bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Cell Wall Composition on the Fossilisation of Bacteria and the Implications for the Search for Early Life Forms
Authors: Westall Frances 
Published: July 2016

AbstractThe oldest cell-like structures on Earth are preserved in silicified lagoonal, shallow sea or hydrothermal sediments, such as some Archean formations in Western Australia and South Africa. Previous studies concentrated on the search for organic fossils in Archean rocks. Observations of silicified bacteria (as silica minerals) are scarce for both the Precambrian and the Phanerozoic, but reports of mineral bacteria finds, in general, are increasing. The problems associated with the identification of authentic fossil bacteria and, if possible, closer identification of bacteria type can, in part, be overcome by experimental fossilisation studies. These have shown that not all bacteria fossilise in the same way and, indeed, some seem to be very resistent to fossilisation. This paper deals with a transmission electron microscope investigation of the silicification of four species of bacteria commonly found in the environment. The Gram positiveBacillus laterosporusand its spore produced a robust, durable crust upon silicification, whereas the Gram negativePseudomonas fluorescens, Ps. vesicularis, andPs. acidovoranspresented delicately preserved walls. The greater amount of peptidoglycan, containing abundant metal cation binding sites, in the cell wall of the Gram positive bacterium, probably accounts for the difference in the mode of fossilisation. The Gram positive bacteria are, therefore, probably most likely to be preserved in the terrestrial and extraterrestrial rock record.
Pattern in the rise of High Technology
Authors: Morrison Philip 
Published: July 2016

AbstractFirst of all, evolutionary convergence works. Both earlier primates and non-primates have long made tools to a pattern. But one presumed master tool, a protolanguage, is not tangible. It is likely to have been present for two million years during which brain volume steadily grew among our predecessors. Then small societies of foragers very rapidly managed worldwide exploration and settlement, created art, and left a tide of novel techniques and artifactswithout any further increase in cranial size. This suggests a new software power, not visible in bony relics. A linguist has identified that second empowering step with a major feature universally found in human language. A precondition for interstellar signaling is ahardwaretechnology far beyond any open to clever foragers. Here the additional requirement may be a population large enough to support such elaborate technology. A new formal model suggests that large population growth is as intrinsic to our kind as language. Should such proposals hold, distant counterparts to human development may be frequent.
The Search for Extraterrestrial Civilizations in Optical Range – Methods, Objects, Results
Authors: Beskin Gregory , Borisov Nikolai , Komarova Victoria , Mitronova Sofia , Neizvestny Sergei , Plokhotnichenko Vladimir , Popova Marina 
Published: July 2016

AbstractPerspectives and possibilities of search for signals of extraterrestrial civilizations in optical range are discussed. Two criteria of an artificial origin of an optical emission – the variations of its intensity which have a time structure of semiotic character and the presence of narrow laser lines are analyzed. For detection and study of these signals we propose to investigate the astronomical objects under suspection with extremely high time resolution – 10−7s. To solve this problem we use a special hard/software photometrical complex MANIA (Multichannel Analysis of Nanosecond Intensity Alterations) which consists of a photometer, a registration system which is a «time-code» converter, a PC/AT 486 computer and a tape recorder. Special statistical methods and programs for the search for and the analysis of any type of brightness variability of astronomical objects on a time scale of 10−7-102s are described. Criteria of choice of objects to search for extraterrestrial civilizations signals in their emission are discussed. To search for civilizations of I type (with energy consumption equal to one for our civilization) it is proposed to investigate 161 stars of F9V-G5V spectral classes in neighbourhood of the Sun with radius of 25 pc. As possible beacons (transmitters) of extraterrestrial civilizations of II type (with energy consumption equal to star luminosity) we propose to consider the objects that have unusual characteristics, particularly, lineless optical spectra. The results of observations of 60 objects of mentioned types and the limits for possible signals power are reported.
Seti Figure of Merit
Authors: Dreher John W. , Cullers D. Kent 
Published: July 2016

