bluuebunny/crossref_metadata_2025_split huggingface dataset:
Giant Radio Pulses from Pulsars
Authors: Singal Ashok K. 
Published: July 2016

AbstractWe present some results from our observations of giant pulses from PSR B0950+08 at 103 MHz. These observations, now extending over a year, have shown the highest rate of occurrence of giant pulses seen from any known pulsar. Large fluctuations in the intensity levels of individual giant pulses and in their occurrence rate per unit interval of time are seen during a single day’s observations, as well as from one day to the next. We conclude that these intensity variations are likely to be intrinsic to the pulsar.
Multi-Frequency Studies of Intrinsic Intraday Variability
Authors: Wagner Stefan J. 
Published: July 2016

AbstractIntraday variability is detected in Blazars throughout the electromagnetic spectrum. Only radio emission is affected by interstellar scintillation. The characteristics of variability observed at different frequencies are often similar and suggest that intrinsic variations also contribute to the changes detected in the radio wavelength regime. This in turn implies very high brightness temperatures.Unambiguous signatures of scintillation and of intrinsic changes have been identified. The properties of intrinsic variations are reviewed to illustrate their potential contribution to variability in the radio domain. Such intrinsic changes need to be discriminated against when studying scintillation in quasars and BL Lac objects. Observations of scintillating sources and of sources with significant intrinsic IDV suggest interesting modifications to the standard paradigm of AGN.
Gravitational Lensing
Authors: Wambsganss Joachim 
Published: July 2016

AbstractIn the roughly 20 years of its existence as an observational science, gravitational lensing has established itself as a valuable tool in many astrophysical fields. In the introduction of this review we briefly present the basics of lensing. Then it is shown that the two propagation effects, lensing and scintillation, have a number of properties in common. In the main part various lensing phenomena are discussed with emphasis on recent observations.
Strong, Variable Circular Polarization in PKS 1519–273
Authors: MacQuart Jean-Pierre , Kedziora-Chudczer Lucyna , Jauncey David , Rayner David 
Published: July 2016

AbstractWe find strong (> 1%) circular polarization in the intraday-variable radio source PKS 1519–273. The source exhibits ~ 12 hourly variability in all four Stokes parameters at 4.8 and 8.6 GHz, and longer timescale variability at 2.5 and 1.4 GHz. The characteristics and frequency dependence of the variability suggest that it is due to interstellar scintillation. VSOP limits on the distance to the scattering screen constrain the brightness temperature to TB > 5 × 1013 K. The fluctuations in total intensity are well-correlated with those in circular polarization, implying that the variable component of the source is −3.8 ±0.4% circularly polarized at 4.8 GHz. The origin of the circular polarization is unclear.
Magnetic Fields in Quasar 3C147 on Milliarcsecond Scales
Authors: Zhang H.Y. , Nan R.D. 
Published: July 2016

AbstractVLBA polarimetric observations of the steep-spectrum quasar 3C147 were made at four frequencies in the available 5 GHz band, from which polarization in one bright feature in the inner jet was detected. The rotation measure of this feature (~ 1300 rad m−2) agrees with the known high rotation measure of the source, which makes it possible to remove the Faraday screen pixel-by-pixel and obtain the intrinsic magnetic field structure. The arch shape of B vectors suggests that a relativistic and distorted jet is being seen in projection.
Extreme Scattering Events: An Observational Summary
Authors: Joseph T. , Lazio W. , Fey Alan L. , Gaume R.A. 
Published: July 2016

AbstractWe review observational constraints on the structures responsible for extreme scattering events, focussing on a series of observations of the quasar PKS 1741–038. VLA observations were conducted to search for changes in the rotation measure and HI absorption during the ESE, while VLBI observations sought ESE-induccd changes in the source’s image. No RM changes were found implying B‖ < 12 mG, and no HI opacity changes were found implying N(HI) < 6.4 × 1017 cm−2. No multiple imaging was observed, but the diameter of the source increased by 0.7 mas, contrary to what is predicted by simple refractive lens modeling of ESEs. We summarize what these limits imply about the structure responsible for this ESE.
Interstellar Scintillation and Clouds of the Interstellar Turbulent Plasma
Authors: Shishov V.I. 
Published: July 2016

