bluuebunny/crossref_metadata_2025 huggingface dataset:
Planetesimal formation in the solar nebula
Authors: Ruzmaikina T.V.
Published: July 2016

Terrestrial planets, cores of giant planets and small bodies of the solar system − comets and asteroids − resulted from the coagulation of interstellar dust grains, and grains which were melted or evaporated and condensed again in the solar nebula.

The paper describes the growth and processing of dust grains and their aggregates, starting from molecular cloud cores through the formation and evolution of the solar nebula and the accumulation of these aggregates in larger solid bodies − planetesimals. Discussed are the processes which could be responsible for the interruption of accumulation in the region of the asteroid belt, and processes which shaped the Kuiper belt.
Dynamics of comets in the collapsing protosolar nebula
Authors: Neslušan L.
Published: July 2016

Comets are created in the cool, dense regions of interstellar clouds. These macroscopic bodies take place in the collapse of protostar cloud as mechanically moving bodies in contrast to the gas and miscroscopic dust holding the laws of hydrodynamics. In the presented contribution, there is given an evidence concerning the Solar system comets: if the velocity distribution of comets before the collapse was similar to that in the Oort cloud at the present, then the comets remained at large cloud-centric distances. Hence, the comets in the solar Oort cloud represent a relict of the nebular stage of the Solar system.
Follow-up astrometry of NEOs at Kleť Observatory – present and future
Authors: Tichá J. , Tichý M. , Moravec Z.
Published: July 2016

The reliable orbit determination of newly discovered NEOs is impossible without precise follow-up astrometry in a sufficient arc of observations. This paper describes the follow-up astrometry NEO programme at the Kleť Observatory. Since 1994 we have used a 0.57-m reflector equipped with CCD camera for confirmations of newly discovered NEO candidates, early follow-up astrometry of NEOs in discovery opposition, recovery of NEOs in second opposition and also follow-up astrometry of poorly observed NEOs in further oppositions. In this field the Kleť Observatory is one of the most productive sites in the world. This programme will be extended to fainter objects with the new 1.02-m reflector − which will become operational at the end of 1998.
V lightcurves and B-V colour of main-belt asteroids
Authors: Blanco C. , Riccioli D.
Published: July 2016

To obtain asteroid photometric lightcurves sufficiently covered to yield the elements necessary to apply the methods for computing their rotational parameters and shape, an observational campaign of main-belt asteroids was undertaken at the Astronomy Institute of Catania University. During more than 40 observational runs, made since 1992 at the M.G. Fracastoro station of Catania Astrophysical Observatory, the lightcurves of more than a hundred asteroids were constructed and the values of rotational axis orientation and of the axes ratio of 50 objects were computed. We present the V lightcurves, the B-V colour, the found values of the synodical rotational period and the lightcurves amplitude of 56Melete,95Arethusa,138Tolosa,198Ampella,212Medea,286Idea,432Pythia\509Iolanda,568Cheruskia,674Rachele,860Ursina,1369Ostaninaand 1469Linzia.The characteristic of the lightcurves and the period values are discussed in comparison with the ones reported in the literature.
Some comments about observations and image processing of comet 29P/Schwassmann-Wachmann 1
Authors: Kubáček D. , Galád A. , Pravda A.
Published: July 2016

Unusual short-period comet 29P/Schwassmann-Wachmann 1 inspired many observers to explain its unpredictable outbursts. In this paper large scale structures and features from the inner part of the coma in time periods around outbursts are studied. CCD images were taken at Whipple Observatory, Mt. Hopkins, in 1989 and at Astronomical Observatory, Modra, from 1995 to 1998. Photographic plates of the comet were taken at Harvard College Observatory, Oak Ridge, from 1974 to 1982. The latter were digitized at first to apply the same techniques of image processing for optimizing the visibility of features in the coma during outbursts. Outbursts and coma structures show various shapes.
The long-term evolution of the main asteroidal belt and the origin of large Mars- and Earth-crossers
Authors: Nesvorný D. , Morbidelli A.
Published: July 2016

Results of numerical simulations show that the orbits of asteroids in the inner part of the main belt may gradually, subject to a chaotic process acting on 10-100 Myr time scales, become more elliptic and start intersecting the orbit of Mars. The subsequent evolution of an asteroid having close encounters with Mars frequently leads to the Earth-crossing orbit. This revolutionary scenario of the origin of near-Earth asteroids was quantified by Miglioriniet al.(1998) and here we discuss some of the aspects of this work.
Electron Acceleration in Solar Flares
Authors: Dröge Wolfgang , Meyer Peter , Evenson Paul , Moses Dan
Published: July 2016

