bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of Variable-Star Observations Using Basicode
Authors: Jurriens Theo
Published: July 2016

The Dutch variable star section of the ‘Nederlandse Vereniging voor Weer-en Sterrenkunde’, founded in 1960, has about 10 to 15 regular observers. Depending on the weather conditions they perform 5 to 10 thousand observations a year. Our observation-recorder Henk Feijth collects the observations on paper and, since 1985, also on computer-cassette. From these contributions Feijth compiles a list on paper for the A.A.V.S.O. The cassette is written in a special format using the BASICODE program, see 2.

The reduction of the observations can be described as following:

1.

Every observer and computer-owner enters each observation as a DATA statement in a BASIC program. So each DATA statement is a record representing one observation, each DATA statement contains 20 characters:

1- 6 Starname

7-10 int(JD-2440000)

11-13 fractional part (3 decimals)

14: or <

15-17 estimate without decimal point

18-20 observer code

So a month of observations is simply a BASIC program consisting of just DATA statements.

2.

The Dutch broadcasting organization (NOS) has designed a kind of ‘Universal’ BASIC called BASICODE (version 2). With the aid of BASICODE computer X can read the programs of computer Y. The observer translates his data statements (the observations) into the BASICODE format. This is saved on cassette and sent to our recorder.

3.

Our recorder enters the monthly observations onto the BBC micro with the aid of the BASICODE translation program. Now the recorder runs a program that changes the star name into the Harvard number. This is done for the observations of every observer. After that the whole bunch of observations is sorted in ascending order of Harvard number and JD.

4.

The file of observations obtained in 3 is used as a source for our own reports, a graphic representation of the observations, and for simulating A.A.V.S.O. record sheets. This ‘end product’ we send to the A.A.V.S.O.
P/Halley: The Disconnection Event of 1986 April 11
Authors: Bergé P.M. , Mahoux G. , Levasseur-Regourd A.C.
Published: July 2016

This work was carried out by an expedition organized by the S.A.F. in 1986 April to La Réunion. The aim was to observe and photograph P/Halley, within the framework of IHW, as part of the Island Network in the southern hemisphere. To be more precise, our work consisted of studying large-scale phenomena: the structure, dynamics and possible disconnection events in the plasma tail. We were lucky enough to observe one of the latter on the night of April 11/12, and describe it here.

For the Island Network, IHW had a number of Schmidt telescopes (Celestron 8). One was lent to the S.A.F. and this is what we used. This telescope has a focal ratio of 1.5, with a 200-mm (8-inch) objective and 300-mm focal length. We used only Kodak TP2415 film, hypersensitized in forming gas (24h at 60°C).
New Trends in the Discovery of Comets by Amateurs
Authors: Merlin J.C.
Published: July 2016

The ways in which amateurs may increase their chances of discovering comets were described. Amateurs discover a considerable proportion of comets, but their contribution is greater among long-period comets. The relative proportions of short-period comets is revealing: 1 in 2 for professional astronomers, 1 in 8 for amateurs. Professional discoveries are largely a by-product of searches for asteroids: the comets have low inclinations (i< 30°) and are faint (m1> 14). Amateurs are most successful in areas close (<60°) to the Sun. Typical apertures are 150-mm, and most comets are brighter than magnitude 10.

Past results show that there is a strong correlation between number of observers and number of discoveries. Several amateurs have discovered comets at great elongations with larger telescopes (≥ 400 mm). The comets tend to be fainter (10 <m1< 12). Several comets have been discovered with simple equipment (200- or 300-mm telephoto lenses) down to magnitude 13.

Calculations of the distribution of discoverable comets show that an average of 14 comets (9 <m1< 14) are missed per year.
Observation and Analysis of Comet Tails
Authors: van de Weg R.L.W.
Published: July 2016

Details of H2O and dust production in P/Halley are mainly derived from amateur observations of cometary tails, leading to a gas/dust mass-ratio. The rotational period (2.21 day) is also found from amateur observations. Velocity and acceleration of the plasma and velocity and direction of the solar wind are also derived, together with size and indications of the mass-distribution function for dust particles.

These techniques have been applied to other comets, giving interesting results on differences between various comets. There is a lot of information available in cometary photographs. The coordination and archival storage of such information is urgently required.
The “Sonate” Campaign
Authors: Mazel Jean , Futaully Robert
Published: July 2016

“Sonate” (Sondages acoustiques pour l’évaluation de la qualité d’images des téléscopes) – Acoustic sounding to estimate the quality of telescope images – is a prime example of professional/amateur collaboration as it involved 3 professionals and 22 amateurs, who, in order to collect the maximum amount of data, relayed one another in 10-day shifts over a period of 4 months in 1984, using the 1-m telescope at the Pic du Midi. A preliminary campaign with the 2-m telescope in 1982 had shown that the profile of sound waves reflected from the layers above a site could be correlated with the quality of telescopic images at the same site.
Long-term Monitoring of Solar Activity by Amateur Astronomers
Authors: Reinsch Klaus
Published: July 2016

Professional solar astronomy concentrates on the study of the atmosphere and interior of the Sun. Little attention is given to “classical” programmes, mainly statistical investigations of solar activity. Although the main properties of phenomena associated with the solar cycle seem to be understood there are still enough details to be explained, making it worthwhile monitoring different indicators of solar activity, even if no immediate results are to be expected. Such routine observations are ideal work of amateur astronomers.

