bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Boundary Conditions for Solar Magnetic Hydrodynamic Flows Using the Method of Characteristics
Authors: Wu S. T. , Wang A. H. , Guo W. P.
Published: July 2016

We discuss the self-consistent time-dependent numerical boundary conditions on the basis of theory of characteristics for magnetohydrodynamics (MHD) simulations of solar plasma flows. The importance of using self-consistent boundary conditions is demonstrated by using an example of modeling coronal dynamic structures. This example demonstrates that the self-consistent boundary conditions assure the correctness of the numerical solutions. Otherwise, erroneous numerical solutions will appear.
On the Out of Phase Appearance of Large-Scale Diffuse Magnetic Field of the Sun with Respect to Sunspots
Authors: Dikpati Mausumi , Choudhuri Arnab Rai
Published: July 2016

We assume the large-scale diffuse magnetic field of the Sun to originate from the poloidal component of a dynamo operating at the base of the convection zone, whereas the sunspots are due to the toroidal component. The evolution of the poloidal component is studied to model the poleward migration of the diffuse field seen on the solar surface and the polar reversal at the time of sunspot maxima (Dikpati and Choudhuri 1994, 1995).
Detection of Langmuir Solitons: Implications for Type III Burst Emission Mechanisms at 2ωPE
Authors: Thejappa G. , Stone R.G. , Goldstein M.L.
Published: July 2016

We present the experimental verification of existing theoretical models of emission mechanisms of solar type III bursts at the second harmonic of the plasma frequency, ωpe. This study is based on the detection of Langmuir and envelope solitons by the Ulysses spacecraft inside three type III burst source regions. We show that the oscillating-two-stream instability, coherent radiation by Langmuir solitons and stochastic phase mixing of the Langmuir waves in the strong turbulence regime are the appropriate emission mechanisms at 2ωpe.
Solar Particles Seen by Ulysses Near 33°S
Authors: Tappin S.J. , Simnett G.M.
Published: July 2016

Observations of a particle event (electrons >40 keV; ions >50 keV) at heliographic mid-latitudes are presented. The particles are shown to originate from an apparently insignificant solar source and to be stored prior to release into the solar wind.
Discovery of Active Galactic Nuclei in Mid- and Far-Infrared Deep Surveys with ISO
Authors: Taniguchi Yoshiaki
Published: July 2016

We present a summary on the discovery of active galactic nuclei in mid- and far-infrared deep surveys with use of the Infrared Space Observatory.
A New MIR/submm Diagnostic for Dust-Enshrouded AGN
Authors: Haas Martin
Published: July 2016

We show that the PAH 7.7μm to continuum 850μm flux ratio can be used to reveal high mid-infrared extinction in ultraluminous infrared galaxies (ULIRGs). While the submm radiation is optically thin and represents the emission from essentially all dust grains, the PAH strength (measured by the peak height of the Polycyclic Aromatic Hydocarbonates at 7.7μm) is sensitive to dust extinction in the mid-infrared (MIR). As an application of the new diagnostic, after dereddening of the central MIR continuum and with the assumption of a disk-like dust distribution seen under a tilted angle, we find increasing evidence for a hidden quasar in the archetypal ULIRG Arp220.
Surveys of Parsec-scale Radio Structures in AGN
Authors: Gurvits L.I.
Published: July 2016

Several recent global and Space VLBI surveys of quasars and other types of AGN provide a wealth of material on milli- and sub-milliarcsecond radio structures in hundreds of sources. Results of these projects are presented with an emphasis on the statistics of redshift- and angular-scale-dependent properties of the milli- and sub-milliarcsecond radio structures. These studies make possible disentanglement of intrinsic (possibly, evolutionary) phenomena of parsec-scale radio structures and the imprints of the cosmological model.
Radio AGN Surveys
Authors: De Breuck Carlos , van Breugel Wil , Röttgering Huub , Carilli Chris
Published: July 2016

