bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and the Pulsar Emission Mechanism
Authors: Boriakoff Valentín
Published: July 2016

Pulsar radio emission is composed in varying proportions of microstructure, subpulses and amorphous emission. Each component has its own time and frequency behaviour. The average pulse profile changes its width with frequency, typically asν−0.26. The location (pulse phase) of the subpulses refered to a fiducial point within the profile follows the sameν−0.26law as the width of the average pulse profile. The fiducial point in the pulse profile follows the interstellar plasma dispersion relation exactly: the source emission at this phase is simultaneous at all frequencies. The subpulse width is typically nearly constant with frequency. Emission of a subpulse may be systematically absent at certain frequency ranges, the pulse profile may be different there. Micropulses are typically very wideband: ∼1GHz or more. Individual micropulse widths are constant with frequency. Its time width distributions have upper limits (0.1-1 ms). The time separation (phase) of any micropulse with respect to the fiducial point is constant with frequency, i.e. it is simultaneous at all frequencies at source. The spectrum of individual micropulses appears to have breakpoints: it is observable atν≤ν(μ co), but not above it. This effect (and not a steep spectrum) seems to account for the smaller number of micropulses at higher frequencies: atνwe see micropulses withν(μ co)>νonly, micropulses withν(μ co)<νare not visible, at low frequencies we will see more micropulses than at high frequencies. Micropulses prefer the conal emission zones, and are very weak or absent in the core emission zones. More than one micropulse can be observed at a given time. Micropulses occasionally appear in trains with a nearly constant time separation, up to 20 micropulses have been observed in such quasi-periodic sequences. Sequence phase and period are variable within a train, they may have discrete values. Such trains can be observed simultaneously at widely separated frequencies. Ocasionally more than one quasi-periodic train may appear at the same time. Subpulses in general follow the linear polarization angle of the average pulse profile, with occasional 90° jumps. Within a micropulse the polarization angle can be constant, or can have a fast swing of ∼ 50°. Micropulse polarization angle can be widely different from that of the subpulse on which it is superimposed.
Observations of Giant Pulses from Pulsar PSR B1937+21
Authors: Thorsett S. E. , Shrauner J. A. , Cognard I. , Taylor J. H.
Published: July 2016

We 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

We 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.
The Polarization of the Crab Pulsar with HST
Authors: Dolan Joseph F. , Boyd Patricia T. , Hill Robert J. , Graham-Smith F. , Lyne A. G. , Biggs James D. , Percival J. W. , Robinson Edward L. , Citters G. Wayne van
Published: July 2016

The linear polarization of the Crab pulsar as a function of pulse phase was observed by the High Speed Photometer on the Hubble Space Telescope in March, 1993. Observations were obtained in a bandpass centered on 2770 A using a 0.25 ms sample time, corresponding to a time resolution of 0.0075 in pulse phase. The UV polarization of the pulsar [Fig. 1] is strikingly similar to that observed in the visible (cf. Smith et al. 1988). The same values of polarization and the same swing of position angle occur through the main and secondary pulses. The polarization pulse profile must be essentially wavelength independent at frequencies above the infrared.
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.
X-ray observations of PSR J0218+4232 and of PSR B1937+21
Authors: Verbunt Frank , Johnston Helen M. , Bruyn A.G. de , van der Klis Michiel
Published: July 2016

Navarro et al. (1995) have discovered a 2.3 ms radio pulsar in a 2.0 day orbit around a low-mass companion. An interesting feature of this pulsar, PSR J0218+4232, is that radio emission is discovered throughout the pulse period; this is taken by Navarro et al. as an indication that the pulsar magnetic field is almost aligned with the rotation axis, and may also be related to the rather high radio luminosity of this pulsar,L400MHZ> 2700 mJy kpc2. The dispersion measureDM= 61.25pc cm−3indicates a minimum distance of 5.7 kpc, according to the model for the free electron distribution in the Galaxy by Taylor and Cordes (1993).
Recent X-ray Observations of Pulsar Nebulae
Authors: Kawai Nobuyuki , Tamura Keisuke
Published: July 2016

Results 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

The 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 > 50 MeV).
Wind Acceleration in Pulsar Magnetospheres
Authors: Takahashi Masaaki , Shibata Shinpei
Published: July 2016