Members of West German local astronomical societies founded the journal Sonne in 1977 to combine their efforts on solar observations. The first issue was presented at a conference on amateur solar observation held in Berlin in April 1977. Sonne is compiled by an editorial staff of 23 amateurs from all over West Germany, and is distributed among nearly 500 readers in 20 countries. With the increasing number of foreign readers, the main articles in Sonne are provided with English abstracts.
GEOS Results for PX Cephei
Authors: Boninsegna Roland
Published: July 2016

This star’s variation was discovered photographically by Romano in 1957. It was included in the GCVS in 1978 as PXCep, and I started to observe it in 1983.

The star is usually at maximum, but on several occasions I was able to observe either a rise or the start of a fall. Finally on 1984 October 21, the first minimum was observed, and then a second one ten days later.

The star’s constant behavior, outside the minima, indicated that is was an EA type of eclipsing binary. The amplitude of the eclipses is about 2.6 mag. Secondary minimum therefore has an amplitude of 0.11 mag., which is undetectable visually.
Meeting the Public: Popular Observatories
Authors: Kleczek Josip
Published: July 2016

“L’homme est infiniment petit par son corps, mais il est infiniment grand par son esprit”. Blaise Pascal

Popular observatories (PO) are an important link between astronomers and the public. Fig.1 represents the flow of information about the Cosmos and the role of POs.

The flow of information about celestial bodies starts with photon emission. The emitted photons carry the information about the moment when they are born. They transfer the encoded information through cosmic space in all directions, among others towards our planet. By ground-based or space-based instruments astronomers decode the information in the photons. The size and shape of celestial bodies are determined with great precision (by photography and interferometry). Direction from which the photons arrive determines the position of their source (astrometry). The amount of photons (photometry), their frequency (spectrophotometry) and the direction of their oscillation (polarimetry) are other information decoded from the incident photons. The observational instruments are the interface between the Cosmos and astronomers’ minds.
Transmission of Astronomical Data and Information by the A.F.A. Videotext System
Authors: Pellequer Bernard
Published: July 2016

Following the introduction of a videotext system in France using MINITEL terminals, the Association Française d’Astronomie organized an astronomical information service. This covers celestial and space events, location of the planets, lists of societies and clubs, bibliography, etc. A practical demonstration of the system in use was given.
The Open Sky Underground
Authors: Beauvois Igor , Las Vergnas Olivier
Published: July 2016

From 1985 March 26 to April 5, a special public astronomical education campaign was mounted in 16 stations of the Paris Metro. Apart from static displays, items included two planetariums, mirror-making, numerous round-table discussions, astronomical films, etc. Millions of people saw some part of these displays and surveys showed that many returned several times. The event was coordinated by the Association Nationale Science Techniques Jeunesse [National Association for Youth Science and Technology] and involved many official and private bodies, 30 astronomical groups, and 420 employees of the RATP [Régie autonome des transport parisiens – Paris city transport authority].
The Activities of Astronomical Clubs
Authors: Bourdeille Christian
Published: July 2016

Recent studies have shown that there are some 60000 amateur astronomers in France. This has been reflected in the number of astronomical clubs that have been formed. This contribution summarized the aims and activities of such clubs, the conditions for their success, and their contribution to scientific astronomy.
The Flammarion Astronomical Society of Montpellier
Authors: Faidit Jean-Michel
Published: July 2016

The Flammarion Astronomical Society of Montpellier was founded in 1902 and remained very active until 1923, when the death of certain prominent members, precipitated its own demise. An observatory in the Tour de la Babote was opened in 1903 but fell into disrepair in the 1920s. One prominent member was Marcel Moye, who on his death in 1939, left his instruments to the S.A.F., accompanied by the sum of 100 000 Fr, half of which was used to endow an award for young astronomers.
Abundances in J-Type Carbon Stars
Authors: Utsumi Kazuhiko
Published: July 2016

It has been found by Utsumi(1985a,b) that in J-type carbon stars of C4-5 and WZ Cas(C9,2J Li), abundances of s-process elements with respect to Fe are nearly normal, while in normal carbon stars of C5-8, heavy metals are overabundant by factors of 10-100, and rare-earth elements are overabundant by a factor of about 10.

In the MK system, most J-type stars are classified as C4-5,4-5 stars which show very strong C2 and CN bands. Yamashita(l972,1975) classified many C7-9 stars most of which are CS or SC stars. His classification of C7-9J stars is mainly based on Cl2C13(0,1)band at 6168 A, C13N(4,0)band at 6260 A, and LiI 6708 A line. In most of C7-9 stars, lines of s-prooess elements are greatly enhanced. It is a question if in all J-type stars abundances of s-process elements are nearly normal or not.
Helium Flashes Through the NCO Reaction
Authors: Arai K. , Kaminisi K. , Hashimoto M. , Nomoto K.
Published: July 2016

It is generally accepted that the helium flash occurs when the 3α reaction commences in the degenerate helium core of low mass stars. In this core, original CNO isotopes have been converted into 14N and the electron Fermi energy becomes large enough to approach the threshold energy for e-capture on 14N. Hence Kaminisi et al. (1975) have pointed out that in these circumstances the 14N(e−, v)14C(α,γ)18O (NCO) reaction may play an important role for igniting the helium flash.

