bluuebunny/crossref_metadata_2025 huggingface dataset:
The Intergalactic Medium
Authors: Fabian A. C. , Kembhavi A. K.
Published: July 2016

The density of intergalactic gas may be an important parameter in the formation of extended radio sources. It may range from ∼ 0.1 particle cm−3 in the centres of some rich clusters of galaxies down to 10−8cm−3 or less in intercluster space. The possible influence of the intracluster gas surrounding NGC 1275 on its radio emission is discussed, and the possibility that a significant fraction of the X-ray background is due to a hot intergalactic medium is explored in some detail.
Symmetry in Radio Galaxies
Authors: Ekers R. D.
Published: July 2016

One of the most striking properties of the radio galaxies is the predominance of a symmetrical double lobed structure. Any model to explain the energy release and collimation in radio galaxies must be able to produce this symmetry as the normal morphology. Although this large scale symmetry in radio galaxies is a well known phenomenon, I feel it is worth reemphasising since our current attention is more sharply focussed on the small scale and often much less symmetric structures which are seen with the higher resolution radio telescopes (VLB, VLA etc).
H/He Ratios for WN Stars in the LMC and the Galaxy
Authors: Perry Douglas N. , Conti Peter S.
Published: July 2016

The chemical abundances of hydrogen, helium, carbon, nitrogen, and oxygen in the winds of W-R stars bears directly on the problem of their evolutionary stage. The commonly held view that W-R stars are highly evolved objects has been based upon the apparent deficiencies of H in their envelopes and the enhanced strengths of CNO lines in the two sequences WN and WC (e.g. Gamow 1943). The picture that emerges is one in which many W-R stars are in the helium burning phase with the WC types more evolved than the WN stars. for this reason it is important to estimate the H content of as many WR stars as possible.
Absolute Spectrophotometry of Wolf-Rayet Stars: Are the Colors the Same?
Authors: Massey Philip
Published: July 2016

Until now, all that we've known about the magnitudes and colors of Wolf-Rayet stars has been based on photoelectric photometry made with 50–150 A wide interference filters, selected to exclude as far as possible the stronger emission lines (Westerlund 1966; Smith 1968, Lundstrom and Stenholm 1979). This was clearly an improvement on the pioneering efforts of Pyper (1966), who obtained broad band photometry and attempted to correct for the presence of emission; nevertheless, with modern detectors it is possible to go one step further.
The Theory of Radiation Driven Stellar Winds and the Wolf-Rayet Phenomenon
Authors: Abbott David C.
Published: July 2016

Peter Conti has a tradition of always talking about 0-type stars at Wolf-Rayet symposia, and Wolf-Rayet stars at 0 star symposia. Since there is no well-developed theory for the origin of the winds of WR stars, it is my pleasure to join Peter's tradition, and to talk mainly about the theory of radiation driven winds in OB stars. The advantage of OB stars is that there exists a fairly complete wind theory, which agrees well with the available observations. The question is, can the mass loss observed from Wolf-Rayet stars be explained by a version of this wind theory which is scaled to the conditions found in the envelopes of Wolf-Rayet stars? The topics I consider are:

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The calculated radiation pressure in OB stars, and its dependence on temperature, density, and chemical composition.

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A comparison between predicted and observed mass loss rates and terminal velocities for OB stars.

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The applicability of the standard radiation driven wind models to Wolf-Rayet stars.

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Speculations on how Wolf-Rayet stars achieve their enormous mass loss rates within the context of the radiation pressure mechanism.
On the Properties of Wolf-Rayet Stars and Their Mass Loss
Authors: Panagia N. , Felli M.
Published: July 2016

From consideration of the observed properties of the envelopes produced by mass loss in WR stars we find that:

a)

The velocity at the optical photosphere is in the range 200–800 km s

b)

The effective photospheric radius for the continuous radiation capable to ionize helium twice (γ < 228 A) is typically 5 to 15 times the optical photospheric radius.

c)

The radiation temperature in the Lyman continuum (γ < 912 Å) is around 5 × 104K. Therefore, most of the stellar radiation is emitted in the far UV and the total luminosity is considerably higher than currently estimated.

d)

Multiple scattering (N ≃ 20) of radiation in the interval 228–504 Å can provide most of the momentum needed to accelerate the wind up to the observed terminal velocities.
A Hot Corona Model for O-Stars and WR Stars
Authors: Robbrecht W. , de Loore C. , Olson G.
Published: July 2016

Atmospheric models are presented for the outer layers of hot stars, O, of and Wolf-Rayet stars. The model is a two component hybrid model, consisting of a rapidly expanding component and a slower component. for the rapidly expanding component the energy sources are radiation pressure, a deposit of internally generated and stored energy, and radiation cooling. In this way a coronal layer with temperatures of the order of 4–7 million K is generated, with an extent of 1 to 2 stellar radii. The mass loss rates range between 10−6 and 10−4 Mo yr−1. The stellar wind velocity at infinity is of the order of 4000 km s−1. It is assumed that this rapid component interacts with the slow component, and gives rise to shocks. The corona as well as the shocks generated by the interaction of the two components can explain the observed X-rays.
The Iron Curtain of WC9 Stars
Authors: van der Hucht K.A. , Conti P.S. , Willis A.J.
Published: July 2016

