bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of Mass Loss from OB and Wolf-Rayet Stars
Authors: Barlow M. J.
Published: July 2016

In this review, three observationally accessible parameters of the winds of OB and Wolf-Rayet stars will be discussed:

(1)

Terminal velocities

(2)

Velocity laws

(3)

Mass loss rates
Line Formation in Winds with Enhanced Equatorial Mass-Loss Rates and its Application to the Wolf-Rayet Star HD 50896
Authors: Rumpl William M.
Published: July 2016

Ultraviolet spectra from the “Copernicus” satellite of the Wolf-Rayet star HD 50896 (Johnson, 1978; Cassinelli and Rumpl, 1982) show several P-Cygni profiles whose emission component has a larger equivalent width than the absorption component (see Figure 1). for lines with saturated absorption components, such as the N V (λλ1239–1243) line, the excess emission is due to thermal emission from the wind. However, for unsaturated lines which are due to scattering, such as the P V (λλ1118–1128) and O VI (λλ1032–1038) lines, the excess emission suggests that the scattering is not spherically symmetric.
The Wolf-Rayet Eclipsing Binary HD 5980 in the Small Magellanic Cloud
Authors: Breysacher Jacques , Moffat Anthony F. J. , Niemelä Virpi S.
Published: July 2016

The Wolf-Rayet star HD 5980, which is probably associated with the bright HII region NGC 346 of the Small Magellanic Cloud, was found to be an eclipsing binary by Hoffmann, Stift and Moffat (1978). Breysacher and Perrier (1980) determined the orbital period, P=19.266±0.003d, of the system whose light curve reveals a strongly eccentric orbit (e=0.47 for i=80°). The behaviour of the light curve outside the eclipses shows that we are dealing with a rather complex binary system. An analysis of the spectroscopic data is presented here.
On the Expected Frequency of WR + Compact Star Systems
Authors: Vanbeveren D. , de Loore C.
Published: July 2016

According to the classical evolutionary scenario for massive close binariesit is qenerally assumed that two WR phases are encountered, i.e. a WR+OB stage and a WR + compact star stage. The survival probability of a massive binary after an instantaneous supernova (SN) explosion critically depends on the assumed asymmetry of the SN explosion, i.e. on the “kick” velocity Vk (Sutantyo, 1978). The purpose of this paper is to make a statistical study on the expected WR + compact star binaries compared to the WR+OB type binaries based on non-conservative massive binary evolution, as a function of Vk which, as we will see, is very poorly known for these types of stars.
The Various Scenarios Leading to WR Stars: Their Relative Importance and the Role of Mixing
Authors: Maeder André
Published: July 2016

Over the last 40 years WR stars have been associated with almost all possible evolutionary stages. Hereafter are listed those scenarios which may be considered as most relevant in view of recent surface abundance determinations (cf. Willis, this meeting).
WR Stars with Ring Nebulae
Authors: Tutukov A.
Published: July 2016

It is shown that most of usually apparently single nitrogen WR stars with ring emission nebulae around them (WN + Neb) are a probable product of the evolution of a massive close binary with initial masses of components exceeding ∼20 MO.
Absolute Magnitudes of Wolf-Rayet Stars: The WN3 and WN4 Sub-Classes in the Large Magellanic Cloud
Authors: Breysacher Jacques , Azzopardi Marc
Published: July 2016

After the systematic survey carried out by Azzopardi and Breysacher (1979, 1980) at La Silla, Chile, with the 40-cm Objective Prism Astrograph, the census of the Wolf-Rayet population (101 stars) in the Large Magellanic Cloud (LMC) can probably be considered as quite complete except, perhaps, for stars located in the core of dense HII regions. The catalogue by Breysacher (1981) includes 100 stars to which one has to add one star of the WN type discovered by Sanduleak (private communication) outside of the survey limits.
Wolf-Rayet Stars Featured in Emission-Line Galaxies
Authors: Kunth D.
Published: July 2016

Emission-line galaxies contain a large number of hot stars responsible for the emissive gas. They offer the opportunity of investigating the initial mass function of stars in regions of active star formation. So far, only integral properties of the ionizing complexes in giant H II regions or emission-line galaxies have been used (Lequeux et al., 1981) but no direct emission-line stellar feature has been thoroughly analyzed.
X-Rays from Wolf-Rayet Stars Observed by the Einstein Observatory
Authors: Sanders W. T. , Cassinelli J. P. , van der Hucht K. A.
Published: July 2016

Preliminary results of three X-ray surveys are presented. Out of a sample of 20 stars, X-rays were detected from four Wolf-Rayet stars and two 08f+ stars. The detected stars have about the same mean value as 0 stars for the X-ray to total luminosity ratio, LX/L = 10−7, but exhibit a much larger variation about the mean. The spectral energy distributions are also found to be like that of 0 stars in that they do not exhibit large attenuation of X-rays softer than 1 keV. This indicates that for both the 0 stars and WR stars much of the X-ray emission is coming from hot wisps or shocks in the outer regions of the winds and not from a thin source at the base of the wind. The general spectral shape and flux level place severe restrictions on models that attribute the lack of hydrogen emission lines to extremely high temperatures of the gas in the wind.
High Resolution Spectroscopy with a Fiber-Linked Echelle-Spectrograph
Authors: Mandel H.
Published: July 2016

