bluuebunny/crossref_metadata_2025 huggingface dataset:
Strong and Weak Magnetic Fields: Nature of the Small-Scale Flux Elements
Authors: Stenflo Jan Olof
Published: July 2016

The 20 year old conclusion that more than 90% of the magnetic flux recorded by magnetographs in quiet and active regions is in strong-field, kG form has recently been supported by direct observations of Zeeman splitting in the infrared (near 1.6 μm). The magnetic and thermodynamic properties of the kG fluxtubes have been explored in considerable detail over the past decade, in particular through Fourier transform spectrometer observations combined with Stokes inversion procedures. The weak fields have proven to be much more elusive, and it was not until last year that the first definite identifications of intrinsically weak (less than kG) fields in the low photosphere could be made, using the Stokes V profiles of an infrared line pair.
Coronal Magnetic Fields Deduced from Radio Methods
Authors: Krüger A. , Hildebrandt J.
Published: July 2016

Major problems of the physics of the solar atmosphere and processes of solar activity are due to the poor knowledge of the magnetic fields outside the photosphere. Unique methods to determine magnetic fields in the corona and chromosphere make use of radio observations in close connection with information obtained in other spectral ranges e.g. the optical and X-ray regions. Based on relevant emission and propagation processes, the basic radio methods providing information on the parent magnetic fields are summarized. Signatures in the microwave and meter wave regions are used to derive magnetic field parameters at different levels in the solar atmosphere of active regions during quiet and flaring conditions. Implications on fine and gross structures are briefly discussed and consequences on acting physical processes mentioned.
Evolving Features of Hβ Doppler Velocity Fields at Sites of Flares
Authors: Li Wei , Ai Guoxiang , Zhang Hongqi
Published: July 2016

We analyzed eight active regions with more than 600 flare kernels and ribbons, and relevant time sequence Hβ chromospheric Dopplergrams. These data showed that during several hours prior to the flares, the velocity field evolves so that the sites of the flare kernels and ribbons become close to the inversion line of the velocity field. This result holds regardless of whether or not the flare sites are wholly located in blue-shifted areas, or are far from the the inversion line of the line-of-sight velocity field, or are partly within red-shifted areas.
Microwave Emission from a Sunspot III. Implications for the Force Balance in a Static Sunspot
Authors: Lee Jeongwoo W. , Gary Dale E. , Hurford G.J. , Zirin H.
Published: July 2016

We present our earlier measurement of the coronal fields above a sunspot in the active region, NOAA #4741, which was obtained using microwave spectroscopy from the Owens Valley Radio Observatory (OVRO) in a form that allows comparison with theoretical models. Our empirical results for the coronal fields are compared with several theoretical models in order to understand the magnetic structure of a static sunspot. It is found that the presence of transverse pressure gradients should be considered to get a satisfactory fit.
Magnetic Field Configuration in Hα Flare Loops and Flaring Arches
Authors: Bhatnagar Arvind , Srivastava Nandita
Published: July 2016

It is concluded from the observations of Hα flaring loops and flaring arches that these are two entirely different phenomena. From the reconstructed shape of flaring loops, it is suggested that the magnetic field lines revert to potential field configuration from sheared non-potential state.
Pre-Eruption Disturbance of an Active Filament
Authors: Wang Jingxiu , Shi Zhongxian
Published: July 2016

A pre-eruption disturbance of an active filament has been observed. The disturbance is characterized by untwisting rotation and vigorous upward motion. It starts at the site where microflares took place, and appears in the late phase of magnetic flux cancellation beneath the central part of the filament, when more than 1020 Mx flux had disappeared.
The Proton Flare and Evolution of Magnetic Fields in a Decaying Active Region
Authors: Zhang Guiqing
Published: July 2016

In this paper, the evolution history of longitudinal magnetic field of a decaying active region (NOAA AR6703) was studied. We also described the X1.9/4B flare occurring in AR6703, as well as the accompaning events, and emphasized in analysizing the features of longitudinal magnetic fields before the flare.
Model Predictions for Magnetic Shear Changes During Solar Flares
Authors: Forbes T.G.
Published: July 2016

Magnetic shear is sometimes defined observationally as the rotation of the photospheric vector magnetic field away from the field direction of a corresponding potential state. It is often assumed that the observational shear is a direct measure of the energy stored in coronal currents. However, this is not true in general as is illustrated here by considering the changes in observational shear in a variety of flare models. Some of these models predict rotations in the photospheric transverse field which are too small to be detected by present day instruments, but other models predict relatively large rotations in highly localized regions. In principle, observations of the transverse field might confirm or eliminate models in the latter group.
The Dynamic Evolutionary Processes of the Magnetic Fields in the Solar Active Region Boulder 5395
Authors: Liu Xin Ping , Zhang Hong Qi , Lin Jing , Liu Gui Lin
Published: July 2016

In this paper, based on observational information we proposed an opening bipolar magnetic field model and studied numerically the dynamic evolutionary processes of the magnetic fields by solving a complete set of MHD equations. The aim is to discuss one of the mechanisms of energy build up of solar flares produced in the active region Boulder 5395.
Evolutionary Characteristics of Large-Scale Magnetic and Velocity Fields
Authors: Ambrož Pavel
Published: July 2016

