bluuebunny/crossref_metadata_2025_split huggingface dataset:
Short-Term Wind and Photospheric Activity in Be Stars Deduced from Campaigns with the IUE Spacecraft
Authors: Peters Geraldine J. , Gies Douglas R. 
Published: July 2016

AbstractFrom 1985–96 twelve multiwavelength campaigns on 15 Be stars were carried through using data from the IUE spacecraft to study the phenomenon of short-term spectroscopic and photometric variability. Highlights from recent work on this database are presented here. Three classes of variability have been identified: 1) The FUV flux and wind strength are correlated, 2) The FUV flux varies cyclically but wind variability if present does not correlate with the flux, and 3) The wind strength cyclically varies but does not correlate with light variations. For Class 1 the period is usually less than the star’s expected rotational period, but for Classes 2 & 3, the period is sometimes close to Prot. We have employed a cross-correlation technique to extract information on the nature of the line profile variability (lpv). Evidence for nonradial pulsations (NRP) in low-order modes is found for objects in Classes 1 & 2, the light variations appear to be caused by a modulation of the star's photospheric temperature, and the hot crest of the NRP wave is in front when the star is bright. For Class 1 stars the wind is enhanced over the hot crest. The mass loss in Class 3 may originate from a localized active region on the star and the importance of NRP in these stars remains unknown.
Polarimetry as a Diagnostic of Circumstellar Envelopes
Authors: Bjorkman Karen S. 
Published: July 2016

AbstractPolarimetric observations of stars can provide useful diagnostics of the geometry and physical conditions of the circumstellar envelope. This paper reviews the application of polarimetric techniques to hot stars (with particular emphasis on Be stars) and the status of polarization observations, and discusses some recent developments that improve our ability to make and to interpret such observations. Polarization measurements, bolstered by the increasing availability of new instruments on larger telescopes, continue to improve toward both higher signal-to-noise ratio and higher spectral resolution. Because of this we can begin to address specific questions of the physics of the circumstellar envelopes, since polarization provides a means to separate the effects of the photosphere from those of the envelope. New theoretical and analytic approaches are improving our ability to interpret spectropolarimetric data. We now are able to determine characteristics such as disk opening angle, density, and temperature. Furthermore, polarimetric observations in new wavelength regimes (e.g. ultraviolet and infrared) are opening new avenues to investigate circumstellar disks. The combination of spectropolarimetry with other kinds of data, such as spectroscopy, photometry, and interferometry, shows promise for providing stringent tests for theoretical models of the circumstellar envelopes of Be stars.
Line Profile Modeling of Disks
Authors: Hummel W. 
Published: July 2016

AbstractIn this talk I give a short overview of models for spectral lines in Be stars disks which I think are quite instructive. I then examine the arguments for my own model assumptions and discuss selected topics concerning radiative line transfer calculations in three dimensions. We show that symmetric Hα emission lines of Be stars can be understood in terms of Keplerian disks. It is also demonstrated that one-armed global disk oscillations provide the best available solution to understand the long-term V/R variations in Be star emission lines.
On the Fe II Dielectronic Recombination in Stellar Envelopes
Authors: Cruzado Alicia , Ringuelet Adela E. 
Published: July 2016

AbstractWe are interested in the atomic processes taking place in the envelopes of early type stars; the first part of our project consists of an investigation of the dielectronic recombination (DR) of metals. In earlier papers, we have studied the DR of Mg II and its contribution to the IR continuum; now, we are interested in accomplishing similar results analysing the Fe II atom.
Be Envelope Properties Determined from Fe II Emission Lines
Authors: Chauville J. , Ballereau D. , Cidale L. , Morrell N. , Friedjung M. , Zorec J. 
Published: July 2016

AbstractApplying the SAC (self absorption curve) method to χ Oph (HD 148184) we conclude that Fell emission lines are optically thick. We estimate the excitation temperature of the permitted Fe II line formation region and the dimensions of this region. We conclude that this region may possibly have a non-uniform density structure.
59 Cygni: A Tilted ϕ Persei like System
Authors: Rivinius Th. , Štefl S. 
Published: July 2016