A compact fiber-linked echelle-spectrograph has been designed and constructed at the Landessternwarte Heidelberg-Königstuhl and was successfully tested during its first observation period in the end of May 1987. The optical design of the instrument is discussed in general terms and preliminary results of the first observations are presented. The reduction of several CCD frames has shown that the real properties of the spectrograph are within a few percent of the calculated ones.
High Resolution Spectrograph Needs for Stellar Seismology
Authors: Frandsen S⊘ren
Published: July 2016

There are two ways to become a famous observing astronomer: 1) by discovering something new and exciting, 2) by detecting a phenomena, which has been predicted, but not observed before.
A Search for Radial Velocity Oscillations in Procyon
Authors: Libbrecht Ken G.
Published: July 2016

I describe here a new technique for precision radial velocity measurements, using an iodine absorption cell in front of the slit of a high resolution spectrograph. A CCD in a continuous readout mode records a timeseries of stellar spectra with a duty cycle of unity. In January 1987, observations were obtained on two clear nights with bad seeing. No oscillations were detected in the data, but the technique shows promise for significantly better results under better conditions.
High S/N Spectroscopy of Pre-Main Sequence Stars I
Authors: Appenzeller I.
Published: July 2016

The spectra of PMS stars usually are superpositions of contributions from a relatively normal photosphere, an often strongly enhanced chromosphere, and of circumstellar matter related to stellar winds, accreation flows, jets, and cool circumstellar disks. Only high S/N data allows a reliable separation of these different contributions. Because of the high optical depths of PMS chromospheres, the PMS photospheres often can be observed in the very weak spectral lines only, which are undectable on low S/N spectrograms. Finally, magnetic fields are assumed to play a particularly important role for the appearance and evolution of PMS objects. Their spectroscopic measurement requires very high S/N data.
Effective Temperatures and Gravities for O-Type Stars Determined from High Precision Line Profiles and Wind-Blanketed Model Atmospheres
Authors: Bohannan B. , Voels S. A. , Abbott D. C. , Hummer D. G.
Published: July 2016

Analysis of line profiles obtained with astronomical instrumentation capable of high signal-to-noise ratio spectroscopy have contributed significant new precision to the determination of the basic stellar parameters of hot, luminous, mass-loosing stars. Accurate measurement of such stellar properties as effective temperature and helium abundance for stars of spectral type O and early B is important not only to the physics of these stars but also to the environment in which they are located. The overall goals of the work we summarize here are to refine the spectral-type vs. temperature calibration for the most massive stars and to determine helium abundances for stars that are loosing mass at a rate sufficiently high to affect their evolution. Details of our procedures are described in the analysis of ξ Puppis by Bohannan et al. (1986).
Theoretical Constraints from Asteroseismological High S/N Observations
Authors: Däppen W.
Published: July 2016

The two firmly established cases of many-mode observations, the Sun and Kurtz's Ap stars, suggest that in stars extremely small pulsation amplitudes are to be expected. If spectroscopic Doppler techniques are used to measure the velocity pattern, then it is obvious that with better resolution and higher S/N ratio of the spectral lines the sensitivity to detect velocity amplitudes increases. Observed pulsation frequencies of any star will put new constraints on the theory of stellar evolution. Besides addressing the two most important issues, namely determination of age and chemical composition, observed periods will also help resolve open questions in the physics of stellar interiors.
Abundance Stratifications in the Atmospheres of Ap Stars: The Case of Gallium
Authors: Alecian G. , Artru M.-C.
Published: July 2016

The abundances are usually determined assuming homogeneous concentrations for all elements in the line forming region. If diffusion driven by radiation occurs, this condition is not verified and the element stratification affects the equivalent widths as well as the line profiles. We shall illustrate these problems by a study of the gallium case. A synthetic spectrum of the Ga II resonance line λ 1414.401 Å has been computed assuming that gallium is stratified according a recent theoretical study of the diffusion of this element.
Measurements of Magnetic Fields on Cool Stars
Authors: Saar Steven H.
Published: July 2016

I discuss the some of techniques used (and problems involved) in measuring stellar magnetic fields on cool stars, and detail how these measurements are broadening our understanding of stellar magnetic activity.
Data Analysis
Authors: Cayrel R.
Published: July 2016

The relationship between the r.m.s. photometric accuracy on the data points of a stellar spectrum and the final accuracy on abundances and physical parameters derived from these data is discussed.
Precise Atomic Data
Authors: Huber Martin C. E.
Published: July 2016

We discuss the three questions: Why do we need accurate atomic data for stellar spectroscopy? What accuracy is needed? And: How can the accuracy of oscillator strengths be assessed? In conclusion we comment on the state of the art, stress the importance of uncertainty estimates and also discern between precision and accuracy.
Accurate Spectroscopy of Intermediate and Late Spectral Types
Authors: Holweger H.
Published: July 2016

Elemental abundances in the Sun and in meteorites are examined with respect to their qualification as a standard ofpopulation I composition. Some problems that arise in connection with spectroscopic determinations of abundances in the Sun, and in other late-type stars, are discussed with emphasis onphotospheric modelsanddepartures from LTE.
A Photospheric Solar Iron Abundance from Weak FeII Lines
Authors: Pauls U. , Grevesse N. , Huber M. C. E.
Published: July 2016

