bluuebunny/crossref_metadata_2025 huggingface dataset:
Limitations of Observational Cosmology
Authors: Kafatos Menas
Published: July 2016

Unlike the usual situation with theoretical physics which is testable in the laboratory, in cosmological theories of the universe one faces the following problems: The observer is part of the system, the universe, and this system cannot be altered to test physical theory. Even though one can in principle consider any part of the observable universe as separate from the acts of observation, the very hypothesis of big bang implies that in the distant past, space-time regions containing current observers were part of the same system. One, therefore, faces a situation where the observer has to be considered as inherently a part of the entire system. The existence of horizons of knowledge in any cosmological view of the universe is then tantamount to inherent observational limits imposed by acts of observation and theory itself. For example, in the big bang cosmology the universe becomes opaque to radiation early on, and the images of extended distant galaxies merge for redshifts, z, of the order of a few. Moreover, in order to measure the distance of a remote galaxy to test any cosmological theory, one has to disperse its light to form a spectrum which would cause confusion with other background galaxies. Since the early universe should be described in quantum terms, it follows that the same problems regarding quantum reality and the role of the observer apply to the universe as a whole. One of the most fundamental properties of quantum theory, non-locality, may then apply equally well to the universe. Some of the problems facing big bang cosmology, like the horizon and flatness problems, may not then be preconditions on theoretical models but may instead be the manifestations of the quantum nature of the universe.
A New Way for Testing of Light Deflection in Earth Orbit or Beyond
Authors: Yi-Ping Qin
Published: July 2016

According to the principles of light deflection, different occulting times of an occultation respond to different basic theories of physics. An occulting way for testing of light deflection in earth orbit or beyond may be possible and is proposed. An application is studied and some suggestions are presented.
Drift Acceleration at Interplanetary Shocks
Authors: Erdös G. , Balogh A.
Published: July 2016

Scatter-free acceleration of energetic particles by quasi-perpendicular interplanetary shocks is investigated. A brief review is given on the predictions of the gradient drift acceleration model concerning the energy, time, and angular dependence of the particle flux caused by a single shock encounter interaction. The angular distribution of ions in the energy range 35 keV to 1 MeV has been determined by the low-energy ion spectrometer aboard the ISEE 3 spacecraft at several shock associated events. Reflections of particles from the shock were clearly identifiable by the loss cone in the upstream pitch angle distributions. The measurements were compared to the predictions of the gradient drift acceleration model, showing a qualitative agreement in many respects. However, bidirectional distributions observed at nearly perpendicular shocks cannot be explained in the framework of the single shock encounter mechanism. It is suggested that multiple intersections of the field lines with the surface of the shock, forming magnetic traps on the upstream side, are responsible for the observed bidirectional distributions. Results obtained from numerical test particle simulations are discussed and compared to observations. A qualitative agreement between model calculations and measurements confirms that the energetic particles are trapped and accelerated, due to special field line topology, on the upstream side of the shock. It is also argued that the collapse of the trap by the convection of the field lines through the shock is accompanied by a considerable increase of the particle flux, which may be responsible for the shock spikes.

Subject headings: acceleration of particles — interplanetary medium
Strong Double Layers, Existence Criteria, and Annihilation: An Application to Solar Flares
Authors: Volwerk Martin , Kuijpers Jan
Published: July 2016

We present some conditions for the stability of a strong double layer in a warm, current-carrying plasma, which can be extended into the relativistic regime. We apply a model for plasma heating by the electron beam emitted from the double layer and show that this leads to a finite life time of the double layer. We also show that the radio emission accompanying this process can well describe the observed phenomena in Type I radio bursts using a direct emission mechanism, not involving Langmuir waves.

Subject headings: plasmas — Sun: flares — Sun: radio radiation
On the Asymmetry of the Distribution of the Anomalous Cosmic-Ray Component in the Heliosphere
Authors: Fichtner Horst , Sreenivasan S. Ranga , Fahr Hans-Jörg , Rucinski Daniel , Grzedzielski Stanislaw
Published: July 2016

An analysis based on a fluid type equation for the spatial diffusion of the anomalous component of cosmic rays in the solar wind is presented. The source distributions of the high-energy particles are related to the pick-up ion flux intensities at the position of the heliospheric shock. Due to the strong asymmetric distributions of the different species of pick-up ions in the heliosphere and a possible aspherical termination shock of the solar wind, the source distributions are expected to exhibit element specific upwind-downwind asymmetries. An analytical treatment of the problem, using boundary conditions derived from observations by the Pioneer and Voyager satellites, leads to an estimate of the asymmetries of the anomalous component in the heliosphere. The investigation is performed in two stages: the problem is solved for an axially symmetric heliosphere in the first instance, and a latitudinal variation of the solar wind velocity as well as in the hydrodynamic diffusion coefficient is incorporated to model the effects of a heliospheric magnetic field in the second.

