bluuebunny/crossref_metadata_2025 huggingface dataset:
Superhumps in the SU UMa Star AK CNC
Authors: Mennickent R. , Nogami D. , Kato T. , Worraker W.
Published: July 2016

We have observed AK Cnc during the 1995 March superoutburst, by means of differential V – U photometry. The observations were obtained at Las Campanas (Chile), Ouda Station (Kyoto, Japan) and in England. Superhumps with amplitude 0.2 mag appeared at least 4d after maximum. They evolved from a single peak structure, developing a secondary peak during decline, until they reached a double-wave modulation with 0.05 mag amplitude, after 8 d. After removing linear trends in our data, the following ephemeris was found:

This superhump period was confirmed, independently, with our homogeneous set of 462 V magnitudes, obtained at LCO, then adding 63 U data points and finally considering all the dataset, consisting of 789 V + U magnitudes. The superhump period is slightly larger than that reported by Kato (1995) during the 1992 January superoutburst (0.06735(5)d). Our results imply an orbital period Porb = 0.065(2) d, using the relationship given by Howell & Hurst (1994). The eruption duration was ≳ 10 d, and its amplitude > 6 mag. An abrupt and short luminosity decrease occured ≈ 12 d after maximum. Eleven outbursts have been observed since 1992 January, being the minimum reported lag between successive eruptions: 40 d. More details will be given in a future publication.
The Long Period Dwarf Nova UY Pup in Outburst
Authors: Lockley J. J. , Wood Janet H. , Jones D. H. P. , Mineshige S.
Published: July 2016

UY Pup is a little studied, frequently out bursting dwarf nova whose brightness varies from V ~ 13.5 mag in outburst to V ~ 15.8 mag in quiescence, which typically lasts ~15…25 d. We observed it spectroscopically at the INT in La Palma on 1989 Febuary 15 and 16 during outburst maximum. In this outburst, the rise lasted at least 3 d and there was a long decline of about 6…9 d. The whole outburst lasted about 18 d (Mattei, private communication).
Accretion Disc Viscosity
Authors: Tout Christopher A.
Published: July 2016

We review the various physical processes that could lead to viscosity in accretion discs. A local magnetic dynamo offers the most plausible mechanism and we discuss a simple model in some detail. The dynamo operates even in partially and very weakly ionized discs without much modification.
Synthetic Spectra for Accretion Discs: The UV Absorption Spectrum
Authors: Wade R. A.
Published: July 2016

With my collaborators (Ivan Hubeny, NASA/Goddard Space Flight Center; Marcos Diaz, Catherine Grant, and Darren Williams, all of Penn State), I am computing the structure of discs and their corresponding UV spectra for a large grid of choices of the white dwarf mass Mwd and the mass transfer rate Ṁ. In our approach, we divide the problem into a number of parts, each corresponding to a particular FORTRAN-implemented computer program. Program TLUSDISK computes the vertical structure for individual rings in the disc (T, ρ, ne, τ versus Z). The rings are treated independently, as plane-parallel entities without irradiation, obeying the standard expression for Teff as a function of Mwd, Rwd and Ṁ. With this vertical structure, program SYNSPEC computes the detailed local (rest frame) spectrum for each ring. Both specific intensities and angle-averaged fluxes can be computed. Program DISKSYN is used to combine the spectra of individual rings to obtain the integrated or whole-disc spectrum, taking into account Doppler shifts (dependent on the chosen disc inclination) and limb darkening. Finally, program ROTINS is used to smooth the spectrum to an appropriate instrumental resolution. Intermediate results, e.g., from TLUSDISK or SYNSPEC, are stored for repeated use.
A Quantitative Study of Limb Darkening in Accretion Disks
Authors: Diaz M. P. , Wade R. A. , Hubeny I.
Published: July 2016

The UV emission of accretion disks was synthesized for a grid of optically thick models that cover the high-Ṁ nova-like regime, aiming to quantify the effect of limb darkening in the integrated and radially resolved spectrum of the disk.
Disk Instabilities in the Black Hole Binaries
Authors: Cannizzo J. K.
Published: July 2016

I will briefly review recent progress in our understanding of the global propagation of accretion disk instabilities operating in interacting binary systems in which the accreting star is a ~ 10 M⊙ black hole. A detailed discussion of this work can be found in Cannizzo, Chen & Livio (1995).

The X-ray light curves of the brightest and best studied X-ray novae – systems such as A0620–00, GS2000+25, GS1124–68, and GRO J0422+32 – are notable in two respects: the rise times are fast (a few days) and the decays have an exponential character, where the e–folding time constant is about 30 to 40 d (Mineshige, Yamasaki, & Ishizaka 1993, hereafter MYI). It is noteworthy that outbursts in dwarf novae also decay exponentially, with the time constant being about a factor of 10 shorter. In this contribution I will discuss the constraints on the physics of accretion disks which the (observed) exponential decay enables us to make.
Optical flickering and shot noise in AM Her systems
Authors: Larsson S. , Larsson B.
Published: July 2016

The emission from AM Her systems show a variety of time-variable phenomena, including flickering with a typical power spectrum slope of −1 to −2. The optical flickering is usually modeled as, or assumed to be, a shot noise process with many overlapping simultaneous shots. Panek (1980) found that, for AM Her, a consistent model could be constructed with randomly occurring 70… 90 s rectangular shots. The power spectrum had a v−2 shape above 0.02 Hz as expected, although it is not clear whether a break in the slope of the power spectrum was actually seen around 0.01 Hz. There are many additional reports in the literature of ‘characteristic time-scales’ on the order of tens of seconds. However we are not aware of any case where the reported time-scale has been supported by e.g. a break in the power density spectrum. It is easy to show that the usual method of estimating a ‘characteristic time-scale’ from the auto correlation function of de-trended data will suggest such a characteristic time-scale even if none is present in the original time series. The evidence for shot noise in AM Her light curves therefore needs a re-examination. In this paper we give a short summary of our analysis of optical flickering in V834 Cen, based on high speed photometry obtained at ESO in 1987. Details will be reported elsewhere.
Infrared Spectroscopy of Nova V705 Cas
Authors: Evans A. , Geballe T.R. , Rawlings J.M.C. , Scott A.D.
Published: July 2016