We present a short overview of radio surveys for AGN, including the ‘complete’ flux limited surveys and ‘filtered’ surveys. We also describe our ultra-steep spectrum search for the highest redshift radio galaxies, and our follow-up VLA and ATCA observations of the most distant (z = 5.19) and the most luminous z <2 radio galaxy known.
AGN From the Perspective of New Approaches in Astrophysics
Authors: Iskudarian S.G.
Published: July 2016

In all probability, AGN are one of the most convincing observable gleams of the Superforce in the Universe.
Helical Structures in Seyfert Galaxies
Authors: Moiseev A. V. , Afanasiev V. L. , Dodonov S. N. , Mustsevoi V. V. , Khrapov S. S.
Published: July 2016

Seyfert galaxies with Z-shaped emission filaments in the Narrow Line Region (NLR) are considered. We assume that observable Z-shaped structures and the velocity pattern of the NLR may be explained as tri-dimensional helical waves in the ionization cone.
Correlation of Optical and X-ray Radiation of NGC 4151 and 3C 390.3. Preliminary Results
Authors: Novikova Olga A. , Bochkarev Nikolai G.
Published: July 2016

The correlation of optical and X-ray radiation of some AGN is studied. We used low signal-to-noise data from the All-Sky Monitor of the Rossi X-ray Timing Explorer (2-10 KeV) and broad-band photometry of the optical continuum obtained mainly during the last several years through the "AGN Watch" program.
The evolution of the Kuiper belt during the formation of the outer planets
Authors: Melita M.D. , Brunini A.
Published: July 2016

A self-consistent study of the formation of planetary bodies beyond the orbit of Saturn and the evolution of Kuiper disks is carried out by means of an N-body code where accretion and gravitational encounters are considered. This investigation is focused on the aggregation of massive bodies in the outer planetary region and on the consequences of such process in the corresponding cometary belt. We study the link between the bombardment of massive bodies and mass depletion and eccentricity excitation.
The long term evolution of Atens and Apollos
Authors: Dvorak R.
Published: July 2016

In this review we report on the investigations of the long term dynamics of the Near Earth Asteroids (NEAs). In the first part some theoretical results concerning the dynamical structure of the NEA belt are explained. We then present our knowledge of the long term evolution of the orbits of NEAs for time intervals up to several million years which were derived by extensive numerical integrations. An interesting point of investigation is the steady flux from the Atens to the Apollos and vice-versa which is caused primarily by close encounters with the Earth and Venus. We also report the results concerning the probability of collisions of the NEAs with these planets. Finally the possible capture of such objects into Trojan-like orbits − thus moving in a 1:1 resonance with one of the inner planets − is discussed.
Veritas family age revisited
Authors: Knežević Z.
Published: July 2016

A progess report is given for the project of redetermination of the estimate of an upper limit to the age of the Veritas asteroid family, derived originally by Milani and Farinella (1994). The results obtained so far are consistent with the conjecture of a young age of this family (< 100 Myr).
How many binaries are there among near-Earth asteroids?
Authors: Pravec P. , Wolf M. , Šarounová L.
Published: July 2016

The near-Earth asteroids 1991 VH, 1994 AW1and (3671) Dionysus have been identified as binary systems. They are similar each to other in some of their characteristics. This leads us to a suggestion that there is present a similar mechanism of their creation and/or evolution and that there exists a sizeable population of binaries among NEAs. From a simple geometric model, we estimate that a probability that a binary system with the characteristics similar to the three binaries contains signs of occultation/eclipse phenomena in its lightcurve (thus allowing a detection of the binarity) in particular geometric conditions ispocc~0.30. Then, the actual number of binary NEAs present in a studied sample of NEAs isN =10+8-5. Since the studied sample of NEAs contains effectively 59 objects, we estimate that ∼ 17% of NEAs are binary, this value is uncertain by a factor 2, however.
Brightness of long-period comets at large heliocentric distances: II. The computer catalogue for 1945-1957
Authors: Svoreň J.
Published: July 2016

