bluuebunny/crossref_metadata_2025 huggingface dataset:
Cometary Activity, Discrete Outgassing Areas, and Dust-Jet Formation
Authors: Sekanina Z.
Published: July 2016

Major progress has recently been achieved in the understanding of the coma morphology of dust comets. The conceptual models for the various types of feature observed in the coma (jets, spirals, halos, fans, etc.), their computer simulation, and the hydrodynamic models for jet formation are critically reviewed, and evidence for anisotropic, strongly collimated flows of ejecta emanating from discrete active regions (vents) on the rotating cometary nuclei is presented. The techniques employed to generate synthetic comet images that simulate the observed features are described and their relevance to the primary objectives of coma-morphology studies is exemplified. Modelling of temporal variations in the water emission from discrete active regions suggests that production curves asymmetric with respect to perihelion should be commonplace. Critical comparisons are offered with the activity profiles of Encke’s comet and with light curves of disappearing comets and comets that undergo outbursts. Discussed next is the potential evolutionary significance of nuclear shape, the fractional area of the surface that is active, the vents’ erosion rate, and available information on their activation, aging, dormancy, migration, rejuvenation, and extinction. Recent developments in the understanding of the processes that cause the nongravitational perturbations of cometary motions are reviewed and the observed discontinuities are identified with birth of new sources and/or deactivation of old vents.
The Electrodynamics of Charged Dust in the Cometary Environment
Authors: Horanyi M. , Mendis D.A.
Published: July 2016

Dust in the plasma and radiative environment of a comet is necessarily electrically charged. This charging has both physical and dynamical effects on the dust, being particularly important on the smallest particles observed in the dust size spectrum. In this paper, these dynamical effects are reviewed and the pertinent observations are discussed.
The Global Interaction of Comets with the Solar Wind
Authors: Flammer K. R.
Published: July 2016

The global interaction of the solar wind with a comet as it orbits the Sun is reviewed. After a brief survey of the flow transition regions observed at comet Halley is presented, theoretical models are given for the cometocentric distance of the bow shock, the cometopause, and the ionopause. In addition, predictions are made as to what heliocentric distance these boundaries should form at. The results of these models are compared with the in situ observations at comet Halley.
Historical Comets Over Bavaria: The Nuremberg Chronicle and Broadsides
Authors: Olson R. J. M. , Pasachoff J. M.
Published: July 2016

The first widely distributed printed comet images appear in the Nuremberg Chronicle, whose Latin edition appeared in 1493, followed closely by a German edition. In the first section, we begin our consideration with the comet image that has frequently been cited as a representation of the A.D. 684 apparition of Comet P/Halley. To better understand this image, we present a thorough survey of the 13 comet images that appear in the Chronicle, all reproduced from four woodblocks, representing 14 apparitions between A.D. 471 and A.D. 1472. In the second part, we present an analysis of the unpublished preparatory drawings for the comet images in the handwritten Exemplars (manuscript layout dummies) for both the Latin and German editions in the Stadtbibliothek, Nuremberg. Finally, in the third part, we demonstrate how the Chronicle presaged the proliferation of broadsides--woodcut prints that functioned like tabloids of the sixteenth and seventeenth centuries. We examine broadsides recording historical comets over such Bavarian cities as Nuremberg and Augsburg. In spite of their superstitious, hysterical journalism, fed by turbulent political and religious upheavals, these broadsides reveal a nascent scientific attitude.
Correlators for interferometry – Today and Tomorrow
Authors: Chikada Yoshihiro
Published: July 2016

History of correlators for radio interferrometer is briefly reviewed. Advantages and disadvantages of various methods are discussed and the most appropriate ways are given for various interferrometers. Challenges to the next generation short-wavelength interferrometer are also discussed.
Compatibility issues in VLBI
Authors: Wietfeldt R. D. , D’Addario L. R.
Published: July 2016

New VLBI systems are under development in many countries in preparation for large dedicated arrays, including orbiting radio telescopes to be launched in the 1990s. In particular, several new recording systems and correlators are being constructed: the VLBA in the U.S., the S2 in Canada, and the K4/VSOP in Japan. This paper reviews the issues of technical compatibility among these systems in an effort to facilitate global VLBI experiments.
Opacity at the Owens Valley Millimeter Array
Authors: Scott Stephen L. , Woody David P.
Published: July 2016

We have measured the opacity at the Owens Valley Millimeter Array with tip curves at frequencies from 95 to 248GHz. These measurements have been interpreted using a model and then scaled to a standard frequency of 100GHz. The unique aspect of this data is the wide range of frequencies covered and the use of receivers with different sideband gain ratios.
The Bispectrum analysis technique in millimeter interferometry
Authors: Morita Koh-Ichiro
Published: July 2016

We propose an application of the bispectrum analysis technique in millimeter interferometry, which is used in the speckle masking technique. For the millimeter interferometry, in which atmospheric phase fluctuations are very serious, not only bispectrum phase but also bispectrum amplitude is good observable. We have developed an algorithm to reconstruct images directly from bispectrum. We have made good maps with this algorithm in the case of both simple and compact sources.
Phase calibrators for MERLIN
Authors: Patnaik A.R. , Browne I.W.A. , Wilkinson P.N. , Wrobel J.M.
Published: July 2016

