bluuebunny/crossref_metadata_2025 huggingface dataset:
The Diffuse Interstellar Bands And Organic Molecules In Space
Authors: Snow Theodore P.
Published: July 2016

The diffuse interstellar bands have been recognized for over 75 years, and remain unidentified today. This family of broad interstellar absorption features, now numbering well over 100, has been the subject of a great deal of speculation, intensive observations, and lately has stimulated the interest of chemists as well as astronomers. In this review I briefly summarize the history of the problem and then provide an overview of the current state of affairs. I emphasize recent evidence that the carriers are large molecular species, most likely organic in nature, which are abundant in the diffuse interstellar medium. If so, then the ultimate identification of the responsible species will provide a new window into the detailed chemical and physical properties of the interstellar gas. I also discuss constraints imposed on the carriers by a recent reassessment of the interstellar carbon abundance.
Organics In Comets
Authors: Mumma Michael J.
Published: July 2016

The birth-endowed organic fraction of the newly formed (hot) Earth was destroyed by thermal decomposition during the cooling epoch. After Earth cooled sufficiently, an early organic inventory was likely replenished by the impact of comets and asteroids — a process which continues even today. The present organic composition of comets and asteroids can provide information relevant to this secondary organic seeding of the planets, for comparison with scenarios leading to self-replicating organic entities. Although impacts no longer deliver organics in significant quantities, compared with the existing terrestrial inventory, small bodies can deliver their organics intact to Earth‘s surface while giant impacts may cause punctuated extinction of living species (and create opportunities for renewed speciation). Hence, the exogenous organic flux has great importance for life’s origins and terminations. Current knowledge of the organic composition of comets is reviewed, and recent progress in our understanding of the chemical evolution of organic material from its formation to its incorporation into comets and later into planets is outlined. The need for detailed quantitative chemical analysis of material obtained directly from the cometary nucleus is indicated.
On the Nature of the Newly Discovered Extrasolar Planets
Authors: Guillot Tristan , Saumon Didier , Burrows Adam , Hubbard William B. , Lunine Jonathan I. , Marley Mark S. , Freedman Richard S.
Published: July 2016

The discovery of planets around nearby stars gives us hope that life may be able to develop close to our solar system. It should also shed light on the problem of the formation of planets in general. In the past few years, we have developed theoretical evolutionary models of solar and extrasolar giant planets. With the help of these models, we discuss the nature and characteristics of these «new planets», in aid of both NASA’s and ESA’s recent plans to directly detect them.
Infrared Interferometers for Observing Extra-Solar Planets
Authors: Fisher Philip C. , Houston Joseph B. , Stuhlinger Tilman W.
Published: July 2016

Concepts are outlined for ground - and space-based interferometers for observing nearby extra-solar earth-like planets (in the 8-20 μ range). The collecting elements are special coronagraphs, two of which constitute part of a Michelson interferometer. Performance characteristics are compared to those inferred for several competing systems. One conclusion is that one could construct a groundbased instrument that seems superior to the Keck interferometer system («superior» meaning up to a tenfold increase in angular resolution in each of two orthogonal directions, up to a tenfold increase in sensitivity, and a ten-fold lower cost). Space-based instruments of comparable/superior (?) performance to the Oases-1 and-2 systems might also be constructed.
The Tempo and mode(S) of Prebiotic Evolution
Authors: Lazcano Antonio
Published: July 2016

Different current ideas on the origin of life are critically examined. Comparison of the now fashionable FeS/H2S pyrite-based autotrophic theory of the origin of life with the heterotrophic viewpoint suggest that the later is still the most fertile explanation for the emergence of life. However, the theory of chemical evolution and heterotrophic origins of life requires major updating, which should include the abandonment of the idea that the appearance of life was a slow process involving billions of years. Stability of organic compounds and the genetics of bacteria suggest that the origin and early diversification of life took place in a time period of the order of 10 million years. Current evidence suggest that the abiotic synthesis of organic compounds may be a widespread phenomenon in the Galaxy and may have a deterministic nature. However, the history of the biosphere does not exhibits any obvious trend towards greater complexity or «higher» forms of life. Therefore, the role of contingency in biological evolution should not be understimated in the discussions of the possibilities of life in the Universe.
Self-Replication and Evolution in Primordial Mutually Catalytic Sets
Authors: Segré Daniel , Pilpel Yitzhak , Glusman Gustavo , Lancet Doron
Published: July 2016

A kinetic model for random mutually catalytic chemical sets is used here to estimate the probability for the spontaneous origin of molecular self-replication. Simplifying assumptions on the chemistry in such systems enable us to explore the possible mechanisms for chemical evolution of simple metabolic networks, and the emergence of well organized structures. The model affords an estimate of the probability that a given rate of growth or replication will appear by chance in a pre-biotic milieu, thus assisting in understanding the potential precursors of life.
Optical and Infrared Seti
Authors: Townes Charles H.
Published: July 2016

When in 1959 Cocconi and Morrison first suggested communication with extraterrestrial intelligence and showed it could be done in the microwave region, there were no lasers. In addition, since the hydrogen line at 21 centimeters was the only astronomical line known at that time in the microwave region, it seemed unique and the obvious place to look. Only one year later, however, the laser came along and shortly after that the use of lasers for SETI could also be suggested (Schwartzet al., 1961). And still later, a number of important microwave lines at various frequencies were detected from interstellar clouds, making a choice of frequency less obvious.