For the period September 1978 to December 1982 we have identified 55 solar flare particle events for which our instruments on board the ISEE-3 (ICE) spacecraft detected electrons above 10 MeV. Combining our data with those from the ULEWAT spectrometer (MPI Garching and University of Maryland) electron spectra in the range from 0.1 to 100 MeV were obtained. The observed spectral shapes can be divided into two classes. The spectra of the one class can be fit by a single power law in rigidity over the entire observed range. The spectra of the other class deviate from a power law, instead exhibiting a steepening at low rigidities and a flattening at high rigidities. Events with power-law spectra are associated with impulsive (< 1 hr duration) soft X-ray emission, whereas events with hardening spectra are associated with long-duration (> 1 hr) soft X-ray emission. The characteristics of long-duration events are consistent with diffusive shock acceleration taking place high in the corona. Electron spectra of short-duration flares are well reproduced by the distribution functions derived from a model assuming simultaneous second-order Fermi acceleration and Coulomb losses operating in closed flare loops.
The Association of Flares to Cancelling Magnetic Features on the Sun
Authors: Livi Silvia H. B. , Martin Sara , Wang Haimin , Ai Guoxiang
Published: July 2016

Previous work relating flares to evolutionary changes of photospheric solar magnetic fields are reviewed and reinterpreted in the light of recent observations of cancelling magnetic fields. In line-of-sight magnetograms and H-alpha filtergrams from Big Bear Solar Observatory, we confirm the following 3 associations: (a) the occurrence of many flares in the vicinity of emerging magnetic flux regions (Rust, 1974), but only at locations where cancellation has been observed or inferred; (b) the occurrence of flares at sites where the magnetic flux is increasing on one side of a polarity inversion line and concurrently decreasing on the other (Martres et al, 1968; Ribes, 1969); and (c) the occurrence of flares at sites where cancellation is the only observed change in the magnetograms for at least several hours before a flare (Martin, Livi, and Wang, 1985). Because cancellation (or the localized decrease in the line-of-sight component of magnetic flux) is the only common factor in all of these circumstances, suggest that cancellation is the more general association that includes the other associations as special cases. We propose the hypothesis that cancellation is a necessary, evolutionary precondition for flares. We also confirm the observation of Martin, Livi, and Wang (1985) that the initial parts of flares occur in close proximity to cancellation sites but that during later phases, the flare emission can spread to other parts of the magnetic field that are weak, strong, or not cancelling.
Solar and Stellar Magnetic Fields and Atmospheric Structures: Theory
Authors: Parker E. N.
Published: July 2016

This presentation reviews selected ideas on the origin of the magnetic field of the Sun, the dynamical behavior of the azimuthal field in the convective zone, the fibril state of the field at the photosphere, the formation of sunspots, prominences, the spontaneous formation of current sheets in the bipolar field above the surface of the Sun, coronal heating, and flares.
Solar Flares: High-Energy Radiation and Particles
Authors: Rieger Erich
Published: July 2016

Due to the Sun's proximity flares can be investigated in the gamma-ray regime and flare generated particles can be measured in space and related to particular events. In this review paper we focus on the problem of particle acceleration by using as observational ingredients: the fluxes and spectra of particles inferred from gamma-ray measurements and observed in interplanetary space, the temporal characteristics of flares at high-energy X- and gamma-rays and the distribution of gamma-ray flares over the solar disc.
Solar Flares: The Gradual Phase
Authors: Švestka Zdeněk
Published: July 2016

One has to distinguish between two kinds of the gradual phase of flares: (1) a gradual phase during which no energy is released so that we see only cooling after the impulsive phase (a confined flare), and (2) a gradual phase during which energy release continues (a dynamic flare).

The simplest case of (1) is a single-loop flare which might provide an excellent opportunity for the study of cooling processes in coronal loops. But most confined flares are far more complicated: they may consist of sets of unresolved elementary loops, of conglomerates of loops, or they form arcades the components of which may be excited sequentially. Accelerated particles as well as hot and cold plasma can be ejected from the flare site (coronal ‘tongues', flaring arches, sprays, bright and dark surges) and these éjecta may cool more slowly than the source flare itself.

