bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mean Magnitudes and Colours of Six Cepheids in Three Red Globular Clusters of the Large Magellanic Cloud
Authors: Demers Serge 
Published: July 2016

AbstractPhotographic B and V light curves are determined for six variables, with periods longer than one day, in and near NGC 1751, NGC 1953, and NGC 2121. New photoelectric sequences are used to calibrate the plates. The mean magnitudes and colours of these variables are similar to the magnitudes and colours of Classical Cepheids of the same period. The photometric properties of these variables are unlike Population II Cepheids in the Galaxy but are comparable to field Cepheids of the Large Magellanic Cloud.
On the Two Oosterhoff Groups of Globular Clusters
Authors: Van Albada T. S. , Baker Norman 
Published: July 2016

AbstractThe observational evidence leading to the classification, following Oosterhoff, of globular clusters containing RR Lyrae stars into two distinct groups, is summarized and discussed in the light of results of stellar evolution theory and pulsation theory. The dichotomy is caused, at least in part, by a dichotomy in the ‘transition period’ between the type-ab and type-c stars which reflects a difference in effective temperature at the transition point. When this difference is accounted for, there remains a smaller average difference between the groups, though no longer a clear dichotomy, that is probably a mass and luminosity effect. If this remaining difference is interpreted as a luminosity effect the average difference in luminosity between the two Oosterhoff groups is at most 0.1 mag. It is suggested that Christy’s theoretical relationship between transition period and luminosity cannot be valid, at least not for clusters of different Oosterhoff groups. It is conjectured that the transition-temperature dichotomy may be a reflection of different predominant directions of evolution along the horizontal branch, accompanied by a hysteresis effect in the pulsations.
The Helium Abundance in the Envelopes of the Bluest RR Lyrae Stars in Globular Clusters and Dependence of Globular Cluster Variable Star Properties on Chemical Composition
Authors: Mironov A. V. 
Published: July 2016

AbstractThe helium abundance Y in the envelopes of RR Lyrae stars in globular clusters has been estimated. The values of Y range from 0.07 to 0.59. The properties of variable stars in globular clusters of two types distinguished by a type of dependence of the horizontal branch form on the chemical composition are compared. The clusters of type I are shown to be on the average poorer in RR Lyrae stars than those of type II. The RR Lyrae stars in type I clusters are on the average brighter by 0.1 mag. It is found that as Y increases, the cluster richness in W Virginis variables decreases.
On the generalized restricted problem of three bodies
Authors: Duboshin G. N. 
Published: July 2016

AbstractThe particular case of the complete generalized three-body problem where one of the body-points does not exert influence on the other two is analysed. These active material points act on the passive point and also on each other with forces (attraction or repulsion), proportional to the product of masses of both points and a certain function of the time, their mutual distances and their first and second derivatives. Furthermore it is not supposed that generally the th ird axiom of mechanics (action = reaction) takes place.One determines the conditions for some particular solutions which exist, when the three points form the equilateral triangle or remain always on a straight line.Finally, some conclusions on the Liapunov stability in the simplest cases are drawn.
Structure and evolution of the asteroid belt
Authors: Chebotarev G. A. , Shmakova M. Ya. 
Published: July 2016

AbstractInvestigations concerning the structure of the asteroid belt make it possible to distinguish four main stages in its evolution. The first stage. The formation of a certain number of protoplanets (ten-hundred) between the orbits of Mars and Jupiter, simultaneously with major planets. The protoplanets had the dimensions of the presently largest asteroids. The peculiarity of their orbits consisted of a predominance of large inclinations. The second stage. The unstable “primary” asteroid belt which came into existence as a result of mutual collisions of the protoplanets and occupied the zone with daily mean motion between 300 and 990″. Numerous close encounters of asteroids with Jupiter. The formation of planets having unusual orbits (Hidalgo, the Trojans and others). The formation of a wide gap (300–540″) which separated the stable asteroid belt from Jupiter’s orbit. The third stage. The stable asteroid belt in the zone 540–990″. The predominance of planets of “the spherical” subsystem. The formation of gaps corresponding to “acute” commensurabilities in mean motions with Jupiter. The fourth stage. The present asteroid belt occupying the zone 450–1110″. The asteroid belt gradually expanded in the direction towards the Sun. The bulk of young planets concentrating in the ecliptic plane. The total mass of the asteroid belt during the time of its existence has decreased to a fraction of its former value.
On the motion of comet P/d’Arrest
Authors: Klepczynski W. J. 
Published: July 2016