Subject headings: acceleration of particles — cosmic rays — shock waves — solar wind
Positron Annihilation Radiation from the 1991 November 15 Flare
Authors: Kawabata K. , Yoshimori M. , Suga K. , Morimoto K. , Hiraoka T. , Sato J. , Ohki K.
Published: July 2016

The gamma-ray spectrometer on Yohkoh has detected the positron annihilation line at 511 keV produced during the 1991 November 15 flare (X1.0/3B). The 511 keV line fluence, integrated over the time interval of 22:37:50-22:38:14 UT, is (6.7 ± 2.2) photons cm−2 . The time profile of 511 keV line exhibited long decay time compared with the electron bremsstrahlung and prompt gamma-ray line components. From the analysis of time profile of the 511 keV line, we come to the following conclusions: (1) the main source of positrons is deexcitation of 16O *6.052 by e+ – e- pair emisson. (2) β+ −emitting nuclei of 31S, 29P, 27Si, 26mAl, 25Al,23Mg, 19Ne, and 21Na are also important sources of positrons in the decay phase. (3) The density of the positron annihilation region in the photosphere is 1016 cm−3 . (4) Most likely interpretation of the time profile is that at least 50% of positrons annihilate in coronal flare loops with a density of 1012−1013 cm−3 and with a temperature of 106 −3 × 106 K.

Subject headings: nuclear reactions, nucleosynthesis, abundances — Sun: flares — Sun: X-rays, gamma-rays
The Flare of 1989 September 9, 09:09 UT: Does Coronal Loop Collision Initiate Efficient Gamma-Ray Emission?
Authors: Aurass H. , Hofmann A. , Rieger E.
Published: July 2016

Vector magnetogram data and Hα pictures together with data published by Chupp et al. lead us to conjecture that in the presented case a contact between the rising two-ribbon flare current sheet and a coronal loop connecting two nearby plage regions initiates efficient high-energy γ-ray emission.

Subject headings: Sun: corona — Sun: flares — Sun: X-rays, gamma rays
Quiescent Microwave Emission from Late-Type Stars
Authors: Güdel Manuel
Published: July 2016

A diversity of stellar classes has been detected to be prolific sources of low-level, “quiescent” microwave radiation. This emission is, in most cases, attributed to the persistent presence of mildly relativistic electrons in the coronae. Frequent or continuous particle acceleration is required to maintain a high level of gyrosynchrotron emission. In this paper, observations relevant to our understanding of quiescent microwave emission from stars are reviewed, with emphasis on nondegenerate, late-type stars. Though the nature of the acceleration process remains unknown, a large amount of crucial information is presently available, in particular observations of timescales of slow variations, estimates of particle energies, model calculations based on spectral observations, and correlative studies with soft X-ray emission.

Subject headings: acceleration of particles — radio continuum: stars — stars: activity — stars: coronae — stars: late-type — stars: magnetic fields
Unpulsed High-Energy Radiation from the Crab Pulsar and Nebula
Authors: Cheung W. M. , Cheng K. S.
Published: July 2016

Generally, people believe that the unpulsed high-energy gamma rays from the direction of Crab Nebula and pulsar comes from the nebula. But it is entirely possible that the unpulsed high-energy gamma rays from the direction of the Crab Nebula and pulsar are actually emitted from a region extending to a couple of light cylinder radii from the pulsar instead of from the extensive nebula. In this conference paper, we study the possibility that the unpulsed high-energy gamma rays from 100 MeV to 10 GeV are emitted from the extensive nebula. In our model, two pulsed photon beams from two different outer gaps cross each other beyond the light cylinder and result in pair production. Since the pitch angles of these pairs do not correlate with the local magnetic field, and the typical mean free path for pair production is comparable to the local radius of curvature, the subsequent synchrotron radiation and inverse-Compton scattering produce unpulsed X-rays and gamma-rays respectively.

Subject headings: acceleration of particles — gamma rays: theory — ISM: individual (Crab Nebula) — pulsars: individual (Crab) — radiation mechanisms: nonthermal
Disk-Accreting Magnetic Neutron Stars as High-Energy Particle Accelerators
Authors: Hamilton Russell J. , Lamb Frederick K. , Miller M. Coleman
Published: July 2016

Interaction of an accretion disk with the magnetic field of a neutron star produces large electromotive forces, which drive large conduction currents in the disk-magnetosphere-star circuit. Here we argue that such large conduction currents will cause microscopic and macroscopic instabilities in the magnetosphere. If the minimum plasma density in the magnetosphere is relatively low (≲109 cm−3 ), current-driven micro-instabilities may cause relativistic double layers to form, producing voltage differences in excess of 1012 V and accelerating charged particles to very high energies. If instead the plasma density is higher (≳ 109 cm−3 ), twisting of the stellar magnetic field is likely to cause magnetic field reconnection. This reconnection will be relativistic, accelerating plasma in the magnetosphere to relativistic speeds and a small fraction of particles to very high energies. Interaction of these high-energy particles with X-rays, γ-rays, and accreting plasma may produce detectable high-energy radiation.