AbstractData on interstellar diffraction and refraction scintillation of pulsars are analyzed. Comparison between theory and the observational data shows that two types of spectra for electron density fluctuations are realized in the interstellar medium: pure power law and piecewise with a break. The distribution of turbulent plasma in the Galaxy has a three component structure. Component A is diffuse and it is distributed outside of the spiral arms of the Galaxy. Component BI is cloudy and associated with Galactic arms. Component BII is extremely nonuniform and associated with HII regions and supernova remnants. The origin of the interstellar plasma turbulence is considered, and possible sources of turbulent energy are discussed. The contribution of supernova bursts in the interstellar gas ionization and generation of turbulence are analyzed among other factors.
Interstellar Scintillation Studies of Pulsars and Distribution of Scattering Plasma in the Local Interstellar Medium
Authors: Bhat N.D. Ramesh , Gupta Yashwant , Pramesh Rao A. , Preethi P.B. 
Published: July 2016

AbstractPulsar scintillation measurements from the Ooty Radio Telescope (ORT) are used to investigate the distribution of scattering in the Local Interstellar Medium (LISM; region of ≲ 1 kpc of the Sun), specifically the region in and around the Local Bubble. A 3-component model, where the Solar neighborhood is surrounded by a shell of enhanced plasma turbulence, is proposed for the LISM. Further, the Ooty data, along with those from Parkes and other telescopes are used for investigating the distribution of scattering towards the nearby Loop I Superbubble.
Extending the Observable Zenith Angle of FAST Using an Offset Feed
Authors: Guoding Li , Nan R. , Peng B. 
Published: July 2016

AbstractThe five hundred meter aperture spherical radio telescope is will use an active spherical reflector. When the zenith scan angle is changed, the illuminated part of the reflecting surface is made to fit a paraboloid of revolution in real time by active control. The maximum zenith scan angle | ψmax | of FAST is 30° under conditions of the geometry selected in order that the feed does not illuminate the ground. The result of this paper shows that the maximum zenith scan angle | ψmax | can be extended to 69° by offsetting the feed.
Far-Red Spectroscopy of Peculiar Stars and the GAIA Mission
Authors: Munari Ulisse 
Published: July 2016

AbstractThe coming GAIA Cornerstone mission by ESA will provide micro-arcsec astrometry, ∼10 bands photometry and far-red spectroscopy for a huge number of stars in the Galaxy (109). GAIA spectroscopy will cover the range 8480–8740 Å which includes the CaII triplet and the head of the Paschen series. In this paper we address the diagnostic potential of this wavelength range toward detection of peculiar stars.
The Massive Close Binary in the δ Ori A Triple System
Authors: Harvin James A. , Gies Douglas R. 
Published: July 2016

AbstractWe present an analysis of short-wave, high-dispersion ultraviolet spectra of the triple star δ Ori A from the International Ultraviolet Explorer Satellite’s (IUE) Final Archive. These spectra were cross-correlated against AE Aur to find the components’ radial velocities, which were then used to produce the system’s orbital elements. The long-period tertiary star in the δ Ori A system was not seen in the resulting cross-correlation functions (CCFs). The close binary’s eclipses allow the orbit’s inclination to be estimated by modeling of its Hipparcos light curve. The primary star appears to have a mass of 11.2 M⊙ and the secondary seems to have a mass of 5.6 M⊙, both of which are about 1/3 of the expected values for stars of their MK types. Although we expected the massive close binary in the δ Ori A system to be a pre-Roche lobe overflow (RLOF) system, these masses appear to require that it be a post-RLOF system. The full description of this work, including the tomographic separation of the spectra for the close binary’s components, appears in Harvin et al. (2002).
Interferometric Observations of η Carinae - the VLTI Takes Its First Glimpse at the Central Source
Authors: Kervella P. , Schöller M. , van Boekel R. , di Folco E. , Correia S. , Glindemann A. , Paresce F. , Richichi A. , Tarenghi M. , Wittkowski M. 
Published: July 2016

AbstractWe describe the first long-baseline interferometric measurement ever made of the luminous blue variable η Carinae. η Car was observed with the Very Large Telescope Interferometer (VLTI) with the 8.2 m Unit Telescopes as well as with the 40 cm test siderostats on three different baselines. We will detail the measurements and data analysis and discuss briefly the implications of the derived visibility on the morphology of the central source. Furthermore we will discuss the future possibilities of interferometric observations and will show that η Car is one of the prime candidates for imaging with the VLTI.
The Interacting Binary Be Star HR 2142
Authors: Peters Geraldine J. , Gies Douglas R. 
Published: July 2016