The high resolution and the high light-gathering power of a Fourier–transform spectrometer (FTS) afford the observation of very weak lines in laboratory spectra. Thus it became possible to determine an accurate solar iron abundance from Fe II lines that are weak in the solar spectrum: we measured the branching fractions of a few such lines whose upper levels lifetimes are known.
A High S/N Spectroscopic Study of Alpha Centauri A
Authors: Furenlid Ingemar , Meylan Tom
Published: July 2016

A fine analysis of Alpha Cen A relative to the Sun has been carried out. Over 500 absorption lines have been used in deriving a consistent solution involving abundances, Teff, log, g, microturbulence and blanketing. Light elements, up to zinc, are overabundant by around 0.15 dex, while heavy elements have solar abundances.
The Iron Abundances, [Fe/H] in the Four Nearest Open Clusters: Pleiades, Ursa Major Stream, Coma Berenices and Hyades
Authors: Cayrel R. , de Strobel G. Cayrel , Campbell B.
Published: July 2016

Iron abundances, [Fe/H] have been studied in G and K dwarfs of the four nearest clusters. With the exception of the Pleiades stars which are all fainter than the 10th magnitude, the observational material consists of high resolution, high S/N spectra taken at the coudé Reticon spectrograph of the Canada, France Hawaii Telescope. The Hyades is the only cluster with a significative overmetallicity with respect to the Sun.
Rotation, Activity and Lithium Depletion in the Hyades Late Main Sequence
Authors: Rebolo R. , Beckman J. E.
Published: July 2016

Selecting stars with previously measured or estimated rotational periods we measured Li equivalent widths in 8 stars of the Hyades late main sequence. Combining our data with literature values, we derive a homogeneous set of Li abundances. Plotting log N(Li) against Rossby number we can separate the effects of temperature and rotation. We find for stars later than F8 increased depletion with longer period, at constant surface temperature. Discounting, as improbable, spurious abundances due to surface activity effects, we give a tentative view of the implications of these results for stellar modelling.
Bimodality and Lithium Abundance on the Upper Main Sequence of the Open Cluster NGC 752
Authors: Beckman J E , Rebolo R.
Published: July 2016

Spectra of resolution λ/Δλ∼2 ×104 and good S:N ratio are presented in the range containing the 7Li doublet at 6707 Å for 9 main sequence or slightly evolved stars in NGC 752 (age ∼2 ×109 years). We investigate the suggested main sequence bimodality using spectroscopic indications of binarity and high rotational velocity, as well as the Li abundance to supplement previous photometry.
High-Dispersion Spectroscopy of the Ofpe/WN9 Stars R84 and S61 of the LMC
Authors: Wolf B. , Stahl O. , Seifert W.
Published: July 2016

The Ofpe/WN9 stars R84 and S61 of the LMC have been studied with high-dispersion spectroscopy in the optical and satellite-UV range. The high resolution and high S/N spectra in the optical range are particularly distinguished by strong emission lines of H, HeI and [NII]. The comparison of R84 with S61 shows that the peculiar emission line spectrum is not caused by the previously found late type companion of R84. We find that the UV spectra of both stars closely resemble those of late O-supergiants but all absorption lines are violet-shifted by about 250 km s−1 (R84) and about 200 km s−1 (S61). The absorption lines are stronger than in normal O-type stars. The UV-resonance lines indicate low terminal wind velocities of ≈ 900 km s−1 only. Unlike to normal O-type stars the AlIII-resonance lines also show pronounced P Cygni profiles with an even lower edge velocity (vedge ≈ 400 km s−1). Tne mass loss rates (>6.10−6 Mo yr−1) are comparable to rates found in normal luminous hot stars. However, the wind appears to be much more gradually accelerated similar to the wind of the galactic supergiant P Cygni. It is suggested that the Ofpe/WN9 transition type stars are the hotter counterparts of the early B-type P Cygni stars.
Chemical Composition as a Signature of Stellar Evolution - The Barium Stars
Authors: Lambert David L.
Published: July 2016

The hypothesis that Barium stars are the product of mass transfer across a binary system is reviewed with special attention given to the chemical composition of AGB stars (the mass-losing star in the binary) and the Ba stars (the mass-gaining star).
Cosmological Signatures in High S:N Spectra
Authors: Beckman J. E. , Pagel B. E. J.
Published: July 2016

We review briefly the observational status of abundance determinations for those elements produced in the first seconds of a “standard” Big Bang Universe, showing that although [4He] and [D] appear not to be mutually compatible there is still room for reconciliation via astration of D, for values consistent with estimated [7Li]. New limits to production cross-sections for 7Li appear to limit Nv (the number of light neutrino types) to no more than 3. Non-standard models with fluctuations are briefly considered; they are attractive because they use Ω = 1 and may also yield early C, N, O in significant quantities. The true value of 7Li [10-9 or 10−10 w.r.t. H] is the critical test here. We show where spectra of improved S:N are needed to progress in constraining cosmological models.
On the Determination of UT1 by the BIH and the U.S.S.R. Time Service
Authors: Yatskiv Ya. S. , Korsun' A. A. , Mironov N. T.
Published: July 2016