To 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

We 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):

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Synthetic stellar evolution

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mass and radius as a function of time (Eggleton et al. 1989)

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Accurate treatment of close encounters

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Perturbations of binaries and stable multiple systems - Exchange reactions (involving triple and binary-binary interactions) - Collisions → blue stragglers

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Binary evolution (primordial and dynamically formed)

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Tidal interactions (Mardling & Aarseth 1996) - Stable mass transfer - Common envelope evolution - Magnetic braking - Gravitational radiation - Mergers (including blue stragglers)

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Mass loss

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Stellar winds - Supernovae - Evaporation of stars from the cluster

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Neutron star formation

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Supernovae with kick velocities of Lyne & 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

The 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

Disk-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.
The nature of V Sagittae
Authors: Wood Janet H. , Lockley J.J.
Published: July 2016

We discuss previous models of V Sge and, in light of our new phase resolved spectroscopy data, suggest a new model: a colliding wind.
Winds from Cataclysmic Variables
Authors: Drew J. E.
Published: July 2016

The 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

Hubble 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).
Numerical Simulations of Advective Flows Around Black Holes
Authors: Chakrabarti Sandip K. , Ryu D. , Molteni D. , Sponholz H. , Lanzafame G. , Eggum G.
Published: July 2016

Observational results of compact objects are best understood using advective accretion flows (Chakrabarti, 1996, 1997). We present here the results of numerical simulations of all possible types of such flows.

Two parameter (specific energy ε and specific angular momentum λ) space of solutions of inviscid advective flow is classified into ‘SA’ (shocks in accretion), ‘NSA’ (no shock in accretion), ‘I’ (inner sonic point only), ‘O’ (outer sonic point only) etc. (Fig. 1 of Chakrabarti, 1997 and references therein). Fig. 1a shows examples of solutions (Molteni, Ryu & Chakrabarti, 1996; Eggum, in preparation) from ‘SA’, ‘I’ and ‘O’ regions where we superpose analytical (solid) and numerical simulations (short dashed curve is with SPH code and medium dashed curve is with TVD code; very long dashed curve is with explicit/implicit code). The agreement is excellent. In presence of cooling effects, shocks from ‘SA’ oscillate (Fig. 1b) when the cooling timescale roughly agrees with postshock infall time scale (Molteni, Sponholz & Chakrabarti, 1996). The solid, long dashed and short dashed curves are drawn for T1/2 (bremsstrahlung), T0.4 and T0.75 cooling laws respectively. In the absence of steady shock solutions, shocks for parameters from ‘NSA’ oscillate (Fig. 2) even in the absence of viscosity (Ryu et al. 1997). The oscillation frequency and amplitude roughly agree with those of quasi-periodic oscillation of black hole candidates. When the flow starts from a cool Keplerian disk, it simply becomes sub-Keplerian before it enters through the horizon. Fig. 3a shows this behaviour where the ratio of λ/λKeplerian is plotted. When the flow deviates from a hot Keplerian disk, it may develop a standing shock as well (Fig. 3b) (Molteni et al. 1996).
Magnetic Flux Transport in Protostellar Accretion Disks
Authors: Contopoulos John , Königl Arieh
Published: July 2016

Centrifugally driven winds from the surfaces of magnetized accretion disks are a leading candidate for the origin of bipolar outflows and have also been recognized as an attractive mechanism for removing the angular momentum of the accreted matter. The origin of the open magnetic field lines that thread the disk in this scenario is, however, still uncertain. One possibility is that the field lines are transported through the disk, but previous studies have shown that this process is inefficient in disks with turbulent viscosity and diffusivity. Here we examine whether the efficiency can be increased if angular momentum is transported from the disk surfaces by large-scale magnetic fields instead of radially by viscous stresses. In this picture, the removal of angular momentum is associated with the establishment of a global poloidal electric current driven by the radial EMF in the disc, and it does not necessarily need to involve super-Alfvénic outflows. We address this problem in the context of protostellar systems and present representative solutions of the time evolution of a resistive disk that is initially threaded by a uniform vertical field anchored at a large distance from its surfaces. We assume that the angular momentum transport in the disk is controlled by the large-scale magnetic field and take into account the influence of the field on the disk structure.
Time-Resolved Optical Spectroscopy of V795 Herculis
Authors: Dickinson Rachel J. , Prinja Raman K. , Rosen Simon R. , King Andrew R. , Hellier Coel , Horne Keith
Published: July 2016