Subject headings: acceleration of particles — accretion, accretion disks — gamma rays: theory — plasmas — radiation mechanisms: nonthermal — stars: neutron
Electron Acceleration in Short-Lived Radio Transients
Authors: Ball Lewis
Published: July 2016

A short-lived (weeks-months) burst of radio emission, assumed to be synchrotron radiation, is sometimes associated with objects detected as soft X-ray transients. The “synchrotron bubble model” which has been applied to these radio transients assumes that the source is initially optically thick, and the model therefore takes no account of the details of the electron acceleration required. The initial increase in the radio flux is attributed to decreasing absorption in the expanding source. Observations of the soft X-ray transient GRS 1124 – 68 (X-ray Nova Muscae 1991) showed, for the first time, the rising phase of such a radio transient. Another radio source, the Galactic Center Transient, was discovered serendipitously in the radio and observed throughout its rise and decay. In both cases the radio flux was a decreasing function of frequency throughout the periods of increasing and decreasing flux, which is not consistent with the optically thick assumption of the synchrotron bubble model. When this assumption is discarded the mechanism responsible for producing the ultrarelativistic electrons, or at the very least the rate at which those electrons become available, must be considered. A generalization of the simple model to include a source which supplies relativistic electrons with a constant energy spectrum is discussed. While such a model can go some way toward matching the observations, it is suggested that the time is ripe for an explicit model of the electron acceleration mechanism. Some of the features such a model may have are presented.

Subject headings: acceleration of particles — radio continuum: general — radiation mechanisms: nonthermal — X-rays: bursts
Do Gamma-Ray Bursts Originate from an Extended Galactic Halo of High-Velocity Neutron Stars?
Authors: Hartmann Dieter H. , Brown Lawrence E. , The Lih-Sin , Linder Eric V. , Petrosian Vahé , Blumenthal George R. , Hurley Kevin C.
Published: July 2016

The γ-ray burst brightness distribution is inhomogeneous and the distribution on the sky is nearly isotropic. These features argue against an association of γ-ray bursts with those Galactic objects that are known to exhibit a strong concentration toward the Galactic center or plane. The observed statistical properties indicate a cosmological origin. Circumstantial evidence suggests that neutron stars are involved in the burst phenomenon. Here we consider Population II neutron stars in an extended Galactic Halo (EGH) as an alternative to cosmological scenarios. The BATSE data indicate a small deviation from isotropy near the 2 σ level of statistical significance. If confirmed for an increasing number of bursts, these anisotropies could rule out cosmological scenarios. On the other hand, EGH models require small anisotropies like those observed by BATSE. We consider simple distribution models to determine the generic properties such halos must have to be consistent with the observations and discuss the implications of the corresponding distance scale on burst models.

Subject headings: gamma rays: bursts — stars: neutron — stars: Population II — stars: statistics
The NORT: Network of Oriental Robotic Telescopes
Authors: Hajjar Roger , Querci François R. , Querci Monique
Published: July 2016

In this paper, we present the NORT, a network of oriental robotic telescopes originally proposed in 1993 by Querci & Querci to study stellar variability. The NORT project covers all of northern Africa and Asia near the tropic of Cancer. The interest generated among a number of astronomers in countries from the Arab World and Asia offers a solid basis for the rebirth of astronomy and astrophysics and space sciences in developing countries. The number of national projects for telescopes in different countries makes the NORT a framework of choice to coordinate and stimulate these separate efforts by the creation of a NORT steering committee.
High-Speed Photometry of Bright roAp Stars With Small Telescopes
Authors: Kurtz D.W.
Published: July 2016

The rapidly oscillating Ap stars are magnetic peculiar A stars which pulsate in multiple p modes with periods in the range of about 6 to 16 minutes with their oscillation axes aligned with the oblique magnetic axes of the stars. Some of these stars have the richest frequency spectra of any non-degenerate stars other than the sun. This paper shows how photometric observations using small telescopes can be used to work on several astrophysically interesting problems posed by these stars. An example of high precision photometry is shown. The proof of oblique dipole pulsation, the distortion of pulsation modes (probably by the magnetic field), and the determination of asteroseismic luminosities are all discussed. The latter, especially when combined with new theoretical developments concerning magnetic field-pulsation interaction, suggests that Ap stars have lower effective temperatures and/or smaller radii than has been previously thought. It is pointed out that this may be related to the recently discovered extreme discrepancy in effective temperature determined from the wings and cores of the Hα line.
Search for Variable Stars in the Open Cluster NGC 2539
Authors: Choo K.J. , Kim S.-L. , Yoon T. S. , Chun M.-Y. , Sung H. , Park B.-G. , Ann H. B. , Lee M. G. , Jeon Y.-B. , Yuk I.-S.
Published: July 2016

We report on the results of CCD photometric observations of the open cluster NGC 2539. Eight new variable stars have been found in the observed field of this cluster. However, no γ Doradus-type variability was found among the member stars.
Observations of Variable Stars With a Small Telescope at Tabriz University
Authors: Jassur D. M. Z. , Adabi F. , Cham N.A.
Published: July 2016

For more than a decade a small group of Astronomers has been monitoring variable stars of different types. In the present contribution I will present the observations of chromospheric active binaries and near contact binaries and the results obtained from their analysis.
NEOPAT: Near-Earth Object PATrol program
Authors: Moon Hong-Kyu , Chun Moo-Young , Byun Yong-Ik , Han Wonyong , Kim Seung-Lee , Jeon Young-Beom , Kang Yong-Woo
Published: July 2016

