bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Centre-of-Mass Velocity of a Radially Pulsating Star: Insights from NLTE Models
Authors: Sasselov Dimitar D. 
Published: July 2016

AbstractThe problem of deriving the centre-of-mass velocity of a radially pulsating star is reexamined. New observations of line asymmetry and Non-LTE radiation hydrodynamics point to a systematic effect of about 1 km s−1 in Cepheids.
On the Variability of Supergiant Stars
Authors: Burki G. , Kienzle F. 
Published: July 2016

The la-type supergiants of spectral type B to G are probably all variable in radial velocity and luminosity; in addition, on the average, the amplitude of the variations increases with increasing intrinsic luminosity and are larger for the earliest and latest spectral types (Abt, 1957; Maeder & Rufener, 1972; Burki et al., 1978; Grenon, 1993). The variations are not strictly periodic, but can be frequently described by a characteristic time Tc, i.e., some kind of ‘most probable periodș (e.g., Sterken, 1977; Rufener et al., 1978; Percy et al., 1979; van Genderen et al., 1992).It is possible to define a Tc-luminosity-colour relation for the supergiant stars (Maeder & Rufener, 1972; Burki, 1978). However, this relation exhibits a large dispersion, due to the imprecise luminosity and colour determinations for these stars and, essentially, to the fact that each supergiant can show very different Tc values. Good determinations of >Tc require very long-term, continuous, photometric monitorings.
Pulsation Properties of a Sample of Mira and OH/IR Stars
Authors: Gaylard M. J. , West M. E. 
Published: July 2016

AbstractWell-sampled light curves have been obtained for 1612-MHz hydroxyl masers in Mira and OH/IR stars monitored with the Hartebeesthoek radio telescope. Pulsation modes are investigated via the ratios of the observed periods in the maser variations.
Light Curve Analysis of Long Period Pulsating Stars with the Wavelet Method: The semiregular star V Boo
Authors: Szatmáry K. , Gál J. , Kiss L. L. 
Published: July 2016

AbstractWe have collected long data series of some SR and Mira stars from data banks. In many cases the light curves show strong fluctuation or variation in the period, phase and amplitude. The detection of the significant changes of these parameters is important from the point of view of pulsation theory and stellar evolution. We present here the analysis of V Boo. The used method is the Fourier and wavelet analysis in order to point out the modulations in the frequency and amplitude.
Pulsating Degenerate Stars in the EC Survey
Authors: Stobie R. S. , Koen C. , Kilkenny D. , O’Donoghue D. 
Published: July 2016

For asteroseismological reasons the discovery of new pulsating degenerate stars is important. Bradley (1993) lists the number of known pulsating white dwarfs at that time - 23 known DAV (ZZ Ceti) stars, 7 known DBV stars and 5 known DOV (PG1159) stars. Of these degenerate pulsators 80% (including all DBVs) are in the northern hemisphere. This illustrates the great incompleteness in the search for such objects in the southern hemisphere.The Edinburgh-Cape Blue Object Survey is a potential source of candidate degenerate pulsators in the southern hemisphere (Stobie et al. 1992). The blue stellar objects are identified from COSMOS scans of U and B plates taken with the UK Schmidt Telescope. Follow-up photometry and spectroscopy are being obtained at the South African Astronomical Observatory (SAAO) to classify and determine the nature of each blue stellar object. Currently, over 190 DA white dwarfs have been identified, of which the majority are not in existing catalogues (O’Donoghue et al. 1993). From these white dwarfs, we have selected DA stars with B-V colours near or within the range 0.15 ≤ B-V ≤ 0.25 together with all the non-DA degenerate stars (DO, DB, etc.) to monitor for variability.
The Effect of Proper Motion on in Pulsating Stars
Authors: Pajdosz G. 
Published: July 2016

AbstractWe show that the proper motion of a pulsating star results in a secular increase of the radial velocity of the star and consequently contributes to the observed . We found that this mechanism is very important in studying period changes in pulsating DA white dwarfs, where its effect is comparable with the expected evolutionary period change in these stars due to their cooling.
Studies in Flickering
Authors: Welsh W. F. , Wood Janet H. , Horne K. 
Published: July 2016

