bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cepheid Radii and Distances
Authors: Laney C. D. , Stobie R. S. 
Published: July 2016

Laney & Stobie (1995) (LS95) have determined Baade-Wesselink radii for 49 galactic Cepheids using BVRI and JHK photometry. Four of the possible magnitude-colour combinations were studied in detail — namely, (V,B–V), (V,V–Ic), (K,V–K) and (K,J–K). In that paper and in the present note we have used the maximum likelihood method of Balona (1977) as recently modified to allow for the nonlinear effects of the non-negligible radius excursions of Cepheids.One major advantage of infrared photometry is that the light variation at K is dominated by the change in surface area, unlike the light variation at V which is dominated by temperature changes. Another is that (as shown both empirically and by model atmospheres) one may use a J–K or V–K colour index to calculate the surface brightness at K without having to worry very much about the effects of varying surface gravity or Doppler broadening velocity, while the same is definitely not true when optical colour indices are used to calculate the surface brightness at V.
The H0 Key Project: Cepheids in NGC925, M101 and M100
Authors: Hughes S. M. G. 
Published: July 2016

AbstractAs part of the Extragalactic Distance Scale Key Project, the Hubble Space Telescope has been used to identify Cepheids in M100, M101 and NGC925, and to measure distances derived from the Cepheid PL relation. For M100, the distance of 17.1 ± 1.8 Mpc has been used to infer a preliminary value for H0 of ~ 80 km/s/Mpc, which brings the age of the Universe derived from the standard model of the Big Bang into conflict with the ages of the oldest stars.
Interferometry of Cool Pulsating Stars
Authors: Haniff Chris 
Published: July 2016

AbstractThe drive for high-angular resolution from the ground has led to the development of optical and near infrared interferometric telescopes analogous to radio synthesis arrays. These now provide a diffraction-limited imaging capability well suited to studies of nearby cool giants and supergiants. In this review I summarise the current status of these instruments, their scientific potential for studies of cool pulsating variables (LPVs), and present some recent results that highlight the promise that such methods hold.
A New Asymptotic Treatment of g-modes of a Star
Authors: Smeyers P. , Van Hoolst T. , Boeck I. De , Decock L. 
Published: July 2016

An asymptotic representation of low-frequency, linear, isentropic g-modes of a star is developed without the usual neglect of the Eulerian perturbation of the gravitational potential. Our asymptotic representation is based on the use of asymptotic expansions adequate for solutions of singular perturbation problems (see, e.g., Kevorkian & Cole 1981).Linear, isentropic oscillation modes with frequency different from zero are governed by a fourth-order system of linear, homogeneous differential equations in the radial parts of the radial displacement ξ(r) and the divergence α(r). These equations take the formThe symbols have their usual meaning. N2 is the square of the frequency of Brunt-Väisälä. The functions K1 (r), K2 (r), K3 (r), K4 (r), depend on the equilibrium model, e.g.,We introduce the small expansion parameterand assume, for the sake of simplification, N2 to be positive everywhere in the star so that the star is everywhere convectively stable.
Asteroseismology in Praesepe: the case of EP Cnc
Authors: Belmonte J.A. , Claret A. , Hernández F. Pérez 
Published: July 2016

AbstractOn the 1992 STEPHI IV campaign, the multi-periodic δ Scuti stars BN Cnc and BU Cnc of the Praesepe cluster were monitored during a three-week, three-continental run (Belmonte et al. 1994). Five and six frequency peaks, respectively, were recorded as a result of the campaign. In a subsequent paper (Pérez Hernández et al. 1995, hereafter Paper I), an attempt to identify these frequency peaks as pulsation modes was done. An important point is that both stars belong to the same cluster and, hence, more severe constraints than for isolated stars can be imposed. Recently, Breger et al. (1994) have reported results on EP Cnc, another δ Scuti in Praesepe. This star is also multi-periodic, showing three frequency peaks above the noise level. In the present work we extend our analysis to this star.
Slowly Variable Early F-type Stars
Authors: Balona L.A. , Krisciunas K. 
Published: July 2016

AbstractA third periodicity is found in the early F-type star γ Dor which probably rules out an interpretation in terms of differential rotation of a spotted star. One of the two periods in 9 Aur is not visible in the radial velocity. This is not explained by the star spot model, but may indicate that the two periodicities are nonradial pulsations of different spherical harmonic degrees.
Velocity Variations of the roAp Star γ Equulei: Probing a puzzling pulsator
Authors: Matthews Jaymie M. , Scott Sandra 
Published: July 2016

