bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evolution of multiple black hole nuclei in merged galaxies
Authors: Valtonen Mauri , Mikkola Seppo , Heinämäki Pekka 
Published: July 2016

AbstractThe evolution of three and four black hole clusters which arise in mergers of small galaxy groups have been simulated. Typically, the chaotic dynamics of these multiple black hole systems leads to a decay via the slingshot process. Orbits of 100,000 initial configurations have been calculated and the final configurations have been classified in seven different categories. Examples of the orbits in each category are illustrated.
The Be Phenomenon: Connections to B-supergiants
Authors: Kaufer Andreas 
Published: July 2016

AbstractIn this contribution the spectral characteristics, physical properties, and the evolutionary status of B-type supergiants is reviewed with respect to the Be phenomenon. Long-term monitoring campaigns in the UV and the optical have recently revealed the distinct variability patterns of the photospheric and the emission-line spectra of this class. The various proposed scenarios for the spatially structured circumstellar envelopes and their rotational modulation are presented. The possibility of generating and maintaining large-scale wind structures by photospheric processes which structure the underlying stellar surfaces is discussed. Some open questions in connection with these hypotheses will be identified.
Hipparcos Positions of B/Be Stars on the HR Diagram
Authors: Briot Danielle , Robichon Noel 
Published: July 2016

AbstractAbsolute magnitudes of Be and B stars are computed for each spectral type and luminosity class V and IV, using the Hipparcos parallax measurements. Some simulations have been carried out in order to estimate the effects which could bias the mean absolute magnitude calculations. As a result, only stars with σπ/π < 15% have been used. A first result is that B stars are fainter than previous estimations by about 0.5 magnitude on average. We then observe that on average Be stars are brighter than B stars of the same spectral type and this over-luminosity increases with the spectral type. A possible interpretation is proposed based on the fact that the rotational velocity of the late Be stars is near the critical rotational velocity.
NRP Modeling of the Line Profile Variations ofλEri in the 1994 Campaign
Authors: Kambe Eiji , Hirata Ryuko , Fabregat Juan ,   1994 Campaign Team
Published: July 2016

AbstractWe report attempts to model the observed line-profile variations (lpv) of λ Eri during a productive spectroscopic and photometric campaign in 1994 November. We find that none of the nonradial pulsation spheroidal modes withm= −1 — −3 could explain thelpvassociated with the dominant 16.9 hr period since the horizontal velocity components and the temperature variations dominate thelpvfor such modes. In contrast, certain tesseral toroidal modes can reproduce the observedlpvwell both for the main 16.9 hr period and the 6.45 hr period.
Theory of Global Disk Oscillations
Authors: Okazaki Atsuo T. 
Published: July 2016

AbstractWe discuss the characteristics of global oscillation modes in Be disks and review recent studies related to the disk oscillation model. Since the m = 1 modes are present only in near Keplerian disks and the mode confinement occurs only in the region in which the radial flow is subsonic, the model of global disk oscillation strongly prefers the viscous decretion disk scenario proposed by Lee et al. (1991), whereas it is incompatible with the wind-compressed disk scenario of Bjorkman & Cassinelli (1993), which predicts angular-momentum conserving disks with supersonic radial flow. Based on the viscous decretion disk scenario, we discuss transonic solutions of decretion and examine the effect of viscosity on the global one-armed modes.
Paschen and Brackett Lines in Be stars
Authors: Cidale L. , Zorec J. , Maillard J.P. , Morrell N. 
Published: July 2016

AbstractThe activities detected in Be stars indicate that the formation of the circumstellar envelope and its structure cannot be studied independently of the phenomena taking place in the outermost layers of the central stars. Assuming that related to the stellar activity there is an expanding atmospheric region with temperatures Te > Teff followed by an envelope with a decreasing temperature, we calculated hydrogen line profiles for different velocity fields and different positions of temperature maxima relative to the underlying photosphere. Results show that the Hα line is not very sensitive to changes introduced to the stellar atmosphere and to the nearby circumstellar layers. Moreover, the Hα emission line profiles look like those produced by disc-like circumstellar envelopes seen pole-on, although the model for the circumstellar envelope is spherical. However, the first members of the Paschen and Brackett series are strongly sensitive to any changes introduced in the photospheric and exophotospheric layers. We conclude that the study of these lines may then be valuable to obtain new insight on the activity of central stars and on the phenomena involved in circumstellar envelope formation in Be stars.
Long–term Variability of π Aqr
Authors: Bjorkman K.S. , Miroshnichenko A.S. , McDavid D.A. , Pogrosheva T.M. 
Published: July 2016