High resolution optical spectroscopy of V795 Herculis shows complex time- and phase-dependent behaviour of the disk emission. Separate low- and high-velocity fluctuations phased on the 2.6 hr orbital period are observed in the wings of the Balmer lines, prompting a gas stream overflow model.
SPH Simulations of Protoplanetary Perturbers in Gas Disks
Authors: Maddison Sarah , Barge Pierre
Published: July 2016

We use Smoothed Particle Hydrodynamics (SPH) to numerically investigate gap clearing around a protoplanetary body in a selfgravitating gaseous disk. It has been suggested that proto-Jupiter regulated it’s own growth by clearing a gap around itself and thus halting accretion.
The Effect of the Nova Explosion on the Evolution of Cataclysmic Variables
Authors: Naylor T. , Somers M.W.
Published: July 2016

Classical nova outbursts are thermonuclear explosions on the surfaces of the white dwarfs in cataclysmic variables. The explosion heats the surface layers of the white dwarf, which are expected to cool on a timescale of a hundred years. The hot white dwarf should have two obvious effects on the system.

(1)

It will heat the surface of the accretion disc and secondary star, increasing the overall luminosity of the system.

(2)

By irradiating the surface of the secondary star it may bloat it and drive more mass transfer, thus again increasing the overall luminosity.
Optical Low States of the Supersoft X-Ray Source RXJ0513.9–6951
Authors: Reinsch K. , van Teeseling A. , Beuermann K. , Abbott T.M.C.
Published: July 2016

The transient luminous soft X-ray source RXJ0513.9–6951 (Schaeidt et al., 1993, A&A 270, L9) is a high-mass-transfer binary system (Cowley et al., 1993, ApJ 418, L63; Pakull et al., 1993, A&A 278, L39) with a probable orbital period of 0.76 days (Crampton et al., 1996, ApJ 456, 320). Here, we summarize the results of a quasi-simultaneous optical and X-ray monitoring (see Fig. 1). The sudden decrease of the optical flux, the accompanying reddening, and the turn-on in the soft X-ray band can be quantitatively described by variations in the irradiation of the accretion disk by the hot central star (Reinsch et al., 1996, A&A 309, L11). In this simple model, we consider a white dwarf with nuclear burning of accreted matter (van den Heuvel et al., 1992, A&A 262, 97), surrounded by a flat standard disk. In the optical high state, accretion at near-Eddington rate occurs and the white dwarf photospheric radius must be considerably expanded causing an enhanced illumination of the disk and the secondary. In the optical low state, the photosphere shrinks in response to a temporarily slightly reduced mass-transfer rate. At the same time, the effective temperature increases, and the soft X-ray flux becomes detectable with ROSAT. This model does not depend on the particular cause for the drop in the accretion rate and can describe the optical/ X-ray variability with the total luminosity changing by less than 20 %.
Thirty Years of VLBI: Early Days, Successes, and Future
Authors: Moran J.M.
Published: July 2016

The early days of VLBI are discussed, with emphasis on the fifteen experiments performed in the U.S. and Canada in 1967. Some key technical ideas are described that influenced the development of the technique, including digital fringe rotation, bandwidth synthesis, spectral phase referencing, phase closure and self-calibration, and water vapor radiometry.
Model of a Precessing Jet in 3C 279
Authors: Abraham Z. , Carrara E.A. , Zensus J.A.
Published: July 2016

The parsec scale radio jet of 3C 279 presents a number of superluminal features that move along straight trajectories with constant velocities. The position angles P.A. of these trajectories, projected in the plane of the sky, and the velocities βobs of the individual components are different. We interpret the differences in the these velocities as differences in the angle between the jet and the line of sight and apply the model of a precessing beam to the data. All the geometrical parameters of the precessing jet and the Lorentz factor γ of the relativistic particles are determined. The model predicts the behavior of the Doppler factor δ as a function of time and we verify that its maximum value occurred at the epochs in which strong optical and X-ray flares were observed.
VLBI of Southern EGRET Identifications
Authors: Murphy D.W. , Tingay S.J. , Preston R.A. , Meier D.L. , Jones D.L. , Edwards P.G. , Costa M.E. , Lovell J.E.J. , McCulloch P.M. , Jauncey D.L. , Reynolds J.E. , Tzioumis A.K. , King E.A. , Nicolson G.D. , Quick J.F.H. , Wan T.-S. , Shen Z.-Q.
Published: July 2016

