bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Energy Gamma-Ray Observations of Active Galaxies
Authors: Fichtel Carl E.
Published: July 2016

During the period from 1992 May to early 1992 November, the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory obtained high-energy gamma-ray data for most of the sky. A total of 18 active galaxies have been seen with high certainty, and it is expected that more will be found in the data when a more thorough analysis is complete. All of those that have been seen are radio-loud quasars or BL Lacertae objects; most have already been identified as blazars. No Seyfert galaxies have been found thus far. If the spectra are represented as a power law in energy, spectral slopes ranging from approximately −1.7 to −2.4 are found. A wide range of z-values exists in the observed sample, eight having values in excess of 1.0. Time variations have been seen, with the timescale for a significant change being as short as days in at least one case. These results imply the existence of very large numbers of relativistic particles, probably close to the central object. Although a large extrapolation is required, their existence also suggests that these active galactic nuclei may be the source of the extragalactic cosmic rays.

Subject headings: acceleration of particles — galaxies: active — gamma rays: observations — quasars: general
High-Energy Radiation From Active Galactic Nuclei
Authors: Sikora Marek
Published: July 2016

Two recent findings concerning high-energy radiation properties of active galactic nuclei—discovery of breaks in hard X-ray spectra of Seyfert galaxies, and discovery of huge fluxes of hard gamma rays from blazars—seem to press us to change our standard views about radiation production in these objects. I review briefly the existing radiation models, confront them with the newest observations, and discuss newly emerging theoretical pictures which attempt to account for the discoveries.

Subject headings:galaxies: active — galaxies: nuclei — radiation mechanisms: nonthermal
The Whole Earth Telescope: An International Adventure in Asteroseismology
Authors: Kawaler Steven D.
Published: July 2016

Today, we are beginning to probe the interior of stars through the new science of stellar seismology. Certain stars, ranging from our own Sun to white dwarfs, undergo natural vibrations that can be detected with sensitive time-series photometry and/or spectroscopy. Since the signal we seek is an unbroken time-series to allow determination of the vibration frequencies, data from a single-site is usually incapable of uniquely identifying the pulsation modes, no matter how large the telescope being used. In many cases, the observational goals can be achieved using small-ish telescopes in well-coordinated global networks. Here, I briefly describe the work of one such international network of observatories and scientists known as the Whole Earth Telescope (WET). With the WET, we have sounded out the interiors of a large number of nonradially pulsating stars. Over the past 14 years, WET has observed dozens of stars in 20 separate observing campaigns. Our team has wide span of interests, and has observed several other classes of objects such as delta Scuti stars, CV stars, pulsating sdB stars, and rapidly oscillating Ap stars.
Early Results from HETE-2
Authors: Kawai N. , Yoshida A. , Tamagawa T. , Matsuoka M. , Shirasaki Y. , Ricker G. , Crew G. , Doty J.P. , Levine A. , Vanderspek R. , Villasenor J. , Monnelly G. , Atteia J.-L. , Vedrenne G. , Olive J.-F. , Boer M. , Fenimore E.E. , Galassi M. , Issler J.-L. , Colongo C. , Hurley K. , Jernigan J.G. , Lamb D.Q. , Graziani C. , Pizzichini G. , Woosley S. , Takagishi K. , Hatsukade I. , Yamauchi M. , Cline T.
Published: July 2016

The High Energy Transient Explorer 2 is a small scientific satellite designed to detect and localize gamma-ray bursts (GRBs). The coordinates of GRBs detected by HETE-2 will be distributed to interested ground-based observers within seconds of burst detection, thereby allowing detailed observations of the initial phases of GRBs. HETE-2 was launched successfully on October 9, 2000. The GRB positions will start to be delivered after a few months of the complete testing and calibration of the spacecraft system and the science instruments.
A Spectrograph for Prompt Observations of Gamma-Ray Bursts with a 1-m Telescope
Authors: Kawabata Tetsuya , Ayani Kazuya , Fujii Mitsugu , Urata Yuji , Kawai Nobuyuki , Ebizuka Noboru
Published: July 2016

We are developing a new slit-less spectrograph for gamma-ray bursts (GRBs) at Bisei Astronomical Observatory. We can quickly point the 1-m telescope to the GRB coordinates provided by HETE-2 via the GRB Coordinates Network. The pointing is readjusted when the position is refined to 5” accuracy by the small optical telescope RIBOTS using the optical image of the GRB, and we then take an exposure immediately with the slit-less spectrograph.
Optical and Near-IR Monitoring of Symbiotic Binary Systems
Authors: Mikołajewska Joanna
Published: July 2016

Symbiotic stars are long-period interacting binary systems in which an evolved red giant star transfers material to its much hotter compact companion. Such a composition places them among the most variable stars. In addition to periodic variations due to the binary motion, they often show irregular changes due to nova-like eruptions of the hot component. In some systems the cool giant is a pulsating Mira-type star usually surrounded by a variable dust shell. Here, I present results of optical and IR monitoring of symbiotic systems as well as future prospects for such studies.
A Near Infrared Camera Refrigerated by Two Stirling Machines – an Alternative to Robotic Telescopes
Authors: Ishitsuka I. José K. , Wada Takehiko , Ieda Fumihiko , Tokimasa Noritaka , Kuroda Takehiko , Morimoto Masaki , Miyaji Takeshi , Omodaka Toshihiro , Ueno Munetaka , Hasegawa Wataru , Narusawa Shin-ya , Waki Yoshifumi
Published: July 2016