The VLA was used to derive a catalogue of phase–reference sources for MERLIN. These sources can also be used for other interferometer arrays such as the VLBA. The positions of the sources in the catalogue are repeatable to about 5 milliarcsec rms.
The Multi-resolution CLEAN
Authors: Wakker B.P. , Schwarz U.J.
Published: July 2016

We describe a modification to CLEAN which alleviates some problems for extended sources. This is accomplished by combining the results of a number of conventional CLEAN operations, each done at a different resolution. The algorithm is called “Multi-Resolution Clean” or “MRC”. Experiments on model sources have shown that it works well even when the source is so extended that the usual CLEAN becomes impractical. For extended sources, MRC enhances the signal-to-noise ratio, resulting in an easier definition of the area of signal. Moreover, MRC is in principle faster than a standard CLEAN because less δ-functions are needed. This work was published in Astr. Ap., 200, 312.
A new method of analysis and reduction of VLBI observations
Authors: Arias E. F. , Biasi M. S. de
Published: July 2016

In this paper we develope an inertia! system of coordinates introducing a new observable: the arc between a pair of radio sources. We shall discuss how the conditional equation involving all the parameters is written in diferent systems when the observations are performed with a two and a three-element interferometers.
mm VLBI – High resolution imaging
Authors: Bååth Lars B. , Booth Roy S.
Published: July 2016

Development of receivers and the new technique to perform global fringe fitting on Mk3 data have now made it possible to produce hybrid maps at 100 GHz.
Aperture Synthesis imaging from the Moon
Authors: Burns Jack O.
Published: July 2016

Four candidate imaging aperture synthesis concepts are described for possible emplacement on the Moon beginning in the next decade. These include an optical interferometer with 10 μarcsec resolution, a submillimeter array with 6 milliarcsec resolution, a Moon- Earth VLBI experiment, and a very low frequency interferometer in lunar orbit.
Imaging with a Homogeneous Millimeter Array
Authors: Holdaway M.A.
Published: July 2016

Presented here are the results of simulations of the effects of various errors on the imaging capabilities of the compact (72 m) configuration of a 39 element homogeneous millimeter array using the mosaic algorithm to image sources larger than the primary beam. Included in the errors investigated to date are systematic and random pointing errors, Gaussian receiver and atmospheric noise, and primary beam errors. Various methods of quantifying the quality of the reconstructed image are also discussed.
The IRAM Plateau de Bure Interferometer
Authors: Lucas Robert
Published: July 2016

We give here a brief report on the status of the IRAM Interferometer which is now in operation on Plateau de Bure.
Introduction
Authors: Takeuti M.
Published: July 2016

A historical sketch of the nonlinear theory of variable stars is outlined briefly. The main break-through came from the hydrodynamic study of stellar pulsation. From a theoretical point of view, coupling needs to be discussed more carefully. The impact of new opacities on the astrophysical problems is also discussed.
Accretion Disk Instabilities
Authors: Mineshige S.
Published: July 2016

Basic properties of accretion disk instabilities are summarized. We first explain the standard disk model by Shakura and Sunyaev. In this model, the dominant sources of viscosity are assumed to be chaotic magnetic fields and turbulence in gas flow, and the magnitude of viscosity is prescribed by so-called a model. It is then possible to build a particular disk model. In the framework of the standard model, accretion disks are stationary, but when some of the basic assumptions are relaxed, various kinds of instabilities appear. In particular, we focus on the thermal limit-cycle instability caused by partial ionization of hydrogen (and helium). We demonstrate that the disk instability model well accounts for the basic observed features of outbursts of dwarf novae and X-ray nova. We then introduce other kinds of instabilities based on the α viscosity model. They are suspected to produce time variabilities observed on a wide range of timescales in close binaries and active galactic nuclei.
Line-Profiles of F Supergiant Stars as Candidates of Proto-Planetary Nebulae
Authors: Tamura S. , Takeuti M. , Zalewski J.
Published: July 2016

In this report the results of spectroscopic observations on selected F supergiant stars as the candidates of proto-planetary nebulae (PPNs) are presented. Volk and Kwok(1989) selected nearly one hundred new candidates of PPNs based upon the scenario on the evolution of them. They summarized four classes of stars which should be the PPNs and are described in various papers. These are (i) High galactic latitude supergiants, (ii) Nonvariable OH/IR stars, (iii) Low color temperature infrared objects, and (iv) R. CrB. In order to examine the extended envelope of the PPNs we have started our project to obtain the Hα profile which should give us some clue to the structure of the envelope. We are mainly concerned with F supergiant stars. Our sample objects are mostly classified as pulsating or semiregular variables.
Period Analysis of theδScuti Star HD93044
Authors: Zong-Li Liu
Published: July 2016

HD93044 was observed electrophotometricaly on April 21, May 1, 2 and 4, 1991 at Xinglong Station of Beijing Astronomical Observatory. Combining the data with Li Zhiping’s data together and a period analysis was completed using a program which consists of a combination of Fourier transforms of prewhitened data and the multifrequency least squares of brightness residuals (LSR). Three pulsation frequencies (11.90809, 16.79553, 22.44827 cycles per day) with visual amplitudes between 0.0056 and 0.0203 mag were found. The solution fits the observations to +0.0071 mag which is equal to the mean square deviation of observations. The first frequency (11.90809 cycles per day) must be the right value of the fundamental frequency of HD93044.
Observation and Statistical Analysis of ZZ Piscium
Authors: Satoh H. , Saijo K. , Yanagita T.
Published: July 2016