The paper is a compilation of more than 3500 magnitude estimates of 20 long-period comets observed at the heliocentric distances larger than 2.5 AU with the well determined orbits which passed the perihelion from 1945 to 1957. This is the second part of the catalogue of long-period comets. The first part (covering 1861-1941) was published in the Planet. Space Sci. The compilation is continuing up to date and after finishing it will be a supplement to the short-period CLICC/A catalogue compiled by Kamél and ICQ archive compiled by Greenet al.The list contains dates of observations, apparent brightness of the comets and the types of magnitudes, methods, diameters of objectives and the light-gathering powers of the telescope used, types of instruments, names of observers and references to the original literature as well as the calculated values of the heliocentric and geocentric distances and phase angles. The collected brightness data formed a basis for study systematic corrections among various observers, instruments and methods, for construction of photometric curves, perihelion asymmetry study, calculation of dimensions of cometary nuclei, study of interrelations between dynamical and physical parameters, and many others. The catalogue exists only in computer version and can be obtained from the author by e-mail.
What happened with the comet 71P/Clark?
Authors: Szutowicz S.
Published: July 2016

Discovered in 1973, 71P/Clark had made only five revolutions around the Sun. The motion of the comet has been subjected to a constant small deceleration between 1973 and 1989 and then a dramatic jump in the nongravitational perturbations occured. To explain the discontinuity in the comet's nongravitational effects a change in the surface distribution of active areas and a nucleus orientation was considered. The model of discrete source of out gassing was employed in the orbital calculations. From numerical fitting of the model parameters to positional observations the spin-axis orientation, localizations and outgassing areas of two active regions have been derived and the orbit successfully improved. The nucleus radius was estimated as equal to 0.76 km.
The gravity influence of the regular and irregular Galaxy field on the stability of the Oort cloud
Authors: Chujkova N.A. , Nagoga M.A. , Maximova T.G.
Published: July 2016

The problem of the determination of the tidal influence of the Galaxy gravity field on the equilibrium of the Solar system boundary zone is investigated. The coordinates of regions with maximum time and space variations of the tidal influence are determined. These regions may be the possible sources of young comets. The frequencies of the periodical movements of the Solar system, caused by both the total Galaxy gravity field and the internal field of the nearest stars, are determined. The hypothesis explaining the coincidence of the periods of the Solar system oscillation and the geodynamic activity by the increase of the comets passing near the Sun-Earth is presented.
Stellar Flare Spectral Diagnotics: Present and Future
Authors: Foing Bernard H.
Published: July 2016

Stellar spectral diagnostics are of utmost importance to test fundamental concepts of flare physics such as particle beam versus suprathermal heating, atmospheric response, mass motions, microflaring, statistics and recurrence of flares, flare activity and stellar interior. We review some of these diagnostics (from photometry, optical, and ultraviolet spectroscopy at medium- and high-spectral resolution, X-ray, and radio observations). Specific diagnostics from line and continuum fluxes, density sensitive lines, broadening and velocity field effects and the comparison with semi-empirical models are also described.

Some results on stellar flares obtained from previous multi-wavelength observing campaigns are presented. Future satellite missions and ground-based observatories, with new techniques for obtaining high spectral and temporal resolution, are discussed in light of their possible contribution to our understanding of solar and stellar flares.
The Role of Eruption in Solar Flares
Authors: Sturrock Peter A.
Published: July 2016