AbstractWe develop a figure of merit for SETI observations which is anexplicitfunction of the EIRP of the transmitters, which allows us to treat sky surveys and targeted searches on the same footing. For each EIRP, we calculate the product of terms measuring the number of stars within detection range, the range of frequencies searched, and the number of independent observations for each star. For a given set of SETI observations, the result is a graph of merit versus transmitter EIRP. We apply this technique to several completed and ongoing SETI programs. The results provide a quantitative confirmation of the expected qualitative difference between sky surveys and targeted searches: the Project Phoenix targeted search is good for finding transmitters in the 109to 1014W range, while the sky surveys do their best at higher powers. Current generation optical SETI is not yet competitive with microwave SETI.
Pulsating Components of Eclipsing Binaries: New Asteroseismic Methods of Studies and Prospects
Authors: Mkrtichian D.E. , Kusakin A.V. , Gamarova A.Yu. , Nazarenko V. 
Published: July 2016

AbstractWe give a brief review on the present status of our research of A-F pulsating components of semi-detached Algol-type systems. We suggest a new asteroseismic approach for estimating the evolutionary stage of the mass-accreting components of Algols during rapid and slow mass-transfer phases, asynchronization and differential rotation.
Dwarf Cepheid Radii and the Distance Scale
Authors: Laney C.D. , Joner M. , Schwendiman L. 
Published: July 2016

AbstractBaade-Wesselink radii for dwarf Cepheids (High Amplitude Delta Scuti stars) can give luminosities and distances independent of the classical Cepheid distance scale. Using optical and IR photometry together with precision radial velocities, the authors have obtained radii and luminosities for 7 stars, and combined these with two from the literature, obtaining results consistent with the luminosities of the 3 dwarf Cepheids with good Hipparcos parallaxes. Classical Cepheids and dwarf Cepheids appear to fit the same PL and PR relations. The results imply ‘bright’ RR Lyrae absolute magnitudes giving an LMC distance modulus of 18.51-18.54, in agreement with the distance derived from classical Cepheids.
Application of the Image Subtraction Method to the OGLE-I Observations
Authors: Kopacki Grzegorz , Kołaczkowski Zbigniew , Pigulski Andrzej 
Published: July 2016

AbstractThe analysis of the OGLE-I data using the standard profile-fitting software yielded a large set of new variable stars. However, due to the severe crowding of the images many variables may have been missed. Therefore, we decided to reanalyze these data by means of the image subtraction method. Our main goal was the detection of new variables. In addition, we intend to extend the time-base of the observations for the variables found in the course of the OGLE-II project (Udalski et al. 1997). We present the preliminary results of our study.
Spectroscopic Nonadiabatic Observables as a New Tool for Mode Identification in β Cep Stars
Authors: Daszyńska J. , Cugier H. 
Published: July 2016

AbstractWe present a new method of mode identification based on the line profile variations. We calculate time series of Si III 455.26 nm for models of β Cep stars with a mass of 10 M⊙. The Spectroscopic observables are amplitude ratio and phase difference for various oscillation parameters derived from the line profile changes. Based on the computed values we plot diagrams to search for the best discriminators of modes.In most Spectroscopic diagrams the unstable modes are grouped in well-defined regions with different m-values, and a few of them give also separation with respect to l-values. Moreover, on the basis of almost all of the diagrams we can distinguish the prograde modes from the retrograde ones, and the zonal modes from those with m ≠ 0.In this paper we discuss also the influence of the inclination angle, the amplitude of the radius variation and the equatorial velocity on the diagnostic values of the Spectroscopic diagrams.
The Main Parameters of SPB Stars on the Basis of IUE Spectra
Authors: Niemczura E. 
Published: July 2016

AbstractWe derive mean stellar parameters for 14 SPB stars observed during the IUE satellite mission, using an algorithmic procedure fitting theoretical flux distributions (Kurucz, 1996) to the IUE low-resolution spectra. We focus our attention on the metallicity parameter [m/H]. We found the mean value of [m/H] = -0.27 ± 0.22.
53 Piscium, an SPB Star with Activity
Authors: Le Contel J.-M. , Mathias P. , Chapellier E. , Valtier J.-C. 
Published: July 2016