To examine the non-linear oscillation and period change of white dwarf variables, ZZ Psc is discussed observationally. As a result of data reduction we found two major periods, 680 seconds and 860 seconds, but could not find chaotic behavior of ZZ Psc.
Nonradial Oscillations in Zeta Ophiuchi in 1991
Authors: Kambe E. , Ando H. , Hirata R.
Published: July 2016

The line-profile variations have been found in many early-type stars surrounding the classical β Cephei variables in the H-R diagram. The feature of the variations has not been known enough mainly because of their periods of about one day. To specify the cause of the variations, however, it is necessary to make clear their features such as the multi-periodicity, the relation between the photometric variations and the spectroscopic ones, and the cause of existence or non-existence of mode (or period) switching (Balona 1991, Smith 1991). In Be stars, the correlation of the amplitude of the variations with their emission cycle is also important (Ando 1986).
Bifurcation in Hydrodynamic Models of Stellar Pulsation
Authors: Aikawa T.
Published: July 2016

Phenomena of bifurcation in hydrodynamic stellar models of radial pulsation are reviewed. By changing control parameters of models, we can see qualitatively different pulsation behaviors in hydrodynamic models with transitions due to various types of bifurcation.

In weakly dissipative models (classical Cepheids). the bifurcation is induced by modal resonances. Two types of the modal resonances found in models are discussed: The higher-harmonic resonances of the second overtone mode in the fundamental mode pulsator and of the fourth overtone mode in the first overtone pulsator are relevant to observations. The subharmonic resonance between the fundamental and first overtone modes is confirmed in classical Cepheid models.

In strongly dissipative models (less-massive supergiant stars), the bifurcation of nonlinear pulsation is induced by the hydrodynamics of ionization zones as well as modal resonances. The sequence of the bifurcation sometimes leads to chaotic behaviors in nonlinear pulsation. The transition routes from regular to the chaotic pulsations found in models are discussed with respect to the theory of chaos in simple dynamical systems: The cascade of period-doubling bifurcation is confirmed to cause chaotic pulsation in W Virginis models. For models of higher luminosity, the tangent bifurcation is found to lead intermittent chaos.

Finally, hydrodynamic models for chaotic pulsation with small amplitudes observed in the post-AGB stars are briefly discussed.
Nonlinear RR Lyrae Models with New Livermore Opacities
Authors: Guzik J. A. , Cox A. N.
Published: July 2016

A. N. Cox recently showed that a 20% opacity decrease in the 20,000–30,000 K region as indicated by the new Livermore OPAL opacities reconciles the discrepancy between pulsation and evolution masses of double-mode RR Lyrae variables. Nonlinear hydrodynamic calculations were performed for RR Lyrae models of mass 0.75M⊙, 51L⊙, andZ= 0.0001 (Osterhoff II type) including this opacity decrease. The Stellingwerf periodic relaxation method was used to converge the models to a limit cycle, and the Floquet matrix eigenvalues calculated to search for a tendency of the fundamental mode to grow from the full-amplitude overtone solution, and the overtone mode to grow from the full-amplitude fundamental solution, thereby predicting double-mode behavior. Models ofTeff< 7000 K with the opacity decrease have positive fundamental-mode growth rates in the overtone solution, in contrast to earlier results by Hodson and Cox (1982), and models withTeff> 7000 have positive 1st overtone growth rates in the fundamental-mode solution, but double-mode behavior was not found.
On The Nature of Interstellar Organic Chemistry
Authors: Charnley Steven B.
Published: July 2016

A theory for the origin of all organic molecules observed in regions of massive and low-mass star formation, as well as in dark molecular clouds is described. On dust grains, single atom addition reactions and stability of the intermediate radicals, mechanisms similar to those believed to form the organic component of the Murchison meteorite, lead to a very limited number of mantle compositions depending upon the degree of hydrogenation. The key step in the theory is the formation of the formyl radical by H atom addition (by quantum tunnelling) to CO. Subsequent H atom additions lead to formaldehyde and methanol, as previously suggested; C, N, and O atoms can also undergo additions to HCO. For increasing hydrogenation, the mantle types include one in which there is little contribution from formyl-initiated chemistry; one in which an acetylenic chain develops through C atom additions; and others where the acetylenic chain is increasingly hydrogenated to form aldehydes and alcohols. Following evaporation of grain mantles, such as occurs in protostellar «hot cores», these molecules can form new organics, for example, by alkyl cation transfer from alcohols. In dark clouds, different mantles lead to different gas phase organics. This scenario accounts naturally for the formation of many interstellar organics for which none presently exists, predicts observable correlations between specific interstellar molecules, indicates the presence of many new organic molecules and why several others are not observed.
Catastrophic Impacts and the Drake Equation
Authors: Chyba Christopher F.
Published: July 2016

Over the past quarter century, our understanding of the impact history of the Solar System has greatly improved. This chapter considers how this increased knowledge affects our evaluation of the chances for other intelligent communicative civilizations in the Galaxy. In addition, the role of impacts is examined for insight into the long-standing debate over whether the evolution of technical intelligence is contingent upon extremely special circumstances, or might instead be a likely outcome of many different but parallel evolutionary pathways.
Organic Syntheses During the Impact of a Comet with a Gaseous Planet
Authors: Guaita Cesare , Crippa Roberto , Manzini Federico
Published: July 2016

