bluuebunny/crossref_metadata_2025 huggingface dataset:
Radio Observations of Hii Regions in M33
Authors: Israel F. P. , van der Kruit P. C.
Published: July 2016

The Westerbork Synthesis Radio Telescope was used to map the continuum radiation of M33 at 1415 MHz. Of 67 radio sources with fluxes S> 1.8 mJy (3σ), 60% coincide with Hα sources. These are all intrinsically stronger than 4 × the Orion nebula, i.e., they are giant Hiiregions. The two strongest sources, NGC 604 (58 mJy) and NGC 595 (20 mJy), are similar to W51.
Observational Aspects of Supernova Remnants
Authors: Mills B. Y.
Published: July 2016

A supernova event may lead to four observable features: a pulsar, an expanding nebulosity, a radio source and an X-ray source. The great majority of supernovae do not produce observable pulsars, and discussion is restricted largely to the other features. An increasing number of X-ray sources is now being detected and the structure and spectrum of the stronger sources investigated; these observations yield information about the physical state of the remnant. Recently, 11 new optical and radio remnants have been found in the Magellanic Clouds. These have led to a good determination of the Σ – D relation, thus providing a more reliable distance scale for galactic SNR, but have also shown that a one-to-one correspondence between a radio source and a supernova event is questionable. When these remnants are combined with corrected earlier catalogues and a new southern catalogue containing a high proportion of distant old remnants the number of known SNR is about 150. The evolution of galactic SNR may be investigated empirically, and although the derived rate of occurrence is very uncertain a rate of about 2 supernovae per century is consistent with most determinations. The galactic SNR are distributed rather like the radio disc emission, but more closely confined to the galactic plane, and selected SNR show evidence of a spiral pattern.
Polarization Observations of Supernova Remnants
Authors: Milne D. K. , Dickel John R.
Published: July 2016

Polarization and total power at 5000 MHz and 2700 MHz have been obtained for 30 supernova remnants (SNR) using the 64-m radio telescope at Parkes. This large sample includes a range of SNR from the young bright objects (such as Kepler's SNR) through the old faint sources such as MSH 14-63. Among the old remnants, the individual SNR have very varied properties, but several general conclusions emerge from our study. (1) In many cases, the polarization of the galactic background is as strong as that of the SNR and can vary significantly over the angular extent of the SNR. (2) The Faraday rotation is generally small and varies quite uniformly across the source. (3) The magnetic field patterns, although associated with the SNR, do not show any particularly characteristic pattern or relations to the total-power structure of the source.
VLA and Optical Mapping of the Quasar PKS 0812+020
Authors: Ghigo F. D. , Rudnick L. , Johnston K. J. , Wehinger P. A. , Wyckoff S.
Published: July 2016

Observations are reported of the remarkable object PKS 0812+020, the first quasar found to have optical emission in one of its radio lobes. A distinct radio jet is also seen, and there is radio and optical evidence that the quasar is near the center of a galaxy cluster.
Two Peculiar Radio Galaxies in A1367
Authors: Gavazzi G. , Jaffe W.
Published: July 2016

We observed the cluster of galaxies A1367 to map the structure of the cluster and that of the radio galaxy 3C264. We report on 3C264 and on the peculiar galaxy UGC6697.
Systematics of Large-Scale Radio Jets
Authors: Bridle Alan H.
Published: July 2016

Radio jets occur in sources with a wide range of radio luminosities, and in 70% to 80% of nearby radio galaxies. There may be two basic types of large-scale (>1 kpc) jet — B‖-dominated one-sided jets in sources with luminous radio cores, and B⊥-dominated two-sided jets in sources with weak radio cores. The large-scale jets that have been observed at high linear resolution are well collimated within a few kpc of their cores, then flare and recollimate further out. Their brightness-radius evolution is often “subadiabatic”.
The Quasar Jet 4C 32.69 at 1.4 GHz
Authors: Dreher J. W.
Published: July 2016

One of the most luminous radio jet sources known is 4C 32.69, identified with a z=0.67 QSO. It has previously been mapped at 5 GHz by Potash and Wardle (1980, PW hereafter). Here a 1.4 GHz VLA map of comparable resolution is presented and compared to the earlier map.
Seyfert Galaxies
Authors: Wilson Andrew S.
Published: July 2016

Observations of sample of Markarian Seyferts with the VLA indicate that a large fraction possess linear radio structure on a scale of a few hundred parsecs to a few kiloparsecs. The radio components generally straddle the optical nucleus and several sources are simple doubles. Similar structures are seen in the classical Seyferts NGC 1068, 4151, and 5548. NGC 4151 is probably best interpreted as a jet. A few sources (e.g. Mark 315, NGC 7469) exhibit diffuse, non-aligned radio structure on a scale similar to that of the linear sources. The radio axis in linear sources is misaligned with respect to the rotation axis of the galaxy disc by a large angle. The linear sources are discussed in terms of a model of a supersonic beam or jet which is “disrupted” by interaction with interstellar gas in the inner part of the galaxy (often a spiral). Two aspects of this interaction are emphasised. Firstly, the curved shape of the radio sources in NGC 1068 and NGC 4151 is ascribed to beam bending by the ram pressure of the rotating interstellar medium. Simple models of this process are shown to be consistent with the observations. Secondly, it is suggested that the broadened forbidden lines in Seyferts originate in part from interstellar gas accelerated outwards by the beam. This picture accounts for some of the empirical correlations found between radio and optical forbidden line properties.
Radio Observations of Markarian 8
Authors: Heeschen D. S. , Heidmann J. , Yin Q. F.
Published: July 2016