We, therefore, examine the effects of the NCO reaction on the evolution of low mass stars. A key ingredient of the NCO reaction is that the density reaches the threshold for e-capture (ρth≃ 106 g cm−3). Evolutionary sequences are presented for the cases of accreting helium white dwarfs (Hashimoto et al. 1986) and a 0.7 M⊙, Population II star ascending the giant branch.
Evolutionary Helium and CNO Anomalies in the Atmospheres and Winds of Massive Hot Stars
Authors: Walborn Nolan R.
Published: July 2016

The ubiquitous evidence for processed material in the atmospheres, winds, and circumstellar ejecta of massive stars will be reviewed. A broad array of normal and peculiar evolutionary stages is considered, up to and including Type II supernova progenitors. The quantitative analysis of these spectra is difficult, and until recently for the most part only qualitative or approximate results have been available. However, several important current programs promise reliable abundance determinations, which will enable detailed comparisons with recent evolutionary calculations. A significant emerging result is that the morphologically normal majority of both hot and cool supergiants may already display an admixture of CNO-cycle products in their atmospheres. It may become possible in this way to identify blue supergiants returning from the red supergiant region, as appears to have been the case for the SN 1987A progenitor.
NLTE Analysis of the Wolf-Rayet Star HD193077 (WN5+abs)
Authors: Schmutz W. , Hamann W.-R. , Wessolowski U.
Published: July 2016

A model atmosphere code that accounts for the special physical conditions in Wolf-Rayet atmospheres (Hamann and Schmutz, 1986; Wessolowski et al., 1987) is used to analyse the spectrum of the Wolf-Rayet star HD193077 (WN5+abs). The stellar parameters are determined such that the profiles of the helium lines He I λλ4471, 5876, He II λ5412, and the absolute visual magnitude are reproduced.

In order to estimate the systematic errors introduced by the model assumptions, we perform some test calculations. Instead of the velocity-law exponent of ß=1, another fit is obtained with ß=0.5 (Fig. 1). This fit yields an effective temperature of about 3000K higher than with ß=1. In order to simulate the effect of the suspected hydrogen content, a further fit (Fig. 2) is made when one free electron per helium atom is added artificially. This has only marginal influence on the derived temperature (+100K). Thus, we conclude that our model assumptions may introduce a systematic error of the order of 5000K.
Dust Driven Winds in Late Supergiants
Authors: Sedlmayr Erwin , Dominik Carsten , Gail Hans-Peter
Published: July 2016

The oool extended shells of giants and supergiants are well known to be places of copious dust formation as indicated by the occurrence of pronounced extinction, reddening, and polarization of the continuous star light and by the appearance of particular absorption features, both manifesting the interaction of photons with particles considerably larger than atoms or molecules.

The accepted explanation of these phenomena is the formation of circumstellar dust, i.e. small solid particles with a typical size of the order of 0.1 micron. However, the analysis of these effects yields only information on the interaction of photons with certain functional groups within the clusters - e.g. Si-O, C-H, C-C bending and Si-O, C-C,... stretching vibrations - and thus allows no definite determination of the “real” physical structure and chemical composition of the grain particles. Therefore, observational conclusions concerning the properties of circumstellar dust can provide only some “mean” information which allows no definitive conclusions regarding the true nature of the observed grains (geometrical shape, crystalline structure,...?).
Atmospheric Evidence of Evolutionary Processes in Interacting Binaries
Authors: Kondo Yoji
Published: July 2016

The preceding invited paper by Sahade (1987) gave a balanced overall picture for the subject matter. I shall attempt to complement his talk in discussing two classes of atmospheric diagnostics of the evolutionary processes in interacting binary systems. These are: (I) Abnormal abundances of elements in the atmosphere resulting from the nuclear processes in the stellar interior. (II) Mass flow as a consequence of the evolution of either of the components and the Algol type binaries.

There are several classes of objects with abundance anomalies, such as Am stars. At least some of these objects are known close binaries. In particular, most Am stars appear to be close binary stars. However, the physical causes of the metallic overabundances in those stars are still unclear. We shall in the following examine Algol type binaries for abundance anomalies.
SN 1987A: An Australian View
Authors: Dopita Michael A.
Published: July 2016

The explosion of SN 1987A in the LMC during the early hours of February 23 1987, has presented southern observers opportunity, unique in our lifetime, to gain a new insight into the supernova phenomenon. Fortunately, SN1987A has risen to the challenge, and has shown us that many of our comfortable pre-conceptions about Type II events will have to be revised in fascinating and sometimes unexpected ways. This paper is an attempt to describe what has been learnt so far wth an emphasis on the research being carried out in Australia. All references are dated 1987 unless otherwise specified.
Light Curve Models for SN 1987A and Diagnosis of Supernova Interior
Authors: Nomoto Ken’ichi , Shigeyama Toshikazu , Hashimoto Masa-aki
Published: July 2016

Presupernova evolution of the progenitor of SN 1987A, hydrodynamics of explosion (shock propagation, explosive nucleosynthesis), optical light curve due to shock heating and 56Co decay, and X-ray and γ-ray light curves are calculated and compared with the observations of SN 1987A. Constraints on the mass of the hydrogen-rich envelope Menv (i.e., mass loss history) and the helium abundance in the envelope are obtained from the progenitor’s blue-red-blue evolution as well as from the light curve. The explosion energy E and the mass and distribution of 56Ni are inferred from the light curves. Models and observations are in reasonable agreement for E/Menv = 1.5 ± 0.5 × 1050 erg/M⊙, Menv = 5 - 10 M⊙, and MNi ∼ 0.07 M⊙. Mixing of 56Ni into the envelope is indicated.

