been proposed that lead to the formation of binary systems consisting of a degenerate dwarf in orbit with a neutron star. In fact, most degenerate dwarfs in close-binary systems are probably the cores of evolved stars whose envelopes have been stripped by one or more episodes of common-envelope evolution. Once the envelope has been removed, the newly exposed core of the giant will have an effective temperature and radius that are considerably larger than the corresponding quantities in an older, highly degenerate dwarf. It is important for at least two reasons to evaluate the subsequent cooling history of such objects: (i) For detached binaries, we want to be able to infer from the current effective temperature and luminosity of the degenerate dwarf the elapsed time since the core of its progenitor giant was exposed, (ii) For semi-detached binaries, we must know the evolution of the radius of the degenerate dwarf in order to compute important relationships among the orbital period and its rate of change, the mass of the degenerate dwarf, and the mass-transfer rate.
The Frequency of Cepheid Binaries
Authors: Russo G.
Published: July 2016

We summarize the methods now available to detect the presence of companions to Cepheids, and then we analyze the results of the application of the recent photometric method proposed by Fernie (1980). If applied to the set of VBLUW observations of southern Cepheids carried out by Pel (1976), this method gives a frequency of about 25%, which is consistent with the more recent spectroscopic determinations (Gieren, 1981). The importance of the IUE satellite to directly observe the U flux emitted by the B-companion is emphasized.
On the Group Formation of Stars in Stellar Associations
Authors: Mirzoyan L.V.
Published: July 2016

The discovery and study of stellar associations by Ambartsumian (1947, 1954 a) proved two fundamental points regarding the star formation process, e.g., Mirzoyan, 1976. One of them is that the formation process still continues in the present evolution of the Galaxy, and this thesis is not disputed now. According to the second, stars form as physical groups of multiple stars and star clusters, which become stellar associations during the initial phases of their evolution.
The Age of the Triple System HD 165590
Authors: Bakos Gustav A. , Tremko Jozef
Published: July 2016

It has been found that the close spectroscopic pair of this system consists of a G type primary and a late type secondary, which most likely is a T Tauri star. As such, the system is semidetached and a mass transfer takes place between the components.
On the Distribution of Young Spectroscopic Binary Stars Over the Major Semiaxes of their Orbits
Authors: Popova E.I. , Tutukov A.V. , Shustov B.M. , Yungelson L.R.
Published: July 2016

About 60% of stars of the disc population in our Galaxy are close binary systems (CBS). Half of the known CBS are spectroscopic binary stars (Kraitcheva et al., 1978).

To know the distribution of a correlation between the masses of CBS components and semiaxes of their orbits is necessary for the investigation of the origin and evolution of CBS. For such statistical investigations, a catalogue of CBS was compiled at the Astronomical Council. The catalogue is based on the 6th Batten catalogue (Batten, 1967), its extensions (Pedoussant and Ginestet, 1971; Pedoussant and Carquillat, 1973) and data published up to the end of 1980 (Popova et al., 1981). Now it is recorded on magnetic tape and contains data on 1041 spectroscopic binaries; 333 of them are stars with two visible spectra. The latter are mostly systems prior to mass exchange and the distribution of physical parameters in these systems reflects the distribution and presumably conditions at the time of formation. Using some assumptions, we can obtain for spectroscopic binaries masses of the components M1 and M2 (or the ratio q = M1/M2) and semiaxes of their orbits. Masses of components with the known sin i were obtained by the usual technique; when sin i was not known, masses were estimated from the spectra. We shall discuss here the distribution of CBS in the M-a plane.
Mass Loss in Algol-Type Stars: Implication on their Evolutionary Stage
Authors: Mardirossian F. , Giuricin G.
Published: July 2016

We have examined the observational data of 102 Algols in order to clarify the implications on their evolutionary scenario of various assumptions concerning mass and angular momentum loss during mass transfer. We have found that case B mass exchange is strongly favoured for Algols of relatively low total mass (~ M < 7 Mʘ), while case A predominates, though not so widely as expected in Algols of higher total mass.
Structural Models for Beta Lyrae-Type Disks
Authors: Wilson R.E.
Published: July 2016

Equilibrium structural models are computed for a thick, selfgravitating disk in a binary system. Accretion onto the star is limited by the star's rapid rotation (the system is a double-contact binary). The potential formulation is taken from a previous paper, and represents the gravitational potential as that of a massive wire. Corrections to the stellar structure differential equations for the distorted geometry are applied, and the equations are integrated and solved by the fitting point method. The energy is supplied by viscosity. Energy transfer is by convection, and is appreciably superadiabatic throughout the disk. A mass of 0.5 Mʘ is assumed. Representative results are: “central” temperature, 67000 K; “central” pressure, 5 x 1011 dynes/cm2; “equal volume” radius, 17 Rʘ; luminosity, 5 x 103 Lʘ. The model “radius” is in excellent agreement with the observational value for β Lyrae. The model luminosity is slightly higher than the available rate of expenditure of gravitational energy, indicating that a lower disk mass (perhaps 0.25 Mʘ) should be tried.
Origin and Evolution of Contact Binaries of W UMa Type
Authors: Rahunen Timo , Vilhu Osmi
Published: July 2016