We have undertaken VLBI observations of 8 Southern Hemisphere EGRET radio sources. Using our data as well as data obtained from the literature we have examined the difference in radio properties between gamma-ray loud and gamma-ray quiet radio sources. In particular, we find no evidence that gamma-ray loud radio sources lie preferentially in sources with straight radio jets as has been suggested.
Magnetic Fields in AGN
Authors: Wardle J. F. C.
Published: July 2016

We review VLBI polarization results. In particular, we discuss the a) “shock in jet paradigm”, b) the orientation of the magnetic field in jets as a function of optical identification, c) rotation measure and Faraday dispersion measurements as a probe of the narrow line region, and d) future directions of polarization observations. Results we emphasize are i) there is still a strong correlation between optical L/C ratio or EW and magnetic field orientation in the jets of blazars, even for high redshift weak-lined objects, ii) observed rotation measures are much smaller than expected from the properties of the NLR, except for some CSS sources. Also iii) a faint boundary layer or sheath (with a parallel magnetic field) has been observed around the jet of the weak-lined blazar 1055+018, and iv) circular polarization has been detected for the first time in the jets of 3C 84 and 3C 279.
A VSOP Survey Program Pre-launch Continuum Survey
Authors: Edwards P. G. , Fomalont E. B.
Published: July 2016

The VSOP Survey Program will observe a complete survey of flat-spectrum sources at 5 GHz. In order to determine which of the sample sources are strong and small enough to be detected with VSOP, a pre-launch survey of 377 continuum sources north of δ > −43° was conducted at 5 GHz with the VLBA over 24 hours in June 1996. About 250 of the sources had correlated flux densities ≥ 0.4 Jy between MK–SC and have been included in the VSOP survey sample.
Comparison of Total Flux and VLBI Properties of a Sample of 15 AGN at 22 GHz
Authors: Wiik K. , Valtaoja E.
Published: July 2016

A sample of 15 bright AGN has been observed at 22 GHz with two epoch global VLBI observations. The sample consists of all sources in the complete 2 Jy catalogue of Valtaoja et al. (1992) previously unobserved at 22 GHz VLBI. We have begun to investigate how much structural information can be derived just from total flux density (TFD) monitoring and how to use total flux density observations to complement space VLBI observations. As an example we present Doppler boosting factors derived in four different methods.
Structure and Variability of Sources from Geodetic VLBI-Data
Authors: Pyatunina T. B.
Published: July 2016

8 GHz maps of 39 radiosources have been obtained with ≈ 0.5 mas resolution from geodetic VLBI-data. Structure variability has been investigated on ≈ monthly interval during the bursts of radio emission of two sources 0059+581 and 0202+149 in period from June 1994 to February 1996. Bright jet components in the sources show no steady outward motion, but may be some oscillations near stationary positions.
A Multi-Frequency VLBI Total Intensity and Polarization Study of the BL Lacertae Object 0716+714
Authors: Kovalev Y. Y. , Gabuzda D. C. , Krichbaum T. P. , Alef W. , Witzel A.
Published: July 2016

New polarization-sensitive global VLBI and VLBA images of the BL Lacertae object 0716+714 at 6 cm (1991.4) and 3.6 cm/1.3 cm (1994.2) are presented. The source shows a compact, one-sided core–jet structure in structural position angle ~ 13°. The 3.6 cm total intensity image shows the jet beginning to curve toward the arcsecond-scale structure, which lies in position angle ~ −45°. Comparison with previously published data suggests that the apparent velocity of a 6 cm jet component is > 1.09 ± 0.15c, if the red shift of 0716+714 is z > 0.3. Linear polarization from the VLBI core was detected at all three frequencies; in addition, polarization from the innermost jet component was detected at 1.3 cm. This compact jet polarization appears to be quite high, ~ 50%, and to be aligned with the jet direction, which can be understood if it is a transverse shock. The VLBI core polarization at our earlier epoch was perpendicular to the VLBI jet direction, but had rotated to align with the jet direction by the later epoch, about a year later. This rotation may indicate the imminent birth of a new VLBI component (shock).
The Ultimate Fate of CSOs
Authors: De Young D. S.
Published: July 2016