Long-term evolution of solar large-scale magnetic fields in relation to the local active phenomena is studied. The changes of the magnetic flux distribution are influenced by the horizontal transport of magnetized plasma. The whole system of magnetic field changes is interpreted as a global process which is controlled by the large-scale convective patterns. The large-scale horizontal velocity field of transporting motions is determined in various approaches with similar results. Regions with positive divergence in the field of horizontal flow field are found to be closely connected with the occurrence of solar active regions. The process of the horizontal flow was analysed by the “cork” method. The corks reveal a pattern of giant cells which are persistent for several solar rotations. These large cells are interpreted as giant convective elements. Occurrence of new strong magnetic flux in regions of positive divergence is then interpreted as a result of emergence of flux in the upflowing parts of that pattern.
Generation of Plasma Flows and Filamentation of Magnetic Fields in the Solar Atmosphere
Authors: Ryutova Margarita
Published: July 2016

Nonlinear effects in dynamics of solar magnetic fields which, in particular, determine the evolution of solar magnetic structures and their lifetimes, are discussed. By some analogy with the effects of acoustic streaming in usual hydrodynamics the general definition of these effects as “magneto acoustic streaming” is proposed.
VLBI Observations of Turbulence in the Inner Solar Wind
Authors: Spangler Steven R.
Published: July 2016

I discuss the use of Very Long Baseline Interferometer (VLBI) phase scintillations to probe the conditions of plasma turbulence in the solar wind. Specific results from 5.0 and 8.4 GHz observations with the Very Long Baseline Array (VLBA) are shown. There are several advantages of phase scintillation measurements. They are sensitive to fluctuations on scales of hundreds to thousands of kilometers, much larger than those probed by IPS intensity scintillations. In addition, with the frequency versatility of the VLBA one can measure turbulence from the outer corona ~ 5 –10 R⊙ to well past the perihelion approach of the Helios spacecraft. This permits tests of the consistency of radio propagation and direct in-situ measurements of turbulence. Such a comparison is made in the present paper. Special attention is dedicated to measuring the dependence of the normalization coefficient of the density power spectrum, on distance from the sun. Our results are consistent with the contention published several years ago by Aaron Roberts, that there is insufficient turbulence close to the sun to account for the heating and acceleration of the solar wind. In addition, an accurate determination of the relationship could aid the detection of transients in the solar wind.
Eruptive Prominence Associated with Limb Flare of 25 January 1991
Authors: Uddin Wahab , Verma V.K.
Published: July 2016

We have observed an eruptive prominence at the east solar limb on 25 January 1991 which started earlier than 0623 UT and was associated with a limb flare (S16 E90) of class 1B/ X10.0. We have recorded a huge mass ejection in the corona by the limb flare associated eruptive prominence. The eruptive prominence ejected a part of the loop in the corona with maximum speed of about 1280 km/sec. The ejected material attain height upto 150,000 km in the corona and finally faded/disappeared in the corona. During the ascending phase of the prominence material in the corona there was a unscrewing of the loop system associated with the eruptive prominence. The type II, III, and IV radio bursts were also reported by a number of Radio Observatories during observation of the eruptive prominence. The high flux of sudden ionospheric disturbances and the solar radio emissions on fixed frequencies (245-80000 MHz) were also recorded. The eruptive prominence associated with limb flare also shows increased proton flux (>10 MeV) during its occurence. The flare was classified as X10.0 flare. In this paper we have analysed the observed data and compared it with the theoretical model of the solar flare.
An Essay on Terminology, Myths, - and Known Facts: Solar Transient - Flare - CME - Driver Gas - Piston - BDE - Magnetic Cloud - Shock Wave - Geomagnetic Storm
Authors: Schwenn Rainer
Published: July 2016

In the field of solar-terrestrial relations a clear and unique terminology is needed in order to abolish and avoid unnecessary confusion between the scientists from several involved disciplines. For example, the widely used abbreviation CME (for coronal mass ejection) has turned out to be somewhat misleading. Early on it had been known that other than coronal material is often involved in such events. The discoverers observed transient events of mass ejections from the sun, which could be observed in the corona owing to the newly available coronagraphs. This article is meant to clarify the terminology, with emphasis on giving credit to the original discoverers and the terms they introduced. With this aim in mind I suggest some minor modifications of the terminology.
The Hamburg All-Sky Bright QSO Surveys
Authors: Reimers Dieter , Wisotzki Lutz
Published: July 2016

Over the past decade, our team has pursued a quest to search for the optically brightest quasars in the entire extragalactic sky, by means of automated quasar selection using digitised objective prism spectra. We give a brief overview over the observational database and selection strategies and present some of the major survey highlights
QSOs from a Variability-and-Proper Motion Survey
Authors: Meusinger Helmut , Brunzendorf Jens , Scholz Ralf-Dieter , Irwin Mike
Published: July 2016