Markarian 8, a clumpy irregular galaxy (Casini et al. 1979), was observed with the VLA at 20 cm (Mar. 19, 1981; 26 ant.) and 6 cm wavelengths (June 12, 1980; 18 ant.) The structure is alike at the two wavelengths, consisting of 3 distinct clumps imbedded in a diffuse envelope of about 40 arcsec extent. Figure 1 shows the 6 cm structure. At higher resolution the clumps break up into several components. The 20 cm structure is shown in Figure 2, which also compares the optical and radio morphologies. There is excellent general agreement, suggesting a common origin of emission in the clumps.
SS433 — Observing Evolution in a Precessing, Relativistic Jet
Authors: Hjellming R. M. , Johnston K. J.
Published: July 2016

We commonly refer to the central “object” in extra-galactic radio sources as the “engine” that is the root cause of many radio source characteristics. We frequently ask, COULD “engines” at the cores of extra-galactic sources: (1) be compact objects with accretion disks; (2) eject well-collimated supersonic jets; (3) show relativistic effects in ejected material; (4) produce twin-jets; (5) produce one-sided jets; and (6) initiate highly polarized synchrotron radiation sources? SS433 is a binary star system with radio and optical jets that is relevant because it is a “little engine that could”, and does, do all of these things. Further, we can observe changes in SS433 on time scales from hours to several months, and these data allow one to study evolution of jets in a more thorough fashion than is possible for extra-galactic sources.
Simple Formula for Radio Jet Surface Brightness
Authors: Henriksen R. N.
Published: July 2016

Henriksen, Bridle and Chan (1981; HBC) have proposed that the energy for the synchrotron emission of radio jets is derived ultimately from the turbulent hydrodynamic eddy cascade between the Taylor wave number, kT, and the Kolmogorov wave number. This cascade is established during the development of a turbulent jet by the shearing action of large-scale vortical entrainment of ambient material (Brown & Roshko, 1974).
Vortex Accretion Funnel / Relativistic Beam Models of Double Radio Sourci
Authors: Scott H. A. , Lovelace R. V. E.
Published: July 2016

A consistent model of extra-galactic double radio sources must evidently involve all aspects of the source from the underlying power source to the production of the radio lobes. Here, we give an overview of our work on the different aspects of a self-consistent model which includes gravitational accretion of fluid with angular momentum as the power source, the production of hydrodynamic or relativistic particle-beam jets, and the formation of expanding radio components.
Black Holes and the Origin of Radio Sources
Authors: Thorne Kip S. , Blandford Roger D.
Published: July 2016

Powerful, extragalactic radio sources might be fuelled by energy release near a massive black hole. In this article we describe some relativistic effects which may be relevant to this process. We use Newtonian language so far as possible and illustrate the effects with “simple” analogies. Specifically, we describe the gravitational field near a black hole, Lens-Thirring and geodetic precession, electromagnetic energy extraction of the spin energy of a black hole and the structure of accretion tori around a black hole.
X-Ray and Optical Observations of Quasars
Authors: Tananbaum Harvey , Marshall Herman L.
Published: July 2016

The first Einstein observations established that quasars, as a class, are luminous X-ray emitters (Tananbaum et al. 1979). Since then, one of our major programs has been to carry out further X-ray and optical observations to improve our estimate of the contribution of quasars to the 2 keV extragalactic isotropic X-ray background and also to reconcile number counts of discrete X-ray sources with reported optical number counts of quasars (cf. Zamorani et al. 1981 and references therein). This paper is a preliminary report on our observations of the 1.7 square degree field studied originally by Braccesi and his colleagues (Formiggini et al. 1980 and Braccesi et al. 1980). A more detailed presentation of our results is in preparation (Marshall et al., 1981).
Detection of a Broad HI Absorption Feature at 5300 km Sec−1 Associated with NGC 1275 (3C84)
Authors: Crane P. C. , van der Hulst J. M. , Haschick A. D.
Published: July 2016

Observations of NGC 1275 at ∼ 1396 MHz with the NRAO line interferometer in 1974 and 1976 suggest the presence of a very broad, shallow HI absorption feature centered at ∼ 5300 km sec−1. These observations were repeated in 1981 June with the Very Large Array using a greater bandwidth to determine a satisfactory baseline.
Radio Flux Flicker of Extragalactic Sources
Authors: Heeschen D. S.
Published: July 2016

Compact sources (compactness evidenced by flat/complex spectra) display a “flicker” in their intrinsic centimeter wavelength radiation, with an amplitude of about 2% and a characteristic time scale of a few days.
Polarization Variability of Some Compact Radio Sources
Authors: Komesaroff M. M. , Milne D. K. , Rayner P. T. , Roberts J. A. , Cooke D. J.
Published: July 2016

Figure 1 shows observations for four sample sources from the Parkes 5 GHz polarization monitoring programme. Interesting features illustrated include

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Sudden changes of the position angle of the linear polarization by ≳ 70° in PKS 0537-441 and 1253-055 (3C279).

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A linear increase in the position angle of the polarization of PKS 2134+004 through 70° over 3/12; years.