AbstractCurrent information on the nature of the HR 2142 system is presented. The circumstellar material (CSM) including the mass flow toward and away from the mass-gaining B star has been studied from ∼ 100 IUESWP HIRES images obtained from 1979–95 and ground-based CCD data from KPNO acquired between 1985–2001. The strength and velocity behavior of the infall components to the UV Si ɪɪ lines seen during the primary shell phase (PSP) from Φ ∼ 0.70−0.98 resembles that observed in conventional Algol systems, but the inferred mass infall rate is too small to account for the massive Hα-emitting disk about the B primary. The cause for the mass outflow observed during the secondary shell phase (SSP) remains unknown, but a localized plasma that has been identified from phase-dependent variations in the emission component to Heɪ λ6678 may be part of the SSP phenomenon. Although the secondary remains undetected in the optical/IR spectral regions, UV data currently do not yield strong support for the presence of an O subdwarf as in the Φ Per system. HR 2142 may represent and earlier evolutionary stage of Φ Per and a possibly similar Be binary 59 Cyg.
Fluorescence and Chromospheric Activity of V471 Tau
Authors: Vaccaro T.R. , Wilson R.E. 
Published: July 2016

AbstractThe red dwarf + white dwarf eclipsing binary V471 Tau shows a variable Hα feature that varies from absorption during eclipse to maximum emission during white dwarf transit. In 1998 we obtained simultaneous BVRI photometry and Hα spectroscopy, with thorough phase coverage of the 12.5 hour orbital period. A binary star model was used with our light curve, radial velocity, and Hα data to refine stellar and orbital parameters. Combined absorption-emission profiles were generated by the model and fit to the observations, yielding a red star radius of 0.94R⊙. Orbital inclination 78° is required with this size and other known parameters. The model includes three spots 1,000 K cooler than the surrounding photosphere. The variable Hα profile was modeled as a chromospheric fluorescing region (essentially on the surface of the red star) centered at the substellar point. Additional emission seen outside our modeled profiles may be large co-rotating prominences that complicate the picture.
Imaging Ejecta from the Final Flash Star V605 Aql
Authors: Hinkle Kenneth , Joyce Richard , Ridgway Steven , Close Laird , Lebzelter Thomas , Hron Josef , Andre Karin 
Published: July 2016

AbstractThe cloud of ejecta resulting from a final helium shell flash in V605 Aql has been imaged in both optical emission lines and infrared continuum. The obscuring circumstellar dust cloud, whose effects were first seen in 1923, is shown to be bipolar, suggesting dust formation takes place in a disk surrounding this star. The ongoing stellar mass loss in V605 Aql is part of the final flash episode, which has been ongoing since 1919. The pre-final flash planetary nebula, A58, is nearly circular. This implies that significant changes in the mass loss process occur between the AGB and final flash stages.
H 1504+65 – The Naked Stellar C/O Core of a Former Red Giant Observed with FUSE and Chandra
Authors: Werner Klaus , Rauch Thomas , Barstow Martin A. , Kruk Jeff W. 
Published: July 2016

AbstractH 1504+65 is an extremely hot hydrogen-deficient white dwarf with an effective temperature close to 200 000 K. We present new FUV and soft X-ray spectra obtained with FUSE and Chandra, which confirm that H1504+65 has an atmosphere primarily composed of carbon and oxygen. The Chandra spectra show a wealth of absorption lines from highly ionized oxygen, neon and magnesium and suggest relatively high Ne and Mg abundances. This corroborates an earlier suggestion that H1504+65 represents a naked C/O stellar core or even the C/O envelope of an O/Ne/Mg white dwarf.
The Massive Contact Binary RY Scuti: A WR+OB Progenitor and Its Compact Nebula
Authors: Smith Nathan , Gehrz Robert D. 
Published: July 2016

AbstractRY Scuti is a massive contact binary in a critical Roche-lobe overflow phase, and it may be an immediate progenitor of a WR+OB binary system like V444 Cygni. It may also have something in common with the eruptive binary HD 5980 in the SMC. RY Scuti is a nearby eclipsing binary, but basic parameters like the mass and evolutionary state of its individual components seem difficult to nail down because it is a common-envelope system. It is also surrounded by a compact double-ring nebula with geometry and kinematics that have interesting implications for its mass-loss mechanism. Some recent results of high-resolution imaging and spectroscopy of the nebula are reviewed here.
HD 101065 – Przybylski’s Star: A Most Peculiar Star
Authors: Kurtz D.W. 
Published: July 2016

