bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two-Color Observations of RR Lyrae Stars in M14
Authors: Wehlau Amelia , Potts Nicholas 
Published: July 2016

AbstractTwo-color photographic photometry has been carried out on RR Lyrae variables in M14. The position of these variables in the color-magnitude diagram is shown, and it is noted that there is a lack of horizontal branch stars to the red of the variable star gap. Color-amplitude, period-amplitude and color-period relations for the RR Lyrae variables measured are shown.
The system of short period meteor streams
Authors: Lindblad B. A. 
Published: July 2016

AbstractThe orbital characteristics of precisely reduced photographic meteors were studied. Most photographic meteors move in short period, direct orbits with orbital periods inbetween those of Jupiter and Mars. Practically no meteors have (Orbital periods coincident with those of the planets Jupiter, Mars and Earth.A search among all precisely reduced, photographic meteors revealed a number of new – or previously not well studied – meteor streams. For 18 short period meteor streams the scatter in the orbital elements 1/a,πand Ω was studied. An almost linear relation was found between the mean orbital energy of a meteor stream (– 1/a) and the standard deviation σ(1/a), indicating a progressive increase in the orbital scatter with decreasing mean distance to the sun. An index of mean meteoroid density was computed for 11 of the short period streams. The mean density increases with decreasing semi-major axis.The results are interpreted as indicating that the short period meteor streams are initially formed in orbits with periods slightly shorter than Jupiter’s. As the streams gradually drift inwards towards the sun under the influence of various drag forces the individual stream members spread out and only the high density, resistant meteors still remain, or can be recognized, as stream members.
Kinematics and Ages of UV Ceti Stars
Authors: Poveda A. , Allen C. , Herrera M.A. 
Published: July 2016

AbstractThe kinematic properties of 93 UV Ceti stars of the solar neighborhood are studied, based on a list of flares within 25 pc of the Sun (π ≥ 0".04). With updated values for their distances, proper motions and radial velocities (Gliese & Jahreiss 1991) space velocity dispersions are calculated for these stars. It is found that the total velocity dispersion of the flare stars (σ=30±3 km s−1) is similar to that of the F5 V stars from the same catalogue, for which the conventionally estimated mean age is about 3 · 109 years. A number of flare stars are identified as members of the Hyades, Sirius or Pleiades groups. The velocity dispersions found for the nearby flare stars, as well as their scale height and the membership of some of them to young kinematic groups, indicate that they belong to the young disk population. A small number (7) of UV Ceti stars have kinematics corresponding to the thick disk or halo population. Their long-lived chromospheric activity is interpreted as due to coalescence of old contact binaries. The question of the age of Proxima Centauri is examined in the context of our results, and found to be compatible with the ages of a Centauri A and B.
Young and Old Subsystems of Flare Stars
Authors: Mirzoyan L.V. , Hambarian V.V. 
Published: July 2016

Photographic observations with wide-field telescopes of flare stars in the Orion association and the Pleiades cluster have been carried out since 40 years. About 500 flare stars were found in each of these systems. The ages of these stellar systems differ by one or two orders of magnitude (Mirzoyan 1991). This fact allows us to compare them, in order to show that they fit into the concept, suggested first by Haro (1957), that the evolutionary status of flare stars is a stage of red dwarf star evolution which follows that of the T Tau stars (Haro 1976, Ambartsumian & Mirzoyan 1970).The basic difference between the Orion and Pleiades subsystems of flare stars has been known for a long time: the coexistence of flare stars and T Tau stars in the Orion association, and the absence of the latter group in the Pleiades. Some of the T Tau stars show flare activity (Haro 1964). This fact and the existence of multiple systems of trapezium type, which are dynamically unstable, in the Orion association, are arguments in favour of an evolutionary connection between these two types of stars.
Flare Star Observations with a Single-Photon Counting Imaging Detector
Authors: Casperson Donald E. , Priedhorsky William C. , Baron Miles H. , Ho Cheng 
Published: July 2016

AbstractAt Los Alamos National Laboratory we are developing a new imaging sensor which combines high spatial and high temporal resolution over a large area format, while maintaining single-photon counting sensitivity and sustaining a high count rate. The detector is called a microchannel plate with crossed delay line readout, or MCP/CDL. This detector is ideally suited to the observation of weak transient events, such as stellar flares from red dwarf flare stars in our Galaxy. At present we are initiating an experiment with the MCP/CDL detector which will utilize a 30-cm aperture f/7 telescope to characterize U-band, B-band, and V-band emission from such low-luminosity flare stars, and to search for weak optical transients associated with other astrophysical sources.
PU Vul: 15 Years of Studies, Important Findings and Remaining Mysteries
Authors: Gershberg R.E. 
Published: July 2016

