bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Four Channel Photoelectric Photometer
Authors: Walker G. A. H. , Hill G. , Morris S. C. 
Published: July 2016

AbstractA simultaneous four channel photoelectric photometer has been used successfully by astronomers at the Dominion Astrophysical Observatory in the past three years to measure the colours of some 2000 stars. The optics consist of a small grating spectrograph with quartz lenses. Windows in the focal plane of the camera isolate four spectral regions and the light is fed to separate EMI photomultipliers. The photometer is not designed for very faint star observations, consequently D.C. techniques are used. Although the photomultipliers are not refrigerated, a 2 per cent precision is possible in the measurement of the colours of a star of V = 12 in a 1 min integration with a 16-inch telescope. Provided stars are bright relative to the sky background, measured colours are insensitive (±001) to transparency variations of up to three magnitudes caused by normal light cloud. The outputs of the photomultipliers are integrated on capacitors and timing is controlled by a crystal oscillator. An integrator and associated control circuitry are shown schematically in Figure 1. The integrators are read automatically by a digital voltmeter and the results together with time and other data are punched out on paper tape. A block diagram of the data acquisition system is given in Figure 2. After conversion of the tape to a card deck the data is processed in the computer. The system has proved to be very stable and mean errors in single observations of each colour are between 0004 and 0007. The most time consuming part of the process is in the careful editing and sieving of the results for erroneous data generated by line voltage spikes, mispunches, and observer mistakes.
The Performance of GALAXY
Authors: Pratt N. M. 
Published: July 2016

The GALAXY measuring engine was designed for the automatic measurement of glass photographic plates taken with Schmidt telescopes. These plates contain the negative images of tens of thousands of stars, with image sizes from 15 μm upwards. To carry out this task GALAXY works in two modes: search phase and measurement phase.In search phase, GALAXY scans preset areas of the plate with a spot of light from a CRT in a linear raster scan. The transmission through the plate is monitored and each time the light spot crosses a star image, the reduction in transmission is recorded. The coordinates of the star are derived to a nominal accuracy of 16 μm and these coordinates output to paper tape.
To the Explanation of the Intrinsic Polarization of the Light of Some Red Long Period Variables
Authors: Friedemann CH. 
Published: July 2016

Summary:The time dependent polarization of the light of some red long period variables can be explained using the simple model of the oblique rotator. Near the magnetic poles the dust, particles in the outer layers of the stellar atmosphere could be aligned in the magnetic field by the DAVIS-GREENSTEIN mechanism. For the stars VCVn, L2 Pup, R Leo and R Peg the spatial orientation of the rotational axis, the angle between the magnetic poles and the rotational axis and the period of the revolution of the magnetic poles around the rotational axis were derived from the observational material. The proposed hypothesis gives an explanation of the essential observational facts concerning the intrinsic polarization of some of the red variables.
Applications of the Dollfus Polarization Modulator in Stellar Polarimetry
Authors: Tinbergen J. 
Published: July 2016

„An astronomer is someone to whom a factor of 10 is important, but a factor of 2 is not.“ If we agree about this, we may say that stellar polarization is 1% and that we wish to measure that polarization to l% accuracy. Polarimeters therefore need an accuracy of 0,01 % (of the total intensity).In general, stellar polarimetry has been rather a delicate measurement. This is because its nature is differential, i. e. the information required is the small difference between two large observables. There are two general classes of polarimeter, single-detector and two-detector. In the single-detector polarimeters the observables are measured one after the other by the same detector and time-varying attenuations cause errors. In two-detector polarimeters, differences between the two channels cause errors. In both cases extreme stability is required. The solution is to use the single-detector type, but to alternate between the two observables faster than any of the time-varying attenuations. This type of polarimeter uses some sort of polarization modulation.
Radio Observations of Flare Stars
Authors: Wilson A. J. 
Published: July 2016

Observations of the radio emission from the red dwarf flare stars in the solar neighbourhood have been made at Jodrell Bank since 1958. In Australia, observations have been made both of these flare stars and of the early type flare stars in stellar aggregates. Observations in both Britain and Australia have been hampered by the difficulties involved in obtaining radio and optical coverage at the same time.In the initial Jodrell Bank programme, at a frequency of 240 mhz, between 1958 and 1960, 474 hours of observations were obtained, mostly on UV Ceti, and 13 events compatible with bursts of radio emission from the star were seen, but due to poor seeing conditions at the Cambridge Observatories the correlation between radio and optical flares could not be established, although the rate of occurence of radio events was similar to the reported rate for optical events of a few magnitudes.
Variable X-Ray Sources
Authors: Kellogg Edwin M. 
Published: July 2016