AbstractThe differences between numerically approximated partial derivatives and partial derivatives obtained by integrating the variational equations are computed for Comet P/d’Arrest. The effect of errors in the IAU adopted system of masses, normally used in the integration of the equations of motion of comets of this type, is investigated. It is concluded that the resulting effects are negligible when compared with the observed discrepancies in the motion of this comet.
the effects of resonance with Jupiter in the system of short-period comets
Authors: Kresák L̆ubor 
Published: July 2016

AbstractStructural effects of the resonance with the mean motion of Jupiter on the system of short-period comets are discussed. The distribution of mean motions, determined from sets of consecutive perihelion passages of all known periodic comets, reveals a number of gaps associated with low-order resonance; most pronounced are those corresponding to the simplest commensurabilities of 5/2, 2/1, 5/3, 3/2, 1/1 and 1/2. The formation of the gaps is explained by a compound effect of five possible types of behaviour of the comets set into an approximate resonance, ranging from quick passages through the gap to temporary librations avoiding closer approaches to Jupiter. In addition to the comets of almost asteroidal appearance, librating with small amplitudes around the lower resonance ratios (Marsden, 1970b), there is an interesting group of faint diffuse comets librating in characteristic periods of about 200 years, with large amplitudes of about±8% in μ and almost±180° in σ, around the 2/1 resonance gap. This transient type of motion appears to be nearly as frequent as a circulating motion with period of revolution of less than one half that of Jupiter. The temporary members of this group are characteristic not only by their appearance but also by rather peculiar discovery conditions.
Origin and evolution of comets
Authors: Everhart Edgar 
Published: July 2016

AbstractA Monte Carlo study is described that leads to an understanding of the evolution of comets, particularly how the short-period comets can arise. Some results have appeared in the March 1972 issue of Astrophysical Letters, Vol. 10, pages 131–135 (Paper I), but further results are presented here for the first time.This is a report of a particular study and is not a general review of the subject. References to many other papers are given in the above article. Here it suffices to mention that the author has read and profited by the excellent papers by Belyayev, Callandreau, Chebotarev, Delsemme, Dobrovolskij, Havnes, Kazimirchak-Polonskaya, Kresak, Levin, Lyttleton, Marsden, H. A. Newton, Oort, Öpik, Porter, Roemer, Russell, Sekanina, Shteins, Sitarski, Strömgren, Tisserand, Vsekhsvyatskij, and Whipple, as well as many others. Many of the ideas here are not new, but they are implemented for the first time on a really high speed computer.A fundamental assumption whose consequences are to be developed is that all comets initially approach the solar system on near parabolic orbits.
On possible mechanisxms for dust ejection from comets
Authors: Dobrovolsky O. V. 
Published: July 2016

There are three different mechanisms for dust generation in comets described in the literature on comets.First case. Simple ejection of primordial dust particles from the nucleus by outflowing gas.Second case. Creation of dust particles on the surface of the nucleus as a mineral crust is formed and destructed by mini-explosions. The crust may originate either as a result of accumulation of primordial particles or directly bear on the surface during sublimation of appropriate substances even when there are no mineral particles in the nucleus at all. Periodical mini-explosions create a quasi-continuous outflow of particles.Third case. Dust particles originate in the gas phase in the vicinity of the nucleus like soot particles in a flame as a result of condensation of carbon moleculae vapor (Dolginov’s mechanism).
The structure of meteor streams associated with Comet Halley: Eta Aquarids and Orionids
Authors: Hajduk Anton 
Published: July 2016