In autumn 1979, the young W. Wenzel - at this time he was only 50 years old - came to the Byurakan meeting on flare stars and informed the participants about a recently discovered flaring object: the Kuwano-Honda object = PU Vul. During that time, FU Ori and related stars were the most intriguing variable objects, and PU Vul had shown some similar features such as the rate of brightening and the spectrum at maximum. It turned out to be an extremely interesting object, and the Crimean team has studied it for the last 15 years. Over this time, this team included T.S. Belyakina, N.I. Bondar, K.K. Chuvaev, Yu.S. Efimov, R.E. Gershberg, V.I. Krasnobabtsev, E.P. Pavlenko, P.P. Petrov, I.S. Savanov, N.I. Shakhovskaya, N.M. Shakhovskoy, A.G. Shcherbakov and V.A. Shcherbakov, and we collaborated with V.I. Shenavrin from Russia, with D. Chochol, J. Grygar and L. Hric from former Czechoslovakia and with V. Piirola, I. Tuominen, M. Poutanen and J. Huovelin from Finland.Now the number of publications on PU Vul approaches one hundred. It was established that PU Vul is a symbiotic nova, the object among the known variables of this type, whose explosion became observable most recently (with the possible exception of Wakuda’s object in Sgr, Grebel et al. 1994), and many details have been observed from the very beginning of the flare. I intend to list the most interesting findings and the most intriguing remaining mysteries of PU Vul.
UBVRI Photometry of AE Aquarii in July-August 1994
Authors: Beskrovnaya Nina , Ikhsanov Nazar , Bruch Albert , Shakhovskoy Nikolaj 
Published: July 2016

The most striking feature of the close binary system AE Aqr is its unique photometric behaviour - irregular alternations of quiet and active phases without noticeable transition periods. Although extensive photometric observations of AE Aqr have been carried out for more than forty years (see Bruch 1991 and references therein), the mechanism of its flaring activity is still poorly understood and the star - although generally classified as a cataclysmic variable - does not fit well into any of the subclasses.According to us, much insight into this peculiar object can be gained by an investigation of the connections between the flaring activity of AE Aqr and the strictly periodic oscillations at 33s, identified as the spin period of the primary. The latter have been seen in optical (Patterson 1979) and UV light (Eracleous et al. 1994), in X-rays (Patterson et al. 1980) and in TeV γ rays (Meintjes et al. 1992). There are contradictory reports about the relation between their amplitude and the flaring activity in AE Aqr: Patterson (1979) noted that the amplitude of the pulsations increases during active phases, while Eracleous et al. (1994) observed that their characteristics are not strongly affected by the flares.
Gamma-ray Bursts: Observational Overview, Searches for Counterparts, and BACODINE
Authors: Fishman G.J. , Barthelmy S. 
Published: July 2016

AbstractThe basic pioperties of γ-ray bursts are reviewed. Many of these properties have been known for over two decades, although new and more detailed observations have been made by Compton Observatory in the past three years. The new observation with the greatest impact has been the observed isotropic distribution of bursts along with a deficiency of weak bursts. This is not compatible with any known Galactic population of objects.The observation of a γ-ray burst counterpart in another wavelength region has yet to be made, even though there have been substantial efforts in this pursuit from a wide variety of observations in many wavelength regions. Perhaps the greatest chance for a simultaneous or rapid observation of a γ-ray burst counterpart lies with the newly-developed BAtse Coordinates Distribution NEtwork (BACODINE) system. The objectives and characteristics of this system are described.
Pulsation and Evolution. An observer’s viewpoint
Authors: Waelkens C. 
Published: July 2016

AbstractWe review observational evidence on the interaction between stellar pulsation and evolution. We discuss to what extent observations of pulsating stars with variable amplitudes and pulsation periods have implications on our understanding of stellar structure and evolution. The probable link between mass loss and pulsation in AGB stars and in hot luminous stars appears to be the strongest way in which pulsations affect evolution. We point out the possibility that forced oscillations in the components of binaries may have important consequences on evolution, that could offer an explanation for some classes of peculiar evolved objects.
Seismological Properties of Evolutionary Delta Scuti Models Using OPAL Opacities
Authors: Guzik Joyce A. , Bradley Paul A. 
Published: July 2016

