bluuebunny/crossref_metadata_2025 huggingface dataset:
The Composition and Structure of White Dwarf Atmospheres Revealed by Extreme Ultraviolet Spectroscopy
Authors: Barstow Martin A. , Hubeny Ivan , Lanz Thierry , Holberg Jay B. , Sion Edward M.
Published: July 2016

The ROSAT and EUVE all-sky surveys have resulted in an important change in our understanding of the general composition of hydrogen-rich DA white dwarf atmospheres, with the photospheric opacity dominated by heavy elements rather than helium in the hottest stars (T > 40, 000 K). Most stars cooler than 40,000 K have more or less pure H atmospheres. However, one question, which has not been resolved, concerned the specific nature of the heavy elements and the role of helium in the hottest white dwarfs. One view of white dwarf evolution requires that H-rich DA stars form by gravitational settling of He from either DAO or He-rich central stars of planetary nebulae. In this case, the youngest (hottest) DA white dwarfs may still contain visible traces of He. Spectroscopic observations now available with EUVE provide a crucial test of these ideas. Analysis of data from the EUVE Guest Observer programme and EUVE public archive allows quantitative consideration of the sources of EUV opacity and places limits on the abundance of He which may be present.
Extreme Ultraviolet Spectroscopy of Magnetic Cataclysmic Variables
Authors: Paerels Frits , Hur Min Young , Mauche Christopher W.
Published: July 2016

A longstanding problem in the interpretation of the X-ray and extreme ultraviolet emission from strongly magnetic cataclysmic variables can be addressed definitively with high resolution EUV spectroscopy. A detailed photospheric spectrum of the accretion-heated polar cap of the white dwarf is sensitive in principle to the temperature structure of the atmosphere. This may allow us to determine where and how the bulk of the accretion energy is thermalized. The EUVE data on AM Herculis and EF Eridani are presented and discussed in this context.
The Three-Dimensional Structure of EUV Accretion Regions of AM Her Stars: Analysis of EUVE Light Curves
Authors: Sirk Martin M. , Howell Steve B.
Published: July 2016

We present EUV light curves for a number of AM Her systems observed either as guest observer targets or with the EUVE Right Angle Program. We have formed light curves for eight AM Her stars and show in our presentation the similarities and differences present. We draw some conclusions by grouping the systems by inclination, magnetic field strength, and accretion region geometry. In order to understand the physical structures responsible for the EUV emissions, we have developed a software model to generate synthetic light curves. We find that the EUV accretion regions in the systems UZ For, VV Pup, and AM Her cannot be fit with a flat spot confined to the white dwarf surface, regardless of its shape or brightness profile. Rather, a small, symmetric, raised spot is the only shape consistent with the data. The light curves for systems EF Eri, RE1149+28, AN UMa, and V834 Cen show evidence for additional structure that precedes the primary accretion region in phase. Our model indicates that a large portion of the light curve in each system is seen in absorption. Finally, in three systems, we detect a very gradual rise and fall in the EUV flux (<5% of the peak flux) at phases when the spot is completely obscured behind the white dwarf (WD) limb. We attribute this detection to emission from the accretion column that decreases exponentially with distance from the WD and detect emission at heights up to 15% of the WD radius.
EUVE and VLA Observations of the Eclipsing Pre-Cataclysmic Variable V471 Tauri
Authors: Cully S.L. , Dupuis J. , Rodriguez-Bell T. , Basri G. , Siegmund O.H.W. , Lim J. , White S.M.
Published: July 2016

We present observations of the eclipsing binary V471 Tauri by the Extreme Ultraviolet Explorer (EUVE) and the Very Large Array (VLA). The EUV spectrum is dominated by the continuum of the hot white dwarf and the time-averaged spectrum is fitted by a 33.1 ± 0.5 × 103 K pure hydrogen white dwarf atmosphere assuming log g = 8.5. An ISM hydrogen column density of 1.5 ± 0.4 × 1018 cm−2 is required to explain the attenuation of the white dwarf spectrum thus setting the HI column in the line of sight of the Hyades cluster. The He II λ304 Å line is in emission and varies over the orbital period of V471 Tauri following a sinusoidal modulation with the maximum reached when the K star is at inferior conjunction. Transient dips are detected at orbital phase −0.12 in the SW and MW spectrometers integrated lightcurves but are notably absent in the LW lightcurve indicating the occulting material is ionized. The VLA observation suggest the presence of a K star coronal magnetic loop between the two stars reconnecting with the white dwarf magnetic field. Such a structure could be the occulting source needed to explain the dips seen in the lightcurves of V471 Tauri in the EUV.
EUV Line Intensities of Fe X
Authors: Young P.R. , Mason H.E. , Bhatia A.K. , Doschek G.A. , Thomas R.J.
Published: July 2016

The 4 configuration, distorted wave calculation of Bhatia & Doschek (1995) (hereafter referred to as BD95), together with the ground transition calculation of Pelan & Berrington (1995) are here used to predict the intensities of the Fe X EUV lines, which are then used to derive electron densities from several solar spectra, including the recent SERTS spectra.
An Instrument to Study the Diffuse EUV Astronomical Background
Authors: Bowyer S. , Edelstein J. , Lampton M. , Morales L. , Mercader J. Perez , Gimenez A.
Published: July 2016

