bluuebunny/crossref_metadata_2025 huggingface dataset:
Short-Term Amplitude Variation of FM Com (=HR 4684)
Authors: Pararó M. , Pena J. , Peniche R. , Ibanoglu C. , Tunca Z. , Evren S.
Published: July 2016

Using unpublished data obtained in 1982 at Mexico and Turkey combined with Hungarian observations the process of amplitude variation of the frequency at 18.5 c/d is shown. The time scale of the amplitude increase is less than 100 days.
Physical Characters of HD 93044
Authors: Zhiping Li
Published: July 2016

The measurements of uvby Hβ of HD 93044 were obtained in April 1991. and the observational results that the star locates nearly in the middle of δ Scuti instability strip with somewhat deviation to red edge. According to Crawford (1979) and Philip’s (1979) calibrations, the effective temperature, absolute visual magnitude and surface gravity are obtained to be Teff = 7300±200 K, Mv = l.m33±0.39 and logg = 3.7±0.15, respectively. The observational results of Δmi = 0.01 give an estimate of [Fe/H] = —0.003 ± 0.18, so the opinion of metallic deficient is not supported obviously. The observations show the reddening index E(b — y) to be 0.014 which is 1.4 times as large as the standard deviation of Crawford’s (1979) statistics.
Observation of a Variable, ZZ Ceti White Dwarf: GD154
Authors: Pfeiffer B. , Vauclair G. , Dolez N. , Chevreton M. , Fremy J. R. , Herpe G. , Barstow M. , Kleinman S. J. , Watson T. K. , Belmonte J. A. , Kepler S. O , Kanaan A. , Giovannini O. , Nather R. E. , Winget D. E. , Provencal J. , Clemens J. C. , Bradley P. , Dixson J. , Grauer A. D. , Fontaine G. , Bergeron P. , Wesemael F. , Claver C. F. , Matzeh T. , Leibowitz E. , Moskalik P.
Published: July 2016

The ZZ Ceti stars form a class of variable white dwarfs: the hydrogen dominated atmosphere ones, which do pulsate in an instability strip in the effective temperature range 13000K-11500K. We know 22 such ZZ Ceti white dwarfs. Their variations are caused by nonradial g-mode pulsations with periods are in the range 100-1000 seconds.

A subsample of the ZZ Ceti stars shows amplitude variations on time scales of the order of one month. These variations could be driven by nonlinear phenomena.
Capabilities of the Optical Monitor for the Research in X-Ray Source and Stellar Variability
Authors: Antonello E. , Maraschi L. , Citterio O.
Published: July 2016

The project of an Optical Monitor (OM) for X-ray satellites, in particular the JET-X (Joint European Telescope for X-ray astronomy) experiment (Wells et al., 1991), derives from the scientific need of having complete data coverage at various wavelengths, UV and optical, of the observed X-ray sources, because these data are essential for a deeper understanding of the various classes of objects. When studying variable sources and/or transient astronomical phenomena, one needs that the multifrequency observations be performed essentially at the same time, because it is the knowledge of the simultaneous optical and X-ray behaviour of a source which contributes substantially to the clarification of its nature. In principle optical observations simultaneous with X-ray ones can be performed from ground based telescopes. However the complexity of satisfying the constraints typical of the optical telescopes (weather conditions, source observability) and of the X-ray instrumentation (e.g. orbital constraints) lead inevitably to a substantial loss of observing time. Therefore the only practical way of having an optimal utilization of the time available for X-ray observations, together with the wealth of scientific potential of simultaneous UV-optical observations, is to have a small telescope to be part of the same space mission.
Wind Variability of LBV Stars
Authors: Israelian G. L.
Published: July 2016

General properties of Luminous Blue Variables (LBV) have been reviewed by Lamers (1987). The LBV’s are all close to the Humphreys-Davidson luminosity upper limit. The semi periods of the photometric microvariations with ΔV ~ 0.1m are about twice as large as for normal supergiants of the same L and Teff, and 4-20 times larger than the fundamental mode for radial pulsations. So, it is likely due to nonradial pulsations. During shell ejections, which accompanied by moderate photometric variations of ΔV ~ 1m, Lbol remains constant. This fact has been explained by the quasiperiodic variations of Teff and the radius of pseudo-photosphere (Lamer 1986). LBV’s are less stable than normal supergiants so that any internal instability has more effect on their envelopes. The nature of these instabilities remains unknown. We have found some interesting peculiarities which can throw light to this problem.
Long-Term V/R Variations of be Stars Due to Global One-Armed Oscillations of Equatorial Disks
Authors: Okazaki Atsuo T.
Published: July 2016

We study the long-term variations of Balmer line profiles due to global one-armed oscillations in Be-star disks. In order to examine the qualitative effects of oscillations on line profiles, we assume that the eigenfunctions of one-armed nonlinear oscillations are similar to those of linear oscillations. Computing the line profiles for various values of disk parameters, we find that in small disks or in disks with steep density gradients the one-armed fundamental modes cause remarkable variabilities similar to the observed V/R variations.
Photochemical Evolution of Interstellar/Precometary Organic Material
Authors: Allamandola Louis J. , Bernstein Max P. , Sandford Scott A.
Published: July 2016