AbstractThe story of HD 101065, Przybylski’s star, is one of a forty-year controversy over the nature of what is arguably the most peculiar star in the sky, a controversy that is only now being resolved fully. Our current understanding is that HD 101065 is the coolest (Teff ≈ 7400 K) and the most peculiar of the Ap SrCrEu stars. The existence of this most peculiar star, and other Ap stars, has been the source of some very interesting stellar astrophysics with applications far wider than the understanding of just the stars themselves.
The Characteristics of Magnetic CVs in the Period Gap
Authors: Tovmassian Gaghik , Zharikov Sergey , Mennickent Ronald , Greiner Jochen 
Published: July 2016

AbstractWe have observed several magnetic cataclysmic variables located in the range between 2 and 3 hours, known as the period gap. This work was prompted by the recent discovery of RXJ1554.2+2721. It has 2.54 hours orbital period and shows almost pure cyclotron continuum in a low luminosity state, similar to HS1023+3900, HS0922+1333 and RBS206. These are low accretion rate polars (LARPs) known to have mass transfer rates of order of a few 10-13M⊙/year. The aim of the study was to find out, if magnetic systems filling the period gap are in any way different from their counterparts outside that range of periods. The only significant difference we encounter is a much higher number of asynchronous magnetic systems towards longer periods than below the gap.
The Chandra Observation of the IP TX Col
Authors: Schlegel Eric M. , Salinas Anandi 
Published: July 2016

AbstractWe present a preliminary look at the serendipitous observation of the intermediate polar TX Col by Chandra. The ~52 ksec observation is uninterrupted, providing an opportunity to disentangle the light curve and power spectra components. We illustrate the energy-dependence of the power spectrum.
Hard X-ray Observations of Magnetic Cataclysmic Variables
Authors: Singh K. P. , Rana V. R. , Mukerjee K. , Barrett P. , Schlegel E. M. 
Published: July 2016

AbstractHard X-ray light curves and spectral parameters from our analysis of X-ray data of five AM Her type systems – V2301 Oph, V1432 Aql, EP Draconis, GG Leonis, & V834 Cen, and one intermediate polar – TV Col, observed using the Rossi X — ray Timing Explorer (RXTE) satellite are presented. A new improved ephemeris has been derived for V2301 Oph using the mid-eclipse timings. Average intensity variations, without any change of shape of the light curve or hardness ratio, are observed on timescales of a few days to a few months in V2301 Oph. V1432 Aql shows erratic variations on a timescale of a day, at least two sharp dips near orbital phases 0.35 and 0.5, and a total eclipse. Hard X-ray eclipses are also reported in EP Dra and GG Leo. V834 Cen shows intensity variations on yearly timescale and is found to be in a low state in 2002. In TV Col, a binary orbital modulation at 5.5h, in addition to the spin period of 1910s, is reported for the first time. Maximum spectral temperatures in Polars have been determined and used to estimate the masses of the white dwarfs.
Far-UV FUSE Spectra of Peculiar Magnetic Cataclysmic Variables
Authors: Mouchet Martine , Bonnet-Bidaud Jean-Marc , Roueff Evelyne , Abada-Simon Meil , Beuermann Klaus , de Martino Domitilla , Desert Jean-Michel , Ferlet Roger , Fried Robert , Gänsicke Boris , Howell Steve , Mukai Koji , Porquet Delphine , Szkody Paula 
Published: July 2016

AbstractWe present far-UV spectra of the three magnetic cataclysmic variables (MCVs) BY Cam, V1309 Ori and AE Aqr obtained with the FUSE satellite. These MCVs have revealed strongly unusual NV and CIV UV resonance lines. The FUSE spectra exhibit broad OVI lines as well as a strong NIII line at 991Å, while the CIII 1175Å line is nearly absent, supporting non-solar CNO abundances of the accreting matter in these sources. The spectrum of BY Cam shows molecular H2 lines which might be of circumstellar nature. The flaring activity of AE Aqr is also observed in the far-UV range. The radial velocities of the broad OVI components in AE Aqr are orbitally modulated and would indicate an emission region close to the magnetosphere.
The CNO problem in Magnetic Cataclysmic Variables
Authors: Bonnet-Bidaud Jean-Marc , Mouchet Martine 
Published: July 2016