High resolution (Δλ ≈ 0.1å) IUE spectra have been obtained of the two WC9 stars HD 164270 and HD 136488, covering the wavelength range λλ1150–2050. The former star shows P Cygni profiles indicating a stellar wind terminal velocity of v∞ ≈ −1400 km s−1, and the latter v∞ ≈ −1800 km s−1. A common feature in the spectra of both stars is narrow displaced absorptions due to Fe III (UV34) transitions arising from a metastable lower level. These features are displaced at subterminal velocities (−830 km s−1 for HD 164270 and −1030 km s−1 for Hd 136488) and are believed to be formed in the deceleration region of their stellar winds. The properties of these inferred Fe III circumstellar shells derived from these data are discussed.
A Spectroscopic Search for Duplicity Among a Complete Sample of Northern Galactic Wolf-Rayet Stars
Authors: Lamontagne R. , Moffat A.F.J.
Published: July 2016

We have analysed new spectroscopic observations of 22 population I WR stars in a sample defined by b<12.5 mag, 18h<α<6h, δ > −30°. This completes the search for orbital duplicity among all of the 30 pop I WR stars contained within these limits. We thus have an unbiased data base in a volume segment bounded by a distance of 3–4 kpc for WNE and WC stars , and 4–5 kpc for WNL stars Although more observations are still needed in some cases, we have found several new binary systems. Some of these are low-amplitude, single-line binaries, often with runaway velocities and/or large separations from the galactic plane. We consider them to be candidates for a WR + collapsar stage, as originally predicted by Tutukov and Yungelson (1973) and de Loore and De Grève (1975).
Spectral Variations of Theta Muscae (WC 6 + O 9.5 I) in the Ultraviolet
Authors: Beeckmans F. , Grady C.A. , Macchetto F. , van der Hucht K.A.
Published: July 2016

High and low resolution spectra of the spectroscopic triple star θ Muscae were studied for time-variability. Within 7 min no variations were found in the low resolution data. On a time scale of 8 days and longer, variations in the P Cygni profiles of the resonance lines occur. These may be explained as variable mass loss from the system, or as aspect effects in an asymmetric wind flow.
Origin and Evolution of Wolf-Rayet Stars
Authors: Tutukov A. , Yungelson L.
Published: July 2016

The larger part of close binary components with initial mass exceeding ∼20 Mo becomes WR stars in the core helium burning stage. Some of the most massive WR stars may be products of evolution of single massive stars with initial masses exceeding ∼50 M0 if the mass loss in the infrared supergiant stage is effective enough. The Ledoux criterion of convective stability seems more promising to explain the observed properties of WR stars.
Low Mass Wolf-Rayet Stars: Theory
Authors: Renzini Alvio
Published: July 2016

It is well known that the Wolf-Rayet phenomenon is not restricted to some bright and massive stars, presumably in their core hydrogen-burning or helium-burning phase, but that it is also encountered among the central stars of some planetary nebulae (PNe). The PN nuclei are generally regarded as the evolutionary product of low and intermediate mass stars (with initial masses M.1 below ∼5 M⊙), which have lost most of their hydrogen-rich envelope during the so-called Asymptotic Giant Branch (AGB) phase. Correspondingly, their present mass cannot exceed the Chandrasekhar limit (∼1.4 M⊙), and their internal structure consists of a highly degenerate carbon-oxygen core containing most of the stellar mass, surrounded by an intershell region of mass ΔMCSH, and by a very low-mass envelope (Me < ∼10−3 M⊙).
Subluminous Wolf-Rayet Stars: Observations
Authors: Heap Sara R.
Published: July 2016

Fully ten percent of the Wolf-Rayet stars known in our galaxy are central stars of planetary nebulae. These stars are highly-evolved stars of approximately one solar mass. The existence of WR characteristics in the spectra of central stars as well as in massive, younger stars proves conclusively that WR spectra are a phenomenon that occurs in hot stars of widely different masses and evolutionary histories. Just what this phenomenon is — the nature of the instability that drives the wind — is not known, but the phenomenon is associated with a prior event in the star's evolutionary history. The common event that links Wolf-Rayet stars is loss of most, if not all of the outer, hydrogen-rich envelope just prior to the onset of WR characteristics. As Tutakov (this volume) and others have emphasized, there are many ways for a star to lose its H-rich envelope. These ways include mixing, ejection via a wind, or, in the case of a close binary, ejection via Roche-lobe overflow. The existence of WR-type central stars implies simply that we should include one more path leading to the Wolf-Rayet phenomenon, and that is, ejection to form a planetary nebulae.
A Reclassification of WC and “O VI” Central Stars of Planetary Nebulae, and Comparison with Population I WC Stars
Authors: Méndez Roberto H. , Niemela Virpi S.
Published: July 2016

We have started a study of WC central stars of planetary nebulae, including “O VI” objects which show WC characteristics. One of our purposes was to check, all along the WC spectral sequence, if the emission lines of planetary nuclei are narrower than for Population I objects, as they are in the case of the WC9 central star BD+30°3639 (Smith and Aller 1971).
Ring Nebulae Associated with Wolf-Rayet Stars
Authors: Chu Y.-H.
Published: July 2016