Using angular momentum loss estimates from single star studies, it is shown that detached binaries are good candidates as progenitors of contact binaries. Three theories constructed for contact binary evolution (DSC, TRO and AML, see Fig. 1) are discussed. The DSC and TRO theories require a contact binary formation mechanism which produces unequal components (fission) while the AML theory can start from equal components (initially detached binaries). In all theories the end-product is a single star.

The stability of unequal entropy models was studied using a formula (2) which couples the energy transfer with the depth of contact and with the entropy difference. The models experience cyclic behaviour on a time scale of 106-107 years (Fig. 2) and the contact never breaks even on the nuclear time scale. This is the important consequence of a formula of type (2). Similar behaviour (with similar formula) is expected also for TRO models and even for DSC models if the discontinuity can be preserved during one cycle period.

The DSC and TRO theories, which at first sight look quite different, are in fact complementary. The most probable contact binary theory is perhaps a suitable combination of all three. In this theory angular momentum loss is the new and important factor which may manifest itself in the UV- and X-ray activity observed in W UMa stars.
On the Spatial Density of W UMa Type Stars
Authors: Budding E.
Published: July 2016

Attention is directed to the anomalous incidence of W UMa stars, which can be regarded as coming from not only a disproportionately large accumulation among close binary systems with primaries later than around mid-F spectral type, but also as a deficit at early types.

Doubt is placed on the necessity of a straightforward identification of W UMa type light curves with contact binaries; and this allows some reduction in the estimated spatial incidence of contact binaries, from the figure of Van't Veer (1975), to 8 x 10-4 of all stars.

The incidence is considered, with the aid of some simplifying assumptions, as an example of the general evolution of the distribution of binary systems in the primary spectral type - orbital period plane, subject to some known mechanisms of binary evolution.
Remarks on the Evolutionary Status of Cataclysmic Variables
Authors: Vogt N.
Published: July 2016

The basic binary parameters (masses, system dimensions) of all cataclysmic variables are essentially identical, but there is a great variety in the outburst behaviour. Since there is no evident physical reason for this, it is suggested that nova and dwarf nova variability are periodically repeating states of activity of the same binary. After the nova eruption first follows a postnova state (very low disc mass), later the dwarf nova states BV Pup, U Gem and Z Cam (slowly increasing disc mass and outburst frequency, finally standstills), and finally the UX UMa state (permanent standstill) which is terminated by a new nova outburst. The mass of the disc increases continuously during this cycle. Also the mean mass transfer and accretion rates vary slowly from 1018 g s-1 at beginning and end of the cycle to 1016 g s-1 at mid-cycle, as a U Gem star. The nova outburst is understood in terms of a thermonuclear runaway near the surface of the white dwarf, the dwarf nova outburst is due to intermittent accretion of gas which was accumulated in the outer disc during quiescence (several arguments in favor of this model are given). The time interval between consecutive nova outbursts is of the order of 105 years. The secular evolution of a cataclysmic binary is characterized by a period decrease from 10h to 1h5 in a time scale of 1010 years. The star probably passes the period gaps in the ultra-short period domain in form of no-contact configurations.
Variability of Soft X-Ray Emission of Ex Hydrae Observed with Einstein Observatory
Authors: Kruszewski A. , Mewe R. , Heise J. , Chlebowski T. , van Dijk W. , Bakker R.
Published: July 2016

The cataclysmic variable star EX Hydrae has been observed with the High Resolution Imager (HRI) and the Imaging Proportional Counter (IPC) onboard the Einstein Observatory. The X-ray position is coincident within 3 arcsec of the optical position as measured on Schmidt survey plates. During a 15 1/2 hour observation with IPC we have searched for a modulation of the X-ray flux. Strong evidence for a 67 min period (one of two known optical periods) has been found in the energy range 0.1-3.5 keV with the IPC. The time dependence of modulations is used to discuss a model and evolutionary status of this close binary system.
A review of radar observations of Saturn’s rings
Authors: Ostro Steven J . , Pettengill Gordon H.
Published: July 2016

Saturn’s rings are the most distant radar-detected planetary entity, and the only radar-detected ring system. Neither distinction is likely to be reinquished during this century.