AbstractWe present our recent photometric and spectroscopic observations of the bright classical Be star π Aquarii and analyse those available in literature. This star currently shows only weak signs of circumstellar emission and a low optical brightness. Physical parameters of the underlying star are determined from data obtained during quiescence, while those of its circumstellar disk are estimated during the active period.
Effect of Instability-Generated Clumping on Wind Compressed Disk Inhibition
Authors: Owocki S. P. , Cohen D. H. 
Published: July 2016

AbstractIn rapidly rotating stars with a purely radially driven stellar wind, conservation of wind angular momentum can lead to formation of an equatorial Wind Compressed Disk (WCD). However, for a line-driven stellar wind, recent 2D hydrodynamical simulations based on a localized, Sobolev treatment of the line-force indicate that nonradial components of the line-force can effectively inhibit formation of such a WCD. This presentation will describe current efforts to extend such 2D simulations to a nonlocal, smooth-source-function treatment of the line-force that can incorporate the intrinsically strong instability of line-driving to formation of small-scale, clumped structure. Key questions are how such small-scale clumped structure affects the nonradial line-force components that arise from large-scale velocity-gradient asymmetries, and in particular whether such nonradial forces can still inhibit WCD formation in a clumped flow. The results have important implications for the viability of the WCD mechanism as a paradigm for disk formation in Be stars.
The Steep Spectrum Pulsar Population
Authors: Kaplan D. L. , Cordes .J. M. , Condon J. J. 
Published: July 2016

AbstractWe have sampled the population of compact (θ≤ 25") radio sources with spectral indices 1.5 ≤ α ≤ 3.2 (whereSv∝v—α) using two large scale radio surveys. This yields a statistically useful sample of 74 radio sources withS1.4GHz≥ 2.5 mJy andS365MHZ≥ 200 mJy. The majority of the sources appear to be extragalactic, resembling either high redshift radio galaxies or relic radio galaxies. However, six known pulsars were detected, as well as 16 sources of unknown nature that appear too small and have spectra too steep to be extragalactic. We are using VLBA, pulsar searching, optical/IR spectroscopy, and other techniques to definitively classify these sources. If any are new pulsars, they are potentially very interesting as they were missed by previous surveys.
Millisecond Pulsars and a WSRT Search for Candidates
Authors: Tian W. W. , Strom R. G. , Stappers B. , Zhang X. Z. , Wu X. J. , Ramachandran R. 
Published: July 2016

AbstractSeven millisecond pulsars (MSPs) have been identified from the NVSS by positional coincidence. Our examination of the characteristics of about, 280 known pulsars and 40 MSPs has shown that they have high polarization and a steep spectrum. We identify likely MSP candidates from both the NVSS at 1.4 GHz and the WENSS at 325 MHz. The first sample of 14 candidates has been observed by the WSRT using PuMa at both 92 and 21 cm in May 1999. From our preliminary analysis of the 382 MHz data, we find no evidence for MSPs in the first sample.
Glitch Behavior of the Pulsar B1822–09 in the Range 0.1–2.3 GHz
Authors: Shabanova T.V. , Urama J.O. 
Published: July 2016

AbstractResults of timing observations of the glitching pulsar B1822–09 made practically simultaneously at widely separated frequencies of 0.1 and 1.6/2.3 GHz during seven years since 1991 to 1998 are discussed.
Pulse Fluctuation Properties at 35 MHz
Authors: Asgekar Ashish , Deshpande A. A. 
Published: July 2016