However, the most important flares on the Sun are flares of type (2) in which a magnetic field opening is followed by subsequent reconnection of fieldlines that may continue for many hours after the impulsive phase. Therefore, the main attention in this review is paid to the gradual phase of this category oflong-decay flares. The following items are discussed in particular: The wide energy range of dynamic flares: from eruptions of quiescent filaments to most powerful cosmic-ray flares. Energy release at the reconnection site and modelling of the reconnection process. The ‘post-flare’ loops: evidence for reconnection; observations at different wavelengths; energy deposit in the chromosphere, chromospheric ablation, and velocity fields; loops in emission; shrinking loops; magnetic modelling. The gradual phase in X-rays and on radio waves. Post-flare X-ray arches: observations, interpretation, and modelling; relation to metric radio events and mass ejections, multiple-ribbon flares and anomalous events, hybrid events, possible relations between confined and dynamic flares.
The Cerro Tololo Data System
Authors: Lasker Barry M.
Published: July 2016

As early as 1968, increases in the complexity of photoelectric observing programs and the variety of sophisticated photometric instruments in use at the Cerro Tololo Inter-American Observatory necessitated the acquisition of a digital data-recording and instrumentation-control system. The diversity of projects to be done with such a system and the obvious need of provisions for extensive future modification and expansion made apparatus oriented around hard-wired logic clumsy and uneconomical. Clearly, the heart of the system was to be a digital computer.
The Automatic Control of Large Optical Telescopes
Authors: Walker G. S.
Published: July 2016

The aims of the automatic control system are to position the mechanical axis of the telescope to specified right ascension and declination coordinates, and to track the right ascension axis smoothly at sidereal rate, atmospheric refraction variations being taken care of by an auto-guider. The design problems involved fall naturally into two groups, the mechanical ones of measuring the rotations of the axes and of applying drives to these, and the electronic ones of providing supervisory control and calculation facilities.

Solutions to these problems depend to a large extent on whether automatic control is being added to an existing telescope with existing drive systems, or a new telescope design is being carried out with automatic control in mind, and on whether an on-line process control computer is to be incorporated or not.
The Edinburgh Automatic Star Follower
Authors: Adam G. R.
Published: July 2016

The automatic star follower or autoguider described in this paper was designed for the Edinburgh 40/60 cm Schmidt camera. The stellar image in the focal plane of the 15 cm f/18 guide telescope is split optically to produce four stationary images which are sampled by a single image dissector tube, whose sequential output signals are proportional to the intensity of illumination in each quadrant. These signals are compared to produce error signals which are a measure of the radial displacement of the star. Guiding corrections in both right ascension and declination are applied to the fine motions of the Schmidt drive mechanism.

Measurements made on a typical plate given an exposure time of 30 min, and using guide stars down to magnitude 8.5 indicate a guiding accuracy of better than 0.14 arcsec or 2 μm at the focus of the guide telescope.
The U.S. Naval Observatory Automatic Measuring Machines, Present and Future
Authors: Strand K. Aa.
Published: July 2016

The automatic measuring machine acquired by the U.S. Naval Observatory in 1966 was built by Nuclear Research Instruments (NRI) in Berkeley, California, based upon design specifications by the Naval Observatory and upon a considerable amount of innovative engineering by NRI. The performance of the machine and the results obtained over the past four years clearly show that a reliable high speed measuring system has been achieved. Hence, when requirements developed for a second machine it was decided to copy the earlier machine, incorporating modifications which the present state of the art permit and which were not available when the machine was designed in 1963.
Auromatic Centering on Photographic Star Images
Authors: Høg Erik
Published: July 2016

A method for precise centering on photographic star images is proposed. The image is moved only once across one scanning slit for the first coordinate and then across another slit for the orthogonal coordinate.

The photometric values are stored and treated in an on-line computer. The relative opto-mechanical simplicity suggests the application of the method to existing comparators.
The Videometer An Instrument for Quantitative Measures on Solar Flares
Authors: Reid John H. , Vorhaben K. H.
Published: July 2016

At optical wavelengths the solar flare is a very complex phenomenon, and one of the major problems in the study of solar flares has been to find a consistent and reliable method of classifying them. A survey of the published data will quickly show that a solution has still to be found. A second problem is to find some parameter which will accurately represent the temporal variation of the flare. The relatively small amount of photometric measures available shows that there is a need for a rapid method of characterizing the flare’s intensity and areal fluctuations. In comparison to other astronomical measurements, the techniques used in measuring and classifying flares are primitive and highly subjective. The present system of classification differs only slightly from the pioneering efforts, and little attempt has been made to take advantage of the technological developments to remove the observer’s subjectivity—in fact, the latest classification scheme actually increases it!
A New-Star-Counting Device
Authors: Tanabe H. , Mori K.
Published: July 2016

Measurements of the magnitude distribution and integrated color of stellar fields in many parts of the sky by the star-counting method are important for studies of the structure of the Galaxy and the distribution of interstellar matter. On the other hand, in quantitative studies of the airglow and zodiacal light, we have to know the integrated brightness of the star field in order to subtract the background light from the measured light.