AbstractSome polars like BY Cam are characterized by unusual CNO line ratios compared to other polars and non-solar abundances have been suggested to explain this anomaly. We present here a first attempt to constrain the elemental abundances in these systems by applying a specific ionisation model combined with a geometrical description of the accretion column where these lines are thought to be formed. The line luminosities have been computed using the CLOUDY plasma code for different ionisation spectra and column extension. We show here selected results and compare to the values observed in “peculiar” magnetic CVs. The model applied to BY Cam confirms that ionization models with solar abundances fail to reproduce the observed line intensity ratios. Assuming the model to be valid, the induced best abundances imply an overabundance of N (x25), underabundance of C (:8) and nearly solar O (:2), in line with CNO reprocessing.
Cyclotron Emission Features in the Spectra of Polars with Low Accretion Rates
Authors: Gospodchikov E. D. , Serber A. V. 
Published: July 2016

AbstractWe calculate non-LTE transfer of cyclotron-harmonics radiation in the hot spot of an accreting magnetic white dwarf (WD) in the case where the contribution of the accretion column to the observed radiation is negligible. The observed cyclotron spectra of a polar with a low accretion rate are found. Based on the theory developed, we interpret the cyclotron emission line spectra of the systems and determine physical conditions in the emission regions of HS 1023+3900 and HS 0922+1333.
Accretion Flow along a Dipolar Field: Application to Intermediate Polars
Authors: Canalle João Batista Garcia , Wu Kinwah , Cropper Mark , Ramsay Gavin , Saxton Curtis J. 
Published: July 2016

AbstractA hydrodynamic formulation for accretion flow channeled by a dipolar magnetic field is constructed using a curvi-linear coordinate system natural to the field structure. We solve the hydrodynamic equations and determine the velocity, density and temperature profiles of the post-shock accretion flow. The results are applied to accretion flows in intermediate polars. We have found that for systems with massive white dwarfs (~ 1 M⊙) the temperature profiles in the flow can differ significantly to those obtained from models in which the accretion column is assumed to be cylindrical.
An Investigation of Radio Emission in Magnetic Cataclysmic Variables
Authors: Mason Paul A. , Gray Candace 
Published: July 2016

AbstractThe origin of radio emission in magnetic CVs is a long standing problem without a satisfactory solution. We review the radio observations of both non-magnetic and magnetic CVs and discuss possible emission mechanisms. We pose the following questions: Is the presence of a magnetic white dwarf a necessary condition for radio emission? Is there a single cause for the radio emission or are there several radio emission mechanisms? We revisit the suggestion that asynchronism or at least the lack of strict magnetic locking might be a necessary condition for radio emission.
Bi-Modality in the short-term photometric Properties of the Intermediate Polar V1062 Tau
Authors: Lipkin Y. , Leibowitz E. M. , Orio M. 
Published: July 2016

AbstractWe conducted coordinated time-resolved observations of the long-period Intermediate Polar V1062 Tauri at the WIYN Observatory in Kitt Peak, Arizona and at Wise Observatory, Israel, and follow-up observations at the second site. We confirm the presence of two previously reported periodicities of the system: a long period (P≈10 h) which was interpreted as the orbital period of the underlying binary system, and a shorter one (P≈ 1 h), which was interpreted as the spin of the white dwarf. Our data also revealed a third photometric periodicity, corresponding to the orbital sideband of the spin period (OSB). The amplitude of the OSB was found to be strongly correlated with the varying brightness of the system at the orbital cycle.Our observations suggest bi-modality in the photometric characteristics of the star. In one mode, the light of V1062 Tau varies with the spin period of the white dwarf, whereas the OSB is undetected. In the other mode, the OSB is the main modulation at short time-scales, and the spin period is absent from the light curve. Switching between the two modes occurred three times during the 10 weeks that spanned our observations. Also, we detected an outburst of 1.1 mag, which lasted between ~1 and ~5 days. In addition to the outburst, secular variations in the brightness of the star (0.3 mag on time scale of a few of tens of days) suggest that the system was in a brief low state during 2002 January.
The Secondary Stars in Short Period (Magnetic) Cataclysmic Variables
Authors: Howell Steve B. 
Published: July 2016

AbstractWe review the recent knowledge base pertaining to causes for mass accretion variations (high/low states) in highly magnetic cataclysmic variables (i.e. polars). We then examine what theory has to say about the properties of the secondary stars (the mass donors) with respect to those CVs with very short orbital periods. Finally, we use recent observations of EF Eri in an extended low state to provide direct observational evidence which shows that this CV, as well as a few others, likely contain very low mass, sub-stellar secondary stars.