bluuebunny/crossref_metadata_2025_split huggingface dataset:
ROSAT observations of non-magnetic CVs
Authors: van Teeseling A. , Verbunt F. , Beuermann K. 
Published: July 2016

In non-magnetic cataclysmic variables the accreted matter forms an accretion disk around the white dwarf. In the boundary layer between the white dwarf and the accretion disk the accreted matter decelerates from Keplerian velocities to the rotation velocity of the white dwarf. If the accretion rate is high the boundary layer would be optically thick and cool (T ~ 105K), and if the accretion rate is low the boundary layer would be optically thin and hot (T ~ 108K) (Pringle & Savonije 1979).There are several observational problems with this simple picture: a soft X-ray component could only be detected so far in 5 dwarf novae in outburst and not in any nova-like variable. Also in high-accretion-rate systems there is a hot optically thin X-ray source, which has, however, an X-ray luminosity which is much less than the UV luminosity of the system (van Teeseling & Verbunt 1994). Finally, there is evidence for orbital modulation in the X-rays from some systems (e.g. van Teeseling et al. 1995).
V1974 Cyg (Nova Cyg 1992) - A Possible Link to SU Uma Stars
Authors: Retter A. , Leibowitz E. M. , Ofek E. O. 
Published: July 2016

V1974 Cyg erupted on 1992 February 19, and was the brightest nova since V1500 Cyg. It soon became an object of massive international multiwavelength observational study.Some major photometric features of the nova were investigated by DeYoung & Schmidt (1994), and Semeniuk et al. (1994,1995). They found two periodicities in the nova light curve. While the shorter 0.081263 d period was present during the 1993 and 1994 observations, the longer 0.0850 d period was only observed from 1994 July. Semeniuk et al. (1995) interpreted the shorter period as the orbital period of the binary system, and the longer one as caused by the rotation of the white dwarf due to a magnetic field.
The Spectrum of the old Nova V603 Aql observed with the HST
Authors: Friedjung M. , Selvelli P. L. , Cassatella A. 
Published: July 2016

AbstractSpectra of the old nova V603 Aql taken with the HST-GHRS did not reveal resonance doublet absorption components arising in material ejected in the 1918 outburst. However absorption components, probably produced by a disk wind, were observed, though most line emission probably comes from regions associated with an accretion disk. Most strikingly, dramatic line profile variations on time-scales of not much more than 10 m were seen.
A New Type of Asymmetric Outflow in the Recurrent Nova RS Oph in Quiescence
Authors: Iijima T. 
Published: July 2016

AbstractH I emission lines in the spectrum of the recurrent nova and symbiotic star RS Oph in quiescence are sometimes accompanied by blue- or red-shifted broad emission components. The displacements of the broad components from the narrow lines change from −1300 to +1200 km s−1, but possibly not continuously. The broad components seem to appear in some restricted regions on the spectra. An asymmetry between the blue- and red-shifts is noticed.
The peculiar symbiotic star CH Cyg – a bright counterpart of cataclysmic variables?
Authors: Leedjärv Laurits 
Published: July 2016

CH Cyg has begun to show symbiotic features only since 1963. Up to now four outbursts of CH Cyg have been recorded, the fifth going on at the present time. CH Cyg reveals a lot of peculiarities as compared to ‘normal’ symbiotic stars (extended inactive periods between the ‘symbiotic’ periods; the most extended active period in 1977–1986 including the ejection of bipolar radio jets; a stage of increased activity since 1992, with peculiar profiles of the Balmer emission lines etc.); see Mikolajewski, Mikolajewska & Khudyakova (1990) for further references.Classical models for explaining the outbursts of symbiotic stars (e.g. Mikolajewska & Kenyon 1992) are unable to account for the behaviour of CH Cyg. The magnetic rotator model has been proposed and developed by Mikolajewski & Mikolajewska (1988, 1996). The model includes a wind accreting, magnetic (B ~ 107 G), rapidly rotating (P ~ 8 m) white dwarf (WD) as the hot component of the symbiotic system. A strong magnetic field prevents matter from the red giant’s wind being accreted onto the WD surface in the usual way. Instead, three stages of accretion could be considered: inactive, propeller and accretor state.
A close look at the outburst of the very slow symbiotic nova PU Vul – a triple system
Authors: Chochol D. , Tamura S. , Kanamitsu O. , Pribulla T. , Tajitsu A. 
Published: July 2016