Nova V705 Cas was discovered on 1993 December 7, several days before maximum light. The light curve indicates that t2 ≃ 40 d (see e.g. [4]), characteristic of dust-forming novae. The light curve went into decline on day 58, indicating the formation of an optically thick dust shell. IR spectra have been obtained regularly since outburst using the cooled grating spectrometer CGS4 on the United Kingdom InfraRed Telescope (UKIRT). We present here the results of ongoing IR spectroscopic monitoring of this nova.
Radio Emitting X-Ray Binary Stars
Authors: Spencer R. E.
Published: July 2016

Some of the most astrophysically interesting objects are found among the radio-emitting X-ray binary stars (REXRB). The class includes the well-studied objects such as SS 433, Cyg X-3 and Sco X-1. The recent discoveries of relativistic ejection of radio knots in the X-ray transients 1915+105 (Mirabel & Rodriguez 1994) and 1655–40 (Hjellming & Rupen 1995) well illustrate the extreme nature of some of these objects.

X-ray binaries are semi-detached binary stars in which matter is transfered from a more or less normal star onto a neutron star or black hole. X-ray satellites have detected large numbers of these objects (193 in a recent catalogue by van Paradijs 1995). However only a small fraction of these are known to have radio emission (e.g. Hjellming 1988).
The Period Distribution of Supersoft Sources
Authors: Kahabka P.
Published: July 2016

The observed and predicted orbital period distributions of supersoft sources are in good agreement.
The Supersoft Source RXJ0019.8+2156: New Photoelectric Observations
Authors: Bartolini C. , Guarnieri A. , Piccioni A. , Solmi L.
Published: July 2016

RXJ0019.8+2156 is a Supersoft X-ray Source (SSS) discovered by ROSAT and identified (Beuermann et al. 1995) as an object of magnitude V = 12.2, brighter than any other known SSS. The mass function and the optical spectrum are similar to CAL 83, but the X-ray luminosity seems to be lower. The main light variations are: a cyclic modulation with a 15.8 h period and a 0.3 mag amplitude, a quasi-periodic pulsation less than 0.1 mag in 2 h (Beuermann et al. 1995), variations of about 1 mag over a time-scale of 20 yr and small irregular fluctuations on a time-scale of weeks to months (Greiner & Wenzel 1995).

The most promising model, at present, involves a binary system in which a hot 1 M⊙ white dwarf with an accretion disk is accreting at a mean rate of Ṁ ≈ 10−7 M⊙yr−1; sporadic hydrogen burning caused by an unstable mass transfer (Greiner & Wenzel 1995) seems to be present.
On the Origin of the Abundance Anomalies in IK Peg
Authors: Smalley B. , Smith K.C. , Wonnacott D.
Published: July 2016

IK Peg is a binary system comprising a pulsating A-type star in orbit with a massive white dwarf. A detailed abundance analysis of IK Peg A has been performed. It is found that the Ca and Sc abundances are approximately solar, and the Fe-group elements slightly enhanced. IK Peg is not a classical Am star but the results are not inconsistent with its spectroscopic classification as a marginal Am star. An excess of Ba and Sr are found. These anomalies could be explained by radiative diffusion processes operating in the atmosphere of IK Peg A, even though it is undergoing small-amplitude pulsations. Alternatively, since the companion is a massive white dwarf, these anomalies could be the result of mass transfer during the common envelope phase of the binary system’s evolution.
Star/Disk Interaction in the Nuclei of Active Galaxies
Authors: Lin D.N.C.
Published: July 2016

The most definitive evidence for an accretion disk is provided by the discovery of megamasers (Claussen et al. 1984) which appear to be located in a molecular torus around the nucleus of the mildly active galaxy NGC 4258. Confirmation of Keplerian rotation speed was obtained from radio interferometer (Nakai et al. 1993) and VLBI observations (Greenhill, this volume). Based on the correlation between the spatial locations and radial velocities of the masers, Moran et al. (1995) deduced that the masers are located in a disk at radii R = 0.13–0.26 pc around a black hole with a mass M ≈ 3.5 × 107M⊙ (Watson & Wallin 1994, Maoz 1995). A limit on the thickness (H < 2.5 × 10−3R) is deduced from the velocity dispersion of the maser sources. The mass-diffusion time scale is estimated to be τd > 1015 α−1 s, where α is the viscosity parameter. An efficient angular-momentum transfer mechanism (α > 0.1) is needed for τd ≈ 108 yr, which is the disk evolution time scale inferred from the correlation between interacting galaxies and intense AGN activities (MacKenty 1989, Hernquist 1989). A relatively large value of a is also required to account for the accretion rate needed to power the X-ray flux of NGC 4258.
UV and X-Ray Variability of 3C 390.3
Authors: Wang Ting-gui , Wamsteker Willem , Cheng Fu.-Zhen
Published: July 2016