AbstractFlickering is a poorly understood phenomenon associated with accretion processes, but this does not suffice to make it interesting. Why then should we bother studying this ‘noise’? Three reasons come to mind: (i) flickering is a fundamental signature of accretion, to the point of being a necessary characteristic (if it doesn’t flicker, it’s not a CV); (ii) energetically, flickering is not a small effect and can contribute up to a few tens of percent of the total luminosity of the system (hence it is often more luminous than the entire secondary star); (iii) flickering is inherently a time-dependent phenomenon and it is hoped that it can provide clues to the nature of the disc viscosity, something that time-independent theory cannot provide.
IUE and Optical Spectra of RZ LMI and ER UMa Throughout their 19 and 43 Day Cycles
Authors: Szkody Paula , Silber Andrew , Honeycutt R. K. , Robertson J. W. , Hoard D. W. , Pastwick Lora 
Published: July 2016

AbstractIUE and optical data were obtained throughout the supercycles of RZ LMi and ER UMa during 1993/94. While most of the spectral and photometric characteristics are consistent with disk changes in systems with a relatively high accretion rate and low inclination, the cause of the high accretion rate in this subset of SU UMa stars is not known.
Population Studies of Cataclysmic Variables
Authors: Ringwald F. A. 
Published: July 2016

Cataclysmic variables (CVs) are idiosyncratic objects, but progress can be made by studying groups of them. To do this, one must identify samples that are representative of their true properties. Because of the wide variety of physics that occurs in CVs, they have a complex phenomenology in which effects are still being discovered (e.g. permanent superhumps: Patterson & Richman 1991). CV outbursts have their own complex phenomenology (but see Osaki 1995a,b and this volume, for ideas on unification for dwarf novae), so it is unwise to rely on outburst properties to give unbiased samples.One wants to identify CVs by some property common to all of them. One such property is flickering; another is color excess. CVs are very blue, especially in the ultraviolet, with U – B < −0.46 for 95% of CVs (Bruch & Engel 1994). This color index also defines inclusion in the Palomar-Green (PG) survey (Green, Schmidt & Liebert 1986), and a preliminary list of PG CVs was given by Green et al. (1982). My Ph.D. thesis (Ringwald 1993) completed this work, being the first optically selected complete sample of CVs at high latitude. At the same time, Andy Silber was writing his Ph.D. thesis on an X-ray-selected sample of CVs, from the HEAO-A1 MC-LASS survey (Silber 1992). One might say I was Andy’s optical counterpart.
The Rise and Fall of α-Model Viscosity
Authors: Hessman F. V. , Obach C. 
Published: July 2016

AbstractFor nearly two decades, our only useful model for the viscosity in accretion disks has been the so-called ‘α-model’. However, it has become clear that the simplest models –in which α is constant – are inadequate to explain the range of behaviours seen in real disks. We show that the properties of steady-state, vertically-averaged models can be determined without any assumptions other than that the disks obey the classical Navier-Stokes equation. These solutions have derived values of α which vary with radius by many orders of magnitude even in small CV disks.
The Flares of AE Aqr
Authors: Eracleous M. , Horne K. , Livio M. , Welsh W. F. 
Published: July 2016

AbstractThe enigmatic flaring activity of AE Aqr, which extends from the radio to the X-ray bands, may be the exotic outcome of a relatively feeble accretion flow onto the rapidly spinning white dwarf. We summarize and interpret the results of recent observations by HST and ROSAT of the aperiodic flares. Optical and UV flares are tightly correlated and are clearly involved in powering the emission lines. The spectrum of a flare consists of a Balmer continuum, and a plethora of emission lines, which vary synchronously. The large optical/UV flares are not accompanied by large X-ray outbursts. The radial velocity curves of the UV lines, and of Hα, suggest that they originate in the accretion stream. The observational results dis-favor scenarios invoking coronal activity on the secondary star or instabilities at the disk/magnetosphere interface. Rather, they support a recently proposed scenario in which the accretion flow consists of blobs which are shocked upon encountering the white dwarf magnetosphere.
The Magnetic Field of the Intermediate Polar RE 0751+14
Authors: Väth H. 
Published: July 2016