There are at least five types of variable galactic X-ray sources (i. e. „stars“) known:
Pulsar, as NP0532Transient Sources as Cen XR-2Quasi-periodic rapid variables, as Cyg X-1Periodic rapid variables, as Cen X-3Aperiodic variables, as Sco X-1
On the Radiation Mechanism of Pulsars
Authors: Grewing M. , Heintzmann H. 
Published: July 2016

AbstractIt is assumed that pulsars are rotating neutron stars surrounded by a strong dipolar magnetic field, the dipole axis being inclined with respect to the rotation axis. It is further assumed that the intense low frequency electromagnetic waves generated under such circumstances can indeed propagate. It can then be shown that charged particles interacting with such outgoing spherical waves are very efficiently accelerated to relativistic energies. During the acceleration which is almost instantaneous the particles emit a short duration pulse which resembles the observed emission characteristics of pulsars.
Observational selection and statistics of asteroids
Authors: Kiang T. 
Published: July 2016

In statistical studies of asteroids we usually deal with the osculating elementsa, e, π, i, Ω, and either the mean opposition magnitudem0or the absolute magnitudeg. We deliberately overlook the remaining osculating element, the mean anomaly at epoch, because we are not normally interested in the relatively fast changes in the complexion of the system brought about by the Keplerian motion; rather, we are concerned with the average complexion where each asteroid is replaced by a ring with aline densityρinversely proportional to the orbital speed. As is well known, Gauss used such rings to calculate secular inequalities, but here we give them a probabilistic interpretation:ρ. dλ is to be taken as the probability that an asteroid with given values of the elements is found in some particular range dλ of heliocentric longitude. We therefore putwhere dMis the interval in the mean anomaly corresponding to dλ. The function ρ is known from elementary theory of elliptical motion, but is rather complicated to write out explicitly.
Recent estimates for the mass of Jupiter based on minor planets
Authors: Klepczynski W. J. 
Published: July 2016

AbstractA survey of recent determinations of the mass of Jupiter based on analyses of the motions of minor planets is presented. The minor planets which were used in these investigations have their mean motion commensurable to Jupiter’s mean motion in the ratio 2: 1, 3:2 and 5: 2. A weighted mean value for the reciprocal mass of Jupiter of 1047.364 ±0.005 (me) is derived. Suggestions for future considerations are presented.
VLBI Observations of Flares in RS CVn Binary Systems
Authors: Trigilio Corrado , Umana Grazia , Migenes Victor 
Published: July 2016

RS Cvn systems have been studied very extensively at radio wavelengths and a large fraction of them have been found to be strong radio sources, with 6 cm radio luminosities in the range between 1015 and 1018 erg s−1. The radio flux density is highly variable and it usually shows two different regimes: active periods, characterized by a continuous strong flaring which can last for several days, and quiescent periods, during which the flux density goes down to a few mJy. These characteristics indicate the non-thermal nature of the radio emission which is driven by magnetic activity of these systems, seen in other spectral regions. In this scenario, the radio flux arises from the interaction between the magnetic field of one or both components with mildly relativistic particles, i.e. gyrosynchrotron emission.Due to the erratic nature of radio flares in RS CVn binaries, most VLBI observations have been performed during quiescent periods. Only the 1983 UX Ari observation (Mutel et al. 1985), carried out during an intense outburst, allowed the first, and still the unique, hybrid map of a RS CVn binary, which revealed a core-halo morphology of the radio source.It is still not clear if the flare events are localized in very compact regions of the corona of one component or if the entire binary system is involved. VLBI measurements in both active and quiescent periods are extremely important to determine the characteristic dimensions and the structure of the radio source.
Radio Flares in HR 1099 (V711 Tau)
Authors: Umana G. , Trigilio G. , Leto G. , Catalano S. , Rodonò M. 
Published: July 2016

