bluuebunny/crossref_metadata_2025 huggingface dataset:
Type II Supernova Photospheres and the Distance to Supernova 1987A
Authors: Chilukuri Manorama , Wagoner Robert V.
Published: July 2016

Among the many historic opportunities provided by the recent supernova in the LMC is that to improve our understanding of the physical conditions in the neighborhood of supernova photospheres, even though 1987A was initially characterized by radial and time scales smaller (by a factor 5–10) than “standard” more luminous SNII. Two consequences of this understanding, which we shall focus on in this contribution, are (a) an estimate of the (frequency-dependent) location and thickness of the photosphere and (b) the only direct determination of the distance of the supernova (via the generalized Baade method). We find that the photosphere is sharp enough to allow the use of plane-parallel geometry in the calculation of the emergent continuum spectral flux, if we confine our attention to those epochs (temperature T ~ 5000−6000 K) at which hydrogen is recombining at the photosphere. We also find that the distance to this supernova is 43 ± 4 kpc. The reliability of this determination should improve when accurate spectrophotometric data for dates other than March 1 become available to us.
Calculated Late Time Spectra of Supemovae
Authors: Axelrod Timothy S.
Published: July 2016

We consider here the nebular phase spectra of supernovae whose late time luminosity is provided by the radioactive decay of 56Ni and 56Co synthesized in the explosion. A broad variety of supernovae are known or suspected to fall in this category. This includes all SNIa and SNIb, and at least some SNII, in particular SN1987a. At sufflciendy late times the expanding supernova becomes basically nebular in character due to its decreasing optical depth. The spectra produced during this stage contain information on the density and abundance structure of the entire supernova, as opposed to spectra near maximum light which are affected only by the outermost layers. A numerical model for nebular spectrum formation is therefore potentially very valuable for answering currently outstanding questions about the post-explosion supernova structure. As an example, we can hope to determine the degree of mixing which occurs between the layers of the “onion-skin” abundance structure predicted by current one dimensional explosion calculations.
Lα Radiation and CaII Ionization in the TYPE II Supernovae at Late Times
Authors: Chugai Nikolai N.
Published: July 2016

The ionization of CaII by the Lα quanta in the envelope of the type II supernova 1970g on 270th day is considered. The ratio CaII/CaIII is found to be very low (<0.1). This results in the low theoretical intensities of the CaII emission lines; they are at least an order of magnitude weaker than the observed ones. The implications are discussed.
Time Profile of the Neutrino Burst from the Supernova 1987A
Authors: Suzuki Hideyuki , Sato Katsuhiko
Published: July 2016

SN1987A gave us the first opportunity to study the supernova core directly by providing us the neutrino signal from the core. The observational data of the neutrino flux detected by Kamiokande[1] and IMB[2] show surprisingly good agreements with the theoretical predictions as a whole[3,4]. The fundamental concept of the collapse driven supernova explosion is confirmed for the first time. On the other hand, there are some puzzles. The most peculiar feature of the data is the 7 seconds gap of the Kamiokande data. The first 8 events of Kamiokande were detected in 2 seconds, following the 7 seconds gap and the last 3 events in 4 seconds. Of course just only 7 seconds gap is not unnatural if small neutrino flux come. But there were detected 3 events after the gap. These 3 events may not be produced by the weak flux. We can estimate the time integrated luminosity of corresponding to the last 3 events and get the large value such as 7 · 1052erg [5]. Can we get out of this inconsistency, 3 events after the 7 seconds gap? If not, we may need to consider some nonstandard mechanism of the neutrino emission at the late time. In order to investigate the probability of the case in which there is a 7 seconds gap before 3 events, we have performed Monte Carlo simulations for the simple model of neutrino flux.
Nucleosynthesis in exploding massive Wolf-Rayet stars
Authors: Eid M.F. El , Langer N.
Published: July 2016

Recent observations of the young supernova remnant Cas A (Fesen et al., 1987) suggest an exploding Wolf-Rayet (WR) star of WNL type as a progenitor of this object. The majority of the WR stars seems to originate from massive O-stars of M > 40 M⊙. According to current investigations (Schild and Maeder, 1984; Langer, 1987; cf. also: Langer, this volume) WNL stars rank among the most massive WR stars. Hence, it is possible to assume that the stellar progenitor of Cas A was indeed a very massive star.

As shown by Langer and El Eid (1986), (see also Woosley, 1986) a population I star of initially 100 M⊙ may loose enough mass during its evolution up to core He exhaustion to become a WN star of ∼ 45 M⊙, which then mainly consists of oxygen (more than 80%) synthesized during He burning.
Thermal X-Rays due to Ejecta/CSM Interaction in SN 1987A
Authors: Masai K. , Hayakawa S. , Itoh H. , Nomoto K. , Shigeyama T.
Published: July 2016

The X-ray spectrum observed by Ginga is characterized by a component below 10keV which decreases with increasing photon energy, and a component above 10keV which is nearly flat. This unusual X-ray spectrum may be understood as follows; X-rays below 10keV is likely to be due to thermal emission coming from the shock-heated ejecta, and X-rays above 10keV to be due to γ-ray degradation inside the ejecta. If thermal emission due to the collision of the ejecta with circumstellar matter (CSM) is responsible for X-rays below 10keV, the epoch of the collision can be estimated to be ∼ 0.2yr after the explosion if ∼ 0.5yr is the time when the X-ray flux at ∼ 10keV reaches its maximum. The X-ray light curve then requires the inner radius of CSM to be ∼ 1×1016cm for an expansion velocity, Vex ≃2×109cm s−1.
The X-Ray Spectrum of the Cygnus Loop with GSPC
Authors: Tsunemi Hiroshi , Manabe Makoto , Yamashita Koujun
Published: July 2016