We have developed and tested a new near infrared camera equipped with a 512 × 512 PtSi CCD and cooled by two independent Stirling Cycle refrigerators. The camera, installed on the 60 cm reflector telescope of the Nishi-Harima Astronomical Observatory (NHAO) since April 2000, has begun regular observations toward infrared objects. Since the reasonable cost and lower maintenance needs of the camera make it more attractive, we introduce it as an alternative to robotic telescopes.
Revealing Variety of Comets by Long-Term Monitoring Observation with a 50-cm Telescope
Authors: Watanabe Jun-ichi , Fukushima Hideo
Published: July 2016

We have been monitoring comets using the 50-cm telescope at the Mitaka campus of the National Astronomical Observatory, Japan since 1996. Over 20 comets, including bright ones such as comet C/1995 O1(Hale-Bopp), have been observed over long-term periods, namely over large heliocentric distance scales. Our samples show variety of comets in terms of both morphological and temporal variations. Several typical examples of various morphology, probably due to dust, are shown to emphasize the importance of long-term monitoring of comets.
INTEGRAL and Small Telescopes
Authors: Mowlavi Nami , Kretschmar Peter , Türler Marc , Produit Nicolas
Published: July 2016

The future INTEGRAL satellite, to be launched in 2002, will observe the universe in gamma-rays. Parallel observations in other wavelengths are desirable for many gamma-ray objects, the most famous being certainly the gamma-ray bursts.

In this article, we present the INTEGRAL mission and its scientific objectives. We then give three examples of astrophysics fields for which combined gamma ray and optical observations are recommended. Small telescopes would be ideally suited for many of the studies.
Russian/Former Soviet Union Experience in Small Telescope Usage for Investigation of Interstellar Matter (ISM) and Nebulae
Authors: Bochkarev N.G.
Published: July 2016

The deepest tradition in ISM study in the optical range was built in Russia/FSU by V.Fessenkov, the founder of Fessenkov Astrophysical (Aph) Institute (AFIF, Kazakhstan) and G.Shain (Crimean Aph.Obs. - CrAO, Ukraine). The tradition was handed over to SAI (Moscow) by I. Shklovski and S.Pikelner, to Abastumani Aph. Obs. (AAO, Georgia), where a catalogue of dark nebulae (Khavtassi, 1960) was produced, and to Byurakan Aph. Obs. (BAO, Armenia).

For a long time 0.3-0.7 m telescopes were used for determination of interstellar extinction in the Galaxy by the standard technique (SAI; Engelhart Astron. Obs. of Kazan Univ., Russia; AAO; BAO and others. The most sophisticated investigations were carried out in Lithuania (e.g. Straizys, 1977; Sudzius, 1974).
Asymptotic Methods in the Nonlinear Mean-field Dynamo
Authors: Sokoloff D.D. , Shukurov A. , Ruzmaikin A.A.
Published: July 2016

We discuss the methods and results of analysis of nonlinear mean-field dynamo models based on α-quenching in two asymptotic regimes, namely for weakly and highly supercritical excitation. In the former case the spatial distribution of the steady-state magnetic field is close to that given by the neutrally stable eigenfunction of the corresponding kinematic dynamo. In the latter case the magnetic field distribution within the main part of the dynamo volume is presumably determined by the balance between the Lorentz and Coriolis forces while near the boundaries boundary layers arise in which the field adjusts itself to the boundary conditions. The asymptotic behaviour of the highly supercritical αω-dynamos is sensitive to the particular form of dependence of the mean helicity on magnetic field while α2-dynamos are less sensitive to this dependence.
The Prolonged Minima and Maxima of Solar Activity
Authors: Dermendijev V.N. , Buyukliev G.T. , Shopov Y.Y.
Published: July 2016

We study a new indirect index of solar activity – the Intensity of Luminescence of Cave Flowstone Microzones. This index correlates directly with the solar activity. Using a time series of the index with resolution 4-5 pixels/year we study some of the statistical properties of the solar activity cycle during 28 prolonged minima and 21 prolonged maxima.
The Longer Term Evolution of Magnetic Field and Mass Flow in a Decaying Active Region
Authors: Zhang Hongqi , Ai Guoxiang , Wang Haimin , Zirin Harold , Patterson Alan
Published: July 2016

During September 24-29, 1987, the longitudinal magnetic fields of a decaying active region (AR 4855) were observed almost continuously at Big Bear and Huairou Solar Observatories. The target consisted of an αp sunspot and surrounding enhanced network. We achieved a 75-hour coverage with 4 night-time gaps of six to eight hours. The images were then combined to made a continuous movie.