This article focuses on two problems involved in the development of models of solar flares. The first concerns the mechanism responsible for eruptions, such as erupting filaments or coronal mass ejections, that are sometimes involved in the flare process. The concept of ‘loss of equilibrium’ is considered and it is argued that the concept typically arises in thought-experiments that do not represent acceptable physical behavior of the solar atmosphere. It is proposed instead that such eruptions are probably caused by an instability of a plasma configuration. The instability may be purely MHD, or it may combine both MHD and resistive processes. The second problem concerns the mechanism of energy release of the impulsive (or gradual) phase. It is proposed that this phase of flares may be due to current interruption, as was originally proposed by Alfvén and Carlqvist. However, in order for this process to be viable, it seems necessary to change one's ideas about the heating and structure of the corona in ways that are outlined briefly.
Cyclotron Lines in the Spectra of Solar Flares and Solar Active Regions
Authors: Zheleznyakov V. V. , Zlotnik E. Ya.
Published: July 2016

It was shown by Zheleznyakov and Zlotnik (1980a, b) that in complex configurations of solar magnetic fields (in hot loops above the active centres, in neutral current sheets in the preflare phase, in hot X-ray kernels in the initial flare phase) a system of cyclotron lines in the spectrum of microwave radiation is likely to be formed. Such a line was obtained by Willson (1985) in the VLA observations at harmonics of the electron gyrofrequency. This communication interprets these observations on the basis of an active region model in which thermal cyclotron radiation is produced by hot plasma filling the magnetic tube in the corona above a group of spots. In this model the frequency of the recorded 1658 MHz line corresponds to the third harmonic of electron gyrofrequency, which yields the magnetic field (196 + 4) G along the magnetic tube axis. The linewidth Af/f ∼ 0.1 is determined by the 10% inhomogeneity of the magnetic field over the cross-section of the tube; the line profile indicates the kinetic temperature distribution of electrons over the tube cross-section with the maximum value 4 x 106 K. Analysis shows that study of cyclotron lines can serve as an efficient tool for diagnostics of magnetic fields and plasma in the solar active regions and flares.
Recent Computer Installations at the Hale Observations
Authors: Dennison Edwin W.
Published: July 2016

Approximately two and a half years ago we started to design a comprehensive computer controlled system to handle data and control telescopes at the Hale Observatories. Our previous experience with hard-wired digital data systems had adequately demonstrated that digital systems can increase the astronomical observer’s efficiency by at least a factor of two, that is, we had found that our observers, when using these digital data systems were able to observe twice as many stars per night as they had previously. We became painfully aware of the fact that the hard-wired systems were extremely difficult to modify for new observing requirements. It therefore appeared logical to develop a data system using a small computer which had the facility of permitting the addition of a large number of new devices without modifying the hardware which had been previously constructed. This concept has the advantage that new observing instruments can be added by constructing new hardwire peripheral devices and developing new software. During the development time of a new device it is always possible to insure that the instrument can be returned to its previous configuration by loading the computer with its previous program. This permits an observer to use the same equipment configuration for a period of years even though the capability of the basic system has been greatly enlarged.
Computer Control of the Vacuum Solar Telescope
Authors: Dunn Richard B.
Published: July 2016

The Vacuum Solar Telescope has been described elsewhere by Dunn (1964, 1969). A brief summary of its characteristics is included here as background for discussing the computer control of this instrument.

This telescope is altazimuth in design. Image rotation is accomplished by rotating the inner tube structure together with all the auxiliary instruments. Azimuth and elevation torque motors drive the two mirrors at the top of the tower to track the sun automatically. The inputtothe servo is derived from a photoelectric guider. When clouds intervene, the servos are switched from the photoelectric guider to an electromechanical coordinate converter that also generates the signal for the rotation of the table. An elaborate 25: 1 synchro system connects the mirror servos to the coordinate converter.
A Four Channel Photoelectric Photometer
Authors: Walker G. A. H. , Hill G. , Morris S. C.
Published: July 2016

A 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.
Photoelectric Astrometry
Authors: Villamediana J. Francisco , Fredrick Laurence W.
Published: July 2016