Recently Readhead et al. (1996b) have presented empirical evidence that CSOs evolve into larger double sources many kpc in extent. The implications of this are explored analytically and numerically. It is found that pure luminosity evolution on the small scales of CSOs is unlikely in the presence of any ambient density gradients. However, the transition from CSO to MSO may involve a nearly constant lobe advance speed as suggested by Readhead et al.. This seemingly unphysical result can be seen to result from the interaction of the propagating jet with its surrounding medium.
Short-Term Variability of Sagittarius A* at Millimeter Wavelengths
Authors: Tsutsumi T. , Kawabata T. , Miyazaki A. , Tsuboi M.
Published: July 2016

We present preliminary results from the observations of the Galactic Center compact source, Sgr A* at 3 and 2 millimeter wavelengths using the Nobeyama Millimeter Array to monitor flux density variations on timescales shorter than a month. Such high spatial resolution observations at millimeter wavelengths are important to shed more light on the origin of the variability and the nature of this compact source. Our observations indicate the flux density varies at least by ~30% in one to two weeks at 3 mm.
Water Maser Emission and the Parsec–Scale Jet in NGC 3079
Authors: Trotter A. S. , Moran J. M. , Greenhill L. J.
Published: July 2016

We have imaged the H2O maser and 22, 8, & 5 GHz continuum in the nucleus of NGC 3079, using the NRAO VLBA. The maser features are distributed over ~ 2 pc along an axis aligned with the plane of the kpc–scale edge–on molecular disk. The masers are not angularly coincident with any detected continuum emission. The two brightest continuum features, which trace a parsec–scale jet, have similar spectra that peak at frequencies ν > 5 GHz. We also detected faint maser emission along the jet axis.
Multi-Epoch VLBA Observations of the SiO Maser Emission Towards R Aquarii (R Aqr)
Authors: Boboltz D. A. , Diamond P. J. , Kemball A. J.
Published: July 2016

We have observed ν = 1, J = 1 – 0, 43-GHz SiO maser emission towards the symbiotic Mira variable R Aqr at four different epochs in the stellar pulsation cycle using the VLBA.
An Update on Radio Supernovae
Authors: Van Dyk Schuyler D. , Sramek Richard A. , Weiler Kurt W. , Montes Marcos J. , Panagia Nino
Published: July 2016

The radio emission from supernovae (SNe) is nonthermal synchrotron radiation of high brightness temperature, with a “turn-on” delay at longer wavelengths, power-law decline after maximum with index β, and spectral index α asymptotically decreasing with time to a final, optically thin value. Radio supernovae (RSNe) are best described by the Chevalier (1982) “mini-shell” model, with modifications by Weiler et al. (1990). RSNe observations provide a valuable probe of the SN circumstellar environment and constraints on progenitor masses. We present a progress report on a number of recent RSNe, as well as on new behavior from RSNe 1979C and 1980K, and on RSNe as potential distance indicators. In particular, we present updated radio light curves for SN 1993J in M81.
Galilean Satellites and the Galileo Space Mission
Authors: Lieske J.H.
Published: July 2016

The Galileo spacecraft arrived at Jupiter in December 1995 to start its two-year mission of exploring the Jovian system. The spacecraft will complete eleven orbits around Jupiter and have ten more close encounters with the outer three Galilean satellites, after the initial close approach to Io on December 7, 1995. Since the Io encounter occurred closer to Io than originally designed, the spacecraft energy change was greater than nominally planned and resulted in an initial spacecraft orbital period about 7 days less than that designed in the nominal tour. A 100-km change in the Io-encounter distance results in an 8-day change in initial period of the spacecraft. Hence the first Ganymede encounter was moved forward one week, and the aim points for the first two Ganymede encounters were altered, but all other encounters would occur on their nominal dates and at the nominal altitudes. This was accomplished without expending spacecraft fuel and resulted in the first Ganymede flyby occurring on June 27, 1996 rather than the nominally scheduled July 4.