AbstractWe present the first results of our project of calculating the evolutionary and seismological properties of δ Scuti models using Livermore OPAL opacities. We calculate the radial and low-degree nonradial nonadiabatic pulsation frequencies for a 1.8 and 2.0M⊙ model. Our radial first overtone/fundamental mode period ratios are × 0.772, which agree well with observed period ratios. We find a dense spectrum of unstable nonradial modes including both low order g-type modes and low to intermediate order p—type modes, confirming that we need a selection mechanism allowing only some modes to grow to observable amplitudes.
Mira Variables: Theory versus Observation
Authors: Wood P.R. 
Published: July 2016

AbstractThe identification of the mode of pulsation of Mira variables remains a major problem. Recent angular diameter measurements of solar neighbourhood Miras suggest large radii consistent with first overtone pulsation. On the other hand, the pulsation velocity amplitudes of Mira variables point to fundamental mode pulsation. There is some marginal evidence from multiple modes in Miras that the prime pulsation mode is the first overtone, while distinct (K,logP) sequences in the Magellanic Clouds point to the Miras being fundamental mode pulsators. The above confusing evidence is presented and discussed. Finally, the (K,logP) relations in the SMC and LMC are compared in order to determine if there is any metallicity dependence.
Cepheids and LPVs in and around Magellanic Cloud Clusters
Authors: Sebo K.M. , Wood P.R. 
Published: July 2016

AbstractV and I band CCD photometry of the young clusters NGC 330 (SMC), NGC 1850, NGC 2058 and NGC 2065 (LMC) has been used to find variable stars in and around the clusters. The variables detected are mostly Cepheids and long-period variables (LPVs). Here we outline some results of these studies.
HST UV Observations of the Disk and Wind of V795 Her
Authors: Rosen S. R. , Prinja R. K. , Drew J. E. , Mason K. O. , Howell S. B. 
Published: July 2016

AbstractHST UV observations of V795 Her reveal a strong 2.6-h orbital variation in the prominent UV lines, in contrast to earlier (IUE) evidence of a 4.8-h period. Only the C IV line contains a strong blue-shifted, wind formed absorption component. Several lines exhibit a ‘narrow’ absorption feature near rest velocity which may originate in the disk, and a blue-shifted emission feature which accounts for most of the line profile variability.
On the Turbulent Viscosity Prescription in Accretion Discs
Authors: Godon Patrick 
Published: July 2016

AbstractThe validity of the standard α viscosity prescription in turbulent accretion discs is analyzed. It is found that the α viscosity prescription is no longer valid when the disc is not Keplerian. The analysis is based on simple scaling arguments for fully developed turbulences in accretion discs. An analytical treatment is carried out for geometrically thin, non-Keplerian discs in vertical hydrostatic equilibrium, and is compared with the standard values of the viscosity in the boundary layer region and with the viscosity prescription derived from a general causal equation for the evolution of the stress tensor.
Mass and Angular Momentum Flows in Magnetic CVs
Authors: King A. R. 
Published: July 2016

AbstractI review recent progress in understanding the accretion geometry and angular momentum flows in magnetic CVs. The recent discovery that AE Aqr is an ejector demonstrates that the criterion for disc formation depends on the spin rate of the white dwarf, in addition to the strength of its magnetic field. It seems likely that AE Aqr represents one phase of a cyclic evolution followed by magnetic CVs. An important consequence is that an observed white dwarf spin rate is not uniquely determined by current properties of the system (e.g. magnetic field and instantaneous accretion rate), but also by its history.
The Possible Contribution from the Accretion Disk During the Quiescence of VW Hyi
Authors: Huang M. , Sion E. M. , Hubeny I. , Cheng F. H. , Szkody P. 
Published: July 2016

AbstractWe have re-analyzed UV spectra of the dwarf nova VW Hyi during its quiescence, obtained with the Faint Object Spectrograph (FOS) on Hubble Space Telescope (HST), by considering the possible contribution from the accretion disk, which was not included in the previous analysis.
VW Hyi: A Rapidly Cooling White Dwarf?
Authors: Gänsicke Boris T. , Beuermann Klaus 
Published: July 2016