The BBSO Videomagnetograph (VMG) System was originally developed by Leighton and Smithson and has been improved in recent years (Zirin, 1985). This system has made it possible to study very weak photospheric magnetic structures.
Fe I Line Asymmetries and Shifts Caused by Pressure Broadening
Authors: Kršljanin V. , Vince I. , Erkapić S.
Published: July 2016

In order to test the validity of the usual neglect of pressure line shifts in investigations of Fe I line asymmetries and shifts, we calculated synthetic line bisectors and shifts of 96 moderate and weak photospheric lines, taking into account both hydrogen- and electron-impact shifts and neglecting the velocity fields. Absolute pressure line shifts obtained are less than or appr. equal to 50 m/s and the largest relative shifts along the bisectors are about 40 m/s. We found pronounced dependences of both shifts and bisectors on the energy of the upper level in transitions and on the transition array.
The Solar Corona over the Recent Saros
Authors: Pasachoff Jay M.
Published: July 2016

We are now at both the maximum of the solar activity cycle and at the most populated part of the saros. I discuss the solar corona over the recent saros and its changes with the solar activity cycle. We consider the scientific value of eclipse studies and how they relate to other ongoing coronal studies on the sun and other stars.
The Differential Rotation and Evolution of Spots on UX Arietis from a Sequence of Doppler Images
Authors: Vogt Steven S. , Hatzes Artie P.
Published: July 2016

We present a sequence of three Doppler images of the spotted RS CVn star UX Arietis obtained over a 5-month interval from August 1986 through January 1987. The spot distribution was quite complex and consisted of a large stable polar spot, a spot near the equator, and several other spots at intermediate positive and negative latitudes. The time intervals between successive images were small enough that we were able to reliably track the evolution of the spot distribution, measuring accurate longitudes, latitudes, and areas of the major spots, as well as their drift rates in longitude and latitude. The longitudinal drifts of spot features at equatorial, intermediate, and high latitudes yielded an accurate measurement of differential rotation. We find that the spotted primary of UX Arietis is indeed rotating differentially and in the sense opposite to that of the Sun, i.e. the poles rotate faster than the equator. The equator is synchronized to the orbital angular velocity, and the angular velocity increases towards either pole. The angular velocity distribution can be expressed as Ω(°/day) = −55.91 + 1.09(±0.09) sin2∅, where ∅ is the latitude. The amount of differential rotation, parameterized as the ratio of the difference between the equatorial and polar angular velocities to the equatorial angular velocity, is then α = −0.020(±0.002), as compared to a value of α = +0.2 for the Sun.
Chromospheric Surface Structures on EI Eridani and HD 199178
Authors: Neff James E.
Published: July 2016

Several groups at this meeting are presenting maps of the spatial distribution of either brightness or effective temperature in the photospheres of rapidly-rotating, late-type stars. It is generally believed that structure seen in these maps traces the magnetic topology, in analogy with the Sun. We expect the structure of the outer atmospheres (i.e., chromosphere and corona) of these stars to be even more directly tied to the magnetic topology; the magnetic structure is three-dimensional. In order to probe the radial dimension of stellar atmospheres, we need to combine maps of the spatial distribution of emission from chromospheres and coronae with these detailed photospheric maps.

Along with collaborators at Armagh, Catania, Boulder, Paris, Helsinki, and Stony Brook, I have been obtaining high-dispersion ultraviolet spectra of several rapidly-rotating, late-type stars using the IUE spacecraft. I discuss results for two stars, El Eridani and HD 199178, for which photospheric maps are presented elsewhere at this conference.
Activity, Colour Anomalies and Temperature Determination in Solar-type Stars
Authors: Fabregat J. , Reglero V. , Suso J. , Armentia J.E.
Published: July 2016

The presence of photometric anomalies in broad band colours produced by chromospheric activity was first suggested by Campbell (1984). He defined the colour anomaly δ(B–V)V–K as the deviation from the mean relation (B–V)–(V–K) for Hyades dwarfs, and found this anomaly correlated well with several activity indicators.

Since the work of Campbell, several authors have discussed the relation between activity and colour anomalies, obtaining diverging results. This discussion is relevant because long baseline photometric colours are the most reliable temperature indicators, and the presence of such anomalies implies that no consistent temperature scales can be obtained for stars with different activity levels. These topics have been recently reviewed by Soderblom (1989).
Radial Velocity Variability of K Giants
Authors: Hatzes Artie P. , Cochran William D.
Published: July 2016

At McDonald Observatory we have been monitoring the relative radial velocities of a sample of K giants. The technique employed uses the telluric O2 lines near 6300 Å as a reference for measuring the stellar line shifts. We demonstrate that precisions of 10 m s−1 are possible with this technique. We present radial velocity data covering a 2 year time span for α Boo, α Tau, and β Gem. All of these stars show both long term variations (~ several hundred days) with a peak-to-peak amplitude of about 400 m s−1 and short term variations (~ few days) with a peak-to-peak amplitude of about 100 m s−1. The long term variations may be due to the rotational modulation of surface active regions whereas the short term variations may be indicative of pulsations.
Stellar Zeeman Analyses: Effects of Multi-component Atmospheres
Authors: Marcy G.W. , Basri G. , Valenti J.A.
Published: July 2016

We simulate the radiative transfer of Zeeman-broadened lines in an active star containing both quiet and flux-tube regions. A traditional one-atmosphere Zeeman analysis of these synthetic lines yields magnetic field measurements systematically inaccurate by up to 40%. However, two atmospheric components alone cannot reproduce the observed line strengths, luminosities or photometric constancy of active stars.
Two Kinds of Activity in Late-type Stars
Authors: Katsova M.M.
Published: July 2016

Several years ago we proposed a method for the analysis of X-ray observations of late-type stars. It allowed the determination in a uniform manner of coronal base electron densities for more than 40 late-type stars, in terms of a one-temperature consideration of homogeneous spherically symmetric coronae (Katsova et al., 1987). Fig. 1 shows the results as a function of spectral type. Comparison of our results with values for different kinds of solar regions shows that physical characteristics of F and G star coronae correspond to densities less than those in active regions on the Sun. Values for the active K-M0 stars are comparable with those of dense steady condensations found directly above large sunspots.