We observed the Cygnus Loop with Gas Scintillation Proportional Counter (GSPC) on board Tenma satellite. GSPC has an energy resolution two times better than that of a proportional counter (PC). Fig. 1 shows the spectrum with the crosses being the pulse height data with ± 1σ statistics. Superposed upon the data point is the best fit model spectra folded through the detector response.
Observations of stellar winds in early type stars
Authors: Conti Peter S.
Published: July 2016

I have been asked to review the “observations” of winds in “early-type” stars. This normally means stars of spectral type OB and those of the Wolf-Rayet (WR) class. In this paper I will concentrate on the massive population I stars of these types, and primarily the O and WR classes on which most of the recent work has been done. The early B type supergiants share many of the wind properties of the O stars but the later supergiant types, Be stars, and main sequence stars may not. Stellar winds are a ubiquitous phenomenon among these early type stars (Snow and Morton 1976). We see evidence of their winds in the resonance line P Cygni profiles in the UV region, in the emission lines of Hα and λ4686 He II in the optical spectrum, and in the free-free emission from the ionized plasma as observed in the IR and radio regions of the spectrum.
The iron curtain of the WC 9 star HD l64270
Authors: van der Hucht Karel A. , Conti Peter S.
Published: July 2016

The emission lines in the optical and UV spectrum of the WC 9 star HD 164270 indicate a terminal velocity of its wind of v∞ ≈ 1400 km s-1. In the UV spectrum Fe III absorption lines appear from transitions with metastable lower levels. Because they are displayed over only 830 km s-1, it is suggested that they are formed in the decelerating part of the wind. A radius of 1.8 x 104 R⊙, is found for the circumstellar Fe III shell. This value is within the range of radii calculated by Cohen et al. (1975) for the dust shells of WC 9 stars.
Profils de la raie Hα par television analogique
Authors: Andrillat Y. , Fehrenbach Ch.
Published: July 2016

High resolution profiles of the Hα line are derived for about thirty Be stars and several bright stars by means of the anological television system. The profiles obtained with this method fairly agree with the theoretical ones (a Lyrae).
Mass loss rates for twenty one Wolf-Rayet stars
Authors: Barlow M.J. , Smith L.J. , Willis A.J.
Published: July 2016

Mass loss rates have been derived for twenty one WR stars encompassing most subtypes in the WN and WC sequences, from measurements of their infrared free-free fluxes. The resultant mass loss rates show a range of only a factor of four. WC stars generally have larger mass loss rates than WN stars, the mean rates being Ṁ(WC) = 4.1x10-5 M⊙y-1 and Ṁ(WN) = 2.7x10-5 M⊙y-1. Optical and ultraviolet data have been used to estimate bolometric luminosities for a range of WR spectral types, and it is shown that the derived mass loss rates are too large to be powered by radiation pressure. The total kinetic energy ejected into the interstellar medium through mass loss during the WR phase of a massive star is estimated to be 7x1050 ergs, comparable to that of a supernova event.
Mass outflow in AG Carinae and a comparison with P Cygni
Authors: Bensammar S. , Gaudenzi S. , Rossi C. , Johnson H.M. , Thé P.S. , Zuiderwijk E.J. , Viotti R.
Published: July 2016

AG Car is a variable supergiant surrounded by a small ring nebula. Its ultraviolet and optical spectrum, and UV to IR energy distribution are similar to those of P Cyg with v∞ = -290 km s-1. Also the strength of the 2200 A band is the same and suggests E(B-V) = 0.55 for both stars. The possible variability of the infrared flux is discussed.
Radio observations of O-type stars
Authors: Felli M. , Panagia N.
Published: July 2016

Eight O-type giants and supergiants, selected for being relatively isolated in the sky, have been observed at 5 GHz with 17 antennae of the partially completed VLA (NRAO, Socorro, New Mexico: The National Radio Astronomy Observatory is operated by Associated Universities under contract with the National Science Foundation) on October 7 and 8, 1979. The integration times ranged between 38 and 187 minutes. The results are displayed in Table 1. Most of the stars (6 out of 8) were not detected. The upper limits given in Table 1 for these stars correspond to the 3σ noise level. Possible detection has been achieved for the two supergiants HD 225160 and HD 30614 both with a flux density of 0.15 mJy. Although this flux is equal to the 3a noise level, the detections can be considered to be real because 1) Excellent positional coincidence is found between stars and the radio peaks (better than 1”) 2) The observed source pattern corresponds very well to the expected response to a point-like source.
The fraction of O-type supergiants in our galaxy in the LMC and in the SMC: an evidence of the correlation between mass loss rate and chemical abundance
Authors: Bisiacchi G.F. , Firmani C.
Published: July 2016

The distribution of the spectral types of the WR stars in our galaxy is different at different distances from the galactic center. This distribution is also different in all three galaxies, in our, in the LMC and in the SMC. These results have been interpreted as due to the dependence of the mass loss rate from the original chemical abundace which is known to be different in these objects.