Using strict selection criteria, we have searched for ring nebulae associated with Wolf-Rayet stars in the Galaxy and the Magellanic Clouds. In our search, 15 WR ring nebulae are identified in the Galaxy (Chu 1981a; Chu 1981b, Paper G1), 9 in the Large Magellanic Cloud, and none in the Small Magellanic Cloud (Chu and Lasker 1980, Paper LI; Chu 1981a). We have subsequently observed the morphology and kinematics of these 24 nebulae to study their nature. The data and analyses are reported in G (galactic) and L (LMC) series of papers. These nebulae and their references are listed in Table 1. This table is nearly, but not quite, complete. An extremely careful search might result in more cases, e.g., NGC6357 (Lortet et al. 1981). In a later search by Heckathorn et al. (1982), more ring nebulae are suggested; however, only three cases (associated with HD92740, HD187282, and HD211564) are more convincing. We have obtained some data for these nebulae and will discuss them in a conclusion paper of the galactic series (Chu et al. 1982, Paper G8).
Wolf-Rayet Stars in the Magellanic Clouds: Spectroscopic Binaries and Masses
Authors: Moffat A.F.J.
Published: July 2016

Repeated spectra to V-mag 13.0 (13.5) have been obtained since 1978 for the 25 (5) brightest WR stars in the LMC (SMC). More than half of these are orbiting spectroscopic binaries, mainly SB1 for the luminous subclasses WN6-9, and SB2 for the rest. Together with galactic data, the Cloud SB2's lead to a correlation between mass ratio WR/OB and WR spectral subclass for each of the WN and WC sequences. This correlation is interpreted as an evolutionary sequence in which the peeling-off process of the strong stellar wind exposes successively hotter regions and eventually converts WN to WC at a point in time which appears to depend on the ambient metal abundance.
The Scientific Career of Jesse L. Greenstein
Authors: Boesgaard Ann Merchant
Published: July 2016

The scientific career of Dr. Jesse L. Greenstein covers nearly 60 years, a thousand nights on various telescopes, and several hundred papers. He has made substantial contributions in a number of major research areas including interstellar work, stellar abundances and nucleosynthesis, faint blue stars, white dwarf stars, comets, and quasars. He has combined productive research with distinguished service to our profession in a truly exemplary manner.
Introductory Talk
Authors: de Strobel G. Cayrel
Published: July 2016

The idea to organize a Conference on high S/N spectroscopy came to me several years ago, in the beginning of the eighties, when the first tracings of Reticon spectra of 8 and 9 magnitude stars were published. I suddendly realized that the quality of those spectra was comparable to those we find in the at lasses of the Sun, Procyon, Arcturus and of a very few other very bright stars. I thought at that epoch, probably at the top of Mauna Kea, that when high-resolution spectroscopists will have collected enough high S/N results, then, time would be ripe to discuss the impact of these results on our Knowledge of Stellar Physics.
The Most Efficient Tool for very High Resolution and very High Signal to Noise Ratio Spectral Observation of Stars
Authors: Jiang S. Y.
Published: July 2016

Today even for the most efficient spectrograph combined with a large telescope the light efficiency is only about 0.01 to 0.1 for spectral resolving power R larger than 10000 in optical wavelength band (OWB). Consequently for a very high signal to noise ratio spectral observation of rather bright stars still needs very large telescope. The main reason is that there are too many optical surface with rather low light efficiency and serious light loss at the limited slit width. In this paper we suggest a very high efficiency telescope-spectrograph system which will give an overall light efficiency varied from 0.21 at 400 nm to 0.44 at 700 nm, four fold higher than before. Using this system for R = 100000, S/N larger than 100 the limiting magnitude will be about 15.
High Signal to Noise Observations with a Photon Counting Array
Authors: Rodgers A. W. , Harding P. , Bloxham G. , Bessell M. S.
Published: July 2016

A simple high speed image widener is described which allows effective count rates of up to 100hz to be achieved with photon counting detectors thus allowing rapid accumulation of high signal to noise data in bright star spectroscopy.
Fiber Fed Spectrograph for Line Variability Studies
Authors: Felenbok P. , Guérin J.
Published: July 2016

In our studies of activity in pre-main sequence Herbig Ae/Be stars we are mainly interested in searching rotational modulation of line profile. If the period of star rotation is of the order of one or two days, the data collected from a single site is insufficient. This led us to start correlated observations from two or three sites spread as much as possible in longitude. Our first bi-site observations started in 1982 on AB Aur from two observatories located 11 hours apart.: CFHT in Hawaï and OHP in France. To achieve a high flexibility and to gain access to telescopes without attached spectrographs. We built an instrument that is mobile and specially designed for line profile studies.
Photometric Characteristics of Data from the Hubble Space Telescope Goddard-High Resolution Spectrograph
Authors: Ebbets Dennis C. , Heap Sara R. , Lindler Don J.
Published: July 2016

The G-HRS is one of four axial scientific instruments which will fly aboard the Hubble Space Telescope (ref 1,2). It will produce spectroscopic observations in the 1050 A ≤ λ ≤ 3300 A region with greater spectral, spatial and temporal resolution than has been possible with previous space-based instruments. Five first order diffraction gratings and one Echelle provide three modes of spectroscopic operation with resolving powers of R = λ/ΔΔ = 2000, 20000 and 90000. Two magnetically focused, pulse-counting digicon detectors, which differ only in the nature of their photocathodes, produce data whose photometric quality is usually determined by statistical noise in the signal (ref 3). Under ideal circumstances the signal to noise ratio increases as the square root of the exposure time. For some observations detector dark count, instrumental scattered light or granularity in the pixel to pixel sensitivity will cause additional noise. The signal to noise ratio of the net spectrum will then depend on several parameters, and will increase more slowly with exposure time. We have analyzed data from the ground based calibration programs, and have developed a theoretical model of the HRS performance (ref 4). Our results allow observing and data reduction strategies to be optimized when factors other than photon statistics influence the photometric quality of the data.
TH 7832CDZ (TH X31513) Bilinear CCD Array for Astronomy Applications
Authors: Coutures J. L. , Boucharlat G.
Published: July 2016