In 2000, Korea Astronomy Observatory launched the Near-Earth Object Patrol (NEOPAT) program. NEOPAT has conducted follow-up observations of NEOCP (NEO Confirmation Page) objects and discovered 52 new main-belt asteroids during the observation runs. We initiated collaboration with the Yonsei Survey Telescopes for Astronomical Research (YSTAR) team for NEO search. Wide-field of view, fast read-out time, and fully autonomous data pipeline will enable us to detect and track NEOs with a high efficiency. Scheduled to begin active operations in mid-2001, our survey system is going to be the first network of robotic telescopes for NEO search with automatic access to both hemispheres.
CCD Photometry of Two Asteroids (895) Helio and (165) Loreley
Authors: Woo H.-S. , Kim S.-L. , Chun M.-Y. , Park M.-G.
Published: July 2016

We have presented photometric results for two asteroids (895) Helio and (165) Loreley. The observations were performed from 2000 Oct. to 2001 Jan. using the 61cm telescope installed at Sobaeksan Optical Astronomy Observatory in Korea.
Monitoring of AGNs at the Shanghai Astronomical Observatory
Authors: Qian B.C. , Tao J.
Published: July 2016

This paper briefly introduces the program, equipment and results of monitoring of AGNs carried out at Shanghai Astronomical Observatory.
Bright Young Star Candidates in the Rosette Nebula
Authors: Chiang P.S. , Chen W.P. , Li J.Z. , Chu Y.-H.
Published: July 2016

We identified possible optical young stars in the Rosette Nebula by using the IRAS and the ROSAT databases. The previously reported “diffuse” X-ray emission has been resolved into point sources. Forty-seven point sources are detected above 3-sigma of the X-ray background, and twenty-seven of these have stellar counterparts. Some of the young star candidates appear to be associated Herbig-Haro nebular features.
Stable and Unstable Solutions of the Nonlinear Dynamo Problem
Authors: Meinel Reinhard
Published: July 2016

A local potential approach to nonlinear dynamo models which allows the use of variational techniques to investigate the problem of stability is introduced. The method applies at least to quasi-kinematic dynamo models, i.e. to models which include the back-reaction of the magnetic field on the fluid motion in a simplified way. A special application leads to a previously investigated one-dimensional dynamo model which shows a coexistence of a periodic solution (limit cycle) with two stable steady solutions of opposite polarities. The inclusion of some small-amplitude noise leads to interesting transition phenomena which may be of relevance to explain the behaviour of astrophysical dynamos. A simple dynamical system with a two-dimensional phase-space is used for illustration.
Nonlinear Nonaxisymmetric Dynamos for Active Stars
Authors: Moss David
Published: July 2016

Recent observations seem to have detected large scale nonaxisymmetric structures on active giant stars. These structures are plausibly associated with underlying, dynamo generated, nonaxisymmetric magnetic fields. Such developments have motivated the development of a computer code to solve the nonlinear mean field dynamo equation in spherical geometry with no imposed geometrical symmetries. The nonlinearity is a simple α-quenching. The nature of the stable solutions found depends quite sensitively on the assumed spatial distribution of both α-eflect and differential rotation, and also on the degree of supercriticality of the dynamo. Such a dynamo model with stable, purely nonaxisymmetric solutions is described in this paper.
αΛ-dynamos
Authors: Brandenburg A. , Moss D. , Rieutord M. , Rüdiger G. , Tuominen I.
Published: July 2016

In contrast toαω-dynamos, where the angular velocity is arbitrarily prescribed, we consider hereαΛ-dynamos, for which the differential rotation and meridional circulation are solutions of the momentum equation. The non-diffusive parts of the Reynolds stress tensor are parameterized by theΛ-effect. In earlier investigations we have shown that the turbulent magnetic diffusivity has to be much smaller than the eddy viscosity, otherwise the dynamo is not oscillatory or else the contours of constant angular velocity are cylindrical, contrary to observations. In the present paper we investigate the effects of compressibility.
Λ-effect, Meridional Flow and the Differential Solar Rotation
Authors: Rüdiger G. , Tuominen I.
Published: July 2016

Rotation laws for the solar convection zone are produced by theΛ-effect in rotating anisotropic turbulence fields. In this paper we use the structure of the turbulence parameters introduced by Rüdiger and Kichatinov (1990), based on a simplified turbulence model. When we neglect the meridional circulation, for small inverse Rossby numbers the angular velocity isolines are spherical, while for increasing inverse Rossby number they approach more and more the helioseismologically derived shape. This simple picture becomes more complicated if the meridional circulation is allowed to act as an angular momentum transporter.
Differential Rotation as an Axisymmetric Resonant Mode of Convection
Authors: Chan Kwing L. , Mayr Hans G.
Published: July 2016

Recent results from helioseismology (see Goode, these Proceedings) have shown that the inferred contours of the solar angular velocity are more or less radial in the convection region, and the rotation becomes uniform below. These observations contradict the prevailing numerical models of Taylor columns which predict angular velocity contours parallel to the rotation axis of the Sun. Thus, an alternative explanation of solar differential rotation is called for.