The star 53 Psc (HD 3379, B2.5IV) has been observed as variable by several authors (Sareyan et al., 1979) with frequencies around 10 c d–1 and has been classified as a β Cephei star. Conversely, other authors (e.g. Percy, 1971) found it to be constant.New high resolution, high signal-to-noise ratio, Spectroscopic observations have been performed at the Observatoire de Haute-Provence in 1996 over 11 nights. The spectral domain covers around 200 Å and is centered on Hδ. Radial velocities were deduced from an auto-correlation technique with a scatter around 0.4kms−1.No high frequency variations are observed. Three frequencies have been detected with a false alarm detection above the 1 % level. A fourth one may be present but its amplitude is below this 1 % level. Results are displayed in Table 1.
Non-Adiabatic Quantities in δ Scuti and γ Dor Stars: a Comparison between Observations and Theoretical Non-Adiabatic Models
Authors: Garrido R. , Moya A. , Claret A. 
Published: July 2016

AbstractPhase lag, ψT and R, a parameter measuring the departure from adiabaticity, can be derived directly from multicolor photometry. The same quantities can also be calculated from theoretical non-adiabatic pulsation models. We present here some preliminary theoretical results which indicate that these quantities depend on the mixing length parameter used to treat convection in the standard ML theory. The comparison favours models with α values between 1 and 1.5Hp. Non-adiabatic models also predict the observed phase lags for the newly discovered α Dor g-mode pulsating stars.
Differential Time-Series Photometry of BL Camelopardalis: Revisited
Authors: Kim Chulhee , Jeon Y.B.- , Kim S.-L. 
Published: July 2016

AbstractNew differential time-series observations of the white dwarf BL Camelopardalis were obtained using the B and V filters. It was confirmed that BL Cam is a double star but the effect of the secondary star on the periods is almost negligible. The (O-C) diagram and periods were analyzed.
Frequency Analysis of a Subset of Fundamental Mode RR Lyrae Stars from the MACHO Project Large Magellanic Cloud Database
Authors: Welch D.L. , Kovács G. , Cook K.H. , Alcock C. , Allsman R. , Alves D.R. , Axelrod T. , Becker A. , Bennett D. , Drake A. , Freeman K. , Geha M. , Griest K. , Lehner M. , Marshall S. , Minniti D. , Nelson C. , Peterson B. , Popowski P. , Pratt M. , Quinn P. , Rodgers A. , Stubbs C. , Sutherland W. , Vandehei T. ,   The MACHO Collaboration
Published: July 2016

AbstractWe present the preliminary results of a frequency analysis of 1457 fundamental mode RR Lyrae (RR0) stars in the Large Magellanic Cloud (LMC) from MACHO Project photometry. We find the same classes of pulsational behavior as were found in our earlier survey of first overtone RR Lyrae (RR1) stars. Variables whose prewhitened power spectra contain one or two peaks close to the main frequency component in the original power spectra are commonly known as Blazhko-type variables. The present analysis shows the overall frequency of Blazhko-type stars in the total RR0 population analysed to date to be ≈ 10%. This is lower than the often cited Galactic field/globular rate of 20-30% (Szeidl, 1988).The incidence rate of Blazhko-type variability in the LMC appears to be about three times higher in RR0 stars than in RR1 stars. This puts important constraints on possible models of the Blazhko effect.
Changes in Solar Oscillation Frequencies during the Current Activity Maximum: Analysis and Interpretation
Authors: Dziembowski W.A. , Goode P.R. 
Published: July 2016

AbstractWe describe systematic changes in the centroid frequencies and the splitting coefficients as found using data from MDI on board SOHO, covering cycle 23. The data allow us to construct a seismic map of the evolving solar activity - covering all latitudes. At lower latitudes, the temporal evolution closely tracks that of butterfly diagram. The additional information from higher latitudes in the map is of a significant activity in the polar region, peaking at activity minimum in 1996. The most plausible source of solar oscillation frequency changes over the solar cycle is the evolution of the radial component of the small-scale magnetic field. The amplitude of the required mean field changes is ∼ 100 G at the photosphere, and increasing going inward.
Influence of a Uniform Coronal Magnetic Field on Solar p Modes: Coupling to Slow Resonant MHD Waves
Authors: Vanlommel P. , Debosscher A. , Andries J. , Goossens M. 
Published: July 2016