Piirola, Hakala & Coyne (1993) modeled the optical/IR light curve of RE 0751+14 assuming a uniform shock structure and neglecting the hard X-ray emission. In this paper, we model the light curves at optical/IR and hard X-ray wavelengths and include the effects of the shock structure.We base our model on accretion onto a white dwarf with a displaced magnetic dipole for a range of likely white dwarf masses. We find that the observed intensity variations of X-rays and in the I band over one spin period largely determine the position of the emission regions. Furthermore, the observed maximum X-ray flux constrains the specific accretion rate. We deduce that the magnetic field at the pole is likely to be in the range 9 .. .21 MG, which is consistent with the estimates of Piirola et al. (1993). It had been proposed previously that there must exist asynchronous rotators with sufficiently strong magnetic fields such that the binaries will evolve into AM Her binaries (Chanmugam & Ray 1984; King, Frank & Ritter 1985). With this deduced high magnetic field RE 0751+14 is the most likely example of such a system known to date.
Long-Term Brightness Changes of Two CVs
Authors: Sokolov D. A. , Shugarov S. Yu. , Pavlenko E. P. 
Published: July 2016

AbstractThe long-term light curves of the AM Her type binary BY Cam and the nova-like variable PG 2133+115 are presented. The BVR observations were carried out at a 0.5 m telescope equipped with a high sensitive TV tube superisocon (Abramenko et al. 1978), the UBV photoelectric data were obtained at 0.6 and 1.25 m telescopes and the photographic estimates were made from the negatives obtained at the 0.4 m astrograph in Crimea.Both stars show high and low brightness states. They show similar behaviour in some respects: the amplitude between high and low states was about two magnitudes in B, but the duration of a low state was approximately two months for BY Cam and 1… 2 years for PG 2133+115.
Recent Progress on the Polar QS Tel: The HST Results
Authors: Clayton K. L. , Rosen S. R. , Osborne J. P. 
Published: July 2016

AbstractWe report on the Hubble Space Telescope (HST) observation of the polar, QS Tel, made during 1994 June. Orbital modulation is present in both the continuum and lines. A narrow dip is observed in the continuum folded light curve. The spectrum of the occulted source during this dip is broadly consistent in shape with the Rayleigh-Jeans tail of the EUV source.
Preliminary analysis of a Hubble FOS spectrum of VW Hyi in quiescence: A DAZQ white dwarf and accretion belt/ring
Authors: Sion E. M. , Huang M. , Cheng F. H. , Hubeny I. , Szkody P. 
Published: July 2016

AbstractWe present a preliminary analysis of the UV spectrum of the dwarf nova VW Hyi during early quiescence, obtained with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST). The data were obtained approximately one day after the end of a normal outburst.
The ROSAT observations of classical novae
Authors: Orio M. , Ögelman H. , Balman S. 
Published: July 2016

We observed a number of classical and recurrent novae in the Galaxy and the LMC with the ROSAT X-ray telescope and searched the archival data for other serendipitous observations. Preliminary results show that only 9 out of 37 observed objects were bright enough in X-rays to be detected with ROSAT, either in outburst or at quiescence.Three basic mechanisms can cause X-ray emission from classical or re-current novae. The first is hot hydrogen burning in a thin shell of the remnant envelope left on the white dwarf after the nova explosion. Hydrogen burning post-novae should be blackbody like emitters at nearly Eddington luminosity (as per the ‘supersoft’ X-ray sources). In our sample, only GQ Mus (Nova Mus 1983, see Ögelman et al. 1993; Shanley et al. 1995) and V1974 Cyg 1992 (Krautter et al. 1996) had these characteristics. Remarkably, among 10 LMC novae that had an outburst in the last 47 yr none was detected as a ‘supersoft’ X-ray source. The 3 σ upper limits for the black-body temperatures of the post-nova white dwarfs are mainly in the range 20… 30 eV. A post-nova can also emit X-rays because of shocks occurring in the ejected shell (e.g. O’Brien et al. 1994). Three out of four classical novae that were observed in outburst displayed a hard X-ray component in the ROSAT energy band, which might be due to a shocked shell. Finally, X-ray emission is expected from quiescent nearby novae because of accretion. Only four nearby accreting sources were detected; the ROSAT upper limits for the non-detected quiescent novae are Lx < 1031… 1032 ergs−1, assuming a thermal plasma at kT = a few keV.
Detection of the Irradiated Red Dwarf in WY Sge (Nova 1783)
Authors: Somers M. W. , Mukai K. , Naylor T. , Ringwald F.A. 
Published: July 2016