Infrared observations, combined with realistic laboratory simulations, have revolutionized our understanding of interstellar ice and dust, the building blocks of comets. Since comets are thought to be a major source of the volatiles on the primative earth, their organic inventory is of central importance to questions concerning the origin of life. Ices in molecular clouds contain the very simple molecules H2O, CH3OH, CO, CO2, CH4, H2, and probably some NH3and H2CO, as well as more complex species including nitriles, ketones, and esters. The evidence for these, as well as carbonrich materials such as polycyclic aromatic hydrocarbons (PAHs), microdiamonds, and amorphous carbon is briefly reviewed. This is followed by a detailed summary of interstellar/precometary ice photochemical evolution based on laboratory studies of realistic polar ice analogs. Ultraviolet photolysis of these ices produces H2, H2CO, CO2, CO, CH4, HCO, and the moderately complex organic molecules: CH3CH2OH (ethanol), HC(= O)NH2(formamide), CH3C(= O)NH2(acetamide), R-CN (nitriles), and hexamethylenetetramine (HMT, C6H12N4), as well as more complex species including polyoxymethylene and related species (POMs), amides, and ketones. The ready formation of these organic species from simple starting mixtures, the ice chemistry that ensues when these ices are mildly warmed, plus the observation that the more complex refractory photoproducts show lipid-like behavior and readily self organize into droplets upon exposure to liquid water suggest that comets may have played an important role in the origin of life.
Infrared Signatures of Prebiology - or Biology?
Authors: Wickramasinghe Nalin C. , Hoyle Fred , Al-Mufti Shirwan , Wallis Daryl H.
Published: July 2016

Data on infrared spectra of astronomical sources and on the unidentified infrared bands is reviewed and compared with a range of predictions from organic models of interstellar grains. The best fits to a wide range of data appear to require the widespread occurrence of functional groups distributed in exactly the proportions that characterise biosystems. The question of whether these agreements are consistent with extraterrestrial prebiology, or even cosmic biology is discussed.
Interaction of Energetic Particles with Extraterrestrial Ice
Authors: Pirronello Valerio
Published: July 2016

The interaction of energetic particles with ice mixtures can induce important chemical effects. Such interactions occur in several environments in space and may produce complex prebiotic molecules whose formation may help to shed some light on the fascinating problem of the origin of life in our Universe. Experimental work performed by several groups to simulate as closely as possible conditions and processes occurring in extraterrestrial scenarios is reported. Special attention is paid to applications of the results of laboratory investigations to interstellar and cometary environments.
Comets and Life on the Primitive Earth
Authors: Orò Juan , Cosmovici Cristiano B.
Published: July 2016

Comets may have contributed substantial amounts of water, volatiles and organic precursors such as HCN for the synthesis of biochemical compounds on the primitive Earth. This suggestion followed closely the prebiotic synthesis of adenine, purines and amino acids from HCN. Recent studies on the terrestrial heavy noble gases provide evidence that comets are the principal external source of Earth’s volatiles. During the encounter of comet Halley strong jets of CN, C2, C3and NH2were measured from Earth observatories, and by spacecraft mass spectrometry HCN, formaldehyde, adenine and many other organic compounds were detected, except amino acids. Obviously the latter require liquid water for their formation. Therefore upon capture of comets by the Earth, and melting of the frozen water, the synthesis of most biochemical compounds could take place readily. The detection of water, HCN and other organics of cometary origin after the impact of Comet SL-9 with Jupiter demonstrated the capability of survival of these molecules even after catastrophic events. Thus on the Earth HCN could be converted into purines, cyanacetylene, after hydration and condensation with urea, into pyrimidines, and formaldehyde into monosaccharides. In the presence of phosphates, which have been detected in cometary IDPs, nucleotides could also be synthesized. In conclusion, comets probably provided the necessary molecular precursors for the generation of life on the Earth.
Mars: was There an Ancient Eden?
Authors: Owen Tobias C.
Published: July 2016

The clear evidence of water erosion on the surface of Mars suggests an early climate much more clement than the present one. Using a model for the origin of inner planet atmospheres by icy planetesimal impact, it is possible to reconstruct the original volatile inventory on Mars, starting from the thin atmosphere we observe today. Evidence for cometary impact can be found in the present abundances and isotope ratios of gases in the atmosphere and in SNC meteorites. If we invoke impact erosion to account for the present excess of129Xe, we predict an early inventory equivalent to at least 7.5 bars of CO2. This reservoir of volatiles is adequate to produce a substantial greenhouse effect, provided there is some small addition of SO2(volcanoes) or reduced gases (cometary impact). Thus it seems likely that conditions on early Mars were suitable for the origin of life – biogenic elements and liquid water were present at favorable conditions of pressure and temperature. Whether life began on Mars remains an open question, receiving hints of a positive answer from recent work on one of the Martian meteorites. The implications for habitable zones around other stars include the need to have rocky planets with sufficient mass to preserve atmospheres in the face of intensive early bombardment.
Titan’s Atmosphere and Surface from Infrared Spectroscopy and Imagery
Authors: Coustenis Athena , Lellouch Emmanuel , Combes Michel , Wittemberg Renald , McKay Christopher P. , Maillard Jean-Pierre
Published: July 2016