On the other hand it has been proposed by Chiosi et al. (1974) and confirmed by Bisiacchi et al. (1978) that most of the 0 supergiants should be stars in the hydrogen burning phase. These authors also find evidence that the large relative number of supergiants among th 0 and early B type stars must be related to the longer time spent by the evolutionary tracks with mass loss at the low gravity region. Recently, a new empirical formula has been proposed by Chiosi (1980) for the mass loss rate as function of the luminosity and temperature of the stars.
Thermal instability of hydrogen burning shells in very massive stars
Authors: Tanaka Y. , Arimoto N. , Takeuti M.
Published: July 2016

Stothers and Chin (1972) examined numerically thermal instability of H burning shells in very massive stars. They reported the discovery of the thermal pulses in the shell on a stage of the contracting core just after the core exhaustion. Their results, however, are inconsequential because the pulses are very feeble and the mechanism of such feeble pulses is not well known at the shell burning phases. In this note, we summarize our analytical method and the results on the possibility of such feeble pulses in H burning shells, of which detailed procedure is described in another paper(Tanaka et al., 1980).
Mass loss from metal-poor stars
Authors: Chiosi C. , Bertelli G. , Nasi E. , Greggio L.
Published: July 2016

1. Introduction

It is essential to consider the effect of mass loss to understand the distribution of supergiant stars in the HR diagram. This research concerns the evolution of massive stars with X=0.700 and Z=0.001 during the phases up to central Heexhaustion with the inclusion of mass loss. Such low value of Z has been chosen in order to allow a comparison with the supergiant stars of SMC. The rate of mass loss is formulated as in Chiosi, Nasi and Sreenivasan (1978). More specifically, in the range of high effective temperatures, we adopt the mass-loss rate relationship for radiation pressure driven wind of Castor, Abbott and Klein (1975), whereas in the range of low effective temperatures we assume the mass loss rate to be driven by the acoustic flux mechanism of Fusi Pecci and Renzini (1975).
How massive the Wolf-Rayet stars are?
Authors: Niemelä Virpi S.
Published: July 2016

If the Wolf-Rayet stars are produced by the evolution of massive stars with mass loss (Paczynski 1967, Conti 1976) from 0 stars to WN stars and thereafter to WC stars, then we may expect to observe a correlation of decreasing mean masses in the same sense as the evolution.Information about the masses of TO stars are obtained from studies of binary systems with WR components. Table 1 presents the today available data for the WN type stars.
Miras, mass loss, and the origin of planetary nebulae
Authors: Willson L. A.
Published: July 2016

Mira variables are found at the tip of the asymptotic giant branch, with L≈3000-5000Lʘ and TeH3000K. (Feast 1981; Willson 1981a). They are fundamental mode pulsators (Willson 1979, 1981a). A typical Mira has P~350 days, R~200-300Rʘ, M~1-2Mʘ (Willson 1979; 1981a). From the atmospheric velocities of the Miras plus a fundamental mode period-massradius relation one finds present masses for the Miras which are not very different from their progenitor masses (Willson 1981a). This suggests that pre-Mira mass loss is moderate -- ≲20% of the mass is lost before pulsation starts. In fact one expects only moderate mass loss before the Mira stage;
Mass loss from interacting close binary systems
Authors: Plavec Mirek J.
Published: July 2016

Mass outflow from interacting close binary systems, accompanied by loss of orbital angular momentum, appears to be a very important process affecting the evolution of binary stars. Together with accretion on the mass-gaining component, it is the least understood aspect of the general complex process we call “evolution with mass transfer and/or mass loss”, or, more briefly, “interaction”. It is therefore very imperative to assemble and examine all available facts or hints about mass loss.
Non conservative massive binary evolution (how much mass leaves the bnary during the evolution from OB+OB to WR+OB)
Authors: Vanbeveren D.
Published: July 2016

The observations give us on one hand the mass ratio (q) distribution of OB+OB type binaries in a stage prior to Roche lobe overflow (RLOF), and on the other hand the q distribution of WR binaries which are considered to be in a stage after RLOF. By comparing both distributions one may hope to be able to say something about the mass loss during RLOF.
Observation of mass loss in R CrB during the visual light minimum
Authors: Rao N. Kameswara
Published: July 2016

R CrB at minimum light shows three type of spectra: 1) an absorption line spectrum similar to that observed at maximum light; 2) a sharp emission line spectrum mainly due to singly ionised metals which is displaced to the blue by 3 to 10 kms-1 with reference to the absorption spectrum observed at maximum. This is supposed to be a kind of permanent feature which exists even at the time of light maximum; 3) a broad emission line spectrum consisting of mainly λ3889 of Hel, H and K lines of Call and the D lines of Nal. The widths of the broad emission features indicate expansion velocity of 200 kms-1, much greater than the escape velocity (Gaposchkin 1963, Rao 1975).
Properties of optically thick winds driven by radiation pressure
Authors: Friedjung M.
Published: July 2016

Conditions are derived for supercritical winds, accelerated by the radiation pressure of an object above the Eddington limit. A relation between the different energy fluxes is found. The conditions seem to be satisfied by novae, and perhaps by η Car. They are not satisfied however by the symbiotic star Z And.
Subionization and decelerated-flow in the vicinity of a B-shell star
Authors: Zorec J.
Published: July 2016

