bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Spectropolarimetric Atlas of 61 Bright Northern Be Stars
Authors: Bjorkman Karen S. , Meade Marilyn R. , Babler Brian L. 
Published: July 2016

AbstractWe are developing an atlas of spectropolarimetric observations of 61 bright northern Be stars obtained from 1989-94 using the halfwave polarimeter (HPOL) at the 0.9m telescope of the University of Wisconsin Pine Bluff Observatory (PBO). The data cover the wavelength range from about 3400-7600Å, with a spectral resolution of about 25Å. This atlas will contain all data (297 observations total) obtained as part of a survey program with HPOL during the time when the detector in use was a dual Reticon array; the survey observations with HPOL continue, using a new CCD detector which extends the spectral coverage out to 1.05μm and improves the spectral resolution to about 12Å. The CCD observations will be presented later in a second volume of the atlas.Only a brief summary of the findings of the survey from the first 5 years of the project is presented here. A full analysis of the data will be included in a paper to be published elsewhere. The general wavelength dependence of polarization for classical Be stars can be considered on the basis of these observations, and results on polarimetric variability are available. In particular, we find that 56% (20 of 36) of the Be stars observed 3 or more times from 1989-94 show significantly variable polarization at the level of 0.1% changes (inclusion of preliminary results from the continuing CCD survey indicates that the percentage is even higher). The timescales for these changes range from as short as night-to-night to as long as several months. Several of the stars showed evidence for polarimetric “outbursts” during the time period covered by the observations.
The Connection between Classical Be Stars and Herbig Ae/Be Stars
Authors: Böhm T. , Balona L.A. 
Published: July 2016

AbstractWe use a phenomenological approach to derive new constraints on the mass loss mechanisms working in the classical Be and the Herbig Ae/Be stars, which represent two groups of stars located very nearby in the HR diagram. We discuss observational similarities of classical Be and Herbig Be stars on one side, and stress, on the other side, the major differences between Herbig Ae and Herbig Be stars. For further details and a detailed bibliography, see Balona & Böhm (2000). A more quantitative approach will be needed and is deferred to future work.
Direct Optical Imaging of Be Disks
Authors: Stee Philippe 
Published: July 2016

AbstractInterferometry in the visible now provides milliarcsecond spatial resolution and thus can be used for studying the circumstellar environment of Be stars. In this review I will first introduce the two basic quantities that an interferometer can access: the modulus and the phase of the visibility. I will illustrate how these two quantities can be used to understand the physics of Be disks through recent results from the VLA, the MkII and the GI2T interferometers. I will insist on the importance and the potential of coupling high angular resolution with high spectral resolution to the study of Be disks. Since the possibility of direct optical imaging of Be disks will be limited due to complexity and time consumption, I will present the role models can play in interpreting high angular resolution observations when direct imaging become difficult. Finally I will draw up a list of challenging objectives for the next generation of synthetic arrays (GI2T/REGAIN, Keck, ST3, VLTI) which will bring new understanding of active hot stars physics.
Pulsations in 66 Oph: Multiperiodicity in He I 6678
Authors: Floquet M. , Neiner C. , Briot D. , Chauville J. , Hubert A.M. , Ballereau D. 
Published: July 2016

Abstract66 Oph has shown recurrent short-lived outbursts nicely detected from ground-based and space (Hipparcos) photometry.Spectroscopic observations of He I 6678 and Hα lines were performed in June 1997 and June 1998. Search for short-term periodicities was done in He I 6678 line profiles as in equivalent width EW, radial velocity of the line centroid, and V and R components. At least two frequencies were present: ν = 4.0 c/d and ν = 2.2 c/d. The phase distribution of these frequencies over the line profile corresponds in the nrp frame to g-modes with ℓ ~ 3 − 4 and ℓ = 2 respectively.
The Formation and Structure of Circumstellar Disks
Authors: Bjorkman J.E. 
Published: July 2016

AbstractSeveral theories have been proposed to explain the origin of Be star disks. Among them are Wind-Compressed Disks, accretion disks, decretion disks, and “explosive” ejections. In reviewing these mechanisms, I first concentrate on the current status of the Wind-Compressed Disk model. In particular, I discuss how non-radial forces may prevent disk formation and then discuss various physical effects that may restore the disk. Second, I examine the observational evidence and what it tells us about the structure of the disk. Of particular interest is evidence in favor of Keplerian disks. Finally, I discuss theories for Keplerian disk formation and some of the constraints such theories must satisfy.
Physical Properties of Circumstellar Envelopes in Be Stars Derived from their Long-term Spectrophotometric Variations
Authors: Moujtahid A. , Zorec J. , Hubert A.M. 
Published: July 2016