We have performed observations of Titan in the near-infrared since 1991, using both spectroscopy and imagery. A higher geometric albedo is observed near the Greatest Eastern Elongation than near the Greatest Western Elongation or Conjunctions. The surface is within reach for telescopes at 1.075, 1.28, 1.6 and 2.0 micron, so we simulated Titan’s geometric albedo in order to derive the surface albedo at all longitudes. Titan’s leading hemisphere appears brighter than the trailing one by 20-25% at 1.08; 1.28 and 1.6 μm, and by 35% at 2.0 μm, with spectra compatible with H2O everywhere. We have then simulated the presence of a mountain on Titan covering 50% of the leading hemisphere disk, varying its height and introducing a higher surface albedo when required. We find that a relief can not reproduce the whole geometric albedo differences observed between the two hemispheres. Some other additional component bright at 1.0 and 2.0 μm must then be invoked. Candidates are tholins or CH4, which can exist on the top of a mountain if the temperature is lower than 90 K.
Missions to Mars: an Overview and a Perspective at the Turn of the Century
Authors: Marov Mikhail Ya.
Published: July 2016

The principal objectives of Mars exploration and their potential benefits involve many problems of scientific importance, technological developments and the general trend for future human settlements beyond the Earth. The comparative planetology approach emphasizes Mars and Venus as two extreme models of the climate evolution on the inner planets which are of great ecological importance. The climatic history of Mars is of particular interest because of the implications for life and global change on the Earth. The origin of life on the early Earth can also be related to the similar conditions on the two planets during the early phase of Solar system evolution. Mars has been central to the space programs of the former USSR and USA since the beginning of the space age, the most successful being the two Viking mission in 1976. These robotic missions, representing a period of baseline data collection, significantly expanded our knowledge but also gave rise to many new important questions. Dramatic shortfalls in the funding of space programs changed a short period of excitement culminating in the proclaimed human mission to Mars when the Cold War was over. A new strategy for planetary exploration (the «faster-cheaper-better» concept) tends to modify the former programs significantly. This new strategy at the turn of the century which, projected into the new millenium, strictly confines the targets in the Solar system and specifically Mars exploration. Nonetheless, it represents a challenge for the launch of capable small missions with significant scientific returns. Human flight and Mars settlement, while being considered as a milestone in the history of humankind and a multifaced endeavour, would require, however, a great investment of international resources.
Resolving the Continuum Emission from Disks around Ttauri Stars
Authors: Welch William Jack , Mundy Lee , Looney Leslie
Published: July 2016

We report recent observations at millimeter wavelengths in which we have been able to resolve the continuum emission from the proto-stars HLTau and L1551/LRS5. Baselines of over one kilometer have been recently added to the BIMA array, enabling angular resolutions of better than 0.5 arcsecond at 2.7 mm wavelength. Using this new resolution, we have been able to image the continuum from HLTau and L1551/IRS5, finding a disk of radius of the order of 100 AU for HLTau and a binary of about 45AU separation for L1551/IRS5.
Natural Masers and Lasers and Bioastronomy
Authors: Strelnitski Vladimir , Mazeh Tsevi
Published: July 2016

We discuss three possible applications of natural masers and lasers interesting to bioastronomy: 1) the study of protoplanetary circumstellar disks, 2) the study of extrasolar planets, 3) interstellar communications. Masers and lasers in hydrogen recombination lines are observed from the circumstellar disk of a massive star MWC349 A and serve as probes of the disk’s kinematics and structure. They give, in particular, some indications for avoidin the central (R≈ 40 AU) part of the disk, which may be caused by a forming planetary system. We demonstrate that masers (but not lasers) in molecular lines from the atmospheres of the recently discovered extrasolar planets on close orbits around their suns (51 Peg, τ Boo) can be detectable with theexisting ground-basedradioastronomical facilities. The importance of such a detection solicits a deeper analysis of general properties of the planetary masing and lasing and an analysis of the candidate lines to be searched. We argue against the use ofnaturallasers for SETI.
The Origin of Biological Information
Authors: Eigen Manfred
Published: July 2016

What is the distinguishing feature of a living system that singularizes it from every non-living chemical ensemble, regardless of the extent of the complexity? The differentiable characteristic of the living system is information. Information assures the controlled reproduction of all the constituents, thereby ensuring the conservation of viability. Information – unlike energy – is not subject to a conservation law. Hence the fundamental question behind the origin of life is: How can information originate?

Information theory, which was pioneered by Claude Shannon, cannot answer this question: this theory is most successful in dealing with problems of coding and transmission. In principle, the answer was formulated 130 years ago by Charles Darwin: The information that is unique for life evolves by virtue of natural selection. Today we can be more specific: natural selection is a non-equilibrium process. It is an inherent consequence of mutagenous self-replication at several levels of organization: for instance it is evident in molecules such as nucleic acids, in molecular complexes such as viruses and in autonomous formes of life such as micro- or higher organisms. New physical concepts have been introduced in order to deal quantitatively with the dynamics of the molecular generation of genetic information. They provide a physical foundation for Darwinian behaviour, yet they introduce major modifications in its interpretation. The lecture deals with these physical concepts, such as «sequence space», «quasi-species» and «hypercycles» and will scrutinize their adequacy for rationalizing experimental results obtained with molecular model systems and with viruses under natural conditions. Elucidating the principles of molecular self-organization has made possible to construct automated machines that make it possible for genetic information to evolve under controlled conditions in an abridged time scale.
Panspermina Revisited: Astrophysical and Biological Constraints
Authors: Wesson Paul S. , Secker Jeff , Lepock James R.
Published: July 2016