The first laser was built in 1960. But the laser perhaps came along unnecessarily late; there is no principle of science or technology involved in lasers that was not understood as early as the 1920s. One can find an early discussion by Tolman (1924), for example, about so-called «negative absorption,» produced by molecules in excited states. At that time, the coherence of stimulated radiation was not completely clear, but Tolman said it was probably coherent, even though that it had not yet been mathematically proven. In a few years, it was proven and so all the principles were known. Lasers could indeed have been invented at that time, even though their variety would have been limited because solid state physics and infrared spectroscopy were not very far along.
Interstellar Communication Channel Search of 49 Stars Closer than 11.5 PC
Authors: Zadnik Marjan G. , Winterflood John , Williams Andrew J. , Wellington Kelvin J. , Vaile Roberta , Blair David G. , Tarter Jill C. , Backus Peter R. , Norris Ray P. , Heiligman Gary
Published: July 2016

We report on a search for narrow band emissions from the vicinity of 36 solar type (F6 to K4) target stars and 13 other non-solar type stars within 11.5 parsecs at 5 possible interstellar beacon frequencies of π*fH, 2π*fH, e*fOH, e*(fOH+fH) and3He (4.462, 8.925, 4.532, 8.393 and 8.666 GHz respectively). The frequencies were selected by scaling important naturally occurring lines by fundamental constants. The stars were selected for a distance of less than 11.5 parsecs to give sufficient time for a nearby civilisation to have detected early Earth radio leakage signals and to have replied. The search was carried using the 64-m Parkes telescope with the Phoenix instrumentation and the 22-m Mopra telescope for candidate verification. The instrument combination allowed for a low interference, high resolution, high sensitivity search. We did not detect any signals from any of the target stars. If a civilisation at a distance of 10 pc had beamed 10 kW signals at us using a 100-m dish, we would have detected the transmission at the 10 sigma level. Thus we can exclude signals above this level.
The Serendip IV Interference Rejection and Signal Detection System
Authors: Cobb Jeff , Donnelly Charles , Bowyer Stuart , Werthimer Dan , Lampton Michael
Published: July 2016

The SERENDIP Interference Rejection and ETI Notification system (SIREN) is a software package developed at UC Berkeley for use in the search for extraterrestrial intelligence (SETI). Originally designed for and used by the SERENDIP III project, it is being substantially rewritten for use with SERENDIP IV. This paper will present the SIREN system and discuss the algorithms employed. SIREN performs both interference rejection and signal detection. The end result of SIREN processing is a database of candidate ETI signals. The most interesting candidates will be the subject of a targeted search.
A One Square Kilometer Radiotelescope: Design Challenges
Authors: Wellington Kelvin J.
Published: July 2016

SETI searches, as well as radioastronomy, require large radiotelescopes for high sensitivity. In recent years a strong scientific case has been made for the construction of a radiotelescope operating at decimeter wavelengths with an aperture of about one square kilometer. Such an instrument would have a sensitivity about two orders of magnitude greater than is currently available. However, current projections indicate that this will require about an order of magnitude reduction in cost per unit area compared to existing structures in order to make it financially feasible. This reduction will demand new and innovative approaches in design. Even with this reduction in capital cost such a facility is expected to be several hundred million dollars. Such a major facility will need to be developed as an international project. The International Radio Science Union (URSI) and the International Astronomical Union (IAU) have recognized this and set up a joint Working Group to facilitate the development. Several countries and institutes have become actively involved and are working together in an international framework. Several different design approaches are currently being studied. These vary from a small number of large spherical radiotelescopes, through a moderate number of medium-sized parabolic antennae, to a phased array of a large number of small nonmoving «tiles». Each approach has advantages, disadvantages and particular challenges.
No known Energy Source can Power Manned Interstellar Flight
Authors: Ksanfomality Leonid V.
Published: July 2016

We consider a possible future energy source: deuterium-helium thermonuclear reaction. When this source is used even with no losses the closest star (4.4 l.y.) cannot be reached during the human lifetime. Calculations prove that the averaged speed of such an interstellar probe consisting only of deuterium fuel (with no mass for any construction!) and the module for astronauts with the mass of about 0.01 of the total mass of the mission, cannot exceed 17,600 km/s, and the two-way flight duration is 150 years. Even with the totally unrealistic mass of the module of 0.0001 of the total mass, it is still 105 years. Unless some as yet undiscovered physics leads to new sources of energy, interstellar flights piloted by a single generation of humans will remain a dream forever.
Detecting Interstellar Migrations
Authors: Matloff Gregory L. , Pazmino John
Published: July 2016