The reference systems for the determination of UT1 and polar coordinates are discussed. Some arguments are given in support of the adoption of the mean pole origin (MPO) defined by the mean latitudes of the observatories. Taking into account the frequency response of the filters used by the BIH and the U.S.S.R. Time Service, the effects of the errors of the adopted nutational coefficients and tidal variations of the vertical are estimated.
An Analysis of the Rotational Acceleration of the Earth
Authors: McCarthy Dennis D. , Percival Donald B.
Published: July 2016

The nature of the irregular fluctuations in the speed of the Earth's rotation was investigated using ninety-day means of UT2 - A.1 determined at the U. S. Naval Observatory. Data from June 1955 to April 1978 were included in this study. Statistical analysis of the excess length of day shows no evidence for the persistence of discrete values for periods on the order of five years. No statistical basis for the existence of discrete “turning points” in the rotational speed could be found.

Spectral analysis of the acceleration data shows that the rotational acceleration of the Earth during this period of time may be represented by a constant term plus random changes in acceleration occurring with a frequency greater than once per year. The magnitude of these changes appear to be consistent with estimates of meteorologically induced changes in the rotational acceleration.

An autoregressive integrated moving average (ARIMA) model was fit to the excess length of day data. This model permits simulated series of excess length of day data to be constructed. These simulated series show a statistical similarity to observations made since 1820. However the apparently large changes in the acceleration which occurred around 1870 and 1900 are twice that which can be reasonably accounted for by this model. The details of this analysis will be published later.
Polar Coordinates and UT1 - UTC from PZT Observations
Authors: Djurovic D.
Published: July 2016

Use of new techniques (Doppler, laser, VLBI) has yielded such results that many astronomers believe that in the near future these techniques will replace classical instruments for observations of the Earth's rotation. None of the modern techniques has furnished observational series which demonstrate that systematic errors in the polar coordinates and UT1 are stable over sufficiently long intervals. Investigations of known phenomena such as sudden changes of the secular term in UT1 - UTC (Munk and MacDonald, 1960), changes of the amplitude and phase of the seasonal irregularities (Fliegel and Hawkins, 1967; Pavlov and Staritzin, 1962), secular motion of the mean pole (Mihailov, 1971; Markowitz, 1960), continental drift (Stoyko, 1938; Djurovic, 1976), quasi-diurnal nutation of Molodenskij (Popov, 1963; Toomre, 1974; Rochester et al., 1974), etc., are complicated by the existence of systematic error variations (accuracy), and to a smaller degree, on the accidental errors (precision). The BIH and IPMS make use of individual series of astronomical latitude. ϕi, and (UTO - UTC)i from up to 82 classical instruments (Guinot, 1976). If the systematic errors in these series are independent, the polar coordinates and UT1 - UTC determined from a combination of observational series would result in an improvement of accuracy by at least one order of magnitude through the mutual compensation of the variation in systematic errors. At present, however, it is uncertain whether mutual independence of modern observations (a basic condition for mutual compensation of errors) will be better than that of the classical instruments.
Preliminary Analysis of Astrolabe Observations at Merate Observatory During the Period 1970–1977
Authors: Buffoni L. , Carta F. , Chlistovsky F. , Manara A. , Mazzoleni F.
Published: July 2016

Results of observations made with the Danjon astrolabe at Merate Observatory in the period from 1970 through 1976 were analyzed. The observational program and methods have been discussed previously (Buffoni et al., 1975a, b). The observational accuracy of the observations was compared with that of the Paris and San Fernando instruments. No substantial difference was found.
The Reference Systems
Authors: Kovalevsky J.
Published: July 2016

In order to discuss accurately the motions of the Earth in space, it is necessary to define rigorously two readily accessible reference systems. The conception and the realization of celestial absolute systems and terrestrial coordinate systems are discussed. It is suggested that these systems of reference ought to be defined with a minimum of theoretical or observational constraints. Examples of such ideal reference systems are given, together with some desirable properties for intermediate systems.
Concept for Reference Frames in Geodesy and Geodynamics: The Reference Directions
Authors: Grafarend Erik W. , Müller Ivan I. , Papo Haim B. , Richter Burkhard
Published: July 2016

Modern high accuracy measurements of the non-rigid Earth are to be referred to four-dimensional, i.e., time and space-dependent reference frames. Geodynamics phenomena derived from these measurements are to be described in a terrestrial reference frame in which both space and time-like variations can be monitored. Existing conventional terrestrial reference frames (e.g., CIO, BIH) are no longer suitable for such purposes.

The ultimate goal of this study is the establishment of a reference frame, moving with the Earth in some average sense, in which the geometric and dynamic behavior of the Earth can be monitored, and whose motion with respect to inertial space can also be determined.

The study is conducted in two parts. In the first part problems related to reference directions are investigated, while the second part deals with positions, i.e., with reference origins. Only the first part is treated in this paper.

The approach is based on the fact that reference directions at an observation point on the Earth's surface are defined by four fundamental vectors (gravity, Earth rotation, etc.), both space and time variant. These reference directions are interrelated by angular parameters, also derived from the fundamental vectors. The interrelationships between these space and time-variant angular parameters are illustrated in a commutative diagram–tower of triads, which makes the derivation of the various relationships convenient.