We have carried out a series of calculations involving bacteria and viruses embedded in dust grains that are ejected from our solar system by radiation pressure, and travel through space to other star systems. Under many conditions, this kind of panspermia is impractical, mainly because the ultraviolet radiation of the present Sun kills the micro-organisms. However, if the organisms are shielded by an absorbing material like carbon and if ejection takes place in the late-Sun (red giant) phase, there is a significant probability that these micro-organisms can reach another star system alive. In addition to panspermia with living micro-organisms, we note that it is possible to seed the Galaxy with dead ones, whose DNA fragments might provide the initial information necessary to start biological evolution in favorable environments.
Brain-Behavior Relations in Primates and Cetaceans: Implications for the Ubiquity of Factors Leading to the Evolution of Complex Intelligence
Authors: Marino Lori
Published: July 2016

This paper describes the results of a project aimed at addressing questions about the evolution of intelligence by utilizing comparisons of brain-behavior relations in cetaceans (dolphins and whales) and primates. Three specific questions were asked. First, have any cetaceans reached a hominid level of encephalization? Second, are cetacean-primate comparisons of brain organization useful for grappling with the differences that are bound to exist between any extraterrestrial organism and ourselves? Third, are there similarities in brain-behavior relations in cetaceans and primates that suggest behavioral evolution is shaped by general factors? Brain and body weights for cetacean and primate species were collected and compared with each other and with data on brain organization and social behavior. The results revealed that a hominid level of encephalization is not unique in mammalian history. Furthermore, cetacean-primate comparisons can be useful in understanding the different ways in which information processing systems can be organized. Finally, a comparison of the relation between encephalization and social group size in primates and cetaceans preliminarily suggests that similar mental capacities can be achieved through different independent evolutionary paths and that there may be factors common to behavioral evolution in all intelligent organisms.
Project Argus and the Challenge of Real-Time All-Sky Seti
Authors: Shuch H. Paul
Published: July 2016

Project Argus, a global effort of the non-profit SETI League, Inc., seeks to achieve continuous microwave monitoring of all four pi steradians of space, in real time. This most ambitious SETI project ever undertaken without benefit of Government support will ultimately involve 5,000 small radiotelescopes worldwide, built, maintained and operated by private individuals (primarily radio amateurs and microwave experimenters), coordinated so as to miss no likely candidate signals, and providing independent verification of any interesting signals detected. Prototype stations went into operation in 1996; full sky coverage is planned for 2001. Sensitivity and range are assessed by comparison of current capabilities to those in place at the Ohio State Radio Observatory nineteen years ago, when the so-called «Wow!» signal was detected. The «Wow!» signal serves as a convenient benchmark, even though its exact nature remains unknown. Should a similar candidate signal appear during the fully deployed phase of Project Argus, it will not evade detection. Though utilizing just a small satellite TV dish as its antenna, each station achieves range and sensitivity on a par with the Ohio State Big Ear radio telescope, circa 1977. This paper explores the technological breakthroughs which have made this level of performance possible.
Upgrade of the Mini Spectrum Analyzer
Authors: Montebugnoli Stelio , Bortolotti Claudio , Buttaccio Salvo , Cattani Alessandro , Maccaferri Andrea , Maccaferri Giuseppe , Miani Cristiano , Orfei Alessandro , Roma Mauro , Tuccari Gino , D’Amico Nicola , Grueff Gavril
Published: July 2016

The upgrade of the mini spectrum analyzer, built at the Medicina radiotelescope station laboratories and devoted to the Jupiter-SL9 crash on July 94, is presented. The new version of the spectrometer allows precise spectroscopy measurements and it has just been used for the Hyakutake comet observations (May 96) with very promising results. The same system could be used in small SETI activities with a possible future involvement of the Medicina/Noto antennas in this program.
Seti Space Missions
Authors: Maccone Claudio
Published: July 2016

SETI from space is currently envisaged in three ways: i) by large space antennas orbiting the Earth that could be used for both VLBI and SETI (VSOP and RadioAstron missions), ii) by a radiotelescope inside the Saha far side Moon crater and an Earth-link antenna on the Mare Smythii near side plain. Such SETIMOON mission would require no astronaut work since a Tether, deployed in Moon orbit until the two antennas landed softly, would also be the cable connecting them. Alternatively, a data relay satellite orbiting the Earth-Moon Lagrangian pointL2would avoid the Earthlink antenna, iii) by a large space antenna put at the foci of the Sun gravitational lens: 1) for electromagnetic waves, the minimal focal distance is 550 Astronomical Units (AU) or 14 times beyond Pluto. One could use the huge radio magnifications of sources aligned to the Sun and spacecraft; 2) for gravitational waves and neutrinos, the focus lies between 22.45 and 29.59 AU (Uranus and Neptune orbits), with a flight time of less than 30 years. Two new space missions, of SETI interest if ET’s use neutrinos for communications, are proposed.
A Search for Short-Term RV Variations in Early-Type Binaries
Authors: Lehmann H. , Scholz G. , Hildebrandt G.
Published: July 2016