AbstractThe influence of a constant coronal magnetic field on solar global oscillations is investigated for a simple planar equilibrium model. The model consists of an atmosphere with a constant horizontal magnetic field on top of a unmagnetized solar interior. The focus is on the possible resonant coupling of global solar oscillation modes to local slow continuum modes of the atmosphere and the consequent damping of the global oscillations.
Pulsating Red Giants: New Results
Authors: Percy J.R. , Bakos A.G. , Dunlop H. , Hussain A. , Kassim L. , Kastrukoff R. , Nyssa Z. , Wilson J.B. , Henry G.W. 
Published: July 2016

AbstractWe have (1) accumulated long-term (up to 15 years) photoelectric photometry of 76 bright pulsating red giants (PRGs) and related stars, with V amplitudes of 0.04 to ≥ 1 magnitude; (2) used a variety of techniques, including autocorrelation, to determine both “short” radial pulsation periods, and long secondary periods; (3) determined pulsation modes using the Q-value method; the modes range from fundamental to second overtone, independent of temperature; (4) tested wavelet analysis on small-amplitude PRGs; (5) made a special study of PRGs with amplitudes less than 0.1 magnitude; and (6) called further attention to the problem of the long secondary periods of these stars. Our studies provide a “model” for the analysis and interpretation of larger, fainter surveys such as MACHO and OGLE.
FCAPT Observations of Late B and Early A Supergiants and AGB S Stars
Authors: Adelman Saul J. 
Published: July 2016

AbstractI discuss single-channel differential observations of late B and early A supergiants and AGB S stars obtained with the Four College Automated Photoelectric Telescope. The suggestion of periods longer than several years often seen in the seasonal mean magnitudes of both kinds of stars requires confirmation. I used Program Period98 to derive the most important frequencies for Deneb and for three AGB S stars.
From Planetary Nebulae to White Dwarfs: Constraints from the Asteroseismology of the Pulsating Planetary Nebula Central Star RXJ 2117+3412
Authors: Moskalik P. , Vauclair G. 
Published: July 2016

AbstractWe summarize the results of an asteroseismological study of the pulsating planetary nebula central star RXJ 2117+3412.
A Flower on a WIRE: Asteroseismology of a Massive Star
Authors: Cuypers J. , Aerts C. , Buzasi D. , Catanzarite J. , Conrow T. , Laher R. 
Published: July 2016

AbstractRecently it became clear from a line profile study that the β Cephei star β Crucis (Mimosa) is multiperiodic with at least three modes excited. Observations of this star by the star tracker of the WIRE satellite have now confirmed the multiperiodicity in the light variations. A total of 5 million observations covering 17 days was analysed and the three main periods are in perfect agreement with the line profile results. The amplitudes are small (3, 2.7 and 0.6 millimag for the dominant modes), but this is not surprising in view of the mode identifications derived from the line profiles. More periods could still be present, including the one earlier suggested by the radial velocity data.
The MONS/Rømer Experiment
Authors: Kjeldsen H. 
Published: July 2016

AbstractThe aim of the MONS (Measuring Oscillations in Nearby Stars) project is to use observations of stellar oscillations to perform an asteroseismic analysis of stellar interiors. We expect to obtain high precision oscillation measurements on a sample of 20 bright stars as well as oscillation data at a slightly lower level of precision, but on a larger sample of bright stars. MONS will be launched on the Danish Rømer satellite in mid 2005.
Seismological Constraints on Convective Penetration in the Sun
Authors: Berthomieu G. , Morel P. , Provost J. , Zahn J.-P. 
Published: July 2016

AbstractPenetrative convection is expected below stellar convection sones, where it should achieve a nearly adiabatic stratification. A theoretical prediction of the penetration depth has been recently made by Zahn (1991) which includes an arbitrary parameter ζ depending on the properties of the convective motions. We use the helioseismological constraints to calibrate the value of this parameter.
Beryllium and Lithium Abundances in Stars with a Range of Metallicities
Authors: Lopez Ramon J. Garcia , Martin Eduardo L. , Rebolo Rafael , Beckman John E. , Mckeith Conal D. , Webb John K. , Pavlenko Yakov V. 
Published: July 2016

AbstractWe present new beryllium abundances for three unevolved stars with [Fe/H] in the range −0.4 to −1.6. The Be II doublet is detected in the three stars. A spectral synthesis analysis has been conducted to derive the abundances. We briefly discuss their Be and Li abundances, together with a wide sample of stars from the literature, in the context of mixing processes below the convection zone.
The Abundances of Vega from the Ultraviolet Spectrum
Authors: Castelli Fiorella 
Published: July 2016