AbstractThe very slow nova PU Vul was discovered by Honda and Kuwano in 1979 after the rise from B ~ 15…16 mag to a maximum B ~ 9 mag. The object has been studied by many authors (for references see Belyakina et al. 1989; Vogel & Nussbaumer 1992) but a clear picture of the system was not given. Two minima of different duration were observed in the system in the active stage, in 1980-81 and 1993-94 (Kolotilov et al. 1995). Nussbaumer & Vogel (1996) ascribed the minima to eclipses of the hot component by the cool M giant in a binary with orbital period of 4900±100 d. Our period analysis of the preoutburst B data (Liller & Liller 1979) by Stellingwerf’s (1978) method revealed a period of 4858 d. We found the third minimum in 1926-28 (lasting for 500…630 d) in these data.
The 35 Day Cycle of Her X-1
Authors: Schandl S. , Meyer F. 
Published: July 2016

AbstractThe 35 d period in the observed X-ray and optical light curves of Her X-1 can be understood in terms of a warped accretion disk precessing in the tidal field of the companion. We propose that repulsive forces of the X-ray driven coronal wind acting on the disk causes and maintains the warp of the disk (Fig. 1). The resulting shape of the precessing disk reproduces the main features of the observed X-ray light curve [1]. Based on the calculated disk shape we model the dip structure in the X-ray observations as caused by the interaction between the accretion stream and the warped disk.
ASCA Observations of LINERs
Authors: Terashima Y. , Kunieda H. , Iyomoto N. , Makishima K. , Serlemitsos P. J. 
Published: July 2016

ASCA observations have revealed the presence of low-luminosity AGN in ~10 LINERs as a hard point sources at the nucleus. The X-ray continuum shapes (photon indices Γ ≈ 1.8) are very similar to those of Seyfert galaxies (Makishima et al. 1997, Serlemitsos et al. 1996). An iron emission line is observed from heavily absorbed low-luminosity AGNs (Makishima et al. 1997), while M81 is the only object among those with small intrinsic absorption from which an iron line detected (Ishisaki et al. 1996) on account of limited photon statistics for other objects.We summed up the ASCA spectra of 5 LINERs which host low-luminosity AGN of low intrinsic absorption to search for an iron emission line. We used 7 observations of 5 objects (NGC 1097, NGC 3310, NGC 3998, NGC 4450, and NGC 4594) to make a composite spectrum. All the objects have very similar X-ray characteristics (spectral slope, intrinsic absorption, no short time-scale variability; Iyomoto et al. 1996, Serlemitsos et al. 1996).
Parameter Space of Shock Formation in Adiabatic Flows
Authors: Lu Ju-Fu , Yu K.N. , Yuan F. , Young E. C. M. 
Published: July 2016

We study shock formation in a stationary, axisymmetric, adiabatic flow of a perfect fluid in the equatorial plane of a Kerr geometry. For such a flow, there exist two intrinsic constants of motion along a fluid world line, namely the specific total energy, E = −hut, and the specific angular momentum, l = −uφ/ut, where the uμ’s are the four velocity components, h is the specific enthalpy, i.e., h = (P + ε)/ρ, with P, ε, and ρ being the pressure, the mass-energy density, and the rest-mass density, respectively.As shown in Fig. 1 (Fig. la is for a Schwarzschild black hole, i.e. the hole’s specific angular momentum a = 0; Fig. lb is for a rapid Kerr hole, i.e. a = 0.99M, where M is the black-hole mass, and prograde flows: and Fig. 1c is for a = 0.99M and retrograde flows), in the parameter space spanned by E and l there is a strictly defined region bounded by four lines: three characteristic functional curves lk(E), lmax(E), and lmin(E), and the vertical line E = 1. Only such a flow with parameters located within this region can have two physically realizable sonic points, the inner one rin, and the outer one rout. In between there is still one more, but unrealizable, sonic point, rmid. The region is divided by another characteristic functional curve lc(E) into two parts: in region I (= Ia + Ib) only τout is realized in a shock-free global solution (i.e., that joining the black-hole horizon to large distances), while in region II (= IIa + IIb) only rin is realized.
Metal Abundances and Ionization in QSO Broad Emission-Line Regions
Authors: Hamann F. , Shields J.C. , Cohen R. D. , Junkkarinen V.T. , Burbidge E.M. 
Published: July 2016