AbstractThe binarity of 59 Cygni was confirmed and orbital parameters from the radial velocity curve of the primary derived. The observed emission variability resembles the one of ɸ Per in quite some detail, suggesting a similar nature of the companion: a hot, compact star.
Selfconsistent Models of Winds from Rotating Early-Type Stars – Application to B[e] star winds
Authors: Petrenz P. , Puls J. 
Published: July 2016

AbstractWe present results of 2.5-D radiation hydrodynamical simulations of winds from rapidly rotating stars. For the first time, we consider the dependence of the line statistics on local density and radiation temperature implying a spatial variation of the force-multiplier parameters k, α and δ which control the dynamics of the flow.We apply our models to the problem of disk formation in B[e]-star winds.
Be stars in X-ray binary systems
Authors: Coe M.J. 
Published: July 2016

AbstractThis paper will review the status of our observations and understanding of Be stars in X-ray binary systems. In virtually all cases the binary partner to the Be star is a neutron star. The circumstellar disk provides the accretion fuel and hence stimulates the X-ray emission, whilst the neutron star provides a valuable probe of the environment around the Be star. The results coming from studies of such systems are helping in our understanding of the Be phenomenon.
New JHK Photometry of LS I +61 303
Authors: Martínez-Núñez S. , Fabregat J. 
Published: July 2016

AbstractWe present new JHK photometry of the Be/X-ray binary L SI +61 303, obtained during the period 1994-1998. The IR light curves do not show the modulation with the orbital period apparently present in the smaller photometry set analyzed by Paredes et al. (1994).The reddening-corrected standard photometric values indicate that the circumstellar envelope is optically thick at infrared wavelengths, and much denser than those of isolated Be stars. It is argued that this higher density is produced by disk truncation due to the presence of the compact object in a close orbit.
High-Precision NBPP Timing Measurements at Nançay
Authors: Cognard I. , Lestrade J.-F. , Backer D.C. , Ray P.S. , Foster R.S. , Cadwell B.J. 
Published: July 2016

The Nançay radiotelescope in France is a large collecting area (7000m2) with receivers around 1.4, 1.7 and 3.5GHz. At this observatory, we are conducting frequent high-precision timing observations of 5 millisecond pulsars (PSR B1937+21, B1821-24 since 1988; J1643-1224, J1713+0747 and B1620-26 since 1996) with a swept frequency oscilllator based on a DDS as a dedisperser.The most interesting result from these dense series of observations is the detection of several Extreme Scattering Events in direction of B1937+21 and possibly in direction of B1821-24 (Cognard, 1993,Nature,366, 320; Cognard &amp; Lestrade, 1996, in ASP Conf. Ser. Vol 105, Pulsars: Problems and Progress (San Francisco: ASP), 469; Lestrade, Rickett &amp; Cognard 1998, A&amp;A,334, 1068). The flux density variations and TOA fluctuations observed have been used to estimate the size (several AU) and electron density (a few hundreds electrons cm−3) of the discrete ionised clouds localized in the interstellar medium that are thought to be responsible for this phenomena. The number of events recorded at Nançay in direction of B1937+21 yields the space density 105– 106pc−3for these clouds. This density is very large and is about 100 times higher than the density estimated from Extreme Scattering Events observed in direction of extragalactic radio sources (Fiedler et al., 1994,ApJ,430, 581). This might mean that the line of sight to B1937+21 is peculiar. This is being investigated with additional observations of a larger array of pulsars at Nançay with the Navy-Berkeley-Pulsar Processor (Figure 1) This processor NBPP (Foster et al., in ASP Conf. Ser. Vol 105, Pulsars: Problems and Progress (San Francisco: ASP), 25) has been used to acquire pulsar search data for 2 years at Nancay and we are now using its real-time folding capability.
Timing of the young pulsar J1907+0918
Authors: Xilouris K. , Lorimer D.R. , Dowd A. 
Published: July 2016

AbstractWe have extensively searched for periodic signals in the area of the soft gamma-ray repeater SGR 1900+14, at 430 and 1410 MHz with the Arecibo telescope. Our observations did not reveal the 5.16-s periodicity reported for the magnetar down to a 430-MHz flux density limit of 150μJy. During the search we discovered a 226-ms radio pulsar, PSR J1907+0918. The period derivative implies the characteristic age for this pulsar is only 38 kyr. Independent evidence in support of this apparent youth are the unusually high degree of circular polarization and its relatively flat radio spectrum. The close proximity of PSR J1907+0918 to SGR 1900+14 suggests that they may have evolved from a massive binary system. Regardless of this possibility, it is presently not clear to us that SGR 1900+14 is associated with the supernova remnant G42.8+0.6.
Periodicities in Rotation and Pulse Shape in PSR B1828–11
Authors: Lyne A. G. , Stairs I. H. , Shemar S. L. 
Published: July 2016