The extreme ultraviolet (EUV) diffuse background is the most poorly known of any of the diffuse astronomical backgrounds. Only upper limits to this flux exist, obtained with spectrometers with very crude (from ≈ 15 to 30 Å) resolution; these limits are generally one to two orders of magnitude larger than the expected sources of cosmic flux. A variety of source mechanisms have been postulated to radiate in this bandpass; the most discussed is the hot phase of the interstellar medium. A speculative possibility is that hot dark matter in the form of massive, radiatively unstable neutrinos in our Galaxy will produce a unique line in this bandpass. We describe an instrument employing a new type of spectrometer which will provide ~5 Å resolution and unprecedented sensitivity for diffuse EUV radiation. The instrument will be carried aboard the newly developed Spanish Minisat satellite.
Recent Developments in Stellar Pulsation Theory
Authors: Gautschy A.
Published: July 2016

A major driving force behind the efforts invested in stellar pulsation calculations in the recent years was certainly the success story of the new generation of opacity data. The new opacities did not only solve old problems but they also increased the complexity of quantitative stellar pulsation studies. Besides surveying the consequences of the new generation of stellar opacities for pulsation theory we also address more formal aspects of dealing with stellar oscillations. The section reviewing recent literature on the application of stellar pulsation theory to different classes of pulsating variables is strongly biased towards the high-luminosity part of the Hertzsprung-Russell (HR) diagram. We finish by mentioning recent changes in our beliefs concerning the envelope structure of oscillating white dwarfs.
The Mass Loss Rate — Period Relation in Carbon Miras
Authors: Groenewegen Martin
Published: July 2016

The relation between mass loss rate and pulsation period in carbon Miras is discussed. The dust mass loss rate is very low (about 2 10−10 M⊙yr) up to about P = 380 days, where there is a sudden increase. For P > 400 days there is a linear relation between log and P. The change in the mass loss rate near 380 days may be related to radiation pressure on dust becoming effective in driving the outflow.
Observations and Interpretation of Luminous Blue Variables
Authors: Lamers Henny J.G.L.M.
Published: July 2016

The different types of variations of LBVs are discussed. The “typical LBV variations” have amplitudes of ΔV ≃ 0.5 to 2.0 magnitudes and irregular time-scales of months to years. This is due to changes in the stellar radius and the effective temperature. Modelling of this variability for one star, S Dor, shows that the radius of the star varies between 100 and 380 R⊙, the effective temperature between 20,000 and 9,000 K, and the luminosity between log L* = 6.10 to 5.9. The variation of the radius is not an apparent variation of the effective radius of the wind due to a variable mass loss rate (which has often been assumed) but it is a true variation of the radius of the star itself. The changes in L* suggest that about 10−3 to 10−2M* takes part in the expansion of the star. The irregular microvariations with amplitudes of about ΔV ≃ 0.2m on timescales of weeks are probably due to non-adiabatic pulsations with mode-interaction. We argue that LBVs are close to their effective Eddington Limit and discuss a qualitative scenario to explain their location in the HR-diagram.
Cepheid Binaries: Frequency and Mass Ratios
Authors: Evans Nancy Remage
Published: July 2016

Ultraviolet spectroscopy with the IUE satellite has been used to survey all Cepheids brighter than 8th magnitude to identify blue companions. The derived binary frequency is 21% with blue companions which implies that 34% would have been found from a large radial velocity survey. A second study has used deep IUE exposures of Cepheids showing orbital motion to determine the distribution of mass ratios in Cepheid binaries. Low mass companions are strongly preferred, especially when corrections for incompleteness are included.
On the HαEmission Phase ofβCep
Authors: Kaper L. , Mathias P.
Published: July 2016

During the past five years, we monitored the Hαline ofβCep. The strength of the Hαemission, first discovered in 1990, is linearly declining with time. Several options are explored, but a satisfactory explanation for the recurring phases of Hαemission is not yet found.
NRP Modes in a Be Star Zeta Oph
Authors: Kambe E. , Hirata R. , Kato M. , Ando H. , Kennelly E. J. , Walker G. A. H. , Štefl S. , Tarasov A. E.
Published: July 2016

Two large sinusoidal variations with periods of 3.337 hrs and 2.018 hrs and other smaller variations have been detected from the period analysis of Hel Λ 6678 spectra obtained by our multi-site campaign for ζ Oph in May, 1993. The resultant periodgram is considerably improved (aliasing free) from those in previous publications. The periodicity may be consistent with previous studies except ambiguities of aliasing. It is surprising that almost all detected periods have a common superperiodicity of about 10.05 hrs. We emphasise the importance of multi-site campaign for the study of line-profile variations (lpv) in early-type stars.
A First Search for Rapid Variations of Stellar and Circumstellar Balmer Discontinuity in Be Stars
Authors: Štefl S. , Baade D. , Cuypers J.
Published: July 2016

Spectrophotometric observations of the Be star ηCen obtained in May, 1993 show smooth variations of both the stellar and circumstellar Balmer discontinuity (BD) on a time scale of hours. Simultaneous photometry and high-resolution spectroscopy suggest possible correlations with the large-amplitude brightness and line-profile variations.
Consequences of Rapid Rotation on Mode Identification
Authors: Soufi F. , Goupil M. J. , Dziembowski W.A. , Sienkiewicz R.
Published: July 2016

The present work deals with the effect of rotation on the adiabatic oscillation frequencies of stellar models. Here, rotation, as described in a perturbation theory, is said to be rapid in the sense that second order perturbation effects have to be taken into account. Rotation has two second order effects on the oscillation frequencies: departure from equidistance within a given multiplet split by rotation and an overall shift of the multiplet itself. The first effect has been investigated for realistic models of δ Scuti stars in uniform rotation (Dziembowski & Goode, 1992), whereas H. Saio’s study includes both effects for a polytrope of index 3 in uniform rotation (Saio 1981). Both effects are investigated for realistic models of δ Scuti stars. Results for the overall shift for a 2 M⊙ model in rapid uniform rotation (v up to ∼ 200 km/s) are outlined below. The rotation rate corresponding to this surface velocity is Ω = 1.44 10−4 rad/s.
Independent Distance Determinations to Milky Way Cepheids in Open Clusters: A progress report on four stars
Authors: Giere Wolfgang P. , Matthews Jaymie M. , Mermilliod Jean-Claude , Welch Douglas
Published: July 2016