Earth- and spacecraft-based data were employed in developing ephemerides in support of the Galileo space mission. An analysis of CCD astrometric observations from 1992–1994, of photographic observations from 1967–1993, of mutual event astrometric data from 1973–1991, of Jovian eclipse timing data from 1652–1983, of Doppler data from 1987–1991, and of optical navigation data from the Voyager spacecraft encounter in 1979, produced the satellite ephemerides for the Galileo space mission.
Space Debris – The Short Term Orbital Evolution in the Earth Gravity Field
Authors: Wnuk Edwin
Published: July 2016

Two aspects of the orbital evolution of space debris – the long-term evolution and the short-term one – are of interest for an exploration of the near- Earth space. The paper presents some results concerning the estimation of the accuracy of predicted positions of Earth-orbiting objects for the short-term: a few revolutions or a time-span interval of a few days. Calculations of predicted positions take into account the influence of an arbitrary number of spherical coefficients of the Earth gravity potential. Differences in predicted positions due to differences in the best contemporary geopotential models (JGM-2, JGM-3 and GRIM4-S4) are estimated with the use of an analytical theory of motion and a numerical integration.
Using Close Encounters of Minor Planets for the Improvement of their Masses
Authors: García A. López , Medvedev Yu. D. , Fernández J. A. Moraño
Published: July 2016

The orbits of 6807 numbered minor planets on the time interval 1975–2010 have been integrated. The possibility of determining masses for asteroids with close encounters with each other has been investigated, including several kinds of situations. The importance of the observational time arc, as well as the distribution of observations, for determining the masses are shown. The mass of asteroid (24) Themis from its perturbations on asteroid (2296) Kugultinov, and the mass of (10) Hygiea from its perturbations on (1259) Ógyalla have been determined.
Precession and Nutations of Mars calculated with Kinoshita’s Model
Authors: Bouquillon S. , Souchay J.
Published: July 2016

This paper presents the theoretical study of precession and nutation of Mars in a rigourous way. For this work we choose a natural reference system, based on the concept of non-rotating origin, and the appropriate canonical variables. Then, we solve the equations of the problem by taking into account the effects of the Sun, the Earth, Jupiter, and satellites of Mars, Phobos and Deimos.
Orbital Arc Length as a Universal Independent Variable
Authors: Floria Luis
Published: July 2016

A uniform treatment of the two-body problem leads to a differential time transformation to introduce the arc length along the orbit as the independent variable. The transformation is integrated in terms of the classical anomalies.
Analytical Effects of Gravitational Waves on the Motion of an Artificial Satellite
Authors: Youssef M.H. , Ahmed M.K.
Published: July 2016

The motion of an artificial satellite in the Earth’s gravitational field is discussed in the post-Newtonian framework including the effect of weak gravitation waves using the perturbation technique of the canonical Lie-transformations. Two successive canonical transformations are used to derive analytical expressions for the short-period, long-period and secular perturbations of orbital elements. The solution is expressed in terms of the Delaunay variables.
Monitoring Earth Orientation Using Various Techniques: Current Results and Future Prospects
Authors: Gambis D.
Published: July 2016

Until 1972, astrometry based on a network of optical instruments was the only technique able to monitor the Earth orientation (polar motion, Universal Time and nutation). Since various techniques have shown their capability to give all or a part of these parameters: Doppler observations of navigation satellites, laser ranging to the Moon and to dedicated artificial satellites, Very Long Baseline Interferometry (VLBI) and more recently GPS and DORIS. The different Earth Orientation Parameters (EOP) series obtained by the individual techniques are inhomogeneous in time span, quality, time resolution – which supports the concept of combined solutions taking advantage of the various contributions.

The main task of IERS is the maintenance of both a conventional terrestrial reference system based on observing stations and a conventional celestial reference system based on extragalactic radio sources and also the matrix product allowing the transformation between these two systems which takes into account precession-nutation, polar motion and Earth rotation.