Photodiode linear arrays are perfectly adapted for spectral analysis. The TH 7832CDZ bilinear array is a new device specially adapted to low level detection (exposure < 7 nJ/cm2) with a reading efficiency of the photodiode signal better than 97% on all the dynamic range (> 70 dB).
On High Signal to Noise Spectroscopy with CCDs
Authors: Fort Bernard
Published: July 2016

This communication presents a very quick overview of major trends in CCD development and somes ideas on how to use a CCD for spectroscopy with H.S.N. ratio.
The Chromospheric Spectrum of the ζ Aur Binary HR 6902
Authors: Griffin R.
Published: July 2016

Observations of the composite-spectrum binary HR 6902 around the time of total eclipse reveal absorption features that are due to the chromosphere of the G9 II primary star. By the application of o method of digital subtraction we have succeeded in isolating the spectrum of the stellar chromosphere.
Search for Rotational Modulation in Pre-Main Sequence Herbig Ae/Be Stars
Authors: Catala C. , Czarny J. , Felenbok P.
Published: July 2016

The Herbig Ae/Be stars (Herbig, 1960; Finkenzeller and Hundt, 1984) are widely believed to be intermediate mass (2-5 M⊙) pre-main sequence stars. In the past few years, a big effort has been made to model their outer layers, and it has been shown that they possess stellar winds and extended chromospheres (Catala et al., 1984; Catala et al., 1986a; Catala and Kunasz, 1987).
Balmer Emission Profiles in Radially Pulsating Stars: The Case of the Double Hα Emission
Authors: Gillet D.
Published: July 2016

We present new high resolution profiles of Ha emissions in radially pulsating stars (RR Lyrae, W Virginis, RV Tauri, Mira stars and Classical Cepheids). Depending on phase, these profiles can show an apparent absorption within the emission close to the Hα laboratory wavelength. The origin of this feature is discussed in the framework : (a) of a composite of a single emission and a deep photospheric absorption (RR Lyrae, W Virginis and RV Tauri stars); (b) of a true absorption caused by cool hydrogen above the shock wave producing the emission; (c) of a geometric model in which the absorption is a lack of emission. Recent observations (Hα profiles of Mira stars S Car and T Cen), which show that the absorption dip is below the continuum level, are in favour of the true absorption model.
Some Constraints on Chromospheric Modelling for Solar-Type Stars with High S:N Spectra
Authors: Foing B. H. , Castelli F. , Vladilo G. , Beckman J.
Published: July 2016

High signal to noise spectra are required in chromospheric modelling because chromospheric emission lines are formed in a boundary layer under conditions of NLTE and in non-hydrostatic equilibrium, as well as in multiple magnetically-controlled streams, with horizontal structure on several scales, and vertical velocity fields. To obtain useable estimates of energy dissipation with height we have obtained sequences of spectra from F8 to K5 and for stars of different activity levels. These comprise Call H and K, the IR triplet, and MgII h and k obtained with the ESO CAT+CES or IUE. We outline the constraints such observations place on models and indicate theoretical and observational difficulties.
Doppler Imaging of Variable Early-Type Stars
Authors: Baade Dietrich
Published: July 2016

Line profile–variability (LPV) is very wide–spread among early–type stars. With the exception of inhomogeneous surface abundance distributions associated with magnetic fields, the LPV of bona fide non–magnetic stars is consistent with (often only with) nonradial pulsation (NRP). Peculiar surface chemistry and NRP may even be mutually exclusive, and there are other indications that in spite of the ubiquity of NRPs the distribution of their characterizing parameters in the HRD is far from being uniform. This may be important for uncovering the driving mechanism of NRPs in early–type stars.
High Time Resolution Spectroscopic Observations of Stellar Shock Waves
Authors: Cottrell P. L. , Lawson W. A. , Smith S. M.
Published: July 2016

An absorption line–splitting phenomenon, first reported by Cottrell and Lambert (1982a), has been shown to occur at about maximum light in the semi-regular pulsations of the R Coronae Borealis (RCB) star, RY Sgr (Lawson 1986). This has been interpreted as a shock wave propagating through the photospheric layers (Lawson and Cottrell 1986). We present spectroscopic observations of this star, taken to coincide with this line–splitting event. A sequence obtained during 1986 October revealed that this event extended over about 6 days (out of a period of about 40 days) and began at about the bluest B-V. This colour maximum, which corresponds to maximum photospheric temperatures and minimum radius, leads the V maximum by about 6 days.
Ultraviolet Spectral Imaging
Authors: Neff James E.
Published: July 2016

I discuss the general problem of determining the spatial structure in the outer atmospheres of active, late-type stars. There are several major differences between the problems of imaging photospheres and of imaging chromospheres. Because of these differences, chromospheric spectral imaging must be based on a direct deconvolution of the observed emission line profiles. I present results based on IUE spectra of AR Lac (=HD 210334).
Magnetic Field Measurements on Late-Type Stars: A New Technique
Authors: Marcy Geoffrey W. , Basri Gibor
Published: July 2016