Presently, it is not feasible to construct a thermally-relaxed, dynamically self-consistent numerical model of the solar convection zone (see Chan and Serizawa, these Proceedings). It is then appropriate to explore simplified models that may shed some light. A number of analytical models have been proposed for the solar differential rotation, and the reader is referred to the book by Rüdiger (1989) for a comprehensive review of this subject. Here, we report on some recent development on the convective resonance model proposed by Chanet al.(1987; hereafter referred as CSM).
Diagnostics of the Solar Dynamo Using the Observed Pattern of Surface Magnetic Fields
Authors: Stenflo J.O.
Published: July 2016

The solar surface represents for the solar dynamo an outer boundary that is directly accessible to observations. The evolutionary and rotational properties of the magnetic fields at this boundary can be empirically determined using existing synoptic magnetograph data. The derived properties provide detailed constraints on the underlying theory, such that an inversion approach to the dynamo problem becomes feasible. Ambiguities in the interpretation may be removed using the independent constraints from helioseismology.
The Large-scale Magnetic Field in the Global Solar Cycle: Observational Aspects
Authors: Makarov V.I. , Sivaraman K.R.
Published: July 2016

The global solar cycle is considered as an interaction of 3 types of activity: at low-latitude (sunspots), at high-latitude (polar faculae) and the weak magnetic field. The properties of single and 3-fold reversals of the polar magnetic field are considered. The variation spectrum of the large-scale magnetic field of the Sun is analyzed in the range of 1–30 nHz. A dependence between the rate of a poleward meridional flow and phase of the global cycle is discussed.
The Rotational Modulation of Ca II K in the Sun
Authors: Sattarov I. , Hojaev A.
Published: July 2016

The most widely used indicator of the stellar magnetic activity is the flux in the CaII K-line core (K-index) (Baliunas and Vaughan, 1985). The K-index data have also been used for measuring the rotation of stars. But using the method for the Sun gives different results (Keil and Worden, 1984; Singh and Livingston, 1987). The reason for the observed differences, besides those indicated by Singh and Livingston, may be the character of the distribution of active regions. This study is based on observations made at Tashkent Astronomical Observatory and the data published in SGD for solar cycle 21. We study the longitudional distribution of sunspots and plages. Some intervals of active longitudes (IAL) were selected and the evolution of them was studied. Active regions were found to concentrate in certain longitude intervals which are in nearly rigid rotation. Fig. 1 shows the longitudinal distribution of sunspots areas for 1983-84, as an example.
Large Scale Patterns on the Solar Surface Indicated by Microwave Observations
Authors: Vršnak B. , Pohjolainen S. , Teräsranta H. , Urpo S. , Brajša R. , Ruždjak V. , Schroll A. , Jurač S.
Published: July 2016

A large set of observations of the Sun at 37 GHz is analysed. An association of 99% is found between the regions of brightness temperature depression and the magnetic field inversion lines. Observations indicate a possible existence of “giant cells” with duration of 1-2 years and a longitudinal extension up to 90°.
The History of Activity of the Sun and its Rotational Period on the ZAMS
Authors: Stępień Kazimierz
Published: July 2016

The rotation period of the Sun after it reached ZAMS is estimated from the present rotation rate, average X-ray emission flux and average calcium emission flux. Taking into account all existing uncertainties it is concluded that this initial period was within the range 1–9 days, with the most probable value 2–3 days. Possible influence of the solar activity on evolution of life on the Earth is briefly discussed.
The Art of Surface Imaging
Authors: Piskunov N.E.
Published: July 2016

We intend to analyze the reliability of surface imaging of stars based on high resolution spectroscopy and the technique of inverse problem solution. Both astrophysical and mathematical aspects including different regularization methods are reviewed. The influence of the different factors on the resulting map is discussed and it is shown that the simultaneous use of different kinds of observational data (spectroscopy, photometry, polarimetry etc.) is very useful in providing additional constraints for the solution. The recent results in the surface imaging of Cp- and late-type stars show the way for further progress: the use of more adequate mathematical description of the stellar atmosphere and the simultaneous consideration of various surface inhomogeneities.
Surface Imaging of El Eri
Authors: Hackman T. , Piskunov N.E. , Poutanen M. , Strassmeier K.G. , Tuominen I.
Published: July 2016

We present maps of the temperature distribution on the spotted RS CVn-type binary EI Eri (HD 26337), obtained by means of the surface imaging technique described in the Colloquium (Piskunov, 1991). Images were calculated for two separate lines for two epochs of observation. For one epoch we also calculated an image using a blend of several lines. The reliability of the maps is confirmed by comparing the simultaneous photometric observations with the light curves calculated from the temperature maps.
Linear Polarization and Magnetic Fields in Cool Stars
Authors: Huovelin J. , Saar S. H.
Published: July 2016

Observations and theoretical models of broadband linear polarization (BLP) in cool stars are discussed. Two effects, 1) differential saturation in magnetically sensitive absorption lines and, 2) Rayleigh and Thomson scattering are considered as the possible causes of the BLP. Results of theoretical models, and comparisons with observations are summarized.
Polarimetric Observations of Active Cool Binaries
Authors: Koch R.H. , Elias N.M. , Holenstein B.D. , Piirola V. , Scaltriti F. , Coyne G.V.
Published: July 2016

For a sample of RS CVn binaries Busso and collaborators (Busso et al., 1987, 1988; Busso and Scaltriti, 1990) compared the observed energy distribution from the UV to the near-IR (and to IRAS bandpasses for some objects) with those calculated from the known radii and spectral types of the stellar components. About 25% of the sample gave evidence of an IR excess up to 0.7 mag, generally starting from the I-band. The excess is significantly larger than observational error. These same authors ascribe the excess to a thin dust shell surrounding the binary. Using the “dirty silicates” model by Jones and Merrill (1976) they find for the shell a temperature range of 1500 K to 2000 K, an optical depth of about 0.01 at 10 micrometers in the shell, and a distance of the shell from the stars to be typically about 100 times the radius of the larger star.
Activity of Relatively Close Binaries
Authors: Schrijver Carolus J. , Zwaan Cornelis
Published: July 2016