We developed a procedure to disentangle the different radial velocity variations due to orbital motion, rotation, and pulsation based on an iterative mutual subtraction of orbital and short-term contributions. The method was successfully tested on a data set of over 2200 spectra of the eclipsing β Cep star EN Lac spanning a time interval of about 90 years. We further applied the procedure to early type binaries. For the A1 III star 21 Her we found short-term variations which indicate the presence of rotationally split nonradial pulsation (NRP) modes.
A New Way to Resolve Cepheid Binaries
Authors: Evans Nancy Remage , Massa Derck
Published: July 2016

We have measured the centroid shift of low resolution HST FOC spectra as the dominant star changes from the Cepheid to the hot companion. With this approach we have resolved the AW Per system and marginally resolved the U Aql system.
RR Lyrae Stars in the Globular NGC 3201: Light Curves, Reddening, and Distance
Authors: Layden Andrew
Published: July 2016

RR Lyrae stars (RRL) are a favourite standard candle for globular clusters and other old stellar populations, yet recent absolute magnitude calibrations, MV(RR), span more than 0.2 mag. Precise distance estimates for nearby globular clusters will eventually be available through satellite-based trigonometric parallaxes (Layden, these proceedings), thus providing a resolution to this old problem.

Here, we present a progress report on our high quality time-series photometry of RRL in the nearby globular cluster NGC 3201 - the first obtained for this cluster with a CCD. The resulting light curves provide accurate intensity-mean apparent magnitudes and reddening estimates, which will in turn be used to calibrate MV(RR) once a satellite-based parallax for NGC 3201 is available.
Using SX Phœnicis Variables in M55 and Theoretical Period-Luminosity (-Colour-Metallicity) Relations for Distance Determination
Authors: Petersen J.O. , Freyhammer L.M.
Published: July 2016

Theoretical period-luminosity and period-luminosity-colour-metallicity relations are used to give distance estimates for the globular cluster M55 from detailed data for 24 SX Phœnicis variables published recently by Pych et al. (2001). With accurate determinations of effective temperatures for the SX Phe stars application of period-luminosity-colour-metallicity relations will lead to improved distances and more secure mode identifications.
Time Series CCD Photometry of the Globular Cluster M 53
Authors: Jeon Y.-B. , Kim S.-L. , Lee H. , Lee M.G.
Published: July 2016

Through time-series CCD photometry of the globular cluster M 53, we have discovered eight new SX Phoenicis type stars. All the new SX Phoenicis stars are located in the blue straggler star region in the color-magnitude diagram of M 53. In addition, we have obtained light curves for 45 known RR Lyrae stars.
SX Phe Variables in Globular Clusters
Authors: Rodríguez E. , López-González M.J.
Published: July 2016

We have compiled an extensive and up-dated list of SX Phe-type pulsators in globular clusters. In addition, SX Phe variables discovered in the Carina dwarf galaxy and other ones probably belonging to the Sagittarius dwarf galaxy are included. This catalogue is intended to be an up-dated list of all the SX Phe stars, in globular clusters and galaxies, known until now. The stars and their most significant parameters are listed together with references to studies of individual stars and notes for a number of variables. In addition, the references on the discovery for each variable and sources for photometry are also listed. Some relevant distributions are also analysed. The analysis of metal abundances and mean periods shows that both parameters are correlated in the sense that the periods of the variables are longer as the metallicity of the stellar system is higher.
Pulsating B-Type Stars in Young Open Clusters
Authors: Pigulski A. , Kopacki G. , Kołaczkowski Z. , Jerzykiewicz M.
Published: July 2016

During the last several years about a dozen young northern clusters and associations have been observed in our program of searching for B-type variables. As far as B-type pulsators are concerned, we found that (i) young northern open clusters are a few times less abundant in β Cephei stars than the southern ones, (ii) all newly discovered SPB stars seem to be monoperiodic.
Astero-Oscillometry: Gauging Stars with Oscillations
Authors: Maintz M. , Rivinius Th. , Baade D. , Štefl S.
Published: July 2016

Astero-oscillometry is presented as a new method for deriving stellar parameters on the basis of a physical modeling of line profile variability (lpv) caused by nonradial pulsation (nrp). First applications to rapidly rotating B-type stars show that the method is able to yield reasonable stellar parameters. The radii are systematically smaller compared to those derived by conventional methods. This could be attributed to possible effects of rapid rotation on stellar evolution. Since the method requires only one or a few pulsation modes to be excited, it is ideally suited to investigating early-type stars.
Evolution of Am and Ap Stars
Authors: Richard O. , Michaud G. , Richer J.
Published: July 2016

This work is a continuation of the Montréal stellar evolutionary model development (Richard et al., 2001 and references therein) where the effects of atomic diffusion are taken into account for 28 elements (see Turcotte, these proceedings), along with an approximate treatment of turbulent transport (Richer et al., 2000).