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Distinct bursts of circular polarization in PKS 0430+052, 0537-441 and 1253-055. In PKS 0430+052 (3C120) such a burst coincides with the possible superluminal expansion (Walker et al., 1981). In PKS 1253-055 (3C279) a burst of circular polarization is currently occurring at a time of very low linear polarization.
Superluminal Expansion of 3C 273
Authors: Pearson T. J. , Unwin S. C. , Cohen M. H. , Linfield R. P. , Readhead A.C.S. , Seielstad G. A. , Simon R. S. , Walker R. C.
Published: July 2016

Figure 1 shows hybrid maps of the core of 3C 273B at five epochs, made with arrays of 4 or 5 VLBI antennas. The maps span a period of 3.5 years. They all show a bright eastern peak and a lower-brightness extension to the west. There is a local maximum in the western extension between 6 and 8 milliarcsec from the main peak. This “blob” moves steadily further away from the main peak along a roughly straight line in PA −116° ± 2°. Compare this with the position angle of the 25-arcsec optical jet, −137°. The maps show a slight curvature to the south with increasing separation from the main peak. Lower-resolution VLBI maps at lower frequencies show that this curvature continues at greater separations, suggesting a smooth connection between the milli-arcsecond position angle and the position angle of the optical jet. In our latest map (1981.09) the blob is no longer detectable with the limited dynamic range of the VLBI network (about 20:1).
Superluminal Expansion of the Quasar 3C 345
Authors: Unwin S. C.
Published: July 2016

VLBI hybrid maps of the compact radio structure in 3C 345 at 5.0 and 10.7 GHz show a core-jet morphology, with two components in the jet separating from the core with apparent transverse velocities ≃ 8/h c (for Ho = 100 h km/s/Mpc and qo = 0.05). These “knots” decay as they move down the jet, with lifetimes ≃ 2–3 years.
Optical Spectra of Radio-Loud and Radio-Quiet Active Galactic Nuclei
Authors: Osterbrock Donald E.
Published: July 2016

Many radio galaxies have strong emission lines in their optical spectra. The fraction with such lines is much larger than in “normal” galaxies. Radio galaxies generally also have very bright nuclei; thus those with strong emission lines are similar in both respects to Seyfert galaxies. Hence radio and Seyfert galaxies are both generally considered to be similar physical objects: active galactic nuclei. Their observational properties show they are closely related to quasars (quasi-stellar radio sources) and (radio-quiet) QSOs. A short table of the space density of these objects, culled from many sources, chiefly Schmidt (1978) and Simkim, Su and Schwarz (1980) is given below. Although all the numbers are quite uncertain, there is no doubt that the radio-loud objects are relatively rare. With less certainty, it appears that the ratio of numbers of radio galaxies to Seyfert galaxies is about the same as the ratio of numbers of quasars to QSOs.
X-Ray Emission from BL LAC Objects: Comparison to the Synchrotron Self-Compton Models
Authors: Schwartz Daniel A. , Madejski Greg , Ku William H.-M.
Published: July 2016

As one part of our joint study of the X-ray properties of BL Lac objects, we compare the measured X-ray flux densities with those predicted using the synchrotron self-Compton (SSC) formalism (Jones ET AL. 1974). Naive application of the formalism predicts X-ray fluxes from 10−3 to 105 those observed. We therefore ask what we can learn by simply assuming the SSC mechanism, and looking for ways to reconcile the observed and measured X-ray fluxes. This paper reports our investigation of beaming factors due to relativistic ejection of a radiation source which is isotropic in its own rest frame. We conclude that large Lorentz factors, Γ ≳ 10, do not apply to BL Lac objects as a class.
A Consequence of the Asymmetry of Jets in Quasars and Active Nuclei of Galaxies
Authors: Shklovsky I. S.
Published: July 2016

It is concluded that many, if not most, jets are truly one-sided. The hypothesis that the powerful radio emission of quasars and radio galaxies is caused by ejections of “plasmoids” originating in super-critical accretion on massive black holes is discussed. Because of asymmetry in the ejection of plasmoids from the thick accretion disks which form around massive black holes, the latter acquire considerable recoil momentum and should escape from the nuclei of the galaxies with large velocities. This provides a possibility for explaining a number of evolutionary effects and an approach to solving the problem of “dead” quasars.
Near-Infrared Photometry of Southern Galactic Wolf-Rayet Stars
Authors: Sterken C. , de Loore C.
Published: July 2016

Allen et al. (1972) observed 40 WR stars in the |1.6µ| and |2.2µ| bands, and found evidence of interstellar dust emission in the WC9 stars Ve 2–45, AS320 and HD 313643. Hackwell et al. (1974) reported 2.3 to 23 µ photometry of 19 WR stars and concluded that the excess infrared radiation from the Wolf-Rayet stars (except for the WC9 stars) could be explained by free-free emission from a hot circumstellar shell. Gehrz and Hackwell (1974) found from 2.3 to 23 µ photometry that three out of four WC stars appear to be embedded in thick circumstellar dust (graphite) shells, and concluded that WC9 stars may form a distinct Wolf-Rayet class. Cohen et al. (1975) derived energy distributions of 23 Wolf-Rayet stars from 3µ-11µ scanner spectrophotometry and infrared photometry, and concluded that WN stars show only free-free emission whereas only WC stars show dust. The excesses in WC9 stars are interpreted as thermal emission by graphite grains.
Synthetic Spectra for WN Stars
Authors: Wehrse R.
Published: July 2016