Three types of spectra have been extensively observed among mainsequence B stars. B-normal is the classical absorption spectrum which defines a normal main-sequence B star. Be is a B-normal spectrum except : (i) some absorption lines, notably the first hydrogen Balmer series members, are replaced by emission lines; (ii) some lines from some singlyionized metals, not normally present in B stars, sometimes appear, either in emission or absorption. Be-shell is a Be spectrum with narrow and deep absorption cores in the Balmer and singly-ionized metal lines. A fourth type, B-shell, has been identified as a B-normal, absorption, spectrum except for the presence of FeII lines, and narrow, deep absorption cores in these and the hydrogen Balmer lines. Once thought to each represent a different kind of star, these spectra are now realized to simply represent different temporal phases, which one and the same star can traverse, apparently in no (as yet) fixed order. Some of the brightest stars --- eg γ Cas, 59 Cyg, Pleione --- have been observed in all of the 3 prominant phases; some stars, in only some of them; 70 % of the B stars have been observed only in the B-normal phase.
Mass loss and ΔY/ΔZ ratio
Authors: Chiosi C. , Matteucci F.
Published: July 2016

The ΔY/ΔZ abundance ratio is studied taking into account mass loss from intermediate and massive stars, and the Yz vs. Z relation of Peimbert and Serrano (1980a).
The Measurement of Long-Period Oscillations at Sacramento Peak Observatory and South Pole
Authors: Stebbins Robin , Wilson Christopher
Published: July 2016

A program to measure long-period brightness oscillations at the solar limb has been pursued at Sacramento Peak Observatory for several years. Past improvements in observing technique and data analysis are reviewed. The encouraging results aid in the verification of the reality and the origin of oscillatory signals. However, the main stumbling block to this and other observational programs is the length of observing sequences imposed by the day/night cycle. The South Pole has received considerable attention as a site where extended observations might be possible. Currently, the Sacramento Peak program is developing a South Pole telescope designed for the observing technique and data analysis proven in Sunspot. A review of pertinent South Pole site parameters is given here for other workers who may be considering South Pole observations. Observing sequences longer than 150 hr are possible, though rare. Data sets of this duration are very attractive for solar oscillation studies.
Solar Diameter(s)
Authors: Rösch J. , Yerle R.
Published: July 2016

Because of the renewed attention now paid to the solar diameter, its variations from equator to pole, or its secular or long-period changes, the question: what is a solar diameter? is not meaningless. Two kinds of definitions may be given: either astrophysical, each one relating to a specific physical parameter, or observational, relating to a given quantity to be measured. Only the second kind is directly accessible, and astrophysical definitions should be linked to these quantities, once they are determined with the highest possible accuracy. In practice, all the programs under way refer to the point of the limb where the brightness gradient is maximum, or to a higher order approximation of the shape of the profile. Two of them are compared: the Pic-du-Midi experiment, using fast scans of the limb to define the inflection point after a correction for the blurring effect of the atmosphere, and the SCLERA experiment, using the algorithm called FFTD to eliminate this correction. The advantage of a fast scan is emphasized, and the remark is formulated that, once the signal is digitized and stored, FFTD or any processing of it can be performed. In collecting day-long one-limb scans to calibrate the blurring correction, the authors have found fluctuations of the maximum brightness gradient which provide a new entry to the field of solar oscillations.
Rotational Splitting of Solar Five-Minute Oscillations of Low Degree
Authors: Claverie A. , Isaak G. R. , McLeod C. P. , van der Raay H. B. , Roca Cortes T.
Published: July 2016

An analysis of 28 contiguous days of whole disk observations of the solar surface by means of optical resonant scattering in the K 769.9 nm line, taken at the Teide Observatory at Izana during July-August 1980, have thus far yielded two significant facts. Firstly when the results of an iterative sine-wave fitting procedure are considered in the period range 2-3 h, although the expected daily harmonics corresponding to 1/8, 1/10, 1/11, and 1/12 of a day are clearly seen the l/9th contribution is significantly absent. It is suggested that this results from an interference between a signal of 160 min (l/9th of a day) with the daily harmonic. It is further pointed out that the observatories at which the 160 min oscillation has been seen, Crimea, Pic du Midi, and Stanford are all separated by integral numbers of 160 min, and thus the phase of the 160 min oscillation relative to the daily observation window is constant. However, the Teide Observatory is situated at a half integral number of 160 min periods relative to the others. Thus when constructive interference exist at the first three sites destructive interference will exist at the latter. It is thus concluded that the non-existence of a peak corresponding to the l/9th harmonic of a day in the sine-wave fit data is strong indirect evidence for the existence of the 160 min signal.

An analysis of those same data in the 5 min region has revealed the now well established pattern of discrete frequencies and with the increased resolution obtainable from 28 contiguous days of data, clearly showed the existence of splitting by rotational effects. In all 33 discrete lines were considered in the frequency range 2.4–3.85 mHz, which could be divided up into 3 groups, each of 11 lines, corresponding to the l = 0, l = 1, and l = 2 modes. This definitive classification was possible as the lines are split into (2l + 1) components yielding easily identifiable singlets, triplets and quintuplets. This first observation of the rotational splitting of solar oscillations gave the further information that the splitting of 0.75 ± 0.10 μHz indicated that the solar interior is rotating more rapidly than the observable surface (uniform rotation would yield a splitting of 0.4 μHz). A comparison of the widths of the individual peaks, with the intrinsic resolution of the data string ( ~ 1/T where T = length of the data string), showed that these were consistent with a high Q value oscillation, a fact which is further confirmed by the very existence of singlets triplets and quintuplets in the data.