We used the CEFF equation of state and the Bahcall nuclear energy generation routine. The Rosseland opacity is computed at each time step, from the OPAL monochromatic opacities for 21 elements (to which we added locally computed spectrum tables for Li, Be, and B) for each mesh point in the model for the current local chemical composition. Convection and semi-convection are taken into account in every species’ diffusion velocity and in the determination of the thermal gradient (Richard et al., 2001). The models also take into account gravitational settling, thermal diffusion, radiative accelerations and turbulent transport. The radiative accelerations are from Richer et al. (1998). The turbulent transport is modeled as a diffusion process (Richer et al., 2000) with diffusion coefficient: DT = ωD(He)0 (ρ/ρ0)n where D(He)0 is the Ηe atomic diffusion coefficient at density ρ0.
Time-Resolved High-Resolution Spectroscopy of roAp Stars
Authors: Kochukhov O. , Ryabchikova T.
Published: July 2016

We report results of Spectroscopic monitoring of the roAp stars γ Equ, α Cir and HR 3831 with the ESO 3.6-meter telescope. Series of very high-resolution and high S/N spectra allowed to resolve changes of line profiles due to the pulsations. We found that pulsational behaviour of all three roAp stars is dominated by the variations of the doubly ionized rare-earth lines. Detailed analysis of the pulsational changes of Nd III and Pr III spectral features allowed us to identify the pulsational mode of γ Equ and to study rotational modulation of the pulsational pattern in the spectra of α Cir and HR 3831.
Effects of Dipole Magnetic Fields on Axisymmetric p-Mode Pulsations
Authors: Saio Hideyuki , Gautschy Alfred
Published: July 2016

We investigated nonradial pulsations in the presence of a dipole magnetic field in a non-rotating 1.7 M⊙ ZAMS star. Formally, like in the case of pulsation-rotation coupling (Lee & Saio, 1986), the angular dependence of the pulsations is expanded into a series of spherical harmonics of different latitudinal degrees l. To start with, we considered only axisymmetric (m = 0) modes under the adiabatic and the Cowling approximations. In contrast to previous studies of pulsation-magnetic field interaction (Dziembowski & Goode, 1996; Bigot et al., 2000; Cunha & Gough, 2000), we retained the latitudinal derivatives of the perturbed quantities.
Radial Velocity Studies of roAp stars: Rotational Modulation in HR 1217
Authors: Hatzes A.P. , Mkrtichian D. , Kanaan A.
Published: July 2016

We present the preliminary results of our analysis of the precise radial velocity (RV) measurements of the roAp star HR1217. We have obtained over 2000 spectra of this star (54 hours of coverage) covering a complete rotation period using the 2-d coude echelle spectrograph of the McDonald Observatory’s 2.7m telescope. Our RV data show rotational modulation in both the amplitude and phase of the pulsations. The broad-band (covering 110 Å) RV semi-amplitudes of the f2 mode (=2.65 mHz) varied in the range of 25 m s–1 to 200 m s–1.
GSC 4778-00324, a New Small-Amplitude Multiperiodic δ Scuti Star
Authors: Lampens P. , Van Cauteren P. , Niarchos P. , Gazeas K. , Manimanis V. , Arentoft T. , Wils P. , Bruch A. , Garrido R. , Shobbrook R.
Published: July 2016

A careful analysis of the light curves of comparison stars to the intermediate amplitude δ Scuti star V1162 Ori observed in 1999/2000 within an international campaign (Arentoft et al., 2001) revealed two new variable stars: GSC 4778-00324, a small-amplitude δ Scuti star, and GSC 4778-00001, an eclipsing variable (see http://www.lunarpages.com/bho for a map of the field). Here, we will concentrate on the first of these.

Since the colour indices (Handler, 2000) put GSC 4778-00324 right in the middle of the δ Scuti instability strip, we decided to monitor its variability (Van Cauteren & Lampens, 2000) taking as much advantage as possible from the international campaign on V1162 Ori and adopting the same comparison stars. The new observations were performed between October 1999 and March 2001, mainly from the Greek and Belgian sites, making use of a standard V filter. We collected and used 2866 data points for GSC 4778-00324 (V = 10.26; b − y = 0.20).
Asteroseismic Analysis of Pulsating Subdwarf B Stars
Authors: Charpinet S. , Fontaine G. , Brassard P.
Published: July 2016

We briefly present a method to perform detailed asteroseismological analyses of pulsating subdwarf B (sdB) stars (also referred to as the EC14026 stars). We use a forward approach based on the computation of large grids of sdB stellar models (each model being analyzed with a linear nonadiabatic pulsation code) to derive, in an objective way, the most appropriate set of model parameters that can best reproduce the observed period spectrum of a given sdB pulsator. We discuss an illustrative application of this method to the pulsating sdB star PG 1047+003, for which we derive the fundamental parameters Teff, logg, Mtot, and Menv.
Nonlinear Convective Pulsation Models of Second Overtone SMC Cepheids
Authors: Marconi M. , Bono G. , Caputo F.
Published: July 2016

Nonlinear convective pulsation models representative of SMC Cepheids pulsating in the second overtone mode are presented. Model predictions are compared with observations and implications are derived for second overtone selection criteria. The role of overtone Cepheids as distance indicators is finally investigated and the derived distance scale is at odds with the so called short distance scale.
Pulsation in Cool Hydrogen Deficient Stars
Authors: Pikall Holger
Published: July 2016

Models for hydrogen deficient stars are presented for different L/M-ratios and temperatures typical for RCB and HdC. Initially, we searched for unstable pulsation modes and identified their character using a simple linear code based on matrix methods. In a second step, we employed our fully-implicit Radiation-Hydro-Dynamics code to obtain amplitudes, radial velocities and lightcurves. For small L/M-ratios, nonlinear periods are close to the linear ones. Cooler models show strong shock-waves, which are suggested to play a key role in the dust formation of RCB stars which will be our ultimate goal.
Non-Linear Radial Pulsation Models for the Early-Type Helium Stars V652 Her and BX Cir
Authors: Montañés Rodríguez P. , Jeffery C.S.
Published: July 2016

Hydrogen-deficient early-type stars have an extremely high surface helium abundance (> 98% by number) and have represented a considerable challenge to stellar evolution theory. Recent work supports the view that they are the product of a merger between two white dwarfs.