Light curves of exploding bare helium stars are also calculated to see whether the observed Type Ib supernova light curves can be accounted for.
A Simple Treatment of the Problem of Radiative Transfer in Supernova-Like Envelopes
Authors: Isern J. , López R. , Simonneau E.
Published: July 2016

Since the only direct information, on the physics of supernova explosions comes from spectrophotometry of their light curves, it is wortwhile to put considerable effort on understanding the properties of supernova atmospheres. Two problems appear, however, in doing so. First, the mean free path of a photon in the region where the Spectrum forms (the atmosphere) is an important fraction of the supernova size and the plane parallel approximation breaks down. Second, the roles of scattering and absorption in the formation of the continuum are not clearly determined.

The complications introduced by spherical geometry arise from the angular derivative terms in the transfer equation and from the high degree of anisotropy introduced by the geometry. The complications introduced by scattering arise from the presence of the mean intensity in the source term of the transfer equation. As an outcome, its numerical solution is time consuming, and classical simplifications are not possible due to the strong anisotropy of the radiation field. In hydrodynamical calculations it is better to calculate the moments of the radiation field, but the success of this method depends on the possibility of replacing the infinite set of differential equations by the equations of low order moments plus a closure relationship that keeps all the properties of the higher moments.
Origin of a Diffuse Galactic Emission at 511 KEV
Authors: Signore M. , Vedrenne G.
Published: July 2016

Recent results of SMM on the galactic 511 keV annihilation radiation exhibit a constant flux during 4–5 years, in total disagreement with post 1980 balloon observations. However, all these results are compatible if one admits the existence of a variable point source near the Galactic Center of FP ∼ 10−3 ph cm−1 s−1 and a diffuse interstellar source of positrons: FD ∼ 1.5−1.8 10 ph cm−2 s−1 rad−1. Evaluations of 26Al and 56Co decays contributions have been given last year (2) and that of 44Ti decays more recently (3). We have studied the nature of the sources of the main e+ − emitting radioisotopes − SN and novae − and their galactic distributions using the observational data at 511 keV and at 1809 keV, the galactic angular distributions considered by Leising and Clayton (4) and the nucleosynthesis of the models of novae and SN of Woosley and his collaborators (5).
Is a stellar wind inherent in WR–stars throughout the whole of their evolution?
Authors: Gershberg R.E.
Published: July 2016

In addition to certain manifestation of a stellar wind during steady states of WR-stars that we have heard here about I have two notes on their extremal stages of evolution which may be also connected to such a hydrodynamical event.

The first note. There is a pecular object, HM Sge that had brightened for several magnitudes during several months. It has a strong emission spectrum that is similar to a planetary nebula spectrum in general, and it was suggested that we register a planetary nebula birth. However, in Crimea we have found that a total width of H-alfa emission line is ~ 2000 Km/sec and a central part of its profile is asymmetric significantly. These features exclude a genetic, relationship between HM Sge and Planetary nebulae.
Mass loss from hot stars below the main sequence
Authors: Viotti R. , Rossi L. , D'Antona F.
Published: July 2016

The evolutionary implications of mass loss from post-asymptotic giant branch stars is discussed, with reference to the UV observations of sdO's.
Mass loss from α Ori
Authors: Tanabe T. , Kamijo F.
Published: July 2016

High dispersion spectrograms of α Ori are obtained. Several strong absorption lines which have circumstellar components are measured. Assuming the plane-parallel envelope and thermal equilibrium, the mass loss rate is estimated as 1x10-6 Mʘ/yr.

To obtain the mass loss rate of red giant stars is very important in connection with the study of the stellar evolution. Several authors have observed circumstellar lines and obtained mass loss rate using precise theories of radiation transfer. However, accuracy of the studies seems to depend not on the adopted theories but on the dispersion of spectrograms, since the structure of the circumstellar space is too complicated to be expressed by,e.g.,single expansion velocity. Because our spectrograms have higher dispersion, compared with others, our study is meaningful, though the assumed model is very simple.
Stellar variability and individuality: observations and implications (invited paper)
Authors: Costero R. , Doazan V. , Stalio R. , Thomas R.N.
Published: July 2016

Customarily, one assumes that the internal structure of the star is not changed by a mass-flux from the atmosphere; thus one changes evolutionary calculations with mass-loss from those without it only by homologously decreasing the mass at each static evolutionary step. Furthermore, it is customary to assume that the mass-flux can be expressed in terms of only the thermal parameters (luminosity, Tepp) or (g, Teff). Sometimes rotation is introduced, but only as a modification of equatorial gravity, not of internal nonthermal structure. The phenomena of large-amplitude variability in times short compared with evolutionary ones, and of individuality (two stars of the same taxonomic class having different atmospheric distributions of Te and density) invalidate such static evolutionary calculations. We summarize the evidence for such large-amplitude variability in Be and la supergiant B stars. We also summarize the evidence for individuality as exhibited by observations: of OVI in OB stars; of x-ray luminosity across the HR diagram; of far-UV spectra of O stars; and of visual and far-UV spectra of Be stars. These observational results require nonthermal fluxes of mass and nonradiative energy to be imposed from below by the subatmosphere; which implies a nonthermal structure of subatmosphere and at least some part of the interior. Such nonthermal structure must then be included in evolutionary calculations. Thus current observations of nonthermal mass-flux from essentially all stars require including a nonthermal internal structure, not simply a mass-loss, in evolutionary calculations.
Winds in late-type stars: Mechanisms of mass outflow
Authors: Linsky Jeffrey L.
Published: July 2016

