bluuebunny/crossref_metadata_2025_split huggingface dataset:
Non Circular Disks in am CVn Systems?
Authors: Solheim J.-E. 
Published: July 2016

The AM CVn stars are mass transferring, interacting binary, white dwarf systems with orbital periods of 15…45 minutes. Hydrogen is completely lost from these systems, and we observe small helium disks which may show thermal and tidal instabilities if the mass transfer rate is large enough (Osaki 1995). A tidal instability brings the disk into a superoutburst state, and in the light curve we may observe superhumps. Based on the observed periods and mass transfer rates we can divide the AM CVn stars into three groups:A: In permanent superoutburst: AM CVn and EC 15330-1403B: Regular superoutbursts: CR Boo, V803 Cen and CP EriC: Not yet observed superoutburst: GP ComGroup A consists of systems with disks which are too hot to decline into a low state. These disks are in a constant superoutburst state, analogous to nova-like CVs which show no outbursts, but still exhibit permanent superhumps (Skillman & Patterson 1993). Group B shows normal outbursts which can trigger superoutbursts, analogous to the VY Scl dwarf novae. The group C object may also be a superhumper, but with very infrequent outbursts analogous to the SU UMa stars (Warner 1995). In the following we will discuss evidence for superoutbursts in these systems, and the likelihood for these systems to develop elliptical disks.
The 71-Second Oscillation of DQ Her at 2180 Å
Authors: Robinson E. L. , Zhang E. , Bless R. C. , Dolan J. F. , Elliot J. L. , van Citters G. W. 
Published: July 2016

AbstractThe 71-s modulation in the light curve of the old nova DQ Her has a mean semi-amplitude of 1.8% at 2180 Å, although the amplitude varies by at least a factor of two from orbit to orbit. The disturbance in the amplitude and phase of the modulation during eclipses is similar to that observed at visual wavelengths. We conclude that at 2180 Å, as at visual wavelengths, the modulated flux is reprocessed and comes from the accretion disk.
On the Long-Term Light Curve Behaviour of the Intermediate Polar TX Col
Authors: Buckley D. A. H. 
Published: July 2016

TX Col (1H0547–407; Porb = 5.72 h) is an intermediate polar (IP) with spin and synodic (beat) periods of 1911s and 2106 s respectively (Buckley & Tuohy 1989). EXOSAT observations (Tuohy et al. 1986) showed the beat period dominated at higher energies (ME; 1… 9keV), while the spin period was stronger in softer X-rays (LE1; 0.1… IkeV). The high flux level, and pulse fraction (>70%), of the soft X-rays were unique in an IP at that time. Now three other IPs, recently discovered from the ROSAT survey, have been found to show a true separate soft X-ray component, similar to the polars (Motch & Haberl 1994).The strength of the synodic X-ray period in TX Col was, until the recent discovery of the variable polarised IP, RX J1712.6–2414 (Buckley et al. 1995), unique. This was taken as evidence for direct accretion onto the magnetosphere (e.g. Mason, Rosen & Hellier 1988), through a component of the accretion stream overflowing the disc (Hellier 1992).
X-ray and optical observations of BY Cam
Authors: Ramsay Gavin , Mason Paul A. 
Published: July 2016

We present preliminary results of an analysis of X-ray and optical data of the asynchronous AM Her star BY Cam [1]. We use X-ray data from EXOSAT (0.1… 50 keV), Ginga (1.5… 50 keV) and ROSAT (0.1…2.0 keV) and optical data obtained during a 45-day campaign in 1994.There are 4 known periods: the orbital period (201.30 m), the spin period of the white dwarf (199.3303 m), a spin-orbit beat period (14.15 d) and a side-band period (197.4 m). The detection of this side-band period lends credence to the theory of [2], who suggest that for a stream accreting, diskless, magnetic CV a frequency, f = 2ωspin − Ωorb (=197.399 m), will appear as a strong spike in the power spectrum for certain systems. Wu & Mason (this volume) discuss a competing model where Pspin = 197.4 m.
Observations of Novae in M51, M87, and M101: A Preliminary Report
Authors: Shafter A. W. , Ciardullo R. , Pritchet C. J. 
Published: July 2016