A computer program is described which calculates the structure and the radiation field (including high resolution spectra) of spherically extended and moving atmospheres. Some preliminary results for models of WN stars (L/L0= 105, M/M0= 10, Teff= 30 000 K, and M=3 · 10−5 MOy−1) are presented and discussed.
Theories for the Winds from Wolf Rayet Stars
Authors: Cassinelli Joseph P.
Published: July 2016

The massive and fast winds of Wolf Rayet stars present a serious momentum problem for the line-driven wind theories that are commonly used to explain the fast winds of early type stars. It is perhaps possible for the winds to be driven by lines, if multiple scattering occurs and if there are a sufficient number of lines in the spectrum so that large fraction of the continuum is blocked by line opacity in the winds. Several other mechanisms are discussed, in particular two that rely on strong magnetic fields: a) Alfven wave driven wind models like those recently developed by Hartmann and MacGregor for late type supergiants and b) the “Fast Magnetic Rotator” model that was developed by Belcher and MacGregor for the winds from pre-main sequence stars. In either model, large magnetic fields (≈104 gauss) are required to drive the massive and fast winds of Wolf Rayet stars. Smaller fields might be possible if the multiple scattering line radiation force can be relied on to provide a final acceleration to terminal velocity.
The Evolution of Massive Stars — The Production of Binary WR Stars
Authors: de Loore C.
Published: July 2016

A large part of the stars of the galactic disk are binaries. Abt and Levy (1976,1978) estimate that more than 50% of B type stars are members of binary or multiple systems, and about 50% are close binaries. According to Conti et al. (1980) the total fraction of certain or probable binaries among O stars is about 36 percent. This means that during the evolution their components can fill their Roche volumes, and consequently have to lose mass in order to keep the star within the allowed surface. Several review papers dealing with the evolution of binaries were published recently: Paczynski (1971,1980), van den Heuvel (1976), de Loore (1980,1981), Webbink (1979).
Gradients in Supergiant and WR Stars Across the Galactic Plane
Authors: Bertelli G. , Chiosi C.
Published: July 2016

The conclusion by Maeder et al.(1980) that the strong gradient in NR/NWR results from the effect of metal content on the rate of mass loss is reconsidered. We suggest that the above gradient simply reflects a simi lar gradient in the progenitor stars, although effects of metallicity cannot be excluded.
On the Structure and Evolution of the OB-Companions in Wolf-Rayet Binaries
Authors: Hellings P. , Vansina F. , Packet W. , Doom C. , De Grève J.P. , de Loore C.
Published: July 2016

The treatment of close binary evolution changed from conservative (total mass and angular momentum constant) to non-conservative (a certain fraction of the matter expelled from the mass losing star, the primary, leaves the system, carrying away a fraction of the total angular momentum). Only the evolution of the mass losing star was computed in detail; the evolution of the accreting star was estimated in a very simple way by computing the evolution in the normal way just like for single stars, but taking into account the mass increase.
The UV Spectrum of the Central Star of NGC 40
Authors: Benvenuti P. , Perinotto M. , Willis A.J.
Published: July 2016

This paper presents a preliminary study of the IUE UV spectrum of the planetary nebula NGC 40. Details of the observations are given in Table 1 which were obtained in the low resolution (Δλ ∼ 6å) spectrophotometric mode using both SWP (λλ1150–2000) and LWR (λλ1850–3250) spectrographs. All data were acquired using the large (10′x20′) apertures. SWP3076 was taken with the centre of the aperture offset by 7′.5N of the central star: all other images were obtained with the slot centred on the nucleus.
Wolf-Rayet Stars Associated to Giant Regions of Star Formation
Authors: D'Odorico Sandro , Rosa Michael
Published: July 2016

Data on Wolf-Rayet (WR) stars in extragalactic H II regions and emission line galaxies are presented and discussed. The sample is still limited and inhomogeneous but two important points appear to be already established: a) The WR stars are more numerous than the blue supergiants at least in same phase of the evolution of the stellar clusters which ionize the giant H II regions, b) when the WR stars are detected, two cases are apparently observed, one in which only WN, the other in which both WN and WC, are present.
Time-Dependent X-Ray Observations of Wolf-Rayet Binaries with 0-Type and with Suspected Compact Companions
Authors: Moffat A.F.J. , Firmani C. , McLean I.S. , Seggewiss W.
Published: July 2016

Each of four WR binaries has been observed in the 0.1 −5 keV range on four consecutive days for a total of ∼ 104 sec with the IPC on the Einstein Observatory. One of the stars is the well-known WN5 + 06 binary V444 Cyg; the other three have suspected compact companions; all have periods close to four days.

Neither HD 197406 (WN7) nor HD 96548 (WN8) was detected; hence Lx (0.5–3.0 keV) ≲ 1032 erg s−1, which is on the low side, even for 0-stars. EZ CMa (WN5) and V444 Cyg are moderately strong, variable X-ray sources with Lx (0.5–3.0 keV) ≃ 1033 erg s−1, kT ≃ 0.5 keV and NH ≃ 1022 cm−2. These values suggest that the X-ray flux arises in the outer part of the wind. The variable component may be produced by collision of two winds.