On this basis, activity can be explained as an increase in that part of the stellar surface that is occupied by strong local magnetic fields. This is illustrated in the table where we compare magnetic field measurements by Saar and Linsky (1988) with our calculations.
Ca II H and K and Hα, and Li Abundances in the Pleiades Late K Main-Sequence
Authors: López R. J. García , Rebolo R. , Beckman J. E. , Magazzù A.
Published: July 2016

We have observed seven main sequence stars in the Pleiades, with B – V between 0.98 and 1.41 (5100–3900 K), and with a wide range of rotational velocities, in Ca II H and K, Hα and have derived Li abundances. Our results, combined with literature data, indicate that the most chromospherically active stars are rapid rotators, and that at a given effective temperature the Li-rich stars show the highest chromospheric activity. A different surface coverage of active regions could influence the dichotomy observed in the Li abundance distribution.
Is ξ Boo AB a Young or an Evolved System? A Model Atmosphere Analysis
Authors: Savanov I.S.
Published: July 2016

We perform a model atmosphere analysis of ξ Boo A, and make estimates for the secondary component. The abundances of 25 elements for ξ Boo A are obtained with the parameters: Teff=(5300 ± 100) K, log g= 4.1 ± 0.2, ξt = 0.5km/s. The atmosphere of ξ Boo A is deficient in Y and Zr, but overabundant in Ba and rare earth elements. We confirm the high Li abundance in ξBoo A (logA(Li) = 2.1), while Li is strongly underabundant in the secondary relative to the Sun. From comparison with evolutionary calculations we find that ξ Boo A has mass 0.95 M⊙, radius 1.4 R⊙ we also determine a rotational velocity v sin i = 8 km/s. We conclude that, in spite of its relatively high rotation rate and high chromospheric activity, it is already evolved from the main-sequence.
He I 5876 Å Line in the Study of Chromospheric Activity in F-type MS Stars
Authors: López R. J. García , Rebolo R. , Beckman J. E. , McKeith C. D.
Published: July 2016

We have measured the He I D3 line, λ5876 Å, in 32 F-type young open cluster stars and in 4 field stars. Combining our results with previous observations of D3 we strengthen the following conclusions: (a) Sub-surface convective zones appear, on the main sequence, around F0 (B – V ~ 0.3). (b) The stars between F0 and F5 (0.3 ≲ B – V ≲ 0.42) are chromospherically “active” irrespective of age, which implies a heating mechanism not affected by evolutionary effects. In this range the activity in D3 and X-rays are uncorrelated. (c) For stars later than F5 the correlation among all the activity indices, chromospheric and coronal, shows a common energy source. Convective zones here should be deep enough to generate magnetic fields capable of supplying this energy, and also for braking the rotation.
Hα Emission in the Giant Components of RS CVn Systems
Authors: Frasca A. , Catalano S.
Published: July 2016

The Hα line of hydrogen is a very powerful tool for the study of the solar chromosphere (plages, flares, prominences). Although it is difficult to derive in a simple way quantitative information, like chromospheric temperature and electron density, because of the very extensive depth of its formation and the very complex mechanism of excitation, Hα has been successfully used to study the chromospheres of active stars (Herbig, 1985). Moreover this diagnostic has proved to be very useful for the study of surface inhomogeneities and transient phenomena like flares in systems of the RS CVn type and other active stars (Bopp, 1981; Bopp et al., 1988; Fraquelli, 1982).

With the aim of investigating the behaviour of chromospheric activity, we have undertaken an extensive monitoring of Hα emission in a selected group of RS CVn binaries (Strassmeier et al., 1988). We report here preliminary results of the observations obtained in 1988–1989.
Coronal Magnetic Fields of Algol Binaries from Microwave Spectra
Authors: Umana G. , Trigilio C. , Hjellming R. M. , Catalano S. , Rodonò M.
Published: July 2016

Algol-type binaries are basically known to undergo hydrodynamic processes related to mass exchange between components. Recent observations on radio, X-ray emission and flare-like events have raised the question of possible magnetic activity in the secondary component of these systems (Hall, 1989).

From a microwave emission survey we have shown that the radio emission from Algol systems cannot be accounted for by thermal emission from an hot corona (T ≥ 107K) and that their radio luminosities compare very well with those of the magnetically active RS CVn systems (Umana et al., 1990).
Further Evolution of V 1016 Cygni, 1974-77
Authors: Ciatti F. , Mammano A. , Vittone A.
Published: July 2016

V 1016 Cygni is a peculiar variable star, whose brightness increased from about 16 mag in 1963 (previously it was known to have a LPV spectrum) to about 11 mag in 1967. Since then it has been nearly constant at maximum. Our last photometric observations, from May to August 1977, indicate that the star is still in its protracted maximum at a constant brightness. We have measured B = 11.1 and V = 10.8 (± 0.2 mag s.e.).
Ap-Star Models
Authors: Mestel L.
Published: July 2016

Phenomenology

The outstanding observational facts that impress the theorist studying the magnetic Ap stars are as follows:

1) The very strong, large-scale magnetic fields, inferred from the integrated Zeeman effect. Typical polar fields are 103- 104gauss, the strongest known being =3.5 x 104gauss.