The objective of this paper is to present the evolution, the state of the art and future prospectives concerning the multi-technique EOP combined solution made at IERS/CB.
Solar-Radius Variations Over a Solar Cycle Observed with the Tokyo Photoelectric Meridian Circle
Authors: Yoshizawa M.
Published: July 2016

As the Sun shows the well-known magnetic activity of eleven-year period, many other interesting observational features of the Sun have been examined in connection with the solar cycle. The diameter of the Sun is one of these interesting observable quantities. The apparent radius of the Sun has been observed regularly since 1985 with the Tokyo Photoelectric Meridian Circle (Tokyo PMC) at Mitaka. Here, we show the average value of the solar radii observed by us. We also show that the annual-mean values of the observed radii take the smallest value near the solar-cycle maximum, in 1989 and 1990, and the largest ones around the solar-cycle minimum, in 1986 and 1994. The average peak-to-peak shift of the annual-mean solar radius for the solar cycle is ΔR⊙/R⊙ ~ 1.2 × 10−4, which is close to the relative change of the frequency of the 5-minute p-mode solar oscillation within one solar cycle.
The History of Solar Prominence Research: Historical Introduction to IAU Colloquium No. 167 “New Perspectives on Solar Prominences”
Authors: Tandberg-Hanssen Einar
Published: July 2016

We trace the history of observational solar prominence research from the early period when total solar eclipses provided the only means of observation, via the introduction of photography and spectroscopy in the 1860’s, to the present epoch when application of the Zeeman and the Hanle effects makes possible determination of the all-important magnetic fields in prominences.

Dividing prominence models into two classes, those that treat the support of the prominence against gravity and those concerned with the physical conditions in the prominence plasma itself, we describe the progress made in both classes of models since the 1950’s, when the first models were proposed. Finally, we comment on the necessity of combining aspects of the two classes of prominence models into a comprehensive picture that can account for the global nature of prominence support and stability, and where the adjacent coronal structures play an important role.
Concerning Magnetic Field Measurements in Prominences Using Zeeman and Hanle Methods
Authors: Bashkirtsev V.S. , Mashnich G.P.
Published: July 2016

A critical review is made of the results of magnetic field measurements in prominences obtained by the Zeeman and Hanle methods. By considering the example of three prominences, some discrepancies between the methods are shown. The authors consider that the magnetic field measurements by the Hanle method inadequately represent the actual magnetic field pattern. To overcome these discrepancies a comparative analysis of magnetic field measurements in prominences by both methods is required.
Vector Magnetic Fields at the Base of Filaments and the Filament Environment
Authors: Wang Jingxiu , Li Wei
Published: July 2016

Based on an analysis of three active filaments in AR 6891, we find that vector magnetic fields at the base of filaments and the filament environment is characterized by the following: (1) The transverse field is parallel along the magnetic neutral line for most of the filaments. The average transverse field beneath the filaments is more than 400 G. (2) The horizontal gradient of the line-of-sight field crossing the neutral line is, more or less, constant along the major fraction of a filament, but very steep at the two ends. The average gradient is 0.06 G/km. (3) For each of the filaments there is a squeezing magnetic structure which represents an intrusion of a satellite bipole into the main flux system. The neutral line for a squeezing magnetic structure has a large curvature, a strong sheared transverse field of more than 1 KG, and a steep field gradient of approximate 0.3 G/km. (4) The transverse field and field gradient are clearly enhanced before the filament eruption.
Formation of Thin Current Sheets in the Solar Atmosphere
Authors: Cheng C.Z. , Choe G.S.
Published: July 2016

In a two-dimensional quadrupolar magnetic field geometry, it is demonstrated that various magnetohydrostatic equilibrium field configurations containing current sheets can be formed either by changes in thermal properties or by footpoint displacement. The shape of current sheets depends on the mass distribution in flux tubes. If the mass per flux tube is maximum at the center of the low-lying bipolar arcades, a current sheet is formed between these two arcades along the separatrix line as the plasma temperature (or the shearing footpoint displacement) is increased above a critical value. If the mass per flux tube is higher in the outer tubes of the bipolar arcades than in the inner ones, a current sheet with a sharp downward-pointed tip hanging at a distance above the bottom boundary is formed when the temperature is decreased below a critical value. Resistive magnetic reconnection in the latter type current sheet results in a magnetic island wrapped in dipped field lines, which is regarded as a plausible prominence field configuration.
The Prominence-Corona Transition Region and the Problem of Prominence Oscillations
Authors: Oliver R. , Ballester J.L.
Published: July 2016