We present the results of the first three years of a single dish radio monitoring of HR 1099 we are carrying out using the the 32m radiotelescope at the Noto VLBI station of the Istituto di Radioastronomia of the Italian Consiglio Nazionale delle Ricerche (C.N.R.).These data, together with other observations available from literature, constitute a database which shed light on the radio emission from this system.HR 1099 tends to undergo extended periods of strong activity, interrupted by periods of low flux density level, as can be seen from the radio behaviour on a timescale of several months. The switching between flaring and quiescent periods is not random and, at the moment, it is not possible to associate a characteristic duration to each phase.
Sunspot Proper Motion and Flare Frequency
Authors: Csepura G. , Győri L. , Galal A.A. 
Published: July 2016

Flare activity of solar active regions is generally believed to depend on a sheared configuration of magnetic fields (Hagyard et al. 1984). There are cases when the shear necessary for a flare can be attributed to the emergence of a new flux in the spot group (Wang 1992). But, perhaps, a newly born active region can also influence the magnetic field configuration in a nearby active region (Poleto et al. 1993, Gesztelyi et al. 1993). In this paper we are interested primarily in the influence of a newly emerging spot group on a nearby one.The three neighbouring active regions NOAA AR 6412(B-C), 6413(A) and 6415(D) have been studied between 13-22 December 1990. White-light pictures for studying sunspot proper motion and area evolution were taken at Gyula Observing Station (Hungary), Debrecen Heliophysical Observatory (Hungary) and Helwan Observatory (Egypt). Times and positions of the flares were taken from the Solar Geophysical Data (No. 558, part 1, February 1991).
Flare Activity Among Nearby Stars
Authors: Shakhovskaya N.I. 
Published: July 2016

I selected the common objects from our Data Base on 234 UV Cet Flare Stars and Related Objects and the Third Catalogue of Nearby Stars by Gliese & Jahreiss (CNS-3). It is found that manifestation of flare activity (FA) (flares in any spectral region or photometric variability caused by spots) is observed on 143 flare stars (FS) out of the 3803 CNS-3 stars within 25 pc of the Sun with absolute magnitudes Mv from 5.2 (Sp G2 V) to 18.8 (Sp dM5e − dM6e).Magnitudes and spectra of flare stars: For each MV-interval, Table 1 gives the “mean” spectral class (Sp), the number of FS (Nf) and the portion of FS among other red dwarf stars from CNS-3 (Nf/N). Absolutely fainter stars include a higher portion of known FS. However, observational selection effects can cause this dependence, because the probability is higher to register flares over the background radiation of a faint star. The observed portion of FS among all red dwarfs from CNS-3, which are fainter than Mv=5, is about 5%.
Observations of High-Frequency Activity of EV Lacertae
Authors: Zhilyaev B.E. , Verlyuk I.A. 
Published: July 2016

The flare star EV Lac shows a wide variety of activity phenomena on a wide range of time scales. These are the well-known “classical” solar-like flares, the short-time flare events (Gershberg & Petrov 1986, Karapetian & Zalinian 1991, Tovmassian & Zalinian 1988, Tsvetkov et al. 1986, Zhilyaev 1994), and the long-duration variations caused by starspots and rotation (Petterson 1980). However, the “classical” flares are not such a frequent phenomenon as one gets used to think. As noted by Roizman & Kabitchev (1985), a considerable fraction of flares shows a complicated multipeak structure with sudden onset and decay. Their interpretation along the lines of classical models favored for solar-like flares is very problematic.Here, we report the detection of high-frequency chaotic variability (flickering) in EV Lac. Optical flickering is observed in cataclysmic binaries, and in X-rays it is observed in low-mass X-ray binaries. As a rule, flickering is an accretion phenomenon. Strange as it may seem, EV Lac as a visual binary has the analogous property.
BD+47°819, an A-type Flare Star with Peculiar Spectroscopic Variation
Authors: Wang Jun-Jie 
Published: July 2016

Stellar flares are one of the most challenging problems in astrophysics. Up to now, most of the detected flare stars are of late spectral type (e.g. UV Cet type stars etc.). Non-classical flare stars with early spectral type are very rare.Recently, an A5-type flare star BD+47°819, near the open cluster α Persei, was discovered (Wang 1993). The flare U amplitude was 1m.5 in ten minutes. The V magnitude of the star was 9m.25 during the quiescent state.On 1993 February 28 and March 1, spectroscopic observations of BD+47°819 were madewithn the 2.16 m telescope of Beijing Astronomical Observatory. A grating with a dispersion of 5nm/mm was used. Figs. 1 (a) and (b) show the observed spectra in the two nights. The exposure time for each spectrum was 15 minutes. Fig. 1 (a) shows a strange feature, an “emission line” at around 676 nm. Is this a real feature?
The Long-Term Behaviour of BY Dra
Authors: Panov K.P. , Ivanovo M.S. , Stegert J.S.W. 
Published: July 2016