A new technique for detecting and measuring magnetic fields on cool stars is presented, incorporating both an improved observational approach and a rigorous LTE theoretical treatment. We have identified two lines in the near infrared, one of which is very sensitive to Zeeman broadening and the other relatively insensitive, that are easily accessible to CCD and Reticon detectors. The lines are modelled by solving numerically the equations of transfer for the Stokes parameters in a full model atmosphere, permitting computation of all relevant depth-dependent physics such as polarized line opacities and broadening sources. We have obtained high resolution, high S/N spectroscopic observations of several G and K dwarfs and have synthesized the two lines using two free parameters, namely, the average field strength, B, and the fraction, f, of the surface covered by fields. For the chromospherically active stars ε Eridani and Xi Boo A, we find B=1000, f=35% and B=1200, f=40%, respectively. A careful study has been made of various sources of broadening to determine their ability to mimic Zeeman broadening, and none is capable of doing so.
Spectropolarimetry of Magnetic Stars: HD 125248
Authors: Mathys G. , Stenflo J. O.
Published: July 2016

We present preliminary results about the magnetic field of the Ap star HD 125248, from spectra recorded in RCP and LCP light with the Zeeman analyzer of the CASPEC at ESO.
Physical Input for the Determination of Stellar Abundances
Authors: Gustafsson B.
Published: July 2016

The fundamental parameters and the physical modelling and data used in the analysis of high-resolution high S/N spectra of stars are discussed. Particular emphasis is led on recent developments in these respects and the importance of further improvements is stressed.
A New Look at the Am Stars
Authors: Burkhart C. , Coupry M. F. , van't Veer C.
Published: July 2016

High resolution, high signal-to-noise observations are required for a better understanding of the Am stars and related topics. Two examples are shown : the relationship between lithium content and temperature in the Am stars of the Hyades cluster and the observational problem induced by multiple spectroscopic binarity frequent among the Am stars.
Solar Flux Atlas from 296 to 1300 nm
Authors: Furenlid Ingemar
Published: July 2016

The solar flux atlas is presented and some basic information on the observations is given.
Iron Lines and Surface Gravity Determination for τ Ceti
Authors: Arribas S. , Roger C. Martinez
Published: July 2016

We present a spectroscopic analysis for the gravity determination of τ Ceti on the basis of a new and high quality set of data. The iron lines are studied by using the Oxford oscillator strengths. The results are compared with those obtained with “solar” oscillator strengths. Non-LTE effects seem to be important in this star. The Fel at λ 526.955 nm line is used to apply the Blackwell and Willis (1977) method to determine the surface gravity. The derived log g is 4.70±0.1.
Chemical Composition of the Four Hyades Giants
Authors: Arimoto N. , Cayrel de Strobel G.
Published: July 2016

Differential detailed analyses with respect to ε Vir of the four Hyades giants have been carried out on high resolution high S/N CFHT Reticon spectra. The preliminary results are given below.
Lithium Abundances in a New Sample of Metal Deficient Dwarfs
Authors: Rebolo R. , Molaro P. , Beckman J. E.
Published: July 2016

We have measured the Li abundance in a sample of 37 field dwarfs of low metallicity (−0.6 ≥ [Fe/H] ≥ −3.2). Stars with [Fe/H] < −1.4 (“EMD” stars) form a much more homogenous population w.r.t.7Li than do the stars with somewhat higher metallicities. We argue in detail that the warmer EMD stars (6000K< Teff< 6300K) show little Li depletion, and that their asymptotic Li abundance log N(Li) = 2.2 (±0.15) is the best available approximation to a primordial value.
Beryllium Abundances of F Dwarfs
Authors: Budge Kent G. , Boesgaard Ann Merchant , Varsik John
Published: July 2016

We have obtained spectra near 3130 Å of 23 F and G main-sequence stars at 0.05 Å px−1. We have made preliminary estimates of the equivalent widths for the Be II doublet at 3130.4 and 3131.1 Å by means of a comparison procedure that matches each star against a standard star of similar spectral type with known Be abundance. It appears that stars that are deficient in Be are very uncommon. The halo dwarf, HD 76932, clearly has Be.
The 12C/13C Ratio in Unevolved Cool Stars
Authors: Chmielewski Y. , Lambert D. L.
Published: July 2016

We show that the carbon isotope ratio 12C/13C in the atmosphere of dwarf stars can be determined with reasonable accuracy from high resolution, high signal-to-noise ratio observations of the CH G-band in their spectra. Lines suitable for this purpose are selected from consideration of the solar case, for which 12C/13C = 89 is derived. A preliminary analysis of these features in the spectra of μ Her, δ Eri and τ Cet yields 12C/13C values of 84, 80 and 150 respectively.
New Determination of the “Decade” Fluctuations in the Rotation of the Earth 1860–1978
Authors: Morrison L. V.
Published: July 2016

Observations of the Earth's rotation have shown irregular variations of rate which have characteristic times of decades. These have been attributed to transfer of angular momentum between core and mantle by some mechanism such as inertial coupling, viscous stress, electromagnetic coupling or stresses produced by topographic features on the core mantle boundary.
On the Long-Period Variations in the Rate of the Earth's Rotation
Authors: Emetz A. I. , Korsun' A. A.
Published: July 2016

The maximum entropy power spectrum (Smylie, et al., 1974) of the Earth's rotational speed was calculated using data from 1900 to 1976. Two series of data were analyzed. The first was a series of δω/ω) determined from annual UT1 - ET data from 1900 to 1976. The second was a similar series derived from the mean monthly data of UT1 - TAI. Linear trends were removed from both series before analysis. Using the second series of data, significant periods of 2.8, 3.7, 7.0, and 10.5 years were found. The first series showed significant periods at 6, 10, 13, 22, and 57 years. Of these periodicities those at 22 and 57 years showed the largest amplitudes (0.454 ± 0.097 × 10−8 and 1.431 ± 0.104 × 10−8 respectively).
Etude Succinte du Catalogue Fondamental FK4 a Partir des Observations Faites a l'Astrolabe
Authors: Billaud G.
Published: July 2016