Ten years have passed since the initial detection of radar echoes from Saturn’s rings (Goldstein and Morris, 1973) shattered prevailing notions that typical ring particles were 0.1 to 1 mm in size. (The single fact that microwave radar echoes are detectable requires a substantial density of particles larger than about one centimeter.) During the past decade, additional radar studies of the rings have been conducted, using the λ13.5-cm and λ12.6-cm systems at the Jet Propulsion Laboratory’s Goldstone Tracking Station and the λ112.6-cm system at the National Astronomy and Ionosphere Center’s Arecibo Observatory.
Inclinations of the Uranian rings
Authors: French Richard G. , Elliot James L.
Published: July 2016

A kinematic model of the orbits of the nine known Uranian rings was fitted to available stellar occultation data, including a new set of times from the 26 April 1981 occultation obtained from the Anglo-Australian Telescope (AAT). The results of the fit reveal that seven of the nine rings have significant inclinations with respect to the equatorial plane of Uranus. The inclinations are typically a few hundredths of a degree.
Rings around Neptune?
Authors: Elliot James L.
Published: July 2016

Observation of two stellar occultations by Neptune in 1981 led to an upper limit of 0.07 on the optical depth of any equatorial rings with radii greater than 31,400 km. An occultation by Neptune on 15 June 1983 will provide an opportunity for a more extensive search for rings.
Structure and dynamics of Saturn's rings as seen by the Voyager stellar occultation
Authors: Esposito L.W.
Published: July 2016

The stellar occultation of δ Scorpii by Saturn's rings shows radial structure in Saturn's rings down to the resolution element of ~100m. Density waves, embedded moonlets, and other proposed mechanisms are insufficient to explain the observed structure. A limit of less than 100 density waves are likely to be found in the rings in the current data. Unresolved waves do not seem to play a major role, either. A detailed search and histogram of optical depth in the outer B ring show no evidence of embedded moonlets. The mass of Saturn's rings is 5(±3) x 10-8of Saturn's mass. Power spectra of the rings show no dominant individual wavelengths: we do not see any preferred size for radical structure in the rings. A straightforward comparison of earth-based photometry and the viscosity and mass density of the rings inferred from density wave observations leads to a model of the rings that is many-particles thick. The vertical thickness of the rings would be about 50 m.
The eccentric ringlet at 1.29 RS
Authors: Porco C. , Borderies N. , Danielson G.E. , Goldreich P. , Holberg J.B. , Lane A.L. , Nicholson P.D.
Published: July 2016

We present preliminary results of an examination of the eccentric ringlet near 1.29 R, in Saturn's inner C ring. Situated near the Titan 1:0 apsidal resonance, this feature provides an opportunity to study the behavior of a ring under the influence of both the gravity field of a major planet and the potential of an external satellite.

The data sets used for this analysis consisted of seven Voyager images of this ringlet, ranging in resolution from 60 to 5 km/pixel, plus data obtained from three UVS stellar occultations and one Radio Science occultation. Three observations occurred within a day of Voyager 1 closest approach and seven within 5 days of Voyager 3 closest approach. The Voyager encounters were separated by 286 days. Of the seven Voyager images used, only the three highest resolution frames were corrected for geometric distortion. Therefore, the results presented here must be considered preliminary.
Micron-size particles detected near Saturn by the Voyager plasma wave instrument
Authors: Gurnett D.A. , Grün E. , Gallagher D. , Kurth W.S. , Scarf F.L.
Published: July 2016

During the Voyager 2 Saturn encounter the plasma wave instrument detected a region of intense impulsive noise centered on the ring plane at a distance of 2.88 Saturn radii, slightly outside of the G ring. The noise has been attributed to small micron-size particles hitting the spacecraft. Investigation of various coupling mechanisms suggests that the noise was produced by impact ionization of particles striking the spacecraft body, thereby releasing a cloud of charge particles, some of which are collected by the plasma wave antenna. Reasonably reliable estimates of the charge yield per unit mass are available from laboratory impact ionization measurements. Based on the assumption that the voltage induced on the antenna is proportional to the mass of the colliding particle, a method is developed to determine the mass and size distribution of the particles from the rms voltage of the induced noise and the impulse rate. The results obtained show that the mass distribution varies as m-3, and that most of the particles detected had radii in the range from 0.3 to 3 µ meters. The effective north-south thickness of the particle distribution is 106 km. The mass distribution function derived from these data is shown to be in reasonable agreement with optical depth estimates obtained from Imaging measurements and absorption effects detected by energetic charged particle measurements.
An Earth-based attempt to detect S.E.D. at 21 centimeters
Authors: Lecacheux A. , Biraud F.
Published: July 2016

We tried to observe Saturn Electrostatic Discharges at 1420 MHz using the radiotelescope at Nancay, first during Saturn 1981 opposition, the during Voyager 2 fly-by. The obtained flux upper limit indicates a spectrum steeper than about f**(-1).
Resonance identifications in Saturn’s rings
Authors: Wiesel M.E. , Franklin F.A.
Published: July 2016