AbstractThe long-term visible spectrophotometric variations depicted by the following parameters: V the apparent visual magnitude; Φrb the gradient of the observed Paschen energy distribution and D the total Balmer discontinuity (BD) of 49 Be stars in different spectrophotometric phases (SPh-E: spectrophotometric phase where the second component of the BD is in emission; SPh-A: spectrophotometric phase where the second component of the BD is in absorption) were translated into CE physical parameters. These parameters are: R/R* the mean extent of the CE zone that produces the visible energy distribution; Tenv its mean temperature; τ the continuum opacity at λ0.56μm. The results obtained show that the triplet of parameters (V, Φrb, D) do not depend on the (R/R*, Tenv, τ) set of parameters in the same way if Be stars are in a SPh-E or in a SPh-A phase. Independently of the spectrophotometric phase, Tenv always decreases as a linear function of (R/R*)−1. In SPh-E it is (R/R*,)−1 ≤ 0.7, and in SPh-A it is (R/R*)−1 ≥ 0.7. All SPh behaviours can be summarized by the relation ∂Tenv/∂(R*/R) = ∂Tenv/∂τ × ∂τ/∂(R*/R) ≥ 0, which describes different spectrophotometric behaviours in both SPh-E and SPh-A phases.
Variability of the Hα Emission in the Be Star o Andromedae
Authors: Panko E. , Tarasov A. 
Published: July 2016

AbstractThe parameters of the Hα line profile of the Be star o And were determined from observations carried out during the period 1985 - 1998. At this time the line has undergone significant changes – from a pure absorption photospheric profile with no sign of an envelope in 1985 to the transition into the shell phase with a very narrow and deep absorption component in 1989. During 1991 - 1998 the Hα emission remained at the level achieved in 1989. The line profile showed short-term changes. The envelope development in the time interval 1985 - 1998 does not confirm the previously found period of 8.5 years.
Stellar and Circumstellar Activity in the Be Star EW Lac from the Multi-site 1993 Campaign
Authors: Hubert A.M. , Floquet M. , Hirata R. , McDavid D. , Zorec J. , Gies D. , Hahula M. , Janot-Pacheco E. , Kambe E. , Leister N.V. , Stefl S. , Tarasov A. 
Published: July 2016

AbstractThe Be shell star EW Lac was observed in September 1993 during a multi-site campaign. Results from visual spectroscopy and polarimetry are summarized here. He I 6678 profiles have been compared to previous observations held in 1989 and show an additional complex and highly variable circumstellar component which can due to material expelled from the star just prior to these observations. Two groups of frequencies are found again in 1993 observations compared with 1989 ones. In the frame of nrp, they could be associated to low degree g-modes.
Photometry and Spectroscopy of X Per During the Years 1996-1999
Authors: Piccioni A. , Bartolini C. , Bernabei S. , Galleti S. , Guarnieri A. , Valentini G. 
Published: July 2016

AbstractUBVRI photoelectric monitoring of the Be star X Per, a transient X-ray binary, during the last four years, along with some optical spectra are presented and briefly discussed in the context of the long term behaviour of the system.
Ionization Structure and Mass Loss for Rapidly-Rotating Near Main-Sequence B Stars
Authors: Bjorkman J.E. , Abbott B.P. 
Published: July 2016

AbstractUsing the wind-compressed disk model to determine the density and velocity of a rapidly rotating wind, we calculate the 2-D ionization structure and corresponding line profiles. We find that previous estimates of the mass-loss rate based on spherically symmetric models may be a factor of 5–10 too small.
New Radiation Driven Wind Solutions Including Stellar Rotation: Applicability to Be stars
Authors: Curé Michel 
Published: July 2016

AbstractThe theory of radiative-line driven wind including stellar rotation is re-examined. After a suitable change of variables, new analytical equations for the mass loss rate and position of the critical point are derived. A non-linear equation for the position of the critical point is obtained, in order to solve it, a β-field is used, and in addition to the standard CAK critical point two other critical points as function of star’s rotational speed (Vϕ) are founded. When the stellar rotation velocity is approximate or greater than 0.8 × Vbreak–up, the CAK critical point is located far away in the wind (r > 4R*) and there we have again only one critical point. Numerical solutions from this new critical point are obtained, they have very low terminal velocities (approx. 400 km/sec). The applicability of this new solution in the frame of Be stars are discussed.
Glimpses of Be Binary Evolution
Authors: Gies Douglas R. 
Published: July 2016