The exact value of the speed of internal rotation of the Sun can only be deduced from these data by a model dependent calculation. The simplest of these would suggest that if the core were almost equal to the solar diameter then it is rotating twice as fast as the surface, whereas if the core were only 15 % of the solar diameter, it would be rotating at 9 times the surface rate.
Variability in the Power Spectrum of Solar Five-Minute Oscillations
Authors: Hill Frank , Toomre Juri , November Laurence J.
Published: July 2016

Two-dimensional power spectra of solar five-minute oscillations display prominent ridge structures in (k, ω) space, where k is the horizontal wavenumber and ω is the temporal frequency. The positions of these ridges in k and ω can be used to probe temperature and velocity structures in the subphotosphere. We have been carrying out a continuing program of observations of five-minute oscillations with the diode array instrument on the vacuum tower telescope at Sacramento Peak Observatory (SPO). We have sought to establish whether power spectra taken on separate days show shifts in ridge locations; these may arise from different velocity and temperature patterns having been brought into our sampling region by solar rotation. Power spectra have been obtained for six days of observations of Doppler velocities using the Mg I λ5173 and Fe I λ5434 spectral lines. Each data set covers 8 to 11 hr in time and samples a region 256″ × 1024″ in spatial extent, with a spatial resolution of 2″ and temporal sampling of 65 s. We have detected shifts in ridge locations between certain data sets which are statistically significant. The character of these displacements when analyzed in terms of eastward and westward propagating waves implies that changes have occurred in both temperature and horizontal velocity fields underlying our observing window. We estimate the magnitude of the velocity changes to be on the order of 100 m s -1; we may be detecting the effects of large-scale convection akin to giant cells.
The Observations of 80-min Oscillations in the Quiescent Prominences
Authors: Bashkirtsev V.S. , Kobanov N.I. , Mashnich G.P.
Published: July 2016

Oscillations of the line-of-sight velocities with periods were detected in quiescent prominences, with coordinates φ = –75° W and φ = –18° W, respectively.
Quiescent Coronae of Active Chromosphere Stars
Authors: Golub Leon
Published: July 2016

The EINSTEIN Observatory has for the first time provided high sensitivity X-ray measurements of quiescent coronal emission from a large sample of dwarf stars. We now have observed a sufficient number of the nearby M-dwarfs to determine an X-ray luminosity function and we have explored the activity and variability of these stars to the extent of observing, for the first time, X-ray flares with simultaneous groundbased optical and IUE ultraviolet coverage.

The M dwarfs are found to have a much higher degree of variability in X-rays than does the Sun; however, in most cases a quiescent level is definable. We will discuss the quiescent emission from these stars and the changes in quiescent level on time scales from hours to ~ 1 year. We have determined coronal temperatures for many of these stars; they are generally hotter than the Solar corona and some of the more active dM stars have Tcor ~ 107 K.

Arguments are presented in support of the hypothesis that M-dwarf coronae are magnetically dominated, as is the Solar corona. We then examine the usefulness of loop model atmosphere calculations in elucidating the coronal heating mechanism and the ways in which observations may be used to test competing theories. The X-ray measurements can be used to predict magnetic field strengths on these stars, with testable implications.
Optical Photometry of Flares and Flare Statistics
Authors: Byrne Patrick B.
Published: July 2016

This review discusses optical observations of flares and the results gleaned from these. Excellent reviews of flare activity have been published in the past and one might mention in particular Kunkel (1975), Gershberg (1978) and Gurzadyan (1980). In general these have been more broadly based than the present review incorporating other aspects of flare stars e.g. BY Dra variability, spectroscopic observations, etc. Since these other aspects of flare star behaviour are being covered elsewhere in this volume we will confine ourselves exclusively to optical photometry of the flare phenomenon itself. We will also confine ourselves to the solar-neighbourhood flare stars (i.e. the UV Ceti stars) since other contributors will discuss the T-Taurl, RS CVn, BY Dra and other flaring objects.
Quiescent And Flaring Radio Emission From dMe Stars
Authors: Gibson D. M.
Published: July 2016

In reviewing radio studies of M-dwarf flare stars one is struck by the curious way in which the field developed. Indeed, that is twenty years old may be the greatest surprise, for if one imagines the largest solar flares occurring at distances comparable to the nearest stars the expected flux densities would be < 10 mJy. Yet, despite the fact that detection thresholds in 1963 were about two orders of magnitude higher than the expected value, Lovell et al. (1963) made extensive observations and reported the. detection of UV Ceti. This remarkable discovery was followed immediately by detections of V371 Ori (Slee et al., 1963) and EV Lac (Lovell et al., 1964). One might have thought that these unexpected discoveries would have spurred significant interest in this new field but they did not.
Possible Origins of the 12µ Emission Lines in the Solar Spectrum
Authors: Goldberg Leo
Published: July 2016