Up to the present, these star-counts have been made only for limited areas of the sky, since these measurements were made by using a reading microscope, and they would require much time and labor to extend the measurements to larger sky areas.
Computerized Microphotometry of Stellar Spectrograms
Authors: Latham David W.
Published: July 2016

Let me begin my description of how we have been doing computerized microphotometry with a brief history of the hardware and its evolution. Then I’ll get on to the more interesting topic of what we do with the data after we get them into the computer.

In 1966, the Shock Tube Laboratory at Harvard College Observatory took delivery of a David Mann microphotometer. Briefly, this $50 000 instrument can measure positions in an area 250 x 250 mm to an accuracy of about 1 μn. The limiting resolution of the measuring slit approaches 1 or 2 μm at the plate, and the drift in the photometer output is on the order of 1 per cent in 12 hours.
Microphotometer Digital Data Processing
Authors: Hutchings J. B.
Published: July 2016

In the past several years many, if not most, observatory microphotometers have been made or adapted to give digital output. At the same time, astronomers have been faced with the task of specifying exactly all the folk lore and experience necessary to reduce microphotometer output, so that the task can be performed by a computer. In addition to the speed and accuracy gains therefore, we have also been obliged to separate the subjective from the objective in this processing, and this may be the most important improvement of all.

Knowing that many other observatories have developed similar programming systems, this paper presumably does not contain much that is startlingly new, but it is hoped that it may promote the exchange of ideas desirable to overcome common difficulties and avoid duplication (or multiplication) of effort.
Automatic Computer Reduction of Astronomical Television Images
Authors: Deutschman W. A.
Published: July 2016

During the 15 months that we operated the Celescope experiment on the Orbiting Astronomical Observatory, we acquired 8700 television frames of star fields containing a total of approximately 10 000 stars.

Figure 1 shows an example of one of these frames. Note the target ring, an aluminum deposit on the target of the tube, in each corner of the picture; the shadow in the upper left corner; the calibration lamp just below the center of the picture; and its ghost slightly below and to the left. All other objects are stars. Each frame consists of 256 scan lines designated by the number k, with each line containing 251 pixels (picture elements) designated by the numberl, making a total of 65 000 intensity points I(k,l). The frames are divided into two spectral regions by two filters—lines 1 to 128 have one spectral range, lines 129 to 256 have a different one. Hence, each frame is reduced as two half frames in the first portion of the reduction system.
Polarization of Young Shell Variables
Authors: Breger M.
Published: July 2016

Stellar polarization between 3000 and 7500 Å has been measured in NGC 2264. Out of 37 stars (including many variables) 4 are definitely polarized, while 3 others show weak polarization. The mean (interstellar) cluster polarization is found to be very small. The highest polarization (4,6 %) is found in a T Tauri star. W 90, a variable below the main sequence, has the highest polarization found among the A and F stars (2, 6%). With the exception of W46, polarization peaks in the blue implying small particle sizes. A good correlation is found between the size of polarization and (other) shell characteristics. These measurements confirm the recently proposed shells in some pre-main sequence stars which appear to be too faint for their color, but fail to detect any new stars with extensive shells. This suggests that some of the scatter in the color-magnitude diagram amongst the A and F stars is real because of an age spread between 1 and 3 X 106 years.
Some Properties of Magnetic Variables
Authors: Rakoš Karl D.
Published: July 2016

It is certain, that the mechanism causing variations of the magnetic field and spectral lines in Ap stars must also cause variations in their luminosities. The light curves are synchronous with the magnetic variations and usually the maximum of the positive magnetic field strength coincides with the minimum of the light curve. In the past the oblique rotator theory was not able to explain easily such brightness change. There is no simple reason to suppose, that the brightness of the surface of a star would increase or decrease at one magnetic pole only. Since that time a few stars were found with some indications for secondary minima and maxima in the light curves, but the first established double wave in a light curve was recently found by H. M. MAITZEN and K. D. RAKOš in HD 125 248 (1970), see Figure 1. It is a very exciting result, only the light curve in yellow light shows two maxima and two minima. The light curves in blue and ultraviolet are very smooth and show no evidence for secondary waves.
The Visual and Infrared Spectrum 1968—-71 of MHα 328-116 = V 1016 CYG — Note III —
Authors: Ciatti F. , Mammano A. , Rosino L.
Published: July 2016

The peculiar object MHα 328-116 was included in the spectroscopic programme of Asiago since 1965. Its spectral evolution during 1965—66 and 1966—67 has been described in two previous communications (hereafter referred to as Paper I and Paper II) by MAMMANO and ROSINO (1966, 1968).
Photometry of Long Period Variables in the Magellanic Clouds
Authors: Butler C. J.
Published: July 2016