We report on a search for QSOs via variability and zero-proper motion. Candidates were selected by means of indices for overall variability, long-term variability, proper motion and image structure measured on a large number of Schmidt plates with a time-baseline of three decades. Spectroscopic follow-up observations of the candidates brighter than the pre-estimated completeness limit, Blim ≈ 19.7, of the survey revealed about 200 QSOs and Seyfert 1s with redshifts z ≈ 0 — 3. We describe the survey strategy and discuss the properties of the resulting QSO sample.
Probable Associations of BL LAC Objects with Zwicky and Abell Clusters
Authors: Torosyan O.Kh.
Published: July 2016

BL Lac’s may be found everywhere in space. But they are the dominant members in all systems of which they are part.
Infrared Surveys for AGN
Authors: Smith Harding E.
Published: July 2016

From the earliest extragalactic infrared studies AGN have shown themselves to be strong infrared sources, and IR surveys have revealed new populations of AGN. I briefly review current motivations for AGN surveys in the infrared and results from previous IR surveys. The Luminous Infrared Galaxies, which in some cases house dust-enshrouded AGN, submillimeter surveys, and recent studies of the cosmic x-ray and infrared backgrounds suggest that there is a population of highly-obscured AGN at high redshift. ISO Surveys have begun to resolve the infrared background and may have detected this obscured AGN population. New infrared surveys, particularly the SIRTF Wide-area Infrared Extragalactic Legacy Survey (SWIRE) will detect this population and provide a platform for understanding the evolution of AGN, Starbursts and passively evolving galaxies in the context of large-scale structure and environment.
Results from ISOCAM Deep Surveys: An Answer on the AGN Contribution to the Cosmic Infrared Background
Authors: Aussel Hervé
Published: July 2016

The amount of energy contributed by type-2 AGNs to the Cosmic Infrared Background (CIB) has recently been the subject of some debate, since models have shown it could be responsible for up to half. If this were the case, this contribution should be taken carefully into account before using the combined CIB and COB to derive the density of metals in the universe. I argue here that an observational answer to this problem comes from ISOCAM deep surveys performed at 15 μm, that do resolve into discrete sources the bulk of the CIB at 140 μm. Studies of the X-ray properties of these sources allow us to assess whether or not they are dominated by AGNs, and to derive that the type-2 AGNs contribution to the CIB is not greater than 20%.
Blazars from the CLASS Survey
Authors: Marchã M. J. M. , Caccianiga A.
Published: July 2016

This paper presents preliminary results from the CLASS blazar sample; the aim is to study the cosmological properties of radio selected BL Lacs and their closest relatives, the other low radio luminosity flat spectrum sources.
The AGN Content of Hard X-ray Surveys
Authors: Comastri Andrea , Vignali Cristian , Brusa Marcella
Published: July 2016

Multiwavelength observations of the hard X-ray selected sources discovered by BeppoSAX, Chandra and XMM-Newton surveys have significantly improved our knowledge of the AGN population. The increasing number of X-ray obscured AGN so far discovered confirms the prediction of those AGN synthesis models for the X-ray background based on the Unified scheme. However, follow-up optical observations of hard X-ray selected sources indicate that their optical properties are quite varied and the simple relations between optical and X-ray absorption are by no means without exception. Moreover there is evidence of a substantial number of luminous X-ray sources hosted by apparently normal galaxies. In this paper the results obtained from multiwavelength observations of hard X-ray selected sources discovered by BeppoSAX and XMM-Newton are presented and briefly discussed.
The X-ray Variability of High-Redshift QSOs
Authors: Manners J. , Almaini O. , Lawrence A.
Published: July 2016

We present an analysis of X-ray variability in a sample of 156 radio quiet quasars taken from the ROSAT archive, covering a redshift range 0.1 < z < 4.1. Through combining light curves in ensembles we are able to identify trends in variability amplitude with luminosity and with redshift. The decline in variability amplitude with luminosity identified in local AGN (z < 0.1) is confirmed out to z = 2. There is tentative evidence for an increase in QSO X-ray variability amplitude towards high redshifts (z > 2) in the sense that QSOs of the same X-ray luminosity are more variable at z > 2. The simplest explanation for this effect may be that high-redshift QSOs are accreting at a higher efficiency than local AGN.
AGN Selection by Size of Dominant Emission
Authors: Augusto Pedro , Gonzalez-Serrano J. Ignacio
Published: July 2016

The potential of AGN surveys extends to structure-related objectives: e.g. to study the size and properties of the NLR in AGN. From a complete sample of 1665 radio sources, we selected fifty-five with features on ~0.2-2 kpc scales (core/jet flux ratio <7:1) for further study. Here, we summarize the radio interferometric selection technique used and speculate on the prospects for optical surveys (using a size criterion).
Survey and Analysis of 1-22 GHz Spectra for the Full Sample of 660 AGNs North of Declination −30°
Authors: Kovalev Y. Y. , Nizhelsky N. A. , Kovalev Yu. A. , Zhekanis G. V. , Bogdantsov A. V.
Published: July 2016