AbstractModels of close binary evolution predict that mass gainers will be spun up to speeds close to the critical rotational velocity while the mass donors will appear as stripped down He stars, white dwarfs, or neutron stars. I argue here that the mass gainers are closely related to the Be stars. I present a list of the known Be binary systems which consists of those with bright, Roche-filling companions and those with faint or undetected companions. Notably absent are Be + B systems which are expected if the Be phase is a stage in the life of a single star. We now have the first example of a Be + He star system in the binary, ϕ Per, and taken together with the well known Be X-ray binaries, there is clear evidence that some fraction of Be stars are created in binaries; whether all such rapid rotators are so formed remains unknown.
Origin of Circumstellar Matter in the Spectroscopic Binary CX Dra
Authors: Iwamatsu Hidetoshi , Hirata Ryuko , Masuda Seiji 
Published: July 2016

AbstractWe examine the periodic component in the polarization of CX Dra, a spectroscopic binary with an orbital period of 7 days. We find that this component originates in dense matter located in the direction preceding the secondary by about 4.5° from the primary-secondary direction. This dense scattering region is attributable to the region where the Hα emission peak is formed, i.e. the gas stream or hot spot on the accretion disk of the primary. Its mass is estimated as 1.3 · 10−11M⊙ in its well developed phase.
The Spectral Distribution of Be/X-ray Transients Implies Supernova Kicks
Authors: Negueruela Ignacio 
Published: July 2016

AbstractBe/X-ray binaries are generally assumed to have formed as the result of the evolution of moderately massive binaries in which mass is transferred semi-conservatively from the originally more massive component on to its companion. An alternative model proposes a binary system with a very massive component which loses a large fraction of its mass via very unconservative mass transfer. This scenario allows the formation of Be/X-ray binaries without requiring an asymmetric supernova explosion. We show that the observed properties of most Be/X-ray binaries for which an orbital solution has been found are incompatible with this model.
Summary and Future Directions
Authors: Marlborough J. M. 
Published: July 2016

AbstractA summary of the Alicante meeting, entitled The Be Phenomenon in Early Type Stars, is presented here. The emphasis at this meeting was on Be stars, but possible connections to other types of stars were also considered. Some suggestions for the directions of future approaches are provided. The meeting was dedicated to the late Mercedes Jaschek, Carlos Jaschek, and Arne Slettebak, all of whom made significant contributions to our current understanding of Be stars.
New Pulsars from Arecibo Drift Scan Search
Authors: Somer A. 
Published: July 2016

AbstractWe report the discovery of 3 pulsars, PSR J0030+0451, PSR J0711+09, and PSR J1313+09 that were found in a three dimensional (DM, period, position) search at 430 MHz using the 305m Arecibo telescope. PSR J0030+0451 is a nearby 4.8-millisecond solitary pulsar. Spin and astrometric parameters are presented for the three new pulsars. We have measured significant polarization in the millisecond pulsar, PSR J0030+0451, over more than 50% of the period and use these data and also a morphological decomposition of the profile to briefly discuss magnetospheric models.
The Effelsberg Search for Pulsars in the Galactic Centre
Authors: Kramer M. , Klein B. , Lorimer D. , Müller P. , Jessner A. , Wielebinski R. 
Published: July 2016

AbstractWe report the status of a search for pulsars in the Galactic Centre, using a completely revised and improved high-sensitivity double-horn system at 4.85-GHz. We also present calculations about the success rate of periodicity searches for such a survey, showing that in contrast to conclusions in recent literature pulsars can be indeed detected at the chosen search frequency.
Pulsar Timing at the Radiotelescope Effelsberg
Authors: Lange Ch. , Wex N. , Kramer M. , Doroshenko O. , Backer D.C. 
Published: July 2016

AbstractWe present results of timing observations, obtained at the 100 m-Radiotelescope Effelsberg since 1994. The quality of the pulse arrival times, recorded with the coherent de-disperser EBPP since October 1996, is excellent. Our TOAs are well suited for the measurement of binary parameters of binary pulsars with short orbital periods. Some results are presented.
The microlensing probability of the pulsars located in globular clusters
Authors: Larchenkova Tanya 
Published: July 2016

AbstractWe have used the effect of Shapiro delay of the pulsar radiation in the gravitational lensing approximation. The microlensing probabilities for pulsars located in globular clusters 47 Tuc (NGC 104) and M15 (7078) in the case of rather large impact parameters was calculated.
Evidence for Free Precession in the Pulsar B1642–03
Authors: Shabanova T.V. , Urama J.O. 
Published: July 2016