We have undertaken a programme to calibrate the Cepheid PL relation zero-point by obtaining distances of Cepheids in open clusters and associations via the visual surface brightness technique. Results are now available for four stars (SZ Tau, CF Cas, CV Mon and DL Cas) and others are currently under analysis. Preliminary results suggest the ‘ZAMS-fitting’ distances to the host clusters are systematically smaller than those we derive from Cepheid surface brightnesses.
RR Lyrae Variables in NGC 7006
Authors: Wehlau Amelia , Slawson Robert W. , Nemec James M. , Butterworth Steve
Published: July 2016

B and V CCD frames of the globular cluster NGC 7006 have been obtained to study the period change rates and determine photometric colours for the RR Lyr variables.
Miras and Galactic Populations
Authors: Mennessier M.O. , Luri X. , Figueras F. , Torra J.
Published: July 2016

In order to exploit the imminent HIPPARCOS data we have developed a new Maximum-Likelihood method to determine luminosity calibrations and kinematical properties with as bias-free as possible estimates. In most cases the samples are inhomogeneous, containing stars of several types. The method includes a way to separate the different groups. We applied the method to Mira variables contained in the HIPPARCOS Input Catalogue.
Obscured AGB Stars in the LMC
Authors: Zijlstra Albert , Loup Cecile , Waters Rens , Whitelock Patricia , Guglielmo Francois
Published: July 2016

We have carried out a search for obscured AGB stars in the LMC, observing fields in the vicinity of faint IRAS sources. About 25 heavily reddened AGB stars were found, with bolometric magnitudes close to the classical AGB limit of Mbol = −7.1. 10−µm. photometry for 5 sources show that these are oxygen-rich; they are similar to the Galactic OH/IR stars. Mass-loss rates vary between 5×10−4 and 2×10−6 M⊙ yr−1. We find no evidence that the mass-loss rates vary with luminosity. Neither do the mass-loss rates differ in a clear systematic way between the SMC and the LMC. The expansion velocities appear to be slightly lower in the LMC than in the Galaxy. All of the luminous stars for which periods are available have luminosities significantly above the period-luminosity relation derived for optical LMC Miras.
STARS - A Seismic Telescope for Astrophysical Research from Space
Authors: Roxburgh Ian W
Published: July 2016

STARS is a proposed asteroseismology (and stellar activity) space mission which is currently under phase A study in the European Space Agency as a candidate for the Medium Size Mission (M3).
The Nova-Like Variables
Authors: Dhillon Vik
Published: July 2016

We review optical observations and theoretical models of the non-magnetic nova-like variables (UX UMa, VY Scl and SW Sex stars). A brief discussion of the classification scheme is followed by a statistical overview of the observed properties. The most important features of each of the sub-classes are then reviewed, concluding with a summary of the theoretical models invoked to understand these systems.
Spectrally Resolved Maps of Optically Thick Accretion Disks
Authors: Baptista R. , Horne K. , Hubeny I. , Long K. , Mauche C. W. , Rutten R. G. M. , Wade R. A.
Published: July 2016

We report first results of the HST/FOS time-resolved, low-resolution spectroscopy of the eclipsing cataclysmic variable UX UMa, including multi-wavelength mapping of its accretion disk in the ultraviolet region.
Simultaneous Multiwavelength Observations of Dwarf Novae Systems at Quiescence and in Outburst
Authors: Tovmassian G. , Echevarria J. , Perez E. , Jones D. H. P. , Shara M. , Tapia M. , Bohigas J. , Gilmozzi R. , Costero R. , Lopez J. A. , Roth M. , Alvarez M. , Rodriguez L. F. , De Lara E. , Stover R. , Martinez-Roger C. , Garzon F. , Astrian N. , Zoldos E. , Mattei J. , Bateson F.
Published: July 2016

The results of photometric and spectroscopic observations of dwarf novae are presented. The data were obtained during an international program of multiwavelength observations, held in 1986 February at several observatories, of dwarf novae during the first and subsequent days of outburst. During the campaign numerous dwarf novae were monitored in order to catch them in outburst. Preliminary results and analysis of some objects are reported elsewhere. A total of 30 dwarf novae were observed in the northern and southern hemispheres. Among them 37% were caught in outburst, including 10% on the rise to outburst and 17% in decline. Photometric observations were carried out in the UBVRI system and colour indexes were calculated.
Spectrophotometry of 106 To-Be-Confirmed CVs
Authors: Zwitter Tomaž , Munari Ulisse , Bragaglia Angela
Published: July 2016

We present a status report on our ongoing spectrophotometric program to survey as many as possible of the 359 objects in the 751 entry Downes & Shara (1993) catalogue of CVs that are reported as having no published spectroscopy.
Rotational Disturbance in BG CMI
Authors: Garlick M. A.
Published: July 2016

I report on the independent discovery of a feature in BG CMi which resembles a rotational disturbance (RD). A similar effect has already been reported in the He IIλ 4686 line, whereas here it is seen in the Balmer lines, 0.25 orbital cycles prior to that reported previously. These results suggest that BG CMi is at a relatively high inclination.
An ASCA Observation of the Eclipsing Dwarf Nova HT Cas
Authors: Mukai K. , Schlegel E. M. , Swank J. H. , Naylor T. , Wood Janet H.
Published: July 2016

We report on a 1-day ASCA observation of the eclipsing dwarf nova HT Cas. We confirm the presence of an X-ray eclipse, which is narrow and deep. The data are consistent with the X-rays originating entirely from the immediate neighborhood of the white dwarf. We draw some preliminary conclusions on the boundary layer and other relevant issues.
Nova Outbursts on Rotating Oblate White Dwarfs
Authors: Scott A. D.
Published: July 2016

Observations of spatially resolved nova shells and reconstructions from emission line profiles show that a ring/blob asymmetry in the ejecta of novae is very common (Martin 1989). The polar blobs expand more rapidly than the equatorial rings, giving the ejecta an overall prolate geometry.