When Saturn’s oblateness perturbations are included, a single classical resonance splits into a resonance band structure. We have derived expressions for resonance location, libration region width, and the maximum librator range. We compare these predictions to areas of the C and B rings, the Cassini division, and the F ring, and offer some thoughts on possible mechanisms involved.
Evolution of collisional systems
Authors: Brahic André
Published: July 2016

The dynamical evolution of planetary discs in the gravitational field of an oblate planet and a satellite is numerically simulated.
A simple model of saturn’s rings – revisited
Authors: Henon M.
Published: July 2016

We describe a crude model of the rings based on a power-law distribution for particle size. The parameters of the model are determined from apparent thickness and radar-radio observations. A number of quantities are derived: mass of the rings, mean surface density, size of largest particle, time scale for dynamical evolution, minimal size of gap-forming particles, number and size distribution of the gaps, kinematic viscosity. Comparisons with observations and with numbers derived in other ways meet with mixed success. The most serious problem lies in the derived time scale for the radial spreading of the disk, which is less than 10 million years.
Structure and dynamical processes in Saturn's rings
Authors: Terrile Richard J.
Published: July 2016

The Voyager encounters have provided the first high resolution look at the Saturn ring system. Images of the rings reveal several classes of dynamical processes active in creating and maintaining large scale structure. These classes include variable ring features attributable to the influence of external satellite resonances, ring structure induced by the shepherding effects from external and possibly internal satellites, smooth eccentric ringlets contained within clear gaps in the ring and the dynamics of spokes which may represent a transient ring atmosphere.
Diffusion instability in a bi-modal disc
Authors: Ward W.R. , Harris A.W.
Published: July 2016

A simplified model of radial diffusion in a particle disc with a bi-modal size distribution is presented. The large particle component excites the small particles’ dispersion velocity via gravitational scattering. The resulting small particle viscous stress goes through a maximum near τ ~ √3 Such a stress profile promotes the development of high and low optical depth zones. The resulting ringlet appearance is due primarily to the distribution of small particles, which produce most of the optical depth but may constitute only a minor portion of the system’s mass.
Weak dynamical effects in the Uranian ring system
Authors: Freedman Adam P. , Tremaine Scott , Elliot James L.
Published: July 2016

A number of weak gravitational forces were examined for their kinematic effects on the Uranian ring system, in an attempt to account for residual errors of ~2 km in the ring positions and a few times 10-3deg/day in the apse precession rates. The principal conclusions are as follows: (1) perturbations by the five known satellites are too small to have observable effects with the best current estimates of the satellite masses. (2) Limits can be set on the masses of inter-ring “shepherd” satellites from their influence on precession rates and their radial perturbations on the rings. For example, the maximum mass of a shepherd satellite between rings 4 and 5 is ~ 1019gm. (3) Using the best available ring parameters, there is no convincing evidence that the rings are associated with resonances with known satellites. The only close association is of rings 5, α and γ with three-body resonances due to Miranda and Ariel. It is more likely that the putative shepherd satellites may occupy resonances. (4) The known satellites can cause anomalous residuals by changing the position of Uranus relative to the system barycenter during the occultation. The maximum change, so far, during the 1977 March 10 event, was 1.6 km. This effect will be investigated with the MIT Uranus ring model.
Stochasting modeling of planetary ring systems
Authors: Hart Robert W.
Published: July 2016

This paper models maximum entropy configurations of idealized gravitational ring systems. Such configurations are of interest because systems generally evolve toward an ultimate state of maximum randomness. For simplicity, attention is confined to ultimate states for which interparticle interactions are no longer of first order importance. The planets, in their orbits about the sun, are one example of such a ring system. The extent to which the present approximation yields insight into ring systems such as Saturn's is explored briefly.
Dynamics of neutral small particles
Authors: Mignard F.
Published: July 2016

The dynamics of small grains are reviewed when the radiation pressure forces are added to the gravitational attraction.

In the first section we attempt to summarize the studies dealing with the interaction matter - radiation. The problem consists in the computation of the momentum transfer between a grain and the radiation field. The flie's theory of scattering is used for this purpose and the results come out as the value of the ratio of the radiation pressure force to the gravitational force for various material of different sizes.

The motion of a grain in an heliocentric orbit is discussed through the second section and includes conditions for a particle to be ejected from the solar system, abrupt change of the orbital elements due to fragmentation along with continuous variation generated by sublimation and sputtering. Likewise the Poynting- Robertson drag is considered and some results are given concerning the lagrangian points L4 and L5 when radiation forces are taken into account.