BY Dra has been extensively monitored for flares and spot-modulation of brightness at the Bulgarian National Astronomical Observatory (Panov & Ivanova 1993). Its mean light level exhibited remarkable changes in the past, due to the emergence and disintegration of photospheric spots, and different cycles have been proposed for the long-term changes of the BY Dra activity. This star is still believed to be a good candidate for cyclic variations, presumably similar to the sunspot activity cycle. After a spectacular drop in brightness in 1965 — 1967, and a subsequent rise in the early 70s, the mean light remained approximately constant during 1977 - 1991. A brightening of BY Dra occurred in 1992.In Fig. 1, the light curves are shown for 1991, 1992 and 1993 in the V-band and in B — V. Phases were calculated with the ephemeris of Chugainov (1966):JD (min. light) = 2438983.612 + 3.836 · EFrom Fig. 1, it is apparent that the mean visual light, which was about V = 8.20 in 1991, increased in 1992 by 0m.10, and a further increase by another 0m.03 occurred in 1993. The phase of minimum light in 1992 indicates that the position of the spot remained approximately the same in stellar longitude as in 1991. However, in 1993 the position of the spot changed by almost half a period.
MANIA Complex – Hardware and Software for the Investigation of Optical Variability on Time Scales 10−7−102 s
Authors: Beskin G.M. , Neizvestny S.I. , Plokhotnichenko V.L. , Zhuravkov A.I. 
Published: July 2016

One of the basic astrophysical problems is the search for and investigation of brightness fluctuations of celestial objects on time scales comparable with the mean time between registered photons. To facilitate this a special mathematical formalism was developed (Shwartsman 1977, Plokhotnichenko 1983).At the Special Astrophysical Observatory, photometric equipment has been developed which allows these ideas to be explored observationally and which also allows to study light curves of astrophysical objects using classical methods.This equipment and these methods are used in the search for and study of variable objects with time resolution 10−7 s in the MANIA (Multichannel Analysis of Nanosecond Intensity Alterations) experiment. The hardware consists of a photon-counting photometer for synchronous detection in different colour bands, a specialized “time-code” converter (Quantochron 3-16), measuring photon arrival times with an accuracy of 20 ns and a PC AT 386 and DAT-cassette recorder. Our equipment allows the uninterrupted accumulation of 108 photocounts with a rate up to 375 kHz without distortions in 28 or 216 parallel channels (Zhuravkov et al. 1994). The software permits the investigation of variability on time scales 10−7 − 102 s.
Middleterm Flares in T Tau Stars of the Tau — Aur Complex
Authors: Hojaev Alisher 
Published: July 2016

Light variations of different kinds appear to be one of the characteristic features of T Tau stars. They are mainly caused by changes in the continuum radiation. The availability of large observational databases makes it possible to investigate different patterns of variability such as stochastic, quasiperiodic and quasicyclic ones with typical time scales from days to years, as well as sporadic flare and fuorlike outbursts. Recent attempts in classification of the photometric variability of PMS-stars were made by Herbst (1994). In this paper, we study the observational results on flares in T Tau and related stars belonging to the Taurus-Auriga complex, which resemble that of ordinary flare stars.A census of T Tau stars with homogeneous observations of short and middleterm flares is presented in Table 1. Our selection criteria were: pre- and postilare levels of brightness ought to be quasiquiescent; the amplitude has to be more than 3 times the value of standard error; the duration of brightening does not exceed a few hundred minutes; the lightcurve shape should be similar to that of a typical flare. For convenience, all observational data in Table 1 are divided into 3 subgroups.
Observations of Short-term Dips in the Orion Variables DD Serpentis and AB Aurigae
Authors: Verlyuk I.A. 
Published: July 2016