A photographic survey of variable stars in the Magellanic Clouds is currently in progress at Dunsink Observatory, using photographic material obtained with the ADH telescope. In the course of this investigation a number of Long Period Variables have been measured, most of which lie in the LMC. Several are previously known Harvard Variables (prefixed HV) but some are new discoveries (prefixed DV). The co-ordinates of the new Long Period Variables are listed in Table I.
Spectral Investigations of UV Ceti-Type Flare Stars and Search for New Variables of this Type Carried out at Crimea
Authors: Gershberg R. E. , Shakhovskaya N. I. , Schöffel E.
Published: July 2016

During last years, after Budapest Colloquium, flare star investigations have been continued at the Crimean Astrophysical Observatory. The purpose of the investigations was to specify spectral features of flares, to research quantitatively spectra of the stars in quiet state and to search for new variables of this type.
The Red Dwarf Stars of the UV Ceti-Type in the Neighbourhood of the Sun
Authors: Shakhovskaya N. I. , Schöffel E.
Published: July 2016

The intensive patrol observations of red dwarf stars during last years, carried out in the Crimea, Chile, Catania, South Africa, Armenia, Japan and other observatories led to appreciable increase of number of known UV Ceti-type objects. It permits us to complete the known lists of the variables (1—4). At the same time it is worth-while to define more precisely the criteria to consider a star as the UV Ceti-type variable, and to carry out strong selection of the certain UV Cet-type variables from the objects suspected to be this type variables.
Rapid Balmer Line Variability in Ap Stars
Authors: John Wood H.
Published: July 2016

It is the purpose of this paper to briefly summarize the results of an eight-year observational program on the Balmer-line behavior of magnetic and related stars. In addition, new data on the interesting 79-minute variable SX Phe will be presented.
Duplicity and its Consequences among Variable Stars in General
Authors: Larsson-Leander G.
Published: July 2016

The consequences of stellar duplicity for variable stars in general are reviewed. Gravitational effects, radiation effects and effects due to gaseous streams and mass transfer are considered. The possibility of tidal interactions, modulating the pulsations ofβCMa andδSct variables, is among the topics treated in some detail.
On Stothers’ and Simon’s Binary-Star Hypothesis for Beta Canis Majoris Star Pulsation
Authors: Percy John R. , Madore Katherine
Published: July 2016

The β CMa stars are short-period pulsating variable stars lying slightly above the upper main sequence. Although they have been known and studied for 70 years, little is known about the nature and cause of their pulsation.

STOTHERS and SIMON (1969) have recently advanced an hypothesis – hereinafter known as the hypothesis – which proposes that all β CMa stars are the former secondary components of massive binary systems. The former primary components, being more massive, have evolved first, have shed their envelopes by rapid mass loss, and have deposited helium-enriched material from their cores upon the surfaces of the secondary components. This causes the secondary components (now the primary components) to become unstable, via the so-called „μ-mechanism“, to nuclear-energized radial pulsations.
A Search for Spectroscopic Binaries among Southern Cepheids
Authors: Lloyd Evans T.
Published: July 2016

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

A method of photoelectric photometry of the components of visual double stars is briefly described. Observations of ADS 9701 = δ Ser and of UV Aur = ADS 3934 B are presented to demonstrate the usefulness of this technique for the accurate photometry of variables in close visual double stars.
Simultaneous Photometric and Image-Tube Spectroscopic Observations of Short Period Binary Systems and Rapid Intrinsic Variables
Authors: Walker M. F.
Published: July 2016

An extremely important new frontier in variable star research lies in the application of image tube techniques to the study of the spectroscopic phenomena in extremely rapid intrinsic variables and in short-period binary systems. Within limits, the use of image tubes for the spectroscopic observation of constant or slowly varying stars can be regarded as a convenience — as a means of increasing the efficiency of use of time at the telescope; the same results could, in principle, be obtained by observing for a longer time by conventional means. However, when one wishes to observe rapid changes, there is no substitute for the higher information collection rate provided by the image tube. Electronographic image tubes are especially well suited to this type of investigation owing to their high quantum efficiency, high resolution, large storage capacity, and linearity of response. Typically, image tubes of this type may have quantum efficiencies of 10% to 20%, an information-rate gain of 10 to 20 over the fastest photographic plate (baked Kodak IIaO at 4000 A), and resolutions between 80 and 100 lp/mm. With proper choice of photographic emulsion to record the electronic images, a linear relationship exists between photographic density and intensity of the incident light up to densities of about six, making electronographic image tubes especially valuable for spectrophotometric observations. Despite the great potential of this technique, very little work of this type has so far been done. In this paper I shall outline some of the results that have been obtained at Mount Hamilton to illustrate the possibilities of this type of observational research.
Eruptive Binaries
Authors: Smak Józef
Published: July 2016