The last section deals with the motion of a grain about a planet. The solution of this problem has recently been updated and the orbital evolution of a grain is presented for a sphericla planet. In order to make the solution relevant for the planetary rings it is adapted to allow for the planet's oblateness.
The formation of spokes in Saturn's rings
Authors: Morfill G.E.
Published: July 2016

Starting from the assumption that electromagnetic interactions are in some way related to the formation of spokes, it is shown that energy constraints and spoke observations suggest an evolutionary spoke formation model rather than a sudden imprint of an unspecified phenomenon. It is further shown that relatively small (100's km) plasma clouds, interacting both with the magnetosphere and with small dust particles from the ring, can obtain high radial velocities. The “dynamo” which drives the plasma cloud, is a direct result of the difference in the azimuthal velocity components of the corotating plasma and the Keplerian (charged) dust, with its associated azimuthal current. In its wake, the plasma cloud leaves an almost radial trace of sub-micron sized dust elevated above (or below) the ring plane. Finally, the question of the origin of the plasma clouds is addressed. There could be several processes, e.g. meteorite impacts, electric discharges in the ring, particle acceleration along parallel electric fields etc. Each process has its own characteristic signature, and more work (analysis of measurements and theory) is needed to differentiate between them.
The gravito-electrodynamics of charged dust in planetary ring systems
Authors: Mendis D.A. , Hill J.R. , Northrop T.G.
Published: July 2016

Solid bodies within planetary magnetospheres could be charged, under a variety of circumstances, to sizable electrostatic potentials. While this charging has only physical effects on the larger bodies (e.g., electrostatic levitation and blow-off of fine loose dust from their surfaces), it can have both physical (e.g., electrostatic erosion and disruption) and dynamical effects on the smaller (micron and sub-micron sized) dust grains. Here we will confine ourselves to the dynamics of such small grains moving under the combined influence of the planet's gravitational and the electromagnetic forces within the co-rotating regions of planetary magnetospheres, where the observed ring systems are located.
The formation of the terrestrial planets from lunar sized planetesimals
Authors: Aarseth Sverre J. , Lecar Myron
Published: July 2016

We have performed a numerical simulation of the formation of the terrestrial planets from lunar sized planetesimals. The simulation was confined to a plane and included the gravitational forces between planetesimals as well as the Sun. When two planetesimals physically collided, they were merged into one.

Initially, two hundred moons were distributed with uniform surface density, from 0.5 to 1.5 AU. The eccentricities were zero at the start: the average eccentricity grew to 0.06 in 10,000 years. After 65,000 years we were left with five bodies, the two largest of which each had 3/4 of an Earth mass. This system is extremely stable to further evolution and an additional mechanism may be required to reduce the number of bodies to one or two.
Asteroid compositional «rings»: clues to the compositions of primordial planetesimals in the middle solar system
Authors: Tedesco E.F.
Published: July 2016

It has recently been established that the distribution of asteroid taxonomic types at distances between 2.1 and 5.3 astronomical units is highly structured. There are four major, overlapping but nevertheless compositionally distinct, “rings” of asteroids present within this range of heliocentric distance. These “rings”, within which ~ 80% of each of four major taxonomic types (S, C, P, and D) fall, are centered at 2.6 (0.7), 2.9 (0.8), 3.4 (0.7), and 4.6 (1.5) AU respectively, where the numbers within parentheses are the ring “widths” in AU. The overall physical resemblence between the asteroid “rings” and planetary rings is poor; physically the asteroid belt more closely resembles a debris strewn satellite system. This structure is consistent with these objects having been formed directly from the solar nebula at, or near, the heliocentric distances at which we find them today. Once the mineralogy of these taxonomic types is firmly established, and complications arising from post-accreationary metamorphism are dealt with, they may be used as probes of physical conditions in the early solar system. In particular, the identification of primordial planetesimals will allow us to obtain a first-hand look at the siblings of the planetesimals responsible for the final stage of planetary accretion.
Radio Supernovae: The Detection of SN 1961V in NGC 1058
Authors: Cowan John J. , Henry Richard B. C. , Branch David
Published: July 2016

We report the radio detection of supernova 1961v in NGC 1058. SN 1961v has a spectral index of -0.4 ± 0.1. At the distance of NGC 1058, the absolute monochromatic luminosity of this source is comparable to that of Cas A. A second nonthermal source with a spectral index of -0.3 ± 0.1 was also detected in NGC 1058 and is likely to be a remnant of a supernova that was not optically detected. The two radio sources, and two optically faint H II regions that coincide with the radio sources, are separated by only 3.5".
Instabilities Driven in Young Supernova Remnants by Electron Heat Conduction
Authors: Bedogni R. , D’Ercole A.
Published: July 2016

Adiabatic models of supernova remnants (SNRs) show very large temperature gradients. The effect of thermal conduction on the Sedov solution was studied by a number of authors (Solinger et al., 1979; Cox and Edgar, 1983; Cowie, 1977).