There is no evidence of harder X-rays coming from accretion onto a compact star. Nevertheless, the presence of a collapsar is not excluded at hv ≲ 5 keV, where absorption in the WR wind would likely reduce the X-ray flux to a level which is masked by the flux coming from the hot stellar wind.
Lines Profile Variations and Binarity in Wolf-Rayet Stars
Authors: Bisiacchi G.F. , Firmani C. , de Lara E.
Published: July 2016

The ratio of binaries among the WR stars is subject of many discussions essentially due to two reasons: First, the important role that the presence of a companion can play in the evolution of a massive star and as consequence in the interpretation of the evolutionary phase of the WR stars. Second, the strong difficulty to determine the binarity of the WR stars due to the width of the spectral lines.
Summary of Symposium
Authors: Smith Lindsey F.
Published: July 2016

The task I have would appear to be an impossible one. The assembled company is to be congratulated. In the ten years since the last WR Symposium, you have systematically investigated every correlation that appeared at that time to be emerging, and found most of them untrue: The WR spectra are no longer pure emission spectra (Conti et al., 1979); the WN sequence is not a simple sequence of ionisation (Leep, this symposium, session I, henceforward referred to by session number only) or of H abundance (Willis, II; Perry & Conti, II) or of mass loss rate (Barlow; Hogg; Abbott et al., III). The Of, WN and WC stars are no longer discrete classes but are bridged by intermediate types (Conti, I; Willis and Stickland, VI; Williams, IV) and there are now WO stars (Hummer & Barlow, I & V) and supermassive stars (Cassinelli et al., V) as well. The Ring Nebulae are no longer around only strong-line, single WN stars, but are found around any type of WN star, WC stars and binaries (Heckathorn et al.; Chu; Lortet et al., VI). At best, I can hope to highlight a few things about which the majority of us will agree and to point out a few contradictions.
Limitations and Future of Reticon Detectors
Authors: Walker Gordon A. H.
Published: July 2016

Linear arrays of self-scanned silicon diodes have been used in astronomical spectroscopy for over a decade. With care in the flat-fielding and data reduction they can be calibrated to better than 0.1%. They are still the best detector for signal to noise levels >100 when continuous wide-band coverage is needed. CCD's should be capable of this spectrophotometric performance but, for the forseeable future, the lack of a large format and their high cost only make them competitive for spectroscopy of single spectral features or multiple echelle spectra.
High Quality Echelle Observations of T Tauri Stars
Authors: Basri G.
Published: July 2016

This is a very brief review of the high resolution line profile work that has been done on very young stars. The spectral anamolies peculiar to these stars are mentioned, with some discussion of what may give rise to them. The Hα line is discussed most extensively, as the most work has been done with it. While progress has been made in understanding the general nature of T Tauri spectra, there are very large gaps in our current understanding of the emission lines from these stars.
Variability of Some Be Stars on High-Resolution, High S/N Spectra
Authors: Hubert A. M. , Hubert H. , Dagostinoz B. , Floquet M.
Published: July 2016

Rapid variability in Be stars could be understood by non radial pulsations or by rotation of an inhomogeous surface brightness distribution…

The structure and the variability of the Hα and of the HeI λ6678 lines have been investigated with an optical fiber spectrograph and a CCD camera. The signal to noise ratio, measured in the continuum, is between 300 and 500.

Weak changes in the Hα emission line profile of γ Cas have been detected on time-scale of hours and days. This line has an asymmetric profile exhibiting only one blue-shifted maximum while the HeI λ6678 has a double-peak emission, superimposed to the photospheric contribution, with a violet to red peak ratio V/R >1.

The Hα emission line of φ Per exhibits a complex structure with significant changes in its core, from night to night and on a short time scale <lhr. The HeI λ6678 presents a blue-shifted asymmetric emission (red-winged) superimposed to the photospheric contribution.

Furthermore the Hel photospheric line λ6678 of the B6 star o And has presented notable variations in its profile during the 2 observational campaigns, which do not seem correlated to the photometric period of 1.57 day.
A Modelling of Line Transfer in Supergiant Envelopes
Authors: Gesicki Krzysztof
Published: July 2016

A computer code that solves the transfer equation in moving atmosphere is prepared for analysis of variability in circumstellar spectral lines. This model gives a theoretical line shape, which consists of a symmetric photospheric line and superposed on it a P-Cyg type component originated in the envelope. Comparison between calculated and observed line profiles will be used to analyze 6 A/mm spectra of F-K supergiants.
NLTE-Effects in Profiles of Paschen and Brackett Lines of an AOIV Star γGem
Authors: Chalabaev A. A. , Borsenberger J. , Maillard J. P. , Praderie F.
Published: July 2016

Profiles of the hydrogen Paß, Paγ and Brγ lines of an A0IV star γ Gem were obtained at a high resolution to investigate at what degree the hydrogen IR lines can be useful for fine tests of the NLTE model atmospheres. All three lines show a deep and narrow absorption core in a good qualitative agreement with the predictions of the available NLTE models for B stars, thus proving that the NLTE effects are important for A stars as well. New NLTE models were computed to extend the grid down to 9500 °K and to include 8 discrete levels of H atom into the energy balance. However, further theoretical work is necessary to compare the observed profiles and the theory.
Spectroscopy of Cool Stars from IUE Data
Authors: Judge P. G.
Published: July 2016

After nine years of operation the IUE satellite continues to provide valuable spectra of cool stars from 1200 to 3100 Å. The impact of these spectra has been greatest in studies of the outer regions of the atmospheres, above the photospheres, allowing the general properties of stellar chromospheres, transition regions and winds to be established. After outlining these properties, I focus on studies based on high signal–to–noise echelle spectra (λ/Δλ ∼1.2 ×104) of single stars, showing how high quality emission line profiles have been used to derive constraints on the outer atmospheric structure, which in turn have been used to examine models of heating and mass loss.
The Buying Power of High Signal-to-Noise Ratios in Spectroscopy
Authors: Gray David F.
Published: July 2016