A large amount of CO has been detected above many SL9/Jupiter impacts. This gas was never detected before the collision. So, in our opinion, CO was released from a parent compound during the collision. We identify this compound as POM (polyoxymethylene), a formaldehyde (HCHO) polymer that, when suddenly heated, reformes monomeric HCHO. At temperatures higher than 1200°K HCHO cannot exist in molecular form and the most probable result of its decomposition is the formation of CO. At lower temperatures, HCHO can react with NH3 and/or HCN to form high UV-absorbing polymeric material. In our opinion, this kind of material has also to be taken in to account to explain the complex evolution of some SL9 impacts that we observed in CCD images taken with a blue filter.
Formation, Frequency and Spacing of Habitable Planets
Authors: Lissauer Jack J.
Published: July 2016

Models of planet formation and of the orbital stability of planetary systems are described and used to discuss estimates of the abundance of habitable planets which may orbit stars within our galaxy. Modern theories of star and planet formation, which are based upon observations of the Solar System and of young stars and their environments, predict that most single stars should have rocky planets in orbit about them. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets orbiting within or near the habitable zone could either prevent terrestrial planets from forming, destroy such planets or remove them from habitable zones. The implications of the giant planets found in recent radial velocity searches for the abundances of habitable planets are discussed.
From Brown Dwarfs to Planets
Authors: Mayor Michel , Queloz Didier , Udry Stéphane , Halbwachs Jean-Louis
Published: July 2016

The burst of discoveries of planets and brown dwarfs during the past year has revealed an unexpected diversity of planetary systems. 51 Pegasi, the first extrasolar planet detected in orbit around a solar-type star appears to be the prototype of a new family of Jovian planets, the «Hot Jupiters». Though the physical mechanisms underlying the orbital decay of protoplanets are already understood, we are far from having a general view of planetary formation and of the diversity of planetary systems. If the orbital decay of protoplanets is sometimes so efficient, what is the frequency of planetary systems like ours, what is the frequency of telluric planets, what is the limit between planets and brown dwarfs?
The Lick Observatory Planet Search
Authors: Butler R. Paul , Marcy Geoffrey W.
Published: July 2016

We have constructed a precision Doppler technique with which we have detected 6 extrasolar planets to date. Doppler precision is achieved by inserting an iodine absorption cell in the telescope, providing a fiducial wavelength scale against which to measure Doppler shifts. Our current precision is 3 m s−1, which corresponds to one part in one hundred million in wavelength, or 1/1000 th of a pixel on the CCD detector. As of 1996 August, our survey of 120 stars has revealed six stars that show velocity variations consistent with Jupiter-mass companions in Keplerian orbits. These objects span a greater range of orbital radii and eccentricity than the planets in our own solar system. Three of these objects are «51 Peg-type» planets with circular orbits having radii 0.15 AU or less. The other three objects have masses between 1.7 and 6.5 MJUP, eccentricities between 0.01 and 0.6, and semi-major axes between 0.4 and 2.1 AU. We have not found any objects having masses between 10 and 80 MJUP, the domain usually associated with brown dwarfs. These six new companions represent a new population of objects having extremely low masses, similar to that of Jupiter. We have begun a survey of an additional 400 stars using the Keck 10-m telescope, which will allow the detection of Neptune-mass planets.
Prebiotic-Related Chemistry in the Present Outer Solar System
Authors: Raulin François , Coll Patrice , Gazeau Marie-Claire , Bruston Paul
Published: July 2016

There are numerous places in the outer solar system where the formation of the starting ingredients which are involved in the early terrestrial prebiotic chemistry is currently going on. Organic chemistry is largely present in the outer planets, particularly in Titan. Titan has a dense atmosphere, mainly composed of N2and CH4and very rich in organic compounds, both in gas and aerosol phases. Because of the low temperature of Titan’s environment, liquid water is currently absent from the satellite and compounds of low stability at the (Earth) laboratory temperature, and very reactive, are still or may be present. However, Titan study should provide information on prebiotic chemistry – at least prebiotic chemistry in absence of liquid water. This quasi-planet thus appears as a natural laboratory enabling to study prebiotic evolution toward complex organic systems in a planetary environment over a long time scale. A detailed study of such a natural prebiotic laboratory is precisely one of the main objectives of the Cassini-Huygens mission. With the sending of the Cassini orbiter around Saturn and the Huygens probe in the atmosphere of Titan, this mission, due to be launched in October 1997, for a Saturn arrival in 2004, will offer a unique opportunity to study in detail extra-terrestrial prebiotic processes, together with important implications in the field of bioastronomy and the origins of life.
Molecular Evolution of Aminoacyl tRNA Synthetases and Origin of Universal Genetic Code
Authors: Ishigami Masahiro , Ihara Hideshi , Shinoda Hiroyuki
Published: July 2016

It is thought that living things first appeared on the primitive earth 35 hundred million years ago. At that time, a primitive protein synthesis mechanism was thought to have been established, a genetic code system evolved, and a universal genetic code system developed. Aminoacyl tRNA synthetase must have evolved with the genetic code system. The aim of the present study is to clarify the evolution of aminoacyl tRNA synthetase and the process and era of the establishment of the universal genetic code system.
Can Spores Survive a Million Years in the Radiation in Outer Space? Part I: Protection against Photons above 0.5 KEV
Authors: Mileikowsky Curt
Published: July 2016