AbstractWe report on the observation of highly-periodic, correlated variations in the rotation and pulse shape of PSR B1828–11. Three harmonically-related periodicities of 100, 500 and 250 days are seen in both the rotation rate and profile shape. The 0.7% modulation in period derivative is apparently related to oscillatory changes in the magnetospheric configuration. The origin of the periodic effects most likely lies in the free precession of the neutron star.
Geodetic Precession in PSR B1534+12
Authors: Stairs I. H. , Thorsett S. E. , Taylor J. H. , Arzoumanian Z. 
Published: July 2016

AbstractWe present Arecibo observations of PSR B1534+12 which confirm previous suggestions that the pulse profile is evolving secularly. This effect is similar to that seen in PSR B1913+16, and is almost certainly due to general relativistic precession of the pulsar’s spin axis.
General Relativistic Precession of the Spin Axis of Binary Pulsar B1913+16: First Two Dimensional Maps of the Emission Beam
Authors: Weisberg Joel M. , Taylor Joseph H. 
Published: July 2016

AbstractRelativistic spin-orbit coupling should cause the spin axis of Binary Pulsar B1913+16 to precess at a rate of about 1 deg / yr. As a result, the pulse profile is expected to exhibit secular evolution. Weisberg, Romani, &amp; Taylor (1989), and Weisberg &amp; Taylor (1992) found that the intensity ratio of the two conal components changed at a one percent per year rate from 1981 to 1989, but that their spacing did not measurably change. They attributed these observations to our line of sight passing across the middle of a patchy cone of emission. Recently Kramer (1998) found that the intensity ratio continued its secular change for another decade, and also detected a narrowing of the conal component separation.We present our analysis of eighteen years of 21 cm pulse profile data. We confirm that the profile is narrowing as precession finally carries our line of sight away from the emission beam axis, and we map the beam in two dimensions. The beam is elongated in the latitude direction, and the degree of elongation grows with radius.
Astrometry of Southern Pulsars
Authors: Legge David 
Published: July 2016

AbstractA preliminary determination of the proper motion and parallax of the Vela pulsar was made using phase-referencing VLBI. The measured proper motion in right ascension and declination are respectively,µα= −49.8 ± 0.2 mas yr−1andµδ= 30.5 ± 0.1 mas yr−1. The parallax of Vela was calculated to beπveia= 3.16 ± 0.33 mas, which corresponds to a distance ofpc.
Polar-Fluxtube Emission ‘Weather’ of Pulsar B0943+10: Polarisation, Modes, & Theoretical Implications
Authors: Rankin Joanna M. , Deshpande Avinash A. 
Published: July 2016

AbstractBuilding on the analysis of the previous paper by one of us, we here turn first to a discussion of B0943+ 10’s chaotic “Q” mode and then to the polarisation properties of its “B”-mode radiation. Here again, we see evidence that the plasma processes responsible for pulsar emission may be organized into a system of columns. In short, 0943+10 provides unprecedented insight into the phenomena comprising what might be termed pulsar polar-fluxtube “weather”.
Giant Pulses from the Crab Pulsar
Authors: Hankins Timothy H. 
Published: July 2016

AbstractRecent observations of the “giant” radio pulses received from the Crab pulsar are reviewed. The frequency range over which they have been detected spans at least two decades, and individual pulses appear to have a frequency span of 3:1 or more. The pulse structure is dominated by scattering at frequencies below about 2 GHz; at higher frequencies the intrinsic pulse width is about 1µs with nanostructure extending down to 10 ns. The polarization structure may be contaminated by scattering at low frequencies and the polarization is weak and highly variable at high frequencies. No definitive emission mechanism with testable hypotheses for the giant pulses has been put forth. One of the most promising, based on the collapse of plasma solitons, predicts nanostructure bandwidths narrower than what is seen for the giant pulses themselves, though the observations do not show wideband correlation of the shortest resolvable intensity structure.
Single Pulse Analysis of the Core-Dominated Pulsar B0611+22
Authors: Kern Jeffrey S. 
Published: July 2016