Braut and Noyes (1982,1983) have reported the detection of about 40 unidentified emission lines near 12µ in the solar spectrum. The strongest lines, at 811.578 cm-1 and 818.062 cm-1, respectively, appear as broad, shallow absorption lines, less than 3% deep, with central, emission reversals projecting 5-10% above the continuum. The emission lines strengthen at the limb and over spot penumbrae but seem to be absent over spot umbrae. The full width at half-intensity of the emission lines is about 5 km/sec, but the absorption widths are more than 10 times as broad. Over spot penumbrae, the Zeeman splitting of the emission lines is striking. The lines have the appearance of a Zeeman triplet; the central component is nearly absent at the center of the disk but is very strong near the limb where the field is viewed perpendicularly to the line of sight. The splitting over spot penumbrae is about 10 times the width of the central component, and is consistent with that of a spectral line with a Landé g-factor of unity in a magnetic field of 1500 gauss. Braut and Noyes (1982, 1983) point out that the 12 u lines are a potentially powerful tool for magnetic field measurements in stars. Further observational details will be found in their referenced papers.
Very Long Baseline Interferometry of Solar Flares
Authors: Kuijpers J. , Tapping K.F. , Graham D.
Published: July 2016

The aim of the VLBI experiment was a search for the occurrence of subarc- second microwave emission centres as tracers of the initial energy release in solar flares. The observations extended over the period April 28 to May 3, 1981 and were performed with the 25 m telescopes at Onsala (Sweden) and Dwingeloo (Netherlands) at a wavelength of 18 cm (1663 MHz). The baseline was 619 km long giving a minimum angular width of the interference fringes of 0.06’. This corresponds to a spatial scale of 40 km at the solar disc centre.
Periods of Unevolved Late-Type Close Binaries: Evidence of Magnetic Activity
Authors: Giuricin G. , Catalano S. , Mardirossian F. , Mezzetti M.
Published: July 2016

Our study of the period distribution of about 200 FGKM-type unevolved close binaries has revealed a strong deficit of short-period systems.This finding may be connected with the occurrence of a very efficient mechanism of orbital angular momentum loss via magnetic braking by stellar wind, in the earliest evolutionary phases.
IUE Spectra of RS CVn Stars
Authors: Andrews A.D. , Byrne P.B. , Butler C.J. , Linsky J.L. , Simon T. , Marstad N. , Rodonò M. , Blanco C. , Catalano S. , Marilli E. , Pazzani V.
Published: July 2016

The characteristic optical light curves of RS CVn - and BY Dra-type variables are believed to represent non-uniform distribution of dark spots akin to sunspots which are revealed by rotation. By analogy with the Sun, strong magnetic fields probably underlie this phenomenon, extending upwards into the chromosphere and corona, enhancing the emission from regions that overlie the spots. Previous work on the BY Dra variable AU Mic (Ref.l) did not clarify whether the fluxes from chromospheric and transition region lines were rotationally modulated in the sense that the phase of maximum emission was in register with spot visibility or minimum light. This important question prompted the need for further collaborative IUE, optical and radio work.
Coronal and Chromospheric Structure in AR Lac - II: Physical Characteristics of the Atmosphere
Authors: Walter F.M. , Gibson D.M. , Basri G.S.
Published: July 2016

In this series of papers we report on an effort to deduce the morphology of the chromosphere and corona of AR Lacertae, an eclipsing RS CVn system (Hall 1976), via observations at UV, radio, and X-ray wavelengths during a complete orbital cycle. In another paper (Gibson, Walter and Basri 1982, Paper I), we present the observational data and general constraints on the morphology of the coronae. The full study will be published elsewhere (Walter, Gibson, and Basri 1982).
Activity of Contact Binaries
Authors: Rucinski S.M. , Vilhu O. , Kaluzny J.
Published: July 2016

We discuss observational results for indicators of elevated activity of contact (W UMa-type) binaries. References are made to results for fast rotating single and detached binary (MS) stars: they are discussed in the accompanying paper by Vilhu and Rucinski.
On the Origin of H2 in T Tau Stars
Authors: Strazzulla G. , Pirronell V. , Foti G.
Published: July 2016

Narrow-band spectrophotometry observations (Cohen, 1975) showed that the extremely young star HL Tau has an absorption feature at 3.1 μm well matched by extinction from pure ice solid grains (radius a≈0.3μm, mice ≈10-4 gr cm-2). This feature, not present in others (more evolved) T Tau stars, suggests that ice may be only found around the very youngest T Tau stars and progressively disappears as starsbecome increasingly visible through their circumstellarshells (Cohen, 1975).
Theory and Observations of Negative Preflares in UV Cet Stars
Authors: Grinin V.P.
Published: July 2016

Negative preflares (NPFs) of UV Cet stars, which were first observed by Italian astronomers |1|, are a highly unusual type of preflare activity without direct analogy in solar flares. The rarity of these events in the visual region leads to difficulties in statistical investigations. At present one can consider as reliably established only that the mean NPF-amplitudes increase and the probability of their appearance decreases with a shift toward blue |2|. According to |3| NPFs are observed mainly before flares of smaller amplitudes. Beginning in 1974 at the Crimea and the Astronomical Institute of Tashkent a series of works on the theory and observation of NPFs was carried out. A short review of these is given below.
Long Periods in the Three-Dimensional Motion of Trojan Asteroids
Authors: Bien R. , Schubart J.
Published: July 2016

The long periods caused by Jupiter, or Jupiter and Saturn in the motion of a Trojan are studied by numerical integration. Orbital inclinations between 0° and 50° are considered. Results on the length of the periods and on their main effects in the osculating elements are presented. It turns out that secular resonances can be important for the evolution of Trojan orbits.
The Mechanism of Branching of Three-Dimensional Periodic Orbits from the Plane
Authors: Robin I.A. , Markellos V.V.
Published: July 2016

