bluuebunny/crossref_metadata_2025_split huggingface dataset:
Astrometry of SiO Masers: First detections of circumstellar SiO maser emission at λ = 7 mm using three European VLBI stations
Authors: Colomer F. , Graham D. , Krichbaum T. , Rönnäng B.O. , de Vicente P. , Barcia A. , Booth R.S. , Witzel A. , Gómez-González J. , Baudry A. 
Published: July 2016

The positions of circumstellar molecular masers relative to each other, to the central star, and to the compact extragalactic sources are of astrophysical and astrometrical interest. The SiO masers at λ = 7 mm are especially interesting as the maser spots are located very close to the photosphere of the star. For astrometry we would like to see a proper distribution of the maser spots and several epochs of observations in order to estimate the position of the central star and eventual motions of the spots.The optical position of this star can be determined with ground-based astrometric facilities, and many of the stars showing SiO emission are in theHipparcoscatalogue. A link between the Optical and Radio Reference Frames is achieved in a second step relating the maser spot positions to the Extragalactic Reference Frame (EGRF) established with VLBI (Baudryet al., 1984).
Microwave Background interferometry in Cambridge
Authors: Jones Michael E. 
Published: July 2016

AbstractInterferometric methods of studying the Cosmic Microwave Background (CMB) have some distinct advantages over the switched-beam techniques which have mostly been used. However, most existing interferometers are not well suited to CMB observations, for a variety of reasons. These include poor temperature sensitivity due to a low filling factor, and systematic effects which limit the maximum possible integration time. A new instrument, the Ryle Telescope, has been developed in Cambridge which has a high temperature sensitivity (120 μK in 12 h) and the ability to integrate for several hundred hours on the same field. It will be used to study the CMB on angular scales of a few arcminutes, with particular emphasis on the Sunyaev-Zel’dovich effect. A second instrument to study the CMB on angular scales of tens of arcminutes, the Cosmic Anisotropy Telescope (CAT), is also being developed.
One Zone Modeling of Irregular Variability of Stellar Convective Envelope
Authors: Unno W. , Xiong D.-R. 
Published: July 2016

AbstractOne zone modeling of the irregular variability of red super-giants is intended with regard to the nonlinear coupling of finite amplitude pulsation with convection. The nonlocal mixing length is employed for the evaluation of the convective flux, the turbulent pressure and the turbulent power of temperature fluctuations. The radial pulsation and the Boussinesq convection are assumed for simplicity. The one zone is defined as the layer having the entropy maximum and the minimum at the bottom and at the top, respectively. The quasi-adiabatic approximation is consistent with this definition in fixing the zone to the same mass range. The spatial derivatives are evaluated under the assumption of homologous changes with the equilibrium homologous parameters. Then, a set of 6 simultaneous first order nonlinear ordinary differential equations are obtained as the one zone representation of the irregular variability of the convective envelope.
Variability of X-Ray Emission from Cen X-3 Observed with Ginga
Authors: Kanetake R. , Takeshima T. , Makishima K. , Takeuti M. 
Published: July 2016

Simplified stellar models like as one-zone models can be oscillated in chaotic state (Saitou et al. 1989). It is natural to consider that the irregular variations of Galactic X-ray sources might be caused from nonlinear oscillation of accretion disks or related flow. We studied the variability of Cen X-3 for applying the nonlinear theory to it.The X-ray of Cen X-3 observed with Ginga from 22nd to 24th of March, 1989 are analyzed. Since Large Area Counters (LAC) of which the area of detector is 4,000 cm2 are used. The data used here is obtained the range of 1,000 sec from 14 h 25 m on March 23rd with the time resolution of 0.25 sec. The energy bands are 1.7~4.6 keV, 4.6~9.3 keV, 9.3~19 keV, and 19~37 keV, respectively.Takeshima et al. (1991) show that Cen X-3 is at the high state, when the X-ray from the source is not veiled by non-ionized matter (Schreier et al. 1976). So that we ignore the effect of circumstellar matter around the source.
Predicting Variable Star Light Curves
Authors: Serre T. 
Published: July 2016

AbstractI present a new method to test determinism, in particular the nonlinear behavior, in observed time series of pulsating stars, based on a recent prediction method which exploits the dynamical system theory. A method for filling gaps in data has thereby been constructed. Estimated bounds to the necessary embedding dimension can be obtained and chaotic divergences can be estimated.
The Onset of Quasi-Periodic Variations in Be Stars
Authors: Kogure T. , Mon M. , Suzuki M. 
Published: July 2016