We present the results of an analysis of the UV and X-ray variability of the broad-line radio galaxy 3C 390.3 over 15 years. The UV continuum of 3C 390.3 showed large variations with amplitudes of up to a factor of 10. The variations of C IV and Lyα are highly correlated with the UV continuum, and are delayed with respect to the continuum variations by 65-120 days with the red wing of both C IV and Lyα leading the blue wing, implying that the C IV and Lyα-emitting gas is infalling towards the center. The C IV/Lyα ratio is positively correlated with both the continuum flux and UV line strength. The overall UV/optical to X-ray spectrum can be described by a single power law with αuvx = 0.90. The behavior of C IV/Lyα variations might be related to this hard ionizing continuum in 3C 390.3.
The Nature and Origin of Structure in Broad Emission Line Profiles
Authors: Gaskell C. Martin , Snedden Stephanie A.
Published: July 2016

We postulate that all structure in broad lines can be explained by a central component (at the systemic redshift) and the addition of two ‘displaced components’, one blueshifted and the other redshifted. We have been able to successfully classify all Balmer-line profiles on this basis. 3C 390.3-type objects are merely examples where the shifts of the displaced components are unusually large. We believe that the displaced peaks are less prominent in the UV lines because the higher ionization lines are broader.
The Effect of a Variable Anisotropic Continuum Source upon the Broad Emission-Line Profiles and Responses
Authors: Goad Mike , Wanders Ignaz
Published: July 2016

Optical monitoring data over several years in combination with the reconstructed 1-d response function for C IV obtained from the 1993 HST monitoring campaign of NGC 5548, reveal that: (a) radial motion does not dominate the gas kinematics (Korista et al. 1995); (b) line-profile variations occur in fixed regions of velocity space, a core and two wing components, are stochastic in nature, and appear to be unrelated to reverberation effects (Wanders & Peterson 1996). Wanders et al. (1995) showed that these variations are broadly consistent with a spherical BLR geometry populated with optically thick clouds following randomly inclined circular Keplerian orbits, and illuminated by an anisotropically emitting point source of ionizing continuum radiation. Here we provide a brief description of this model and summarize its basic properties. A more thorough analysis is presented in Goad & Wanders (1996).
Hydromagnetic Wind Model for the Broad-Line Region of NGC 5548
Authors: Bottorff M.C. , Korista K.T. , Shlosman I. , Blandford R.D.
Published: July 2016

A hydromagnetic wind model from a dusty molecular disk (Emmering, Blandford, & Shlosman 1992) was applied to the BLR in NGC 5548 and produced synthetic C IV line profiles as a function of time. The model C IV profiles are compared to data from the 1993 IUE/HST campaign and properties of the the BLR of NGC 5548 are inferred.
Associated Absorption at Low and High Redshift
Authors: Elvis Martin , Mathur Smita , Wilkes Belinda J. , Fiore Fabrizio , Giommi Paolo , Padovan Paolo
Published: July 2016

Combining information on absorbing material in AGN from X-ray and the UV creates a powerful investigative tool. Here we give examples from both low and high redshift.
Bidimensional Spectroscopy with Optical Fibers of Spatially Resolved Emission-Line Regions Around Active Galactic Nuclei
Authors: Arribas S. , Mediavilla E. , del Burgo C. , García-Lorenzo B.
Published: July 2016

We summarize our experience in observing the circumnuclear regions of AGN with the optical-fiber systems that we have developed for the William Herschel and Nordic Optical Telescopes at La Palma.
Shock Excitation of Emission Lines in GPS, CSS, and CSO Sources
Authors: Bicknell Geoffrey V. , Dopita Michael A. , O’Dea Christopher P.
Published: July 2016

The classes of radio-loud AGN known as Gigahertz-peak spectrum (GPS), compact steep spectrum (CSS), and compact symmetric objects (CSO) represent an important sub-class of AGN, constituting, for example, 24% of the Baker, Hunstead, & Brinkmann (1995) sample. Table 1 summarizes some of their key properties.
The Green Bank Northern Sky Survey: Discovery of a New Neutron Star-Neutron Star Binary
Authors: Nice David J. , Sayer Ronald W. , Taylor Joseph H.
Published: July 2016

We have surveyed 15,900 deg2of the northern sky for millisecond pulsars at 370 MHz with the Green Bank 140ft telescope. The telescope was driven along lines of constant declination such that a given point on the sky was observed for two minutes. A Fourier transform spectrometer synthesized 512-channel spectra across 40 MHz in each of two polarizations. Total intensity levels were boxcar averaged at intervals of 256μs, quantized to 1 bit, and written to tape. Data were processed with the Cray C90 of the Pittsburgh Supercomputer Center. The flux limit of the survey was 8 mJy for slow pulsars. A further 1500 deg2were observed with 20 MHz bandwidth, yielding 71% the usual sensitivity.

Eighty-four slow pulsars were detected, of which six were previously unknown. Three recycled pulsars were detected: the relativistic binary B1534+12; the neutron star-white dwarf binary J1022+1001, discovered nearly simultaneously at Arecibo; and J1518+4904, a previously unknown pulsar with a 41 ms rotation period.
Neutron Stars, Strange Pulsars and Strange Dwarfs
Authors: Weber Fridolin , Glendenning Norman K.
Published: July 2016

The hypothesis that strange quark matter may be the absolute ground state of the strong interaction (not56Fe) has been raised independently by Boder and Witten. If the hypothesis is true, then a separate class of compact stars could exist, which are calledstrange matter stars. The properties of the complete sequence of such stars, which range from compact neutron-star-like strange stars to strange dwarfs to strange planets. The latter two constitute the strange counterparts of ordinary white dwarfs and planets, respectively. The properties of these objects are discussed in this paper.
The Effelsberg surveys of pulse shapes
Authors: Kijak Jaroslaw , Kramer Michael , Wielebinski Richard , Jessner Axel , Seiradakis John-Hugh
Published: July 2016

Pulse shapes of pulsars have been observed at many frequencies with the Effelsberg 100-m radiotelescope since 1972. The rationale behind these surveys was to use the great sensitivity of the 100-m telescope of the Max-Planck-Institut für Radioastronomie in particular at high radio frequencies for a complete study of pulse profiles.

