bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Search for Spectroscopic Binaries among Southern Cepheids
Authors: Lloyd Evans T. 
Published: July 2016

AbstractA discussion of radial velocities determined at the Radcliffe Observatory for 20 southern Cepheids and those found in the literature for another 20 stars lead to the conclusion that 15% of Cepheids are members of long period binary systems (1). The observational data were heterogeneous, few stars having been observed by a single observer or with the same instrument over a sufficient length of time to detect long period variations in the mean velocity.
Photometry of Variables in Close Visual Double Stars
Authors: Franz O. G. , Millis R. L. , White N. M. 
Published: July 2016

AbstractA method of photoelectric photometry of the components of visual double stars is briefly described. Observations of ADS 9701 = δ Ser and of UV Aur = ADS 3934 B are presented to demonstrate the usefulness of this technique for the accurate photometry of variables in close visual double stars.
Variable Star Observations from outside the Earth’s Atmosphere: Review and Prospects
Authors: Kondo Yoji 
Published: July 2016

AbstractThe scientific rationale for variable star observations from outside the Earth’s atmosphere will be discussed, followed by a review and discussion of existing observational techniques with reference to their capabilities and limitations. Existing techniques to be discussed will cover aircraft-, balloon-, rocket- and satellite-borne experiments, and observations thus far obtained will also be reviewed. Experiments, planned or under consideration, and also future prospects of obtaining variable star observations from outside the terrestrial atmosphere will be discussed.
The Distribution of Variable Stars in the Galaxy
Authors: Plaut L. 
Published: July 2016

At first, I have to thank Dr. STROHMEIER sincerely for his invitation to the fifth colloquium on variable stars.After SHAPLEY recognized the variable stars as a very useful tool in obtaining the distribution of stars in the galactic system, Dr. HOFFMEISTER was one of the first to investigate the distribution of variable stars by the aid of series of photographic plates of selected regions in the Galaxy. At his observatory at Sonneberg he and his collaborators took many plates which were searched for variables and on which the brightness of these stars was estimated and their distribution studied. The results of these studies are published in a long series of papers in the Sonneberg publications.
On the Nature of the 41-Day Cycle of RR Lyrae
Authors: Detre L. , Szeidl B. 
Published: July 2016

AbstractPhotoelectric observations obtained with the 24-in. telescope of the Konkoly Observatory from 1950 to 1972 show that the amplitudes of the changes of the 0.d57 light-curve in the course of the 41-day cycle undergo considerable cyclic variations. The length of the cycles varies between 3.8 and 4.8 yr. A new cycle always begins with a large phase-shift in the 41-day period; afterwards there is generally no further shift during one 4-yr cycle. Following Julia Balázs’ hypothesis, a tentative model is suggested: The 41-day cycle is the rotation period of the star. Magnetic fields concentrated in a limited longitude zone influence the 0.d57 pulsation in such a way that variations in light amplitude and phase arise as aspect effects of the 41-day rotation period. In this way, the 4-yr cycle can be interpreted as the magnetic cycle of the star. The location of the magnetic fields strongly differs in longitude from cycle to cycle causing the observed large phase shifts at the beginning of a new 4-yr cycle.
Two-Colour Photometry of RR Lyrae Variables in NGC 6981
Authors: Dickens R.J. , Flinn Rosalind 
Published: July 2016

AbstractNGC 6981 =M72 is a globular cluster with a late-type integrated spectrum (G3) and an ultraviolet excess of δ(U–B)=0.15 ±0.05, which places the cluster in the class of intermediate-to-high metal abundance clusters such as M3. The colour-magnitude diagram shows a horizontal branch populated on both sides of the variable star region. Previous work on the periods of the variables has indicated that the cluster is of Oosterhoff type I, with ≈0.55 day. Some results from B and V photometry of 21 RR Lyrae variables are described. Original measurements of about 50 candidate variables were made, including some possible new variables found by blinking plate pairs, but crowding and background photometric problems reduced the number of variables for which reasonable quality data could be obtained with the available 100-in plate material.
Investigation of the orbital motion of comet Churyumov-Gerasimenko 1969 IV (preliminary investigation)
Authors: Belyaev N. A. 
Published: July 2016