The association of Comet Halley with the Orionid and Eta Aquarid meteor streams is not commonly accepted at present. Southworth (1961) has determined the differences in the orbital elements of the Orionid stream and Comet Halley on the basis of 19 photographic meteors and found them to be rather large.Extensive observational material obtained since the beginning of this century, including a homogeneous series of the radar observations, carried out at the Springhill Meteor Observatory during the periods of the Orionid meteor shower activity in 1957–1967 has been used by the author (Hajduk 1971) to study the stream structure and its association with Comet Halley from a statistical point of view.The present analysis is an extension of the paper mentioned, based mainly on the radar observations of the Eta Aquarid meteor shower carried out at the Springhill Observatory during the period 1958–67. The total number of 240,000 radar meteor echoes observed in 670 hours between May 1 and May 10 during each of the years previously cited was used in this investigation. The observed variations in the hourly rates of echoes of different duration enable us to study the density distribution and size distribution of meteoric particles along and across the stream.
High-Resolution Dynamic Spectrum of a Spectacular Radio Burst from AD Leonis
Authors: Abada-Simon Meil , Lecacheux Alain , Aubier Monique , Bookbinder Jay A. 
Published: July 2016

AD Leonis is a very active, single dMe flare star. The similarities between this type of star and the Sun has led to study their radio radiation, which originates from their corona. The high brightness temperatures and other characteristics of most dMe radio bursts can be attributed to a non-thermal, coherent mechanism: plasma radiation or a cyclotron maser instability (CMI) are both plausible explanations. Even for the strongest burst of AD Leo which reached 940 mJy
at 21 cm, it was not possible to discriminate between these two mechanisms (Bastian et al. 1990).Here we present an intense burst from AD Leo, exhibiting strong spikes for which the CMI seems to be the only reasonable explanation. In Sect. 2 we describe the observations, and in Sect. 3 we give an interpretation for this event.
Coherent Radio Bursts from RS CVn Binareis
Authors: Franciosini Elena , White Stephen M. 
Published: July 2016

We present VLA observations of RS CVn binaries which indicate that the low-frequency polarization inversion usually ascribed to the quiescent radio emission of these systems is in fact due to the presence, much of the time, of a coherent burst emission. Fig. 1 shows two examples of this coherent emission in the behaviour of the light curves of HR1099 in left and right circular polarization at 1.4 GHz. The emission is highly circularly polarized, with one polarized component steady or slowly varying in a way similar to the higher frequency emission (Fig. 1a), while the other shows rapid fluctuations on timescales of ∼10s and a slower modulation on longer timescales. The similarity of the time profiles in two 50 MHz-wide sidebands 30 MHz apart indicates that the fluctuating component is broadband; moreover, the sense of polarization at 1.4 GHz is opposite to that of the quiescent emission at higher frequencies (attributed to gyrosynchrotron emission), which is exactly the behaviour attributed to the 1.4GHz quiescent emission of these systems by Mutel etal. (1987).The rapid fluctuations and high polarization are characteristic of a coherent emission process. We argue that a combination of two sources of emission is generally present at 1.4 GHz: a very highly (possibly 100%) polarized coherent component, and a weakly-polarized, steady gyrosynchrotron component. Since the polarization at higher frequencies should be the x-mode of (optically thin) gyrosynchrotron emission, we infer that the low frequency polarization probably represents the o-mode. The observed characteristics of the emission then suggest that the most likely mechanism for the highly-polarized component is plasma emission at the fundamental of the plasma frequency. Such plasma emission is relatively rare on the Sun at 1.4 GHz, but could occur in the hotter coronae of RS CVn systems because the higher temperature reduces the free-free opacity which is thought to absorb 1.4 GHz plasma emission on the Sun.
A Major Optical Flare on the Recently Discovered X-ray Active dMe Star G102-21
Authors: Pagano I. , Ventura R. , Rodonò M. , Peres G. , Micela G. 
Published: July 2016