Observations of the formation of carbonaceous and silicate dusts in the same nova provide unambiguous evidence that abundance gradients exist in the ejecta. Carbonaceous dusts form where carbon is more abundant than oxygen and vice versa for silicates (Evans 1990; Gehrz et al. 1992; Smith, Aitken & Roche 1994; Snijders et al. 1987).
Optical Imaging of Old Nova Shells
Authors: O’Brien T. J. , Slavin A. J.
Published: July 2016

A deep, predominantly Ha, imaging survey of 37 classical nova remnants has just been completed using the William Herschel and Anglo-Australian Telescopes. This has resulted in the detection of new nebular remnants and the resolution of detailed structure in previously known remnants. These data indicate a correlation between nova speed class and the ellipticity of the resulting remnants – those of faster novae tend to comprise randomly distributed clumps of ejecta superposed on spherically symmetric diffuse material, whilst slower novae produce more structured ellipsoidal remnants with at least one, and sometimes several, rings of enhanced emission.
Shaping of Nova Shells by Binary Motion
Authors: Lloyd H. M. , O’Brien T. J. , Bode M. F.
Published: July 2016

Several years after outburst, extended optical emission can be seen around many classical novae. Common features include shells, polar ‘blobs’, equatorial rings and, at least in the case of DQ Her (1934), tropical rings above and below the ‘equator’. We present hydrodynamic calculations of the dynamical effects of the underlying binary system on the material ejected during outburst, and show that many of the features observed in the optical remnants of novae can be reproduced. Polar blobs, banded shells and spherical shells can all be obtained in the model, depending on the speed class of the nova.
The Orbital Period of the Galactic Z Source Sco X-2
Authors: Southwell K. A. , Casares J. , Charles P. A.
Published: July 2016

Sco X-2 is a bright Galactic bulge Z source, whose optical counterpart was discovered in 1990 [?], and observed to exhibit strong Hα emission. We have therefore obtained spectroscopic data in order to determine the orbital period and investigate the nature of the companion star. From an analysis of the Hα emission line velocities, we find a most likely orbital period of 13.94 d. This implies an evolved companion, and is consistent with the currently known orbital periods in other Z sources.
Optical Counterpart of the LMXB GX 13+1
Authors: Groot P. J. , van Der Klis M. , van Paradijs J. , Augusteijn T. , Berger M.
Published: July 2016

We have observed the IR counterpart of the Atoll type LMXB GX 13+1, (Naylor, Charles & Longmore 1991), from 1993 July 11…30, with the Dutch 90 cm telescope at ESO using a Gunn z (0.9–1.0 μm) filter. Over this period 110 usable images (integration time 12 m) were obtained. The data were reduced using the ESO-MIDAS/DAPHOT reduction package. A Lomb-Scargle period search was performed with the PERIOD package.

Fig. 1 shows our Gunn z band image with stars labeled as in Naylor et al. (1991). They propose their star 101 as the IR counterpart. Fig. 2 shows the light curve we obtained for this star. The star is clearly variable on a time-scale of ~ 10 d. To estimate any period more accurately we have made a Lomb-Scargle statistics periodigram (see Fig. 3); maximum power is at 12.6 d. We estimate the error to be ~ 1 day.
Detection of the Secondary Star in X1822–371
Authors: Harlaftis E. T. , Charles P. A. , Horne K.
Published: July 2016

We have detected He I absorption from the companion star to X1822–371 and find a lower limit to its K–velocity of 230±50km s−1. We interpret the He I as arising on the X-ray heated inner face of the companion star.
Low Mass White Dwarfs in Binaries
Authors: Marsh T. R. , Dhillon V. S. , Duck S. R.
Published: July 2016

The lowest mass white dwarfs that can have been produced by single star evolution in the lifetime of the Galaxy have masses of about 0.53 M⊙. There are however several white dwarfs known with significantly lower masses. Evolution in a binary provides a straightforward explanation as the star can lose its envelope before ever burning helium. The products are expected to be short-period binary stars. To test this we have looked at 15 such stars and have found that 8 of them are close binaries. Thus binary evolution does have a major role in the formation of low-mass white dwarfs. We discuss whether the non-detections could also be binary stars.
Hot Subdwarfs in Binaries: Multiwavelength Observations and Evolutionary Implications
Authors: Ulla A. , Thejll P. , Vennes S. , Hansen-Ruiz C. S. , Rasilla J. L.
Published: July 2016

Abstact

We are looking for stellar companions to very hot helium-rich subluminous (sdO) stars by using infrared photometry, optical CCD imaging and spectroscopy. The work is complemented with a comprehensive bibliographic and space-mission databanks search for the objects in our sample (Thejll, Ulla & MacDonald 1995). Companions can be used to indirectly measure the distance to the hot subdwarfs, and give clues about possible binary evolution scenarios. We have therefore gathered and analysed data for 57 hot subdwarfs in a search for IR excesses and companions. 43 of the stars are observed for the first time in the JHK bands and 28 objects are found to have larger IR fluxes than expected from a single sdO.
On the Orbital Period Distribution of Recycled Pulsars
Authors: Nelson L. A. , Rappaport S.
Published: July 2016