A few bright pulsars were observed at 35 MHz for ≳ 1000s using the Gauribidanur Radio Telescope, and the data were analysed to study their single-pulse fluctuation properties (Asgekar &amp; Deshpande, 1999a; &amp; ref.s therein).The well-known drifterB0943+10shows a well resolved two-component profile at 35 MHz. The longitude-resolved fluctuation spectrum (Fig 1) shows a stable phase modulation feature (aliased) at 0.459c/P1, consistent with its drifting pattern seen at higher radio-frequencies. Using the “Cartographic Transform” technique (Deshpande &amp; Rankin, 1999; hereafter DR), we have mapped the pattern of its polar emission at 35 MHz (Asgekar &amp; Deshpande, 1999b) as shown in fig 1. Helped by the larger cone radius at lower frequencies, the subbeams can be sampled in their full radial extent at 35 MHz. These results combined with those at higher frequencies (DR) suggest a steadily rotating system consisting of 20 emission-columns in the polar region as that responsible for the observed fluctuations over the entire range of observed frequencies.
Pulsar Studies at High Radio Frequencies
Authors: Wielebinski Richard 
Published: July 2016

AbstractPulsars were discovered at 81.5 MHz and a lot of the studies of these exciting objects have been made up to the present time at radio frequencies below 1.6 GHz. The reasons for this concentration on the low radio frequency characteristics of pulsars is the fact that the spectra are very steep and that very few radio telescopes exist that are capable of efficient operations at high radio frequencies. The Effelsberg 100-m radio telescope of the Max-Planck-Institut fur Radioastronomie operates regularly up to the frequency of 50 GHz and was used to study pulsars at cm/mm-wavelengths. In the southern skies the Parkes 64-m telescope has been used to study pulsars up to 8.4 GHz. One pulsar has been detected at 87 GHz with the 30-m Pico Veleta telescope of IRAM.The studies of pulsars over the whole frequency range are of great importance because this is necessary for the elucidation of the mechanism that is responsible for the pulsar emission. The high polarization of pulsar radio emission at lower radio frequencies has supported the hypothesis of a coherent emission mechanism, which is required to generate the high luminosity. It has been known for some time that pulsars, unlike other radio sources, have a lower polarization at high radio frequencies. Recently a change of pulsar spectrum, a flattening or possibly an inversion has been observed at the highest radio frequencies. The inversion of the pulsar spectrum seems to coincide with a complete depolarization of some pulsars.Millisecond pulsars are less luminous than normal pulsars. This makes them even more difficult to detect at higher radio frequencies. Recent observations have extended the spectra of ten millisecond pulsars up to 4.85 GHz. The results imply that millisecond pulsars have properties very similar to normal (slow) pulsars, which suggests similar emission mechanisms.
Pulsar radio spectra and the interstellar scintillation
Authors: Malofeev Valerij M. 
Published: July 2016

AbstractA review of the pulsar radio spectra is continued. Two approches of the spectrum construction are considered. The influence of the interstellar stcintillations on the pulsar flux density measurements and spectra is examined. The description of new pulsar spectra catalog is made. Examples of different types of spectra including one for Geminga are presented.
PSR B0656+14: Combined Optical, X-ray & EUV Studies
Authors: Golden Aaron , Shearer Andy , Edelstein Jerry 
Published: July 2016

AbstractPSR B0656+14’s high energy emission is consistent with that of combined magnetospheric and thermal (surface &amp; polar cap) emission. Uncertainties with the radio-derived distance and X-ray instrumentation sensitivities complicate a definitive thermal characterisation however. A re-analysis of combined ROSAT/EUVE archival data in conjunction with integrated &amp; phase-resolved optical photometry is shown to constrain this characterisation.
ASCA Observations of the Crab-Like Pulsar PSR B0540 – 69
Authors: Nagase F. , Endo T. , Hirayama M. , Kawai N. , Itoh M. 
Published: July 2016

AbstractWe report on the spectral and temporal properties of the 50 ms pulsar PSR B0540–69 using ASCA archival data obtained during 1993 to 1995. From the spectral analysis it was found that the spectra of the whole (nebular and pulsed) emission and pulsed emission in the range 1-10 keV can be represented by a single power law of photon index, Γ = 2.00 ± 0.02 and Γpulsed= 1.7 ± 0.3 respectively. The parameters for pulse frequency change during 1993-1995 were obtained using the 9 pulse frequency measurements with ASCA. The parameters derived from the ASCA observations are consistent with the previous measurements, suggesting high stability of this pulsar, ΔΩ/Ω ≲ 0.5 × 10−7over the past 10 years. These results confirm similarity of this pulsar with the Crab pulsar.
Scattering and Diffraction in Magnetospheres of Fast Pulsars
Authors: Lyutikov Maxim , Parikh Anuj 
Published: July 2016