In order to determine the above parameters from observations (e.g., laser ranging, VLBI) using least squares adjustment techniques, a model tower of triads is also presented to allow the formation of linear observation equations. Although the model tower is also space and time variant, these variations are described by adopted parameters representing our current knowledge of the Earth. For details, see Bulletin Géodésique, end of 1978.
Determination of UT1 and Polar Motion by the Deep Space Network Using Very Long Baseline Interferometry
Authors: Fanselow J. L. , Thomas J. B. , Cohen E. J. , MacDoran P. F. , Melbourne W. G. , Mulhall B. D. , Purcell G. H. , Rogstad D. H. , Skjerve L. J. , Spitzmesser D. J. , Urech Jose , Nicholson George
Published: July 2016

The Deep Space Network (DSN) [operated by JPL under contract to the National Aeronautics and Space Administration] is implementing a Very Long Baseline Interferometry (VLBI) capability at DSS 63 (Spain), DSS 14 (California, USA), and DSS 43 (Australia) to support the navigation requirements of planetary space missions. The early development work for this system has already demonstrated the capability of measuring UT1 with a formal accuracy as low as 0.6 msec with only 6 hours of data. Further, a radio astrometric catalog of approximately 45 sources whose positions are known to better than has been constructed. In addition to these measurements, this paper describes the characteristics and anticipated performance of the complete VLBI system being implemented within the DSN for operational use in mid-1979. In particular, one of the capabilities of this system will be the measurement of UT1 and polar motion at weekly intervals. Although the navigation accuracy requirement is only 50 cm for the Voyager mission, this system should be capable of delivering UT1 and polar motion determinations with decimeter accuracy if it is operated at maximum performance. An additional requirement of this operational system is that it have the capability of providing these results within 24 hours of the actual observations.
Recent Results of Radio Interferometric Determinations of a Transcontinental Baseline, Polar Motion, and Earth Rotation
Authors: Robertson D. S. , Carter W. E. , Corey B. E. , Cotton W. D. , Counselman C. C. , Shapiro I. I. , Wittels J. J. , Hinteregger H. F. , Knight C. A. , Rogers A. E. E. , Whitney A. R. , Ryan J. W. , Clark T. A. , Coates R. J. , Ma C. , Moran J. M.
Published: July 2016

Radio interferometric observations of extragalactic radio sources have been made with antennas at the Haystack Observatory in Massachusetts and the Owens Valley Radio Observatory in California during fourteen separate experiments distributed between September 1976 and May 1978. The components of the baseline vector and the coordinates of the sources were estimated from the data from each experiment separately. The root-weighted-mean-square scatter about the weighted mean (“repeatability”) of the estimates of the length of the 3900 km baseline was approximately 7 cm, and of the source coordinates, approximatelyor less, except for the declinations of low-declination sources. With the source coordinates all held fixed at the best available,a posteriori, values, and the analyses repeated for each experiment, the repeatability obtained for the estimate of baseline length was 4 cm. From analyses of the data from several experiments simultaneously, estimates were obtained of changes in the x component of pole position and in the Earth's rotation (UT1). Comparison with the corresponding results obtained by the Bureau International de l'Heure (BIH) discloses systematic differences. In particular, the trends in the radio interferometric determinations of the changes in pole position agree more closely with those from the International Polar Motion Service (IPMS) and from the Doppler observations of satellites than with those from the BIH.
Polar Motion from Laser Range Measurements of GEOS-3
Authors: Schutz B. E. , Tapley B. D. , Ries J.
Published: July 2016

Using two-day arcs of GEOS-3 laser data, simultaneous solutions for pole position components, xp and yp, and orbit elements have been obtained for the period spanning 3 February to 6 March 1976 using three NASA Goddard Space Flight Center laser stations located near Washington, D.C. (STALAS) and on the islands of Bermuda and Grand Turk. The results are in general agreement with the BIH results. However, because of the locations of the laser sites, the xp solution is weaker than the yp solution. The xp and yp estimates were smoothed with a straight line by weighted least squares using the variance associated with the pole estimates as weights in order to reflect the effect of widely different data distributions. The smoothed yp differs by one meter with respect to the BIH smoothed values and the smoothed xp differs by about two meters. Spectral analysis of the results has identified frequencies associated with the orbital motion indicating the need for further improvements in the model of the physical system.
Low Cost Lageos Ranging System
Authors: Bender Peter L. , Silverberg Eric C.
Published: July 2016