Using population synthesis techniques, we investigate the orbital period distribution of ‘recycled’ pulsars. We find that the relative distribution of systems with periods between approximately one and fifty days are reasonably well reproduced. However, the existence of binary pulsars with periods between 70 and ~ 1000 d cannot be explained within the evolutionary framework considered here.
The Relativistic Beaming Model and Superluminal Motions
Authors: Fan J. H. , Xie G.Z. , Zhang Y.H. , Qin Y.P.
Published: July 2016

In this paper, we consider a compilation of 55 objects with known superluminal motions (SM), and whose flux density (X-ray, optical, radio), core dominance parameter (R), superluminal velocity, and radio Doppler factor (δR) are known. Our study shows that SM is consistent with the beaming model, and the relation

is reasonable. The statistical correlation between superluminal velocity and redshift is a result of selection and the statistical correlation between R and brightness temperature (Tob) is actually a reflection of the correlations between δ, R, and Tob for objects with SM. Up to now, 59 objects have been reported to have SM, but for reasons discussed elsewhere (Vermeulen & Cohen 1994), only 55 are considered here.
The HST Spectrum of I Zw 1: Implications of the C III* λ1176 Emission Line
Authors: Laor Ari , Jannuzi Buell T. , Green Richard F. , Boroson Todd A.
Published: July 2016

I Zw 1 is a well-known narrow-line quasar with very strong Fe II emission. High S/N spectra obtained with the HST FOS show a remarkably rich emission-line spectrum. The C III*λ1176 line is clearly detected in emission for the first time in AGNs. This line arises from radiative decay to the 2s2p3Pº0,1,2 metastable levels of C III. The observed flux is ~ 50 times larger than expected from collisional excitation or dielectronic recombination in photoionized gas. The most plausible mechanism for the large enhancement in the C III* λ1176 flux is resonance scattering of continuum photons by C III* ions. This mechanism requires large velocity gradients (~ 1000 km s−1) within each emitting cloud in the BLR. Such large velocity gradients can be induced by forces external to the gas in the BLR clouds, such as tidal disruption, or radiation pressure.
Velocity-Resolved Echo Mapping
Authors: Horne K.
Published: July 2016

We probe the structure and kinematics of Seyfert broad-line regions by using a velocity-delay map to fit simultaneously the observed variations in the continuum and the emission-line profiles. The velocity-delay map of C IVλ1550 emission constructed from 44 IUE spectra of NGC 4151 suggests virial motions, with 107M⊙ inside two light days. Pure inflow and outflow kinematics are ruled out by the approximate symmetry of the map. A stronger redshifted response at small delays suggests either a component with free-fall kinematics, or an outflow with CIV being emitted inward by optically thick gas clouds.
Optical Monitoring of 3C 390.3 in 1995
Authors: Qian Bo-Chen , Tao Jun
Published: July 2016

We present light curves obtained during a seven-month monitoring campaign on 3C 390.3. The source steadily increased by about 0.5 mag from 1995 July to October.
Line Shifts in the Two-Phase Broad-Line Region with Radial Kinematics
Authors: Xue Sui-Jian , Cheng Fu-Zhen
Published: July 2016

We consider in detail the two-phase BLR model with radial infall kinematics. Numerical calculations show that Lyα and C IVλ1549 profiles are blueshifted from their systemic rest-frame velocity, and their profiles are in qualitative agreement with the observations. It seems that the observed velocity differences between the high and low-ionization lines in the spectra of quasars can be understood in such a simple, physical, self-consistent model.
An Analysis of Broad Emission-Line Profiles from HST Data
Authors: Snedden Stephanie A. , Gaskell C. Martin
Published: July 2016

We have analyzed the HST FOS spectra of all quasars in the Stirpe (1990) high S/N line-profile sample and studied line-profile ratios as a function of radial velocity. Some quasars show no sign at all of NLR Lyα. We confirm that Hα is narrower than Lyα (after allowance for NLR contributions). The Lyα/Hα ratios in the cores of the broad lines are all close to or slightly less than case B and values predicted by single-cloud photoionization models. The Lyα/Hα ratio is surprisingly high in the blue wing. With only one exception, the ratios are equal to or greater than the case B value. Intrinsic reddening must be very small in most cases. We also briefly discuss other ratios.
Unusual Balmer-Line Variations in the Radio-Loud AGN 4C 37.43
Authors: Romano P. , Sulentic J. , Marziani P. , Calvani M. , Moles M. , Zwitter T.
Published: July 2016

We present new observations of the quasar 4C 37.43 in the course of a more general study of broad-line profiles in radio-loud AGN. During the most recent observations it became obvious that the broad profile Hβ had changed significantly. Difference spectra show that a new blue component has appeared on the Hβ profile. The centroid of this new component is displaced about 2500 km s−1 from the rest frame [O III] λ5007. A corresponding blueshifted He IIλ4686 component may have also appeared.
Reprocessing Models and the ASCA Spectrum of Mkn 290
Authors: Turner T. J. , George I. M. , Kallman T. , Yaqoob T. , Życki P.T.
Published: July 2016

We describe a warm absorber/emitter model that is used to model the complex X-ray spectrum of Mkn 290. The best fit to the data also includes a contribution from an ionized reflector.
Correlation Between the FWHM of the Broad Emission Lines and the Soft X-Ray Photon Index in the PG Quasars
Authors: Gondhalekar P.M. , Rouillon-Foley C. , Kellettl B.J.
Published: July 2016