AbstractWe present a pulsational RV curve for γ Equ whose amplitude is about 200 m/s and period is roughly 11 minutes. These data, combined with rapid photometry and line-profile variations, are being used to identify the nonradial mode(s) and study mode growth/decay in this unusual star.
Cepheid Distances to Nearby Galaxies
Authors: Gieren Wolfgang P. , Candia Pablo , Fouqué Pascal , Hertling Gisela , Brieva Eduardo 
Published: July 2016

AbstractWe have determined new Cepheid distances on a homogeneous system to nine nearby galaxies with Cepheid observations in the V bandpass, using the extensive calibration of the galactic Cepheid PL(V) relation of Gieren, Barnes & Moffett (1993). Absorption corrections to the observed distance moduli were taken from the RC3 catalog (de Vaucouleurs et al. 1991). For most of the galaxies, the galactic PL(V) relation of GBM gives a very good fit to the Cepheid data.
Thermonuclear Excitation of R-modes in Neutron Stars
Authors: Lee Umin , Strohmayer Tod E. 
Published: July 2016

AbstractNeutron stars display phenomena which result from the burning of accreted nuclear fuel in their surface layers. In addition to producing X-ray bursts and other temporal phenomema, such burning can excite oscillation modes of the neutron star. Here we investigate the stability of R-modes in uniformly rotating neutron stars using nonadiabatic pulsation calculations of steady burning envelopes on accreting neutron stars. We find that the fundamental R-modes are unstable for a large range of accretion rates, and thus might manifest themselves observationally in the power spectra of accreting sources above about 1 kHz.
Temperature Structure of the Disk in V1315 AQL
Authors: Moreno C. , Rutten R. G. M. , Dhillon V. S. 
Published: July 2016

AbstractWe present a progress report on the analysis of time-resolved spectrophotometric observations of the cataclysmic variable V1315 Aql. The spectral range of the data covers the entire Balmer series up to and including the Balmer jump. We aim to use these data to test the steady-state accretion disk model.
Is There Observational Evidence for the Evaporation of the Inner Accretion Disk in Dwarf Novae at Quiescence?
Authors: La Dous C. , Meyer-Hofmeister E. , Meyer F. 
Published: July 2016

AbstractWe present the preliminary results of a comparison of observed general patterns of quiescent dwarf novae and theoretical predictions of the disk evaporation model. We demonstrate that, even though details still have to be clarified, on the whole there is strong evidence that observations and theory are in agreement.
Simultaneous UBVRIJK Photometric and Polarimetric Observations of PQ Gem
Authors: Potter Stephen , Mason K. O. , Cropper M. S. , Bailey J. A. , Hough J. H. 
Published: July 2016

We present simultaneous multiwavelength observations of the intermediate polar PQ Gem (Mason et al. 1992) obtained on 1993 February 18 and 19 using the Hatfield Polarimeter on UKIRT.The data are folded on the 13.9 m spin period in Fig. 1. The light curves are double peaked at long wavelengths, with dips at phase ~ 0.15 and phase ~0.65, but almost sinusoidal in the U and B bands where the phase ~0.65 dip is absent. The percentage of circular polarisation also varies with the spin cycle, most notably in the I band, with both positive and negative excursions. The peaks in the positive and negative polarisation occur at phase ~ 0.15 and phase ~ 0.65 respectively, approximately coincident with the two intensity dips.
QPOS of By Cam in Low and High States
Authors: Pavlenko E. P. , Shugarov S. Yu. , Antipin S. V. , Sokolov D. A. , Borisov G. , Budzinovskaya I. 
Published: July 2016

AbstractWe present the analysis of BV photometry of BY Cam based on observations carried out in Crimea. The long QPOs in brightness were detected in both high and low brightness states. Their typical periods, equal to 6, 12 and 24 m, are found. The amplitude of the QPOs depends on the phase of Pbeat.
Far Ultraviolet Observations of Dwarf Novae made with the Hopkins Ultraviolet Telescope
Authors: Long Knox S. 
Published: July 2016