This paper describes a Lageos laser ranging station design based on single photoelectron detection which could be used to monitor polar motion at all periods, and short-period UT1 variations with high accuracy and at moderately low cost. No comparison has been made with the costs of long baseline radio interferometry (LBI) stations, since the establishment and operation of basic international networks using both approaches seems scientifically well justified. Both LBI and lunar laser ranging results will determine intermediate and long-period UT1 variations and nutation. The LAGEOS laser ranging station design suggested here is similar to the design used in the high-mobility LAGEOS ranging station now being constructed by the University of Texas. It has been shown that 30 cm diameter transmit/receive optics with 10 arc second pointing accuracy and 50 milliwatt average laser power output are usually sufficient to give 70 signal counts in a three minute averaging time, even at 20° elevation angle. Lasers having the desired power at 530 nm wavelength with 10 pps repetition rate and 3 ns pulse length are now reported to be commercially available at moderate cost. The resulting range accuracy for normal points corresponding to the three minute averaging time is three cm, including allowances for absolute calibration of the system, atmospheric refraction correction uncertainties, and Earth tide uncertainties. Much of the pulse-timing electronics needed is commercially available, and many time and latitude stations already have good epoch determination systems. The ten arc second pointing requirement for a 30 cm diameter beam seems considerably easier to meet than the optical requirements for classical observing techniques. A simple beam director with flat mirrors appears quite feasible, with inexpensive encoders on each axis for minicomputer control if desired. A number of special features of the University of Texas high-mobility station would not be needed for a fixed station.
Polar Motion through 1977 from Doppler Satellite Observations
Authors: Oesterwinter Claus
Published: July 2016

Doppler observations of Navy Navigation Satellites have been used to compute pole positions on a daily basis since 1969. Limited results exist for the period 1964 to 1969. Based on Doppler observations from four or five satellites, the standard error for a five-day mean pole position is less than 20 cm. Comparisons are made between BIH, IPMS and ILS results and those obtained from Doppler. It is shown that the six years of reliable Doppler data since 1972 contribute little in finding the Chandler period. Using observations from the three astronomical sources over 12 years yields a Chandler period of 432.0 ± 0.2 days.
Reasons and Possibilities for an Extended Use of the Transit System
Authors: Pâquet P. , Devis C.
Published: July 2016

Observations of Earth rotation and polar motion are now performed on a routine basis by classical astronomical methods and by the satellite Doppler technique.

In the near future the laser is likely to realize its old objective of determining ER and PM with an accuracy of a few milliseconds of arc through ranging to Lageos. VLBI is still in development.

To permit investigation of possible systematic differences, all these techniques should be used simultaneously for a period whose length should not be set in advance.

The Doppler method can still be improved and could be easily introduced at many observatories in support of the Medoc campaign. We present here two possible methods of data condensation which, if implemented, would permit much of the data analysis to be done at the tracking stations and would reduce to a very few the number of parameters required by the central computing agency.
Very First Results of the Medoc Experiment
Authors: Nouel F. , Gambis D.
Published: July 2016

It is already well known that the coordinates of the pole can be derived not only by the classical astronomical methods but also from analysis of the orbits of artificial Earth satellites. The MEDOC experiment (Motion of the Earth by Doppler Observation Campaign) has been initiated by the Groupe de Recherches de Géodésie Spatiale (GRGS) to provide observations and undertake independent analysis for this purpose. Several organisations are participating.
The Geophysical Interpretation of Changes in the Length of the Day and Polar Motion
Authors: Runcorn S.K.
Published: July 2016

The data on the irregular fluctuations in the length of the day and the motion of the pole is of great significance in the geophysicist's task of constructing a model of the earth's interior.

Short term instabilities in the dynamo generating the earth's magnetic field produce what is observed at the surface as the secular variation. These changes induce currents in the lower mantle and the resulting torques appear to be the cause of the irregular fluctuations in the length of the day, although some quantitative problems remain.

The excitation of the Chandler wobble could result from impulsive torques applied to the mantle by very short period (a year or less) local magnetic field disturbances coming to the surface of the core. The alternative mechanism by earthquakes has been much investigated and the possibility of this is still obscure. A test however is available in the polar motion data: a disturbance in its path displaces the subsequent centre of its Chandler motion in the latter theory, but only its amplitude on the former theory. The behaviour of the pole around 1968 supports the core theory, but much more analysis of the polar motion is required.
On Investigations of the Tidal Waves Mf and Mm
Authors: Pil'nik G. P.
Published: July 2016

The comparison of astronomical time observations with the theory of solid-Earth tides makes it possible to determine the Love number, k, which characterizes the elastic properties of the Earth. In addition, the comparison of values of k determined from different tidal waves allows us to judge the accuracy of the nutational theory in astronomical observations since both tides and the Earth's nutation are produced by the same causes.
Active Region Magnetic Fields and cm-λ Emission
Authors: Alissandrakis C. E.
Published: July 2016

The influence of the magnetic field on the structure of sunspot-associated sources at cm-λ has been investigated through model calculations. The case of a source observed with the Westerbork SRT and the structure of a single sunspot source are considered.
Observations of Solar Active Regions at 2 and 6 cm Wavelengths with 3 Arc Second Resolution
Authors: Velusamy T. , Kundu M. R.
Published: July 2016

We have used the Very Large Array of the NRAO to observe solar active regions at 2 and 6 cm wavelengths in May 1979. In this paper we present and discuss the fine structure components of a sunspot associated radio region observed with a resolution of 3″ arc on May 4 and 5, 1979. In this region (McMath 15974) there were two distinct groups of sunspots separated by about 3′ arc. Group I located towards the west limb contained two spots while Group II in the east was a complex containing several spots that emerged during the period of our observations. At 6 cm both the sunspot groups were within the primary beam whereas at 2 cm only Group I was within the field of view. The VLA observations were made at 6 and 2 cm alternating between them every 5 minuts. The region was mapped with a resolution of about 3″ x 3″ using 10 hours of synthesis data on each day.
Solar Observations with the Very Large Array
Authors: Archer J. W.
Published: July 2016