AbstractSingle pulse studies of pulsar radio emission provide a window into the time dependent behavior of the radio loud region. I have analyzed a series of precision polarimetric observations of pulsar B0611+22 to determine the geometry of the emission region. The observations are consistent with a central core emission region, and a periodically present conal component. This identification leads to the surprising result that all emission is from the leading half of the polar cap.
Pulsar spectra analysis
Authors: Maron Olaf , Kijak Jaroslaw , Kramer Michael , Wielebinski Richard 
Published: July 2016

AbstractWe have extended the database of flux density measurements of 280 pulsars made by Lorimer et al. (1995) to frequencies higher than 1.4 GHz and lower than 300 MHz. Our analysis shows that the spectral behaviour of the majority of pulsars can be well described by a simple power law (S~υαwhere= −1.8) though some pulsar spectra are described by a ”broken power law” with a break at high frequenciesυb~ 1.8 GHz.
Mean, individual pulses and spectrum of Geminga radio emission
Authors: Malofeev V.M. , Malov O.I. 
Published: July 2016

AbstractThe measurements of profiles at 102, 87, 59 and 40 MHz are presented. Geminga shows unique character of radio emission: the most steep spectrum, the large changes of pulse widths, phases of pulse time of arrival and the presence of giant pulses.
Signatures of Polar-cap Current Flow in Polarization Angle Sweeps
Authors: Hibschman Johann A. , Arons Jonathan 
Published: July 2016

AbstractUpon re-examining the characteristic polarization angle sweep of rotation-powered pulsars, we find that the sweep is perceptibly shifted by aberrational effects and by polar-cap current flow. In addition to the previously known phase shift of the entire sweep by ΔΦ = −4r/RL, aberration shifts the polarization angle itself by ΔΨ = −(10/3)(r/RL) cos α. Similarly, current flow above the polar cap shifts the polarization sweep by ΔΨ = (10/3)(r/RL)(J/JGJ) COSα, potentially providing a method of directly measuring the magnitude of the current. The competition between these two effects produces a potentially observable signature in the polarization angle sweep.
An Arithmetic Method for Mean Pulse Profile De-disperse of pulsars
Authors: Wu X.J. , Liu X.F. 
Published: July 2016

AbstractIn this paper we discuss an arithmetic method for mean pulse profile de-disperse. We proceed from the principle of dispersion measure, and invert the de-dispersion problem as to refutations of solving integral equations. Under idealization condition, the refutations results fit very well with the given theoretical curvature.
Search for an Optical Counterpart of PSR J0537–6910
Authors: Gouiffès Christian , Ögelman Hakki 
Published: July 2016

AbstractWe have conducted an optical study of the recently discovered very fast (P∼16msec) X-ray pulsar PSR J0537-6910 in the supernova remnant N157B. Broad band imaging has been obtained to study the field around the X-ray position and a high speed photometry programme was carried out in an attempt to detect optical pulses.
OPTIMA An Optical Pulsar Timing Analyser
Authors: Straubmeier Christian , Kanbach Gottfried 
Published: July 2016

AbstractOPTIMA is a small and mobile highspeed photometer which is primarily intended for the observation of young high energy pulsars at optical wavelengths. The detector system consists of a fiber fed photon counter based on avalanche photodiodes, a GPS timing receiver and an integrating CCD camera to ensure the correct positioning of the targeted object. In January 1999, OPTIMA proved its functionality by measuring the lightcurve of the Crab pulsar.
X-ray observations of the high magnetic field radio pulsar PSR J1814–1744
Authors: Pivovaroff M. J. , Kaspi V. M. , Camilo F. 
Published: July 2016

AbstractWe present X-ray observations of PSR J1814–1744, a 4 s radio pulsar with inferred surface dipole magnetic field strength 5.5 × 1013G recently discovered in the on-going Parkes multibeam survey. This pulsar’s spin parameters are very similar to those of anomalous X-ray pulsars (AXPs). X-ray emission is not detected from the position of the radio pulsar in observations withROSATandASCA. The derived upper flux limit implies an X-ray luminosity significantly smaller than those of all known AXPs. These results argue that magnetar mechanism invoked to explain X-ray emission from AXPs must depend on more than merely the inferred surface magnetic field strength as estimated fromPand.
Likely detection of pulsed high-energy γ-rays from millisecond pulsar PSR J0218+4232
Authors: Kuiper L. , Hermsen W. , Verbunt F. , Lyne A. , Stairs I. , Thompson D.J. , Cusumano G. 
Published: July 2016