The observations show, however, that young SNRs such as SN 1006 (Hesser and van den Bergh, 1981) and SN 1572 (Strom, Goss and Shaver, 1982) are in an intermediate state between free expansion and the Sedov phase. In these cases stellar matter cannot be neglected. Following Chevalier (1982), the freely expanding ejecta of a Type I SNR can be modeled in such a way that the inner 4/7 of the mass have constant density and the outer 3/7 have a ρ∝r−7 profile (the "ramp"). The interaction of the ejecta with the uniform circumstellar medium (CSM) gives rise to a pair of shocks. As long as the reverse shock is within the r−7 part of the density profile, the interaction region is described by a self-similar solution (Chevalier, 1982). Such a solution holds for an adiabatic single fluid; the temperature gradient, however, is so large that it may give rise to a quite high heat flux.
Adiabatic Supernova Expansion into the Circumstellar Medium
Authors: Band David L. , Liang Edison P.
Published: July 2016

We perform one dimensional numerical simulations with a Lagrangian hydrodynamics code of the adiabatic expansion of a supernova into the surrounding medium. The early expansion follows Chevalier’s analytic selfsimilar solution until the reverse shock reaches the ejecta core. We follow the expansion as it evolves towards the adiabatic blast wave phase. Some memory of the earlier phases of expansion is retained in the interior even when the outer regions expand as a blast wave. We find the results are sensitive to the initial configuration of the ejecta and to the placement of gridpoints.
Shocked Molecular Gas in the Supernova Remnant IC 443: Models with an Enhanced Ionization Rate
Authors: Mitchell George F.
Published: July 2016

The high molecular abundances seen in IC443 may be due to hot chemistry in shocked gas or to an increase in the cosmic ray ionization rate. New calculations reported here show that shock chemistry dominates over the relevant short time scale.
[Ni II] Emission in Supernova Remnants
Authors: Henry Richard B.C. , Fesen Robert A.
Published: July 2016

Combining new spectrophotometric data on the Orion and Crab Nebulae with detailed calculations, we show that strong [Ni II] λ7378 emission observed in numerous SNR’s may be associated with gas having Ne > 50,000 cm−3.
The Interaction of the Supernova Remnant VRO 42.05.01 with its HI Environment
Authors: Landecker T.L. , Pineault S. , Routledge D. , Vaneldik J.F.
Published: July 2016

VRO 42.05.01 (G166.0+4.3) is a SNR which has broken into and re-energized an old interstellar cavity. Observations of HI in a field containing the SNR show features associated with it. An expanding shell of mass ∼40 M⊙ is associated with the semi-circular shell of the SNR. The cavity, which the SNR has re-energized, is seen in the HI. A cloud of HI of mass ∼25 M⊙ has apparently been hit by the shock and has been accelerated by the post-shock flow.
Two Remarkably Thin CO Filaments Toward the Supernova Remnant G109.1-1.0
Authors: Tatematsu K. , Fukui Y. , Iwata T. , Nakano M.
Published: July 2016

We observed the semicircular supernova remnant G109.1-1.0 in the J = 1-0 transition of CO with the Nobeyama 45-m radio telescope. It is found that two remarkably thin molecular filaments delineate the inner boundary of the X-ray jet feature in this remnant. These filaments seem to have experienced evaporation due to the hot gas in the remnant.
A Newly-Recognised Galactic Supernova Remnant with Shell-Type and Filled-Centre Features
Authors: Barnes Peter J. , Turtle A.J.
Published: July 2016

While the number of galactic supernova remnants (SNRs) now known is fairly large (>150), the subset among these that are known to resemble the Crab Nebula is still distressingly small, about 15 or so (Green, 1984). Thus any object that can be unambiguously included in this exclusive club forms a valuable addition to our knowledge of this class. We report here observations of a newly recognised nonthermal galactic object, G18.94-l.06, having all the hallmarks of the classical shell-type SNRs, while also appearing to have a filled-centre component located inside the shell. Among the known Crab-like remnants, about one third show this dual nature (Green, 1984). This diagnosis of G18.94-1.06 is supported mainly by the variations in spectral index α (Sν∝ να) across the source, as seen between the two observation frequencies, 408 MHz and 5.0 GHz.
SNR Polarization and the Direction of the Magnetic Field
Authors: Milne D.K.
Published: July 2016

At the CSIRO Division of Radiophysics we are currently engaged in a program to map polarization in SNRs at 8.4 GHz. These results are compared with earlier Parkes 5 GHz maps to deduce the direction of magnetic field, Faraday rotation and depolarization.
Barrel-Shaped Supernova Remnants
Authors: Kesteven M.J. , Caswell J.L.
Published: July 2016

We argue that the majority of radio supernova remnants have a three-dimensional distribution of emissivity which is barrel shaped, with little emission from the end-caps. We examine some mechanisms which could produce this distribution.
Infrared Spectroscopy and Mapping of IC443
Authors: Wright Gillian S. , Graham James R. , Longmore Andrew J.
Published: July 2016