Improvement of astrometric accuracy is a major need of astrophysics today. A significant increase in the amount of information about the masses of stars, parallaxes, and proper motions is to be gained. Some improvements have been accomplished in the last few years such as the astrometric reflector like the 61-inch at Flagstaff, (K. Strand, 1967), and the McCormick 40-inch (under construction). Another direction of improvement has been automation of measuring devices such as the Strand Measuring Engine and the Grant Measuring Engine; but one of the large improvements of the future ought to be observations outside the Earth’s atmosphere to the level of diffraction limited images instead of seeing limited images. The concentration of light in a smaller image will then mean both a fainter magnitude reached and a high astrometric accuracy.
The Design and Development of the GALAXY Machine
Authors: Walker G. S.
Published: July 2016

The requirement for a machine of the GALAXY type arose from the large amount of information made available by the photographic plates from Schmidt telescopes. Even a small telescope of this type will produce many thousands of well-defined images per square degree on a single plate. Previously only a few selected images could be measured for position or magnitude in order to keep pace with the production of plates.
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

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.
Models for R Coronae Borealis Stars
Authors: Biermann P. , Kippenhahn R.
Published: July 2016

If we believe in the spectral analysis of the atmospheres of RCrB stars these objects should have a pure helium envelope slightly enriched in carbon (SEARLE 1961, DANZIGER 1965). However, they cannot be homogeneous helium stars since in that case they should be on the helium main sequence in the Hertzsprung-Russell-diagram, whereas they are found in the region of late supergiants. Their internal chemical structure must therefore be more complicated than that of a homogeneous helium star. From the viewpoint of stellar evolution the next degree of complexity would be to have a carbon-oxygen core.
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.
New Flare Stars in the Pleiades Region
Authors: Pigatto L. , Rosino L.
Published: July 2016

In a series of previous papers (ROSINO, 1966; ROSINO-PIGATTO, 1969; PIGATTO-ROSINO, 1971) we have given some results on the systematic search of flare stars in clusters and associations carried out at Asiago with the 90—67 cm Schmidt telescope. We have employed for the survey Kodak 103 a—o or oa—o plates without filter covering a field of 25 square degrees, the flares having been searched with the method of multiple exposures.
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 NP0532

Transient Sources as Cen XR-2

Quasi-periodic rapid variables, as Cyg X-1

Periodic rapid variables, as Cen X-3

Aperiodic variables, as Sco X-1
Variable Radio Emission from X-Ray Sources
Authors: Braes L. L. E. , Miley G. K.
Published: July 2016

Dr. KELLOGG has just described some exciting new observations of X-ray sources made with the UHURU satellite. We shall now move some nine orders of magnitude in wavelength to the opposite end of the electromagnetic spectrum and report measurements of weak radio emission from some of the objects he mentioned. For the detection of weak sources most radio telescopes are not noise limited, but are confusion limited by their low resolution. The aperture synthesis technique minimizes this problem because it enables one to pinpoint the position of weak sources to the order of one second of arc.
On the Radiation Mechanism of Pulsars
Authors: Grewing M. , Heintzmann H.
Published: July 2016

It 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.
The Effect of Binary Motion on Period Changes in RRLyrae Stars
Authors: Coutts Christine M.
Published: July 2016

The present investigation is to determine what apparent period changes if any, would result from binary motions. In particular it is important to know whether or not such apparent period changes could be mistaken for intrinsic period changes caused by evolution.
Variable Stars in Dwarf Spheroidal Galaxies
Authors: Agt Steven Van
Published: July 2016