Interstellar Migrations may occur when a civilization’s star enters the Red Giant phase, thereby dooming the life-bearing planet(s). Ecologically self-contained «world ships», massing billions of kilograms and propelled by hyperthin, space-manufactured solar sails thousands of kilometers in diameter unfurled near the home star are possible vehicles to transfer a threatened civilization to a neighboring star. Consideration of the nearest Red Giants reveals that Pollux is the nearest formerly solar-type Red Giant. Known stellar neighbors of Pollux are surveyed to determine likely directions for an interstellar migration departing Pollux. Such migrations might consist of many world ships launched over millenia on voyages of about 1000 terrestrial-year duration; discovery of such events will be serendipitous. The difficulties of observing solar-sail star ships near Pollux are considered. A facility dedicated to imaging extrasolar planets within 10 parsecs might be capable of detecting these large spacecraft.
The Biophysical Cosmology: The Place of Bioastronomy in the History of Science
Authors: Dick Steven J.
Published: July 2016

The recent discoveries of planets around Sun-like stars, possible primitive Martian fossil life, and conditions on Europa conducive to microbial life, render more urgent the question of the place of bioastronomy in the history of science. This paper argues that the tenets of bioastronomy constitute a «biophysical cosmology», a scientific world view that holds that life is common throughout the universe. Many of the activities of the field of bioastronomy are tests of this cosmology. Like other cosmologies, the biophysical cosmology bears strongly on humanity’s place in the universe. Cosmological status may also be useful in discussing die implications of contact, when one considers the response to other cosmologies as partial, if imperfect, analogues.
Resonance Effect of Binary Orbital Motion upon δ Scuti Type Stars
Authors: Paparó M. , Shibahashi H. , Sterken C.
Published: July 2016

The colour behaviour of θ Tucanae with orbital phase is shown. A break in the residuals is checked as the criterion for stopping the period search. A resonance of the dominant pulsational mode and the period of ellipticity is reported, with a Resonance number of 72.
The Luminosities of δ Scuti Stars
Authors: McNamara D.H.
Published: July 2016

The δ Scuti stars are variables found in the instability strip above the zero-age main sequence. Radial and nonradial pulsation modes have been detected in these stars. The large-amplitude variables with asymmetric light curves are radial pulsators. The pulsation periods are found to be in the period range of 0.03 – 0.25 days. Generally, the light amplitudes are small (total range < 0.3 mag), but some fundamental-mode variables reach 0.70 mag. The majority of the variables have light amplitudes <0.10 mag. Population II δ Scuti variables are frequently called SX Phe stars. Many of these variables have been found in globular clusters, where they populate the blue-straggler domain of the color-magnitude diagrams.
RR Lyrae Variables in Local Group Galaxies: LMC, Leo I. New Results and Distances to these Galaxies
Authors: Clementini G. , Bragaglia A. , Fabrizio L. Di , Maio M. , Carretta E. , Gratton R.G. , Held E.V. , Momany Y. , Rizzi L. , Saviane I.
Published: July 2016

We present new results on a sample of RR Lyrae variables in the bar of the Large Magellanic Cloud (LMC), and report on the first detection of RR Lyrae in the dwarf spheroidal galaxy Leo I. Emphasis is given to the discussion of the distances to these galaxies as derived from their RR Lyrae populations, and of the impact on the “short” and “long” distance scale dichotomy.
Empirical Luminosities and Radii of Stars in the β Cep, SPB and δ Sct Instability Domains
Authors: Jerzykiewicz M.
Published: July 2016

For 26 stars with effective temperatures known from directly measured angular diameters and total absolute fluxes (Code et al., 1976), HIPPARCOS parallaxes (ESA, 1997) can be used to derive empirical luminosities and radii. The empirical effective temperatures and luminosities allow a comparison of the position of these stars in the fundamental H-R diagram with evolutionary tracks. Note that no calibration, photometric or any other, is involved in the process. As noted by Jerzykiewicz & Molenda-Żakowicz (2000), the comparison shows an overall coincidence with the phases of slow nuclear burning of the solar composition evolutionary tracks, computed with OPAL opacities and moderate amount of overshooting from the convective core.

Several of the stars fall in the theoretical β Cep, SPB or δ Sct instability domains. Unfortunately, none of them is known to be an SPB variable, while the two that have been classified as δ Sct stars lack convincing evidence of variability. For the four β Cep stars that occur in the sample, the empirical radii are used to identify the radial order of pulsation.
Interferometric-Doppler Imaging of Nonradial Stellar Pulsations
Authors: Jankov S. , Vakili P. , Domiciano de Souza A. , Janot-Pacheco E.
Published: July 2016

We present the imaging potential of a tomographic technique which combines time-resolved spectroscopy and long baseline interferometry, providing information that cannot be obtained otherwise with each of these techniques separately.
The Effects of Rapid Rotation on Pulsation
Authors: Saio Hideyuki
Published: July 2016

We discuss the properties of pulsations in rotating stars, which include frequency shifts, the effects on the stability of p- and g-modes, and the properties of low-frequency modes whose frequencies are comparable to or less than the rotation frequency.
On the Theory of Oscillations of Rapidly Rotating Stars
Authors: Rieutord M. , Lignières F.
Published: July 2016

We present the current understanding of the dynamical aspects of the oscillations of rapidly rotating stars.
Two-Dimensional Hydrodynamic and Evolution Sequences of Rotating Stars
Authors: Deupree R.G. , Guzik J.A. , Neuforge-Verheecke C.
Published: July 2016

Two-dimensional hydrodynamic simulations were calculated for ZAMS models with Z=0.02, and masses of 3, 5, 8, 12, and 20 M⊙. For each mass five models were calculated - one nonrotating and four with progressively higher rotation rates. The rotating models were categorized by the ratio of the polar to the equatorial radius, with values of 0.985, 0.92, 0.84, and 0.72. The simulations were performed with the fully two-dimensional implicit code ROTORC (actually what is known as 2.5 dimensions, with azimuthal symmetry, but with a conservation law for the rotational velocity in the azimuthal direction).