A linearised treatment is presented of vertical bifurcations of symmetric periodic orbits(bifurcations of plane with three-dimensional orbits) in the circular restricted problem. Recent work on bifurcations from vertical-critical orbits (av = ±1) is extended to deal with the v more general situation of bifurcations from vertical self-resonant orbits (av = cos(2Πn/m) for integer m,n) and it is shown that in this more general case bifurcating families of three-dimensional orbits always occur in pairs, the orbital symmetry properties being governed by the evenness or oddness of the integer m. The applicability of the theory to the elliptic restricted problem is discussed.
Resonant Three-Dimensional Periodic Solutions About the Triangular Equilibrium Points in the Restricted Problem
Authors: Zagouras C.G. , Markellos V.V.
Published: July 2016

In the three-dimensional restricted three-body problem, the existence of resonant periodic solutions about L4 is shown and expansions for them are constructed for special values of the mass parameter, by means of a perturbation method. These solutions form a second family of periodic orbits bifurcating from the triangular equilibrium point. This bifurcation is the evolution, as μ varies continuously, of a regular vertical bifurcation point on the corresponding family of planar periodic solutions emanating from L4.
Characteristics of Periodic Orbits in Elliptical Galaxies
Authors: Caranicolas N.
Published: July 2016

The properties of the characteristic curves of several families of periodic orbits, in a conservative dynamical system of two degrees of freedom, symmetric with respect to both axes, are reviewed. The two main types of families are presented. One sees that the pattern of the characteristics in the exact resonance case is similar to that of the near resonance case except for the basic characteristic . The form of the characteristics can be found theoretically by means of the second integral.
On Topological Stability in the General Three and Four-Body Problem
Authors: Milani A. , Nobili A.M.
Published: July 2016

By simple symmetry and change-of-scale considerations the topology of the level manifolds of the classical integrals of the N-body problem is shown to depend only on the value of the integral z = c2h (total angular momentum squared times total energy). For every hierarchical structure given to the N bodies the problem can be described as a set of N-l perturbed two-body problems by means of a fitted Jacobian coordinate system; in this setting the Easton inequality, relating potential, momentum of inertia and the z integral, is easily rederived. For N=3 the confinement conditions due to this inequality can be described, in a pulsating synodic reference system, as level lines of a modified potential function on a plane.
Radio observations of symbiotic stars
Authors: Kwok Sun
Published: July 2016

One of the defining characteristics of symbiotic stars is the presence of nebular emission lines, which indicates the existence of a circumstellar nebula. Since the excitation and ionization of atomic emission lines depend on the temperature and density of the emission region, line observations (optical or ultraviolet) therefore only selectively probe part of the circumstellar nebule. Radio observations being less sensitive to “hot spots”, reflect the global character of the ionized region and are more suitable for determining the density structure of the nebula. Recent advances in the technique of aperture synthesis allow observations to be made with high resolution (˜0ʺ.1) and direct mapping of nebular structure is now a possibility. Since the circumstellar nebula is most likely to have originated from the stellar components of the symbiotic system, a better understanding of the nebula may provide important clues to the nature of symbiotic stars.
Infrared studies of symbiotic stars
Authors: Allen David A.
Published: July 2016

Infrared photometry and spectroscopy of symbiotic stars is reviewed. It is shown that at wavelengths beyond lym these systems are generally dominated by the cool star’s photosphere and, indeed, are indistinguishable from ordinary late-type giants. About 25% of symbiotic stars exhibit additional emission due to circumstellar dust. Most of the dusty systems probably involve Mira variables, the dust forming in the atmospheres of the Miras. In a few cases the dust is much cooler and the cool component hotter; the dust must then form in distant gas shielded from the hot component, perhaps by an acccretion disk.

Spectroscopy at 2μm can be used to spectral type the cool components, even in the presence of some dust emission. Distances may thereby be estimated, though with some uncertainty.

Spectroscopy at longer wavelengths reveals information about the dust itself. In most cases this dust appears to include silicate grains, which form in the oxygen-rich envelope of an M star. In the case of HD 330036, however, different emission features are found which suggest a carbon-rich environment.
Spectra of individual symbiotic stars
Authors: Oliversen Nancy A. , Anderson Christopher M.
Published: July 2016

In connection with the discussion of the individual symbiotic stars, we present low resolution, flux calibrated spectra and high resolution H α profiles for each of 12 objects.
X-ray detection of the symbiotic star AG Draconis
Authors: Anderson Christopher M. , Cassinelli Joseph P. , Oliversen Nancy A. , Myers Roy V. , Sanders W.T.
Published: July 2016

The symbiotic star AG Draconis was observed by the HEAO-2 Imaging Proportional Counter (IPC) and found to be an unusually intense source of very soft X-rays.
Recent studies of the spectrum of V1016 Cygni
Authors: Muratorio G. , Friedjung M.
Published: July 2016

Two coudé spectra of V1016 Cyg taken on June 24 and 27, 1979 were reduced, using a computer programme developed in Marseille. Radial velocities and full widths at half maximum were measured for the emission lines, and are summarized in the following table were VR is the mean radial velocity in km s-1, DV the velocity corresponding to the mean FWHM and Xi the effective ionization potential for the ion.
The peculiar symbiotic object V1329 Cygni: single-star versus binary models
Authors: Grygar Jiri , Chochol Drahomir
Published: July 2016