The recent advent of HEMT amplifiers has improved the observational sensitivity enormously. Using these new systems it was possible to obtain integrated profiles of 183 pulsars at 1.4 GHz, 46 pulsars at 4.75 GHz and 24 pulsars at 10.6 GHz (see Seiradakis et al. 1995). Furthermore eight pulsars have been studied at 9 mm wavelengths (Kramer et al. 1996).
A 60 Second Periodic Modulation in Crab Pulsar Optical Light-Curve
Authors: Čadež Andrej , Galičič Mirjam
Published: July 2016

The HST High Speed Photometer data and stroboscopic photometry data from the Asiago 1.82m telescope (1994) show a (0.0065±0.0015) magnitude weak modulation peak in Crab’s light-curve at 60 seconds. Hubble data also suggest a phase modulation peak at the same period with the amplitude (0.07 ± 0.02)°. New stroboscopic data from December 1995 Asiago observations suggests the modulation amplitude (0.0045±0.0015) magnitude, consistent with previous results.
The Attenuation of Hard γ-rays in Strongly-Magnetized Pulsars
Authors: Harding Alice K. , Baring Matthew G.
Published: July 2016

We investigate the spectral attenuation due to one-photon pair production and photon splitting in neutron star magnetospheres. The calculations are performed in a Schwarzschild metric, thereby including redshift and field enhancement effects associated with curved spacetime. We find that pair production and splitting totally inhibit emission above around 10-30 MeV in PSR1509-58, whose surface field is inferred to be as high as 3 × 1013Gauss. Model pulsar spectra of splitting cascades for high field cases, where splitting is important, are consistent with the very low cutoff energy in PSR1509-58 for a wide range of polar cap sizes.
Recent Results from the CANGAROO Project
Authors: Dazeley S.A. , Edwards P.G. , Patterson J.R. , Rowell G.P. , Sinnott M. , Thornton G.J. , Wilkinson C. , Hara T. , Hayashida N. , Katsumata H. , Kifune T. , Konishi T. , Matsubara Y. , Matsuoka T. , Mizumoto Y. , Mori M. , Muraishi M. , Muraki Y. , Oda T. , Ogio S. , Ohsaki T. , Sako T. , Sakurazawa K. , Susukita R. , Suzuki A. , Tamura T. , Tanimori T. , Yanagita S. , Yoshida T. , Yoshikoshi T.
Published: July 2016

TheCollaboration ofAustralia andNippon for aGAmmaRayObservatory in theOutback operates two large telescopes at Woomera (South Australia), which detect the Čerenkov light images produced in the atmosphere by electronpositron cascades initiated by very high energy (~1 TeV or 1012eV) gamma rays. These gamma rays arise from a different mechanism than at EGRET energies: inverse Compton (IC) emission from relativistic electrons.

The spoke-like images are recorded by a multi-pixel camera which facilitates the rejection of the large numbers of oblique and ragged cosmic ray images. A field of view ~3.5° is required. The Australian team operates a triple 4 m diameter mirror telescope, BIGRAT, with a 37 photomultiplier tube camera and energy threshold 600 GeV. The Japanese operate a single, highly accurate 3.8 m diameter f/1 telescope and high resolution 256 photomultipler tube camera. In 1998 a new 7 m telescope is planned for Woomera with a design threshold ~;200GeV.
Associations between pulsars and supernova remnants
Authors: Gaensler B.M. , Johnston Simon
Published: July 2016

We have performed Monte Carlo simulations of the Galactic supernova (SN), supernova remnant (SNR) and pulsar (PSR) populations, and find that even ifeverySN forms a fast-spinning pulsar, the number of shell type remnants which are expected to have an associated pulsar is evenlessthan observed. We conclude that most shell SNRs will not have a detectable pulsar associated with them, and that many claimed associations are merely geometric projection.
Distances to Binary Pulsars and Implications for Tests of General Relativity
Authors: Bell J. F. , Bailes M.
Published: July 2016

We propose a new way to measure accurate distances and transverse velocities for some nearby binary pulsars. In many cases the distances will be more accurately determined than is possible by annual parallax, as the relative error decreases ast−5/2. We also note that tests of the general relativistic prediction of orbital period decay of nearby relativistic binary pulsars will be limited to accuracies of a few percent. Nevertheless, PSR B1534+12 observations are consistent with general relativistic predictions if the proper-motion contribution to the orbital period derivative is accounted for.
Observations of a new eclipsing binary millisecond pulsar
Authors: Stappers B. W.
Published: July 2016

We report on the discovery and timing observations of the new eclipsing binary millisecond pulsar J2051–0827. This 4.5ms pulsar is in a 2.4 hour binary orbit with a 0.027 M⊙companion. The companion and the pulsar are separated by only 1 R⊙. The pulsar is often, but not always, eclipsed for approximately 10% of the orbit at frequencies below 660 MHz. This indicates that the eclipse material extends well beyond the Roche lobe. During a number of observations pulses have been detected throughout the eclipse region at 1.4 GHz and 2.0 GHz. The delays measured with respect to the timing model associated with these observations indicate significant structure and variability in the electron column density in the eclipse region.
Orbital Parameters of the PSR B1620–26 Triple System
Authors: Arzoumanian Z. , Joshi K. , Rasio F. A. , Thorsett S. E.
Published: July 2016