Currently planned modifications to the Very Large Array to facilitate solar observations are described. The performance characteristics of the instrument in this observing mode are outlined.
Radio Burst Emission Mechanisms: General Review
Authors: Melrose D. B.
Published: July 2016

This paper is a shortened version of a review of radio emission mechanisms for meter-λ radio bursts.
A Statistical Investigation of Microwave Burst Spectra for the Determination of Source Inhomogeneities
Authors: Schoechlin W. , Magun A.
Published: July 2016

The spectra of a set of 77 microwave bursts of July 1971 to September 1974 as published in Solar Geophysical Data have been fitted with an idealized spectrum of triangular shape. The spectral index of the low frequency part α, the maximum flux density and the associated frequency have been determined. A cluster-analysis carried out on these parameters showed that the sample consists of only one class of events. In the histogram of the spectral index we found a most frequent value of 1.4. Such a low value cannot be explained by the mechanisms normally assumed to account for the low frequency attenuation, as gyroresonance absorption and the Razin effect.
Observations of Solar Type III Radio Bursts with the Nancay Radioheliograph
Authors: Pick M. , Raoult A. , Vilmer N.
Published: July 2016

Results on the space-time evolution of type III burst sources are summarized (Raoult and Pick, 1979) and observations on the temporal characteristics of the circular polarization are presented. It is shown that type III burst sources can be resolved into narrow components. Complex or very large sources may be explained by the occurrence of electron beams which propagate along different diverging paths. Propagating effects in a scattering corona are not required to explain the observations. The origin of the fundamental-harmonic pairs is briefly discussed.
On the Statistical Nature of Type I Bursts
Authors: Elgaröy Öystein
Published: July 2016

During noise storms narrow-band, short-lived bursts make up an important part of the activity. Frequently the bursts show different characteristic arrangements in the frequency-time plane (Elgaröy, 1977). In the present investigation the frequency of occurrence of single bursts and sequences of bursts has been determined. The work started out as a search for statistical evidence for the occurrence of echoes of type I bursts. As progress was made, more attention was devoted to the general question of what was the frequency distribution of events containing different numbers of bursts and the conclusions that could be drawn from the observed distribution.
Complementary Bursts, Coronal Inhomogeneities and New Microscopic Spectral Features of Solar Bursts in Type IV Bursts
Authors: Sawant H. S. , Bhonsle R. V. , Degaonkar S. S. , Takakura T.
Published: July 2016

Complementary bursts (C.B's) have been observed in the decametric range during noise storms and/or type IV activity. These bursts essentially consist of two components, each component having a duration ~ 1 second. The first component shows weak emission or emission gap over a certain frequency range. The second component is observed after a certain delay. If the bursts are assumed to be generated at the fundamental, and if the radiation corresponding to the gap propagates through an electron density irregularity located close to the source along the line of sight, whose cross-section is less than the linear extent of the source, then almost all properties of the C.B.'s can be explained. High sensitivity, and high frequency and time resolution spectra of type IV bursts at 137 MHz revealed new microscopic spectral features displaying “wave-like” and “fork-like” shapes.
Numerical Simulation of Type III Bursts
Authors: Takakura T.
Published: July 2016

By the use of semi-analytical method, modeling of three kinds of type III solar radio bursts have been made. Many basic problems about the type III bursts and associated solar electrons have been solved showing some striking or unexpected results. If the fundamental radio emissions should be really observed as the normal type III bursts, the emission mechanism would not be the currently accepted one, i.e. the scattering of plasma waves by ions.
F & H Solar Radio Emission: Delayed Fundamental
Authors: Achong Anthony
Published: July 2016

The suggestion is made that the excessive time delays between the two components of f-h type III pairs might be partly accounted for by an initial production of the second harmonic only, followed later by the production of both components. The source is assumed to be inside coronal streamers. Theoretical arguments lend some support to the suggestion of a delayed start of the fundamental.
Satellite Observations of Solar Radio Bursts
Authors: Steinberg J.L.
Published: July 2016

Space observations of solar radio bursts have provided the following information:

– From a single spacecraft:

Measurements within the burst source or close to it: fundamental and harmonic type III radio emission, the corresponding plasma waves and spectra of the exciting electrons.

– From a spacecraft and the earth or from two spacecrafts:

A better evaluation of the influence of the ionosphere on some ground-based observations.

Measurements of the beaming of the emission which yield constraints on the radiation mechanism and/or the role of coronal propagation in determining the source size and directivity (type I and III's).

Measurements of the differential time delay which yield for type III:

At short (m- and dam-) wavelengths, some evidence of group delays,

At long (hm- and km-) wavelengths one coordinate of the source.

Complete (3-dimensional) localization of the source at long wavelengths and therefore maps of the heliosphere magnetic field and electron density as well as the source size and, in the future, its polarization.