AbstractWe report preliminary results from a new program of observations of novae in nearby galaxies. The principal goal of the program is to explore the population of nova progenitors through observations of galaxies having a wide range of Hubble types. Here we present preliminary results from observations of the spiral systems M51 and M101, and the giant elliptical, M87. Based on available data, we find no evidence that the luminosity specific nova rate varies across the Hubble sequence.
The Gamma-Ray Spectrum of Classical Novae
Authors: Hernanz M. , José J. , Gómez J. 
Published: July 2016

AbstractWe report on preliminary hydrodynamic simulations of thermonuclear runaways in the hydrogen-rich envelopes of accreting white dwarfs, leading to nova outbursts. A one-dimensional, Lagrangian, implicit, hydrodynamic code (Kutter & Sparks 1972) has been used to reproduce the gross features of a classical nova, from the onset of accretion, through the progress of the outburst up to the expansion stage, where significant mass loss takes place. Special interest is focused on the synthesis of 22Na and 26Al, for their interest in γ-ray line astrophysics. The γ-ray spectrum is built by means of a Monte Carlo simulation.
A Unified Model for the Radio and Optical Images and Spectra of Nova V1974 Cyg 1992
Authors: Hjellming R. M. 
Published: July 2016

AbstractA model for nova shells which is a combination of wind model and spherically symmetric, Hubble flow shell model, fits the light curve, image, and nebular line shape data for Nova V1974 Cyg 1992. The results show that after outburst the shell is ejected by a wind-like outflow with a linear velocity gradient, and that after 180 d this outflow stops. The shape of the elliptical inner boundary at this time determines the subsequent emission measure structure seen in images, light curves, and nebular line profiles.
Nova Outbursts and the Secular Evolution of Cataclysmic Variables
Authors: Schenker K. , Kolb U. , Ritter H. 
Published: July 2016

AbstractWe present calculations of the long-term evolution of CVs which include the influence of nova outbursts. In particular we investigate the consequences of the discontinuous mass loss due to recurring outburst events and the effects of frictional angular momentum loss (FAML), i.e. the interaction of the expanding nova envelope with the secondary. We show that a description assuming continuous mass loss – averaged over a complete nova cycle – is applicable for determining the mean mass transfer rate and the secular evolution both with and without FAML. Between two subsequent outbursts, deviations from the mean evolution depend on the strength of FAML and on the mass ejected during the outburst. Formally FAML is a consequential angular momentum loss [1] and therefore increases the mean mass transfer rate by pushing the systems closer to mass transfer instability. Depending on the actual strenghth of FAML the long-term evolution of CVs could be significantly different from the standard model predictions.
ASCA Observations of Narrow-Line Seyfert 1 Galaxies
Authors: Hayashida K. 
Published: July 2016

AbstractASCA observations of four narrow-line Seyfert 1 galaxies are presented. Among the four sources, two show X-ray spectra consisting of soft and hard components. Rapid X-ray variability is observed in all four sources. We estimate the central black-hole mass of these sources and find indications that the apparent luminosities exceed the Eddington limit under some assumptions.
A Multicolor Study of AGNs and BL Lacs
Authors: Sun W.-H. , Su Yu-Ya , Tang Hsiao-Feng , Malkan Matthew A. , Stone Remington P. S. 
Published: July 2016

AbstractWe present preliminary results of two monitoring projects on AGNs and BL Lacs with four intermediate-band optical filters at Lick Observatory, South African Astronomical Observatory, and Siding Spring Observatory. We applied differential photometry between the target and non-variable field stars to derive the variability amplitudes. All the AGNs varied in all wavebands, with amplitudes from 30% to 90%. The variations in shorter wavelength filters are always larger than in longer wavelength filters. We did not observe significant continuum slope changes. Continuum variations of BL Lacs up to 0.2 mag in 20 minutes were observed. Interestingly, we found a time lag of 6–8 minutes between two seemingly correlated variations observed in the intermediate U band with the 1-m telescope and in broad V band with the 24-in. telescope at SSO.
The Diversity of Broad Emission-Line Profiles
Authors: Stirpe Giovanna M. , Robinson Andrew , Axon David J. 
Published: July 2016