2) The variability of the fields, spectra and luminosities, with the fields often reversing in sign. Typical periods are 5 - 9 days, but periods shorter and very much longer are found, with a small group of stars having periods of several years.

3) The low rotations of most Ap and apparently all known Am stars, compared with normal A stars. The possibility that we are seeing normal A stars pole-on seems statistically untenable.

The "cross-over effect" (Babcock 1956). This describes how the difference in the widths of two circularly polarized Zeeman components of a spectral line becomes particularly large at the phase when the net field becomes small.
Meridional Circulation, Turbulence, and Diffusion Processes in Stars
Authors: Vauclair S.
Published: July 2016

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.

Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.
Magnetic Accretion and Magnetosphere Physics of Peculiar A Stars
Authors: Havnes Ove.
Published: July 2016

We discuss the possibility for applying the magnetic accretion theory to other peculiar A stars than the Sr Cr Eu and Silicon stars. This requires a moderately strong magnetic field in the so-called “non-magnetic” peculiar stars. We find that magnetic fields with polar strengths of up to ˜ 0.1 Tesla (1000 gauss) may exist undetected if the errors of measurement are > ± 0.025 Tesla. If such magnetic fields exist in these stars, overabundances of the order of ∆ log ˜ 2.0 may be produced in the course of 107years. The high overabundances found for many elements can probably not be produced by magnetic accretion. We suggest that the abundances of several elements (especially Ga are considerably overestimated.
Magnetic Fields: Observational Aspects
Authors: Wood H. John
Published: July 2016

A relatively short, time was available for the preparation of this paper. A number of excellent reviews of Ap observations are already in the Literature, notably that by Preston (1971) on surface fields. However, a recent review of developments in techniques for the measurement of magnetic fields in Ap stars was lacking.

Upon arrival at this symposium, we found so many exciting new results and programs underway (and therefore unpublished) that we decided to throw out our original paper and open this session up for reports from people who are making magnetic observations themselves, or who are familiar with active programs in their home countries.
Line Formation with Magnetic Field: Review and Practical Applications
Authors: Hardorp J. , Shore S.N. , Wittmann A.
Published: July 2016

Starting with the full set of equations for the four Stokes parameters as developed by Beckers, we propose a simplified method for computing profiles of Zeeman-split absorption lines in LTE. This method is quick enough to be useful in abundance analyses of Ap stars, but more flexible than earlier approaches.
On the Inhomogeneity of Atmospheric Parameters of Magnetic Peculiar Stars
Authors: Kopylov I.M. , Kumajgorodskaya R.N. , Snezhko L.I. , Sokolov V.V. , Chunakova N.M.
Published: July 2016

Variations of θeffand log geffover the surfaces of the magnetic stars α2CVn and HD 184905 are studied by comparison of the Hγ and Hδ hydrogen line contours measured on 15 Å/mm spectrograms with those calculated from Mihalas models. θeffvaries slightly during the period of rotation of these stars. At the same time log geffshows considerable variations over the surfaces of the stars with an amplitude of order of 0.7.
Properties of Ap Stars in the Ultraviolet
Authors: Leckrone David S.
Published: July 2016

The observational study of the “chemically peculiar (CP) stars of the upper main sequence” (Preston 1974) at wavelengths shortward of 3000 Å began early in this decade with Bernacca and Molnar's (1972) photometric observations of the helium-weak Bp stars and Molnar's (1973) investigation of α2CVn, both with the Wisconsin Experiment Package on 0A0-2. Thus, the present review deals with a subject still in its infancy, but growing rapidly. If we limit the discussion to Ap stars as traditionally defined, i.e. the magnetic Si and SrCrEu stars and the non-magnetic HgMn stars (Preston's groups CP-2 and CP-3, respectively), we find satellite data currently available for the forty-one stars listed in Table 1, and unpublished or unreduced data doubtless exist for other stars as well. In addition to the 0A0-2/Wisconsin experiment, which provided broad-band filter photometry from 1330 Å to 4250 Å and 10-20 Å bandpass spectrum scans from 1150 Å to longward of 3500 Å, data have been obtained with the TD-1A experiments S59 (1.8 Å resolution spectrum scans in the three wavelength intervals 2060 - 2155 Å, 2495 - 2590 Å and 2775 2865 Å) and S2/68 (35-40 Å bandpass spectrum scans over the interval 1350 - 2550 Å).
Preliminary Results of the Study of the Cr-Star ε UMa
Authors: Engin Semanur
Published: July 2016

I report the preliminary results of a study of spectrum-variability and abundance analysis of the chromium-star ε UMa. High dispersion spectrograms (4 and 7Å/mm) obtained at the Haute Provence Observatory were used.
The Energy Distribution of Several Ap Stars
Authors: Hardorp Johannes
Published: July 2016

Energy distributions were observed in closely spaced 50 Å intervals from 3250 Å to 6000 Å and for some stars to 7950 Å. The broad absorption feature at 5200 Å appears in most Ap stars and persists through all phases of light-variation. No sharp absorption edges were found. Of special interest are the large-amplitude light variables HD 51418 and HD 125248. The main differences of their light curves are explained by different aspects of the oblique rotators.
Establishment of Terrestrial Reference Frames by New Observational Techniques
Authors: Bender Peter L.
Published: July 2016

