bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Variable Stars in NGC 6723
Authors: Menzies John 
Published: July 2016

Abstract*.A study has been made of the variables in the Southern Hemisphere globular cluster NGC 6723, which is suspected of being relatively metal-rich on the basis of its colour-magnitude diagram and of its integrated spectral type of G3. Seven new RR Lyrae stars and two bright red, probably semiregular, variables have been found and the suspected variable of Fourcade and Laborde has been confirmed. The complement of RR Lyrae stars is now 27, consisting of 4 c-type and 23 ab-type variables, the mean periods being Pc = 0.d292 and Pab = 0.d537. On the basis of the two-colour diagram of the horizontal branch stars the cluster is considered to be virtually un-reddened. Applying Christy’s models to the data from this study we find the following parameters for the variables: Mv= 1.m10, mass = 0.42 M⊙, and Y=0.4.
Photometric astrometry of minor planets
Authors: Mulholland J. Derral , Nather R. Edward 
Published: July 2016

AbstractThe technique of timing occultation or eclipse events with high-speed photometers, which we shall call “photometric astrometry”, has been used by Evans, Nather, Silverberg and others to obtain lunar occultations with millisecond resolution, to reduce the observation of occultation reappearances to a routine event, to measure the diameter of Io and the diameter and flattening of Jupiter. We propose the possibility of a concerted program to use this technique for the determination of asteroid dimensions and shapes. It appears reasonable to expect that a single observatory could observe about ten events per year in which a sizeable minor planet occults a star that is three magnitudes fainter or less. Such events could be timed to about 10 msec. The development of inexpensive, portable equipment would greatly increase the number of possible events to be observed. Such equipment could open this activity to sophisticated amateur observers, similarly as in the grazing occultation program.
Meteoric storms and formation of meteor streams
Authors: Sekanina Zdenek 
Published: July 2016

AbstractMeteoric storms must be very young formations, since planetary perturbations disperse any dense cloud of meteoroids within several revolutions around the sun. It is shown that, by comparing the dates of appearances of the storms of a meteor stream with the return dates of the parent comet, insight can be gained into the problem of the origin and early evolution of such a stream. Applying a recent theory of particle ejection from comets, we have developed a formula relating the character of motion of a cloud of meteoroids to the circumstances of ejection.Practical application of the method to the Leonid, Perseid and η-Aquarid storms indicates low mass density of cometary meteoroids (not more than 0.3 g/cm3), ejection velocities of tens to hundreds of meters per second (with water vapor as the drag force), and suggests that meteoroids are ejected from periodic comets predominantly after perihelion. This finding contrasts with observational evidence of the type II tails of ‘new’ dust-rich comets. It is concluded that the discrepancy may actually reflect structural differences between the ‘new’ and periodic comets.
Systematic Radio-Observations of UX Arietis: Analysis of Its Variability
Authors: Torricelli-Ciamponi G. , Neidhöfer J. , Massi M. , Chiuderi-Drago F. 
Published: July 2016

UX Arietis is an active binary system with an orbital period of 6.44 days. The presence of long lasting large spots on the surface of the more active star has been deduced from optical observations (Vogt & Hatzes 1991).The observations presented here have been performed from December 1992 until October 1994 using the Effelsberg 100 m telescope. The instrument was available for this program in the gaps between previously scheduled observations. For this reason our observations span a frequency interval between 1.4 GHz (21 cm) and 43 GHz (7 mm), depending on the scheduled receiver at each observing time. These data, which are an extension of those published by Neidhöfer et al. (1993), are shown in Fig. 1, plotted in terms of the known orbital period (6.44 days). The search for different periodicities (by using the Phase Dispersion Minimization method) has shown the existence of two main other periods: at 156 days and at 24 days (Massi et al., in preparation).
A Possible Discovery of a Flaring 1012 eV Gamma-Ray Source near the Red Dwarf EV Lac
Authors: Alekseev I.Yu. , Chalenko N.N. , Fomin V.P. , Gershberg R.E. , Kalekin O.R. , Neshpor Yu.I. , Stepanian A.A. 
Published: July 2016