High S/N is a good first step toward accurate profiles.
Applications of the Doppler Imaging Technique to the Analysis of High-Resolution Spectra of the 3 October 1981 Flare on V711 Tauri
Authors: Linsky Jeffrey L. , Neff James E.
Published: July 2016

An unconstrained four gaussian fit to the Mg II profile near the flare peak indicates that the flare occurred near the central meridian of the K1 IV star, perhaps above a spot. A more likely fit to the same data places the flare at +90 ±30 km s–1 relative to the K1 IV star, indicating significant downflowing plasma.
Stellar Granulation and Photospheric Line Asymmetries
Authors: Dravins Dainis
Published: July 2016

The fine structure of stellar photospheric convection (the stellar equivalent of solar granulation) can be analyzed with the aid of high-resolution spectroscopy. Photospheric absorption lines are slightly asymmetric and wavelength–shifted due to unequal photon contributions from bright and systematically Doppler–shifted granules and from darker intergranular areas. Numerical simulations of stellar surface convection in different stars have now been carried out, and such three–dimensional and time–dependent models predict the detailed stellar line profiles (including asymmetries and wavelength shifts), thus enabling a direct confrontation between observations and theory.
Observational Evidence by Fourier Transform Spectroscopy of Convective Motion in Late-Type Stellar Atmospheres
Authors: Maillard Jean-Pierre , Nadeau Daniel
Published: July 2016

We have obtained FTS spectra of 11 stars of spectral types from MO to M4 III in the infrared K band. The shifts at line bottom of the lines of CO and Fe I show a dependence on excitation energy and line depth similar to that caused by convective motions in the photosphere of the Sun but with a larger amplitude. Time variability is small but important differences appear between individual stars of similar types. From these data it should be possible to obtain quantitative estimates of the convective velocities and horizontal temperature inhomogeneities.
Light Elements as Probes of Stellar Interiors
Authors: Baglin A. , Morel P.-J.
Published: July 2016

For stars cooler than 6400°K, the lithium is observed to be depleted with respect to the universal value for Population I stars. The depletion depends on mass and age and occurs, both during the main-sequence (Hyades) and the pre-main-sequence (Pleiades).
Spectroscopic Variability in Late-Type Dwarfs Using High S:N Spectra
Authors: Foing B. H. , Beckman J. E. , Vladilo G.
Published: July 2016

Monitoring of active late-type dwarfs, spectroscopically with high resolution (λ/Δλ ∼ 105) and high S:N (>300) round their activity cycles, principally in the Call H resonance line, offers techniques to explore (a) plage filling factors (b) 3-dimensional chromospheric velocity fields (c) maps of surface activity via “Doppler Imaging”. In this paper we deal with the use of spectral signatures to derive plage cover.
Short Period Oscillations in Acturus, Aldebaran, and Pollux
Authors: Smith Peter H. , McMillan Robert S.
Published: July 2016

A total of 48 nights of time series data have been obtained for the K giants: Arcturus, Pollux, and Aldebaran. A careful analysis of both single and multi–night sets using the earth's motion as a velocity calibrator has yielded stellar velocity time series accurate to ± 3 m/s per observation. Periodogram analyses of these sets have revealed the existence of oscillations with periods near 2.5 hrs and amplitudes of ± 5 m/s for both Pollux and Aldebaran, but not for Arcturus. Preliminary analysis of a 5-night set for Pollux using the CLEAN algorithm suggests at least three modes separated by about 35 microHertz.
Surface Magnetic Field Measurements in Hot Chemically Peculiar Stars
Authors: Didelon Pierre.
Published: July 2016

The first results of magnetic field measurements are presented here for HD 187474, a slowly rotating Ap star. From resolved Zeeman pattern the strength of the field and its mean inclination were obtained. From differential magnetic broadening a second value of the field strength has been deduced, which is compatible with the previous one. The “Robinson” method has been tested and a good agreement is found between observed and calculated Zeeman broadening of FeII lines. This method can therefore certainly be used to measure the surface field in slow rotating chemically peculiar stars.
The Magnetic Field Geometry and Abundance Distributions of Iron-Peak Elements in the Ap Star 53 Camelopardalis
Authors: Landstreet J. D.
Published: July 2016

Spectra and magnetic measurements of the strongly magnetic Ap spectrum variable 53 Cam have been modelled using a line synthesis programme that calculates LTE line profiles, including magnetic and polarization effects and non-uniform distribution of elements over the star. The magnetic field is found to be reasonably well modelled with colinear dipole, quadrupole and octupole components of strengths (at the strong negative magnetic pole) of −16.3, −7.3, and +4.9 kG respectively. Chromium and iron are almost uniformly distributed with abundances of about 102 and 10 times solar. Ti and Ca, in contrast, are quite non-uniformly distributed; Ti is more than 10 times overabundant near the negative pole and probably underabundant elsewhere, while Ca is overabundant around the positive pole and slightly underabundant elsewhere.
Magnetic Field of Late-Type Stars: A New Approach
Authors: Mathys G. , Solanki S. K.
Published: July 2016

Magnetic field diagnosis in three late-type stars is performed using the multiline technique originally developed by Stenflo and Lindegren (1977) to study spatially unresolved magnetic features on the sun.
Improved Data Reduction Techniques for the ESO CES Plus Reticon Spectra
Authors: Foing B. H. , Crivellari L.
Published: July 2016