AbstractWe present preliminary results from a study of broad-line profiles in active galaxies. A simple model in which the emissivity is a broken power-law function of radius, and the BLR clouds emit anisotropically, yields very good fits to almost all the Ha profiles in our data base.
Broad-Line Profiles and Time Lags of Bloated Stars
Authors: Alexander Tal 
Published: July 2016

AbstractThe bloated stars model for AGN broad-line emission proposes that this emission originates in the mass-loss envelopes or winds of giant stars. I present here a version of the model that simultaneously reproduces typical AGN broad emission-line ratios, line profiles, and linereverberation time lags without excessive stellar collisions. This can be achieved if (1) the bloated star envelope is about 10 times denser than that of normal supergiants, (2) the fraction of the bloated stars within the stellar population falls off as r−2, and (3) the size of the envelope is limited by the black-hole tidal forces.
One-Armed Oscillations of Accretion Disks in AGN: Application to the Warped Maser Disk of NGC 4258
Authors: Okazaki Atsuo T. 
Published: July 2016

AbstractWe present a numerical example of a warping mode in the maser disk of NGC 4258. We find that the characteristics of the mode agree with the observed position and velocity distribution of the maser sources.
Clumpy Scattering Regions in Active Galactic Nuclei
Authors: Kishimoto Makoto 
Published: July 2016

AbstractSimple unified models predict that many Seyfert 2s should be highly polarized ( ≳ 50%), but such highly polarized Seyfert 2s are not observed. As one of the possibilities to explain this problem, the existence of clumpy scattering clouds with optically thick condensations in the nuclear regions is discussed.
Nonlinear Propagation of Pulsar Radiation
Authors: Shukla P. K. , Stenflo L. 
Published: July 2016

AbstractThe nonlinear propagation of pulsar radiation in an electronpositron plasma is considered. Accounting for the pulsar radiation ponderomotive force, the relativistic mass variation, and the plasma magnetization, we obtain a pair of nonlinear equations which exhibit coupling of pulsar radiation with the background plasma slow motions in magnetized plasmas. The modulational/filamentation instability as well as the localization of pulsar radiation are investigated. We conclude that our investigation is relevant to the microstructures in the pulsar magnetosphere.
Observations of Giant Pulses from Pulsar PSR B1937+21
Authors: Thorsett S. E. , Shrauner J. A. , Cognard I. , Taylor J. H. 
Published: July 2016

AbstractWe discuss observations of giant pulses from the millisecond pulsar PSR B1937+21 at 430 MHz, with a baseband sampling system at Arecibo (Shrauner et al., these proceedings) and coherent dedispersion techniques. About one pulse or interpulse per hundred thousand is stronger than 100 times the mean flux density, and the giant pulse strengths follow a power law distribution somewhat shallower than that of the Crab giant pulses. The individual giant pulses appear consistent with impulses shorter than a few microseconds, convolved with an exponential due to interstellar scattering. They are systematically delayed with respect to the average emission, and many are nearly 100% circularly polarized.
Multi-frequency pulsar studies at high radio frequencies
Authors: Kramer Michael , Xilouris Kiriaki M. 
Published: July 2016

AbstractWe report flux density measurements, polarimetric and timing observations of pulsars made at the highest radio frequencies to date, covering the widest frequency range from 1.4 GHz to 86 GHz. We find that the magnetic field maintains its dipolar structure throughout the active part of the magnetosphere, a region located close to the stellar surface and confined to a small slab of a few stellar radii. The change in width and shape of pulse profiles saturates at mm-wavelengths while the depolarization accelerates, leading to almost completely depolarized emission. Two pulsars seem to exhibit a turn-up in their flux density spectrum at mm-wavelengths.
Search for the Optical Counterpart of PSR 1953+29
Authors: Boriakoff V. , Beskin G. , Dossa D. , Fauci F. , Oke J.B. , Tella L. 
Published: July 2016