During UBV photoelectric measurements of G102-21 - a dM3 star recently discovered as a remarkably active X-ray source by Micela et al. (1995) - we have observed the flare shown in Fig. 1 (left panel). The observed flux increase at flare maximum and the energy output (cf. Table 1) make this event one of the largest amplitude and most energetic flares ever detected on UV Cet-type stars.The ratios EU/EB (=8.9) and EU/EV (=3.9) are more than 7 and 2 times larger, respectively, than the mean values found for typical dMe flares by Lacy et al. (1976). Moreover, assuming the empirical relation between the absolute magnitude MV and the mean energy dissipation during a flare (Gurzadyan 1980), the energy released in the U band exceeds the predicted one by a factor of ∼ 3 · 103. Clearly, we observed a rather peculiar and rare event that does not appear to be a typical flare on red-dwarf stars.
Flare in Late-type Stars: UV
Authors: Brendan Byrne P. 
Published: July 2016

Early studies of stellar flares were made entirely in the optical regime. It was recognised that flares arose from the generation of hot plasma within the stellar chromosphere at whose temperature (indicated, for instance, by the presence of a strong, blue optical continuum) a substantial emission in the ultraviolet would be expected. It was not until the advent of space-borne instruments of adequate sensitivity, however, that direct confirmation of this prediction was forthcoming. In this review I examine some results of more than a decade of observation of stellar flares in the UV.The major source of ultraviolet data on stellar flares has been the International Ultraviolet Explorer (IUE) satellite (Boggess et al. 1979). In order to understand the limitations of our current understanding in this area it is important to appreciate some of the characteristics of its instrumentation. IUE’s telescope is of 40 cm aperture and it is equipped with a spectrograph which can operate at two resolutions, i.e. Δλ/λ ∼350 (LORES) and ∼17000 (HIRES). Its detectors are optimised for operation in two wavebands, i.e. ∼1150-1950Å (SW) and ∼1950-3200 Å (LW). IUE’s small apert ure results in a limited sensitivity, a consequence of which is a modest time resolution when studying stellar flares (a long exposure time is needed to gain adequate signal-to-noise). IUE’s elliptical 24-hour quasi-geosynchronous orbit and its resulting interactive mode of operation make continuous monitoring feasible, a feature suiting flare star work.
Flares in Late-type Stars: X-Ray
Authors: Pallavicini Roberto 
Published: July 2016

Flare-like brightenings, similar to those observed on the Sun but on a larger energy scale, are observed in a variety of late-type stars, including classical M dwarf flare stars, RS CVn-type binaries and pre-main sequence (PMS) objects. These events, which are observable over the whole electromagnetic spectrum, are interpreted as due to rapid release of magnetic energy at the star surface. Comprehensive reviews of stellar flares have been presented by Haisch &: Rodonò (1989), Pettersen (1991), Haisch et al. (1991), Pallavicini (1992a), as well as in contributions at this conference. Here I will discuss X-ray emission, with emphasis on flares on M dwarfs and RS CVn binaries.X-ray observations are important because they provide information on the high-temperature coronal portion of the flare and, at least in principle, could give clues as to the primary energy release and particle acceleration. In the stellar case there are severe limitations of the diagnostic capabilities of X-ray observations, in comparison to the solar case. In fact, stellar flares have up to now been observed only at soft X-ray energies (≤ 10 keV) where thermal processes greatly dominate over non-thermal ones (optical continuum observations have to be used in this case as a proxy for hard X-rays). Moreover, stellar X-ray observations are spatially unresolved and so far of poor spectral resolution. Thus, the observational data that are readily accessible are only light curves, average temperatures T and volume integrated emission measures EM = ∫ n2dV, but there is no direct information on parameters such as density, volume and detailed geometry.
Short-Duration X-ray Transients Observed With WATCH on Granat: Are Some of Them Related to Stellar Flares?
Authors: Castro-Tirado Alberto J. , Brandt Søren , Lund Niels , Lapshov Igor , Sunyaev Rashid 
Published: July 2016