Measurements of broad-band 6-frequency 1-22 GHz spectra of 660 compact extragalactic radio sources were performed in 1997 (for declinations −30° < δ < + 43°) and 1998 (north of+49°) at RATAN-600. “Average rest-frame” statistical spectral shapes for different subsamples of sources are analyzed. These shapes and each spectrum observed can be represented as the sum of a spectrum of an extended optically thin component (magnetized envelope/lobe), constant or slowly variable and dominating at lower frequencies, and a spectrum of a compact component (relativistic jet), dominating at higher frequencies, with any type of variability. We have revealed specific radio features of the EGRET sub-sample; this favors the models suggesting a relation between the emission mechanisms in radio and gamma-ray ranges. Sources are sampled for which the most compact VLBI structure is expected.
Rapid Variations in the Seyfert 1 Galaxy Mrk 474
Authors: Valiullin R. R.
Published: July 2016

Spectra of Mrk 474 have been obtained in order to search for short-term (less than one day) variability in the broad Hβ and Hα profiles. Observations were carried out using a slit spectrograph and a three-cascade image tube attached to the 70-cm reflector. The processing of the series of spectrograms, obtained on 1999 April 25, showed a rapid (less than 20 minutes) and powerful increase of the flux in the region of [O III]λ5007. The increase of the flux near maximum (5060Å ± 10Å)appeared to be equal approximately to 300%. The value similar to the FWHM for the long-wavelength excess of the flux was equal to 170Å ± 20Å. The dying-out of the long-wavelength excess lasted approximately two hours.
Statistical results on discovered near-Earth asteroids
Authors: Berinde S.
Published: July 2016

The first part of this paper gives a recent overview (until July 1st, 1998) of the Near-Earth Asteroids (NEAs) database stored at Minor Planet Center. Some statistical interpretations point out strong observational biases in the population of discovered NEAs, due to the preferential discoveries, depending on the objects’ distances and sizes. It is known that many newly discovered NEAs have no accurately determinated orbits because of the lack of observations. Consequently, it is hard to speak about future encounters and collisions with the Earth in terms of mutual distances between bodies. Because the dynamical evolution of asteroids’ orbits is less sensitive to the improvement of their orbital elements, we introduced a new subclass of NEAs named Earth-encounter asteroids in order to describe more reliably the potentially dangerous bodies as impactors with the Earth. So, we pay attention at those asteroids having an encounter between their orbits and that of the Earth within 100 years, trying to classify these encounters.
Orbital evolution of comet 73P/Schwassmann--Wachmann 3 and its meteor streams
Authors: Gajdoš Š. , Galád A. , Klačka J. , Pittich E. M.
Published: July 2016

The orbital evolution of the parent body of comet 73P/Schwassmann-Wachmann 3 and its secondary nuclei B and C after its split at the end of 1995 is investigated. 1500 years backward numerical integration of the parent body and 500 years forward numerical integration of all three bodies were done. Possible consequences of the comet splitting on the population of meteoroids in the vicinity of the Earth's orbit, mainly its manifestation as a meteor shower in 2006, are presented.
Collisional reaccumulation of asteroids
Authors: Campo Bagatin A. , Farinella P.
Published: July 2016

We have developed a new version of the code developed by Campo Bagatin (1994a, b) to model the collisional evolution of the asteroid size distribution. The new code distinguishes between “intact”, unfractured asteroids and asteroids converted by energetic collisions into “piles of rubble”. We have run a number of simulations of the collisional evolution process to assess the size range where reaccumulated bodies should be expected to be abundant in the main asteroid belt. We find that this diameter range ranges from about 10 to 100 km, but may extend to smaller or larger bodies depending on the prevailing collisional response parameters.
Analysis of power law assumptions for short-period comets and Kuiper bodies
Authors: Donnison J.R. , Pettit L.I.
Published: July 2016

A Pareto distribution was used to model the magnitude data for short-period comets up to 1988. It was found using exponential probability plots that the brightness did not vary with period and that the cut-off point previously adopted can be supported statistically. Examination of the diameters of Trans-Neptunian bodies showed that a power law does not adequately fit the limited data available.
Size, physical properties, and orbital evolution of the comet Hale-Bopp (C/1995 O1) nucleus
Authors: Churyumov K.I. , Kruchynenko V.G. , Makarchuk R.V.
Published: July 2016

The equation of the energy balance for the comet Hale-Bopp nucleus is analyzed for the moment when the comet passed perihelion and the sublimation rate (for water) was 1031molecules s−1≈ 3 × 105kgs−1. The minimal value of the nucleus radiusRequ(for γ = 1.0, i.e. the total surface sublimation) equals 14.6 km; for γ = 0.2 (the comet Halley nucleus had approximately this γ value)Requ= 33 km; the thickness of the mineral crust equals ≈ 10−2m for the heat conductivity coefficient ƛ ≈ 0.2 Jm−1s−1K−1. The results of calculations of the orbital elements evolution of the comet Hale-Bopp during one rotation around the Sun show that the comet will not collide with Jupiter (both passages near Jupiter will take place at distances more than 4 AU).
Electron Beam as Origin of White-Light Solar Flares
Authors: Aboudarham J. , Henoux J. C.
Published: July 2016