Previous timing data for PSR B1620–26 were consistent with a second companion mass m2anywhere in the range ∼ 10−3– 1M⊙, i.e., from a Jupiter-type planet to a star. We present the latest timing parameters for the system, including a significant change in the projected semi-major axis of the inner binary, a marginal detection of the fourth time derivative of the pulse frequency, and the pulsar proper motion (which is in agreement with published values for the proper motion of M4), and use them to further constrain the mass m2and the orbital parameters. Using the observed value of, we obtain a one-parameter family of solutions, all with m2≲ 10−2M⊙, i.e., excluding stellar masses. Varyingwithin its formal 1σ error bar does not affect the mass range significantly. However, if we varywithin a 4σ error bar, we find that stellar-mass solutions are still possible. We also calculate the predicted rate of change of the projected semi-major axis of the inner binary and show that it agrees with the measured value.
The relation between recycled radio pulsars and wide low-mass X-ray binaries
Authors: Li Xiangdong , Wang Zhenru
Published: July 2016

The origin and evolution of neutron star magnetic fields has been hotly debated for a long time. Spontaneous field decay was originally proposed with timescales of (5–10) × 106years, while another possible model which associates field decay with mass accretion in the evolution of binary systems has been suggested (see Bhattacharya & van den Heuvel 1991 for a review). The aim of this paper is to examine whether accretion-induced field decay can reproduce the observed properties of the wide binary radio pulsars in quantitative calculations.

In a binary system consisting of a neutron star and a low-mass giant companion, if the initial orbital period is longer than 1 day, mass transfer, taking the form of Roche-lobe overflow, is driven by the nuclear evolution of the giant through radius expansion (Webbink et al. 1983). We assume the mass accretion rateṀof the neutron star is limited to the Eddington accretion rateṀE≃ 10−8M⊙yr−1. If the mass transfer rate is in excess ofṀE, the rest mass is blown from the system in the forms of jets or beams.
Global, Nonaxisymmetric Instabilities in Magnetized Accretion Disks
Authors: Curry Charles , Pudritz Ralph E.
Published: July 2016

We investigate the global stability of a differentially rotating, ideal MHD fluid shell to linear, nonaxisymmetric perturbations. This system, which approximates an accretion disk near its midplane, is known to be unstable to both axisymmetric and nonaxisymmetric local perturbations. Keplerian disks, which are entirely stable in the hydrodynamic case, show the most rapid growth for radially extended shells.
Wind Accretion vs Roche Lobe Overflow in HMXBs
Authors: Blondin John M. , Owen Michael P.
Published: July 2016

We present a series of time-dependent 2D and 3D numerical simulations illustrating the evolutionary sequence between high mass X-ray binaries fed by wind accretion (where the primary star sits well within its critical tidal lobe) and those fed by Roche lobe overflow (where the primary star extends out to its tidal lobe). When the primary lies well within its critical surface we find negligible tidal mass loss enhancement, and a system that is characterized by wind accretion with the development of a photoionization zone around the compact object. As the surface of the primary nears the critical surface, we observe tidally enhanced mass loss via a thin tidal stream, resulting in higher accretion wake densities. For full RLOF we observe the development of a steady accretion disk characterized by a total shadowing of the X-rays in the orbital plane.
Cylindrically-Collimated, Self-Similar MHD Disk Outflows
Authors: Ostriker Eve C.
Published: July 2016

We describe the dynamics of a class of MHD winds from Keplerian-rotating disks. In this model, all flow velocities are assumed to vary self-similarly with spherical radius r as υ(r, θ) ∝ r−1/2, with density varying as ρ(r, θ) ∝ r−q for arbitrary q. At large distances from the disk, the wind is explicitly required to become cylindrically collimated. We find that the asymptotic wind solution has power-law scalings of all flow variables in the cylindrical radius R = r sin θ, and q < 1 is necessary. We describe how the Alfvén criticality condition limits the space of energy and angular momentum parameters defining these wind solutions. We present an example of the run of density, velocity, and magnetic field for a full solution of the wind equations, and compare the properties of these cylindrically-collimated wind solutions to previous work.
Three-Dimensional Global MHD Simulations of Magnetised Accretion Disks and Jets
Authors: Matsumoto R. , Shibata K.
Published: July 2016

We carried out three-dimensional global MHD simulations of jet formation from an accretion disk threaded by large-scale magnetic fields. Numerical results show that bipolar jets with maximum speed υjet ~ υKepler are created. The surface layer of the disk accretes faster than the equatorial part because magnetic braking most effectively affects that layer. Accretion proceeds along spiral channels which correspond to the surface avalanche flow appearing in previous axisymmetric simulations. Spirally shaped low β (= Pgas/Pmag < 1) regions appear in the innermost part of accretion disks where toroidal magnetic fields become dominant.
HST Spatially Resolved Spectra Of Accretion Discs In CVs
Authors: Baptista Raymundo
Published: July 2016

Time-resolved eclipse spectroscopy of the novalike variable UX UMa obtained with the HST/FOS is analized with eclipse mapping techniques to produce spatially resolved spectra of its accretion disk and gas stream as a function of distance from disk center. The results reveal a noticeable asymmetry in the disk emission, with the disk side closest to the secondary star showing pronounced absorption bands in the UV and a Balmer jump in absorption. The spectrum of the infalling gas stream is noticeably different from the disk spectrum at the same radius suggesting that gas overflows through the impact point at disk rim and continues along the stream trajectory, producing distinct emission down to 0.1 RL1.
Polarization Properties of Active Galactic Nuclei
Authors: Hough J. H.
Published: July 2016

One of the main uses of polarimetry over the last decade, has been to identify the nature of AGN that are normally hidden from direct view by an optically and geometrically thick torus, and thereby to unify different classes of AGN. Of growing importance is the role that polarimetry can play in our understanding of the properties and structure of AGN on a size scale which cannot be resolved directly. We review the progress being made in understanding the role of disks, extended scattering regions, and the obscuring torus in AGN.
High-Velocity Maser Emission From Shocks Along Spiral Waves In The Circumnuclear Disk Of NGC 4258
Authors: Maoz Eyal
Published: July 2016