AbstractThe motion of the short-periodic comet 1969 IV has been studied over a period of 400 years (1660–2060). During the above period the comet had as many as 13 approaches within 2.0 AU to Jupiter.The two approaches in 1840 and 1959 resulted in the transformation of the circular orbit (e= 0.1,q&gt; 4 AU) to the elliptic one (e= 0.6,q= 1. 3 AU). Because of this the comet became accessible to observations. It was discovered by K. I. Churyumov in 1969.
Outbursts of comet Schwassmann-Wachmann 1, and the cloud of interplanetary boulders
Authors: Sekanina Zdenek 
Published: July 2016

AbstractIt is suggested that the outbursts of Periodic Comet Schwassmann-Wachmann 1 are triggered by impacts of interplanetary boulders on the surface of the comet’s nucleus. The existence of a cloud of such boulders in interplanetary space was predicted by Harwit (1967). We have used the hypothesis to calculate the characteristics of the outbursts – such as their mean rate, optically important dimensions of ejected debris, expansion velocity of the ejecta, maximum diameter of the expanding cloud before it fades out, and the magnitude of the accompanying orbital impulse – and found them reasonably consistent with observations, if the solid constituent of the comet is assumed in the form of a porous matrix of lowstrength meteoric material. A Monte Carlo method was applied to simulate the distributions of impacts, their directions and impact velocities.
Solar Flares
Authors: Priest Eric R. 
Published: July 2016

AbstractThere are many types of solar flare, but the classic type is a two-ribbon flare with three phases — a preflare phase, a rise phase and a main phase. The properties of these phases are described, together with some recent observational advances in understanding the conditions for solar flares. Such flares are thought to be caused by an eruptive MHD instability which drives reconnection and therefore energy conversion. A review is given of our current understanding of the nature of this instability and the resulting reconnection process, including a recent attempt to describe its three-dimensional nature.
Flare Activity and Cluster Membership Probability of Flare Stars
Authors: Mirzoyan L.V. , Hambarian V.V. , Mirzoyan A.L. 
Published: July 2016

Mirzoyan (1976) showed that the concentration of flare stars around the center of the Pleiades cluster (Alcyone) was the same, irrespective of their proper motions. At that time, however, proper motions of only a few flare stars were known. The result was confirmed on the basis of more extensive observational material (Chavushian 1979, Mirzoyan 1983). Photographic observations of stellar flares in the general galactic field during 181 hours yielded the detection of only a single flare, i.e. the percentage of flare stars in the general galactic field is about 10% of the total number of flare stars detected in the regions of stellar clusters and associations (Chavushian 1979, Mirzoyan et al. 1988).This result shows that flare activity can be considered as a definitive cluster membership criterion, which appears to be a better one than the cluster membership probability, which is based on proper motions. To prove this, cluster membership probabilities (Stauffer et al. 1991) for 408 Pleiades cluster flare stars from the catalogue by Haro et al. (1982), are used (Table 1).
CN Com: a Typical RS Canum Venaticorum Star
Authors: Richter G.A. , Greiner J. 
Published: July 2016

CN Com = CSV 6907 was dicovered by Romano (1958). First we note that the GCVS (and Simbad) coordinates are wrong by ≈2′. Using the finding chart of Romano (1958) and the APM data (digitized POSS), the correct coordinates of CN Com are R.A.(2000.0) = 12h19m47s.0, DEC(2000.0) = +16°30′50″.CN Com is only 8″ distant from the ROSAT X-ray source RX J1219.7+1630 detected during the All-Sky-Survey at a PSPC countrate of 0.022 cts/s. Due to the positional proximity and the absence of other optical objects brighter than 20rmm within the about 30″ error circle, CN Com is very probably the optical counterpart of RX J1219.7+1630.CN Com was investigated on some 600 photographic plates (Sonneberg astrographs 400/1600 mm and 400/2000 mm) of the fields 26 Com and 5 Com, covering the time interval from 1962 to 1994 (with only a very few plates from the years 1967-1974).
A New Technique for Precise Stellar Photometry: Application to Small-Scale Activity of EV Lacertae
Authors: Zhilyaev B.E. 
Published: July 2016

AbstractA new prefiltering technique (PFT) for precise stellar photometry is described. It has been proved that the prefiltered and added high-time resolution data provide an increase in S/N ratio by factors 1.3 — 1.7 in comparison with simple integration. The PFT allows to detect event amplitudes which are comparable to that caused by counting statistics. Adopting the PFT, our observations reveal small-scale flare events in the subsecond range in EV Lac.
Post-flare Coronal Activity on AU Mic Detected by EUVE
Authors: Katsova Maria , Drake Jeremy , Livshits Moissei 
Published: July 2016