AbstractObservations with the Hopkins Ultraviolet Telescope on the Astro-1 and Astro-2 space shuttle missions have provided the first set of moderate (3 Å) resolution far ultraviolet (FUV) spectra of dwarf novae to include the wavelength range between Lyα and the Lyman limit. Important lines which are detected in the HUT spectra of dwarf novae in this wavelength range include S VI λλ933,945, C III λ977, O VI λλ1032,1038, P V λλ1118,1128 and C III λ1176, as well as the higher order Lyman lines. The observations confirm earlier IUE observations that two dwarf novae – U Gem and VW Hyi – have quiescent FUV spectra dominated by the white dwarf, but suggest that the quiescent FUV emission from three other dwarf novae – SS Cyg, WX Hyi and YZ Cnc – are dominated by emission from a hot portion of the disk or a disk corona. The spectra obtained of the dwarf novae Z Cam and EM Cyg in outburst and also of the nova-like variable IX Vel can be modeled reasonably successfully in terms of steady state disks constructed by adding appropriately-weighted stellar model spectra.
Evolution of an Accretion Disk in the Symbiotic Binary CI Cyg
Authors: Mikołajewska Joanna 
Published: July 2016

AbstractWe have combined IUE spectra with optical spectroscopic and photometric data collected over a few orbits of the symbiotic binary CI Cyg to follow the evolution of a disk and boundary layer during a full activity cycle. Our results indicate an extended optically thin disk during quiescent periods, which evolves into an optically thick state in an eruption; a classical boundary layer at the inner edge of the disk ionizes a surrounding H II region in quiescence, and this emission fades during the rise to visual maximum in outburst. This evolution of Ṁ rivals that observed in classical CVs and pre-main sequence stars, so symbiotic systems like CI Cyg represent another opportunity to study the physics of disk accretion.
An Archival Study of HST Observations of Her X-1/HZ Her
Authors: Cheng F. H. , Vrtilek S. D. , Raymond J. C. 
Published: July 2016

Her X-1 is an X-ray pulsar with a rotation period of 1.24 s and a binary period of 1.7d (Tananbaum et al. 1972). The 1.7 d variations in optical and ultraviolet flux are attributed to X-ray heating of the companion star and disk (e.g. Howarth & Wilson 1983, hereafter HW83). The system displays a 35 d period, attributed to the effects of a tilted, precessing, accretion disk. Optical and ultraviolet flux variations continue unchanged throughout. This work is motivated by the following reasons:• The observed IUE spectra have significantly flatter slopes than those predicted by previous models (e.g. HW83).• The observed strength of the Balmer jump is anomalously low compared to that expected for a normal B star (Anderson et al. 1994).• HST observations obtained by Anderson et al. (1994) in order to study emission lines have yielded high quality spectra of the continuum emission from HZ Her, enabling for the first time detailed model fitting efforts.
Doppler Imaging of V404 Cyg in Quiescence
Authors: Casares Jorge 
Published: July 2016

AbstractWe present Doppler images of the accretion disc in the black hole X-ray transient V404 Cyg during its quiescent phase. The Hα map shows evidence for a hot spot, indicating that mass transfer is continuing long after the 1989 outburst. Both the Hα and the IR Ca II emission maps exhibit intense bright spots at the position of the secondary star, which we take as a sign of chromospheric activity. The Ca II emission arises from the outer parts of the accretion disc, and its surface brightness distribution is consistent with dwarf novae discs (I∝R−3/2).
Investigation of the Optical Variability of Relativistic Objects with High Time Resolution
Authors: Mitronova S. N. , Beskin G. M. , Neizvestny S. I. , Plokhotnichenko V. L. , Popova M. Yu. , Zharikov S. , Benvenuto O. G. , Feinstein C. , Mendez M. , Boriakoff V. , Dossa D. 
Published: July 2016

1. Detection of nonthermal optical flares in low mass X-ray binaries. Eleven low-mass X-ray binaries have been observed with the MANIA (Multichannel Analysis of Nanoseconds Intensity Alteration) complex; X0420+32, A0620-00, X1728–169, X1813–14, X1957+11 in 1986 at the 6 m telescope of SAO [7], and 2S0921–630, 4U1543–475, 4U1636–536, 4U1559–487, MXB1735–44, 4U1822–371 in 1991 at the 2.15 m telescope of CASLEO (Argentina) [1]. Analysis of the data using the special y2 and d2 function formalism [4], [6] has shown no brightness variations on time-scales of 10−7... 10 s for all objects except A0620–00 and MXB1735–44.A0620–00. The five millisecond flashes were detected on 1986 February 13 (Fig. 1). The first two flares have durations of 3 ms and 5 ms and their rise times were 1...2 ms. The other three events lasted 0.4…0.5 ms with rise times of about 0.1 ms. The lower limit of the flare amplitudes is 40 counts ms−1 and the corresponding brightness temperatures are 5 109 K for the first two and 5 1011 K for the others.
Rosat and Optical Observations of Supersoft X-Ray Sources
Authors: Reinsch K. , van Teeseling A. , Beuermann K. , Thomas H.-C. , Abbott T. M. C. 
Published: July 2016