Four basic mechanisms have been proposed to explain the acceleration of winds in late-type stars –– thermal pressure gradients, radiation pressure on circumstellar dust grains, momentum addition by Alfvén waves, and momentum addition by periodic shock waves. In this review I describe recent work in applying these mechanisms to stars, and consider whether these mechanisms can work even in principle and whether they are consistent with recent ultraviolet and X-ray data from the IUE and Einstein spacecraft. Thermally-driven winds are likely important for late-type dwarfs, where the mass loss rates are small, and perhaps also in G giants and supergiants, but they cannot operate alone in the K and M giants and supergiants. Radiatively-driven winds are probably unimportant for all cool stars, even the M supergiants with dusty circumstellar envelopes. In principle, Alfvén waves can accelerate winds to high speeds provided the field lines are initially open or forced open by some mechanism, but detailed calculations are needed. Magnetic reconnection is an interesting suggestion for an acceleration mechanism when the field lines are initially closed. For the Mras and semiregular variable supergiants, periodic shock waves provide a simple way of producing rapid mass loss. Thus we are making some progress in understanding mass loss mechanisms for the cool half of the H-R diagram.
Stellar evolution with SMC chemical abundances
Authors: Hellings P. , Vanbeveren D.
Published: July 2016

Evolutionary computations are presented for massive stars between 20 Mo and 100 Mo with chemical abundances holding for the Small Magellanic Cloud, i.e. X = .76 and Z = .003. Mass loss by stellar wind is taken into account during core hydrogen burning. After core hydrogen burning some models are considered as members of close binary systems and are followed during their Roche lobe overflow stage according an early case B of mass transfer. During the core helium burning stage of the RL0F remnants mass loss rates comparable to WR stars are included in order to study the formation and the evolution of WR stars. Comparison with similar galactic computations (Vanbeveren, Packet, 1978) is made.
Massive stars burning helium: the numbers of WR stars and red supergiants in galaxies
Authors: Maeder A.
Published: July 2016

We have calculated evolutionary models of massive stars in the range 15-120 Mʘ from the zero-age sequence up to the end of the carbon burning stage (Maeder, 1981). Three sets of models with different mass loss rates Ṁ have been computed; the adopted parametrisation of Ṁ is fitted on the observations and thus the expression for Ṁ differs according to the location of the stars in the HRD.

In this short note we concentrate on the location of the He-burning stars in the HRD. The helium burning phase, which lasts 8 to 10% of the MS phase, is spent mainly as red supergiants (RSG) and as WR stars (note that for low mass loss, the time spent as A-G supergiants becomes longer).
On the evolutionary time scale of the accreting component in massive close binaries: consequences for the supernova event
Authors: Doom C. , De Grève J.P.
Published: July 2016

The remaining core hydrogen burning lifetime after a case B of mass exchange is computed for the mass gaining component in massive close binaries. Effects of stellar wind mass loss and mass loss during Roche Lobe OverFlow (RLOF) are included. Consequences for the evolutionary scenario are discussed.
Stellar mass loss and HII region morphology in Magellanic irregular galaxies
Authors: Dopita M.A. , Wilson I.R.
Published: July 2016

The problem of the interaction of a strong stellar wind with a massive collapsing neutral hydrogen cloud has been considered and a new class of steady flow solutions found.

The detailed comparison of these models with one filamentary shell, N70 in the LMC, shows that they successfully explain all the observed properties of the HII region and enable mean mass-loss rates to be derived for the central stars.
Observation of Global 160-min Infrared (Differential) Intensity Variation of the Sun
Authors: Kotov V.A. , Koutchmy S. , Koutchmy O.
Published: July 2016

The method developed and the instrument designed for detecting variations of the solar limb darkening at the atmospheric transparency window of the solar opacity minimum region of λ 1.65 µ are described. This differential technique proved to be successful in rejecting undesirable low frequency noises due to the atmosphere and to the instrument. Analysis of observations made in 1977, 1978, and 1981 indicates the persistance of global fluctuations of the IR differential, center-to-limb intensity at the wellknown 160 min period with an average amplitude of about ± 2 x 10-4 in units of the ‘average Sun’ intensity near 1.65 µm.
160-min Oscillations of the Sun as the Mean of Study of its Internal Structure
Authors: Gavryuseva E. A. , Kopysov Yu. S. , Zatsepin G. T.
Published: July 2016

The investigation of the models of the contemporary Sun with a mixed core has shown that the amplitude of some gravity modes of oscillations of the star can be mainly concentrated in the central region. This phenomenon takes place if the node of the amplitude of radial displacement coincides with the boundary of the mixed core. In this case the core can be regarded as a driving generator of the oscillations, determining their period and phase. It is suggested as the explanation of the observational properties of the 160-min oscillation.
Adiabatic Oscillations of Solar Models with a High-Z Convective Zone
Authors: Vorontsov S.V. , Marchenkov K.I.
Published: July 2016