A short study of FK4 catalogue is based on CGA (Billaud G. et al, 1978). Important differences are shown in right ascension as well as in declination and assumptions are made to explain the discrepancies between both catalogues.
On the Relative Motion of the Earth's Axis of Figure and the Pole of Rotation
Authors: Poma Angelo , Proverbio Edoardo
Published: July 2016

The motion of the Earth's axis of inertia has been derived, taking elastic deformation into account, from the polar coordinates determined by the BIH for the period from 1962.0 to 1975.0. Characteristics of the motion of both the pole of inertia and the pole of rotation have been examined. The secular displacement of these poles relative to the pole defined by the low order harmonics C21, S21 determined from observations of satellites seems to confirm that the inertial reference axis has an apparent wandering motion within the deformable Earth.
Velocity of the Motion of the Terrestrial Pole
Authors: Moczko Janusz
Published: July 2016

The results of the spectral analysis of the velocity of the polar motion based on the data of the International Latitude Service (ILS), International Polar Motion Service (IPMS),. Bureau International de l'Heure (BIH), and the Doppler Polar Motion Service (DPMS) are presented.
Nutation in Space and Diurnal Nutation in the Case of an Elastic Earth
Authors: Capitaine Nicole
Published: July 2016

In order to improve the representation of nutation, the effect of elasticity of the Earth on the nutation in space and diurnal nutation of the terrestrial rotation axis is considered and its amplitude is evaluated for the principal terms. The choice between several methods taking this effect into account is discussed. A comparison with the effect induced on nutation by the existence of a liquid core in the Earth's interior shows that the consideration of elasticity alone cannot give any amelioration in the representation of nutation.
The Application of Radio Interferometric Techniques to the Determination of Earth Rotation
Authors: Johnston Kenneth J.
Published: July 2016

Radio interferometric techniques for the determination of Earth rotation are described.
Determination of Polar Motion and Earth Rotation from Laser Tracking of Satellites
Authors: Smith David E. , Kolenkiewicz Ronald , Dunn Peter J. , Torrence Mark
Published: July 2016

Laser tracking of the Lageos spacecraft has been used to derive the position of the Earth's pole of rotation at 5-day intervals during October, November and December 1976. The estimated precision of the results is 0.01 to 0.02 arcseconds in both x and y components, although the formal uncertainty is an order of magnitude better, and there is general agreement with the Bureau International de l'Heure smoothed pole path to about 0.02 arcseconds. Present orbit determination capability of Lageos is limited to about 25 cm rms fit to data over periods of 5 days and about 50 cm over 50 days. The present major sources of error in the perturbations of Lageos are Earth and ocean tides followed by the Earth's gravity field, and solar and Earth reflected radiation pressure. Ultimate accuracy for polar motion and Earth rotation from Lageos after improved modeling of the perturbing forces appears to be of order ± 5 cm for polar motion over a period of about 1 day and about ± 0.2 to ± 0.3 milliseconds in U.T. for periods up to 2 or 3 months.
The Quiet Sun at cm- and mm-Wavelengths
Authors: Fürst E.
Published: July 2016

Soon after the first detection of radio emission from the sun two components of the solar radio radiation were identified: The emission related to active centres on the disk and the radiation of the undisturbed, static solar atmosphere, in which the active regions are embedded. The undisturbed component is observed to vary only slightly during the solar sunspot cycle, it is called the emission of the quiet sun. A theoretical estimate of this component was first given by Martyn (1946) and subsequently developed in more detail by many other authors. The basic observations were performed with poor angular resolution. Still at present most experimental data are taken with angular resolutions of about 1 to 4 arc min, too low to discriminate between the different solar atmospheric fine structures, clearly seen in various spectral lines. The quiet component of the solar radio radiation therefore represents the average emission of an inhomogenous solar atmosphere.
Observations of the Quiet Sun with 6″ Resolution
Authors: Kundu M. R. , Rao A. P. , Erskine F. T. , Bregman J. D.
Published: July 2016

Solar radio emission at centimeter and millimeter wavelengths originates in the chromosphere and transition region and is a useful probe for the temperature and density in these regions. High spatial resolution observations of the quiet sun provide valuable information on the structure of the solar atmosphere. We have performed high resolution (~ 6″ (E-W) x 15″ (N-S)) observations at 6 cm with the Westerbork Synthesis Radio Telescope (WSRT) in June 1976 in order to search for the radio analog of the supergranulation network and to study the extent and symmetry of limb brightening. The use of the WSRT for high spatial resolution solar mapping has been described by Bregman and Felli (1976), Kundu et al. (1977), and others.
Shock Wave Transit Through the Transition Region and Related Radio Fluctuations
Authors: Poletto Giannina
Published: July 2016

The perturbing effects of a shock wave transit through the transition region are evaluated, using a simplified method of solution of the system of partial differential equations describing the fluid motion behind the shock passage. Calculated temperatures and densities are given at successive times during the shock transit. Based on these shocked models, time dependent brightness temperatures are derived at several decimetric wavelengths and compared with the unperturbed values to evaluate the amplitude of the induced brightness fluctuations. Finally, the possibility of detecting such shock induced phenomena is discussed.
Microwave, EUV, and X-ray Observations of Active Region Loops and Filaments
Authors: Schmahl E.
Published: July 2016