We study the effect of chromospheric bombardment by an electron beam during solar flares. Using a semi-empirical flare model, we investigate energy balance at temperature minimum level and in the upper photosphere. We show that non-thermal hydrogen ionization (i.e., due to the electrons of the beam) leads to an increase of chromospheric hydrogen continuum emission, H− population, and absorption of photo-spheric and chromospheric continuum radiation. So, the upper photosphere is radiatively heated by chromospheric continuum radiation produced by the beam. The effect of hydrogen ionization is an enhanced white-light emission both at chromospheric and photospheric level, due to Paschen and H− continua emission, respectively. We then obtain white-light contrasts compatible with observations, obviously showing the link between white-light flares and atmospheric bombardment by electron beams.
Models of Flaring Loops
Authors: Emslie A. Gordon
Published: July 2016

We review the somewhat questionable concept of an isolated flare loop and the various physical mechanisms believed to be responsible, to some degree, for energy transport within the loop structure. Observational evidence suggests a predominant role for high-energy electrons as an energy transport mechanism, and we explore the consequences of such a scenario in some detail, focusing on radiation signatures in the soft X-ray, hard X-ray, and EUV wavebands, as observed by recent satellite observatories. We find that the predictions of flare loop models are in fact in excellent agreement with these observations, reinforcing both the notion of the loop as a fundamental component of solar flares and the belief that electron acceleration is an integral part of the flare energy release process.
Radio Emission From Stellar Flares
Authors: Kuijpers Jan
Published: July 2016

An overview is given of the observations of stellar radio ‘flares', defined as radio emission which is both variable in time and created by explosive releases of magnetic energy. The main sources of such flares are late-type Main-Sequence stars, classic close binaries, X-ray binaries, and pre-Main-Sequence stars.

We summarize the interpretations of these observations in terms of the various incoherent and coherent emission mechanisms. The possible importance of a coherent emission process in electrostatic double layers is pointed out.

We briefly indicate the diagnostic importance of radio emission for the flare process in classic and compact stars. In particular we discuss the possible production of radio flares from interactions between an accretion disk and the magnetic field of the central object.
Hydrodynamic Models of Solar and Stellar Flares
Authors: Peres Giovanni
Published: July 2016

This paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.
Summary of Automation on the AURA 150-inch Telescope
Authors: Crawford D. L.
Published: July 2016

We hope to have a well-planned program tied to the astronomical specifications demanded. We also hope to save time and money, very important considerations in high cost, big science.

I have become really aware of the sink of dollars and man-hours that technology involves, especially so when it is not well defined and well planned. We hope to avoid a near bottomless sink if we can. Total systems design is very important, not just a careful design of each subsystem.

In adopting automation, I want to insist that we don’t lock out certain experimental possibilities that we had before, or lock out certain type people (good ones) who are unwilling or unable to work with the highly sophisticated equipment we’ll be providing. Excellent astronomy has been done with poor equipment used by good astronomers; even the best equipment doesn’t do the best astronomy without the full involvement of good scientists. What I’m saying is, perhaps, that the system has to be our slave, not the reverse, and that we should not be limited by it.

What we want is an improvement in astronomical research, not merely in the gadgetry involved. The key to success may well be to strive for the best possible astronomer-technologist interface.
Aspects of an Integrated Telescope Computer System
Authors: Laustsen S. , Malm B.
Published: July 2016

The art of computing was early recognized by astronomers as being the link between observation and theory. Computing became more and more important with the appearance of electronic computers.

Today we can regard the application of electronic computers in three different aspects.

1.

Theoretical investigations.

2.

Data handling, that means collecting of astronomical observations and reduction to observational results.

3.

Control of telescopes and other astronomical instruments.

The present paper deals with item No. 3 only. It should, however, be emphasized that the combination of items 2 and 3 will lead to fully automatic astronomical observation in the future.
Direct Analysis of Spectra by Image Isocon and Computer
Authors: Walker G. A. H. , Auman J. R. , Buchholz V. , Goldberg B. , Isherwood B.
Published: July 2016

Astronomical spectra are, with few exceptions, still being recorded on photographic emulsions. These generally have the advantages of better spatial resolution and larger available area than existing photoelectric imaging detectors. On the other hand they do suffer from a small dynamic range (15 or 20: 1), reciprocity failure, and a quantum efficiency of less than 1 per cent. Image intensifiers and image orthocons can be used to improve sensitivity, but where photographs are used for the record the other problems tend to remain. Calibration and extraction of the appropriate astronomical information in digital form involves a considerable amount of time and careful work, as one can appreciate from many of the papers presented at this colloquium.
Digital Filtering of Stellar Spectrograms
Authors: Rusconi L. , Sedmak G.
Published: July 2016

This paper deals with the possibility of recovering the information contained in a spectrogram, in the case of line widths larger than the mean period of the granulation noise of the photographic plate. Suppose the spectrogram to be known by means of its microphotometric one-dimensional record,e.g. x(t), where x is the transmittance of the plate at abscissa (wavelength) t. The measurement of the position and shape of a line of the spectrogram, easy when the amplitude of the line exceeds the granulation noise, becomes very hard to do if the S/N ratio approaches unity. Nevertheless, as the power spectrum of the noise has normally a bandwidth larger than the spectrum of the signal, it is possible to reject all the noise power beyond the highest frequency in the signal spectrum, by means of suitable filters. This technique does not lose any useful information, since by definition the information is the signal, while on the contrary it betters the S/N ratio by diminishing the noise power. Of course, as both the signal and noise spectra are continuous, it is not practically possible to perform the filtering without signal losses. However, the technique may be advantageous in all cases, such as highly rotating stars, in which the spectrum of the signal has a cutoff much sharper than the noise cutoff. A simple criterion of applicability is the base width of the lines: if the base width is larger than the granulation noise period, the filtering may result in an improvement of the S/N ratio.
Some Information on the Catania Flare Star Survey
Authors: Cristaldi S.
Published: July 2016

I should like to give some information on the activity of the Catania Working Group on Flare Stars constitued by G. Godoli, M. Rodono and myself.