The use of space techniques for establishing transcontinental and intercontinental distances is progressing very rapidly. We can think of the set of station locations used in either LAGEOS ranging or VLBI measurements as forming the vertices of a polyhedron. After correcting for tectonic plate motions using an adopted model, we expect the geometry of the polyhedron to be fairly stable over periods of the order of a year. However, after some period of time, a new set of station coordinates will be required because of improved data, unexpected station motions, etc. Methods for maintaining agreement with the previous set of station coordinates in some average sense are discussed in this paper. Some of the contributions expected from other new measurement methods also are described.
Origin and Scale of Coordinate Systems in Satellite Geodesy
Authors: Zieliński J. B.
Published: July 2016

The center of mass of the Earth is commonly taken as origin for the coordinate systems used in satellite geodesy. In this paper the notion of the “geocenter” is discussed from the point of view of mechanics and geophysics. It is shown that processes in and above the crust have practically no impact on the position of the geocenter. It is possible however that motions of the inner core may cause variations of the geocenter of the order of 1 m. Nevertheless the geocenter is the best point for the origin of a coordinate system. Mather’s method of monitoring geocenter motion is discussed, and some other possibilities are mentioned. Concerning the scale problem, the role of the constant GM and time measurements in satellite net determinations are briefly discussed.
Dynamics of an Artificial Satellite in an Earth-Fixed Reference Frame: Effects of Polar Motions
Authors: Farinella P. , Milani A. , Nobili A.M. , Sacerdote F.
Published: July 2016

In an Earth-fixed reference frame, polar motions (precession, lunisolar nutation, free nutation) introduce small apparent forces in the equations of motion of an Earth satellite. We discuss the possibilities (a) of integrating the orbit in an Earth-fixed frame when tracking data are used for geophysical applications, and (b) of determining from orbital data a set of unknown parameters describing the long-period wandering of the pole.
Relativistic Reduction of Astronomical Measurements and Reference Frames
Authors: Brumberg V. A.
Published: July 2016

With the accuracy of modern observations the relativistic treatment of the basic astronomical reference frames only requires the consideration of comparatively simple types of metrics such as heliocentric Schwarzschild metric, geocentric Schwarzschild metric and metric of the Earth-Sun system. Dynamical (related to the motion of the bodies) and kinematical (related to the light propagation) characteristics of these metrics enable one to perform the accurate relativistic reduction of astronomical measurements. In this reduction, the choice of specific quasi-Galilean coordinates may remain arbitrary. This paper presents expressions for the main relativistic terms in coordinates of the principal planets and Moon using the PPN formalism parameters β, γ and coordinate parameter α. General formulae for the reduction of radar, radio-interferometric and astrometric observations of planets and for the interpretation of lunar laser ranging are given. For estimating the actual magnitude of relativistic effects, the ephemeris data should be expressed in terms of physically measurable quantities.
A Numerical Study of the Fission Hypothesis for Rotating Polytropes
Authors: Durisen R. H. , Tohline J. E.
Published: July 2016

Analytic stability analyses (Lyttleton, 1953; Chandresekhar, 1969) have shown that Maclaurin spheroids are dynamically unstable to non-axisymmetric perturbations if
Linear and Nonlinear Pulsations of β Cephei Stars
Authors: Cox Arthur N. , Hodson Stephen W.
Published: July 2016

The best known β Cephei variable is a α Virginis (Spica) because it is a binary star (P = 4.01 days) and has a interferometer measurement of its angular diameter. In this study to see if the pulsations can be caused by mixing of hydrogen and helium in the semiconvective zone, the parameters we take are 11.5 M⊙, 26,300 K, 6.5 x 1037 erg/s with an envelope composition of Y = 0.28, Z = 0.02. These data agree within the errors of observations as reported recently by Odell (1980), and the theoretical radial fundamental mode period of 0.171 day compares well with the single observed pulsation period of 0.174 day.
Fast Time-Resolution Spectroscopy of BW Vulpeculae
Authors: Young Arthur , Furenlid Ingemar
Published: July 2016

An experimental Fairchild CCD-211 was placed in the 2.1-m coudé spectrograph at the Kitt Peak National Observatory and used to record an 87 Å spectral band centered on Hα. On the night of 1979 July 11 UT date, this system was used to observe continuously the extreme β Cephei variable BW Vulpeculae throughout one of its 4h 49m cycles with an average exposure of 13 minutes per observation. A total of 18 observations was secured. The results show dramatic profile variations of Hα, including features not previously reported, and extreme variations of the C II λλ6578, 6582 lines, including variations of equivalent width. The fast time-resolution capability and the photometric linearity of the CCD have permitted the detection of subtle effects that have been missed by photographic observations and has led directly to important new interpretations of the complex atmospheric pulsations in this star, including effects of altered opacity on the formation of spectral lines and the suggestion of a helium-ionization heat engine as a mechanism for driving atmospheric pulsations.
Radial and Nonradial Oscillations in Delta Scuti Stars
Authors: Kurtz D. W.
Published: July 2016