Normal mode spectra and neutrino counting rates are calculated for a set of chemically-inhomogeneous solar models. Each model has a core with a high concentration of heavy elements; high opacity makes the core convective. The structure of the envelope is that of the standard model. It is shown that (1) the spectrum of g modes becomes less densely separated than that of the standard model, which simplifies the problem of interpreting 160-min oscillations; (2) low neutrino counting rates may be achieved for a low initial helium concentration in the core; (3) the models do not contradict the frequency spacing of global 5-min oscillations.
On the Influence of Nonlinearities on the Eigenfrequencies of Five-Minute Oscillations of the Sun
Authors: Belvedere Gaetano , Gough Douglas , Paternò Lucio
Published: July 2016

Fitting the results of linear normal-mode analysis of the solar five-minute oscillations to the observed κ – ω diagram selects a class of models of the Sun’s envelope. It is a property of all the models in this class that their convection zones are too deep to permit substantial transmission of internal g modes of degree 20 or more. This is in apparent conflict with Hill and Caudell’s (1979) claim to have detected such modes in the photosphere.

A proposal to resolve the conflict was made by Rosenwald and Hill (1980). They pointed out that despite the impressive agreement between linearized theory and observation, nonlinear phenomena in the solar atmosphere might influence the eigenfrequencies considerably. In particular, they suggested that a correct nonlinear analysis could predict a shallow convection zone. This paper is an enquiry into whether their hypothesis is plausible.

We construct κ – ω diagrams assuming that the modes suffer local nonlinear distortions in the atmosphere that are insensitive to the amplitude of oscillation over the range of amplitudes that are observed. The effect of the nonlinearities on the eigenfrequencies is parameterized in a simple way. Taking a class of simple analytical models of the Sun's envelope, we compute the linear eigenfrequencies of one model and show that no other model can be found whose nonlinear eigenfrequencies agree with them. We show also that the nonlinear eigenfrequencies of a particular solar model with a shallow eonvective zone, computed with more realistic physics, cannot be made to agree with observation. We conclude, therefore, that the hypothesis of Rosenwald and Hill is unlikely to be correct.
On the Detection of Subphotospheric Convective Velocities and Temperature Fluctuations
Authors: Gough D. O. , Toomre J.
Published: July 2016

A procedure is outlined for estimating the influence of large-scale convective eddies on the wave patterns of five-minute oscillations of high degree. The method is applied to adiabatic oscillations, with frequency ω and wave number k, of a plane-parallel polytropic layer upon which is imposed a low-amplitude convective flow. The distortion to the k – ω relation has two constituents: one depends on the horizontal component of the convective velocity and has a sign which depends on the sign of ω/k; the other depends on temperature fluctuations and is independent of the sign of ω/k. The magnitude of the distortion is just at the limit of present observational sensitivity. Thus there is reasonable hope that it will be possible to reveal some aspects of the large-scale flow in the solar convection zone
Torsional Oscillations of the Sun
Authors: Howard Robert
Published: July 2016

A series of digitized synoptic observations of solar magnetic and velocity fields has been carried out at the Mount Wilson Observatory since 1967. In recent studies (Howard and LaBonte, 1980; LaBonte and Howard, 1981), the existence of slow, large-scale torsional (toroidal) oscillations of the Sun has been demonstrated. Two modes have been identified. The first is a travelling wave, symmetric about the equator, with wave number 2 per hemisphere. The pattern-alternately slower and faster than the average rotation–starts at the poles and drifts to the equator in an interval of 22 years. At any one latitude on the Sun, the period of the oscillation is 11 years, and the amplitude is 3 m s-1. The magnetic flux emergence that is seen as the solar cycle occurs on average at the latitude of one shear zone of this oscillation. The amplitude of the shear is quite constant from the polar latitudes to the equator. The other mode of torsional oscillation, superposed on the first mode, is a wave number 1 per hemisphere pattern consisting of faster than average rotation at high latitudes around solar maximum and faster than average rotation at low latitudes near solar minimum. The amplitude of the effect is about 5 m s1-. For the first mode, the close relationship in latitude between the activity-related magnetic flux eruption and the torsional shear zone suggests strongly that there is a close connection between these motions and the cycle mechanism. It has been suggested (Yoshimura, 1981; Schüssler, 1981) that the effect is caused by a subsurface Lorentz force wave resulting from the dynamo action of magnetic flux ropes. But, this seems unlikely because of the high latitudes at which the shear wave is seen to originate and the constancy of the magnitude of the shear throughout the life time of the wave.
Magnetic Fields and Activity of the Sun and Stars: An Overview
Authors: Rosner Robert
Published: July 2016

I review recent work on the observation and theory of solar and stellar magnetic field activity and its relation to stellar activity, with particular emphasis on those aspects relevant to the problem of activity of red dwarf stars.
Global and Photospheric Physical Parameters of Active Dwarf Stars
Authors: Pettersen B.R.
Published: July 2016