All models showed considerable core overshooting. To first order, the value is about 0.5 Hp, but with a fairly large variation of about 0.2 Hp. It is not clear why the variation is so large, but comparison with other turbulence models shows that overshooting/is one of the more sensitive features of the model (Deupree, 1998). However, there are some trends that may be significant. For the two highest masses there was apparently no dependence on the rotation rate, but the three smaller masses showed a linear decrease in the extent of overshooting with increasing rotation. There is a hint that the 20 M⊙ model has slightly larger overshooting than models of the other masses. With the random variations, it is difficult to assign a level of significance to these trends.
Qualitative Explanation of Phase Shifts Observed in Line Profile Variations
Authors: Montgomery M.H.
Published: July 2016

In a series of papers, Telting & Schrijvers (1997) have demonstrated the correlation between the phase shift across a line, ∆Ψ0 and the l-value of a mode. In addition, they found that the phase shift of the harmonic (i.e., at frequency 2ω) was an indicator of m. In this poster, we present a heuristic derivation of these results under a set of idealized assumptions. Within this framework, exact analytical formulae for the Ilrn(x) were calculated, which are available upon request.
The Slowly Pulsating B Star HD 147394
Authors: Briquet M. , Noels A. , Aerts C. , Mathias P.
Published: July 2016

HD 147394 is a Slowly Pulsating B star for which we found three periods in the moments of the Si II 4128-4130 lines: f1 = 0.8008 c/d, f2 = 0.7813 c/d and f3 = 0.6710 c/d. A mode identification is perform ed by using the moment method.
Fundamental Parameters of Be Stars Seen Equator-On
Authors: Zorec J. , Frémat Y. , Hubert A.M. , Floquet M.
Published: July 2016

The geometric deformation, as well as the non-uniform surface gravity and temperature distributions induced by the fast rotation, are taken into account to determine the fundamental parameters of 10 Be stars seen nearly equator-on. The stars occur in the first half of the main sequence evolutionary span, which suggests that their fast rotation is related to initial formation conditions, rather than to evolutionary effects.
Pulsations of Complete Evolutionary Models for roAp Stars: Preliminary Results
Authors: Michaud G. , Brassard P. , Richer J. , Richard O. , Fontaine G.
Published: July 2016

The evolutionary models described in the accompanying poster (Richard et al., these proceedings) have been tested for pulsations using both the adiabatic code developed by Brassard et al. (1992) and the corresponding non-adiabatic code as first used in Fontaine et al. (1994). For the stars of interest, these codes have the great advantages of being potentially able to treat atmospheric regions, as well as being numerically stable and efficient. The required derivatives were calculated by least-square fitting of spline functions to complete opacity tables constructed at each composition of the evolved model. Since there were some 1500 zones for each model, 1500 such tables were constructed and spline functions were fitted to each of them. They then gave directly the derivatives required for the pulsation calculations (see Fig. 1). Note that models equivalent to 1.70T5.3D1K-3 have already been tested for pulsations by Turcotte et al. (2000).
Applications of Non-Adiabatic Radial Pulsation Equations to roAp Stars
Authors: Medupe R. , Christensen-Dalsgaard J. , Kurtz D.W.
Published: July 2016

We apply a code that solves grey radial non-adiabatic pulsation equations with consistent treatment of radiative transfer to the roAp frequency regime. We find evidence for the existence of chromospheric modes at frequencies 2.5 mHz, 3.7 mHz, 4.6 mHz and 5.7 mHz in the equilibrium model we used. We also find that, since the oscillations are not adiabatic at the surfaces of roAp stars, better surface boundary conditions need to be considered in future studies.
Unusual Mode Changes in the δ Scuti Type Variable Star FL Cancri
Authors: Goranskij V.P. , Kusakin A.V.
Published: July 2016

On the base of 105 hour photoelectric monitoring, we show that FL Cnc is a multiperiodic δ Set type variable with rapid night-tonight changes of the amplitudes of the periodic components in the Fourier spectra. We observed an event of pulsating frequency doubling on a time scale of a week, which was treated as an azimuthal mode change.
An Attempt at Mode Identification for V480 Tau
Authors: Di Mauro M.P. , Christensen-Dalsgaard J. , Pijpers F. , Hao J.
Published: July 2016

Spectroscopic observations of the δ Scuti star V480 Tau, obtained during the MUSICOS 1996 campaign (Hao et al., 2001), detected a large number of modes. In order to assess the information available from such data, we compare the observed spectrum of frequencies with the theoretical predictions obtained for models computed by including the effect of fast rotation on global oscillations.
New Observations of the Pulsating PMS Star V351 Ori
Authors: Marconi M. , Ripepi V. , Bernabei S. , Palla F.
Published: July 2016