Recent theoretical investigations of prominence oscillations indicate that the prominence-corona transition region (PCTR) may have a great influence on the magnetohydrodynamic modes of the whole system. We here consider an isothermal prominence embedded in an isothermal corona with a thin PCTR providing a smooth temperature transition between prominence and corona. The effect of the PCTR on the oscillations of the prominence body are investigated.
A Fibril Structure Model for Stellar Prominences
Authors: Oliver R. , Ballester J.L.
Published: July 2016

Extensive observational background exists about the presence of cool material clouds embedded in the stellar coronae of rapidly rotating, late-type stars. Observations of such clouds in HKAqr (Gliese 890) and HD 197890 suggest that the clouds are at heights smaller than the star’s corotation radius and could be looked at as a phenomenon similar to that of solar prominences. Recent observations of solar prominences have reinforced the evidence about their fibril structure made of many long, thin magnetic flux tubes making angles about 25 degrees with the direction of the filament channel, with only the central 10–20% of the magnetic flux tubes filled with cool matter, which can produce a depression at the summits of the flux tubes. Then, assuming a similar structure for the stellar cool clouds, we have looked for the physical characteristics of such stellar prominences, i.e. the size of the flux tube depression, the density, temperature, half-width and supported mass of the cool region, taking into account gravity variation with height and centrifugal acceleration, since such clouds have been detected at great heights within stellar coronae belonging to rapid rotators.
Filament Channels: Essential Ingredients for Filament Formation
Authors: Gaizauskas V.
Published: July 2016

Channels share with their filaments in a hemispheric dependance for the orientation of their axial magnetic fields. This property has significant implications for models of filaments. In support of new model-building exercises, this review examines known signatures of channels, presents evidence that emerging flux plays a key role in creating a new filament channel, and compares channels which form in the belts of active latitudes with those formed closer to the poles.
Force-Free Models of Filament Channels
Authors: Longbottom A.W.
Published: July 2016

A fast multigrid method to calculate the linear force-free field for a prescribed photospheric flux distribution is outlined. This is used to examine an idealized model of a filament channel. The magnetic fields, for a number of different field strengths and positions, are calculated and the height up to which field lines connect along the channel is examined. This is shown to strongly depend on the value of the helicity of the system. A possible explanation, in terms of the global helicity of the system, is suggested for the dextral/sinistral hemispheric pattern observed in filament channels.
Wave Activity and Prominence Eruption
Authors: Baudin F. , Bocchialini K. , Delannee C. , Koutchmy S. , Stellmacher G. , Shibata K. , Veselovsky I.S. , Panasenko O.A. , Zhukov A.N.
Published: July 2016

Observational evidence of 3 and 5 min vertical oscillations of a filament on the disk are recorded. Wave activity was observed before, during and after a filament disappearance, inside and around the filament. Both an Hα brightening and, later, a blowing out of a faint soft X-ray (Yohkoh) loop system occuring in connection with a flare were noticed. The wave activity seems to be a dynamically important ingredient of this erupting prominence.

Propagating MHD waves and convective structures bring their energy and momentum from the photosphere towards the chromosphere up to the coronal heights where they are partially reflected and/or dissipated. The transition from the laminar to the turbulent state of the whole prominence enhances the dissipation rate of the external waves inside this system, adding energy to produce the heating and lifting of the plasma. Internal plasma instabilities could trigger this transition in the framework of a prominence disappearance.
Evolution of a Filament/CH/Magnetic Field Complex
Authors: Ioshpa B.A. , Mogilevsky E.I. , Obridko V.N.
Published: July 2016

SOHO and YOHKOH images, as well as Hα filtergrams and magnetograms from IZMIRAN have been used to analyze the evolution of the related solar phenomena – filament, active region, and accompanying pair of coronal holes – during six solar rotations, with an emphasis on the events observed during August–September, 1996. The whole complex has been considered against the large–scale magnetic fields calculated under the potential approximation. A peculiar point has been found along the changing filament. It is shown that the phenomena under investigation (filament, active region, and coronal hole) form a single complex connected with the magnetic field structure.