It is conceivable that microorganisms could be transported over long distances in space inside natural «vehicles» such as molecular clouds, comets or meteors. To traverse a distance of 30 ly at speeds of 10 km/s (to another planetary system) would then take a million years. Due to the intense radiation in space by both photons and cosmic ray charged particles, microorganisms, including the most radiation-resistant spores known, need radiation protection in order to survive the millionyear dormancy. From the absolute energy distribution in the interstellar medium of the photon radiation of energies from 0.5 keV and up – known by measurement – the dose rates, in Megarads per million years (Mrad/My), have been calculated for spores of volume (1μm3which are assumed to have escaped out into interstellar space. Taking into consideration the energy dependence of photon attenuation in organic material, of absorption restriction in small bodies and of attenuation in the shielding material, these calculations have been done for unprotected spores, for spores in the central regions of seven different molecular clouds characterized by radial column densities from 0.01 to 1.3 g/cm2, and for spores inside porous meteors and in comets. Unprotected spores get almost 1000 Mrad/My from photons over 0.5 keV. Dose reduction by a factor of 1000, necessary for survival against photon radiation can be achieved by: 1) clouds with radial column densities ≥ 0.5 g/cm2; 2) meteors of radius ≥ 2-3 mm; 3) comet ice of radius > 5 mm. Cosmic ray charged particles are not treated in this Part I paper but will be the subject of a forthcomimg Part II paper.
A Galactic Center Search for Extraterrestrial Intelligent Signals
Authors: Sullivan Woodruff T. , Wellington Kelvin J. , Shostak G. Seth , Backus Peter R. , Cordes James M.
Published: July 2016

In June 1995 we used the Parkes 64-m radio telescope to search for narrowband or pulsing signals of extraterrestrial intelligent (ETI) origin from the direction of the galactic center. This strategy was chosen so as to maximize the number of possibly detectable ETI signals within the beam, assuming that they are associated with stars and that their luminosity function is such that they can be detected at a distance of at least a few kiloparsecs. A total of 190 1.2–minute integrations were taken in a region of size 5.0° × 0.6° centered on the galactic center. Many positions in this region were observed 2 or 3 times in order to allow for the possibility of strong interstellar scintillations arising in any ETI signal. The spectrum analyzer was that of Project Phoenix, configured such that it covered both circular polarizations over a 20-MHz bandwidth centered on 1425.0 MHz. This bandwidth was divided into 28.7 million channels with separations of 0.64 Hz. The signal analysis system searched both for slow pulses (periods of at least 2 sec) and narrowband signals with drifts from 0 to 1 Hz/sec. A second antenna located 200 km away was used for immediate follow-up on all candidate signals. No signals of ETI origin were found. A later search of smoothed spectra with 640 Hz resolution also revealed no new features not attributable to manmade interference.
Studies of Radio Frequency Interference at Parkes Observatory
Authors: Backus Peter R. , LaRoque Sam , Tarter Jill C. , Dreher John , Cullers Kent , Patrick Alan , Heiligman Gary
Published: July 2016

From February through early June, 1995, Project Phoenix conducted SETI observations of 209 stars over the frequency range from 1195 to 3005 MHz. A byproduct of this search is a unique data set suitable for studying the Radio Frequency Interference (RFI) environment at the Parkes 64-m telescope in New South Wales, Australia. RFI is an increasing problem for SETI and other radio astronomy observations conducted outside of the «protected» frequency bands. The data analyzed for this paper were «mean baseline» spectra in Left and Right Circular Polarization (LCP, RCP), integrated for either 138 or 276 s, covering a 10 MHz bandwidth with 15,552 channels at a resolution of 643 Hz. Channels were identified as contaminated by RFI when the power in the channel exceeded the mean noise by 3%. The «spectral occupancy», the fraction of time RFI was seen, was determined for each channel. The RFI occupancy for LCP and RCP are distinctly different. Approximately 100 MHz of the spectrum was too heavily contaminated for SETI observations.
Eclipse Mapping of Non-Radial Pulsation in Binary Stars
Authors: Nuspl J. , Bíró I.B.
Published: July 2016

We review a slightly modified method of eclipse mapping, applicable to mode identification in eclipsing binaries containing a pulsating component. The observed light curve is used by the procedure without removing from it the badly determined eclipsing part.
Preliminary Results of a Search for Variable Stars in the Globular Cluster M 13
Authors: Kopacki Grzegorz , Kołaczkowski Zbigniew , Pigulski Andrzej
Published: July 2016

Results of a search for variable stars in the globular cluster M 13 are presented. Comments on the variability of all observed variable or suspected variable stars are given. Five new RR Lyrae stars and one SX Phoenicis star are identified.
AGAPEROS Variables in the LMC
Authors: Schultheis M. , Lebzelter T. , Melchior A.L.
Published: July 2016