Data of long-duration emission arising after the impulsive rise and decay in a flaring event on the red dwarf star AU Mic are discussed. Intensive EUV emission in the band 65-190 Å was registered by the Extreme Ultraviolet Explorer (EUVE) after both impulses during half a day. A similar behavior of the flux in the Fe XVIII 93.9 Å line is detected after the first powerful impulse. The decay of the intensity in the 65-190 Å band and in the Fe XVIII line during this prolonged event is 10 times slower than the time of radiative cooling of coronal loops with a typical flare plasma density. Some difficulties with two explanations of this event proposed earlier are discussed. Explanation (i) - the radiation of dense loops at main phase of the flare, and (ii) - the emission of the low-dense plasma of coronal transients (CME). The temporal behavior of the emission measure is determined for both the 65-190 Å band and the Fe XVIII line fluxes. The total energy emitted in the 1-2000 Å region for the long-duration event lasting almost 12 hours is 3 · 1035 ergs. The following physical model is proposed to explain the prolonged event (Fig. 1): the source of emission is the system of high coronal loops, the size of which is more than the active region scale, but is less than the stellar radius. The temperature of the plasma in the loops decreases from 107 K slowly, during a few hours. The densities in these loops are in the range 1013 cm−3 to 5 · 109 cm−3. Such systems, when the plasma therein becomes cool, are observed in the Hα line during large solar flares (for instance, June 15, 1991) after CME. Some additional post-flare energy input into this high coronal loop systems can be caused by the reconnection in vertical current sheet, and this post-eruptive energy release provides prolonged and intensive EUV emission.Apparently, we are faced here with a new kind of surface activity on late-type stars which is intermediate between impulsive flares on red dwarfs and long-duration, powerful events on subgiants, which are components of RS CVn binaries.The full version of this contribution will be published in Astronomicheskij Zhurnal (Astronomy Reports), 1995, Vol. 72.
X-ray Variability of the Flare Star CC Eri
Authors: Pan H.C. , Jordan C. 
Published: July 2016

The flare/spotted spectroscopic binary star CC Eri (HD 16157) was observed in the periods 1990 July 9-11 and 1992 January 26-27 with the ROSAT PSPC detector (Pan and Jordan 1995). These high quality data give the first information on the temporal and spectral variability of CC Eri in the X-ray energy band.During the ROSAT observations the X-ray intensity of the source is variable on timescales from a few minutes to several hours. The X-ray luminosity is in the range 2.5 – 6.8 × 1029 erg s−1, which is similar to values found from previous measurements with the Einstein IPC and EXOSAT LE. On 1990 July 10 an X-ray flare-like event was detected with an exponential rise time of about one hour and a decay time of about two hours. The X-ray spectrum of CC Eri can be described by current thermal plasma codes with two temperature components or with a continuous temperature distribution. The spectral results show that plasma at Te ∼ 107 K exists in the corona of CC Eri. We find that the X-ray spectrum is also variable and the variations of the emission measure, and to a lesser extent of the temperature, are correlated with the source intensity.
X-ray Observations of the dMe Star EQ1839.6+8002 in 1980-1993
Authors: Pan H.C. , Jordan C. , Makishima K. , Stern R.A. , Hayashida K. , Inda-Koide M. 
Published: July 2016

During Ginga observations of galaxy 3C390.3 on 1991 February 14, a large impulsive flare was detected between 22:30-23:00 UT (Inda et al. 1994). Inda et al. (1994) suggested that the flare was associated with EQ1839.6+8002, an M4Ve star at a distance of 15.2 pc (Fleming et al. 1988). The star has been observed previously with the Einstein IPC and EXOSAT LE (Gioia et al. 1990; Grommi et al. 1991), and more recently with the ROSAT PSPC.In this paper we present the results of an analysis of the observations of EQ1839.6+8002 with Ginga and of the data obtained with the Einstein IPC (between 1980 January and May), the EXOSAT LE (in 1984-1986), and the ROSAT PSPC instruments (in 1991 March, 1992 April and 1993 April).
Magnetic Field Reconnection as a Possible Source of Nonthermal Processes in Accreting Relativistic Systems
Authors: Pustil’nik L.A. 
Published: July 2016