AbstractWe present X-ray, UV and optical observations of the Galactic supersoft X-ray source (SSS) RX J0019.8+2156 and first results of our study of the X-ray and optical long-term variability of bright SSS.
Accretion Disks and Line Emission in AGN
Authors: Rokak E. 
Published: July 2016

AbstractIrradiated accretion disks around massive black holes are expected to produce part of the line spectrum of AGN, but most of the disk emission must be thermal, observed at UV wavelengths. The two emission components, lines and continuum, are fitted by a unique accretion-disk model that gives the mass of the black hole and the inclination of the disk. The distribution of the disk inclination in a complete sample of Seyfert 1 galaxies suggests that their nuclei are orientation-selected, affected by strong absorption at low disk latitudes. The black-hole masses in the same sample confirm the long-standing non-linearity between M and L for AGN and the non-causal relationship between nearby Seyfert 1 galaxies and distant quasars (i.e., pure luminosity evolution is ruled out).Irradiated accretion disks are also combined with the relativistic jet model in order to constrain the orientation and the Lorentz factor of 14 superluminal radio sources. At least for a few objects, the line and the radio data are inconsistent with both models, unless a new parameter (jet bending, a second emission-line component, etc.), is also involved. Despite this inconsistency and the ambiguous evidence for combined disk and jet fits in the remaining superluminal sources, a successful merger of these two models might address questions about the nature of AGN and also constrain the Hubble constant.
The HST Sample of Radio-Loud Quasars: Fe II and Other Correlations
Authors: Wills D. , Thompson K.L. , Brotherton M.S. , Wills Beverley J. , Baldwin J. A. , Carswell R. F. , Browne I. W.A. , Netzer H. 
Published: July 2016

We are analyzing the emission lines and continuum spectra of a sample of ~61 radio-loud quasars to investigate dependences amongst various spectral, radio, and X-ray parameters, in particular to look for dependences of spectral properties on inclination of the the radio-jet axis (Wills et al. 1997).We have carried out conventional correlation analyses, as well as spectral principal-component analyses (SPCA) as described in the previous paper (Wills et al. 1997). We found that the single largest contribution to the spectrum-tospectrum variations was from a component — the ‘first principal component’ (PC1) — that has a more UV (or less red) continuum than the mean spectrum, and a weaker narrow-line (NLR) spectrum. The ‘second principal component’ (PC2) accounts for only 8–12% of the spectrum-to-spectrum variation, contributing a weaker UV, and stronger red continuum, and showing stronger narrow emission lines. There is also a tendency for the broad (BLR) lines in the second principal component spectrum to be narrower (note the sharper He II λ1640 and [O III] λ1663 features redward of the stronger C IV λ1549 emission line, and perhaps a narrow component of the N V λ1240 line redward of Lyα).
A Detailed Comparison of HST FOS and IUE UV Spectra of Selected Seyfert Nuclei
Authors: Koratkar A. , Pesto S. , Evans I.N. 
Published: July 2016

Significant improvements in our understanding of the physical conditions in active galaxies requires the development of sophisticated models that can predict in detail the emission from the nucleus. Accurate measurements of both the UV continua and the many weak diagnostic UV lines provide critical calibrations for such models.Rigorous comparisons of the HST FOS and IUE UV flux calibrations have so far been performed using spectrophotometric standard star spectra. These calibration observations have precision acquisition sequences and the spectra have very high S/N. Such data are not representative of typical FOS observations of an AGN, which often cannot be acquired with the same precision as standard stars, especially for pre-COSTAR data. Furthermore, the UV flux from a typical AGN is several magnitudes fainter than from a spectrophotometric standard star, and is more representative of typical non-stellar fluxes. Flux-dependent effects (in either FOS or IUE) may need to be considered at these lower flux levels.
Spectral Monitoring of NGC 4151 and 3C 390.3 at the 6-m Telescope
Authors: Shapovalova A.I. , Burenkov A.N. , Bochkarev N.G. 
Published: July 2016