We present new photoelectric observations of the Pre–Main-Sequence δ Scuti star, V351 Ori. These new data suggest that V351 Ori could be a multiperiodic variable. The comparison between observations and detailed pulsational models allows us to put independent constraints on the mass and luminosity of the star. The predicted distance is 210 pc, indicating that V351 Ori is much closer than the Orion star forming region. With an inferred mass of ∼1.8 M⊙ and an uncertain evolutionary stage, V351 Ori represents an excellent candidate for future asteroseismological studies that will assess whether it is a young PMS star (∼6 Myr) or an evolved object (∼1 Gyr) leaving the main-sequence.
Irregular Behavior in the Light Variations of 29 Cyg
Authors: Riazi N.
Published: July 2016

The phase space and FFT tools are applied to investigate the irregular behavior of the existing light curves of the λ Boo star 29 Cyg.
Analysis of Long-Term Single-Site Observations of the Pulsating DB White Dwarf GD 358
Authors: Bradley P.A.
Published: July 2016

The pulsating DB white dwarf GD 358 was observed by the Whole Earth Telescope (WET) in 1990, 1994, and 2000. While these observing runs revealed a wealth of pulsation modes, they constitute only three “snapshots” of the behavior of this star. These “snapshots” show that GD 358 has a series of l = 1 modes present in the period range of 420 to 810 seconds, with numerous Fourier Transform peaks at the sums and differences of the l = 1 mode frequencies. In addition, the amplitudes of the l = 1 modes and the sum and difference frequency peaks (which I also call “combination peaks” in this paper) are different in each WET run. These data are not sufficient to determine the time scale of the amplitude changes and whether additional l = 1 modes might be present. For this, we need more frequent data sets, although not necessarily WET data.
Frequency Analysis of δ Scuti and RR Lyrae Stars in the OGLE-1 Database
Authors: Moskalik P. , Poretti E.
Published: July 2016

We discuss the results of a systematic search for multi-periodic pulsations in Galactic Bulge δ Scuti and RR Lyrae stars. Six “normal” double-mode variables pulsating in two radial modes have been identified (5 δ Scuti-type and 1 RR Lyrae-type). In 37 RR Lyrae stars secondary periodicities very close to the primary pulsation frequency have been detected. These periodicities correspond to nonradial modes of oscillation. They are found in ∼ 23% of RRab and in ∼ 3% of RRc variables of our sample.
Combined Modeling of Stellar Evolution and Pulsation
Authors: Csubry Z. , Szabó R. , Kolláth Z. , Buchler J.R.
Published: July 2016

The radial pulsations of variable stars at specified points along their evolution are accurately described with numerical hydrodynamics. The behavior of the pulsations along evolutionary tracks can then be modeled with amplitude equations, whose coefficients are obtained from fits to these hydrodynamical models. To simulate stellar evolution we make the stellar core’s properties time-dependent and can investigate directly the effects on pulsation despite the very different time-scales (dynamical, thermal, evolutionary).
Atmospheric Dynamics of Long Period Cepheids
Authors: Belmont R. , Chadid M. , Mathias P. , Gillet D. , Fokin A.B.
Published: July 2016

We present a Spectroscopic study of two long period Cepheids: X Cyg and SV Vul, together with the prototype of the class.
Observation of γ Doradus Stars in the Space Asteroseismology Era
Authors: Zerbi F.M. , Kaye A.B.
Published: July 2016

Almost 10 years have passed since the first claims of the existence of a new class of slowly pulsating variables near the cool border of δ Scuti instability strip. The consolidated class of γ Doradus variables faces now the challenge of space. In this paper, we review the most recent theoretical and observational results of these stars and we discuss how our knowledge of their nature will benefit from data collected in the forthcoming space-borne asteroseismological missions.
g Modes inγDoradus Stars: a Theoretician’s Quest for Instability
Authors: Löffler W.
Published: July 2016

We present a new implementation of the Riccati method for the linear stability analysis of weakly non-adiabatic g-mode pulsations in γ Doradus stars.
Complex Pulsation-Like Variability of the LBV Star v532 in M33
Authors: Sholukhova O. , Zharova A. , Fabrika S. , Malinovskii D.
Published: July 2016

We present an analysis of a light curve of LBV star v532 (Romano’s star) in M33. The data consist of 881 individual photographic observations from 1960 to 2000. The star shows extremely rich periodic variations. We find that the amplitudes of the periods depend on brightness, as they rise when the star becomes brighter. We suggest that the 13.08-day period corresponds to the star’s rotation, other short periods (∼ 20 – 30 days) represent the star’s pulsations, and the longer periods are instability driven wind pulsations. The spectral variability of v532 is also strong, with the spectrum excitation depending on the stellar brightness.
Dynamical Atmospheres and Mass Loss of Pulsating AGB Stars
Authors: Höfner Susanne , Loidl Rita , Aringer Bernhard , Jørgensen Uffe G.
Published: July 2016