The correlation between the FWHM of Lyα, C IV and Hβ lines and the photon index of the soft X-ray continuum is investigated for a sample of PG quasars. Only the FWHM of Hβ line is correlated with the photon index and this correlation depends on the sample of the AGNs considered.
Are Radio-Loud Quasars Rebellious or are Radio-Quiets Just Plain Untalented?
Authors: Vestergaard M. , Wilkes B.J. , Barthel P.D.
Published: July 2016

We present some of the results of a preliminary statistical study of 20 QSOs. We compare equivalent widths and widths at 40–80% of flux maximum of the Lyα, Si IVλ1400, C IV λ1549, and C III] λ1909 lines between radio-loud and radio-quiet QSO subsamples and with previously reported findings.
Infrared Emission-Line Signatures of Tori in the Nuclei of Seyferts
Authors: Storchi-Bergmann Thaisa , Winge Cláudia , Ward Martin J. , Wilson Andrew S.
Published: July 2016

We present infrared (IR) long-slit spectroscopy of two galaxies with Seyfert 2 nuclei, NGC 2110 and the Circinus galaxy, both known from previous studies to exhibit anisotropic high-excitation gaseous emission. In the “unified models” for Seyferts, this anisotropy is due to collimation of the ionizing nuclear radiation by an optically thick molecular torus which surrounds the nucleus. We have looked for signatures of this torus and its collimating effect in the IR (J and K bands), taking advantage of the reduced relative attenuation at these wavelengths. The two galaxies are found to show extended emission in the lines [Fe II] λl.257 µm, Paβ, H2λ2.12 °m, and Brγ, both along the collimation axis as well as perpendicular to it. The [Fe II] line is found to trace the high-excitation emission, and, in the case of NGC 2110, is more extended along the collimation axis. The H2 emission, although consistent with the presence of a molecular torus, extends for hundreds of parsecs and the derived kinematics is consistent with circular rotation in the plane of the galaxies. The emission-line ratios [Fe II]/Paβ and H2/Brγ are much smaller in Circinus (respectively ~ 0.5 and 1) than in NGC 2110 (~ 7 and ≥ 4, respectively), and indicate the presence of a nuclear starburst in the former galaxy. IR rotation curves were determined for both galaxies. In the case of NGC 2110, the IR rotation curve shows different behavior than the rotation curve determined from optical lines, which shows the importance of obscuration effects in the study of the gas kinematics.
Infrared to Millimeter Spectroscopy and Imaging of Active Galactic Nuclei
Authors: Genzel R. , Lutz D. , Sturm E. , Tacconi L. , Thatte N. , Sternberg A.
Published: July 2016

Observations in the 1 µm to 1 cm wavelength band give important information on the physical processes occurring in and immediately around active galactic nuclei. Concentrating on recent results on ionic, atomic, and molecular emission lines, we discuss as examples the first ISO results on the nature of ultra-luminous infrared galaxies, and near-infrared and millimeter measurements of the central 100 parsecs of the Seyfert 2 galaxy NGC 1068.
Narrow Lines and Continuum Emission in Seyfert 2 Galaxies
Authors: Polletta M. , Bassani L. , Caroli E. , Malaguti G. , Malizia A. , Palumbo G.G.C.
Published: July 2016

A statistical analysis of the relationship between the continuum and the narrow emission lines of a sample of Seyfert 2 galaxies strongly suggests the presence of a starburst emitting at all wavelengths from radio to soft X-rays as well as in the narrow lines.
Shocks and Photoionization in the Narrow-Line Region
Authors: Viegas Sueli M. , Contini Marcella
Published: July 2016

The presence of shocked regions in the narrow-line region (NLR) of active galactic nuclei (AGN) is discussed. Their effect on the physical conditions, in addition to photoionization from the central radiation source, is analyzed. We show that composite models, accounting for both shocks and photoionization, provide a consistent picture of the NLR which accounts for the observed emission-line and continuum spectra and is in agreement with the AGN unified model. The study of a particular object, NGC 5252, strengthens these results. It also shows that, besides explaining the observational data, the models make predictions that can be tested by infrared, optical, and X-ray imaging.
Dynamical Models of the Maser in NGC 4258
Authors: Moran J.M.
Published: July 2016

The presence of two quasars symmetrically displaced from the nucleus of the galaxy NGC 4258 (Pietsch et al. 1994) has given rise to some speculation that they might have some dynamical connection with the high-velocity maser emission seen in the nucleus (Burbidge 1996; Ozernoy 1996). The case that the masers define a simple Keplerian disk is very compelling; nonetheless, it is instructive to investigate whether any other dynamical models could fit the available data.

The evidence that the masers define a thin Keplerian disk can be found in Miyoshi et al. (1995) and Moran et al. (1995). Some of the relevant data are shown elsewhere in this volume (Fig. 2 of Greenhill’s paper). The basic analysis is as follows. The features near the systemic velocity of 470km s−1 show a linear dependence of line-of-sight velocity versus distance along the major axis, while the redshifted and blueshifted high-velocity features show a nearly Keplerian dependence with distance.
A Survey of X-ray–Emitting IRAS Galaxies: A New Class of Objects or Hidden AGNs?
Authors: Dennefeld M.
Published: July 2016

A cross-correlation between the IRAS PSC and the ROSAT All-Sky Survey has provided 242 sources detected in both surveys (Boiler et al. 1992). About half of these have redshifts in the literature and a spectral classification. An unexpected result was the discovery of many galaxies with X-ray luminosities up to a few 1043 ergs s−1, yet without Seyfert characteristics in their optical spectra (e.g., Boiler et al. 1993). To investigate this problem further and evaluate the frequency of occurrence of these peculiar objects, a spectroscopic follow-up has been undertaken to:

• Determine velocities and luminosities for all the unclassified objects.