During the 1994 coordinated observations of the red dwarf flare star EV Lac, the star was monitored in the very high energy (VHE) γ-ray range around 1012 eV with the Crimean ground-based γ-ray telescope GT-48. This telescope consists of two identical optical systems (Vladimirsky et al. 1994) which were directed in parallel on EV Lac.The detection principle of the VHE γ-rays is based on the Čerenkov radiation emitted by relativistic electrons and positrons. The latter are generated in the interaction of the γ-rays with nuclei in the Earth’s atmosphere that leads to an appearance of a shower of charged particles and γ-quanta. The duration of the Cherenkov radiation flash is very short, just about a few nanoseconds. The angular size of the shower is ∼ 1°. To detect such flashes we use an optical system with large area mirrors and a set of 37 photomultipliers (PMs) in the focal plane. Using the information from these PMs which are spaced hexagonally and correspond to a field of view of 2°.6 on the sky, we can obtain the image of an optical flash. The electronic device permits us to detect nanosecond flashes (40 ns exposure time and 12 μs readout dead-time).
Multifrequency Analysis of a UV Ceti Flare on 1991 December 31
Authors: Stepanov A.V. , Fürst E. , Krüger A. , Hildebrandt J. , Barwig H. , Schmitt J.H.M.M. 
Published: July 2016

AbstractAn analysis of optical, radio and X-ray observations of the flare of December 31, 1991 on UV Ceti is presented. Radio spikes at 4750 GHz are interpreted in terms of both ECM and plasma emission. Resulting parameters of the flare plasma are discussed.
Photometric Behaviour of the EXors V1118 Orionis and V1143 Orionis
Authors: Paul C. , Kroll P. , Lehmann T. 
Published: July 2016

AbstractWe investigated the long-term photometrical behaviour of the EXors V1118 Ori and V1143 Ori on the basis of the Sonneberg Plate Archive. About 2800 plates were checked for outbursts of these stars. We found several dozens of plates where the stars appeared to be distinctly brighter than the plate limit. To get magnitudes we have scanned those plates and applied a special method of brightness determination which is currently used at Sonneberg Observatory. Because of the small number of plates we were able to extract only crude estimates of some typical time scales of outburst and quiescent phases.
Spectral Variability and Photometric Behaviour of the Symbiotic Nova PU Vul in 1985-1994
Authors: Efimov Yu.S. , Gershberg R.E. , Savanov I.S. , Shcherbakov A.G. , Shcherbakov V.A. 
Published: July 2016

We present preliminary results of observations of the Hα, HeI 5876 and NaI D lines profiles in spectra of PU Vul. The variability of profiles is confronted with the photometric behaviour. The observations were carried out with a CCD camera, installed in the coudé spectrograph of the 2.6 m Shajn telescope. 68 spectra of the Hα line and 25 spectra in the region of the HeI and NaI lines were obtained.Fig. 1 (left panel) presents the evolution of the Hα line from 1985 to 1994, displaying selected typical profiles in different years. The profiles are shown in a heliocentric wavelength scale and in logarithms of intensity. Variations of line intensity, line width, as well as radial velocity of the centre of weight of the total emission and absorption components are observed.Stronger and more complex variability is observed in the region of the HeI and NaI D lines. The strong P Cyg type absorption in the NaI D lines during 1985-1987 disappeared in later spectra as a result of total ionization of NaI (Fig. 1., right panel). Contrary to that behaviour, HeI 5876 shows variations from a pure absorption profile to a very strong and wide emission profile.
X-ray Bursts
Authors: van Paradijs Jan , Lewin Walter H.G. 
Published: July 2016