Since 1986, we have carried out spectral monitoring of several Seyfert galaxies with the 6-m telescope of SAO RAS to study the structure and kinematics of the broad-line regions (BLR). Here we present the observational results for NGC 4151 and 3C 390.3.In 1986–96, about 150 spectra of the NGC 4151 nucleus were obtained with SP124+TV scanner and 24 spectra with a long-slit (UAGS+CCD) or a multipupil field spectrograph (MPFS + CCD). About 20 spectra of 3C 390.3 were obtained in 1995–96 with the UAGS + CCD and with MPFS + CCD. More detailed information about observations, data processing and results will appear in Shapovalova et al. (1996).
A Search for Optical Line Variability in Narrow-Line Seyfert 1 Galaxies
Authors: Giannuzzo M. Ester , Stirpe Giovanna M. 
Published: July 2016

AbstractWe present the results of a variability study of ‘narrow-line Seyfert 1 galaxies’: in 10 objects out of 12 the optical line flux changed in one year, with no statistical differences in variability with respect to ‘normal’ Seyfert 1s. We discuss how models for NLSls are affected.
Thermal Instability and Alfvén Waves in the Formation of Quasar Clouds
Authors: Gonçalves D.R. , Jatenco-Pereira V. , Opher R. 
Published: July 2016

AbstractWe use thermal instability as a condensation mechanism to form the characteristic clouds of the BLR of quasars. We include in the total heat-loss function the influence of the heating caused by the damping of Alfvén waves. We study the damping mechanisms: nonlinear, resonance surface, and turbulent. From this analysis, we show that this heating mechanism plays an important role in the formation of these clouds.
Disk Emission Lines
Authors: Murray N. , Chiang J. 
Published: July 2016

AbstractA thin disk illuminated by a central source will produce single-peaked broad emission lines if there is a wind emerging from the disk. The velocity gradient in the wind produces an anisotropic optical depth. For optically thick lines, the emission is strongest along directions perpendicular to the Keplerian velocity of the disk. The resulting line profiles are single peaked even though the emitting gas moves on essentially circular orbits. We argue that the broad emission lines seen in quasars, Seyferts, and luminous cataclysmic variables arise in disk winds.
A Link Between Seyfert Emission-Line Widths and X-Ray Continuum Slopes
Authors: Boile Th. , Brandt W.N. 
Published: July 2016

AbstractThis paper reports on AGN with extremely soft X-ray spectra observed with ROSAT. From their optical emission lines, these objects are classified as narrow-line Seyfert 1 galaxies (NLSl), almost all with extremely large Fe II/Hβ flux ratios and relatively narrow optical lines of hydrogen. NLSl have generally steeper soft X-ray continuum slopes than normal Seyfert 1s, and there may exist an anticorrelation between 0.1–2.4 keV continuum slope and the FWHM of the Hβ line. Objects with steep 0.1–2.4 keV continuum slopes and Hβ FWHM > 3000 km s−1 are clearly discriminated against by nature. When simple power-law models are fit to the data, photon indices reach values up to about 5, much higher than is usually seen in Seyfert 1s. Models with smaller-mass black holes and/or higher accretion rates show some promise to explain the relation between the FWHM of the Hβ line and the X-ray continuum slope. We further report evidence for persistent giant and rapid variability in the ultrasoft narrow-line Seyfert 1 galaxy IRAS 13224–3809.
Extended Emission-Line Regions Around AGN
Authors: Robinson A. 
Published: July 2016

AbstractHigh-excitation extended emission-line nebulae around active galactic nuclei probably result either from photoionization of the interstellar medium by beamed continuum radiation, or dynamical interactions between radio sources and the ambient gas, or both. Here I discuss the models based on these mechanisms, and their relative importance in radio-quiet and radio-loud active galaxies.
Near-Infrared Emission Lines in AGNs
Authors: Krabbe A. 
Published: July 2016

AbstractNear-infrared high-resolution imaging and spectroscopic observations of NGC 7469, Mrk 231, IRAS F10214+4724, and Circinus are presented. They indicate the presence of extended star-forming activity in the vicinity of the active nuclei of these galaxies on scales between 10 pc and 1 kpc from the nuclei. The very different distance scales covered by these objects show that the coexistence of AGN and star-formation activity is a common phenomenon. A first-order evolving star-cluster model calculation shows that we are beginning to understand the history and evolution of these circumnuclear star-forming regions.
Shocking Outflows in Seyfert Galaxies: An Imaging Perspective
Authors: Pogge Richard W. 
Published: July 2016

AbstractRepresentative results of a search for structures suggestive of shocked gas in the circumnuclear regions of Seyfert galaxies are presented. At issue is whether we can identify regions that appear to be shocked by outflows from the active nucleus. Such regions will be good targets for future spectrophotometric studies to determine what role shocks play in the physics of the AGN/host-galaxy interaction.