We present a new generation of dynamic model atmospheres for pulsating AGB stars based on a combined solution of hydrodynamics, frequency-dependent radiative transfer, and time-dependent dust formation. At present, we are performing a systematic study of the dependence of atmospheric structure, observable properties and mass loss on stellar parameters and pulsation properties. Preliminary results show a good agreement with observations and a considerable improvement compared to existing grey dynamical models.
The Influence of Dust Properties on the Mass Loss in Pulsating AGB Stars
Authors: Andersen Anja C. , Höfner Susanne , Loidl Rita
Published: July 2016

We are currently studying carbon based dust types of relevance for carbon-rich AGB stars, to obtain a better understanding of the influence of the optical and chemical properties of the grains on the mass loss of the star. An investigation of the complex interplay between hydrodynamics, radiative transfer and chemistry has to be based on a better knowledge of the micro-physics of the relevant dust species.
Pulsating AGB Stars in the LMC
Authors: van Loon Jacco Th.
Published: July 2016

I give a brief review and interpretation of the evolution, mass loss and pulsation of AGB stars in the Large Magellanic Cloud.
The Effects of a Weak Magnetic Field in the Line Profiles of A-type Supergiant Winds
Authors: Verdugo E. , de Castro  Gómez A. , Ferro-Fontán C. , Talavera A.
Published: July 2016

Solutions for the stellar winds of hot luminous stars are obtained by solving the magnetohydrodynamic (MHD) equations, combined with the theory of radiation-driven winds. The formalism is basically the same as developed by Rotstein & Giménez de Castro (1996). We have considered the interaction of radiation pressure with an open magnetic field . The magnetic field lines are pushed by the intense radiation field and adopt a purely radial configuration:

and the polar magnetic flux at the photosphere:

Rotstein & Giménez de Castro (1996) assume all the lines contributing to the radiation pressure are optically thick (α = 1) in order to decouple the MHD equations. Here the model has been improved to adopt a value of α = 0.6 which is a better approach for A-supergiants.
Requirements for Future Photometric and Spectroscopic Observations for Asteroseismology: One Observer’s Perspective
Authors: Balona L.A.
Published: July 2016

We discuss prospects for asteroseismology in stars for which the frequencies of pulsation lie outside the asymptotic regime. The problem of mode identification in this case is the major obstacle. Mode identification techniques from photometric and Spectroscopic observations are discussed.
The Controversial Sun
Authors: Ulrich Roger K.
Published: July 2016

The sun serves as an important test case for a variety of problems related to stellar structure and evolution as well as fundamental physics. The sun also influences the terrestrial environment through its varied outputs. These two aspects of the solar interior combine to generate a surprising level of controversy for such an inherently simple star. I review three topics each of which is the subject of some degree of controversy: 1) the solar neutrino problem, 2) the status of modeling and observational efforts to understand the solar cycle of activity and 3) observational efforts to detect and identify solar g–modes.
CESAM Solar Models
Authors: Morel P. , Berthomieu G. , Provost J. , Lebreton Y.
Published: July 2016

Solar models have been computed using the code CESAM constructed at Nice (Morel, 1992), and the new opacities of Livermore for different mixtures. Their global characteristics, predicted capture rates of neutrinos for the chlorine and gallium experiments and their seismological properties are given.
Restoration of the Atmosphere in Solar Models
Authors: Morel P. , Van’t Veer C. , Berthomieu G. , Cayrel R. , Castelli F. , Goupil M.J. , Lebreton Y. , Provost J.
Published: July 2016

From models of the Sun atmosphere obtained with ATLAS 9 (Kurucz 1992) it appears that the diffusion limit of the transfer equation becomes valid only at depths larger than TR ~ 10. Even with physics as consistent as possible one restores the atmosphere with an accuracy not better than ~ 40%, but with small consequences on solar calibrated models. Despite the eigenmodes have turning points located in the atmosphere, the study of the oscillations reveals differences less than 2μHz when the atmosphere is restored with various assumptions.
Helioseismic Constraints on the Structure of the Present Sun
Authors: Baturin V.A. , Ajukov S.V.
Published: July 2016

Given the chemical composition (essentially the hydrogen abundance), mass and the physics of the interior, the structure of a star is uniquely determined. The usual method for the determination of the hydrogen-abundance profile of the present Sun is via evolutionary calculations. But the existing uncertainties in the physics and evolutionary history suggest considering a more extended set of possible solar models. Here, we examine models with solar values of radius, luminosity and mass, but with arbitrary profiles of the hydrogen abundance in the core. Of course, the profiles X(m/M) must satisfy some (rather weak) restrictions, so that the solar values (determined by fitting) can be attained.
Parameters Teff and log g for Late B and Early A Type Stars
Authors: Gerbaldi M. , Zorec J.
Published: July 2016

We compare the log g parameters of early A and late B type stars determined from model atmospheres with those issued from models of stellar evolution. There is a systematic deviation between both determinations for log g < 3.7 .
The Infrared Excess of Early-Type Stars: Modelling the Iras Observations
Authors: Runacres M. , Blomme R.
Published: July 2016

The IRAS satellite has observed some early-type stars in the infrared part of the spectrum. Most of this infrared radiation is due to free-free scattering in the dense stellar wind of these stars. We modelled this phenemenon by solving the equations of hydrodynamics as well as the radiative transfer equation (for a H and He mixture). This yields continuum fluxes at visible and infrared wavelengths which have been compared with the observations.
A Search for Lithium in Brown Dwarf Candidates
Authors: Rebolo Rafael , Martin Eduardo L. , Magazzu Antonio
Published: July 2016