An X-ray burst is a sudden increase (rise time of order seconds) of the X-ray brightness of an X-ray source, which after reaching its peak decays, generally within a minute. The sky distribution of X-ray burst sources indicates that they are galactic objects (see Fig. 1); their concentration to the direction of the galactic center tells us that they lie at typical distances of ∼ 8 kpc, with corresponding peak luminosities of order 1038 erg s−1. The X-ray and optical properties of the persistent emission of X-ray burst sources show that they are low-mass X-ray binaries, in which mass is transferred from a rather normal low-mass (< 1 M⊙) star to a neutron star. The persistent emission is caused by the conversion of kinetic energy of the transferred matter into heat, at a rate of ∼ GM/R (∼ 0.1c2) per gram of accreted matter. The bursts are caused by unstable thermonuclear burning of material that has accumulated on the neutron star (‘thermonuclear flash’).The global properties of X-ray bursts, in particular their dependence on the mass accretion rate, are fairly well understood. Different from the case of γ-ray bursts (see the contributions by Fishman, Hartmann and Kouveliotou to this Colloquium) the relevant question about X-ray bursts is not ‘What are they?’, but rather ‘What use are they?’. As we will argue here, X-ray bursts may provide us information on the mass and radius of a neutron star. This usefulness of X-ray bursts derives from the fact that the burst emission originates from the surface of the neutron star, unlike the persistent emission caused by mass accretion, of which we only know that it comes from the neutron star’s near vicinity.
Nova Patrol at Abastumani
Authors: Kimeridze Givi N. , Kurtanidze Omar M. 
Published: July 2016

The Schmidt telescope (360-333-625 mm) of the Abastumani Astrophysical Observatory has been used for photographic observations for more than fifty years. It provides a field of 7°.3 (80 mm) and a non-vignetted field of 4° (44 mm). A limiting magnitude of 16m.5 can be reached in 7-8 min exposure on medium sensitivity astronomical films and 18m with fine grain emulsions.Multicolour and polarization observations of a few hundred relatively bright galaxies were carried out by M. Vashakidze during the first two decades of the telescope operation. In the mid-1950s, he also discovered the strong polarization of the Crab nebula. Since 1961, systematic photographic observations are carried out in the framework of the International Cooperation Programme of Supernova Patrol in 24 fields. The telescope is also used to study the brightness variations of eruptive and exploding variable stars.
EUV Emission Sources in Gas-Dynamic Models of Stellar Flares
Authors: Livshits M.A. , Katsova M.M. 
Published: July 2016

A stellar flare model in which the main energy release is located above the chromosphere based on a set of elementary acts of the electron acceleration or impulsive heating of plasma is discussed. The response of the chromosphere to impulsive heating for both a single burst and the simultaneous effect of a set of the bursts is considered.The results of numerical modeling of the process of explosive evaporation of the stellar chromosphere allow us to select 3 classes of EUV emission source: (1) the bursts of the EUV emission in the temperature range of 3 · 104 – 3 · 105 K at the beginning of each of elementary act of the energy release; (2) the bursts of the EUV emission at temperatures T ≈ 106 K, accompanied by outflow of heated plasma; (3) the EUV emission, caused by new features of the process, namely, when the maxima of the distribution of the pressure are forming in the region of the downward-moving thermal front.The properties of the EUV sources, velocities of the plasma motions therein, and possible behaviour of the light curve for an elementary burst are discussed.
Recent Developments in Stellar Pulsation Theory
Authors: Gautschy A. 
Published: July 2016

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractUltraviolet 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

AbstractDuring 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

AbstractTwo 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

AbstractSpectrophotometric 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.
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

AbstractWe 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.
Miras and Galactic Populations
Authors: Mennessier M.O. , Luri X. , Figueras F. , Torra J. 
Published: July 2016

AbstractIn 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

AbstractWe 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.
The Nova-Like Variables
Authors: Dhillon Vik 
Published: July 2016

AbstractWe 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

AbstractWe 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.
Spectrophotometry of 106 To-Be-Confirmed CVs
Authors: Zwitter Tomaž , Munari Ulisse , Bragaglia Angela 
Published: July 2016

AbstractWe 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

AbstractI 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

AbstractWe 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

AbstractA 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

AbstractSeveral 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.