The results of these observations and their interpretation are reviewed and discussed.
One Dimensional High Time Resolution Observations by the Westerbork Array
Authors: Kattenberg A.
Published: July 2016

The Westerbork array has recently been adapted and procedures have been developed to observe the sun at cm wavelengths with high time resolution. One dimensional scans are obtained in both circular polarizations every .1 sec.
Radio and White-Light Observations of Coronal Transients
Authors: Dulk G. A.
Published: July 2016

Optical, radio and X-ray evidence of violent mass motions in the corona has existed for some years but only recently have the form, nature, frequency and implication of the transients become obvious. In this paper I review the observed properties of coronal transients, concentrating on the white-light and radio manifestations. The classification according to speeds seems to be meaningful, with the slow transients having thermal emissions at radio wavelengths and the fast ones non-thermal. I then discuss the possible mechanisms involved in the radio bursts and review the estimates of various forms of energy. It appears that the magnetic energy transported from the Sun by the transient exceeds that of any other form, and that magnetic forces dominate in the dynamics of the motions. The conversion of magnetic energy into mechanical energy, by expansion of the fields, provides a possible driving force for the coronal and interplanetary shock waves.
Decametric Radio Bursts Associated with Coronal Loop Structures
Authors: Gergely T. E. , Kundu M. R. , Golub L. , Webb D.
Published: July 2016

The soft x-ray (2–54 Å) pictures obtained by the S-054 experiment aboard SKYLAB provide an excellent opportunity to study the association of x-ray loop structures with radio bursts. We report here on the properties of meter-decameter wavelength radio bursts which appear to be associated with two different types of loop structures:

a)

Relatively short lived small scale loops, which are observed to link magnetic fields of opposite polarity, called x-ray bright points (XBPs); and

b)

Longer lived loop systems which appear to connect opposite magnetic polarities of an active region and active region complexes as well.
An Interpretation of Solar Flare Microwave Spikes as Gyrosynchrotron Masering
Authors: Holman G. D. , Eichler D. , Kundu M. R.
Published: July 2016

Repeated bursts of microwave emission were observed by Slottje (1978) during the solar flares of April 11 and April 28, 1978. The high brightness temperatures which are inferred for these bursts indicate that a coherent mechanism must be responsible for the observed radiation. Slottje suggests that the emission is plasma radiation at the fundamental plasma frequency. We consider here the alternative possibility that the emission is coherent gyrosynchrotron radiation.
Composite Colour-Magnitude and Colour-Colour Diagrams for Be Stars in Open Clusters
Authors: Mermilliod J.-C.
Published: July 2016

By the end of 1980, the total number of Be stars discovered in the field of open clusters amounted to 180 stars distributed in 60 clusters. Among these, 110 Be stars belong to 32 clusters included in the sample I studied, which contains 75 open clusters younger than the Hyades. But only 88 stars with complete UBV photoelectric photometry have been taken into consideration here. The concept of age groups, defined elsewhere (Mermilliod 1981a), is used throughout the present analysis, as well as the new estimate of the colour excesses and distance moduli I obtained for these 32 clusters. Under the assumption of uniform reddening across the clusters, absolute magnitudes and dereddened colour indices have been calculated for the 88 Be stars.
Statistical Analysis of the Data Available for Be Stars
Authors: Egret Daniel
Published: July 2016

A comprehensive catalogue of more than 1100 Be stars with known MK classification has been prepared at the Strasbourg Stellar Data Center, and is described in an other session of this Symposium (Jaschek and Egret, 1982). The compilation of photometric and spectroscopic data available for these stars has made possible a general statistical approach of the Be star spectral group.
The Vatican Emission Star Survey: Review and Comments
Authors: de Lichtbuer Pierre Cardon
Published: July 2016

Eight years ago a program was started at the Vatican Observatory to search for faint emission-line stars close to the galactic plane. Indeed at that time few early type emission stars were known fainter than V = 12. This survey consists in a double program:the search for emission line stars with the Vatican Schmidt using the objective prism and an appropriate combination of plate and filter in order to have a narrow passband around Hα(McCarthy Treanor 1970);and UBVRI photometry at the Mt. Lemmon facilities of the Univ. of Arizona observatories. Five papers have already been published(Coyne et al 1974, 1975, 1978;Wisniewski et al 1976, 1977). Two more will be published later this year. The Vatican Emission Star Survey(VES) resulted in the discovery of about 1000 new emission-line stars; for 700 of those the photometry is finished.
BCD Spectrophotometry of the Be-Shell Star 88 Her
Authors: Divan L. , Zorec J.
Published: July 2016

The spectrophotometric behavior of the Be/shell stars seems to be different when their second Balmer discontinuity is in emission from that when it is in absorption. We have analysed here a particular case in which the second Balmer jump is in absorption. In this note we compare the results of a BCD analysis concerning the variations of the Be-Shell star 88 Her (HD162732), to the results of the UBV photometry.
Spectroscopic Study of Pleione in 1977–1979
Authors: Hirata Ryuko , Katahira Jun'ichi , Jugaku Jun
Published: July 2016

Shell spectra of Pleione in 1977–1979 are characterized by further increase in their strengths and by the development of the blue-winged profiles without noticeable variation of their radial velocities. The MgII resonance lines at λ2800A have the blue-shifted components with a velocity of-35 km/s relative to the other shell lines. The development of the shell structure is derived. The mass loss rate was 7×10−11 M⊙/yr.