VLBI observations of H2O maser line emission from the central sub-parsec region of the galaxy NGC 4258 have recently revealed a remarkably well-defined, rapidly rotating molecular disk which is viewed nearly edge–on. We show that the peculiar clustering of the maser sources into several distinct clumps which are almost equally spaced apart from one another, and the striking asymmetry in the high-velocity maser spectrum can be naturally explained by spiral activity in the disk.
Compact Radio Cores in the Galactic Center and Elsewhere
Authors: Falcke Heino
Published: July 2016

Compact radio cores are not only common in radio galaxies and quasars but also in many nearby galaxies with low-active, supermassive black holes. One famous example is the Galactic Center source Sgr A*. Recent studies of proper motions and radial velocities of stars in the inner parsec of the Galaxy convincingly demonstrate the presence of a compact dark mass of 2.5 · 106M⊙in the nucleus of the Milky Way. Millimeter VLBI and submm observations of Sgr A*thus probe a region of only a few Schwarzschild radii in diameter. In this paper I will review our current theoretical and observational knowledge of this source and compare it to some famous LINER galaxies like NGC 4258, NGC 3079, and NGC 6500. In all cases these radio cores can be well explained by a standard AGN jet model, and, with the exception of Sgr A*, large scale outflows are observed that have powers comparable to those inferred from the radio cores. Recent VLBI observations of radio-weak quasars and HST observations of Seyfert galaxies indicate that these AGN also produce powerful jets which, however, have relatively less luminous radio cores than radio-loud quasars and the LINERs discussed here. Therefore, jets and compact radio cores appear to be natural constituents of an AGN, but the reason why apparently some jets are radio-loud and others not remains a mystery.
Accretion in the Center of the Milky Way
Authors: Duschl Wolfgang J. , von Linden Susanne
Published: July 2016

We have analyzed the distribution of giant molecular clouds and their radial velocities in the inner ~ 300 pc of the Milky Way in order to deduce the characteristic properties of its large scale motion. We find radial inflow of matter towards the Galactic Center of ~ 10−2 M⊙/yr. Moreover, we have determined the position of individual clouds along the line of sight.
Lifetimes of Circumstellar Disks in Lynds 1641
Authors: Allen Lori E. , Strom Karen M.
Published: July 2016

It is by now evident that most young stars have associated disks and/or envelopes, which may be active (accreting) or passive (reprocessing stellar photons), or both. Knowing how such disks evolve is crucial to our understanding of how stars form, and may be relevant to other questions, such as the time available for the formation of planets in solar nebulae. In this poster we discuss the properties of pre-main sequence circumstellar disks in Lynds 1641 in Orion, the nearest giant molecular cloud complex.
Spectropolarimetry of Double Peaked Broad Hα Lines in Radio Galaxies
Authors: Corbett E.A. , Robinson A. , Young S. , Axon D.J.
Published: July 2016

Spectropolarimetric observations of 3 broad line radio galaxies exhibiting double peaked broad Hα lines, show that two of the sources (Arpl02B and 3C390.3) have single peaked line profiles in polarized flux with a position angle aligned with the jet axis. The third source (3C382) exhibits no polarized line emission at all. The consequences of these observations for the relativistic accretion disk and other BLR models are discussed.
Emission Line Profiles from BeXRBs
Authors: Hanuschik R.W. , Maisack M. , Cao H. , Hummel W.
Published: July 2016

We have measured optical spectra of several BeXRBs. Their Be disks apparently do not differ significantly from those in single Be’s.
Accretion and Outflow Activity in the Earliest Phases of Star-Formation: CO, Sub-mm Continuum, and Near-Infrared Observations
Authors: Hodapp K.-W. , Ladd E. F.
Published: July 2016

Stars in the earliest phases of their formation, i.e., those accreting the main component of their final mass, are deeply embedded within dense cores of dust and molecular material. Because of the high line-of-sight extinction and the large amount of circumstellar material, stellar emission is reprocessed by dust into long wavelength radiation, typically in the far-infrared and sub-millimeter bands. Consequently, the youngest sources are strong submillimeter continuum sources, and often undetectable as point sources in the near-infrared and optical. The most deeply embedded of these sources have been labelled “Class 0” sources by André, Ward-Thompson, & Barsony (1994), in an extension of the spectral energy distribution classification scheme first proposed by Adams, Lada, & Shu (1987).
Stability of Viscous Accretion Tori
Authors: Kleiber R. , Glatzel W.
Published: July 2016

With respect to the stability of accretion tori the linear stability of infinitely long cylinders is investigated taking into account the effect of viscosity. Critical Reynolds numbers as a function of the Mach number and the azimuthal wavenumber of the perturbation are calculated.
Multidimensional Radiative Transfer in Accretion Environments
Authors: Steinacker J. , Henning Th. , Menshchikov A.
Published: July 2016

Most likely produced as thermal emission by dust grains, infrared emission from young stars and active galaxies reveals information about the internal energy source, the spatial distribution of the surrounding matter and its dynamical evolution. In this way, radiative transfer works as a bridge between HD/MHD accretion disk theory and observations. For young stellar objects and active galactic nuclei, the source geometry is of crucial importance for the modelling the emerging radiation. Observations indicate rotationally symmetric accretion disks, tori, or more complicated density structures around multiple sources, making multidimensional calculations necessary.
Physical Parameter Eclipse Mapping
Authors: Vrielmann Sonja , Horne Keith , Baptista Raymundo , Hessman Frederick V.
Published: July 2016

We present a new eclipse mapping technique, which is able to map distributions in physical parameters of accretion disks in ecliping cataclysmic variables.
Dynamics of Low Luminosity Accretion onto Neutron Stars: Spherically Symmetric Models
Authors: Wang John C. L. , Sutherland Ralph S.
Published: July 2016