AbstractWe describe two ongoing studies of QSO broad emissionline regions (BELRs). The first employs the N V λ1240/He II λ1640 and N V/C IV λ1549 line ratios as diagnostics of QSO metallicities. Hamann & Ferland and Ferland et al. showed that many observed N V ratios require enhanced N abundances and Z > Z⊙. Here we present new measurements of large line ratios at redshifts z > 4, which indicate super-solar abundances within ~1 Gyr of the Big Bang (for q0 ≈ 0.5). We also note that the N V line is relatively stronger in more luminous QSOs, in contrast to the well-known Baldwin effect in Lyα, C IV, and O VI λ1034. This unusual behavior in N V could be due to a luminosity-metallicity correlation among QSOs that is coupled to a mass-metallicity relation in their host galaxies.Our second study involves Ne VIII λ774 as a probe of highly ionized gas. We show that a broad emission feature near 774 Å is common in QSOs. Photoionization models indicate that Ne VIII is the most likely identification for this feature. The models also indicate that the Ne VIII emitting gas covers > 40% of the continuum source, has a total hydrogen column density of NH > 1022 cm−2 (for solar abundances) and an ionization parameter of U > 5 (for a nominal QSO continuum shape). This gas would be an X-ray “warm73x201D; absorber — with O VII–O VIII bound-free edges — if it lies along our line-of-sight to the X-ray continuum source.
Emission-Line Properties of z ≥ 4 QSOs
Authors: Shields J.C. , Hamann F. , Foltz C.B. , Chaffee F.H. 
Published: July 2016

AbstractWe report on preliminary results of a program of rest-frame UV spectroscopy of z ≥ 4 QSOs. Despite their high luminosity and inherent youth, these objects exhibit spectra that are generally very similar to those of AGNs at lower z. We find some evidence that the z ≥ 4 systems are described by unusually strong O Iλ1304 emission, which may be a result of elevated metallicity or unusual prominence of the ‘intermediate-line region’. High metallicities are also signaled by strong N Vλ1240 emission, consistent with quasar behavior at z ≈ 2–3.
Emission Lines and the Spectral Energy Distributions of Quasars
Authors: Wilkes B.J. , Green P.J. , Mathur S. , McDowell J.C. 
Published: July 2016

AbstractMany years of study have failed to establish conclusively relationships between a quasar’s spectral energy distribution (SED) and the emission lines it is thought to produce. This is at least partially due to the lack of well-observed SEDs. We present initial results from a line–SED study for a sample of 43 quasars and active galaxies for which we have optical and ultraviolet spectra and far-infrared–X-ray SEDs. We present the results of tests for correlations between line equivalent widths and SED luminosity and slope parameters and compare these results to those from earlier studies. We find that the Baldwin effect is weaker when the luminosity is defined close to the ionizing continuum of that line and conclude that the detailed SED is likely to be important in making further progress.
The Spectra of Dusty Quasars
Authors: Francis Paul J. , Webster Rachel L. , Masci Frank J. , Drinkwater Michael J. , Peterson Bruce A. 
Published: July 2016

AbstractFlat radio spectrum quasars from the Parkes half-Jansky survey show an enormous range of optical to near-IR colors. The spectra of these quasars suggest that this diversity is probably due to variable amounts of dust somewhere along the line of sight.
Results from Five Years of Spectrophotometric Monitoring of 28 Palomar-Green Quasars
Authors: Kaspi Shai 
Published: July 2016

AbstractWe present 5 years of results from a spectrophotometric monitoring program of 28 quasars. The typical sampling intervals are several months. We show the light curves obtained for two quasars, PG 0804+762 and PG 0953+414. Both sources show Balmer emissionline variations which follow those of the continuum with a time lag of order 100 days. This is the first reliable measurement of such a lag in active galactic nuclei with luminosity L > 1045 erg s−1. The broad-line region (BLR) size that is implied is almost an order of magnitude larger than that measured in several Seyfert 1 galaxies and is consistent with the hypothesis that the BLR size grows as L0.5.
IUE Monitoring of the Bright Seyfert 1 Galaxy Fairall 9
Authors: Rodríguez-Pascual P. M. 
Published: July 2016

AbstractAn eight-month spectrscopic monitoring campaign on the Seyfert 1 galaxy Fairall 9 has been carried out with the International Ultraviolet Explorer (IUE) in order to measure continuum-continuum and continuum-emission-line delays for a high-luminosity active galactic nucleus (AGN). The results are consistent with those of previous campaigns on lower luminosity AGNs: (i) there is no measurable time lag between different ultraviolet continuum bands, (ii) the measured time lags for the emission lines are relatively short, and (iii) the more rapid and stronger response to continuum changes of He II, as compared to C IV, is consistent with a stratified broad-line region (BLR) structure.
Is the Broad-Line Region Expanding?
Authors: Liang Kan , He Xiang-Tao , Wang Zhong-min , You Jun-Han 
Published: July 2016