We are conducting a search for lithium in very low mass objects with the aim of discriminating between stellar and substellar objects. Lithium is expected to be preserved in brown dwarfs with M/M⊙ ≤0.06, while it is known to be efficiently destroyed in low mass stars. In this paper we present high resolution observations in the region of the λ 6708 Li I resonance line of 5 very low mass dwarfs. In none of them lithium is detected, implying a Li destruction in their atmospheres of about four orders of magnitude. Our results suggest that these objects are probably very low mass stars rather than brown dwarfs.
Absolute Measurements of Starspot Area and Temperature
Authors: Neff James E. , O’Neal Douglas , Saar Steven H.
Published: July 2016

Photometric and spectroscopic variability of late-type stars frequently has been interpreted as evidence of magnetic activity. The standard picture of stellar activity – inherited from solar observations – includes cool, dark “spots” in the photosphere and hot, dense regions in the chromosphere and coronae. The immediate cause of each of these phenomena is a closed topology of the local magnetic field. Because stars appear as mere points of light, these localized phenomena have not been directly resolvable on stars other than the Sun. Most observed effects are produced by an asymmetric distribution of starspots. If the distribution is symmetric, it would escape detection by most current techniques of light-curve and line-profile modeling. Even more troubling, the stellar properties measured with these techniques describe only a difference between contrasting hemispheres, not an absolute measure.
A Multiline Method to Determine Stellar Magnetic Fields
Authors: Rípodas Pilar , Collados Manuel , Almeida Jorge Sánchez , López Ramón J. García
Published: July 2016

In the past, much effort has been devoted to determine stellar magnetic fields by means of the analysis of two spectral lines with different magnetic sensitivities (see, e.g., Robinson, 1980; Saar, 1988; Basri and Marcy, 1988). However, these methods are largely influenced by the uncertainties caused by, for instance, the presence of blends, uncertainties of atomic parameters, etc. Gray (1984) and, more recently, Basri et al. (1992) used a multiline analysis to measure stellar magnetic fields, reducing the importance of those uncertainties, thus increasing, in a statistical sense, the confidence of the results.

Here we present a new method based on the analysis of the equivalent widths of many Fe I spectral lines. The central idea is to obtain information on the magnetic field from the magnetic strengthening of the equivalent width of spectral lines. This technique has been applied to a weak-emission-line T Tauri star (TAP35) and a main sequence star (ξ Boo A), using data published by Basri et al., (1992).
The Equation of State
Authors: Däppen Werner
Published: July 2016

There are two basic approaches to the equation of state for stellar envelopes and interiors. The traditional method chooses the so-called “chemical picture”, in which the notion of atoms is maintained despite the plasma environment. A mixture of atoms, molecules, ions, electrons and nuclei is considered, and the occurring ionization and dissociation reactions (thus the name chemical picture) are treated according to the entropy-maximum (or free-energy-minimum) principle. The alternative method is based on the so-called “physical picture”, where only fundamental particles (electrons, nuclei) explicitly enter. Through the means of activity expansions, the problems of plasma physics and statistical mechanics are treated simultaneously and on the same footing. For helio- and asteroseismology, an accurate and precise equation of state is essential. Progress towards a better equation of state can be made in several ways: purely theoretical efforts, checks with experiments, including astrophysical data, and comparisons between different theoretical formalisms. Comparisons are useful to assess the domain of temperature and density where the theoretical complications matter, and to determine the diagnostic potential of astrophysical observables for equation of state issues.
The Generation of Internal Waves
Authors: Montalbán Josefina
Published: July 2016

The generation of internal waves in the radiatively stable stellar region by the turbulent motion at the boundary of the overlaying convective zone is similar to the same case in the deep ocean or in the earth atmosphere (Townsend, 1965), and can be described in a simple way as following: When an turbulent fluid element arrives at the boundary of the convective region with a non-zero momentum, it beats and it deforms the interface between both regions. This disturbance of the equilibrium state excites a train of internal waves propagating below the convective zone in the horizontal and vertical directions for the frequencies lower than the characteristic one for the stable stratification (Brunt-Väisälä frequency).
Numerical Simulations of 3D Compressible Convection
Authors: Muthsam Herbert J. , Zöchling Johann
Published: July 2016

Numerical models of a convection zone embedded between two stable layers have been calculated; one is shortly presented and in particular a few items concerning the lower overshoot region are discussed.
V 3903 Sagitarii: A Main-Sequence (07V+09V) Detached Eclipsing Binary
Authors: Vaz L.P.R. , Cunha N.C.S. , Vieira E.F. , Myrrha M.L.M.
Published: July 2016

Photometric and spectroscopic observations of V3903 Sgr are analyzed, and absolute dimensions (masses and radii) are determined to a precision better then 3%.
Small and Intermediate Mass Stellar Evolution - Main Sequence and Close to It
Authors: Noels A. , Grevesse N.
Published: July 2016