AbstractWe estimate the post-outburst cooling time-scale of the white dwarf in VW Hyi, using the available quiescent IUE spectra. The determination of the white-dwarf temperature close to the outburst is hampered because disc emission still contributes to the SWP flux.
Classical Nova Evolution: Clues from Soft X-Ray Emission
Authors: MacDonald James 
Published: July 2016

AbstractMulti-wavelength observations have shown that, after optical decline, the stellar remnants of classical nova outbursts evolve at constant, near-Eddington, bolometric luminosity to high effective temperature (> 2 105 K), before turning off. Here we briefly review the observations of classical novae in this phase of evolution, and discuss what the soft X-ray observations tell us about the mass of the underlying white dwarf and the rate of mass change due to stellar winds and accretion from the stellar companion.
Accreting White Dwarfs and type Ia Supernovae
Authors: Livio Mario , Branch David , Yungelson L. R. , Boffi Francesca , Baron E. 
Published: July 2016

AbstractThe question of the possible progenitors of supernovae Type la (SNe la) is examined. It is argued that SNe la are thermonuclear explosions of accreting C-O white dwarfs. The existing observational evidence favors somewhat models in which the exploding star ignites carbon upon reaching the Chandrasekhar mass. A careful examination of all the potential progenitor classes reveals that when realization frequencies are combined with a variety of observational charcteristics, no single class emerges as containing the obvious progenitors. It is argued that coalescing white dwarfs or supersoft X-ray sources are the most likely progenitor systems. A few critical observations which could help identify the progenitors unambiguously are discussed.
Relativistic Iron Kα Emission in Seyfert Galaxies
Authors: Nandra K. 
Published: July 2016

AbstractEvidence is presented for widespread relativistic effects in the central regions of active galactic nuclei (AGN). A sample of 18 Seyfert 1 galaxies observed by ASCA show iron Kα emission which is resolved, with mean full width at half maximum (FWHM) ~ 50,000 km s−1 for a Gaussian profile. However, many of the line profiles are asymmetric. A strong red wing is indicative of gravitational redshifts close to a central black hole, and accretion-disk models provide an excellent description of the data. Such observations probe the innermost regions of AGN, and arguably provide the best evidence yet obtained for the existence of supermassive black holes in the centers of active galaxies.
The HST Sample of Radio-Loud Quasars: Emission Lines from Lyα to Hβ
Authors: Wills Beverley J. , Brotherton M.S. , Wills D. , Thompson K.L. , Baldwin J. A. , Carswell R. F. , Browne I.W.A. , Netzer H. , Francis P.J. 
Published: July 2016

We have obtained HST and ground-based spectrophotometry of a sample of ~61 radio-loud quasars from shortward of Lyα to longward of Hβ. The aim was to investigate the dependence of quasar properties on orientation of the central engine axis to the observer’s line of sight. As an approximate measure of inclination we use the radio core-dominance, i.e., the ratio of beamed radiocore emission to the emission in the extended lobes at 5 GHz rest frequency. About half the radio sources have core-dominance greater than unity (jet or axis pointed close to our line of sight). Quasar pairs were matched in radio lobe luminosity and redshift to reduce bias caused by strong dependences on intrinsic luminosity.Observation and reduction techniques were standard, and the spectral resolution is equivalent to 230–400 km s−1 (Wills et al. 1993). We have performed correlation analyses among emission-line and continuum parameters, as well as spectral principal-component analyses (SPCA, Francis et al. 1992).
Complete Atlases of Recalibrated Archival HST FOS Spectra of Quasars and AGN
Authors: Pesto S. , Koratkar A. , Blitz E. , Evans I. N. 
Published: July 2016

The ionization structures of AGNs are determined by the specific ionization mechanisms and the shapes of the ionizing continua. The technique of using emission-line intensity ratios to classify objects and investigate their ionization mechanisms is enhanced significantly by combining high-quality UV and optical spectrophotometry. The HST archive is an excellent source of such data.The FOS spectra are recalibrated using the latest ‘average inverse sensitivity’ (AIS) calibration. This new method for flux calibrating FOS data (1) normalizes count data from all apertures to the 4”.3 aperture to account for changes of aperture throughput as a function of the Optical Telescope Assembly focus; (2) corrects the data for time-dependent detector sensitivity degradation; and (3) scales the data to the white-dwarf reference scale. The AIS calibration method has been developed over a period of several years, with improvements applied progressively based on observed deficiencies and/or discrepancies of the existing calibrations. Indeed, the final AIS calibration incorporates corrections in the wavelength overlap regions of adjacent gratings derived based on inconsistencies discovered as a result of this study of over 1000 FOS spectra.
First Results of Optical Monitoring of 3C 390.3
Authors: Dietrich M. , O’Brien P.T. , Leighly K. M. 
Published: July 2016