AbstractWe show that under conditions of strong density modulation the effects of magnetospheric scintillations in diffractive and refractive regimes may be observable. The most distinctive feature of the magnetospheric scintillations is their independence on frequency. Results based on diffractive scattering due to small scale in homogeneities give a scattering angle that may be as large as 0.1 radians, and a typical decorrelation time of 10−8seconds. Refractive scattering due to large scale inhomogeneities is also possible, with a typical angle of 10−3radians and a correlation time of the order of 10−4seconds. Temporal variation in the plasma density may also result in a delay time of the order of 10−4seconds. The different scaling of the above quantities with frequency may allow one to distinguish the effects of propagation through a pulsar magnetosphere from the interstellar medium. In particular, we expect that the magnetospheric scintillations are relatively more important for nearby pulsars when observed at high frequencies.
Pulsar Scintillation Measurements: Is there any evidence for a Local Bubble Shell or effects from pulsar bow shocks?
Authors: Minter Anthony 
Published: July 2016

AbstractBhat et al. (1998) presented a model in which they explain the increase in scintillation bandwidth with decreasing pulsar distance as being due to a shell of scattering material associated with the Local Bubble. However, Britton et al. (1998) concluded that the scattering material for local pulsars is nearer to the pulsar (i.e. possibly in a bow shock or shell near the pulsar). We have investigated the effects of the local bubble shell and pulsar bow shocks on the scintillation bandwidth, the scintillation timescales and the angular broadening of pulsars. We find that a) there is no evidence for a shell of scattering material associated with the Local Bubble because the scintillation timescale data do not fit the Bhat et al. model and the angular broadening measurements do not suggest a scattering screen near the Sun, and b) that pulsar bow shocks cannot produce any enhanced scintillations.
Interstellar scintillation of the radio source associated with the gamma ray burst of 8 May 1997
Authors: Smirnova T.V. , Shishov V.I. 
Published: July 2016

AbstractWe show that variability of the radio source associated with the gamma ray burst of May 8, 1997 can be explained by scintillations on interstellar plasma inhomogeneities in the weak regime at 4.86 and 8.46 GHz, and by the refractive component of saturated scintillations at 1.43 GHz. Cosmological distance of this source R ≊ 1028cm is more preferable. The source has the size about 2μarcsec at frequency 4.86 GHz and the velocity of spreading is about 25μarcsec/year.
Braking Indices for Twenty Pulsars
Authors: Johnston Simon , Galloway David 
Published: July 2016

AbstractWe have derived a formula for the braking index of pulsars via integration rather than the conventional differentiation method. We applied the method to 20 pulsars and find that virtually all the derived braking indices are dominated by the effects of (unseen) glitches, the recovery from which corrupts the value of. However, any real, large, positive braking index has implications for magnetic field decay and offers support to recent models of pulsar evolution.
On the origin and parameters of the pulsar-like white dwarf in AE Aquarii
Authors: Ikhsanov Nazar R. 
Published: July 2016

AbstractThe rapid braking on the white dwarf in the close binary AE Aqr can be explained in terms of the canonical pulsar mechanism provided the magnetic moment of the starμ∼ 1.5 × 1034G cm3. The scenario for the origin of the fast rotating (Ps= 33 s), magnetized white dwarf, which is based on the magnetic field amplification in differentially rotating stars, is presented.
Gravitational Waves and Neutron Stars
Authors: Schutz Bernard F. 
Published: July 2016

AbstractThe first generation of laser-interferomteric gravitational wave observatories will make intensive searches for gravitational radiation from spinning neutron stars. Sensitivity to a number of possible sources, including the Crab pulsar, will be better than any existing observational limits, and will improve dramatically over the next decade. This paper reviews these developments and expectations, and discusses ways in which pulsar radio astronomers and gravitational wave astronomers can benefit from one another’s work.
Polar Motion: A Historical Overview on the Occasion of the Centennial of the International Latitude Service
Authors: Dick Steven J. 
Published: July 2016