Mode identifications from the phase shift between the B-V color curves and the V light curves of Delta Scuti stars are discussed. For five Delta Scuti stars the frequency of highest amplitude is due to pulsation in a radial mode with one or more frequencies due to nonradial modes lying nearby. Thus there may be a resonance between the frequencies of radial and nonradial modes. This behavior has only been found in subgiant and giant stars so far, but this could easily be a selection effect. Theoretical predictions of frequencies for different 1-modes of the same overtone for main sequence, subgiant, and giant stars are needed to compare with these observations. Theoretical predictions of the strength of resonance coupling between radial and nonradial modes as a function of frequency separation are also needed.
The Critical Frequency in the Stellar Pulsation Theory
Authors: Takeuti Mine
Published: July 2016

The standing oscillation in an isothermal semi-infinite plane-parallel atmosphere has a critical frequency. The significance of critical frequency in the stellar pulsation is discussed briefly. The critical period is calculated for the cepheid instability strip. A star having relatively large radius compared with the mass should be examined by the criterion. The pulsational instability is reduced by the linear running wave.
HR 7308, A Short Period Cepheid With Variable Amplitude
Authors: Burki G. , Mayor M.
Published: July 2016

HR 7308 is a F6 lb-11 star of 6th magnitude. Semi-regular photometric variations were detected by Breger (1969) , Percy et al. (1979) find that this star is a new small-amplitude Cepheid, and Burki and Mayor (1980) obtain a period of 1.49107 d. and detect a strongly variable amplitude.
The Evidence for Planetary Progenitor Rotation and for the Long Term Acceleration of the Ejected Nebular Shell
Authors: Kirkpatrick Ronald C.
Published: July 2016

Several theories seek to explain the peculiar shapes of planetary nebulae. Those of Louise, Kirkpatrick, and Phillips and Reay rely on progenitor rotation. The velocity-radius relation for the shells of well observed planetaries do not extrapolate back through the origin, but rather fall short, suggesting that the shell acquires its velocity over a significant period of time. Kirkpatrick’s theory relies heavily on long term acceleration of the nebular shell, and other theoretical studies support the idea of acceleration of the nebular shell up to the time it becomes optically thin to the ionizing radiation from the central star.
Spherical Oscillation Patterns
Authors: Dean Pesnell W. , Coggins James M.
Published: July 2016

Spherical harmonics are an integral part of the study of stellar pulsations. To gain an understanding of how the star is affected by non-radial pulsations, the radial part of the oscillation is plotted, with an assumed sinusoidal time variation. The amplitude of the motion is arbitrarily set at 20% of the radius.
The Core Helium Flash
Authors: Cole Peter W. , Deupree Robert G.
Published: July 2016

The role of convection in the core helium flash is simulated by two-dimensional eddies interacting with the thermonuclear runaway. These eddies are followed by the explicit solution of the 2D conservation laws with a 2D finite difference hydrodynamics code. Thus, no phenomenological theory of convection such as the local mixing length theory is required.
R Coronae Borealis Pulsations
Authors: King David S.
Published: July 2016

The Cepheid-like pulsations of some of the R CrB stars should in principle make it possible to determine their masses and hence to place constraints on possible evolution scenarios. We briefly review the evidence for these pulsations and discuss the problem of how these low-mass, hydrogen-deficient carbon stars could have evolved to their present position in the H-R diagram. Linear and nonlinear pulsation calculations are reviewed. It is found that for these large luminosity to mass ratio (L/M) stars a region of pulsation instability extends considerably hotter than for normal high luminosity Cepheids. The envelopes of these models are so nonadiabatic that the identification of modes becomes very difficult since there is frequently no clearly defined nodal structure. For the most extreme L/M cases it is found that the models are unstable in the sense that they appear on the verge of ejecting the outer layers.
The Effect of Rotation on the Hydrodynamics of Stellar Collapse
Authors: Tohline J. E. , Schombert J. M. , Boss A. P.
Published: July 2016

To date, most of the hydrodynamic calculations that have followed the details of the physics during an iron core collapse (see Bowers, these proceedings, for a review) have been restricted to spherical symmetry and therefore have neglected the role that rotation may play in the hydrodynamics of the collapse (see, however, LeBlanc and Wilson, 1970). If rotation is important, the core will flatten to an oblate spheroidal shape allowing some loss of energy through gravitational radiation; the core could conceivably, dynamically evolve to a toroidal configuration, as has been observed in some models of rotating protostellar clouds (Tohline, 1980b; Boss, 1980b and references cited therein); and it may, through a rotational instability, eventually evolve into a non-axisymmetric structure. It is important to know just how much rotational energy must be present in the pre-collapse core in order for these, or any other significant deviations from spherical symmetry, to become important considerations during a core collapse.
One Dimensional Hydrodynamics of Asteroid-Neutron Star Collisions
Authors: Newman Michael J. , Cox Arthur N.
Published: July 2016

It has been suggested by several authors (e.g., Harwit and Salpeter, 1973) that the observed cosmic gamma-ray bursts might be produced by the collision of comet or asteroid-sized bodies with a compact object. Colgate and Petschek (1980) have discussed the tidal breakup of a solid body approaching a neutron star in central impact, with particular application to the cosmic gamma-ray burst of March 5, 1979. In this work we present the results of simplified one-dimensional hydrodynamic-radiation diffusion calculations of such an occurence.
The Impact on Astronomy of the Discovery of Uranus
Authors: Smith Robert W.
Published: July 2016