Recent observations of the EGRET-telescope aboard the Compton Gamma Ray Observatory (CGRO), results from Čerenkov shower telescopes, and fast variability studies have demonstrated the dominant role of nonther mal processes for some accreting relativistic objects. This is perhaps an unex pected result, because the basic assumption of the standard accretion models (Shakura & Sunyaev 1973, Sunyaev & Titarchuk 1980, Galeev et al. 1979) is the thermal nature of all processes that determine the energy output. At the same time, the recent observations argue that the source of the emission is not the thermal plasma as a whole, but a very small fraction of charged particles accelerated to very high energy (ε/mc2 > (30-1000) with a “universal” energy spectrum nε ∣ ε−α. These observational results suggest a revison of the global approach to the accretion process to find any new (or forgotten “old”) energy conversion mechanisms with predominately nonthermal output (Lynden-Bell 1969, Ikhsanov & Pustil’nik 1994).The nature of the energy source and mechanisms of energy conversion to either plasma heating (“thermal” mode) or to acceleration of charged particles (“nonthermal” mode) is the main question for accretion theories.
Properties of X-ray Flares on Young Stars
Authors: Preibisch Th. , Neuhäuser R. 
Published: July 2016

AbstractThe interest in the giant flares found on young stars results from the fact that their energetics is vastly different from solar flares. The recent ROSAT observations of young clusters yield a good basis for a systematic study of these flares.We have investigated 18 very deep pointed observations of star forming regions in IC348, Chamaeleon, ρ Ophiuchi, and Orion. To study the age dependence of the flare properties we also investigated the observations of the young clusters IC2391, Pleiades, and Hyades. In this way we have evaluated the X-ray emission of several hundred young stars with ages ranging from about 106 years to 7 ń 108 years. We have found 36 large flares on identified cluster members and have determined the flare properties with a simple flare model.The flares show the same relation between the total X-ray flare energy and the quiescent X-ray luminosity as the dM star flares. The total X-ray flare energies decrease smoothly from the very high values found for very young stars to solar values with increasing cluster age. Our results indicate that the large flares on young stars are similar to scaled-up solar-like activity rather than to accretion processes.
Hydrogen and Helium Flashes in Cataclysmic Variables
Authors: Kato Mariko 
Published: July 2016

AbstractLight curve analysis for the decay phase of novae gives estimates of the white dwaif mass, the luminosity (or distance) and the chemical composition of ejecta. Differences in these parameters among nova subclass, i.e. fast, slow and recurrent, are briefly summarized to speculate on their cause. Helium shell flashes occur in mass-increasing white dwarfs, their theoretical light curves are given in UV and visual wavelength bands. An evolutional scenario for fast, slow and recurrent, and slow novae through a helium nova/EUV source-stage toward a type Ia supernova/neutron star formation-stage is given.
Detection of Nonthermal Optical Flashes with 10−3-10−1 s Duration from Some LMXBs
Authors: Beskin G.M. , Neizvestny S.I. , Mitronova S.N. , Plokhotnichenko V.L. , Popova M. Yu. , Benvenuto O.G. , Feinstein C. , Mendez M. , Bartolini C. , Guarnieri A. , Minarini R. , Piccioni A. 
Published: July 2016

In order to study very rapid optical variability of astrophysical objects on time scales between 10−7 s and 102 s (Shvartsman 1977), at SAO the MANIA (Multichannel Analysis of Nanosecond Intensity Alterations) experiment is being used. A special photometric registration system and software has been developed (Beskin et al. 1982’ Plokhotnichenko 1983, Zhuravkov et al. 1994).One of the applications of these tools is the detection of radiation from accreted or ejected plasma near compact objects. A choice between two models of accretion onto compact objects in binary systems - hydrodynamic flow or magnetc flaring (Shakura & Sunyaev 1973, Pustil’nik & Shvartsman 1974) has not yet been made. Recent optical and X-ray observations of X-ray binaries provide information on their (fast) variability, their nonthermal radio emission, generation of very high energy particles, and nonthermal processes in rapid optical flares (Bartolini et al. 1994, Beskin et al. 1994). However, the data are not fully described by classical hydrodynamical models.
Deep Search for Optical Counterparts of Gamma-ray Bursters
Authors: Sokolov V.V. , Kopylov A.I. , Kurt V.G. , Zharykov S.V. 
Published: July 2016