Physical parameters (temperature, luminosity, radius, mass and chemical abundance) of the photospheres of red dwarf flare stars and spotted stars are determined for quiescent conditions. The interrelations between these quantities are compared to the results of theoretical investigations for low mass stars. The evolutionary state of flare stars is discussed. Observational results from spectroscopic and photometric methods to determine the rotation of active dwarfs are reviewed. The possibilities of global oscillations in dwarf stars are considered and preliminary results of a photometric search for oscillation in red dwarf luminosities are presented.
The Structure and Energy Balance in Main Sequence Stars
Authors: Jordan C. , Ayres T.R. , Brown A.
Published: July 2016

High-resolution spectra obtained with the IUE satellite have been used to study the structure and energy balance in the main sequence stars ξ Boo A, α Cen A, α Cen B and ε Eri. The EUV observations are combined with X-ray fluxes to predict the coronal temperatures, the electron pressures and energy lost or transferred by radiation and thermal conduction
Late-Type Ca II Emission-Line Stars in the Southern Hemisphere
Authors: Collier A.C.
Published: July 2016

The results of a photometric and spectroscopic study of twenty-three late-type southern stars with strong Ca II H and K emission are presented.

The presence of photometric variability, with similar properties to the photometric wave phenomenon seen in the RS Canum Venaticorum binaries, is noted in thirteen of the fifteen stars for which extensive photometry was obtained. Of twenty stars for which high resolution radial velocity measurements were obtained, ten are found to be single-lined and seven are found to be double-lined spectroscopic binaries. The periods range from 0.66 up to 53-9 days.
Some Properties of Stellar Transition Regions
Authors: Saxner Mikael
Published: July 2016

Among the strongest lines from stellar transition regions are the resonance lines of N V (1240Å), Si IV (1394 ,1403Å), and C IV (1549Å), which are all observable by the IUE.

In an earlier paper (Saxner, 198l) it was noticed that there is a correlation between the fluxes in these three lines. In Fig. 1 the ratio of the N V to the C IV flux is plotted against the ratio of the C IV to the Si IV flux. Verbally the correlation may be stated as follows: the Si IV flux and the N V flux are covarying; if one is strong the other also tends to be strong, and vice versa. In all cases the C IV line is the strongest.
Stellar X-Ray Activity in the Hyades
Authors: Stern Robert A. , Zolcinski Marie-Christine
Published: July 2016

Observations of the Hyades cluster with the Einstein Observatory and with IUE have uncovered a high level of coronal x-ray emission (Lx≃1029 era s-1 for solar-type stars) and similarly high fluxes of chromospheric and transition region line fluxes compared to the gun (Stern et al.1981, Zolcinski et al. 1981, 1982). A giant x-ray flare from a spectroscopic binary system in the Hyades has also been reported (Stern, Antiochos and Underwood 1982).
Synopsis of by Dra and II PEG Light Curves: Variability and Possible
Evidence of Differential Rotation
Authors: Rodonò M. , Pazzani V. , Cutispoto G.
Published: July 2016

BY Dra (MOVe+MOVe) and II Peg (K2IV-III) are well known noneclipsing spectroscopic binary systems showing the low-amplitude quasiperiodic photometric variability that is typical of spotted stars.

Since the discovery of their variability (Chugainov 1966, Eggen 1968) additional accurate photometry has been carried out (cf. Rodono 1982). On account of their highly variable light curves (LC), we have reanalyzed all the available observations and divided the original data into shorter time-interval sets, so that overlapping LCs with different shape could be separated. Additional LCs obtained at Catania Observatory till 198l were also included.
Solar Flares with SMM and Implications for the Physics of Stellar Flares
Authors: Pallavicini R.
Published: July 2016

XUV flare observations from SMM are discussed and a comparison is made with recent X-ray observations of stellar flares.
Magnetic Development of Flaring Regions at Centimeter Wavelengths
Authors: Kundu M.R.
Published: July 2016

It has been known for many years that the flare build-up manifests at centimeter wavelengths (2-6 cm), in the form of increased intensity and increased polarization of the active region. The flare-associated bursts originate in these intense sources, and the probability of occurrence of bursts increases with the increasing intensity of these narrow bright regions. With the availability of arc-second resolution using the VLA it has been possible to study the nature of this build-up from two-dimensional synthesized maps over short periods before the start of a flare. For a hard x-ray associated impulsive 6 cm burst observed on June 25, 1980 (Kundu, Schmahl, and Velusamy 1981), we produced several 15-minute synthesized maps in total intensity (I) and polarization (V) just before the flare onset (Kundu 1981). Figure 1 shows the central 11x16 regions of 15 minute synthesis maps over the period 14:45-15:45 UT. As can be seen from these Figures, the region is very complex, consisting of numerous components many of which are bipolar. These components have brightness temperatures of 6-9x106 K during the hour before the flare. The burst source was located close to the neutral line of these oppositely polarized regions near B. The burst maximum is identified, with a “+” and the burst extent averaged over the period 1551-1600 UT is shown by the dotted contour in the last map.
Twenty Years of Dedicated Photometry of RS CVn at Catania Observatory
Authors: Blanco C. , Catalano S. , Marilli E. , Rodonò M.
Published: July 2016