AbstractThe phase residuals of PSR B1642-03 obtained during a 30-yr interval since 1969 to 1999 are discussed. Interpretation of observed cyclical residual changes in terms of free precession gives a wooble angle of 0.3 - 0.7 degrees.
Glitches in Southern Pulsars
Authors: Wang Na , Manchester R. N. , Pace R. , Bailes M. , Kaspi V. M. , Stappers B.W. , Lyne A. G. 
Published: July 2016

AbstractParkes timing observations of 31 mostly young pulsars over nearly nine years are described. A total of 29 glitches were detected, of which 19 are previously unreported. Twelve glitches were seen in PSR J1341–6220, making this the most frequently glitching pulsar known, and the largest known glitch was detected in PSR J1614–5047. Distributions of glitch parameters were investigated.
Geodetic Precession and the Binary Pulsar B1913+16
Authors: Karastergiou A. , Kramer M. , Wex N. , von Hoensbroech A. 
Published: July 2016

AbstractA change of the component separation in the profiles of the binary pulsar PSR B1913+16 has been observed for the first time (Kramer 1998) as expected by geodetic precession. In this work we extend the previous work by accounting for recent data from the Effelsberg 100-m telescope and Arecibo Observatory and testing model predictions. We demonstrate how the new information will provide additional information on the solutions of the system geometry.
Numerical solution of the spin angular momenta of millisecond pulsar PSR J0751+1807
Authors: Gong B.P. , Cheng K.S. 
Published: July 2016

AbstractThe motion of the binary pulsar PSR J0751+1807 is assumed to satisfy the gravitational two-body equation (Barker and O’Connell 1975). Then by studying the motion of the binary system from initial state which determined by 3 precession phases of angular momenta (the orbit, the pulsar and the companion star) to the current state which determined by the observations on the orbital inclination. The spin angular momenta of the pulsar and the companion star are obtained.
VLBI Neutron Star Astrometry: Techniques and Initial Results
Authors: Chatterjee Shami , Cordes James M. 
Published: July 2016

AbstractWe outline some new techniques being used and present initial results from a pulsar astrometry program at the NRAO Very Long Baseline Array (VLBA). We find a proper motion of 89.0±0.4 mas/yr and a preliminary parallax of 1.05±0.25 mas for B0919+06.
Timing noise as a source of discrepancy between timing and VLBI pulsar positions
Authors: Rodin A. E. , Ilyasov Yu. P. , Oreshko V. V. , Sekido M. 
Published: July 2016

AbstractPulsar positions obtained by VLBI and timing are compared. The difference between these positions is proven to be mainly due to timing noise. A new method which significantly reduces the difference have been developed.
Parameters of microstructure and noiselike intensity fluctuation in pulsar radio emission measured with submicrosecond time resolution provided by the S2 VLBI recording/playback system
Authors: Popov M.V. , Kondrat’ev V.I. , Altunin V.I. , Bartel N. , Cannon W. , Novikov A.Yu. 
Published: July 2016

AbstractThree bright pulsars (B0950+08, B1133+16, and B1929+10) were observed with the 70-m radio telescope in Tidbinbilla at a frequency of 1650 MHz using the S2 Data Acquisition System which provided continuous recording of pulsar signals in two conjugate bands of B=16 MHz each. Parameters of microstructure have been analyzed using the predetection dispersion removal technique.
Ha, ha, ha, ha, staying alive, staying alive: A radio pulsar with an 8.5-s period challenges emission models
Authors: Young M. D. , Manchester R. N. , Johnston S. 
Published: July 2016

AbstractWe report the discovery of the longest known radio pulsar period. PSR J2144–3933, previously thought to have a period of 2.84 s, actually has a period of 8.51 s. Under the usual assumptions about the stellar equation of state, this pulsar has an average surface dipolar magnetic field strength of ~ 2.0 × 1012G. According to popular theories of the emission mechanism this pulsar should not be emitting radio waves because its long period and magnetic field strength make pair creation impossible for all reasonable magnetic field configurations. Either assumptions about the equation of state are incorrect, or the emission theories must be revised.
Measuring the Size of the Vela Pulsar’s Radio Emission Region
Authors: Gwinn C.R. , Reynolds J.E. , Jauncey D.L. , Hirabayashi H. , Kobayashi H. , Murata Y. , Edwards P.G. , Carlson B. , Dougherty S. , Rizzo D. Del , Britton M.C. , McCulloch RM. , Lovell J.E.J. 
Published: July 2016