AbstractWe present infrared (IR) photometry and optical spectroscopy of the eclipsing old nova WY Sge. According to hibernation theorists the disc in a system a few centuries after outburst should be significantly fainter than in other, more recent, old novae but similar to the discs of dwarf novae in quiescence. Despite the apparent faintness of the late type star we have sufficient information to infer that the face closest to the white dwarf (WD) is irradiated.
Generation of X-Ray Fluctuations in X-Ray Binaries
Authors: Mineshige S. , Takeuchi M. , Negoro H. 
Published: July 2016

AbstractShort-term aperiodic fluctuations with 1/f-like power spectral density (PSD), where f is the frequency, are characteristics of X-ray radiation from X-ray binaries. To investigate a mechanism creating fluctuations, we construct a cellular-automaton model for accretion disks based on the concept of self organized criticality (SOC). In this model, mass accretion takes place either by an avalanche triggered when the local mass density exceeds some critical value, or by a gradual diffusion occurring regardless of the critical condition. With this model, we can reproduce the observational PSD, the distributions of peak intensities of X-ray shots, and non-random temporal distribution of the shots. Possible accretion disk models producing l/f-like X-ray fluctuations are discussed. We conclude that such disks are likely to be advection dominated.
Models of Soft X-Ray Transients and Dwarf Novae
Authors: Lasota J. P. 
Published: July 2016

AbstractModels of Soft X-ray Transients are presented and compared with observations. The importance of inner advection-dominated flows in quiescent transient sources is discussed, as well as the problem of global stability of the standard outer accretion disc. A comparison is made with similar problems in dwarf nova models.
From Common Envelope to Pre-Cataclysmic Variables: An Observational Test of Common Envelope Evolution
Authors: Sarna M. J. 
Published: July 2016

The generally accepted evolutionary scenario for cataclysmic variables (CVs) is common envelope (CE) evolution (Iben & Livio 1993) proposed by Paczyñski (1976). The secondary spirals towards the giant’s compact core converting orbital energy into kinetic energy of the giant’s envelope and the envelope is ejected. The dynamics of the red dwarf and red giant envelope interaction have been studied by several groups (Livio & Soker 1988; Taam & Bodenheimer 1991). After the ejection of the red giant envelope the post common envelope detached binaries (PCEBs) are formed. These can be divided into three groups:• Hot subdwarf with a red dwarf star inside a planetary nebula.• Hot subdwarf with a red dwarf star without a planetary nebula.• Hot white dwarf with a red dwarf star without a planetary nebula. Next, due to angular momentum loss by magnetic braking and/or gravitational radiation, the red dwarf component fills its Roche lobe and a cataclysmic variable is formed.
X-Ray Emission Lines: Present and Future Experiments
Authors: Kunieda H. 
Published: July 2016

AbstractAfter 34 years of X-ray astronomical observations, we approach the time when we will be able to explore AGN using line spectroscopy with newly developed technology and methods. In the beginning, X-rays from AGN were observed using proportional counters in a sort of photometric way, allowing us to determine that the continuum is a power law. This result suggested a predominance of non-thermal emission mechanisms in AGN. Rapid variability on time scales as short as 1000 seconds implied a small size for the X-ray emitting region, of order 1014cm, which is 3 orders of magnitude smaller than the optical emission-line regions.The first detection of line emission from AGN was the Fe-K line by the GINGA satellite. The line energy was 6.4 keV and its equivalent width was about 150 eV in Seyfert 1 galaxies. Detection became possible by use of large-area, low-noise proportional counters. The Fe-K line emission is important in X-ray astronomy because iron is rather abundant and this line is isolated in energy from neighboring lines.The Fe-K line profile has been examined with the CCD detectors on board ASCA. Many Seyfert 1 galaxies exhibit a broad-line profile of more than 1 keV width with an asymmetric tail on the low-energy side. This is explained as the fluorescence line from a relativistic accretion disk around a black hole, which is broadened by the Doppler motion and distorted by the strong gravitational field. The CCD detectors also revealed the absorption edges of warm material in the line of sight, which is ionized by the strong emission from AGN.In the next decade, new spectrometers will be launched which can perform spectroscopy with E/dE > 100: AXAF in 1998, XMM in 1999, and Astro-E in 2000. Dispersive spectrometers on board AXAF and XMM will be powerful tools for low-energy lines, while the calorimeter on board Astro-E will examine the Fe-K line profile. Spectral resolution E/dE of several hundred will reveal the intensity ratio of satellite and resonance lines. This will give us physical parameters, such as the density and absolute size of surrounding matter. We hope that the structure of the nucleus will be more deeply understood using X-ray spectroscopy with new instruments, and we will come close to the level of optical spectroscopy, which has worked well in the study of the outskirts of AGN.
High-Energy Lines in Active Galactic Nuclei
Authors: Netzer Hagai 
Published: July 2016