Whereas the rotation-activity relationship for single cool stars can be described in terms of fundamental stellar properties, the activity in relatively close binaries is enhanced with respect to that of single stars by an amount which depends strongly on the properties of the companion. We consider mechanisms which could cause an excess in activity of binaries, and conclude that it is likely that the presence of a companion affects the interior structure of the stars in such a way that either the efficiency of the dynamo or of the atmospheric heating is enhanced.
Recent Advances in our Understanding of Chromospheric and Coronal Heating Mechanisms
Authors: Linsky Jeffrey L.
Published: July 2016

I will summarize some of the principal scientific results presented at the Conference on “Mechanisms of Chromospheric and Coronal Heating” held on 5-8 June 1990 in Heidelberg, Germany. The Conference included invited and contributed papers on observations that point to specific heating mechanisms and theoretical papers on the heating mechanisms themselves. There were many opportunities for useful interaction between proponents of these two approaches to understanding stellar chromospheres and coronae. I will concentrate on what is being learned from the empirical side, and then summarize the heating mechanisms discussed and for which types of stars they may be applicable.
Magnetic Star Models with Toroidal Component of Field
Authors: Moss D.L.
Published: July 2016

A variety of models of main sequence stars of a few solar masses containing large scale magnetic fields have been published in the last few years. Most of them have contained purely poloidal magnetic fields (with magnetic and rotation axes aligned). Those containing a toroidal field component were either polytropic models, or, if more realistic, the toroidal field was not well behaved at infinity.
On Equatorially Symmetric Models for Magnetic Stars as Suggested by Dynamo Theory
Authors: Krause F. , Oetken L.
Published: July 2016

Dynamo theory suggests that an equatorially symmetric structure of the magnetic field holds for single stars. Assuming that the distribution of elements is connected with the magnetic field, an equatorially symmetric concentration of elements in rings was constructed, which can represent the observed quantities W(t), vr(t), and Heff(t) of the periodic magnetic variable stars. Especially for α2CVn, a model has been found which represents the main features of this star as well as that which pyper derived by harmonic analysis. Generally no severe objections against equatorial symmetry of the physical parameters of magnetic stars have been found.
On The Radii of Ap Stars
Authors: Catalano F.A. , Strazzulla G.
Published: July 2016

From the analysis of the observational data of about 100 Ap stars, the radii have been computed under the assumption that Ap are main sequence stars. Radii range from 1.4 to 4.9 solar units. These values are all compatible with the Deutsch's period versus line-width relation.
Hd 101065 - An Astronomical Enigma
Authors: Przybylski A.
Published: July 2016

HD 101065 is a very peculiar star whose spectrum is dominated entirely by the numerous lines of the rare earths. The only other metals seen in the spectrum are strontium, yttrium, zirconium and barium and traces of calcium.

The effective temperature of the star is 6075° ± 200°K or about 1000°K lower than that of the coolest Ap stars known to date.

HD 101065 is a suitable testing ground for the theories on the formation of Ap stars. The absence of “normal” elements in the atmosphere of the star puts stringent limitations on the choice of the available theories.
Light Variations of Ap Stars: 10-Colour Photometry and its Interpretation by a Magnetic Spot Model
Authors: Schöneich W. , Staude J.
Published: July 2016

Amplitude-wavelength relations obtained by a multicolor photometry of 16 Ap stars are represented. Model calculations show that the characteristic observed features may be explained by assuming, relative to the undistributed photosphere, a different depth dependence of the temperature in a spot caused by the magnetic field.
Photometry of Five Southern Magnetic Stars
Authors: Bartolini C. , Scardovi S.
Published: July 2016

Photoelectric observations carried out in 1970 at Siding Spring Observatory are presented. HD 45677, observed also at Bologna, presents in the time interval 1970-1975 variations of 0m.4; the hypothesis of eclipsing binary is considered. Light variations of 0m.026 with a possible period of about 30dhave been detected in HD 168814. HD 184552 seems to vary with an amplitude of 0m.015 in about 10d, but rapid variations could be present. HD 187474 and HD 204075 stayed constant.
The Sun as a Magnetic Star
Authors: Wilcox John M. , Svalgaard Leif
Published: July 2016

The sun as a magnetic star is described on the basis of recent work on solar magnetism. Observations at an arbitrary angle to the rotation axis would show a 22-year polar field variation and a 25-day equatorial sector variation. The sector variation would be similar to an oblique rotator with an angle of 90° between the magnetic and rotational axis.
Abundance Studies of Peculiar B Stars
Authors: Vilhu O. , Tuominen I.V. , Boyarchuk A.A.
Published: July 2016

Spectroscopic investigation of some peculiar B stars has been carried out. The whole α Scl-group of weak-helium-line stars was analysed. The stars studied (Table) represent a sample of Bp stars in the overlapping region, where several peculiarity phenomena (weak-helium-line, Mn, Si λ 4200) are found at the same effective temperature.
The Ultraviolet Variations of ι Cas
Authors: Molnar M.R. , Mallama A.D. , Soskey D.G. , Holm A.V.
Published: July 2016

The Ap variable star ι Cas was observed with the photometers on OAO-2 covering the spectral range λλ 1430-4250. The ultraviolet light curves show a double wave with primary minimum and maximum at ϕ = 0.00 and 0.35, respectively. Secondary minimum light is at ϕ = 0.65 with secondary maximum at ϕ = 0.85. The light curves longward of λ3150 vary in opposition to those shortward of this “null region”.