We present some evidence of the quasi-periodic long-term variations (QPLV) in the violet-to-red ratio of double-peaked emission lines (V/R variation) and/or in the radial velocities of shell absorption lines for some Be stars. Although the V/R variations are rather prevailing phenomena among Be stars, the QPLV is remarkable by the following characteristics:
(1)The QPLV appears as a sudden onset of repeated V/R variations after a long (10 years), almost stable period, and it persists for a few or several periods in ten or more years.(2)The period and amplitude of V/R variations change from cycle to cycle and from star to star. The variations of radial velocities (RV) of shell absorption lines are usually nearly parallel with the V/R variations.(3)The QPLV appears usually in early type Be stars with large rotational velocities, regardless whether the stars are normal Be or shell stars, and whether they are close-binaries or single stars.
Some Insights into Stellar Structure from Nonlinear Pulsations
Authors: Goupil M. J. 
Published: July 2016

Efficient tools of investigation of stellar pulsation are the integral relations which link oscillation frequencies to the static structure of stellar models, as provided by the linear theory of pulsation (for a review, see Saio, this conference).Similarly, oscillation amplitudes and phases, which arise from nonlinear processes, can be related to the stellar structure by means of amplitude equation formalisms (for a review, see Buchler, this conference).For the simple case of a monoperiodic oscillation, involving only one unstable marginal mode, such a formalism shows that the (limit cycle) radius variations, at time t and mass level m, can be approximated, up to second order of approximation, (Buchler and Goupil, 1984; Buchler and Kovàca, 1986) by:where A, R, Ω, ĸ, £r(m) respectively are the amplitude, stellar radius, linear nonadiabatic frequency, growth rate, radius eigenfunction. Second order nonlinearities generated first harmonic oscillations and change in equilibrium radius about which the star oscillates, as represented by the last two terms in (la) respectively. Analogous expressions are obtained for velocity and light variations, that can be compared with observations.
Hydrodynamics and Multi-Level Non-LTE Radiative Transfer in Pulsating Atmospheres: Cepheids
Authors: Sasselov D. D. 
Published: July 2016

The atmospheres of classical Cepheids cannot be represented adequately by a sequence of hydrostatic equilibrium atmospheric models (see Sasselov and Lester 1990 and references therein). Observational evidence for shocks is also available at least since Kraft (1956). Both the disequilibrium and the non-linear phenomena affect the emergent spectra and spectral line profiles of the Cepheids. In the lower amplitude variables the effects may be subtle, yet still lead to significant systematic discrepancies.We have developed the code HERMES for time-dependent treatment of hydrodynamics and non-LTE radiative transfer in the atmospheres of classical Cepheids with periods shorter than 12 days. Our approach is applicable to stars in which the formed shock waves do not dominate the energy balance of the atmosphere. Consecutive detailed calculations are performed for several multi-level model atoms, including H, Ca II, Mg II, He I and II. We use a 1-D explicit conservative upwind monotonic second-order (in time and space) Godunov-type Lagrangian hydrodynamic scheme. Being a characteristics based scheme it allows natural handling of boundary conditions. The scheme is stable and without artificial dissipation, a crucial necessity for physically meaningful radiative transfer solutions (see Roe 1990, Sasselov and Raga 1991 for more details).
New Opacities and First Overtone Mode Cepheids
Authors: Antonello E. 
Published: July 2016

AbstractSome results of linear adiabatic and nonlinear pulsation models of first overtone mode Cepheids are discussed. New and augmented opacities and a nonstandard mass-luminosity relation have been taken into account. The models indicate the possible importance of the resonance P1/P4 = 2 near P1 = 3 days. The resonance could explain the observed characteristics of the light curve shape of first overtone mode Cepheids.
Coupled-Oscillators
Authors: Tanaka Y. 
Published: July 2016