We present infrared (IR) spectroscopy and imaging of the supernova remnant IC443. [FeII] 1.644µm, Brackett γ and H2 1-0 S(l) were detected. The most striking feature of the spectra is the high [FeII] 1.644µm/Brackett γ ratio, which is typically ~30. We argue that this ratio is due to shock excitation. Two 5’×3’ maps of the remnant in the 1.644µm [FeII] line are used to study the line excitation. The IR [FeII] line is a sensitive probe for regions of shocked gas which is especially useful where the extinction is high, or the shocks are too slow to excite optical lines.
Luminosity of Evolving Supernova Remnants
Authors: Cioffi D.F. , McKee C.F.
Published: July 2016

We present an analytic kinematic model for the evolution of a supernova remnant beginning with the Sedov-Taylor adiabatic stage and continuing through the radiative stage. Using this model, we obtain the luminosity of the radiative shock and the hot interior.
High-Resolution Radial Velocity Mapping of Optical Filaments in Evolved Supernova Remnants
Authors: Greidanus H. , Strom R.G.
Published: July 2016

We report on observations of the kinematical structure of optical filaments in evolved supernova remnants, using an imaging Fabry-Perot interferometer. The radial velocity characteristics as seen in [OIII] λ5007 emission in one area in the Cygnus Loop are described, where four kinematically different components contributing to the emission can be recognized.
Supershells with Induced Large-Scale Supernovae Formation
Authors: Kolesnik I.G. , Silich S.A.
Published: July 2016

We propose a model of expanding supershells regulated by star formation which is induced in HI superclouds by similar shells from a previous evolutionary stage. Compression of pre-existing cloudlets by such shells triggers the formation of massive stars which then
explode at the end of their evolution as supernovae. Efficiency of induced supernovae formation must be less than 1% to fit the observational properties of supershells.
A Statistical Study of the Correlation of Galactic Supernova Remnants and Spiral Arms
Authors: Li Zongwei , Wheeler J. Craig , Bash Frank N. , Jefferys William H.
Published: July 2016

A statistical study of the correlation of Galactic supernova remnants with spiral arms and the disk is presented. SNR apparently have a larger radial scale length than disk stars. We estimate that only about 10 percent of the Galactic SNR have been detected.
Star Formation, Supernovae and the Structure of Disk Galaxies
Authors: Dopita Michael A. , Stromlo Mt.
Published: July 2016

A physical model for bi-modal star formation and the structure of the interstellar medium and the self-regulating evolution of disk galaxies is presented. Stars heavier than about one solar mass are produced as a result of collisions of molecular clouds or in cloud crushing events whereas low-mass stars are produced at a steady rate in dense molecular clouds and the T-Tauri winds resulting maintain the support of these clouds against rapid collapse and fragmentation. Supernova explosions and stellar winds associated with the massive stars maintain the phase structure, and the scale height of the gas. The collective effects of these energetic processes may create a hole in the disk gas, and allow a galactic wind of metalenriched gas to develop.
Properties Of Cool Stellar Components in S-Type Symbiotic Stars
Authors: Taranova O.G. , Yudin B.P.
Published: July 2016

In 1975 Webster and Allen (1975) divided all symbiotic stars into two groups-those in which the 1-4μm continuum show only the presence of a cool star (type S),and those in which dust emission dominates (type D). With the exception of some of yellow symbiotic stars, the dust presence in others correlates with the spectral type of their cool components. That is why one can say that S-type symbiotics contain red giants with spectral type earlier than M6-M7.

At the IAU Colloq. N 7Q Allen (1982) noted that it is difficult to escape the conclusion that symbiotic stars contain normal cool giants. Nowadays it is certaiu to be correct because the modern observations of S-type symbiotic stars have not yet discovered any specific distinctions between their cool stellar components and normal red giants. At the same time it should be noted that some of these, for example, Z And, CI Cyg may be interacting binaries in which the cool component apparently fields its Roche lobe and unstable accretion of gas from the red giant onto its hot companion leads to the out bursts of the latter (Kenyon and Webbink 1984; Yudin 1987).
Polarimetry of Symbiotic Stars
Authors: Khudyakova T.N.
Published: July 2016

In an effort to bring out the variations in the polarization parameters of symbiotic stars that result from their binary character, polarimetry in R, I IR bands was initiated at the Byurakan station of the Leningrad University Observatory in 1974. In addition, U, B, V measurements for some stars have been made. Three telescopes have been used, with mirror apertures of 48, 48, 62 cm.
Slow and Rapid Changes of the Radial Velocities in the Symbiotic Binary CH Cygni
Authors: Skopal A.
Published: July 2016

In the period 1982–1986, new 98 radial velocities (RVs) were determined (at the figures denoted by □). All spectrograms were obtained at the Toruń Observatory. RVs were measured at the Skalnaté Pleso Observatory. The main results are summarized in the figures 1-3. The phase is determined from the middle position of the hot component eclipse (JD 2 446 272) and from the minima difference observed in U light curve (5700d) (Mikolajewski et al., 1987).