AbstractShort-term fadings (dips) in the range of a few seconds with amplitudes from 0m.3 to 1m.2 were discovered in the two T Orions type variables DD Ser and AB Aur. Similar features were observed in T Tau and R CrB by other observers.
Space Densities of Cataclysmic Variables and Nova Recurrence Times
Authors: Duerbeck H.W. , Covarrubias R. 
Published: July 2016

AbstractSpace densities of novae, dwarf novae and novalike stars are derived on the basis of the most recent catalogue of cataclysmic variables and improved values of absolute magnitudes. Assuming that these objects represent different stages of the same type of variable, changing over short-term cycles, we derive an average time interval of 10000 years between two subsequent nova eruptions. During this time, the cataclysmic variable remains almost 2000 years in the novalike stage and the remaining time in the dwarf nova stage, in which a total of nearly 3 · 10−5M⊙ is accreted on the white dwarf primary. This amount is comparable to the average mass of ejected nova shells.
Time Dependence of the UV Resonance Lines in the Cataclysmic Variable Star VW Hyi
Authors: Özkan M.T. , Ak T. , Saygac A.T. , Esenoglu H.H. , Guler S. 
Published: July 2016

AbstractIn this work, we study orbital variations in the ultraviolet resonance lines of the SU UMa type dwarf nova VW Hyi examining spectra in the data archive of the International Ultraviolet Explorer (IUE). We show that VW Hyi exhibits an orbital and long term variability in terms of UV line profiles and continuum flux at 1450 Å during superoutburst.
Flickering in Cataclysmic Variables: Inventory and Perspectives
Authors: Bruch Albert 
Published: July 2016

AbstractStochastic variations on short time scales called flickering are a characteristic feature in the light curves of CVs. Their amplitudes indicate that their origin must be related to one of the principle light sources of these systems. But the physical mechanism behind the flickering is unknown. New attempts to quantify the properties of flickering are presented, and a consistent scenario for its origin is outlined.
Strong X-ray Bursts with Expansion: Oscillations due to Sound Waves in Atmospheres
Authors: Lapidus Iosif , Nobili Luciano , Turolla Roberto 
Published: July 2016

Photospheric expansion has been observed during several powerful type I X-ray bursts, and it is associated with a supersonic outflow driven by the super-Eddington energy release in the thermonuclear He-burning at the base of the envelope (Lewin et al. 1993). Such expanded atmospheres represent perfect background for the propagation of sound, and we believe there is a number of arguments in favor of the reality of these phenomena.We have suggested an acoustic origin for the second range photospheric oscillations detected in the X-ray bursters 1608-522 and 2127+119 (Lapidus et al. 1994). On the basis of our models of radiation driven winds from neutron stars during strongest bursts (Nobili et al. 1994), we have shown that purely radial standing sound waves in expanded spherical envelopes can have periods very close to the observed ones. Both the photosphere and the sonic surface may act as a reflecting boundary; this is the reason of quite different periods in the two sources (0.65 s and ∼ 7 s, respectively).
Quasi-periodic Oscillations and Noise in Accreting Black Holes and Low-magnetic Field Neutron Stars
Authors: van der Klis M. 
Published: July 2016

The X-ray spectrum and the rapid X-ray variability of accreting compact objects have a common origin, and their properties can therefore be expected to be coupled. Indeed, it turns out that the X-ray spectrum and the power spectrum show correlated variations, which occur as a function of variations in the mass fluxx Ṁ.Stellar mass black holes and neutron stars have similar mass and size, and therefore their accretion phenomena may be expected to show similarities. Indeed, similarities exist that indicate that a unified description may be possible. If a particular phenomenon is seen in both neutron star and black-hole candidate systems this shows immediately that it cannot be due to any property that is unique to either neutron stars or black holes, such as the presence or absence of a surface, or of a strong non-aligned magnetic field. The quest for characteristics that are unique to black holes continues - I shall mention a few candidates below.
Optical Sky Monitoring: Past and Future
Authors: Bräuer H.-J. , Vogt N. 
Published: July 2016

AbstractAfter outlining the achievements of photographic sky monitoring at Sonneberg Observatory we describe a concept of a future CCD-based sky patrol. We suggest a world-wide network of 6 identical observing stations which cover the entire sky down to a limiting magnitude of ∼ 18TO and with a time resolution of between 8 and 24 hours. A preliminary technical design is proposed, and the astrophysical and general impact of such a project is briefly discussed.