AbstractPreliminary results are presented of the first (searching) stage of our observational program of the search and study of weak blue star-like objects in the two small γ-ray burst boxes GB 790418 and GB 790613. The basic search purposes are (1) the selection of star-like objects weaker than 23m inside these boxes, (2) the selection of the bluest ones in B — V among these objects. The first result is the fact that there are no blue (with B — V < 0) star-like objects brighter than 24m in both boxes. But in each of these GRB error boxes one blue object with smaller flux was selected for further study to elucidate their nature. In the smallest of the archival GRB error boxes (GB 790613) obtained by three satellite triangulation, the bluest star-like object with V = 24.56(±0.16) and B — V = −0.20(±0.19) is near the center (at the distance < 10") of the GRB box. In the GB 790418 error box, the bluest star-like object with B = 24.40(±0.20), B — V = −0.40(±0.40) is found at ≈50" from the center.
Wide-field X-ray Optics
Authors: Hudec René , Inneman Adolf , Pina Ladislav , Řehák Petr , Gorenstein Paul 
Published: July 2016

AbstractClassical X-ray mirror optics usually has a limited Field of View (FoV) of ∼ 1°. Wide-field imaging can be achieved by lobster-eye type reflecting X-ray optics. We summarise several different approaches and suggest an innovative technology for the production of X-ray reflecting flats and cells necessary to develop one- or two-dimensional wide-field X-ray optics. The technology is based on double-sided, replicated reflecting foils produced by electroforming and CF/composite technologies.
Solar EUV Rocket Telescope and Spectrograph (SERTS) Observations of Fe XII Emission Lines
Authors: Keenan F.P. , Thomas R.J. , Neupert W.M. , Foster V.J. , Greer C.J. , Tayal S.S. 
Published: July 2016

Abstract.Theoretical electron density sensitive emission line ratios involving transitions in the 186–383 Å wavelength range are compared with observational data for a solar active region and a subflare, obtained by the Solar EUV Rocket Telescope and Spectrograph (SERTS). Electron densities derived from the majority of the ratios are consistent with one another, and are also in good agreement with the values of density estimated from diagnostic lines in other species formed at similar temperatures to Fe XII. These results provide observational support for the general accuracy of the diagnostic calculations. In addition, our analysis indicates that a line at 283.70 Å in the active region spectrum is the 3s23p32D3/2−3s3p42P1/2 transition in Fe XII, the first time (to the best of our knowledge) that this line has been identified in the solar spectrum. Several of the line ratios considered are predicted to be relatively insensitive to the adopted electron temperature and density, and the generally good agreement found between theory and observation for these provides evidence for the reliability of the SERTS instrument calibration. The application of the Fe XII diagnostics to EUVE observations of the F5 subgiant Procyon is briefly discussed.
Mode Identification of the β Cephei star BW Vulpeculae
Authors: Aerts C. , Van Hoolst T. , Mathias P. 
Published: July 2016

AbstractWe identify the pulsation mode of BW Vul by means of both the moment method and the method of photometric amplitudes and find a radial pulsation. We briefly study the non-linear behaviour of BW Vul.
Dust Formation and the Doubly-Periodic Variable Stars
Authors: Evans T. Lloyd 
Published: July 2016

AbstractThe doubly-periodic semiregular variable V Hydrae became redder and developed resonance emission lines and bands during the 1992-94 deep minimum, which therefore resulted from the production of a circumstellar dust cloud. This removes the need to postulate a secondary pulsation period, ten times as long as the main pulsation period, in the stellar as opposed to circumstellar envelope.
Cepheids in the Magellanic Clouds
Authors: Welch D.L. , Alcock C. , Bennett D.P. , Cook K.H. , Allsman R.A. , Axelrod T.S. , Freeman K.C. , Peterson B.A. , Quinn P.J. , Rodgers A.W. , Griest K. , Marshall S.L. , Pratt M.R. , Stubbs C.W. , Sutherland W. 
Published: July 2016

AbstractIn the past few years, the Magellanic Clouds have been the targets for several major variable star surveys. The results of these surveys are now becoming available and it is clear that a Renaissance in LMC and SMC variable star research will result. In this review, I will describe the results of such surveys and review the questions that are likely to be answered by further work.With respect to results, I will concentrate on LMC MACHO Project data, including beat Cepheids, discovery statistics, mode identification, Fourier decomposition of lightcurves, and the differences between the LMC and galactic sample.