Two periods can be distinguished in the past history of our subject. The first period, which begun about 100 years ago, was dominated by intensive studies of novae and U Gem type stars at their outbursts and led to a fairly detailed, photometric and — particularly — spectroscopic description of these phenomena. The faintness of all these objects at minimum was a seriously hampering circumstance for observing them spectroscopically outside of their outbursts and it was only about 30 years ago that two pioneering surveys — of novae by HUMASON (1938) and of U Gem type stars by ELVEY and BABCOCK (1943) — begun to unravel their true nature.
Models for Contact Binaries
Authors: Biermann Peter , Thomas H.-C.
Published: July 2016

The well-known problem one has in constructing zero age contact binaries stems from the fact that given two mass values, the ratio of the radii for zero age stellar models differs from that derived from the Roche model (KUIPER 1941). Therefore one cannot achieve contact by adjusting just the distance of the two stars, since if for instance the distance would be such that the critical equipotential surface is of the right volume for the primary to fill it completely, then the secondary would be smaller than its critical equipotential surface and one would end up with a semidetached system.
Variable Star Observations from outside the Earth’s Atmosphere: Review and Prospects
Authors: Kondo Yoji
Published: July 2016

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

At first, I have to thank Dr. STROHMEIER sincerely for his invitation to the fifth colloquium on variable stars.

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

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

NGC 6981 =M72 is a globular cluster with a late-type integrated spectrum (G3) and an ultraviolet excess of δ(U–B)=0.15 ±0.05, which places the cluster in the class of intermediate-to-high metal abundance clusters such as M3. The colour-magnitude diagram shows a horizontal branch populated on both sides of the variable star region. Previous work on the periods of the variables has indicated that the cluster is of Oosterhoff type I, with ≈0.55 day. Some results from B and V photometry of 21 RR Lyrae variables are described. Original measurements of about 50 candidate variables were made, including some possible new variables found by blinking plate pairs, but crowding and background photometric problems reduced the number of variables for which reasonable quality data could be obtained with the available 100-in plate material.
UBV Magnitudes and Colours of 62 RR Lyrae Stars in ω Centauri (NGC 5139)
Authors: Geyer E. H.
Published: July 2016

It has been shown by the author (Geyer, 1967), and independently by Dickens and Woolley (1967), that there occur horizontal branch stars well within the RR Lyrae variable gap of the c–m-diagram of ω Centauri. Variability of these objects is not known, and presumably is unlikely, because the cluster is so well studied for variable stars. For the observationally best studied globular clusters M3, M13, M15 and M92 (Sandage, 1969), this phenomenon is not found. The author’s original published c–w-diagram of NGC 5139 showed about 10 stars with (B–V)≥0.2 and V-magnitudes comparable with those of RR Lyrae stars of the cluster. Unpublished photoelectric measurements of some of these stars, carried out in 1968 with the 40-in photometric reflector of ESO by the author, support this finding. Also the study of blue horizontal branch stars by Newell, Rodgers and Searle (1969) of the Herst-monceux catalog of ω Centauri (Woolley et al., 1966) confirms these results, the importance of which for the understanding of the horizontal branch stars and RR Lyrae variables is obvious.
A Preliminary Investigation of Period Changes For W Virginis Stars in Globular Clusters
Authors: Coutts Christine M.
Published: July 2016

Investigations in recent years have shown that there may be two mechanisms which place stars in the W Virginis instability region (Kraft, 1972). The variables with periods less than 8 days seem to be in the stage of ‘above horizontal branch’ evolution discussed by Strom et al. (1970). The longer period group apparently results when thermal instabilities in the helium burning shell of an asymptotic red giant branch star cause it to loop to the left in the HR diagram. This longer period group has been investigated by Schwarzschild and Härm (1970) and Mengel (1972). The present study has been undertaken to see if there are any notable differences between the period changes of variables belonging to the two groups.
Possible Evolutionary Interpretation of the Dependences on the Diagrams for RR Lyrae Variables
Authors: Goranskij V. P.
Published: July 2016