1) PSR B1953+29, the first millisecond binary pulsar discovered, has a low mass companion with a long orbital period (see parameters in Table 1).2) Shortly after its discovery the averaged pulse profile was observed to change shape in a discrete fashion: two different pulse profiles were alternating (Boriakoffet al1986). Each pulse profile remained the same for typical times of days. This is reminiscent of the mode-changing behaviour of slower pulsars, however, normally such pulsars remain in one mode for only a few minutes.3) Observations with a Cherenkov TeV Gamma-Ray detector have shown a large pulse-profile peak when the data is folded with the correct pulse period. Recent reprocessing of the original data shows the same peak (Bowdenet al1990).4) Comparison with optical photographs revealed a bright star (20-th magnitude) located less than 1 arcsec from the pulsar positions determined with the VLA and from timing. A star of ∼O.2M⊙is expected to be a white dwarf, at the distance of 3.5-5kpc it would be invisible.5) Optical spectral observations of the star with the 5-meter Palomar telescope showed a reddened spectrum without any emission or absorption lines. This is typical of very hot objects.6) CCD images obtained with the Russian 6 meter optical telescope in the Caucasus were taken to pinpoint the location of the star with accuracies better than a small fraction of an arc second. Imperfections of the CCD star images (saturation, etc.), in particular for bright 15-18 magnitude stars, had to be taken into account to pinpoint the center of the observed image. A technique was developed for finding the center of the image with an accuracy better than 0.17 arcsec, a single pixel of the CCD image. Arcs of ellipses were fitted to cross-sections of the star image at different light intensity levels. Down to very low light levels no pulsation was found.
Recent X-ray Observations of Pulsar Nebulae
Authors: Kawai Nobuyuki , Tamura Keisuke 
Published: July 2016

AbstractResults from the X-ray observations of pulsars with ASCA are presented. The surroundings of pulsars are investigated in detail taking advantage of ASCA’s unique capabilities; high spectral resolution and a high throughput over a wide energy range from 0.4 keV to 10 keV. The spectral characteristics of the nebulae of PSR B1509—58 and the Vela pulsar are spectroscopically investigated. A jet-like feature is found from PSR B1509—58. We detected diffuse emission sources in the vicinity of many pulsars. The high probability of finding such diffuse sources for many pulsars suggests that they exist universally for all the active pulsars, and that they are powered by the pulsars. SNR Kes 32 was imaged in X-ray for the first time. Its X-ray properties can be used to examine its association with the nearby pulsar PSR B1610—50.
Pulsar Winds
Authors: Arons Jonathan 
Published: July 2016

AbstractThe shock excitation of pulsar powered nebulae (plerions) is discussed, based on recent theoretical work on the structure of relativistic, collisionless magnetosonic shock waves. This theory is used to outline a model in which theγ−2injection spectrum of the Crab Nebula is satisfactorily accounted for. The same theory suggests a model of the “wisp” features in the Crab Nebula which accounts for these time variable features in the surface bightness as compressions associated with the magnetic overshootswithinthe shock structure. It is pointed out that this theory suggests observable variability in the high energy gamma rays from the Crab Nebula (ε &gt; 50 MeV).
Wind Acceleration in Pulsar Magnetospheres
Authors: Takahashi Masaaki , Shibata Shinpei 
Published: July 2016

AbstractTo explain the pulsar wind acceleration and the energy conversion from the electromagnetic energy to the plasma’s kinetic energy between the pulsar and the nebula’s shock, we study relativistic cold ideal MHD winds in non-radial magnetic field geometry and clarify the critical conditions of trans-fast MHD winds.
A Millisecond Pulsar Progenitor to an Ultra-Compact Low-Mass X-ray Binary
Authors: Lundgren S. C. , Ergma E. , Cordes J. M. 
Published: July 2016

AbstractWe discuss a twist in binary neutron star evolution scenarios in which a millisecond pulsar system is actually aprogenitorfor a low-mass X-ray binary system. After 7 billion years of orbital decay due to gravitational radiation, the millisecond pulsar PSR J0751+1807 will enter a low-mass X-ray binary phase. When the orbital period reaches about 5 minutes, the white dwarf will overflow its Roche lobe, transferring mass to the neutron star. Its predicted observational X-ray parameters are very similar to the ultra-compact low-mass X-ray binary 1820–303. The ultimate fate of the system after Roche-lobe overflow is unknown. One possibility is that the companion may eventually tidally disrupt, leaving a disk of material which could form into planets.
Neutron Star Binaries in Open Clusters
Authors: Aarseth Sverre , Mardling Rosemary 
Published: July 2016