The first purpose of our work is to carry out a sufficient large amount of homogeneous photoelectric observations.

A first series of data, which refer to 1967 and 1968 observations, has already been published in the Supplement of Astronomy and Astrophysics (2, 223,1970).
The Locating of Hot Spots on Components of Algol System
Authors: Walter Kurt
Published: July 2016

The existence of hot spots on components of semi-detached Algol systems has been suspected for a long time, the reason being the distortions observed in many light curves outside of eclipse. However, the question whether such a distortion is caused by absorption or by additional emission and, in the latter case, from which component the emission may come from, could be answered only recently, now that we have a good idea of the trajectories which gas streams follow.
Variables in Globular Clusters, the Common and the Rare
Authors: Hogg Helen Sawyer
Published: July 2016

The title of this talk is really just a different phrasing from one I have used at several IAU meetings on the subject of numbers and kinds of variables in globular clusters. To furnish this material, I have finished the Third Catalogue of Variables in Globular Clusters. Since many of you are coming to this Colloquium with new information, the Catalogue is in draft form with a request that corrections and additions be given me by October 2, after which the draft will go to the printer.

The First Catalogue of Variables in Globular Clusters was published at this observatory in 1939 and the Second Catalogue in 1955. In 1966 appeared the excellent Catalogue of Variables South of Declination—29° by Fourcade, Laborde and Albarracin, with splendid large prints of identification charts.
The Variable Stars in NGC 6723
Authors: Menzies John
Published: July 2016

Abstract*.

A study has been made of the variables in the Southern Hemisphere globular cluster NGC 6723, which is suspected of being relatively metal-rich on the basis of its colour-magnitude diagram and of its integrated spectral type of G3. Seven new RR Lyrae stars and two bright red, probably semiregular, variables have been found and the suspected variable of Fourcade and Laborde has been confirmed. The complement of RR Lyrae stars is now 27, consisting of 4 c-type and 23 ab-type variables, the mean periods being Pc = 0.d292 and Pab = 0.d537. On the basis of the two-colour diagram of the horizontal branch stars the cluster is considered to be virtually un-reddened. Applying Christy’s models to the data from this study we find the following parameters for the variables: Mv= 1.m10, mass = 0.42 M⊙, and Y=0.4.
New determination of the plate constants of the Bordeaux zone of the astrographic catalogue
Authors: Herget Paul
Published: July 2016

The plate constants of the Astrographic Catalogue (A.C.) are subject to improvement from at least two sources: improved positions of the comparison stars, and the elimination of human and typographical errors by the use of electronic data reduction processes. One of the most important purposes of the AGK3 project was to establish more accurate proper motions for these stars than were previously available. Therefore it was necessary to await the results of AGK2—3 in order for us to make full use of them, and we are deeply indebted to Dr. W. Dieckvoss for sending us this material at the earliest possible time. We chose to work with the Bordeaux Zone because Dr. P. Semirot has established a separate catalogue of the positions of the comparison stars of this zone with an epoch of 1953.
Photometric astrometry of minor planets
Authors: Mulholland J. Derral , Nather R. Edward
Published: July 2016

The technique of timing occultation or eclipse events with high-speed photometers, which we shall call “photometric astrometry”, has been used by Evans, Nather, Silverberg and others to obtain lunar occultations with millisecond resolution, to reduce the observation of occultation reappearances to a routine event, to measure the diameter of Io and the diameter and flattening of Jupiter. We propose the possibility of a concerted program to use this technique for the determination of asteroid dimensions and shapes. It appears reasonable to expect that a single observatory could observe about ten events per year in which a sizeable minor planet occults a star that is three magnitudes fainter or less. Such events could be timed to about 10 msec. The development of inexpensive, portable equipment would greatly increase the number of possible events to be observed. Such equipment could open this activity to sophisticated amateur observers, similarly as in the grazing occultation program.
Meteoric storms and formation of meteor streams
Authors: Sekanina Zdenek
Published: July 2016

Meteoric storms must be very young formations, since planetary perturbations disperse any dense cloud of meteoroids within several revolutions around the sun. It is shown that, by comparing the dates of appearances of the storms of a meteor stream with the return dates of the parent comet, insight can be gained into the problem of the origin and early evolution of such a stream. Applying a recent theory of particle ejection from comets, we have developed a formula relating the character of motion of a cloud of meteoroids to the circumstances of ejection.