In the early years of centimetric radio astronomy, even before high resolution techniques were available, it was found that the apparent brightness temperature of the full disk is made up of a background level (the so-called quiet sun temperature) added to which is a contribution roughly proportional to the sum of the sunspot areas on the disk (Smerd 1964, Pawsey and Smerd 1953). Eclipse observations in 1946 at a wavelength of 10.7 cm (Covington 1947) and in 1948 at 10 cm (Piddington and Hindman 1949) and at 3.2 cm (Hagen et al. 1948) showed that the average bright area occupied about 4-thousandths of the disk, and had brightness temperatures of about 5 million degrees. Subsequent interferometric observations have extended and amplified these early studies in several ways. Kundu (1965) has reviewed the literature up to the early 1960's.
Time-Variations of 17GHz Radio Bursts by Multi-Source Structures
Authors: Kosugi Takeo
Published: July 2016

Four multi-source radio bursts observed with the new 17GHz interferometer at Nobeyama are analyzed and presented from the point of view of their time-variations.

Three of them (Sep. 6, 1978; Oct. 9, 1978; and Feb. 17, 1979) were essentially of an impulsive nature and all showed distinct double-source structures. Their polarization structures and time-variations are discussed and compared with type III and type II burst occurrences. The results of the comparison suggest either that electron accelerating regions moved across magnetic lines of force or that a rapid magnetic field rearrangement occurred near an accelerating region.

A quite different type of multi-source radio bursts was observed on Nov.10,1978. It had a long duration of several hours and was associated with type IV bursts at metric and decimetric wavelengths. At least five radio sources were observed to appear at 17GHz. A detailed description of this event is presented in comparison with the evolution of both Hα-flare and type IV bursts.
Radio Emission of the Solar Polar Regions at Millimeter Wavelengths
Authors: Efanov V. A. , Moiseev I. G. , Nesterov N. S. , Stewart R. T.
Published: July 2016

Regions of enhanced radio brightness in the polar areas of the Sun were detected in 1974 at the Crimean Astrophysical Observatory of the Academy of Sciences of the U.S.S.R. The effective temperatures of these regions exceeded that of the undisturbed Sun by 1500 K and 2200 K at 8.2 and 13.5 mm wavelengths respectively. Radio brightness distributions of the Sun obtained with the 22-m radio telescope, at 8.2 and 13.5 mm with angular resolutions of 1!6 and 2!55 respectively are shown in Figure 1. Regions of enhanced radio brightness near the North Pole of the Sun are seen, beside the typical s-sources at middle and low latitudes.
Flare of 1970 March 01: A Review and Further Evidence for Adiabatic Heating
Authors: Mätzler C. , Wiehl H.J.
Published: July 2016

The microwave and hard-X-ray burst of 1970 March 01, 11:27 UT was found to originate from a common thermal plasma with a maximum temperature of 57 keV. The low coronal plasma with an average electron density of about 3.108cm−3 covered a projected area of 5.1018 cm2. In Fig. 1 the time profiles of the emission measure and the temperature are compared with the 10.5 GHz flux while Fig. 2 shows the reversible relationship between the hard X-ray emission measure and temperature during the impulsive phase. The arrows indicate the direction of increasing time. The dashed-dotted line, representing an adiabatic process with an index χ = 5/3, agrees well with the observations showing a compression followed by an expansion (Mätzler et al. 1978).
Nonthermal Microwave Phenomena in Other Stars
Authors: Hjellming R. M. , Gibson D. M.
Published: July 2016

Several classes of “normal” stellar objects exhibit microwave phenomena, predominantly at cm wavelengths. These include RS CVn binaries, Algol-type binaries, M supergiants, and UV Ceti-type flare stars. The emission mechanisms are generally either synchrotron or gryosynchrotron radiation, with the latter being predominant in the numerous RS CVn radio emitters which sometimes exhibit variable circular polarization. “Events” have time scales varying from minutes to days.
The Polarization of Type V Bursts
Authors: Gary D.E. , Suzuki S. , Dulk G.A.
Published: July 2016

From observations with the Culgoora spectropolarimeter operating in the frequency range 24–200 MHz, we find that Type V bursts are often polarized in the opposite sense from the preceding Type III bursts. We present here the results of a statistical study of how frequently this occurs and the relationship of such polarization reversals to the position of the source on the disk of the Sun. We then examine two possible reasons for the reversal of polarization. In a paper published elsewhere (Dulk et al., 1979) we give a more detailed description and include observations of source sizes, positions and brightness temperatures of Type III-V bursts.
Absolute Magnitudes and Intrinsic Colours of Non-Supergiant Be Stars
Authors: Kozok J. R.
Published: July 2016

101 normal Be stars, probable members of 56 galactic clusters and OB-associations, and more than 20 extreme Be stars in the Large Magellanic Cloud were used to derive intrinsic colours of 09-B9 (III-V)e stars. Furthermore, the correlation between the intrinsic colour (U-B)0 and the absolute magnitude of non-supergiant Be stars was confirmed to be

and

The aim of the present investigation is to enlarge the basis for the determination of intrinsic colours and absolute magnitudes by providing a large sample from the southern sky.
An Observing Campaign for Systematic Photoelectric Observations of Bright Be Stars
Authors: Harmanec P. , Horn J. , Koubský P.
Published: July 2016