The variable emission-line object V1329 Cyg (= HBV 475) was discover red by Kohoutek (1969).Crampton and Grygar (1969) identified more than 100 emission lines in the blue portion of the spectrum, while Andrillat (1969) found evidence for the late-type (M) spectrum in the near infrared. This justified the classification of the object among the symbiotic stars. The classification was subsequently confirmed by all authors who studied the spectroscopic evolution of the object.
Spectroscopic observations of AG Dra
Authors: Chang-Chun Huang
Published: July 2016

AG Dra is an interesting symbiotic star, on account of its very high negative velocity and its earlier spectral type among the symbiotic stars. This star has been classified as dG7 (Wilson,1943), K1 II (Roman,1953) and K3 III (Boyarchuk,1966). It has a variable radial velocity.

During summer 1981, spectroscopic observations of AG Dra were performed at the Haute-Provence Observatory using the Marly spectrograph with a dispersion of 80 A mm-1 at the 120 cm telescope and using the Coudé spectrograph of the 193 cm telescope with a dispersion of 40 A mm-1. Professor Ch. Fehrenbach very kindly given me a plate of the star which he had taken in July,1966, using the coudé spectrograph of the 193 cm telescope with a dispersion of 40 A mm-1.
Ultraviolet observations of RR Telescopii
Authors: Ponz D. , Cassatella A. , Viotti R.
Published: July 2016

The ultraviolet spectrum of RR Tel was extensively studied with the IUE satellite since 1978 in both the high and low resolution modes. A comprehensive study of these observations was made by Penston et al.(l98l) who measured more than 400 emission lines. As it is clearly shown in figure 1, the UV spectrum of this symbiotic star is very rich in emission lines. Like in the optical spectrum (Thackeray 1977), the UV spectrum presents emission lines of ions belonging to a wide range of ionization energies, from neutral up to four and five times ionized species (OV, MgV, CaVI, etc.). Permitted, intercombination and forbidden transitions were found which may allow a diagnosis of the physical conditions of the emitting regions. Electron temperatures of 1.2-1.9 104°K and densities of 106-108 cm-3 were derived by Penston et al.
The symbiotics as binary stars
Authors: Plavec Mirek J.
Published: July 2016

Symbiotic stars have become an important testing ground of various theories of binary star evolution. Several physically different models can explain them, but in each case certain fairly restrictive conditions must be met, so if we manage to identify a definite object with a model, it will tell us a lot about the structure and evolutionary stage of the stars involved. I envisage at least three models that can give us a symbiotic object: I have called them, respectively, the PN symbiotic, the Algol symbiotic, and the novalike symbiotic. Their properties are briefly discussed. The most promising model is one of a binary system in the second stage of mass transfer, actually at the beginning of it: The cool component is a red giant ascending the asymptotic branch, expanding but not yet filling its critical lobe. The hot star is a subdwarf located in the same region of the Hertzsprung-Russell diagram as the central stars of planetary nebulae. It may be closely related to them, or it may be a helium star, actually a remnant of an Algol primary which underwent the first stage of mass transfer. In these cases, accretion on this star may not play a significant role (PN symbiotic).
Models for symbiotic stars in the light of the data
Authors: Friedjung Michael
Published: July 2016

Different single and binary models of symbiotic stars are examined. Single star models encounter a number of problems, and binary models are probable. There are however difficulties in the interpretation of radial velocities. Accretion disks play a role in some cases, but winds especially from the cool component must be taken into account in realistic models. There is some evidence of excess heating of the outer layers of the cool component. Outbursts may be related to sudden changes in the characteristics of the cool star wind.
Broadening of the Interplanetary Helium Cone Structure Due to Elastic Collisions of LISM Helium Atoms with Solar Wind Ions
Authors: Fahr Hans J. , Nass Hans U. , Rucinski Daniel
Published: July 2016

Neutral interstellar particles penetrating into the heliosphere, besides being subject there to specific loss processes, suffer elastic collisions with KeV-solar wind ions. The momentum transfer to the neutrals connected with these collisions leads to a loss of angular momentum with respect to the sun and to a fractional compensation of the effective solar gravity. The dynamical particle trajectories hence are changed into non-Keplerians leading to density and temperature distributions differing from those calculated in the past. This is found from a solution of the Boltzmann equation that linearizes the effect of this additional force. It is shown here that the HeI-584A resonance glow of the heliospheric helium cone lead to substantially lower interstellar helium temperatures if re-interpreted on the basis of this revised theory. These temperatures now seem to be in accordance with the derived temperatures for interstellar hydrogen.
Deuterium Abundance in the Local Interstellar Medium
Authors: Ferlet R. , Gry C. , Vidal-Madjar A.
Published: July 2016

We underline the present situation of deuterium abundance evaluation in interstellar space and show that it should be < 10-5. Studiing in more detail the λ Sco line of sight and having observed two Nal interstellar components toward that star, we can show that the D/H evaluation made toward λ Sco is in fact related to the local interstellar medium (less than 10 pc from the sun). Because this evaluation is also < 10-5 it is in stricking contrast with the one made toward α Aur (D/H > 1.8 10-5 ) confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.