The discovery of Uranus was a very much more important event than the addition of one primary planet to the Solar System. Indeed, it was to greatly influence future developments in a number of diverse regions. In this paper we shall consider its impact in three such areas: (l) the research on, and the acceptance of, the Titius-Bode Law; (2) the search for, and subsequent discovery of, a planet exterior to Uranus and (3) the direction of William Herschel’s own career.
The Magnetosphere of Uranus
Authors: Axford W.I.
Published: July 2016

The magnetosphere of a planet, as the name implies, is the region surrounding the planet in which the planetary magnetic field plays a dominant role in determining the behaviour of the medium. The inner boundary of a magnetosphere is the surface of the planet if it has no significant atmosphere (as in the case of Mercury), or the lower ionosphere in the case of planets with atmospheres. The outer boundary, usually termed the “magnetopause”, is shaped by stresses exerted by the solar wind, being blunt on the upstream side, with normal stresses playing a dominant role, and extending in a comet-like “magnetotail” on the downstream side away from the Sun largely as a result of the action of shear stresses. The characteristic size of a magnetosphere, namely the distance Lm (in planetary radii) to the subsolar point is determined approximately by balancing solar wind ram pressure and the magnetic pressure:

where n is the ion number density and Vs the speed of the solar wind, m is the average ion mass, Bo the (dipole) field strength at the surface of the planet and C is a constant of order unity.
The Rotation of Uranus
Authors: Goody Richard M.
Published: July 2016

From the start of this century until the mid-1970’s the rotation rate of Uranus was reported to be 10.8 h in a retrograde sense (see, for example, Allen, 1955), but a cursory examination of the origin of this datum reveals that little confidence should be placed in it.

Three independent techniques for measuring the rotation rate are available, each very difficult and not including the most direct method of observing the motion of features across the disc. Visual observers have reported features from time to time (see Alexander, 1965, for a full historical account), but the mean diameter of Uranus is only 3.6 arcsec and large high contrast features are rare in the visible spectrum, if they exist at all.
Imaging of Uranus and Neptune
Authors: Smith Bradford A. , Reitsema Harold J.
Published: July 2016

Observations of the minute disks of Uranus and Neptune from the surface of the earth present a major challenge to any observatory site and require the most advanced techniques in optical imaging instrumentation. Less than 4 arcsec across, the disk of Uranus would fit within the Great Red Spot of Jupiter in the focal plane of a terrestrial telescope; the smaller disk of Neptune, less than 2.5 arcsec in diameter, is scarcely more than half again that of Ganymede, the largest of the Galilean satellites. At present, both planets are situated at far southerly declinations, making them even more difficult objects for Northern Hemisphere observatories.
The Rings of Uranus
Authors: Brahic André
Published: July 2016

One of the very exciting discoveries in astronomy and planetary sciences in recent times is the detection of a series of narrow rings around Uranus. During more than three centuries, the rings of Saturn have had a special fascination and symbolism and an enormous amount of literature has been devoted to studies of their nature, properties and origin. The discovery of Uranus’s rings, and two years later of Jupiter’s rings has not only renewed interest but also raised a number of new cosmogonical questions.
ASTRONET. The network for analysis and retrieval of astronomical data in Italy
Authors: Sedmak G.
Published: July 2016

ASTRONET, the network for analysis and retrieval of astronomical data planned in Italy, is described with regard to the organization of the network, the hardware, and the standard software environment. ASTRONET starts with four VAX centers operating within 1981, to be expanded to six within 1983.

The network includes colour graphics and PDS plates digitization facilities. The software and graphics standards will be set as compatible as possible to major existing astronomical standards. ASTRONET is planned to be operative within 1983 as an open international astronomical
facility.
Archiving and retrieval of data from the International Ultraviolet Explorer (IUE) mission
Authors: Warren W. H. , Alderman D. F.
Published: July 2016

The data base of IUE spectra available for dissemination to the scientific community presently contains approximately 22,000 separate images. Due to storage space and computer processing time limitations, it was decided to store the data on high density (6250 bpi) specially formatted tapes and to retrieve and reconvert them to the originally supplied format upon request. The archival/retrieval system for the data and an automatic data entry system for creation and maintenance of an indexing data base are described. Suggestions are made for the use of standard formats for future image data storage, retrieval and dissemination.
A data analysis facility for the Faint Object Camera
Authors: Macchetto F.
Published: July 2016

The Faint Object Camera is the ESA instrument to be flown in the Space Telescope. A modern facility is being established to provide the software required to analyse the FOC data. This paper describes the basic hardware and software characteristics of the ESA facility.
Le Centre de Donnees des Amas de Galaxies
Authors: Fernandez A. , Mathez G. , Mazure A. , Nottale L. , Rothenflug R.
Published: July 2016

A Cluster of Galaxies Data Center is in the process of being settled. Its aim will be to collect the data presently scattered in the literature, concerning clusters of galaxies, in all wavelength ranges. We describe its diverse entries and we discuss some specific problems and its possible future utilization.
Centralization of extragalactic data
Authors: Paturel G.
Published: July 2016

We present a project of centralization of extragalactic data concerning normal galaxies.

The project of creating a data bank about galaxies is an old dream. Knut Lundmark had already thought of such a project, but the work never came to anything. The use of computers has made this work possible.