Practical application of the method to the Leonid, Perseid and η-Aquarid storms indicates low mass density of cometary meteoroids (not more than 0.3 g/cm3), ejection velocities of tens to hundreds of meters per second (with water vapor as the drag force), and suggests that meteoroids are ejected from periodic comets predominantly after perihelion. This finding contrasts with observational evidence of the type II tails of ‘new’ dust-rich comets. It is concluded that the discrepancy may actually reflect structural differences between the ‘new’ and periodic comets.
Systematic Radio-Observations of UX Arietis: Analysis of Its Variability
Authors: Torricelli-Ciamponi G. , Neidhöfer J. , Massi M. , Chiuderi-Drago F.
Published: July 2016

UX Arietis is an active binary system with an orbital period of 6.44 days. The presence of long lasting large spots on the surface of the more active star has been deduced from optical observations (Vogt & Hatzes 1991).

The observations presented here have been performed from December 1992 until October 1994 using the Effelsberg 100 m telescope. The instrument was available for this program in the gaps between previously scheduled observations. For this reason our observations span a frequency interval between 1.4 GHz (21 cm) and 43 GHz (7 mm), depending on the scheduled receiver at each observing time. These data, which are an extension of those published by Neidhöfer et al. (1993), are shown in Fig. 1, plotted in terms of the known orbital period (6.44 days). The search for different periodicities (by using the Phase Dispersion Minimization method) has shown the existence of two main other periods: at 156 days and at 24 days (Massi et al., in preparation).
A Possible Discovery of a Flaring 1012 eV Gamma-Ray Source near the Red Dwarf EV Lac
Authors: Alekseev I.Yu. , Chalenko N.N. , Fomin V.P. , Gershberg R.E. , Kalekin O.R. , Neshpor Yu.I. , Stepanian A.A.
Published: July 2016

During the 1994 coordinated observations of the red dwarf flare star EV Lac, the star was monitored in the very high energy (VHE) γ-ray range around 1012 eV with the Crimean ground-based γ-ray telescope GT-48. This telescope consists of two identical optical systems (Vladimirsky et al. 1994) which were directed in parallel on EV Lac.

The detection principle of the VHE γ-rays is based on the Čerenkov radiation emitted by relativistic electrons and positrons. The latter are generated in the interaction of the γ-rays with nuclei in the Earth’s atmosphere that leads to an appearance of a shower of charged particles and γ-quanta. The duration of the Cherenkov radiation flash is very short, just about a few nanoseconds. The angular size of the shower is ∼ 1°. To detect such flashes we use an optical system with large area mirrors and a set of 37 photomultipliers (PMs) in the focal plane. Using the information from these PMs which are spaced hexagonally and correspond to a field of view of 2°.6 on the sky, we can obtain the image of an optical flash. The electronic device permits us to detect nanosecond flashes (40 ns exposure time and 12 μs readout dead-time).
Multifrequency Analysis of a UV Ceti Flare on 1991 December 31
Authors: Stepanov A.V. , Fürst E. , Krüger A. , Hildebrandt J. , Barwig H. , Schmitt J.H.M.M.
Published: July 2016

An analysis of optical, radio and X-ray observations of the flare of December 31, 1991 on UV Ceti is presented. Radio spikes at 4750 GHz are interpreted in terms of both ECM and plasma emission. Resulting parameters of the flare plasma are discussed.
Photometric Behaviour of the EXors V1118 Orionis and V1143 Orionis
Authors: Paul C. , Kroll P. , Lehmann T.
Published: July 2016

We investigated the long-term photometrical behaviour of the EXors V1118 Ori and V1143 Ori on the basis of the Sonneberg Plate Archive. About 2800 plates were checked for outbursts of these stars. We found several dozens of plates where the stars appeared to be distinctly brighter than the plate limit. To get magnitudes we have scanned those plates and applied a special method of brightness determination which is currently used at Sonneberg Observatory. Because of the small number of plates we were able to extract only crude estimates of some typical time scales of outburst and quiescent phases.
Spectral Variability and Photometric Behaviour of the Symbiotic Nova PU Vul in 1985-1994
Authors: Efimov Yu.S. , Gershberg R.E. , Savanov I.S. , Shcherbakov A.G. , Shcherbakov V.A.
Published: July 2016

We present preliminary results of observations of the Hα, HeI 5876 and NaI D lines profiles in spectra of PU Vul. The variability of profiles is confronted with the photometric behaviour. The observations were carried out with a CCD camera, installed in the coudé spectrograph of the 2.6 m Shajn telescope. 68 spectra of the Hα line and 25 spectra in the region of the HeI and NaI lines were obtained.

Fig. 1 (left panel) presents the evolution of the Hα line from 1985 to 1994, displaying selected typical profiles in different years. The profiles are shown in a heliocentric wavelength scale and in logarithms of intensity. Variations of line intensity, line width, as well as radial velocity of the centre of weight of the total emission and absorption components are observed.