AbstractWe derived preliminary abundances from the ultraviolet spectrum of Vega by comparing high-resolution Copernicus spectra with spectra computed with the ATLAS9 code and with updated line lists. The Teff=9400 K, log g=3.90 model, which fits the visual flux and the Balmer profiles is able to fit the ultraviolet flux either with [M/H]=−l and microturbulent velocity ξ= 2 km s−1 or with [M/H]=−0.5 and ξ=0 km s−1. The line spectrum is fitted by ξ=2 ± 0.5 km s−1 and by an iron abundance log (N(Fe)/Ntot)=−5.2 ±0.1 dex. All the observed elements indicate underabundances ranging from about −0.35 dex (C ) up to about −1 dex (Ni, Zn). The origin of the underabundances is an open question.
Turbulence in Stellar Interiors
Authors: Zahn Jean-Paul 
Published: July 2016

AbstractThis review focusses on the most recent work which has been achieved concerning turbulence in stellar interiors. Among all possible causes for such turbulence, the most powerful is certainly the convective instability in unstably stratified regions, but little was known until now beyond the fact that thermal convection is capable of establishing an almost adiabatic stratification. The latest numerical simulations (Stein & Nordlund 1989; Cataneo et al. 1991) show that turbulent convection is highly intermittent, with strong downdrafts carrying most of the energy flux.These plumes penetrate in the stable region below, which they render nearly adiabatic over some distance (Zahn 1991); the penetration depth should be measured soon through acoustic sounding of the Sun (Berthomieu et al. 1992). Such plumes are likely to exist also in a convective core, and to penetrate into the radiative region above (Roxburgh 1989).
A Diffusion Mass-Loss Model for the Ap Star 53 Cam
Authors: Babel J. 
Published: July 2016

AbstractThe mechanism and properties of mass loss are poorly known for Ap stars. Present upper limits on the mass loss rate are of 10−10 M⊙yr−1, a value which does not permit any element separation. Abundance maps could be a very powerful tool to constrain the mass loss rate and the wind geometry of Ap stars, as surface abundances are sensitive to rates as small as 10−15 M⊙yr−1. We here propose a diffusion-mass loss model for 53 Cam and compute abundance distributions in the photosphere of 53 Cam. The mass loss geometry is determined from the Ca II K line profile and its time variation. We obtain that the diffusion-mass loss model explains many spectral features of 53 Cam, both in the UV and visible domains.
New Constraints on the Rotation-Induced Mixing in Stars, from Lithium Observations in Main Sequence F-Type Stars and Subglants
Authors: Charbonnel Corinne , Vauclair Sylvie 
Published: July 2016

AbstractObservations of lithium in F type main sequence stars and subgiants lead to specific constraints on the rotation-induced mixing. The fact that lithium is smoothly depleted in subgiants down to factors as large as 1000 at the end of the sequence can be explained if lithium suffered extra depletion inside the star while it was on the main sequence. We propose a simple consistent model, based on the discussion of rotation-induced mixing developed by Chaboyer and Zahn (1992), which could account for these observations, as well as the observations of lithium on the main sequence.
Apsidal Motion Test: Confrontation Between Theory and Observations
Authors: Claret A. , Gimenez A. 
Published: July 2016

The apsidal motion test in eclipsing binaries is one of the few observational procedures available to study the stellar interior. A careful analysis of empirical data and theoretical models has been performed since more than ten years ago by our group, and in the present communication we show the most recent results obtained from the confrontation between theory and observations.We have carried out an extensive comparison between new stellar models (Claret & Giménez 1992) making use of the latest opacity library by Rogers & Iglesias (1992) and the best available data from double-lined eclipsing binaries (Andersen, 1991). The level at which we can theoretically reproduce the observations of classical absolute dimensions, namely, R and Teff for a given mass, is shown in Figure 1, while Figure 2 shows the fulfillment of the requirements of a common age for the two components of the same system. A very similar good agreement is obtained when we take into account a moderate amount of convective core overshooting. Small differences can be easily explained in terms of metal abundance variations with respect to the adopted average value Z = 0.02. A more detailed check is shown in Figure 3 for some selected systems.