AbstractModal coupling oscillation models for the stellar radial pulsation and coupled-oscillators are reviewed. Coupled-oscillators with the second-order and third-order terms seemed to behave non-systematically. Using the equation by Schwarzschild and Savedoff (1949) with the dissipation term of van del Pol’s type which is third-order, we demonstrate the effect of each term. The effects can be understood by the terms of the nonlinear dynamics, which is recently developing, that is. phase-locking, quasi-periodicity, period doubling, and chaos. As the problem of stellar pulsation, especially of double-mode cepheids on the period-ratio, we examine the dependence on the stellar structure from which the coupling constants in the second-order terms are derived. Eigen functions for adiabatic pulsations had been used for the calculation of the constants. It is noted that only two set of the constants are available, that is, for the polytrope model with n = 3 and a cepheid model without convection. Some examples of nonlinear dynamical effects will be shown.It is shown that if the constants were suitable values, the period-ratio of double-mode cepheids is probably realized. The possibility is briefly suggested.
Pulsational Instability of Accretion Disks around Compact Objects
Authors: Okuda T. , Mineshige S. 
Published: July 2016

AbstractLinear analysis shows that radial oscillations in accretion disks around compact object are overstable to axisymmetric perturbation under a variety of conditions. Furthermore, numerical simulations confirm that the radial oscillations induce quasi-periodic modulations of the disk luminosity. The disk oscillation model may be responsible for quasi-periodic oscillations (QPOs) observed in low mass X-ray binaries (LMXBs), cataclysmic variables (CVs), and other compact objects.
Examples of Comet-Like Spectra among β Pic-Like Stars
Authors: Butner Harold M. , Walker Helen J. , Wooden Diane H. , Witteborn Fred C. 
Published: July 2016

AbstractTo assess the physical conditions in our early solar system, we have to study the disks around other stars.βPic is a main sequence star surrounded by a large dust disk,βPic’s mid-infrared spectrum bears a striking resemblance to the silicate emission seen in some cometary spectra. We have selected a sample of main-sequence stars with similar IRAS properties to those ofβPic and undertaken a systematic survey of their physical properties. We obtained mid-infrared spectra covering the range 8 to 13μm at a resolution of 200 in June 1995. We report on the wide variety of silicate emission features we see and compare to the spectra reported for many different interstellar and interplanetary sources. Even among our small sample of stars, we find examples of silicate emission features that bear a striking similarity to those seen in the spectra of some comets like P/Halley and P/Bradfield 1987. These spectra also resemble the laboratory spectra of Interplanetary Dust Particles (IDPs).
Asteroid and Comet Impact Speeds upon Mars: Significance for Panspermia and the Supply of Organics
Authors: Steel Duncan 
Published: July 2016

AbstractWhilst lithopanspermia depends upon massive impacts occurring at a speed above some limit, the intact delivery of organic chemicals or other volatiles to a planet requires the impact speed to be below some other limit such that a significant fraction of that material escapes destruction. Thus the two opposite ends of the impact speed distributions are the regions of interest in the bioastronomical context, whereas much modelling work on impacts delivers, or makes use of, only the mean speed. Here the probability distributions of impact speeds upon Mars are calculated for (i) the orbital distribution of known asteroids; and (ii) the expected distribution of near-parabolic cometary orbits. It is found that cometary impacts are far more likely to eject rocks from Mars (over 99 percent of the cometary impacts are at speeds above 20 km/sec, but at most 5 percent of the asteroidal impacts); paradoxically, the objects impacting at speeds low enough to make organic/volatile survival possible (the asteroids) are those which are depleted in such species.
Astronomical Influences on Biomagnetic Activity Some 120 MA ago: the Potential for Estimating the Evolution of Ancient Planetary Orbits within the Solar System
Authors: Tarling Donald H. , D’argenio Bruno , Iorio Marina 
Published: July 2016

AbstractStudies of the magnetic properties of sedimentary rocks provide a record of biological activity in the geological past of the Earth. There is increasing evidence that the rate of biological activity reflects, in part, the direct and indirect influence of the Earth’s orbit around the Sun. These orbital changes also influence the strength and direction of the geomagnetic field, showing that orbital changes directly affect the processes generating the geomagnetic field. Therefore the presence of these effects means that past changes in the Earth’s orbit and the rate of rotation of the Earth can be investigated from such geological and geophysical records.
On the Ability of Synchronously Rotating Planets to Support Atmospheres
Authors: Joshi Manoj M. , Haberle Robert M. 
Published: July 2016