We suggest that the broad-line regions (BLRs) of QSOs with broad emissionlines (BALs) are expanding, i.e., the clouds are undergoing radial outflow, as illustrated simply in Fig. 1. At least the following observational facts can be explained:
1.Optical observations show that some moderate and high-redshift QSOs have BALs. The number of these QSOs is about 3–10% of all QSOs (Foltz et al. 1990). One can see in Fig. 2 that very low-redshift QSOs have no BALs.2.Almost all BAL QSOs exhibit zabs < zem.3.High-resolution observations reveal that the widths of the broad absorption lines are narrower than that of the corresponding emission line for all BAL QSOs, i.e. Δλ ab < Δλ em.
Intrinsic Absorption and Emission Lines in Seyfert Galaxies
Authors: Crenshaw D.M. 
Published: July 2016

AbstractRecentHSTspectra indicate that a large fraction of Seyfert 1 galaxies have UV absorption lines that are intrinsic to the active nucleus or its environment.IUEmonitoring or multipleHSTobservations of several sources show that many absorption lines are variable, either as a result of mass motion across the line-of-sight or of changing ionization within the gas in response to variations in the ionizing continuum. The UV absorbers may be related to the warm absorbers seen in the X-ray spectra of many Seyfert galaxies, but a direct connection between the two has not been made. Some of the absorption lines may arise in the emission-line regions in the nucleus or host galaxy, providing valuable clues to their nature.
A Correlation Analysis for Emission Lines in 52 AGN
Authors: Dultzin-Hacyan D. , Sulentic J. , Marziani P. , Calvani M. , Moles M. 
Published: July 2016

AbstractWe recently completed the first comparison of high- and low-ionization broad lines in a sample of 52 AGN. We summarize here the principal results of a correlation analysis for this sample. We then briefly outline a model for the broad-line structure in radio-quiet AGN that is suggested by the correlation analysis.
A Correlated Optical-Infrared Outburst of Mrk 744: Strong Evidence for Thermal Dust Reverberation
Authors: Nelson B. 
Published: July 2016

AbstractSimultaneous optical and infrared monitoring of a sample of 50 Seyfert 1 galaxies and quasars has revealed an outburst of the active galaxy Markarian 744. Cross-correlation analysis indicates that the IR lags the optical light curve by roughly one month. A simple model developed by the author can fully explain the IR variability of this object in terms of thermal dust reverberation.
Near-Infrared View of the Nuclear Region of NGC 1808
Authors: Kotilainen J. K. 
Published: July 2016

AbstractWe discuss NIR imaging of the starburst galaxy NGC 1808. The circumnuclear continuum emission shows no morphological change with wavelength and most of it is produced by an evolved bulge population, not by red supergiants or dust. The line emission arises from distinct hot spots. From comparison of Brγ and Hα fluxes, we derive extinction Av = 3–5 toward the hot spots. From modeling of the line and continuum luminosities, we derive a star-formation rate of 0.1–0.6 M⊙ yr–1 and SN rate ~ 0.4–11 × 10–3 yr–1 per hot spot. The age of the burst is 8–17 Myr for the hot spots and ~ 40 Myr for the nucleus. Finally, evidence for and against hidden Seyfert activity in NGC 1808 is discussed.
Excitation Mechanism of Extended Emission-Line Regions in Active Galaxies
Authors: Evans Ian , Koratkar Anuradha , Allen Mark , Tsvetanov Zlatan , Dopita Michael 
Published: July 2016

AbstractPhotoionization and shock models of the extended emissionline regions (EELRs) in active galaxies demonstrate that the optical emission lines alone are a poor discriminant of the excitation mechanism. Combining optical and UV data provides a discriminant between nuclear photoionization and autoionizing shock models. Hubble Space Telescope UV spectrophotometry of two Seyferts suggests that the EELRs in these objects are probably photoionized by the nucleus.
The S2 Baseband Processing System for Phase-coherent Pulsar Observations
Authors: Wietfeldt R. , Straten W. Van , Rizzo D. Del , Bartel N. , Cannon W. , Bailes M. , Reynolds J. , Wilson W. 
Published: July 2016