In this work, we present preliminary results based on an LMC Bar sample (AGAPEROS) of ⷍ 400 variable stars combined with near-Infared photometry (DENIS). About 50% of our objects are semiregular Variables (SRVs) while 20% are regular Variables with a period range from 30d up to 600d. A second period is present in ∼ 40% of the SRVs. We find a large fraction of regular variables with P < 100d which could be SRVs undergoing a phase of periodic variability. The Period-Colour relation (log P versus I – J), unstudied so far on the LMC, differs from the one found in the Galactic bulge: an effect of metallicity?
A Comparison of the Anelastic and Subseismic Approximations for Low-Frequency Stellar Oscillations: an Application to Rapidly Rotating Stars
Authors: Dintrans B. , Rieutord M.
Published: July 2016

After showing that the anelastic approximation is better than the subseismic one to filter out acoustic waves when studying low-frequency stellar oscillations, we compute gravito-inertial modes of a typical γ Doradus star using this approximation. We show that eigenmodes can be regular or singular, according to the possible focusing towards attractors of the underlying characteristics. Consequences on the oscillations spectrum are then discussed.
An Observational Overview of Pulsations in β Cep Stars and Slowly Pulsating B Stars
Authors: De Cat P.
Published: July 2016

The observational characteristics of the p-modes of β Cep stars are compared to those of the g-modes of slowly pulsating B stars (SPBs). For the β Cep stars, previous reviews based on photometric surveys are updated with recent results from our high-resolution spectroscopic surveys. For the slowly pulsating B stars, it is the first time a broad observational overview can be given.
Do Temperature Variations at the Surface of a Hot Non-Radial Pulsator Change Significantly the Line-Profile Variations?
Authors: De Ridder J. , Aerts C. , Dupret M.-A. , Neuforge C.
Published: July 2016

We present simulations of line-profile variations of Silicon lines in slowly-rotating non-radially pulsating β Cephei stars and SPB stars. Our goal is to examine how sensitive Si lines are to the non-adiabatic temperature variations at the surface of the star. We find that for realistic amplitudes of the velocity field, and for realistic amplitudes and phase differences for the non-adiabatic temperature and gravity variations, the Silicon lines variations are very little affected.
Spectroscopic Monitoring of 10 Northern SPB Candidates
Authors: Mathias P. , Le Contel J.-M. , Aerts C. , De Cat P. , Van Winckel H. , Robbrecht E. , Briquet M. , Cuypers J.
Published: July 2016

We present the results of 1.5 years of Spectroscopic monitoring of 10 bright northern SPB candidates discovered from the Hipparcos mission. All stars have line-profile variations and are periodic, with periods corresponding to high-order g-modes. We therefore confirm them to be new SPBs.
Line Profile and Photometric Variations of the Be Star η Cen
Authors: Levenhagen R. , Leister N. , Janot-Pacheco E. , Zorec J. , Hubert A. , Floquet M.
Published: July 2016

We review the current status of our monitoring project on Be stars. Line profile variations in Helλ667.8 nm were detected in the Be star η Cen, by means of high resolution and S/N Spectroscopic observations. They were interpreted in terms of nonradial pulsations (NRP). The fundamental parameters of η Cen obtained from BCD spectrophotometric data and interpreted using models of rapidly rotating stars, have been used to estimate the stellar rotational frequency.
Chemical Inhomogeneities and Pulsation
Authors: Turcotte S.
Published: July 2016

Major improvements in models of chemically peculiar stars have been achieved in the past few years. With these new models it has been possible to test quantitatively some of the processes involved in the formation of abundance anomalies and their effect on stellar structure. The models of metallic A (Am) stars have shown that a much deeper mixing has to be present to account for observed abundance anomalies. This has implications on their variability, which these models also reproduce qualitatively. These models also have implications for other chemically inhomogeneous stars such as HgMn B stars which are not known to be variable and λ Boötis stars which can be. The study of the variability of chemically inhomogeneous stars can provide unique information on the dynamic processes occurring in many types of stars in addition to modeling of the evolution of their surface composition.
Seismology of δ Scuti Stars: Problems and Prospects
Authors: Goupil M.J. , Talon S.
Published: July 2016

The current state of seismology of δ Scuti stars is reviewed with particular emphasis on seismic signatures of the extension of their mixed central region and of rotation. We refer also to Goupil et al. (2000) and more generally to Breger & Montgomery (2000) for more details.

δ Scuti stars are population I pulsating stars with spectral type A-early F, located on or near the main sequence. They are found in the lower part of the classical instability strip in a HR diagram (Fig. 1). Masses range from ∼ 1.5M⊙ to ∼ 2.5M⊙ and δ Scuti stars are either in a stage of H-core or H-shell burning. On the main sequence, the high temperature sensitivity of the dominant CNO cycle causes a large convective core to develop, which later shrinks leaving behind a gradient ∇μ in the mean molecular weight.
δ Scuti Variables with Periods Longer than 0.25 Days
Authors: Rodríguez E. , Breger M.
Published: July 2016

Variables listed as δ Scuti-type pulsators in the R00 catalogue (Rodriguez et al., 2000) with periods longer than 0.d25 are examined on a star-by-star basis, in order to discriminate their true nature (δ Scuti, RR Lyr or γ Dor-type). From this study, it seems that three stars (DH Peg, UY Cam and YZ Cap) are RR Lyr pulsators rather than δ Scuti variables. Moreover, two variables (AD Ari and DE Oct) seem to be γ Dor variables with the shortest periods known to date (0.d2699 and 0.d2778, respectively).
Amplitude and Period Changes in the δ Sct Star AN Lyncis
Authors: Zhou A.-Y.
Published: July 2016