AbstractPlanets within the habitable zones of M stars are likely to be synchronous rotators, i.e., one side is permanently illuminated while the other side is in perpetual darkness. For such planets to be habitable, horizontal atmospheric motions must be capable of transporting enough heat from the day side to the night side to prevent the atmosphere from freezing out. Simple calculations have shown that the equivalent of approximately 150 mb of CO2is required to prevent atmospheric condensation on the dark side. We now use a 3-dimensional global circulation model in order to better assess the ability of these planets to sustain an atmosphere. The results of this work show that for an earth-sized planet, 100 mb of CO2is required to support an atmosphere, while 1-2 bars are sufficient to allow liquid water everywhere. Planetary systems associated with M stars should therefore not be ruled out in the search for life in the universe.
The Chemical Origin of Life
Authors: de Duve Christian 
Published: July 2016

AbstractFifty years ago, the problem of the origin of life was largely inaccessible to scientific research. Not only was almost nothing known of the conditions that surrounded the appearance of life on Earth, but there was so little understanding of life itself that the problem could not even be defined in concrete terms. The situation is very different today. Astronomical observations, geochemical findings, and laboratory investigations have illuminated the problem with much relevant information. Especially, the basic mechanisms of life are now understood in considerable detail. We know what to look for. Some important notions that have emerged in this way will be briefly surveyed in this essay, which summarizes views presented in two recent books (de Duve, 1991, 1995).
Did A Precellular RNA World ever Exist?
Authors: Rizzotti Martino 
Published: July 2016

AbstractThe so-called «RNA world» is the most fashionable hypothesis on the origin of the biosphere on the Earth. It states that cells derived from aggregates made of RNA in contact with the superficial waters. Its presumed pieces of evidence are drawn either from simulation experiments or from RNA molecules of the present-day organisms. However, both kinds of evidence are better explained by alternative hypotheses.
Surmising Cognitive Universals for Extraterrestrial Intelligences
Authors: Narens Louis 
Published: July 2016

AbstractCognitive universals are concepts that our civilization and technologically advanced extraterrestrial civilizations can easily interpret. The universality of certain mathematically and perceptually based concepts are discussed. It is argued that continuously based concepts are more fertile ground for surmising cognitive universals than discretely based ones, and in particular, one should be suspicious of the use of inductively based numerical concepts, including the totality of natural numbers. Ideas about intuitive evolutionary theory, physical and perceptual invariance, and the efficient processing of information are linked to provide a framework for searching for cognitive universals.
Millions and Billions: The Meta and Beta Searches at Harvard
Authors: Leigh Darren , Horowitz Paul 
Published: July 2016

AbstractThe META and BETA searches for microwave carriers have now completed a decade of observations of the northern sky, using the 26-meter radiotelescope at Agassiz Station. META's results set limits on the prevalence of advanced civilizations transmitting carrier beacons at the HI wavelength. BETA, the next-generation search system, combines greater bandwidth with quick lookback of candidate signals and robust rejection of signals of terrestrial origin. It covers the «waterhole» of 1.4-1.7 GHz, using a 250-million-channel spectrometer, in conjunction with a 3-beam antenna system, producing a 250 Mbytes/s output stream. The philosophy, implementation, and results of these systems will be described.
Southern Hemisphere Seti Survey: Five Years of Project Meta II
Authors: Lemarchand Guillermo A. , Colomb Fernando R. , Hurrell E. Eduardo , Olalde Juan Carlos 
Published: July 2016

AbstractProject META II, a full sky survey for artificial narrow-band signals, has been conducted from one of the two 30-m radiotelescopes of the Instituto Argentino de Radioastronomía (IAR). The search was performed near the 1420 Mhz line of neutral hydrogen, using a 8.4 million channels Fourier spectrometer of 0.05 Hz resolution and 400 kHz instantaneous bandwidth. The observing frequency was corrected both for motions with respect to three astronomical inertial frames, and for the effect of Earths rotation, which provides a characteristic changing signature for narrow-band signals of extraterrestrial origin. Among the 2 × 1013spectral channels analyzed, 29 extra-statistical narrow-band events were found, exceeding the average threshold of 1.7 × 10−23Wm−2. The strongest signals that survive culling for terrestrial interference lie in or near the galactic plane. A description of the project META II observing scheme and results is made as well as the possible interpretation of the results using the Cordes-Lazio-Sagan model based in interstellar scattering theory.
Follow-Up Detection in Project Phoenix
Authors: Cullers D. Kent , Stauduhar Richard P. 
Published: July 2016