The separation of RRab variables into two sequences on the amplitude-period diagram was found by Belserene (1954) for globular cluster variables, and by Detre (1965) for field variables. It is significant that the sequence of short period variables is steeper on this diagram than that for stars of longer period. Szeidl (1965) pointed out that other characteristics of the light curves and photometric quantities such as the asymmetry of light curve ε, mean color index B—V, median magnitude mmed, maximum magnitude mmax are also separated into distinct sequences. Figures 1, 2 and 3 show these sequences on the colour-magnitude, colour-period, period-amplitude (or period-maximum magnitude, minimum magnitude) diagrams for RRab variables in the globular clusters M3, ω Cen and in the dwarf galaxy in Draco. On these figures RRab variables of the long period sequence are marked by crosses. The colour-magnitude and colour-period diagrams for M3 were obtained by Roberts and Sandage (1955); the period-maximum magnitude, minimum magnitude diagram obtained by Szeidl (1965) is constructed for stars measured by Roberts and Sandage. To get the most accurate F-magnitudes and colour indices for variables in ω Cen the data of Dickens and Saunders (1965) and Geyer and Szeidl (1970) have been averaged. The diagrams for RR Lyr variables in the Draco system were obtained by Baade and Swope (1961). The variables which show the Blazhko effect were excluded.
The Evolutionary Status of Population II Cepheids
Authors: Mengel John G.
Published: July 2016

Schwarzschild and Härm (1970, hereafter abbreviated SH) have suggested that the presence of Cepheids in globular clusters can be explained by the occurrence of ‘flashes’ in the thermally unstable helium-burning shells of post-horizontal-branch, or ‘asymptotic-branch’ stars. These flashes in the deep interior of the star produce large changes in the energy flux at the base of the envelope, which in turn cause the position of the model in the Mbol — logTe diagram to move. For most values of the total stellar mass and envelope composition studied by SH, the models simply moved up and down the asymptotic branch in response to a helium shell flash. However in a few cases, characterized by low total mass and a relatively high value of the envelope helium abundance, the models left the asymptotic branch and described loops extending into the region of pulsational instability. The Cepheids of Population II were thus tentatively identified by SH as asymptotic-branch stars that had recently undergone a helium shell flash and whose tracks were as a result describing a loop extending into the instability strip.
De La possibilité pour certains astéroïdes d’être des satellites lointains de Jupiter
Authors: Benest Daniel
Published: July 2016

Nous nous plaçons dans le cadre du problème restreint des trois corps, c’est-à-dire quand la masse deB3devient négligeable par rapport à celle deB1etB2, et nous utilisons la loi de force classique en. J’appelleμle rapportetEl’excentricité de l’orbite elliptique deB2relativement àB1. Les orbites deB3qui nous intéressent étant celles de satellites deB2, nous nous sommes placés en axes tournants-pulsants avec origine enB2. Il est connu que pour les orbites lointaines, seules les rétrogrades (dans ce repère) sont stables;Rem.: une orbite rétrograde par rapport àB2en axes tournants-pulsants peut être directe par rapport àB1en axes fixes (Fig. 1, où le cas de figure représenté suppose que les périodes deB3autour deB2et deB2autour deB1sont très proches).
Sur l’application de la méthode de Laplace-Danjon à la détermination des orbites
Authors: Ionescu Vlăsceanu Victor
Published: July 2016

Dans ce travail on étudie la possibilité d’utiliser un grand arc d’orbite pour l’application de la méthode de Laplace-Danjon à la détermination des orbites.
Investigation of the orbital motion of comet Churyumov-Gerasimenko 1969 IV (preliminary investigation)
Authors: Belyaev N. A.
Published: July 2016

The motion of the short-periodic comet 1969 IV has been studied over a period of 400 years (1660–2060). During the above period the comet had as many as 13 approaches within 2.0 AU to Jupiter.

The two approaches in 1840 and 1959 resulted in the transformation of the circular orbit (e= 0.1,q> 4 AU) to the elliptic one (e= 0.6,q= 1. 3 AU). Because of this the comet became accessible to observations. It was discovered by K. I. Churyumov in 1969.
Outbursts of comet Schwassmann-Wachmann 1, and the cloud of interplanetary boulders
Authors: Sekanina Zdenek
Published: July 2016

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

L’étude présentée est faite conjointement à des observations radioélectriques de météores de magnitude limite estimée à M = 10; une méthoe détection automatique des échos météoriques et un programme de traitement sur ordinateur des données météoriques acquises sont en cours de fonctionnement.
Solar Flares
Authors: Priest Eric R.
Published: July 2016

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

Mirzoyan (1976) showed that the concentration of flare stars around the center of the Pleiades cluster (Alcyone) was the same, irrespective of their proper motions. At that time, however, proper motions of only a few flare stars were known. The result was confirmed on the basis of more extensive observational material (Chavushian 1979, Mirzoyan 1983). Photographic observations of stellar flares in the general galactic field during 181 hours yielded the detection of only a single flare, i.e. the percentage of flare stars in the general galactic field is about 10% of the total number of flare stars detected in the regions of stellar clusters and associations (Chavushian 1979, Mirzoyan et al. 1988).