We useN-body simulations of open clusters to examine the evolutionary history of binaries containing neutron stars. The model includes consistent treatment of all the relevant processes (Aarseth 1996):•Synthetic stellar evolution–mass and radius as a function of time (Eggleton et al. 1989)•Accurate treatment of close encounters–Perturbations of binaries and stable multiple systems - Exchange reactions (involving triple and binary-binary interactions) - Collisions → blue stragglers•Binary evolution (primordial and dynamically formed)–Tidal interactions (Mardling &amp; Aarseth 1996) - Stable mass transfer - Common envelope evolution - Magnetic braking - Gravitational radiation - Mergers (including blue stragglers)•Mass loss–Stellar winds - Supernovae - Evaporation of stars from the cluster•Neutron star formation–Supernovae with kick velocities of Lyne &amp; Lorimer (1994), Drukier (1996) - Accretion-induced collapse
Disk-Corona Models and X-Ray Emission from Seyfert Galaxies
Authors: Maraschi Laura , Haardt Francesco 
Published: July 2016

AbstractThe current status of understanding of the X-ray emission from Seyfert galaxies involves Comptonization of soft photons by hot subrelativistic electrons. After briefly reviewing the early theoretical basis for the presence of hot optically thin plasma in or around accretion disks and the key observations that led to develop the presently popular model of an accretion disk with a hot corona, we summarize recent progress in accretion models that take into account energy dissipation and/or angular momentum transport in the corona. Finally, adopting the simple scheme of a homogeneous plane parallel corona, we discuss in detail the dependence of the X-ray spectrum on the coronal parameters. Despite the strong coupling between optical depth and temperature which determines a spectral shape insensitive to their precise values, moderate spectral changes are possible. The spectral variability patterns can be used as diagnostics for coronal physics and should allow to determine whether the optical depth of the corona is dominated bye+e−pairs.
Ubiquitous Disks in AGN
Authors: Schmidt Gary D. 
Published: July 2016

AbstractDisk-like structures have been inferred to exist in the nuclei of galaxies over the entire range in nuclear activity. These form the essence of the Unified Scheme, which has had great success in accounting for AGN of a wide variety of perceived types. Recent progress along this front is summarized, including new polarimetric results, high-angular resolution optical imaging, and interferometry at radio wavelengths.
Winds from Cataclysmic Variables
Authors: Drew J. E. 
Published: July 2016

AbstractThe winds associated with high states of non-magnetic (diskaccreting) cataclysmic variables are described and discussed. A quick summary of the basic phenomenology is given, and followed by a presentation of some of the more important recent developments in our understanding. The near-ubiquity of orbital-phase linked variability of the UV resonance lines (generally thought of as mainly wind-produced) is noted and its implications are considered. The impact of the much lower-thanexpected boundary layer luminosity upon mass loss rate determinations is also discussed. Current work on the role of radiation pressure (mediated by line opacity) is placed in context.
WFPC2 Studies of the Disk and Jet of HH 30
Authors: Stapelfeldt Karl , Burrows Chris , Krist John , Watson Alan 
Published: July 2016

AbstractHubble Space Telescope imaging of HH 30 has revealed this object to be a prototype young stellar object (YSO) accretion disk system. An optically thick circumstellar absorption disk, 450 AU in diameter, is seen extending perpendicular to highly collimated bipolar jets. The jet width is resolved in the transverse direction and increases with distance from the central star. The size and age of the disk compare well to the early solar nebula during planet formation. HH 30 is the first YSO disk ever observed at 14 AU resolution, and the first viewed close enough to edge-on that the vertical structure of the disk is clearly visible. These HST images of HH 30 offer the first-ever opportunity to directly measure the flaring profile of an astrophysical accretion disk. We have compared the images to model nebulosities calculated in both multiple and single scattering regimes, in the latter case via chi-squared minimization. This analysis constrains the circumstellar density distribution and grain scattering properties. A brief summary of the results is presented here; full details and references appear in Burrows et al., Ap.J. (1996).