Interest in dwarf spheroidal galaxies is motivated by a number of reasons; an important one on the occasion of this colloquium is the abundance of variable stars. The theory of stellar evolution and stellar pulsations is now able to predict from theoretical considerations characteristic properties of variable stars in the colour-magnitude diagram (Iben, 1971). By observing the variable stars in the field, and in as wide a selection of objects as possible, more insight can be obtained into the history of the oldest members of our Galaxy (the globular clusters) and of the dwarf spheroidal galaxies in the Local Group. It is worthwhile to explore the spheroidal galaxies as observational tests for the theoretical predictions of conditions in space away from our Galaxy. The numbers of variable stars in the dwarf spheroidal galaxies are such that we may expect well-defined relations to emerge once reliable magnitude sequences have been set up, the variable stars found, and their periods determined. Six dwarf spheroidal galaxies are presently known in the Local Group within a distance of 250 kpc. In Table I, which lists members of the Local Group, they are at the low-luminosity end of the sequence of elliptical galaxies (van den Bergh, 1968).
Observational Aspects of RR Lyrae Variables in Globular Clusters
Authors: Rosino L.
Published: July 2016

RR Lyrae variables play a prominent role in many of the problems of globular clusters, and from several points of view. In the first place they can be considered as pretty good indicators of population and distance; although they do not form a completely homogeneous set of stars, the knowledge of their mean absolute magnitude gives a powerful means of establishing distances within and outside the Galaxy, and hence of determining the form and size of the Galaxy itself. Moreover, the number of RR Lyrae stars in clusters, the relative frequency of RRc and RRab, types, the length of the transition periods, the array of colors, when correctly interpreted, give important information on the degree of evolution, age and chemical composition of the clusters. Placed as they are in a peculiar region of the H — R diagram of Population II, the RR Lyr variables can be used as a good test of the theories of advanced evolution or the models of pulsating stars.
Period Changes as Evidence for Evolution in ω Cen
Authors: Belserene Emilia Pisani
Published: July 2016

Much has been said at this colloquium to the effect that observed changes in the periods of variable stars are so fast or so abrupt or so quick to change sign that they cannot possibly be attributed to stellar evolution. If you are wondering how this report can dare to make a contradictory claim read the title carefully. It does not promise that there really is evidence for evolution in Omega Centauri. It only proposes to look at the period changes with evolution in mind. We may all decide that the evidence is strong or that it is weak or perhaps that there is no evidence at all.
Short Period Variables in the Magellanic Cloud Cluster NGC 1466
Authors: Norris M. V.
Published: July 2016

NGC 1466 (α1950 = 3h44.m6, δ1950= -71°45’) is a globular cluster which appears to be situated between the two Magellanic Clouds. Previous estimates (Gascoigne, 1966) put it at roughly the same distance from us as the LMC, so it is regarded as a member of the Cloud system. It is globular in appearance, and its colour-magnitude diagram confirms this classification. It has a fairly well-developed horizontal branch, and was found by Wesselink (1970) to be quite rich in variables. The metallicity index, Q, (van den Bergh, 1967) has a value of -0.36 for NGC 1466 (Andrews and Lloyd Evans, 1971). This would rank it with M5 and NGC 6171 as a cluster of intermediate metal content. This comparison is consistent with the value of Δ V for the cluster, which, at 2.m6, is representative of the Δ V values of globular clusters of intermediate metal abundance in the Galaxy.
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 put

where 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

A 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.
A note on a peculiarity in the distribution of the argument of perihelion
Authors: Kiang T.
Published: July 2016

In his sampleD, consisting of 60 orbits withe> 0.30, Kresák (1967) noted that the distribution of the argument of perihelionωis peculiar in that it has pronounced maxima around 90° and 270°. This peculiar feature is not expected from theπand Ω-distributions for the same sample: the former shows an enormous excess around 0° while the latter has a barely significant one around 135°; their convolution cannot produce the observed maxima as regards both amplitude and phase. (The grossly non-uniform distribution ofπin Kresák’s sampleDis as one would expect from the theory of secular perturbation, cf. Kiang 1966).
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%.
Some Results of the Coordinated Observations of the Red Dwarf Flare Star EV Lac in 1986-1994
Authors: Gershberg R.E.
Published: July 2016