Slow changes of the RVs of the absorption components of ionized metals reflect the orbital motion of the hot component only between the phases 0.7 and 0.0. The rapid changes are observed mainly between the phases 0.8 and 0.9. They are created by combination of the emission red wing with the absorption component (Skopal et al., 1987). RVs of the cool component are in antiphase (Tomov and Luud, 1984).
Continued Radio Activity from CH Cygni
Authors: Taylor A.R. , Seaquist E.R. , Kenyon S.J.
Published: July 2016

Following the discovery of the radio outburst and jet formation from CH Cygni in 1984, continued radio monitoring has been carried out with the Very Large Array. We present the preliminary results of these observations, including a high resolution image of the jet in 1986 – 1.5 years after the initial outburst. The star has remained active in the radio, undergoing at least one additional outburst. The radio jet has continued to expand and shows evidence of multiple episodes of ejection along the same axis.
A Review of the R Aquarii System
Authors: Michalitsianos A.G. , Kafatos M.
Published: July 2016

The spatially resolved nebula that characterizes the D–type symbiotic R Aquarii has afforded investigators a unique opportunity to probe the extended emission line regions. Its extensive and complex radio morphology, that includes SiO emission from the only symbiotic associated with maser emission, has provided important clues concerning the mass expulsion process in interacting binary radio stars. Infrared, radio, optical, UV and X-ray observations of the system are discussed in context with models which have been proposed to explain the appearance of the brilliant jet.
The Ultraviolet Spectrum of RX Puppis
Authors: Kafatos M. , Michalitsianos A.G.
Published: July 2016

The UV spectrum of the peculiar star RX Puppis has afforded symbiotic star investigators a wealth of information for unraveling its mysteries. RX Pup and R Aqr, both being of the D-type variety, are now better understood as result of an extended coverage of observations at different wavelengths including radio observations using the VLA. These stars present challenges to our understanding of the symbiotic phenomenon and clues to other astrophysical phenomena like jets. Resolution of the question whether RX Pup has a jet system and an associated system of rings/extended disk or, alternatively, a colliding winds region will be resolved by high resolution radio observations or future observations using the Hubble Space Telescope.
The Photometric Period of AG Pegasi
Authors: Luthardt R.
Published: July 2016

The photometric period of AG Pegasi has been determined to be 813 days on the basis of 165 photoelectrical observations from 1961 to 1986. When splitting the interval different periods were found.
The Causes of the Light Variations in AG Peg
Authors: Yudin B.F.
Published: July 2016

It can be shown that the long–term periodic variations in the U band, distinctly observed in AG peg by UBV photometry (Belyakina 1970) from the early 1960’s with amplitude increasing, over since, have in fact two principal reasons for their existence. One of these is transparency of the envelope to the Lc-emission of the hot component in AG Peg arisen in the 1950’s and increasing since then. The second one is connected with the changes of the transparency of the compact part of the gas envelope located close to the hot component when in moves along its orbit (Yudin 1987). It is interesting to note that for the orbital solution with non-zero eccentricity (Hunchings et al. 1975) the transparency minimum and consequently the flux emission maximum for the gas envelope in AG Peg are observed in the moment when the hot component is close to its apoastron. The amplitude of the periodic variations in V increases due to the existence in AG Peg of the effect of noticeable heating of the cool component’s hemisphere facing its hot companion. Using the TiO bands in the red the cool component in AG Peg is classified as slightly earlier than M2 from illuminated side and slightly later than M3 from the opposite one (Ipatov and Yudin 1986).
The Symbiotic Novae
Authors: Viotti Roberto
Published: July 2016

A small number of symbiotic stars are characterized by a single nova-like outburst with a very slow time evolution and several years of permanence at maximum. We describe in detail RR Tel and discuss the main properties of these objects.
The Symbiotic Star UV Aurigae
Authors: Seal Parag
Published: July 2016

The symbiotic variable UV Aur was observed by Merrill (1941) and Sanford (1944, 1949). UV Aur is classified as C8 ep carbon variable (Kukarkin et al. 1969) with a hot white dwarf and surrounding nebula. Infrared photometric observations have been done by Allen (1982), Noguchi et al. (1981) and Kenyon and Gallagher (1983) in the near infrared region and by woolf (1973) at 2.2 micron to 20 micron region. UV Aur has also been observed by IRAS and IUE Satellite. Polarimetry of UV Aur has been studied by Khudyakova (1985) in the optical region.