• Reevaluate the classification of high X-ray luminosity objects previously not recognized as Seyferts. In particular, spectral resolution or coverage and variability are important parameters to consider if one wants to detect faint signs of Seyfert activity.
Discovery of Five New X-ray–Selected BL Lacertae Objects and Three New Quasars
Authors: Xie G.Z. , Brinkmann W. , Cha G.W. , Laurent-Muehleisen S. , Zhang Y.H. , Li K.H. , Bai J.M. , Liu F.K.
Published: July 2016

Through combined ROSAT and VLA observations, we have identified 19 BL Lac/quasar candidates. In 1994 December, 1995 January and October, and 1996 January 1996, we obtained spectra of all 19 candidates using the 2.16-m telescope of Beijing Astronomical Observatory. The dispersion used is 195 Å mm−1, which yields a dispersion of about 4.65 Å pixel−1, and the wavelength coverage is 3500–7800 Å. Five of these objects are uniformly featureless, and we identify them as BL Lac objects. Three new quasars are also identified. Table 1 presents VLA positions and redshifts for the 5 new BL Lac objects and three new quasars. By checking them in the NASA/IPAC Extragalactic Database (NED) and Véron-Cetty & Véron’s (1993) Catalogue of Quasars and AGNs, and other recent reports about discovery of new BL Lac objects and quasars, we find that these sources are previously unreported.
Optical Identification of the ROSAT All-Sky Survey Sources in Two 2° × 2° Fields
Authors: Zhao Y. , Zhong J. , Wei J. , Hu J. , Li Q.
Published: July 2016

We used the CCD camera and spectrograph of the 2.16-m telescope of Beijing Astronomical Observatory to identify the ROSAT All-Sky survey sources in two 2° Ü 2° fields. Of a total of 16 X-ray sources, we identified 13 of them as follows: two QSOs, two Seyfert galaxies, two active galaxies, two clusters of galaxies, and five late-type stars. Three X-ray sources remained unidentified.
The Spectra of Very Luminous IRAS Galaxies
Authors: Wu Hong , Zou Zhenlong , Xia Xiaoyang , Deng Zugan
Published: July 2016

We discuss new optical spectra and DSS images of a complete sample of very luminous IRAS galaxies. The statistics of classification of spectral types and interactions show that interaction can account for the nuclear activity (AGN and starburst) of ultraluminous infrared galaxies.
A Unified View of How the Study of Emission Lines Furthers Our Knowledge of AGN
Authors: Krolik Julian H.
Published: July 2016

A global view is given of how emission lines have been, and may in the future, be used to enhance our understanding of AGN. Lines from the microwave to the X-ray bands all contribute. Although we have a deep understanding of the physical processes by which line photons are generated, when the circumstances of line emission are complicated, models become too unreliable to provide strong inferences about the rest of the AGN system. At present, the lines which appear the most promising for helping answer the most important questions about AGN are the 22 GHz H2O rotational transition and the 6.4keV FeKα fluorescence.
A high frequency search for highly dispersed pulsars
Authors: Kramer M. , Jessner A. , Müller P. , Wielebinski R.
Published: July 2016

The majority of known pulsars have been discovered by pulsar searches at low radio frequencies (v< 1 GHz). However, such searches are subject to various deleterious effects, viz the Galactic background radiation (∝v−2.8), dispersion smearing (∝v−3) and also scatter broadening (∝v−4.4). Dispersion smearing and, in particular, scatter broadening prohibit the detection of pulsars with high dispersion measures at low frequencies (cf. Fig. 1a). This is highlighted by the fact that all 11 known pulsars with DM>600 cm−3pc have been discovered during the only two surveys performed to date above 1 GHz, i.e. at 1.4 GHz by Clifton et al. (1992) and at 1.5 GHz by Johnston et al. (1992). However, scattering is still a limiting factor at even 1.4/1.5 GHz. For example B1750—24 is observed with a double component profile at 4.85 GHz (Kijak et al. 1996), whereas at 1.4 GHz the components are completely smeared out due to scatter broadening (cf. Clifton et al. 1992). Therefore, the galactic population of highly dispersed pulsars is still not known. In order to reveal this hidden sample, we have recently started a search in Effelsberg at 4.85 GHz where limitations due to scattering are essentially not existent (see Fig. 1a). The use of this extraordinary high frequency for pulsar searches enables us to observe with a large bandwidth but a small number of filterbank channels, so that the necessary computer power is radically reduced. However, the general steepness of pulsar spectra demands a highly sensitive observing system, otherwise, only the most luminous sources can be detected. A serious disadvantage of a high frequency search is the small telescope beam requiring a lot of observing time to search even a small area of the sky. A restriction of the search area is therefore highly recommended.
Fundamental Precision of Pulsar Timing
Authors: Foster Roger S.
Published: July 2016

Although 13 years have passed since the first millisecond pulsar (MSP) was discovered (Backeret al. 1983), it still has the shortest known rotational period (1.56 ms). MSPs are nature’s most stable clocks (Taylor 1991), with timing stabilities that rival atomic clocks on time scales beyond six months (Matsakis & Foster 1996). Specifically, the instantaneous measurement of the period of the original MSP is determined to a precision of ~ 20 attoseconds (10−18s). With such precision, we are able to predict the pulsar pulse arrival times to a small fraction of the rotational period years into the future. MSPs are powerful sources for use in fundamental astrometry and time keeping applications. Collectively, a population of MSPs distributed around the sky can be used to establish a nearly inertial space-time reference frame (e.g. Foster & Backer 1990). Such a pulsar timing array (PTA) could be used to study drifts in Earth based atomic time scales, perturbation in the planetary ephemerides, relativistic corrections in the solar gravitational potential, and limit the energy density of a stochastic background of gravitational waves from the early universe.
Periodic Changes in Intensity and Arrival Time of Pulses from the Vela Pulsar: Evidence for Free Precession?
Authors: Deshpande A.A. , McCulloch P.M.
Published: July 2016

We present dual-frequency measurements on the Vela pulsar with a view to study the slow variations in the pulsed flux and the apparent differences in the pulse arrival times. We examine the data for correlated variations between the pulse intensities and arrival times at the two frequencies and discuss two main possibilities in order to explain the observed behaviour.