We developed routines for intensity, equivalent width, and radial velocity measurements on CES plus reticon spectra obtained with the ESO 1.4m telescope. In order to achieve the optimal recovery of the signal, the noise has to be minimized by removing any parasitical effect. Special care has been devoted to the correction for remanence effects in the reticon dark counts. Typical results are presented and discussed.
Oscillator Strengths from the High S/N Solar Spectrum
Authors: Rutten Robert J.
Published: July 2016

Most of modern solar physics is not concerned with high S/N spectrometry, but rather with high spatial resolution in narrow-band imaging as well as spectrometry, and with high Fourier resolution in helioseismology.
Spectroscopic Studies of 89 HER and HD 161796
Authors: Giridhar Sunetra , Ferro A. A. , Parrao L. E.
Published: July 2016

We have studied the spectra of UU Her stars 89 Her and HD 161796 in the red spectral region. The atmospheric parameters are derived using model atmospheres and spectrum synthesis. LiI line at 6707.8 A° is identified and measured in 89 Her leading to log (Li/H) = 2.3. The variation of the Hα line profile for these stars is also discussed.
Abundances of Light Metals in Field Stars with Metallicity Range −1.2 < [Fe/H] < + 0.3
Authors: Abia C. , Rebolo R. , Beckman J. E. , Crivellari L. , Vila B.
Published: July 2016

High resolution, high S:N spectra are used to determine the abundances of Fe, Ni, Ca, Al and Si in 25 field dwarfs with −1.2<[Fe/H]< +0.3. We find overabundances for Al, Ca and Si in stars with −1.2<[Fe/H]< −0.5 and solar [Ni/Fe] over the whole studied range.
Non-LTE Effects and Abundance Analyses of Halo Stars
Authors: Magain Pierre
Published: July 2016

The possible existence of departures from LTE affecting the abundance analyses of halo dwarfs and subgiants is analysed from the observational point of view, and illustrated by the case of the intermediate halo subgiant HD 76932. High resolution and high S/N Reticon and CCD spectra have been obtained with the ESO Coude Echelle Spectrometer. A detailed model atmosphere analysis has been carried out, which reveals a number of inconsistencies. In particular, the iron abundance derived from the neutral lines shows a very clear excitation potential dependence. Similar effects appear for oxygen and calcium and, possibly, for magnesium, chromium and ionized iron. Some overionization also seems to be present in a number of elements. The impact of these effects on the derived abundances may be rather large (some 0.2 to 0.6 dex). In particular, doubts might be raised about the reality of the oxygen overabundance and the odd-even effect in Na, Mg and Al.
Chemical Evolution and Primordial Nucleosynthesis
Authors: Audouze J. , Vangioni–Flam E.
Published: July 2016

This contribution starts with a very brief updated report on our present knowledge concerning the primordial abundances of the lightest elements (D, 3He, 4He and 7Li). From this information it is claimed here that specific models of chemical evolution able to account for a thorough destruction of D during the galactic history should be involved to reconcile the ratios : η = ηB/ηγ (baryonic density relative to background photon density) predicted respectively from the primordial 4He (Y) abundance and from the primordial D (and 3He) abundance. Among different possibilities; it is shown that galactic evolution models implying variations of the role of star formation (SFR) are more successful for that goal than models implying bimodal star formation. From this analysis it is also argued that contrary to a common belief, a large D destruction rate over the galactic history implies very specific conditions concerning the chemical evolution of our galaxy.
A New Method of Universal Time Computation Used in the State Time and Frequency Service of the USSR
Authors: Belotserkovskij D. Yu. , Kaufman M. B.
Published: July 2016

Processing of astronomical observational data of several time services and the publication of Universal Time of emission of time signals has been carried out in the USSR continuously for fifty years. Currently the Universal Time computations are made in the USSR State Time and Frequency Service using the observational data of eleven Soviet time services and ten time services of socialist countries that have volunteered to participate. The functioning of this system simultaneously with the BIH system that unites time services from all over the world has certain practical advantages. The Soviet Universal Time scale UT1 (SU) may be influenced by some geophysical effects which are characteristic of the Eurasian continent, and consequently, it may be used advantageously for scientific and practical purposes in this region. The agreement between different time scales, produced by various methods and observational data, also makes it possible to evaluate the reliability of these scales.
Derivation of Pole Coordinates in a Uniform System from the Past ILS Data
Authors: Yumi S. , Yokoyama K. , Ishii H.
Published: July 2016

The recomputation of the past ILS observations has been carried out at Mizusawa and partly at Cagliari. Preliminary reduction of the observations at the northern stations has been completed. The coordinates of the pole were calculated preliminarily and were compared with those by Vicente and Yumi (1969, 1970). It is known that the coordinates of the pole in the past ILS reports require considerable corrections which are probably mainly due to errors of the micrometer values. Magnetic tapes of the original observational records and of the individual latitudes are now available on request.
Amelioration des Calculs de Reduction des Observations a l'Astrolabe. Application a la Determination des Termes de 18.6 et 9.3 Ans de la Nutation
Authors: Chollet Fernand
Published: July 2016