AbstractThe study of polar motion, termed “variation of latitude” at the time of its discovery in the late 19th century by F. Küstner and S. Chandler, is of historical interest for many reasons. From a scientific viewpoint, its discovery must be seen in the context of positional astronomy, geodesy and Earth rotation studies. From an institutional viewpoint, the founding of the International Latitude Service (ILS) in 1899 represents an early case of international cooperation in astronomy, preceding the International Astronomical Union by two decades. In addition to discussing these themes in this review, we analyze in some detail the Gaithersburg (USA) station of the ILS as a case study of the early problems and promise of polar motion studies. With milliarcsecond accuracies, polar motion studies are important today not only for astronomy and geophysics, but also for practical problems like spacecraft navigation and positioning.
On the Contribution of the Geodetic Institute Potsdam to the International Latitude Service
Authors: Höpfner Joachim 
Published: July 2016

AbstractThe paper reviews in what ways the Geodetic Institute Potsdam contributed to the foundation of the International Latitude Service (ILS) and took part in its activities through the work of Helmert, Albrecht, Wanach and Mahnkopf. Based on international scientific cooperation, the results were the rectangular coordinates of the polar motion from 1890.0 to 1922.7 at 0.1 year intervals, in particular those derived from the latitude observations at independent stations from 1890.0 to 1899.8, and those derived from the latitude observations at the ILS stations from 1899.9 to 1922.7.
Project MERIT and the Formation of the International Earth Rotation Service
Authors: Wilkins G.A. 
Published: July 2016

AbstractProject MERIT was an international programme to Monitor Earth Rotation and Intercompare the Techniques of observation and analysis. It was conceived by a working group that was set up by the International Astronomical Union in 1978 and was carried through with additional support from the International Union of Geodesy and Geophysics. The first objective was to encourage the development of the use of new techniques, such as laser ranging and radio interferometry, for the regular determination of universal time and polar motion. A successful ‘short campaign’ of observations by six techniques was carried out during the period 1980 August to October. Operational and analysis centres were set up for each technique and a coordinating centre was established at the Bureau International de l’Heure (BIH). The results were reported and discussed at the first MERIT Workshop in 1981.The preparations for the ‘main campaign’, which was held from 1983 September 1 to 1984 October 31, and the plans for the activities that were to follow it were reviewed at the second MERIT Workshop in 1983. Important additional features of the campaign included the use of ‘MERIT Standards’ for the reduction and analysis of the data, the use of electronic techniques for the distribution of data, the comparison of the results with the changes in the angular momentum of the atmosphere and special emphasis on the improvement of the terrestrial reference frame. Proposals for a new International Earth Rotation Service were prepared at the third MERIT Workshop in 1986. The MERIT programme was continued from 1984 until the new service formally started on 1988 January 1. Over the decade the accuracy of the Earth-rotation parameters improved considerably.
Analysis of Long Time Series of Polar Motion
Authors: Schuh H. , Richter B. , Nagel S. 
Published: July 2016

AbstractTwo long time series of polar motion were analysed with respect to a linear drift, decadal variations, Chandler wobble and annual wobble: the C01 series published by the International Earth Rotation Service (IERS) and the pole series which J. Vondrák, obtained by re-analysis of the classical astronomical observations using the HIPPARCOS reference frame (1899.7–1992.0). By a least-squares fit the linear drift of the pole, usually called ‘secular polar motion,’ was determined to 3.31 milliarcseconds/year (mas/yr) toward 76.1° West longitude. For this fit the a priori correlations within each pair of pole coordinates were taken into account, and the weighting function was calculated by estimation of empirical variance components. The decadal variations of the pole path were determined by Fourier analysis. Using a sliding window analysis, the variability of the periods, the amplitudes and the phases of the Chandler wobble and annual wobble was investigated. The variances of the results and the number of iterations needed to get a convergence in the nonlinear approach show that the new time series by Vondrák is more homogeneous and consistent than the IERS C01 series.
On the Chandler periodicity (Polar Motion, LOD and Climate)
Authors: Buffa F. , Poma A. 
Published: July 2016

AbstractThe 14-month Chandler period is associated with the free nutation of the Earth about its spin axis. The observed value of the Chandler period comes usually from the analysis of astronomical series of polar motion data as well as from superconducting gravimeter measurements. At the observation level a periodicity of about 420–440 days also was noticed in microseismic activities. Recently we found evidence of a signal with period similar to the Chandler one in the Sardinia rainfall time series.