The ~ 108−109 old neutron stars in the Galaxy may be undergoing low luminosity accretion from the interstellar medium (Ostriker et al. 1970; Shvartsman 1971). It was first recognized by Shvartsman (1971) that the accretion induced radiation from the stellar surface can heat the infalling material, which in turn inhibits further accretion. This preheating instability has been studied in detail in the high luminosity regime where equilibrium ionization and heating holds (e.g., Buff & McCray 1974; Ostriker et al. 1976; Cowie et al. 1978). In the low luminosity regime, however, dynamical timescales are typically much shorter than atomic timescales so the accretion flow dynamics is strongly coupled to non-equilibrium (NEQ) atomic processes (cf. Blaes et al. 1995).
Binary Star Formation in Disc-Disc Encounters
Authors: Watkins S.J. , Bhattal A.S. , Francis N. , Whitworth A.P.
Published: July 2016

We present results of 3-D self-gravitating hydrodynamical calculations of the encounter between two protostellar discs. We find that the interaction leads to fragmentation of the discs and the formation of new stars and multiple systems.
A New Physical Mechanism to Account for the “Anomalous Viscosity” in Accretion Disks
Authors: Zhang X.
Published: July 2016

A new physical mechanism responsible for producing significant radial mass accretion in the inner disk of spiral galaxies has recently been found (Zhang 1996, ApJ, 457, 125). Since this mechanism depends only on the skewness of the global patterns (one-armed or two-armed spiral patterns, as well as skewed central bars) in the underlying disks, and since this process is collective in nature and produces an effective viscosity many orders of magnitude larger than that due to the microscopic processes, it is likely to be an important candidate for the long soughtafter “anomalous viscosity” in many types of astrophysical accretion disks which admit nonaxisymmetric instabilities.
The Caltech-Jodrell Bank VLBI Surveys
Authors: Pearson T.J. , Browne I.W.A. , Henstock D.R. , Polatidis A.G. , Readhead A.C.S. , Taylor G.B. , Thakkar D.D. , Vermeulen R.C. , Wilkinson P.N. , Xu W.
Published: July 2016

The Caltech-Jodrell Bank VLBI surveys of bright extragalactic radio sources north of declination 35° were carried out between 1990 and 1995 using the Mark-II system, achieving images with a resolution of about 1 mas at 5 GHz. The CJl survey (together with the older “PR” survey) includes 200 objects with 5 GHz flux density greater than 0.7 Jy; the CJ2 survey includes 193 flat-spectrum sources with 5 GHz flux density greater than 0.35 Jy; and we have defined a complete flux-density limited sample, CJF, of 293 flat-spectrum sources stronger than 0.35 Jy. We summarize the definition of the samples and the VLBI, VLA, MERLIN, and optical observations, and present some highlights of the astrophysical results. These include: (1) superluminal motion and cosmology; (2) morphology and evolution of the “compact symmetric objects” (CSOs); (3) two-sided motion in some CSOs; (4) the angular-size-redshift diagram; (5) misalignment of parsec-scale and kiloparsec-scale jets.
The Injector and the AGN Core
Authors: Matveenko L.I. , Pauliny-Toth I.I.K.
Published: July 2016

The fine core-jet structure of 3C 345 and its low-frequency variability are discussed.
Relativistic Jets in Low Power Radio Galaxies
Authors: Giovannini G. , Arbizzani E. , Feretti L. , Venturi T. , Cotton W.D. , Lara L. , Taylor G.B.
Published: July 2016

From VLBI observations of 11 FR I radio galaxies we find that: 1. parsec scale jets are relativistic; 2. 3C 264 shows a relativistic jet decelerating moving from the core to the extended lobes; 3. 3C 338 is a source with asymmetric parsec scale structure and morphological changes, implying proper motion on both sides of the source; 4. 1144+35 is an extended low power radio galaxy with an apparent superluminal motion in its parsec scale radio structure.
The Radio Properties of BL Lac Objects
Authors: Aller M. F. , Aller H. D. , Hughes P. A.
Published: July 2016

The cm-λ properties of BL Lac objects are discussed.
Multi-Frequency VLBI Observations of the GPS Source 1934–638
Authors: Tzioumis A. K. , King E. A. , Reynolds J. E. , Jauncey D. L. , Gough R. G. , Preston R. A. , Murphy D. W. , Tingay S. J. , Meier D. L. , Jones D. L. , Lovell J. E.J. , Edwards P. G. , McCulloch P. M. , Costa M. E. , Kedziora-Chudczer L. , Campbell-Wilson D. , Nicolson G. D. , Quick J. F. H.
Published: July 2016

PKS 1934–638 is an archetypal GPS source, peaking at 1.4 GHz and exhibits almost no flux density variability. VLBI images at frequencies of .843, 2.3, 4.8, & 8.4 were made with the southern hemisphere VLBI array and they reveal that the source is a 42 mas compact double. There is no detectable change in separation over the last 20 years, yielding an upper limit of ~ 0.03c ± 0.2c on any expansion velocity. The spectral shapes of the two components are remarkably similar, despite indications of finer structure on longer baselines. Magnetic field calculations indicate fields of a few mGauss and the results are consistent with equipartition.
Milliarcsecond Structure of the Faraday Effects in 3C 147: “The CSS Prototype with Highest Rotation Measure” (Which Is Not)
Authors: Lüdke E. , Cotton W. D. , Sanghera H. S. , Dallacasa D.
Published: July 2016