Ground-based coude spectra show that the Fe II and Cr II line strengths have a double-wave variation such that maximum strength occurs at minimum ultraviolet light. We suggest that the strong ultraviolet opacities due to photoionization and line blanketing by these metals may cause the observed photometric variations.

We have also constructed an oblique-rotator model which shows iron and chromium lying in a great circle band rather than in circular spots. These elements have been observed to lie in bands along the magnetic equator in several other Ap stars such as α2CVn, HD 173650, and 108 Aqr. Thus, we predict that the inclination of the magnetic dipole field with respect to the axis of rotation is about 84°.
Reference Coordinate Systems for Earth Dynamics: A Preview
Authors: Mueller Ivan I.
Published: July 2016

A common requirement for all geodynamic investigations is a well-defined coordinate system attached to the earth in some prescribed way, as well as a well-defined inertial coordinate system in which the motions of the terrestrial system can be monitored. This paper deals with the problems encountered when establishing such coordinate systems and the transformations between them. In addition, problems related to the modeling of the deformable earth are discussed.
Celestial Reference Frames
Authors: Kovalevsky J.
Published: July 2016

A celestial reference frame is based on some dynamical or kinematic approximation of an absolute coordinate system and is materialized by a fundamental catalogue of stars. It is characterized by the accuracy of the system and the precision of its stellar realization.

The present situation, marked by the construction of the FK5 system and catalogue, is briefly described. It will be an hybrid system based on the discussion of all existing observations. The prospects for improvement in accuracy are good using lunar laser observations or VLBI determination of the positions of extra-galactic radio-sources. Three procedures that may be used to link such a system to a star catalogue are given. A major improvement in precision is expected from the Hipparcos programme and further extensions include essentially the densification of catalogues with stars of magnitudes 10 to 14 using photoelectric automatic meridian instruments.
Some Geodetic Aspects of the Plate Tectonics Hypothesis
Authors: Lambeck Kurt
Published: July 2016

Geodetic observations of gravity, body tides, the Earth’s rotation and crustal motion and deformation potentially provide important constraints in the general inversion of geophysical data for determining the structure and evolution of the Earth. More specifically, the geodetic data provide constraints on the rheology of the planet in the frequency range intermediate between geological and seismic frequencies, on the geologically instantaneous kinematics of the Earth and on the mechanisms responsible for the motions within the Earth, results that are intimately related to the plate tectonics hypothesis. The discussion is limited here to only a few aspects of these “geodetic” aspects of this hypothesis, including deformation along plate boundaries, intraplate tectonics and vertical motions.
Comments on the Terrestrial Pole of Reference, the Origin of the Longitudes, and on the Definition of UT1
Authors: Guinot Bernard
Published: July 2016

The definition of a terrestrial reference pole (TRP) and of a Terrestrial Longitude Origin (TLO), by fixing the stations coordinates of an adopted network seems unrealistic. It is proposed that TRP and TLO be the realized origins of some specified service working in accordance with some stated principles. It is also proposed to clarify the definition of UT1 and to base it on some physical properties.
On the Establishment of Terrestrial Coordinate System by Classical Techniques
Authors: Yatskiv Ya. S.
Published: July 2016

The definition and practical realization of the astronomical system of terrestrial coordinates are discussed. In particular, the separation of secular polar motion and nonpolar drift of observatories are touched upon as far as those phenomena are crucially intertwined with the realization of a terrestrial coordinate system.
On the Annual Earth’s Rotation
Authors: Poma Angelo , Proverbio Edoardo
Published: July 2016

A number of works have presented evidence that the seasonal terms of the Earth’s rotation are variables from year to year. In this paper, introducing a parameter associated to a mean seasonal kinetic energy we show evidence of about 4 year and 7 yr periodicity. This result is briefly discussed.
Local Geometric and Gravimetric Datum and Its Relation to the Global Terrestrial Reference System
Authors: Kelm R.
Published: July 2016

In active tectonic zones relative earth surface displacements of mm-order and, relative gravity disturbances of 0.1 mgal size may be expected between two survey epochs. To monitor and separate these small effects significantly special local free networks have to be designed which are measured by relative observations of highest accuracy (mm-and ygal-level). For the connection of the local nets to a global terrestrial reference system a suitable local datum for point coordinates (geometric datum) and gravity field parameters (gravimetric datum) has to be defined within the terrestrial reference system.
Errors in Pole Coordinate Obtained by the Doppler Satellite Positionings
Authors: Takagi S.
Published: July 2016

The pole coordinate obtained by the Doppler observation of Earth satellite shows good results, but there are some important difference from those of the astronomical observation, for example, that of the IPMS.