We report a study of time-dependent behaviour of the light variations in the δ Set star AN Lyn, based on an analysis of new time-series CCD observations and existing data. The amplitude of the main frequency increased from 1994 to 2000 at a rate of 0.006 mmag/yr. The light variation of AN Lyn can be explained currently by amplitude variability mixed with multiperiodic pulsation. With the extended data base, results on XX Cyg are also reported.
A Review of the Pulsating sdB Stars
Authors: Kilkenny David
Published: July 2016

A brief overview of the relatively new field of pulsating sdB stars is presented together with some recent observational and theoretical developments. A list of known pulsators is included.
Radial Velocities for the Pulsating Subdwarf B Star PG 1605+072
Authors: Woolf V.M. , Jeffery C.S. , Pollacco D.L.
Published: July 2016

We have performed high-speed spectroscopy of the pulsating subdwarf B star PG 1605+072. Its radial velocity variations have frequencies similar to those reported from photometric observations. Peak amplitude ratios are different, probably as a result of power shifting between modes over time. Line-shape variations have also been detected.
Nonradial Pulsations in Classical Pulsators
Authors: Kovács G.
Published: July 2016

Recent analyses of photometric data on globular clusters and galaxies enabled us to study more closely the long-periodic amplitude/phase modulation (Blazhko effect) in classical variables. In the frequency spectra of these stars we see either a doublet or an equally-spaced triplet with a very small frequency separation close to the main component. None of the available theoretical models are able to explain this behavior without invoking some form of nonradial pulsation. In this review we describe the observational status of the Blazhko variables, and discuss the limits of the applicability of the current models to these stars.
Synthetic Nonlinear RR Lyrae Instability Strips
Authors: Szabó R. , Csubry Z. , Kolláth Z. , Buchler J.R.
Published: July 2016

A recently recognized problem is revisited, namely the discrepancy between the structure of the theoretical and the empirical, observationally derived RR Lyrae instability strips. The essence of the discrepancy is that the slope of the empirical fundamental-mode blue edge is much less steep than its theoretical counterpart. The issue was investigated by means of stellar evolution and mode selection captured by nonlinear models.
The Blazhko Effect Unravelled?
Authors: Kolenberg K. , Aerts C. , Chadid M. , Gillet D.
Published: July 2016

A detailed frequency analysis on ELODIE observations of the Blazhko star RR Lyrae (Chadid et al., 1999) clearly revealed the importance of non-linear effects upon the radial fundamental mode (with frequency fP), and a multiplet structure with a separation equal to the Blazhko frequency (f/B) around the main frequency and its harmonics. These results provided strong evidence for the presence of non-radial modes in the star. The identification of these non-radial modes is the following step in our work.
Time-Resolved Spectral Analysis of the Pulsating Helium Star V 652 Her
Authors: Jeffery C.S. , Woolf V.M. , Pollacco D.L.
Published: July 2016

We present a summary of a new time-dependent Spectroscopic analysis of the pulsating helium star V652 Her. The instantaneous properties of the star (effective temperature, surface gravity, radial displacement, etc.) are evaluated throughout the pulsation cycle. The data are used to establish measurements of the mean stellar radius and mass more accurately than hitherto. The first direct evidence of a supersonic shock at minimum radius is also obtained.
Solar-Like Oscillations in β Hydri: Evidence for Short-Lived High-Amplitude Oscillations
Authors: Bedding T.R. , Kjeldsen H. , Baldry I.K. , Bouchy F. , Butler R.P. , Carrier F. , Kienzle F. , Marcy G.W. , O’Toole S.J. , Tinney C.G.
Published: July 2016

Velocity measurements of the G2 subgiant β Hyi with both UCLES and CORALIE show a clear excess of power centred at 1.0 mHz. In the UCLES data we find evidence for a short-lived, high-amplitude oscillation event. If confirmed as a feature of subgiants, such ‘starquakes’ would make it harder to measure accurate mode frequencies and perform asteroseismology.
Asteroseismology with CORALIE: Results on Procyon and β Hydri
Authors: Carrier F. , Bouchy F. , Kienzle F. , Blecha A.
Published: July 2016

The spectrograph CORALIE reaches the radial velocity precision needed for an asteroseismological program on bright solar-like stars. We present here two results obtained with this instrument on the stars Procyon and β Hydri. A third campaign, on α Cen A, is presented independently in these proceedings by Carrier et al.
Confirmation of Solar-Like Oscillations in η Bootis
Authors: Kjeldsen H. , Bedding T.R. , Baldry I.K. , Frandsen S. , Bruntt H. , Grundahl F. , Lang K. , Butler R.P. , Fischer D.A. , Marcy G.W. , Misch A. , Vogt S.S.
Published: July 2016

Kjeldsen et al. (1995) detected excess power in the GO subgiant η Boo from measurements of Balmer-line equivalent widths. The excess was at the expected level, and these authors were able to extract frequency separations and individual frequencies which agreed well with theoretical models (Christensen-Dalsgaard et al., 1995; Guenther & Demarque, 1996). A more detailed discussion of theoretical models for η Bootis was given by Di Mauro & Christensen-Dalsgaard (2001).