All very luminous stars (log L/M > 4) are believed to pulsate, but at effective temperatures around 20 000 K, helium stars with lower luminosities (log-L/M < 3) are also known to pulsate due to iron-group bump instability. The two known cases are V652 Her and BX Cir. Their observed periods are in good agreement with linear theory. Recently high-resolution Spectroscopic observations were used to measure the stellar dimensions and radial velocity curves with high precision.

A hydrodynamic code including recent OPAL opacity data has been used to construct non-linear models of the pulsations of these two stars. The results impose additional constraints on those stellar dimensions, including mass, which remain poorly determined by observation.
A Model of Time-Dependent and Non-Local Convection Included in a Stellar Evolution Code
Authors: Flaskamp Martin
Published: July 2016

The Kuhfuß theory of convection is derived from the exact hydrodynamic equations by means of anelastic approximation and diffusion approximation. In the local and time-independent limit the result is identical to the MLT case. In the more general case the theory includes overshooting and convective mixing as well as time-dependence. We present test calculations in a simple box model and first steps toward the implementation in a stellar code.
Swing Coupling between Stellar Pulsations and Torsional Alfvén Oscillations
Authors: Zaqarashvili T. , Roberts B.
Published: July 2016

We suggest a mechanism of energy transmission from stellar radial pulsations into torsional oscillations in a dipole-like magnetic field. We show that the stellar radial pulsations cause a periodical variation of the Alfén speed which leads to the Mathieu equation for torsional Alfén waves. Harmonics with half the frequency of the pulsations have exponentially growing amplitudes. Then the energy supporting the various type of pulsations can be transformed into purely electromagnetic oscillations of the star.
A Study of Convection with δ Scuti Stars in Open Clusters: the Pleiades
Authors: Suárez J.-C. , Michel E. , Houdek G. , Lebreton Y. , Pérez Hernández F.
Published: July 2016

In this work we propose a preliminary seismic investigation of δ Scuti stars in the Pleiades cluster, focusing on potential diagnostics of convection and core-overshooting. Taking into account the effect of fast rotation in the modelling, we compare observed frequencies for 4 δ Scuti stars with radial linear instability predictions. A satisfying agreement is reached between the predicted ranges of unstable modes and those derived from observations for “low-mass” stars (∼ 1.55M⊙). However, a strong disagreement is found for “high-mass” stars (∼ 1.77M⊙), whatever the mixing length (α) value. These results are compared with previous ones obtained for Praesepe.
Dynamical Stellar Dust Shells: Different Perspectives
Authors: Sedlmayr E.
Published: July 2016

In the last decades considerable progress has been achieved in the physical understanding and modelling of dusty stellar atmospheres and surroundings, as represented by stationary dust driven winds, pulsating shells of Miras and LPVs, episodic phenomena, like occultations of RCrB stars, the atmospheres of brown dwarfs, or even by “hot” objects like dust forming Wolf-Rayet stars.

For all these systems the notions “understanding” and “modelling” depend on the level of the physical approach defined by specific perspectives chosen by a basic “window of perception” for each class of particular objects and its appropriate description within this frame. This is defined by the fundamental assumptions with regard to the global and local appearance and the properties of the considered object, its focused characteristic length and time scales of the various determining processes taken into account, and, of course, by an appropriate body of physical equations necessary for an adequate description within the context of the adopted perspective. In this view, any real approach concentrates on special aspects (or a combination of it), like radiative transfer, wind generation, spectral appearance, dynamical behaviour, global and local stability, cluster nucleation, grain growth and processing, chemistry, interplay of physical and chemical processes, etc. Consequently, any approach projects only particular properties of the considered object, each constituting important ingredients necessary for a final consistent quantitative modelling and a comprehensive physical understanding.
The Pulsation of M-type Miras: Multi-Epoch ISO-SWS Observations and Dynamical Models
Authors: Aringer B. , Jørgensen U.G. , Kerschbaum F. , Hron J. , Höfner S.
Published: July 2016

We present time series of observed and synthetic ISO-SWS spectra of oxygen-rich Mira variables covering the wavelength range between 2.36 and 7.75 μm. The calculations are based on new dynamical models, which have been computed with a non-grey radiative transfer taking into account all relevant molecular opacities. It turns out that many features in the ISO spectra of cool long period variables which could not be reproduced within the framework of classical hydrostatic model atmospheres nor with grey dynamical calculations can now be understood without any additional assumptions. This is especially true for the water bands, which dominate the opacity in the infrared range of M-type Miras.
Requirements for Future Photometric and Spectroscopic Observations for Asteroseismology: One Theorist’s Perspective
Authors: Kawaler Steven D.
Published: July 2016