The Doppler observation of the Navy Navigation satellite has proved to be precise enough to supersede the astronomical observation in the geodynamics. (Anderle, 1965, 1966, 1970, 1971a, 1971b, 1971c, 1974). Yumi et al. (1979) showed that the local terms in the astronomical observation was not found in the Doppler latitude obtained at Mizusawa. This shows the superiority of the Doppler observation to the astronomical one.
Planetary Ephemerides
Authors: Lieske Jay H. , Standish E. Myles
Published: July 2016

In the past twenty years there has been a great amount of growth in radiometric observing methods, as well as in classical optical observations. Through radar ranging and Doppler observations of the planets and spacecraft, we have been able to improve our knowledge of the location and motion of the planets by several orders of magnitude and have succeeded in planning and executing space missions which would have been difficult if not impossible to plan and to perform utilizing the classical ephemerides. We will outline the goals and methods employed by the Jet Propulsion Laboratory in its effort to develop improved ephemerides which accurately reflect the motions of planets in an inertial system.
Systematic Differences between Radio Astrometric Surveys
Authors: Walter H.G.
Published: July 2016

A radio astronomical reference frame has been established from four interferometric position surveys of extragalactic objects. The resulting systematic differences between surveys were studied with different weighting schemes and averaged systematic corrections were derived.
Contribution des Astrolabes au Raccordement des Systemes de Reference “Optique” et “Radio”.
Authors: Débarbat Suzanne
Published: July 2016

Twenty-two radio sources, being bright objects of the Galaxy are observable with astro labe (plus six for those having photoelectric devices). It is about half of the total number (forty-six, figure 2) of objects of the list of galactic objects given by the working group of Commission six of the IAU. Seventeen astro labe stations (figure 2) are interested in a cooperation which final objective is to link the radio and optical reference systems.
1D, 2D and 3D Collapse of Interstellar Clouds
Authors: Tscharnuter W.M.
Published: July 2016

This review is concerned with recent theoretical investigations and numerical models of star formation with varions symmetries. Observations strongly support the fact that stars condense out of cool (≈10 K) and dense (103-104atoms/cm3) interstellar clouds due to gravitational instability and collapse. Bright, young stellar objects (0- and B-stars are always found in the vicinity of coloud complexes.
Collapse, Equilibrium, and Fragmentation of Rotating, Adiabatic Clouds
Authors: Boss A. P.
Published: July 2016

Numerical calculations of the collapse of adiabatic clouds from uniform density and rotation initial conditions show that when restricted to axisymmetry, the clouds form either near-equilibrium spheroids or rings. Rings form in the collapse of low thermal energy clouds and have β = T/|w|≳ 0.43. When the axisymmetric constraint is removed and an initial m=2 density variation is introduced, clouds either collapse to form near-equilibrium ellipsoids or else fragment into binary systems through a bar phase. Ellipsoids form in the collapse of high thermal energy clouds and have β ≲ 0.27. The results are consistent with the critical values of β for instabilities in Maclaurin spheroids, and suggest that protostellar clouds may undergo a dynamic fragmentation in the nonisothermal collapse regime.
Pulsation Modes and Luminosities of the β Cephei Staks
Authors: Jerzykiewicz M. , Sterken C.
Published: July 2016

Assuming that frequencies observed in multiperiod β Cephei variables correspond to normal pulsation modes leads to the following conclusions: (1) a variety of low Z oscillations are excited in these stars, (2) at most one radial mode is seen in any of them.

Pulsation constants can be derived for two β Cephei stars without recourse to photometric calibrations. In both cases a 0.5 mag. downward revision of the Balmer line absolute magnitudes is indicated. Implications of this result for Stellingwerf’s opacity bump mechanism are briefly considered.

The text of the paper will appear in Proceedings of the Fifth European Regional Meeting of the IAU.
Recent Work on Cepheid Variables
Authors: Cox J. P.
Published: July 2016

Recent work on Cepheids is reviewed in the areas of (1) the large-amplitude mode behavior, (2) convection, and (3) Cepheid masses. Initial-value type nonlinear calculations have not yet yielded true double-mode behavior. Yet we have the beginnings of a promising theory of modal selection. Theoretical calculations also yield reasonably located red edges to Cepheid (and Cepheid-like) instability regions.
The Unusual Classical Cepheid Hr 7308: 1966-1969
Authors: Breger Michel
Published: July 2016

The small-amplitude classical cepheid HR 7308 has the shortest period known in our Galaxy for a classical cepheid. 1966-1969 photoelectric observations together with more recent data show a period of 1d.49078 with sinusoidal light variations. Except for the presence of the beat period, no secondary period can be found in the extensive 1966 data. The lack of a secondary period near Pi/Po = 0.7 sets HR 7308 apart from many other short-period classical cepheids.
Pulsation Properties of Mira Long Period Variables
Authors: Cahn Julius H.
Published: July 2016

A matter of great interest to variable star students concerns the mode of pulsation of Mira long period variables. In this report we first give observational evidence for the pulsation constant Q = P(M/R3)½ where P is the period and M and R are the mass and radius in solar units. We then compare the observations with calculations. Next, we review two interesting groups of papers dealing with hydrodynamic properties of long period variables. In the first, a fully dynamic nonlinear calculation maps out the Mira instability domain. In the second, special attention is paid to shock propagation beyond the photosphere which in large measure accounts for the complex spectra from this region. Finally, we review the paper by Wood-Zarro (1980) dealing with the pulsation constant Q.