In 1986-94 a series of coordinated monitorings for the flare star EV Lac has been performed. The observations were aimed to collect homogeneous data on the star both in its active and quiet states, to study its flares and starspots. These photometric patrols were accompanied by monitorings of EV Lac of different other kinds: polarimetric, spectral, radio, UV and high energy studies. In total, these monitorings covered a range from decametre radio wavelengths through IR, optical and UV windows up to very high energy γ-rays. The list of participants of these studies is very large. Up to date the results of 1986, 1987, 1990 and 1991 are published (Gershberg et al. 1991a,b, 1993, Alekseev et al. 1994), the data of 1989 are submitted (Berdyugin et al. 1995), the data of 1992 (Abdul-Aziz et al. 1995) will be submitted in the near future. In 1993, photometric observations were accompanied by monitoring observations of EUVE and IUE, in 1994, VHE γ-ray observations were included. The publication of data collected in 1993 and 1994 is in preparation. In this communication I shall concentrate on several new findings related to the EV Lac flares only.
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 · E

From 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.
Stream Parameters in the Neighbourhood of the L1 Point in W Serpentis-type Binaries
Authors: Karetnikov V.G. , Luthardt-Menchenkova E.V. , Nazarenko V.V.
Published: July 2016

The gas motion in close binary systems has been investigated by several authors using a hydrodynamic method (e.g. Prendergast & Taam 1974, Flannery 1975, Lubow & Shu 1975, 1976). All these researches have, besides important results, a common deficiency: in the analysis of the gas motion, the extent and velocity of the stream in the neighbourhood of the inner Lagrangian point L1 was not calculated. They have been chosen on the basis of general assumptions (the same for all types of close binaries). A fundamental assumption was the small extent of the stream in the neighbourhood of L1 perpendicular to the line connecting the centers of the stars. At the same time the extent and the velocity of the stream near L1 exert a great influence on the further stream motion, on the formation of the circumstellar envelope and finally on the evolution of the close binary system. Therefore the first step in the investigation of the gas motion in a close binary must be the determination of the initial parameters of the stream in the neighbourhood of the point L1.
Monitoring of Flare Stars at Nainital Observatory
Authors: Sanwal B.B.
Published: July 2016

Five UV Cet-type flare stars were photoelectrically monitored during the period 1970 to 1981 using either the Carl Zeiss Jena 1.04m reflector or the 0.56 m reflector of the Uttar Pradesh State Observatory Nainital. Thermoelectrically cooled EMI 6094S and 1P21 photomultipliers were used with the 1.04 m and 0.56 m telescopes, respectively. The sky brightness was also recorded frequently for short intervals during continuous monitoring of the stars.
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.
Influence of Coronal Mass Ejections from the Red Dwarf Component on the Accretion Pattern in CVs and LMXBs
Authors: Minarini Roberto , Beskin Grigory
Published: July 2016

Low-mass main sequence stars show a magnetic activity similar to the Sun and as a consequence they lose mass in the form of a variable stellar wind. In the latest spectral types (red dwarfs) the activity and the mass loss rate appear to increase by a large factor of ∼ 103 with respect to the solar case, reaching Ṁ ∼ 2 · 10−11 M⊙/yr (Badalyan & Livshits 1992, Katsova 1993). The same happens for coronal mass ejections (CMEs), which are the most relevant transient events of mass loss in these objects. In the Sun, these appear as bubbles of coronal material, with dimensions of some fraction of the solar surface, mass M ≃ 2 · 1014 - 2 · 1016 g and ejection velocity v ≃ 3 · 107 - 2 · 108 cm/s, with an instantaneous mass loss rate Ṁ ∽ 10−13 - 10−11 M⊙/yr (Wagner 1984). In red dwarfs, as recently observed, the ejection velocities are higher, up to v ≃ 3 · 108 cm/s and the mass loss rate can reach the value Ṁ ≃ 10−8 M⊙/yr (Mullan et al. 1989, Houdebine et al. 1990). In both cases, the observations suggest that a bubble expands, once ejected, with a velocity of several hundreds of km/s.