This result shows that flare activity can be considered as a definitive cluster membership criterion, which appears to be a better one than the cluster membership probability, which is based on proper motions. To prove this, cluster membership probabilities (Stauffer et al. 1991) for 408 Pleiades cluster flare stars from the catalogue by Haro et al. (1982), are used (Table 1).
CN Com: a Typical RS Canum Venaticorum Star
Authors: Richter G.A. , Greiner J.
Published: July 2016

CN Com = CSV 6907 was dicovered by Romano (1958). First we note that the GCVS (and Simbad) coordinates are wrong by ≈2′. Using the finding chart of Romano (1958) and the APM data (digitized POSS), the correct coordinates of CN Com are R.A.(2000.0) = 12h19m47s.0, DEC(2000.0) = +16°30′50″.

CN Com is only 8″ distant from the ROSAT X-ray source RX J1219.7+1630 detected during the All-Sky-Survey at a PSPC countrate of 0.022 cts/s. Due to the positional proximity and the absence of other optical objects brighter than 20rmm within the about 30″ error circle, CN Com is very probably the optical counterpart of RX J1219.7+1630.

CN Com was investigated on some 600 photographic plates (Sonneberg astrographs 400/1600 mm and 400/2000 mm) of the fields 26 Com and 5 Com, covering the time interval from 1962 to 1994 (with only a very few plates from the years 1967-1974).
A New Technique for Precise Stellar Photometry: Application to Small-Scale Activity of EV Lacertae
Authors: Zhilyaev B.E.
Published: July 2016

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

Data of long-duration emission arising after the impulsive rise and decay in a flaring event on the red dwarf star AU Mic are discussed. Intensive EUV emission in the band 65-190 Å was registered by the Extreme Ultraviolet Explorer (EUVE) after both impulses during half a day. A similar behavior of the flux in the Fe XVIII 93.9 Å line is detected after the first powerful impulse. The decay of the intensity in the 65-190 Å band and in the Fe XVIII line during this prolonged event is 10 times slower than the time of radiative cooling of coronal loops with a typical flare plasma density. Some difficulties with two explanations of this event proposed earlier are discussed. Explanation (i) - the radiation of dense loops at main phase of the flare, and (ii) - the emission of the low-dense plasma of coronal transients (CME). The temporal behavior of the emission measure is determined for both the 65-190 Å band and the Fe XVIII line fluxes. The total energy emitted in the 1-2000 Å region for the long-duration event lasting almost 12 hours is 3 · 1035 ergs. The following physical model is proposed to explain the prolonged event (Fig. 1): the source of emission is the system of high coronal loops, the size of which is more than the active region scale, but is less than the stellar radius. The temperature of the plasma in the loops decreases from 107 K slowly, during a few hours. The densities in these loops are in the range 1013 cm−3 to 5 · 109 cm−3. Such systems, when the plasma therein becomes cool, are observed in the Hα line during large solar flares (for instance, June 15, 1991) after CME. Some additional post-flare energy input into this high coronal loop systems can be caused by the reconnection in vertical current sheet, and this post-eruptive energy release provides prolonged and intensive EUV emission.

Apparently, we are faced here with a new kind of surface activity on late-type stars which is intermediate between impulsive flares on red dwarfs and long-duration, powerful events on subgiants, which are components of RS CVn binaries.

The full version of this contribution will be published in Astronomicheskij Zhurnal (Astronomy Reports), 1995, Vol. 72.
X-ray Variability of the Flare Star CC Eri
Authors: Pan H.C. , Jordan C.
Published: July 2016

The flare/spotted spectroscopic binary star CC Eri (HD 16157) was observed in the periods 1990 July 9-11 and 1992 January 26-27 with the ROSAT PSPC detector (Pan and Jordan 1995). These high quality data give the first information on the temporal and spectral variability of CC Eri in the X-ray energy band.

During the ROSAT observations the X-ray intensity of the source is variable on timescales from a few minutes to several hours. The X-ray luminosity is in the range 2.5 – 6.8 × 1029 erg s−1, which is similar to values found from previous measurements with the Einstein IPC and EXOSAT LE. On 1990 July 10 an X-ray flare-like event was detected with an exponential rise time of about one hour and a decay time of about two hours. The X-ray spectrum of CC Eri can be described by current thermal plasma codes with two temperature components or with a continuous temperature distribution. The spectral results show that plasma at Te ∼ 107 K exists in the corona of CC Eri. We find that the X-ray spectrum is also variable and the variations of the emission measure, and to a lesser extent of the temperature, are correlated with the source intensity.