AbstractDuring 1990-92, the WATCH all-sky X-ray monitor on GRANAT has discovered 6 short-duration X-ray transients. We discuss their possible relationship to peculiar stars. Only one source, GRS 1100-77 seems to be related to a T Tauri star.
ROSAT Observation of a Giant X-ray Flare on the Active Binary Algol
Authors: Ottmann R. 
Published: July 2016

AbstractROSAT/PSPC observations of a long-duration, giant X-ray flare on the eclipsing binary Algol are presented. With a total thermally radiated energy of 7 Ŀ 1036 erg, this flare is one of the largest events ever observed. The flare decay is modeled by means of the quasi-static cooling method, which yields a height of the flare loop arcade of ≃ 1RK, and a plasma density of 1011 cm−3.
ASCA X-ray Spectra of Quiescent and Flaring Emission from AB Doradus
Authors: White S.M. , Pallavicini R. , Lim J. 
Published: July 2016

The Japanese satellite ASCA carries X-ray detectors which combine excellent sensitivity and high spectral resolution. We observed the young, rapidly-rotating K dwarf AB Doradus with ASCA in November 1993. The star’s X-ray flux was essentially steady for the first half of the observation, and then a series of flares occurred during the second half. The flares showed rise times of 30 minutes and decay times of several hours. The quiescent X-ray luminosity was 2 × 1030 ergs s−1 (0.5-10 keV). At the flare peaks, LX(> 0.5 keV)/Lbol = .002.AB Dor has a relatively high count rate in the ASCA data and we can obtain high-quality spectra for different periods of the light curve. In Fig. 1 we present spectra corresponding to the period of quiescence, the rising phase and peak of each of the three flares combined, and the decay periods of each of the flares combined. The rise/peak curve (upper) has been multiplied by 2 for purposes of display. We have subtracted the quiescent spectrum from the flare spectra (i.e., used it as a background spectrum) for this display and subsequent analysis.The detailed differences between these spectra display the importance of the high spectral resolution provided by ASCA. One important difference, not readily evident in this figure, is the Fe K line complex at 6.4-6.7 keV. This line, a diagnostic of hot plasma, is strong in the rise/peak spectrum, moderate in the decay spectrum and weak in the quiescent spectrum. A time profile of the counts in this energy range shows little significant emission during the quiescent periods but strong emission at the flare peaks.
X-ray Flare Rate of T Tauri Stars in Taurus
Authors: Neuhäuser R. , Preibisch Th. 
Published: July 2016

AbstractWe study the X-ray emission of several hundred (young, low-mass, late-type, pre-main sequence) T Tauri stars (TTS) in the Taurus T association, a nearby well-studied region of ongoing star formation. We report on X-ray emission variability of TTS as observed with the flux-limited ROSAT All-Sky Survey (RASS). Since RASS observations are spatially unbiased, we can investigate the X-ray flare rate of TTS on a large sample. We find that large flares are very rare (once per year), while medium-size flares can occur once in ∼ 40 days.
Polarimetric Outbursts in Young Herbig Ae/Be Stars and in Peculiar B[e] Stars
Authors: Yudin R.V. 
Published: July 2016

Quasi-simultaneous optical and IR photometric (BVRIJHK) and optical polarimetric (BVRI) observations were carried out at the 1 m telescope of Assy Observatory (Institute of Astrophysics of the Kazakhstan Academy of Sciences). The photometer-polarimeter of the Pulkovo Observatory (Bergner et al. 1988) was used for the study. All our measurements were done with apertures of 26" and 52".HDE 259431. Our data show a strong polarimetric variability Δp = 2% – 3% and ΔΘ 30° (especially in UV and optical region). Although the general nature of polarization is connected with the dust disk around the star (Dzhakusheva et al. 1988), the polarimetric variability probably has an another origin. This is due to the fact that we have observed a strong polarimetric variability on a time-scale of up to several hours (Dzhakusheva et al. 1988). Incidentally, this rapid polarimetric variability has no correspondence in photometry.