AbstractThe recent observations of a highly ionized, X-ray absorbing gas in active galactic nuclei (AGN) suggest a new nuclear component, the so-called ‘warm absorber’. This gas is likely to be at a temperature of ~ 1–2 × 105 K and is most easily detected in the 0.5–10keV range, where several oxygen absorption edges are often observed.This review describes the properties of warm absorbers and the relation
to other nuclear components, such as the broad-line emitting gas. The stability of the gas is a key issue and analysis shows that it is likely to be thermally stable, at the above mentioned temperature. When successful models are compared to the data, they can be used to infer the column density, composition and level of ionization of the X-ray absorbing gas. They also show that, on top of the strong continuum absorption, the gas must emit X-ray lines that are at the limit of detection by present day X-ray instruments.New calculations of X-ray emission lines emitted by ionized X-ray absorbers are shown and discussed. Various line equivalent widths are defined and examples are shown over a large range of column density and ionization parameter. The equivalent width of the strongest 0.5-5 keV lines is only a few tens of eV, but in cases of obscured X-ray source, like in Seyfert 2s, the lines are measured against the scattered and diffuse radiation with much larger equivalent widths. The X-ray absorbing and emitting gas is responsible also for a fraction of the observed flux of some UV emission lines. It is also the cause of the detection of several UV absorption lines. The calculations predict that some of those absorption lines, in particular 0 VI λ1035, are very sensitive warm-absorber tracers. Thus, analysis of the combined X-ray and UV properties is the best way to identify the location and properties of this gas.Understanding the origin and properties of warm X-ray absorbers is a major challenge of AGN research. Several new ideas are briefly discussed, trying to relate the location, mass, and motion of this gas to what is known about other observed nuclear components.
ASCA Observations of Seyfert 2 Galaxies
Authors: Awaki H. 
Published: July 2016

AbstractWe have observed a sample of Seyfert 2 galaxies with ASCA. The targets were selected based on their [O III] λ5007 flux, the existence of polarized broad lines, and previous X-ray detection. The nuclear luminosities of these galaxies range from 1042 to 1044 ergs s−1 in the 2–10 keV band. Obscured nuclei were found in all galaxies in our sample, with absorption column densities distributed around a value of 1023.5 cm−2.The cold iron Kα line was clearly detected in half of our sample, and emission from He-like and H-like Fe Kα was detected from two galaxies. These lines are explained by fluorescent lines from thick cold matter and warm/hot thin matter. Highly ionized lines originating in starburst activity were also detected from NGC 1068.
X-Ray Observations of Low-Luminosity Active Galactic Nuclei
Authors: Makishima K. , Iyomoto N. , Ishisaki Y. , Terashima Y. 
Published: July 2016

AbstractThrough X-ray observations with ASCA, low-luminosity active galactic nuclei have been found in at least seven near-by spiral galaxies. Some of them exhibit very intense, and possibly broad, Fe-K emission lines. Their time variability is relatively insignificant, in contrast to lowluminosity Seyfert galaxies.
Broad Emission Lines in Active Galactic Nuclei
Authors: Baldwin J. A. 
Published: July 2016

AbstractThis paper assesses what we have learned about the structure of AGN broad-line region (BLR), with emphasis on the work other than reverberation studies in order to complement other recent reviews. Basic photoionization models are briefly described. Current models of the BLR and some of the observations that might distinguish among them are discussed.
IR Spectroscopy of High-Redshift Quasars
Authors: Bechtold Jill , Shields Joseph , Rieke Marcia , Ji Peiwen , Scott Jennifer , Kuhn Olga , Elvis Martin , Elston Richard 
Published: July 2016

AbstractWe have obtained near-IR, optical, and soft X-ray spectrophotometry for a number of bright quasars with 2 ≲ z ≲ 4. The observed ratios of Lyα/Hβ in this sample are smaller than Case B, and span a similar range to those seen at lower redshift. A correlation between the line width of Hβ and X-ray spectral index found for low-redshift PG quasars is also seen for the high-redshift objects.