The data presented here consists of a) Pulse intensities, S635& S950, at S635& S950MHz respectively and b) the ‘residual’ differences in the time of arrival of the pulse at the lower frequency, ΔTOA, with respect to that at the higher frequency. These data, over a span of ~1300 days (during 1988-92), were obtained as a part of the routine monitoring of the Vela pulsar from Mt. Pleasant Observatory of University of Tasmania, Hobart (see McCullochet al. 1990).
Expectancy of large pulsar glitches
Authors: Baykal Altan , Alpar Ali
Published: July 2016

We study the expectancy of large glitches (ΔΩ/Ω > 10−7) from a sample of 472 pulsars other than the Vela pulsar. The pulsars in this sample have exhibited 20 large glitches. In the sample the total observation span is larger than 2000 pulsar years. We assume that all pulsars experience such glitches, with rates that depend on the pulsars’ rotation rate and spin-down rate, and on the glitch model. The superfluid vortex unpinning model gives good agreement with the observed distribution of glitches and with the parameter values deduced for the Vela pulsar glitches.
Microlensing of pulsar-radiation
Authors: Wex Norbert , Gil Janusz , Sendyk Marek
Published: July 2016

When the radiation of a star passes near a massive object, its intensity is magnified due to the microlensing phenomenon. Similar effects should also apply to pulsar signals. However, because of the pulsating nature of pulsar radiation, the flux magnification will be accompanied by a time varying travel-time delay (Krauss and Small 1991, Larchenkova and Doroshenko 1995, Ohnishi et al. 1995, Wexet al. 1996).

Let us denote the epoch of observation byt⊕. A travel-time delay caused by aSchwarzschild-lensis characterized by four parameters:M, the mass of the lens,q, the ratio of the transverse velocity of the lens with respect to the line of sight and the minimum impact parameter,fm, the ratio of the minimum impact parameter and the Einstein radius, andT0, the time of maximum delay. If we denote the ‘intrinsic’ frequency and its derivative with respect to time (corresponding to the barycentric arrival time t =t⊕) by ν andthen, we find for the observed phase of the pulsar at the barycentric timet:
Geometrical effects on radio pulsar profiles and spectra
Authors: Sieber Wolfgang
Published: July 2016

Considering the geometry of the hollow-cone model of radio pulsar emission in detail, one is led to the conclusion that several well-known observed effects may be explained quite easily purely on geometrical terms. It is shown that a steepening of the spectrum (cut-off) may be expected for certain geometrical situations as well as variations in component spectra, e.g. steeper spectra for the central component. These effects appear in addition to the already existing physical variations with frequency.
Pulsar Death at an Advanced Age
Authors: Arons Jonathan
Published: July 2016

Not long ago Rankin (1990) presented strong evidence in favor of a low altitude (r≈R*) dipole geometry for the site of the core component of pulsar radio emission. Arons (1993) gave evidence that spun up millisecond pulsars must have a substantially dipolar large scale field at low altitute. Electron-positron pair creation at low altitude above the polar caps has long been hypothesized to be an essential ingredient of pulsar radio emission. If so, all observed pulsars must lie in the region ofP−Ṗspace where polar cap acceleration has sufficient vigor to lead to the copious pair production. Yet, to date, allinternally consistenttheories of polar cap pair creation have required hypothesizing a large scale (eg, quadrupole) component of the magnetic field with strength comparable to that of the dipole, in contradiction with the evidence in favor of an apparently dipolar low altitude geometry. The internally consistent theories also violate other observational constraints. The discharge models of Ruderman and Sutherland (1975), Gurevich and Istomin (1985), and Jones (1977, 1978, 1979) all accelerate equal, counterstreaming flows of electrons and positrons, thus putting one half of the particle acceleration energy into high energy particle and photon bombardment of the polar caps. The heating causes pulsed thermal X-ray emission from hot spots in excess of what is seen (Ogelman 1993). While the Arons and Scharlemann (1979) model does not have this problem, since the space charge in the starvation zone above the polar cap is made up almost entirely of the outbound beam, in star centered dipole geometry it dramatically fails to account for pulsar emission over most of theP−Ṗdiagram and predicts radio polarization variations in contradiction to the observations (Narayan and Vivekanand 1982).
Microstructure: A Review
Authors: Hankins Timothy H.
Published: July 2016

Pulsar radio intensities contain a rich range of timescale variations ranging from months down to nanoseconds. The shortest of these fluctuations have been calledmicrostructure. The observational properties of microstructure and the astrophysical value of microstructure are discussed.
Postion angle jumps in pulsar linear polarization
Authors: Xu R.X. , Qiao G.J. , Han J.L.
Published: July 2016

The position angle (PA) behaviour of linear polarization of pulsar emission is simulated after considering the relative retardation between the core and conal components, which are believed to be generated from different emission altitudes. The PA will jump 90° at some points where the complete depolarization occurs.