AbstractThe phase-coherent recording of pulsar data and subsequent software dispersion removal provide a flexible way to reach the limits of high time resolution, useful for more precise pulse timing and the study of fast signal fluctuations within a pulse. Because of the huge data rate and lack of adequate recording and computing capabilities, this technique has been used mostly only for small pulsar data sets. In recent years, however, the development of very capable, reasonably inexpensive high-speed recording systems and computers has made feasible the notion of pulsar baseband recording and subsequent processing with a workstation/computer. In this paper we discuss the development of a phase-coherent baseband processing system for radio pulsar observations. This system is based on the S2 VLBI recorder developed at ISTS/York University in Toronto, Canada. We present preliminary first results for data from the Vela pulsar, obtained at Parkes, Australia, and processed at ISTS/York University, and discuss plans for future developments.
Pulsar Velocities – Revisions & Ramifications
Authors: Lorimer D. R. 
Published: July 2016

AbstractThe recent shift of opinion concerning the distribution of pulsar velocities at birth with a mean value of 400-500 km/s has several ramifications for our understanding of the origin and evolution of pulsars. From the present data, there is no convincing evidence for a causal correlation between velocity and magnetic field, any magnetic field evolution in neutron stars or that galactic neutron stars once active as radio pulsars are the sources ofγ-ray bursts. Asymmetric kicks seem the most plausible origin for the high velocities.
Pulsar Period and Magnetic Field Evolution
Authors: Camilo F. 
Published: July 2016

AbstractOne of the important unsolved problems in pulsar astrophysics concerns the formation and evolution of their magnetic fields. We summarize measurements of braking indices and their implications for the spin and magnetic field evolution of young pulsars. An analysis of the period-period derivative diagram suggests one or more of the following: (a) a substantial population of young pulsars remains undiscovered; (b) a large fraction of all slow pulsars may be recycled; (c) magnetic fields in isolated pulsars decay by a factor of a few in the first few million years. We also note that the observed P-Ṗ distribution of millisecond pulsars may be shaped by luminosity evolution.
The velocity distribution of young radio pulsars: simulating the observations
Authors: Hartman J.W. 
Published: July 2016

Lyne &amp; Lorimer (1994) argue that the velocities of young pulsars are much higher than was previously thought. However, recent radio pulsar population synthesis work by Hartman et al. (1996, these proceedings) shows that simulations that use a birth velocity distribution with more pulsars at low velocities, Phinney’s modification of the Paczyński (1990) distributiondescribes the observed magnetic field, period and luminosity distribution equally well as simulations that use the Lyne &amp; Lorimer distribution.We use this radio pulsar population synthesis model to obtain the proper motion distribution of the simulated sample, and from that we calculate the transverse velocity distribution to compare it with the observed transverse velocity distribution. A full report of this work will be given in Hartman (1996).
Rotational Instabilities in Pulsars
Authors: Lyne A. G. 
Published: July 2016

AbstractIn general, radio pulsars are superb clocks. However a few years after their discovery, it became clear that some pulsars show significant departures from their regular slow-down which make their rotation unpredictable. Two main forms of irregularities have been identified – glitches and timing noise – which are most marked in, but not confined to, young pulsars. Both are probably related to the internal structure of the neutron star and the properties of the internal neutron superfluid which prevent the smooth outward flow of angular momentum as the star slows down. In this review, the observational status and statistical aspects of the phenomena are described. We do not discuss in any detail their implications for neutron star structure. Rather, we consider them in so far as they limit studies in which the rotational stability is paramount and may limit the use of pulsars as astronomical chronometers. Glitch activity, the amount of post-glitch relaxation and the amplitude of timing noise all depend roughly linearly on the frequency derivative, implying that even the millisecond pulsars are prone to these effects.
Twelve years of Glitches in the Vela Pulsar
Authors: Flanagan Claire S. 
Published: July 2016

The Vela pulsar (PSR B0833–45) has been observed from Hartebeesthoek RAO since 1984, as part of an ongoing monitoring project. During this time, the pulsar has undergone five sudden and relatively large spin-ups (“glitches”). Good observational coverage was obtained for the four most recent of these events.The post-glitch behaviour of(t) is modelled by:
On the timing histories of the crab, PSR1509-58 and PSR0540-69
Authors: Carramiñana Alberto , Alvarez César 
Published: July 2016

AbstractA simple model of a combined magnetic dipole, gravitational and/or magnetic quadrupole and particle accelerator is applied to simulate the time behaviour of the timing parameters of PSR 0531+21, PSR 1509-58 and PSR0540-69, as well as their energy budget. The model restricts the allowed values for the second braking index and is therefore testable through measurements of.