Astrolabe observations made at Paris have been analysed to obtain more reliable values of the constants of nutation. A new method of reduction which takes account of variations in the zenith distance of the observations gave values for the 18.6 year and 9.3 year terms which are almost the same as those derived by classical methods, but for the annual and semi-annual terms the results are different. It is proposed to apply the new method to other series of observations.
Preliminary UT0 Results from EROLD Data
Authors: Calame Odile
Published: July 2016

The status of the EROLD campaign has already been described in another paper (Mulholland, 1979). Since the beginning of 1977 all of the computer software has been ready to work. With the expectation that at least one other station would be able to operate before the end of 1977, it appeared not very interesting to use the single-station data for the study of UT0 during the last year since the other parameters of the Earth's rotation can be determined only with multiple stations. However, as this situation of a single operating station continues, it seemed to be preferable to attempt some determinations of UT0, even if that represents only a part of the goals envisioned from this campaign. We give here a brief resume of our preliminary results.
Rotational Velocity of an Earth Model with a Liquid Core
Authors: Takagi S.
Published: July 2016

There have been many papers discussing the rotation of the Earth (Jeffreys and Vicente, 1957; Molodenskij, 1961; Rochester, 1973; Smith, 1974; Shen and Mansinha, 1976). This report summarizes the application of the perturbation method of celestial mechanics to calculate the rotation of the Earth (Takagi, 1978). In this solution the Earth is assumed to consist of three components: a mantle, liquid outer core, and a solid inner core, each having a separate rotational velocity vector. Hamiltonian equations of motion were constructed to solve the rotational motion of the Earth.
Oceanic Tidal Friction: Principles and New Results
Authors: Brosche P. , Sündermann J.
Published: July 2016

The main problems of the hydrodynamical integrations are analyzed. New results are presented for the effect of an extreme ice age.
Interferometric Observations of the Extreme Solar Limb at 2.8 and 6 cm During the October 1977 Eclipse
Authors: Hurford G. J. , Marsh K. A. , Zirin H.
Published: July 2016

The radial intensity profile at the extreme solar limb was measured with high angular resolution during the October, 1977 partial solar eclipse using the Owens Valley solar interferometer at 2.8 cm and the VLA at 6 cm. Substantial limb brightening was observed at 6 cm, with a peak brightness temperature corresponding to an 80% increase over the disk value. Much less limb brightening was observed at 2.8 cm. In each case an extended “tail” to the brightness distribution was detected. The results at both wavelengths are consistent with a simple model in which a rough chromosphere is overlaid by a corona in hydrostatic equilibrium with a density of 5 × 108 cm−3 at its base.
Very Large Array (VLA) Observations of Solar Active Regions
Authors: Lang Kenneth R. , Willson Robert F.
Published: July 2016

Very Large Array (VLA) synthesis maps of the total intensity and the circular polarization of three active regions at 6 cm wavelength are presented. The radiation from each active region is dominated by a few intense cores with angular sizes of ~ 0.5′, brightness temperatures of ~ 106 K, and degrees of circular polarization of 30 to 90%. Some of the core sources within a given active region exhibit opposite senses of circular polarization, suggesting the feet of magnetic dipoles, and the high brightness temperatures suggest that these magnetic structures belong to the low solar corona. We also present comparisons between our VLA maps of circular polarization and Zeeman effect magnetograms of the lower lying photosphere. There is an excellent correlation between the magnetic structures inferred by the two methods, indicating that synthesis maps of circular polarization at 6 cm can be used to delineate magnetic structures in the low solar corona.
Solar Burst Observations at Centimeter Wavelengths
Authors: Kundu M. R.
Published: July 2016

The centimeter -wave bursts are simple: they are characterized by a rapid rise in intensity and a slower decline. The burst-radiation is in general smooth, usually free of details in time and frequency and is a partially polarized broadband continuum. It starts almost immediately after an associated Hα flare and originates from a source of small angular size (< 1′ arc). The smooth continuum emission of centimeter-wave bursts has been accounted for by synchrotron radiation from fast electrons accelerated during flares. I shall not attempt to give here a full description of the observational characteristics of centimeter bursts, rather I shall concentrate on certain specific features relevant to the understanding of the generating mechanism of these bursts. More than 20 years ago, centimeter bursts were studied with a spatial resolution as good as ∼ 1′ arc. Even with this resolution the presence of small scale structures on scales of 1′–4′ were observed in cm-λ bursts sources. Since that time both spatial and time resolution have steadily improved; we now have a spatial resolution of ″ and time resolution of ∼ 10 ms. Such resolutions have revealed smaller scale structures of a few arc seconds and more complexity in burst sources. At the same time soft x-ray observations, particularly from Skylab, with resolution better than 5″ (e.g. Kahler et al. 1975; Vorpahl et al. 1975) have given new information about the flare phenomenon. Because of the close association of soft x-ray and cm-λ burst sources, these observations are particularly important for a proper understanding of the generating mechanism of cm-λ bursts, acceleration of electrons and the origin of solar flares.
Digitally Recorded Type I Bursts and Some Theoretical Aspects of Continuum and Burst Generation
Authors: Kattenberg A. , van Hees R.M. , van Nieuwkoop J.
Published: July 2016

In the first part we present the analysis of digitally recorded type-I bursts. The reduction procedure is described and some typical examples and results are presented.

In the second part we propose a model for type-I emission, compatible with low magnetic field strengths.

Incoherent langmuir waves, spontaneously emitted by trapped fast electrons are converted to transverse radiation by coalescence with low frequency whistlers. Recurrent upper hybrid instability in strong m.h.d. pulses explains the bursts in this model.