Most of our present-day knowledge of the photometric behaviour of Be stars still comes from various surveys only. Little attention was paid to systematic studies of possible photometric variability of particular objects on different time scales. Nevertheless, just this kind of information is necessary if one wants to study the physical relationship and/or differences between Be stars and other types of B stars like Beta Cepheids, supergiants, helium-rich stars etc., and to test various models of the Be phenomenon. Long systematic photoelectric observations do exist only for several Be stars. They invariably indicate that the long-term variability - if present - is always the most pronounced one. In some cases, this long-term variability masks the periodic light variations occuring on shorter time scales (see, e.g., the case of CX Dra, Koubský et al 1980).
Stellar Winds and Mass-Loss Rates from Be Stars
Authors: Snow Theodore P.
Published: July 2016

Resonance-line profiles of SiIII and SiIV lines in 22 B and Be stars have been analyzed in the derivation of mass-loss rates. Of the 19 known Be or shell stars in the sample group, all but one show evidence of winds. It is argued that for stars of spectral type B1.5 and later, SiIII and SiIV are the dominant stages of ionization, and this conclusion, together with theoretical fits to the line profiles, leads to mass-loss rates between 10-11 and 3 × 10-9 for the stars. The rate of mass loss does not correlate simply with stellar parameters, and probably is variable with time. The narrow FeIII shell lines often seen in the ultraviolet spectra of Be stars may arise at low levels in the wind, below the strong acceleration zone. The mass-loss rates from Be stars are apparently insufficient to affect stellar evolution.
Variation of Anomalous Stages of Ionization with Spectral Type for Be Stars
Authors: Marlborough J. M. , Peters Geraldine J.
Published: July 2016

One of the interesting results of ultraviolet (UV) astronomy was the discovery of ions from unexpected stages of ionization in spectra of O,B stars. The most common ions concerned are O VI and N V, but also C IV and Si IV in B stars. The presence of these ions is anomalous because generally their abundance is expected to be negligible if they are produced by photoionization by stellar radiation, either in the photosphere or in a cool circumstellar envelope (CE). The same ions are observed in the UV spectra of Be stars. Previous investigations, largely with Copernicus spectra, have reported O VI and N V in late Oe and early Be stars and Si IV in stars as cool as B5 (Marlborough, 1981 and references therein). In this paper we present the results of a preliminary survey of IUE spectra of Be stars covering a wide range of spectral type.
The Peculiar Be Star HD 87643
Authors: de Freitas Pacheco J.A. , Gilra D.
Published: July 2016

IUE observations as well as optical spectral of the peculiar star HD 87643 were obtained. The observed optical Fe II lines are probably formed in a expanding envelope and the rate of mass-loss derived from the analysis of these lines is about 7 × 10−7 M⊙ y−1.
Evidence for Mass Loss at Polar Latitudes in ω Ori and 66 Oph
Authors: Peters Geraldine J.
Published: July 2016

IUE observations of the “pole-on” Be stars ω Ori and 66 Oph have revealed the unexpected presence of high velocity (v ≃ −750 km s−1), relatively narrow (Δλ ≃ 1A) absorption components in the resonance lines of C IV, Si III, and Si IV. The C IV features show structure indicative of multiple shells or clouds. Similar high velocity lines were not observed in other pole-on Be stars considered in the program. The nature of these unusual features and the column densities and mass loss rates implied by them are discussed in this paper.
Recent Changes in the Ultraviolet Spectrum of the Be Star HR 2855
Authors: Peters Geraldine J.
Published: July 2016

High resolution IUE observations of the Be star HR 2855 (HD 58978) spaced five months apart have revealed striking variations in the resonance lines of C IV and N V. The nature of these variations can be seen in Figures 1 and 2.
The Active UV Phase of 59 Cyg
Authors: Doazan V. , Grady C. , Kuhi L. V. , Marlborough J. M. , Snow T. P. , Thomas R. N.
Published: July 2016

Coordinated UV and visual observations of 59 Cyg in 1978–81 show strong mass ejection activity and strong variability in displacements and profiles of superionized lines during the new Be phase, starting from a “quasi normal B” phase in 1977, and increasing irregularly through 1981 to a low and then moderate Hα emission. These data show that visual data alone cannot describe the activity of the star.
UV Observations of λ Cas: Intermittent Mass-Loss Enhancement
Authors: Henrichs H.F.
Published: July 2016

Twenty one high resolution IUE observations made over a two year interval revealed remarkable changes in the profiles of the resonance lines of C IV, N V and Si IV in the B 0.5 IVe star λ Cas. Narrow (FWHM < 100 km s−1), blue shifted (v < 1500 km s−1), absorption components of varying strenghts are observed in addition to the broad, asymmetric, low-velocity absorption lines which seem to be steady.
Hydrodynamical Models of Rotating Magnetic Winds
Authors: Barker Paul K.
Published: July 2016

Numerical investigations of rotating stellar winds driven by a combination of magnetic and line radiation forces show a clear dichotomy: shallow winds have their azimuthal velocity enhanced by magnetic corotation, whereas steep winds may have a diminished circular velocity.
Shapley's Debate
Authors: Hoskin Michael
Published: July 2016

The attempt to make three-dimensional sense of the Milky Way goes back to a most unlikely origin: the English antiquary of the early eighteenth century, William Stukeley, remembered today for associating the Druids with Stonehenge. Stukeley came from Lincolnshire and so was a fellow-countryman of Isaac Newton, and as a result he was privileged to talk with the great man from time to time. In his Memoirs of Newton Stukeley records one conversation they had in about 1720, in which Stukeley proposed that the Sun and the brightest stars of the night sky make up what we today would term a globular cluster, and this cluster is surrounded by a gap, outside of which lie the small stars of the Milky Way in the form of a flattened ring.