AbstractWe describe the expected distribution of intensity for a scintillating source of finite size observed through a scattering medium, including systematic and instrumental effects. We describe measurements of the size of the Vela pulsar, using this technique.
Finding Pulsar Emission Heights from Dual–Frequency Observations
Authors: Nowakowski Leszek A. 
Published: July 2016

AbstractWe present a method that allows to find the radial separation of regions emitting individual components of pulsar average profiles at two radio frequencies. It may also be used for single–frequency observations in pulsars that have intensity–dependent average profiles and/or mode–switching. Preliminary results for three radio pulsars are presented, obtained using average profiles from non-simultaneous observations.
A VLA Search for the Geminga Pulsar at 74 and 326 MHz
Authors: Kassim Namir E. , Joseph T. , Lazio W. 
Published: July 2016

AbstractWe have used the VLA to image the location of the gamma-ray pulsar Geminga at 74 and 326 MHz. Upper limits to the pulse-averaged flux density, taking diffractive scintillation (DISS) into account, areS&lt; 56 mJy (2σ; DISS quenched) at 74 MHz andS&lt; 5 mJy (95% confidence) at 326 MHz. Intrinsic variability appears to be required in order to reconcile our upper limits with previous low-frequency detections.
Single Pulse Polarimetry of the Vela Pulsar
Authors: Kern Jeffrey S. , Hankins Timothy H. , Rankin Joanna M. 
Published: July 2016

AbstractMulti-frequency, single-pulse polarimetric observations of the Vela pulsar have been made using the VLA. These high time resolution measurements allow us to probe the geometry, and the time dependent characteristics of the radio emission region. Evidence for multiple emission components with differing spectral indices is found.
Evolution of Multipolar Magnetic Fields in Isolated Neutron Stars and its effect on Pulsar Radio Emission
Authors: Mitra D. , Konar S. , Bhattacharya D. , Hoensbroech A. V. , Seiradakis J. H. , Wielebinski R. 
Published: July 2016

AbstractThe evolution of the multipolar structure of the magnetic field of isolated neutron stars is studied assuming the currents to be confined to the crust. Lower orders (≤ 25) of multipole are seen to evolve in a manner similar to the dipole suggesting little or no evolution of the expected pulse shape. We also study the multifrequency polarization position angle traverse of PSR B0329+54 and find a significant frequency dependence above 2.7 GHz. We interpret this as an evidence of strong multipolar magnetic field present in the radio emission region.
Analysis of PSR 1641–45 Using Specialized Capabilities of the S2 VLBI Correlator
Authors: Rizzo D.A. Del , Carlson B.R. , Petrachenko W.T. , Everett J. E. , Cordes J. M. 
Published: July 2016

AbstractThe pulsar PSR 1641-45 was observed using the S2 VLBI Recording System at 1.6 GHz with radio telescopes at Tidbinbilla and Narrabri in Australia, and at Hartebeesthoek in South Africa. The data were correlated with the Canadian S2 VLBI Correlator using the ‘fast-dumping’ mode in conjunction with two independent pulsar gates. The high time and spectral resolution capabilities of this correlator permit a detailed examination of dispersion and dispersion-removal effects on individual pulses, and a comparison of these effects from pulse to pulse over the duration of the observation. We give a brief summary of the pulsar processing capabilities highlighted by examples from the PSR 1641-45 data.
PuMa, the new Dutch PulsarMachine
Authors: Kouwenhoven M.L.A. , van Haren P.C. , Driesens D. , Langerak J.J. , Beijaard T.D. , Voûte J.L.L. , Stappers B.W. , Ramachandran R. 
Published: July 2016

AbstractPuMa is a fully digital PulsarMachine the operation at the Westerbork Synthesis Radio Telescope (WSRT). Its design is based on the use of Digital Signal Processors. It has two modes of operation: a baseband recording mode and a digital filterbank mode.
Unpulsed Optical Emission from the Crab Pulsar
Authors: Golden Aaron , Shearer Andy , Beskin Gregory 
Published: July 2016

AbstractUsing the high speed 2-d TRIFFID photometer, we have obtained phase resolved photometry of the Crab pulsar inUBVthat allows us to flux the unpulsed light curve component. Following de-extinction, weighted least-square fitting indicates a power-law exponent ofα= −0.62 ± 0.49. This is steeper than that reported for the peak components and its origin remains unclear with respect to contemporary magnetospheric theory.