Kjeldsen et al. (1995) estimated the average amplitude of the strongest modes to be 7 times solar, corresponding to 1.6 m/s in velocity. 13 individual oscillation modes were identified consistent with a large frequency separation of 40.3 μHz. We note, however, that a search for velocity oscillations in this star by Brown et al. (1997) failed to detect a signal, setting limits at a level below that expected on the basis of the Kjeldsen et al. result.

In this paper we report further observations made in 1998. We observed this star in Balmer-line equivalent width with the 2.5-m Nordic Optical Telescope and in velocity with the 24-inch Lick CAT.
Playing Music with Magnetic Fields
Authors: Foullon C.
Published: July 2016

Through an increase in magnetic field strength, solar magnetic fields in the atmosphere or subsurface of the Sun can explain the frequency shifts observed on the time scale of the solar activity cycle. A separate study of the contribution of internal magnetic layers clarifies the relative importance of these effects. However, at the base of the convection zone, the cyclical change of orientation of magnetic field lines has a larger effect on global mode frequencies than an increase in field strength alone.
Driving g-Mode Pulsation in γ Doradus Variables
Authors: Wu Yanqin
Published: July 2016

Surface convection zones in γ Doradus variables (early F-type g-mode pulsators) can drive pulsation via the ‘convective driving’ mechanism. This mechanism is first proposed and studied in the context of ZZ Cetis (hydrogen-envelope white dwarfs with g-mode pulsations) by Brickhill (1991) and Goldreich & Wu (1999). We implement and develop the convective driving theory to suit the environments on γ Dors, in particular, stronger super-adiabatic gradient and weaker convective flux than those in white dwarfs. This results in a spectrum of gravity-modes being excited in the observed temperature range. However, there are more remaining problems than those that are solved.
On the Equatorial Mass-Loss Rate of Be Stars
Authors: Okazaki A.T.
Published: July 2016

We numerically study the formation process of equatorial disks around isolated Be stars, using an SPH code. We find that the viscous decretion disk model naturally explains the observed disk formation episode of X Per, giving the equatorial mass-loss rate of several ×10−9 (ρ0/10−10 g cm−3) M⊙ yr−1, where ρ0 is the base density of the disk.
Dust and Wind Formation in Low-Metallicity AGB-Stars
Authors: Helling Ch. , Arndt T. , Sedlmayr E.
Published: July 2016

The formation of dust and wind in luminous AGB-stars has been studied so far mainly for solar metallicities. Here, the impact of the dust component on the driving mechanism of the massive outflows and the non-linear coupling to hydro/-thermodynamics leads to the creation of dust-induced shock waves, the occurrence of onion-like spatial dust distributions around the star, time-dependent dust-size distributions, multi-periodicity, and the onset of a super-wind phase (see Sedlmayr, these proceedings). The question remains whether these phenomena appear also in metal-deficient models of AGB-stars like those in the Large Magellanic Cloud (LMC).
Insights from Pulsating Nova Envelopes
Authors: Schenker K.
Published: July 2016

Based on a linear and non-linear study of radial pulsations in the envelopes of classical novae (Schenker, 1999), I discuss the results both from the point of view of pulsation theory as well as their consequences for current nova models. Starting from initially static envelope structures at various stages during the decline of a nova outburst, strong ‘running-wave’ instabilities have been found that rapidly grow into shocks. Improved analytical concepts give a new direction to the interpretation of such highly non-adiabatic radial pulsations. For direct observational confirmation, a search for short period variability in the UV and soft X-ray is suggested during the very late decline phase. Speculative consequences for mass-loss scenarios in novae due to these instabilities will need some more work in the future.
Quasi-Periodic Oscillations in Accretion Discs
Authors: Warner Brian , Woudt Patrick A.
Published: July 2016

Quasi-Periodic Oscillations (QPOs) in Cataclysmic Variable stars (CVs) with periods in the range 100 – 2000 s have been known for 25 years (see Chapter 8 of Warner, 1995a). We distinguish here between QPOs and Dwarf Nova Oscillations (DNOs) – the latter being of shorter period (5 – 50 s) and greater coherence. QPOs appear as brightness modulations and typically have quite short coherence lengths (a few cycles).

QPOs are largely associated with discs transferring mass at a high rate – i.e., dwarf novae during outburst or nova-like variables; but the QPOs are not always present and many systems have not shown QPOs at all.

Generally it is thought that QPOs result from non-radial oscillations of the accretion discs surrounding the white dwarf component in CVs (Carroll et al., 1985; Collins et al., 2000). They could, e.g., be quite coherent oscillations of individual annuli in a disc, each with a different period. Alternatively, a particular oscillation mode may be excited for only a few cycles and then be re-excited at an arbitrary phase. Most theoretical proposals have sought to make the QPOs self-luminous pulsations of the disc, in analogy with the kappa or epsilon processes of stellar pulsation.
Seismic Inversions for White Dwarf Stars
Authors: Takata M. , Montgomery M.H.
Published: July 2016

Inversion methods have been used successfully for the Sun. The stars with the next richest set of observed frequencies are the white dwarfs. We consider here the viability of numerical inversions for these stars. We find that, while the number of presently observed modes in the white dwarf GD 358 is too small for structural inversions, such inversions would be possible if the frequencies of all modes with 1 ≤ l ≤ 3 were observed. This is possible for space observations by e.g. Eddington.