We analyze polarization observations of 3C 147 at milliarcsecond scale which we have made with the VLBA at L, S, and C band and with the MERLIN array at K band. Several constraints placed by the observations on the physical conditions of the magnetoionic gas which produces the Faraday rotation are briefly discussed. Our data show that the Faraday rotation increases towards the VLBI core component with a maximum observed value of RM~ 4600±80 rad m−2. Such a value does not support the inclusion of 3C 147 as a source with exceedingly-high faraday rotation (SEFR), as suggested from published low-resolution observations.
PKS 1718–649, the Nearest GPS Radio Source
Authors: Jauncey D. L. , Tingay S. J. , Preston R. A. , Reynolds J. E. , Tzioumis A. K. , King E. A. , Lovell J. E. J. , McCulloch P. M. , Costa M. E. , Koekemoer A. , Tornikoski M. , Kedziora-Chudczer L. , Campbell-Wilson D. , Nicolson G. D.
Published: July 2016

PKS 1718–649 has a classic GPS spectrum and is identified with the galaxy NGC 6328. At a distance of 56 Mpc, PKS 1718–649 becomes the nearest known GPS radio source.
VLBI Observations of the Seyfert Galaxy IC 5063
Authors: Oosterloo T. , Tzioumis A. , Reynolds J. , Morganti R. , Tsvetanov Z. , McCulloch P. , King E.
Published: July 2016

VLBI observations of IC 5063 are presented.
NGC 1052: A Different Class of H2O Megamaser?
Authors: Diamond P. J. , Claussen M. J. , Braatz J. A. , Wilson A. S. , Henkel C.
Published: July 2016

We present VLBA observations of the H2O megamasers in the LINER galaxy NGC 1052. The structure we observe suggests a different origin for the masers than those seen in NGC 4258.
Imaging of the Arp 220 OH Megamasers with VLBI
Authors: Lonsdale Colin J. , Diamond P. J. , Lonsdale Carol J. , Smith H. E.
Published: July 2016

Global VLBI imaging of the luminous IR galaxy Arp 220 reveals four major emission regions in the 1667 MHz line, each with complex spatial and velocity structure showing intriguing symmetries, suggestive of an AGN-related phenomenon. The continuum emission consists of about a dozen sub-mJy unresolved features which appear unrelated to the maser emission, and are interpreted as radio supernovae in an ongoing nuclear starburst.
VLBA Imaging of UX Ari
Authors: Beasley A. J. , Bastian T.S.
Published: July 2016

We have used the Very Long Baseline Array (VLBA) and the Very Large Array (VLA) to perform multi-wavelength radio imaging of the RS CVn active binary UX Arietis during the period November 16–21 1995. A series of strong flaring events exhibiting optically-thick spectra peaking above 100 GHz and extended source structures consistent with inter-binary emission were detected.
Sgr A* and Company—Multiwavelength Observations of Sgr A* and VLA Search for “Sgr A*’s” in LINERs
Authors: Falcke H. , Goss W. M. , Ho L. C. , Matsuo H. , Teuben P. , Wilson A. S. , Zhao J.-H. , Zylka R.
Published: July 2016

We report first results from a multiwavelength campaign to measure the simultaneous spectrum of Sgr A* from cm to mm wavelengths. The observations confirm that the previously detected submm-excess is not due to variability; the presence of an ultracompact component with a size of a few Schwarzschild radii is inferred. In a VLA survey of LINER galaxies, we found Sgr A*-like nuclei in one quarter of the galaxies searched, suggesting a link between those low-power AGN and the Galactic Center.
VLBA Observations of GRS 1915+105
Authors: Dhawan V. , Mirabel I. F. , Rodríguez L. F.
Published: July 2016

During quasi-periodic flux variations, the core of this galactic superluminal source shows: (a) a flat radio spectrum between 13cm and 2cm; (b) elongation of the core along the axis of arcsecond-scale ejecta; (c) a time-delay of ~4 mins at 3.6cm, relative to 2cm; (d) progressively less variation of the flux at 2cm, 3.6cm & 13cm; and (e) scatter-broadening to 1.9mas at 8.4GHz (135mas at 1GHz).
Water Masers Toward the Low-Luminosity YSO IRAS 05413–0104
Authors: Claussen Mark J. , Marvel Kevin B. , Wootten H. Alwyn , Wilking Bruce A.
Published: July 2016

We report on water maser proper motion in the jet of the YSO IRAS 05413–0104.
ARISE - A Proposed Future Space VLBI Mission
Authors: Ulvestad J. S. , Linfield R. P.
Published: July 2016

We are developing a future space VLBI mission, ARISE, that would involve placing a VLBA-equivalent radio telescope in a highly elliptical Earth orbit. The telescope would operate at VLBI frequencies of 5, 22, 43, and 86 GHz, as well as being capable of single-dish operation at 60 GHz. Fringe-detection thresholds will be less than 10 mJy except at 86 GHz. Key scientific goals include dual-polarization imaging of blazars on the same physical scale as their γ-ray emission, astrophysical and astrometric studies of extragalactic water megamasers, and single-dish observations of O2.
New Observational Techniques and Precise Orbit Determination of Artificial Satellites
Authors: Schutz B. E.
Published: July 2016

Modern observational techniques using ground-based and space-based instrumentation have enabled the measurement of the distance between the instrument and satellite to better than one centimeter. Such high precision instrumentation has fostered applications with centimeter-level requirements for satellite position knowledge. The determination of the satellite position to such accuracy requires a comparable modeling of the forces experienced by the satellite, especially when classical orbit determination methods are used. Geodetic satellites, such as Lageos, in conjunction with high precision ground-based laser ranging, have been used to improve for modeling of forces experienced by the satellite. Space-based techniques, such as Global Positioning System (GPS), offer alternatives, including kinematic techniques which require no modeling of the satellite forces, or only rudimentary models. This paper will describe the various techniques and illustrate the accuracies achieved with current satellites, such as TOPEX/POSEIDON, GPS/MET and the expectations for some future satellites.