AbstractWe report on the likely detection of pulsed high-energyγ-rays from the binary millisecond pulsar PSR J0218+4232 in 100–1000 MeV data from CGRO EGRET. Imaging analysis demonstrates that the highly significantγ-ray source 2EG J0220+4228 (∼ 10σ) is for energies &gt; 100 MeV positionally consistent with both PSR J0218+4232 and the BL Lac 3C66A. However, above 1 GeV 3C66A is the evident counterpart, whereas between 100 and 300 MeV PSR J0218+4232 is the most likely one. Timing analysis using one ephemeris valid for all EGRET observations yields in the 100-1000 MeV range a double-pulse profile at a ∼ 3.5σsignificance level. The phase separation is similar to the component separation of ∼ 0.47 observed at X-rays. A comparison of theγ-ray profile with the 610 MHz radio profile in absolute phase shows that the twoγ- ray pulses coincide with two of the three emission features in the complex radio profile.
Propagation of radio waves in pulsar magnetospheres
Authors: Petrova S.A. , Lyubarskii Yu.E. 
Published: July 2016

AbstractThe morphological classification of pulsar profiles is interpreted within the frame of the primordial hollow-cone emission model taking into account wave propagation in the magnetosphere. In this context the frequency evolution of the profiles as well as the difference in polarization properties of core and conal components can be explained naturally.
Recent developments of inverse Compton scattering model of pulsar radio emission
Authors: Qiao G. J. , Xu R. X. , Liu J. F. , Zhang B. , Han J. L. 
Published: July 2016

AbstractMany theoretical efforts were made to understand the core and conal emission identified from observations by Rankin (1983) and Lyne and Manchester (1988). One of them, named as inverse Compton scattering (ICS) model (Qiao &amp; Lin 1998), has been proposed. It is found in the model that: there are central or ‘core’ emission beam, and one or two hollow conical emission beams; the different emission components are emitted at different heights; owing to different radiation components emitted from different height, the observed emission beams can be shifted from each other due to retardation and aberration effects; the sizes of emission components change with frequencies. Recent developments of the model include: simulations of pulse profiles at different frequencies; studying the basic polarization properties of inverse Compton scattering in strong magnetic fields; computing the polarizations and spectrum of core and cones. A new classification system was also proposed. The main results calculated from the model are consistent with the observations.
High Energy Radiation from Pulsars
Authors: Cheng K.S. 
Published: July 2016

AbstractWe propose a three dimensional pulsar magnetosphere model in which the vertical size of the outer gap is first determined by a self-consistent model in which the outer gap is limited by the pair production from collisions of thermal photons produced by polar cap heating of backflow outer gap current and the curvature photons emitted by the gap accelerated charged particles. The transverse size of the outer gap is determined by local pair production condition. In principle, there are two topologically disconnected outer gaps existing in the magnetosphere of a pulsar and both incoming and outgoing particle flows are allowed. And yet double-peak light curves with strong bridges are most common. Using this model and its local properties, we compare the model results with phase-resolved spectra of the Crab pulsar and Geminga.
Pulsar Magnetospheres: Classical, Quasi-Classical and Quantum Descriptions
Authors: Costa A. A. da 
Published: July 2016

AbstractThe plasma motion in pulsar magnetospheres is no longer classical, but quasi-classical, following stochastic trajectories, when random curvature radiation of high energetic gamma-ray photons takes place. This implies an extension to the relativistic kinetic theory of plasmas. But with high energies involved other quantum radiative processes become important, in the context of vacuum (quantum) electrodynamics. The consequences for pulsar radiation mechanisms will be outlined.
Neutron Star/Supernova Remnant Associations
Authors: Kaspi Victoria M. 
Published: July 2016

AbstractThe evidence for associations between neutron stars and supernova remnants is reviewed. After summarizing the situation for young radio pulsars, I consider the evidence from associations that young neutron stars can have properties very different from those of radio pulsars. This, though still controversial, shakes our simple perception of the Crab pulsar as prototypical of the young neutron star population.