AbstractEffective detection of extraterrestrial radio signals requires elimination of terrestrial interference. However, the sensitivity of standard, two element interferometry, depends on the geometric mean of the antenna areas. This is very disadvantageous if the antennas are not the same size. Project Phoenix performs pseudointerferometry by transmitting detailed signal descriptions to its second site where they are used for confirmation. The primary site uses the larger antenna and square-law detectors. Use of matched filtering and a lower threshold makes detection with the second, much smaller, antenna possible. The pseudointerferometer can handle up to 12 signals having bandwidths of order 1 Hz in a 10 MHz band. In Australia, it allowed observing to complete in less than half the time that would have been required using a single site system.
On the Hydrodynamics of Stellar Pulsation and Stability
Authors: Gough D.O. , Ledoux Paul 
Published: July 2016

AbstractMuch of our knowledge of the hydrodynamics of stellar oscillations is summarized in the now-classical article by Ledoux & Walraven in volume 51 of the Handbuch der Physik. It is from that article that I, and many others, first learned the subject. Most of what we have learned since, aside, perhaps, from what we have learned from nonlinear studies, derives from that work. Even today, what is written in that work is hardly out of date. It is not possible to do justice to even the most outstanding contents of Ledoux & Walraven’s article in a single talk, so I highlight some aspects of further developments that have been of more recent interest, trying to set them into a context of current understanding.
Convective Overshooting: Physical Properties and Seismic Evidence
Authors: Zahn J.-P. 
Published: July 2016

AbstractWe review briefly the different prescriptions which have been proposed to predict the extent of convective penetration (or overshoot) in stellar interiors, and we confront them with the results of numerical simulations and with helioseismic data. It appears that the penetrative motions are structured in plumes, and that thermal diffusion plays an important role in controlling the temperature stratification in the stable domain. The most recent high-resolution simulations suggest that these plumes are less space-filling than thought before, and that they are therefore less efficient in establishing an adiabatic temperature profile. This property is compatible with the solar profiles obtained through acoustic sounding.
Djehuty: a Code for Modeling Whole Stars in Three Dimensions
Authors: Turcotte S. , Bazan G. , Castor J. , Cavallo R. , Cohl H. , Cook K. , Dearborn D.S.P. , Dossa D. , Eastman R. , Eggleton P.P. , Eltgroth P. , Keller S. , Murray S. , Taylor A. 
Published: July 2016

AbstractThe DJEHUTY project is an intensive effort at the Lawrence Livermore National Laboratory (LLNL) to produce a general purpose 3-D stellar structure and evolution code to study dynamic processes in whole stars.
Frequency Analysis of a Delta Scuti Type Component in the Eclipsing Binary Y Cam
Authors: Kim S.-L. , Lee J.-W. , Youn J.-H. , Kwon S.-G. , Kim Chulhee 
Published: July 2016

AbstractWe present CCD photometric results of the eclipsing binary Y Cam with a pulsating component. The dominant pulsation frequency of 15.0473 c d-1 has not changed over 39 years, but its amplitude decreased to about half. The pulsational properties of the second frequency showed great differences between Broglia & Conconi (1984)’s result and ours.
RR Lyrae Stars and Anomalous Cepheids in the Draco Dwarf Spheroidal Galaxy
Authors: Kinemuchi K. , Smith H.A. , LaCluyzé A.P. , Clark C.L. , Harris H.C. , Silbermann N. , Snyder L.A. 
Published: July 2016

AbstractWe present new results on RR Lyrae stars and anomalous Cepheids in the Draco dwarf spheroidal galaxy. We have increased the number of double-mode RR Lyrae stars and found three new anomalous Cepheids. With period-magnitude and period-amplitude diagrams, we discuss the Oosterhoff classification of Draco. Contradictory results were found in that Draco appears to contain both Oosterhoff I and II type RR Lyrae populations.
Frequency Analysis of β Cephei Stars in NGC 4755
Authors: Stankov A. 
Published: July 2016

AbstractWe present the results of the multi-color, two-site observing campaign of β Cephei stars in the young open cluster NGC 4755, from 1999 and 2000. More than 200 hours of time-series photometric U, B, V filter data of the variable stars were acquired. We show a table of the detected frequencies and discuss the results.