Stronger and more complex variability is observed in the region of the HeI and NaI D lines. The strong P Cyg type absorption in the NaI D lines during 1985-1987 disappeared in later spectra as a result of total ionization of NaI (Fig. 1., right panel). Contrary to that behaviour, HeI 5876 shows variations from a pure absorption profile to a very strong and wide emission profile.
X-ray Bursts
Authors: van Paradijs Jan , Lewin Walter H.G.
Published: July 2016

An X-ray burst is a sudden increase (rise time of order seconds) of the X-ray brightness of an X-ray source, which after reaching its peak decays, generally within a minute. The sky distribution of X-ray burst sources indicates that they are galactic objects (see Fig. 1); their concentration to the direction of the galactic center tells us that they lie at typical distances of ∼ 8 kpc, with corresponding peak luminosities of order 1038 erg s−1. The X-ray and optical properties of the persistent emission of X-ray burst sources show that they are low-mass X-ray binaries, in which mass is transferred from a rather normal low-mass (< 1 M⊙) star to a neutron star. The persistent emission is caused by the conversion of kinetic energy of the transferred matter into heat, at a rate of ∼ GM/R (∼ 0.1c2) per gram of accreted matter. The bursts are caused by unstable thermonuclear burning of material that has accumulated on the neutron star (‘thermonuclear flash’).

The global properties of X-ray bursts, in particular their dependence on the mass accretion rate, are fairly well understood. Different from the case of γ-ray bursts (see the contributions by Fishman, Hartmann and Kouveliotou to this Colloquium) the relevant question about X-ray bursts is not ‘What are they?’, but rather ‘What use are they?’. As we will argue here, X-ray bursts may provide us information on the mass and radius of a neutron star. This usefulness of X-ray bursts derives from the fact that the burst emission originates from the surface of the neutron star, unlike the persistent emission caused by mass accretion, of which we only know that it comes from the neutron star’s near vicinity.
Nova Patrol at Abastumani
Authors: Kimeridze Givi N. , Kurtanidze Omar M.
Published: July 2016

The Schmidt telescope (360-333-625 mm) of the Abastumani Astrophysical Observatory has been used for photographic observations for more than fifty years. It provides a field of 7°.3 (80 mm) and a non-vignetted field of 4° (44 mm). A limiting magnitude of 16m.5 can be reached in 7-8 min exposure on medium sensitivity astronomical films and 18m with fine grain emulsions.

Multicolour and polarization observations of a few hundred relatively bright galaxies were carried out by M. Vashakidze during the first two decades of the telescope operation. In the mid-1950s, he also discovered the strong polarization of the Crab nebula. Since 1961, systematic photographic observations are carried out in the framework of the International Cooperation Programme of Supernova Patrol in 24 fields. The telescope is also used to study the brightness variations of eruptive and exploding variable stars.
Detections of Neutron Stars in the Extreme Ultraviolet
Authors: Bowyer Stuart
Published: July 2016

Neutron stars were not expected to be observable in the extreme ultraviolet and hence their detection in this band is a surprise. More important is that EUV observations provide unique new information on these objects. In the accompanying Table 1, I list the neutron stars detected in the EUV with the Extreme Ultraviolet Explorer (EUVE). The binary object Her X-l is the only object detected in the all sky survey. This is not surprising since it is the only neutron star system with sufficient intensity to be detectable in the 500 to 2000 second sky intergrations which are typical for the EUVE all sky survey. All the neutron stars were detected in the 100 Å (Lexan) bandpass. A more complete description of EUVE and the all sky survey are provided in Bowyer and Malina (1991), and in Bowyer et al. (1994).
X-Ray Selected EUV Galaxies: A Quest for the Faintest Extragalactic EUV Sources
Authors: Fruscione Antonella
Published: July 2016

Using data from the public archive of the Extreme Ultraviolet Explorer (EUVE) all-sky survey, we have systematically searched for extreme ultraviolet (EUV) emission (58-174 Å, 0.07-0.21 keV) around approximately 2500 distinct positions in the sky corresponding to known X-ray emitting extragalactic sources. We find that 20 X-ray galaxies are EUV bright and were detected with significance above 4 σ during the EUVE survey: 8 are reported here for the first time (MS 0037.7−0156, Mrk 142, M 65, EXO 1128.1+6908, M 87, Mrk 507, PKS 2005–489 and 1H 2351−315.A). 68 additional galaxies are detected with a lower significance (3 < σ < 4), but the list is affected by a high percentage of spurious sources.
EUV Emission Sources in Gas-Dynamic Models of Stellar Flares
Authors: Livshits M.A. , Katsova M.M.
Published: July 2016

A stellar flare model in which the main energy release is located above the chromosphere based on a set of elementary acts of the electron acceleration or impulsive heating of plasma is discussed. The response of the chromosphere to impulsive heating for both a single burst and the simultaneous effect of a set of the bursts is considered.

The results of numerical modeling of the process of explosive evaporation of the stellar chromosphere allow us to select 3 classes of EUV emission source: (1) the bursts of the EUV emission in the temperature range of 3 · 104 – 3 · 105 K at the beginning of each of elementary act of the energy release; (2) the bursts of the EUV emission at temperatures T ≈ 106 K, accompanied by outflow of heated plasma; (3) the EUV emission, caused by new features of the process, namely, when the maxima of the distribution of the pressure are forming in the region of the downward-moving thermal front.

The properties of the EUV sources, velocities of the plasma motions therein, and possible behaviour of the light curve for an elementary burst are discussed.