The interplay between theory and observation has been particularly close in asteroseismology, ranging from white dwarfs through roAp stars. This trend should continue as the field expands to include new classes such as solar-type stars. This synergistic relationship relies on communication between theorists and observers, but also on healthy skepticism in both directions. Here, I outline a (somewhat personal) view of the theoretical side - what kinds of observations are most helpful for optimizing utility of theoretical research efforts ? Where might theory be of closer guidance as observing programs are planned ?
The Delta Scuti Network: Steps Towards Successful Asteroseismology of Delta Scuti Stars
Authors: Zima W. , Breger M. , Bischof K. , Rodler F. , Stankov A. , Pamyatnykh A. A. , Antoci V. , Lorenz D. , Sperl M. , Zechner R. , Garrido R. , Wood M. , Handler G. , Shobbrook R.R.
Published: July 2016

The Delta Scuti Network (DSN) is a collaboration of astronomers all around the globe who study and observe short-period variables. The field of scientific research includes high-precision photometric and Spectroscopic global campaigns, mode identification techniques, and asteroseismological pulsation modeling. We present results for three stars that are receiving the most attention at the moment: 4 CVn, BI CMi, and 44 Tau. Our results demonstrate that a large number of simultaneously excited nonradial oscillations in stars on and above the main sequence can be detected by conventional means.
Asteroseismology from Space: WIRE Monitoring of the δ Sct Star θ2 Tauri
Authors: Poretti E. , Buzasi D. , Laher R. , Catanzarite J. , Conrow T.
Published: July 2016

Soon after launch in March 1999, the primary science instrument onboard the Wide-Field Infrared Explorer (WIRE) satellite failed due to loss of coolant. However, it proved possible to begin an asteroseismology program using the 52-mm aperture star camera. A few bright stars were monitored with the 512x512 SITe CCD in a bandpass approximately equivalent to V + R; further details about the orbit, the detector and the raw data reduction can be found in Buzasi et al. (2000) and Buzasi (2000). We included the binary star θ2 Tauri among the targets. It is composed of an A7IV primary and an A5V secondary (P = 140.728 d). The primary is a a δ Scuti star which has been observed several times in the last twenty years. Five terms have been determined in its light curve (Breger, 1989 and references therein); Li et al. (1997) demonstrated the amplitude variability of some of these terms by comparing different campaigns.
Test of a New Theory for Stellar Convection using Helioseismology
Authors: Paternó L. , Ventura R. , Canuto V.M. , Mazzitelli I.
Published: July 2016

Two evolutionary models of the Sun have been tested using helioseismological data. The two models use the same input micro-physics (nuclear reaction rates, opacity, equation of state) and the same numerical evolutionary code, but differ in the treatment of turbulent convection. The first model employs the standard mixing - length theory of convection, while the second one employs a new turbulent convection model which overcomes some basic inconsistencies of the standard theory of convection.

The test rests on the calculation of p-mode eigenfrequencies and on the comparison with the helioseismological data.

The comparison shows an overall improvement of the eigenfrequencies calculated with the new model with respect to those calculated with the standard model, although it appears that both models still suffer from inaccuracies especially in the treatment of the surface layers.
Detection Possibility of the Giant Rolls in the Sun
Authors: Baranyi Tünde , Ludmány András
Published: July 2016

The expected giant convection pattern has been studied by using its probable twisting influence on the emerging magnetic fields. The studies carried out on extended computations and material have confirmed the previously found evidence for a pattern with longitudinal wavenumber 1=11 in the year 1977.
Calculation of Ionization Equilibrium for Dense Plasmas
Authors: Gerard Massacrier
Published: July 2016

We propose a new approach to calculate the populations of the different ionic states and ionization stages that may exist in a plasma in thermodynamic equilibrium. A self-consistent scheme is solved for each ionization stage, which couples the local density of free electrons and the atomic structure of this stage.
Angular-Momemtum Transfer by Nonradial Oscillations in Massive Main-Sequence Stars
Authors: Lee Umin , Saio Hideyuki
Published: July 2016

Angular mementum distribution is one of the most important factors for stellar structutre and evolution. Among other mechanisms, angular momentum is transfered by non-axisymmetric oscillations (nonradial oscillations). In this mechanism the angular momentum is carried mainly by the Reynolds stress, which is proportional to the product between radial and azimuthal components of oscillation velocity; i.e., (Φ direction is the direction of rotation velocity). In the linear oscillation analysis, the phase difference between and is with A finite value of δ, which arises from excitation or damping of the oscillation, makes the time average of finite. Positive angular momentum is transfered from the driving zone to the damping zone by a prograde mode (Osaki 1986).
An Improved Equation of State for Hydrogen
Authors: Saumon D. , Chabrier G.
Published: July 2016

An improved theory of fluid hydrogen at high density, based on a detailed treatment of inter-particle correlations and a self-consistent treatment of pressure ionization, has become available recently (Chabrier 1990, Saumon and Chabrier 1991, 1992). We present a preliminary comparison between this new EOS (hereatfer SC) and equations of state frequently used in astrophysical contexts, namely: Fontaine, Graboske and Van Horn 1977 (FGVH), Däppen et al. 1988 (MHD) and Magni and Mazzitelli 1979 (MM).

The SC theory predicts a first-order phase transition in the region of pressure-ionization (the so-called Plasma Phase Transition, or PPT), between an essentially neutral mixture of atoms and molecules (xe– < 10−2), and a partially ionized plasma (xe– ≈ 50 %), with a critical point located at Pc = 0.614 Mbar, Tc = 15300K and pc = 0.35 g/cm3.