In late autumn 1994, the International AGN Watch started a multiwavelength monitoring campaign on 3C 390.3, the first radio-loud AGN to be selected for high temporal-resolution monitoring from the radio domain to X-ray energies. This AGN is is of particular interest since significant variations have been observed on both short and long time scales in both the line fluxes and line profiles (Barr et al. 1980, Veilleux & Zheng 1991).In the optical, spectroscopic data and broad-band flux measurements in B, V, R, and I were obtained. The brightness of 3C 390.3 was calculated relative to the stars in the field. The R magnitudes are based on observations recorded at Calar Alto, Spain, in 1994 December. Generally, AGN spectra are intercalibrated using narrow forbidden emission lines since these lines can be taken as constant on time scales of decades (Peterson 1993). Since the [O III] λλ4959, 5007 flux is variable on time scales of several months (Zheng et al. 1995), these lines were studied in detail. We found that they were constant within ~2% during 1995 (Dietrich et al. 1996). The spectra were therefore intercalibrated by using the narrow forbidden emission lines. 3C 390.3 was also observed with IUE for 14 months (O’Brien et al. 1996) and with ROSAT for nine months in 1995 (Leighly et al. 1996). Radio data were also obtained during a 3-month MERLIN campaign.
C IV λ1549 Emission-Line Profile Variations in AGN
Authors: Türler Marc , Courvoisier Thierry J.-L. 
Published: July 2016

AbstractWe study the C IV λ1549 emission-line profile variations in 18 Seyfert 1-type objects observed with the IUE satellite from 1978 to 1991. The core and the two wings of the line are integrated separately in order to study differences between the wings and the core and between the blue and the red wings. A principal component analysis is applied to spectra of each object. The results suggest the presence of a significant infall component in the line-emitting region of several AGN.
A New Luminosity Effect in QSO Spectra
Authors: Corbin Michael R. , Boroson Todd A. 
Published: July 2016

AbstractComparison of the emission-line and continuum parameters of 48 low-redshift QSOs reveals the asymmetry of the C IV λ1549 broad emission line to be strongly correlated with ultraviolet continuum luminosity, such that increasing luminosity produces increasing redward asymmetry. A similar correlation has been found for broad Hβ. Redward profile asymmetries can be modeled as the result of the gravitational redshift of line photons from the very broad-line region (VBLR) by 109–1010M⊙ black holes, but blueward profile asymmetries require a competing effect such as electron scattering.
Coronal Lines from the BLR, NLR, and ENLR
Authors: Wagne Stefan J. 
Published: July 2016

AbstractWe discuss kinematical evidence that highly ionized (‘coronal’) lines are emitted from gas sharing the same velocity field as the BLR, NLR, and extended NLR. A close correlation between ionization potential and line width and blueshift with respect to systemic velocity suggests a hot outflow being responsible for the emission of coronal lines. This outflow is probably connected to the warm absorber observed in X-rays and the outflowing radio plasma. The high degree of ionization is dominantly due to photons from the blue bump but contributions from shocks are indicated in at least some of the sources observed.
Near-Infrared Imaging Spectroscopy of the Seyfert Nucleus of the Circinus Galaxy
Authors: Maiolino R. , Thatte N. , Kroker H. , Gallimore J.F. , Genzel R. 
Published: July 2016

The Circinus galaxy is a nearby (4 Mpc) spiral that hosts a Seyfert nucleus as deduced by the emission of intense coronal lines (Oliva et al. 1994) and by the prominent ionization cone observed in [O III] images (Marconi et al. 1994).We present K-band imaging spectroscopy of the nucleus of this galaxy obtained by means of 3D, the MPE imaging spectrometer (Weitzel et al. 1996), and ROGUE, a first-order adaptive-optics system (Thatte et al. 1995), mounted on the 2.2-m ESO telescope. The spectral resolution is 1000 and the average optical seeing was about 0”.6 (= 12 pc at the source).