We present a complete set of yearly seasonal light curves (LC) of RS CVn obtained from 1963 to 1982 at Catania Observatory, integrated with two LCs obtained by Ludington (1978) in 1975 and 1976. This unique observation set vividly shows (Figure l) the migrating outside of eclipse “photometric wave” (PW), which was first evidenced by Catalano and Rodonò (1967) and it is now considered the distinctive photometric feature of RS CVn binaries as well as of other spotted stars. By attributing the PW to surface inhomogeneities, or spots, whose visibility is modulated by the spotted star rotation, the present PW migration toward decreasing orbital phases indicates that the angular rotation of the KOIV spotted component is slightly lower than the orbital one. An inspection of Figure 1 readly shows that the almost sinusoidal PW has been fairly stable from 1963 up to 1981, when a double-peaked wave, still present in the 1982 LC, developed. Most probably the “unusual” 1949 LC by Keller and Limber (1951) and the 1976 one by Ludington (1978) were obtained at a similar activity phase.
HK Lacertae
Authors: Olah Katalin
Published: July 2016

HK Lac was observed at Konkoly Observatory between 1976-1981, the details of its story have been described in a previous paper (Olah, 1979).

The aim of this investigation is to give a possible description of the strong variations in the light curve of the star.

Searching for a more accurate period, it became obvious that the same period was not applicable to all the data. Therefore, a new period was derived for each different cycle by the Lafler-Kinman method. Unfortunately, due to the small number of data in the data sets these newly derived periods have an error of about 0.1 day.
The Solar-Type Eclipsing Binary System AI Phoenicis
Authors: Milone E.F. , Hrivnak B.J.
Published: July 2016

AI Phe was discovered to be variable and identified as an EA binary by Strohmeier (1972). Reipurth (1978) subsequently carried out uvby photometry, determined the period (24.5923 d), and noted the lengthy totality of primary minimum and the displacement of the secondary minimum. Imbert (1978) obtained radial velocity curves and determined spectroscopic orbital elements. Imbert also gives a spectroscopic classification of G2V for the primary (hotter) component and approximately G5 for the secondary. AI Phe thus appeared to offer a unique opportunity to study the limb darkening of a non-interacting solar-type star. As an extension of a solar UV limb darkening study (Kjeldseth Moe and Milone 1978), ten IUE spectra were obtained on Aug. 12 in 2 successive shifts (cf Milone et al 1981). In conjunction with this, ground-based 5-colour photometry and spectroscopy were carried out at CTIO and at UTLCO.
The Evolutionary Status of Short-Period RS CVn and Related W UMa Eclipsing Binaries
Authors: Russo G. , Milano L. , Mancuso S.
Published: July 2016

Among the RS CVn stars showing solar-type activity, with spectral types ranging from F to K and total masses up to 4 M⊙, there are two peculiar groups with period less than one day:a)agroup with components well inside their Roche lobes (Short-Period-Group, hereinafter SPG) and b) a group with their components in a thin or marginal degree of contact, with lightcurves of W UMa-W type (hereinafter WWG).
The Variability of the T Tauri Star DI Cephei
Authors: Gahm G.F. , Petrov P.P.
Published: July 2016

It is demonstrated that the light variations of DI Cephei can be explained as due to the combined effect of variable completely grey circumstellar extinction and variable continuous and line emission.
Models of Spots and Flares
Authors: Mullan D.J.
Published: July 2016

MHD effects in stars are seen in their most spectacular form in the processes which are typical of flares. At first sight, it appears that the phenomena of dark spots (whose long lifetimes give an impression of quasi-equilibrium) are inevitably less interesting. However, this is not necessarily true. Laboratory experiments in recent years have shown that there are many more ways to drive a plasma out of equilibrium than to preserve equilibrium. In that sense, then, it is perhaps “easier to understand” why flares should occur in a stellar atmosphere (where convective jostling of field lines creates potential for driving a large number of instabilities) than why a long-lived feature such as a dark spot should persist. Various instabilities which may contribute to flares are discussed by Priest and Spicer (this volume). Here, we summarize work on the equilibrium structure of cool spots in the sun and stars. Since spots involve complex interactions between convective flows and magnetic fields, we need to refer to observations for help in identifying the dominant processes which should enter into the modelling. This summary therefore begins by discussing certain relevant properties of spots in the solar atmosphere.
New Triggering Mechanism for Red Dwarf Flares
Authors: Das M.K. , Tandon J.N.
Published: July 2016

The flare phenomenon associated with dMe stars has received much attention in recent years (Gershberg 1975). Most of the flares have been detected in both optical and radio band (Lovell 1969; Kunkel 197U; Karpen et al, 1977). But as expected (Tandon 1976) only a few display weak soft X-ray emission (Karpen et al, 1977; Haisch and Linsky 1978)- Simultaneous X-ray, optical and radio observations of YZ CMi by Karpen et al (1977) shows no X-ray emission above 3σ level accompanying minor flares. Even coincident X-ray coverage with seven radio bursts shows no enhanced X-ray emission. Recently Haisch et al (1981) detected one well resolved X-ray flare on dM5e flare star Proxima Centauri and one coincident optical and radio flare out of five optical and twelve radio flare events. However, the X-ray flare on Proxima Centauri is not accompanied by any ultraviolet, optical or radio emission. Observations on flare stars show that they are more energetic, 102 - 103 times, than the corresponding solar flares. Considering the flare activity in dwarf M-stars to be similar but more energetic to that of a large solar flare, Tandon (1961) proposed red dwarf flares to be the source of low energy galactic cosmic rays. This hypothesis has been reexplored recently by Lovell (1974).