We present the standard models for small and intermediate main sequence stars and we discuss some of the problems arising with semiconvection and overshooting. The surface abundance of Li serves as a test for other physical mechanisms, including microscopic and turbulent diffusion, rotation and mass loss.
Coulomb Corrections and Globular Cluster Stellar Evolution
Authors: Proffitt Charles R.
Published: July 2016

The effects of Coulomb corrections on the evolution of globular clusters stars are discussed. Coulomb corrections alter the equation of state by about 1% in most of the stellar interior, and for stars of fixed initial parameters, this results in an 8% increase in the ZAMS luminosity and an 8% decrease in the age at the main sequence turnoff. Ages for globular clusters measured by comparing to the turnoff luminosity of theoretical isochrones are lowered by ≈ 4% when Coulomb effects are included.
Spin-Down of Solar-Type Stars with Internal Magnetic Fields
Authors: Charbonneau Paul , Macgregor Keith B.
Published: July 2016

We present a selection of results from a large set of numerical simulations of the spin-down of a solar-type star containing a large scale magnetic field in its radiative interior. Our computations are dynamical, in that they take into account both the generation of the toroidal component by the wind-induced shear endits back-reaction on the azimuthal flow. Our results demonstrate the existence of classes of internal magnetic fields that can accomodate rapid spin-down near the ZAMS, and yield weak internal differential rotation by the solar age.
Asymptotic Theory of Low-Degree Stellar Acoustic Oscillations
Authors: Roxburgh I.W. , Vorontsov S.V.
Published: July 2016

We extend the second-order asymptotic description developed by Tassoul (1980, 1990) to the forth order, taking into account both gravity perturbations and realistic (non-polytropic) structure of the stellar envelope. We examine the accuracy of the asymptotic description by the direct computations for a solar model.
Detecting Convective Overshoot In Solar-Type Stars
Authors: Monteiro M.J. P. F. G. , Christensen-Dalsgaard J. , Thompson M.J.
Published: July 2016

It is important for understanding stellar evolution to constrain observationally how overshoot occurs for stellar conditions. Simplified models of the dynamics (eg. Zahn 1991) indicate that overshoot results in a slightly subadiabatic region beyond the convectively unstable layers, followed by an almost discontinuous transition to radiative stratification. Abrupt changes such as this contribute with a characteristic periodic signal to the frequencies ωn,l, of modes of low degree l (Gough 1990). This signature may therefore be detectable for distant stars. Here we show that the signal is sensitive to the “severity” of the overshoot and, of practical importance for the solar case, how it may be extracted from modes of higher degree. Finally we apply our method to solar data.

To analyze the applicability of the method, we consider four stellar models, Z1 — Z4, with solar mass, radius (R) and luminosity; of these, Z2 and Z4 have overshoot. The bases of the nearly adiabatically stratified region in the models are at radii rd/R = .729, .713, .713 and .700 respectively.
Theory of The Oblique Pulsator Model For The Rapidly Oscillating Ap Stars
Authors: Shibahashi Hiromoto , Takata Masao
Published: July 2016

Recently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We show that the magnetic field on axisymmetric dipole modes distorts the dipole oscillation pattern to have axisymmetric octapole components so that the frequency pattern becomes a septuplet rather than a triplet, and that the additional effect of the rotation leads the frequency pattern to be asymmetric. The formula allows us to get information about the magnetic fields, the rotation, and the geometrical configuration of the star from the oscillation data.
Winds
Authors: MacGregor K.B.
Published: July 2016

It is by now well known that most main sequence stars continuously lose mass as a consequence of the winds they emit. In addition to affecting the thermal and dynamical state of the stellar atmosphere, such mass loss can also induce changes in the interiors of stars. In the present review, we consider a few of the ways in which sustained, wind-like mass loss can alter the physical state of main sequence stellar interiors by examining the differences in internal structure, composition, and rotation between mass-losing and conservatively evolving stars.
Stellar Activity: Constraints Expected From Space Experiments
Authors: Catala Claude
Published: July 2016

Dynamo theory needs to be guided and tested by observations. However, solar observations alone cannot provide sufficient tests of the dynamo models, and constraints obtained from stellar observations are still few, indirect, and poorly related to the properties of dynamos.

This review discusses which parameters must be observed on stars other than the Sun to usefully guide the theoretical efforts and test the resulting models. We show that most of these observables, which characterize the stellar activity phenomena, are accessible only from space, and that space-based experiments are one of the best took to trigger progress in the field of solar and stellar activity in the next few decades.
Lithium Abundance and Activity for 57 Rs Cvn Systems
Authors: Xuefu Liu , Gang Zhao , Huisong Tan , Fangjun Lu
Published: July 2016

High-resolution (0.145A/diode, high signal-to-noise (> 100) Reticon spectra of 57 RS CVn systems, which were observed with the coudé spectrographs of the McDonald 2.1m telescope and Yunnan lm telescope, were used to analyse a correlation between Li abundance and chromospere activity. Li abundances of 57 RS CVn stars, which include 76 detected components have been determined through the determination of equivalent widths of Li doublet (6707.761A + 6707.912A) and Kuruz’s model atmosphere. The model metal abundance and line analysis of 10 RS CVn stars were determined from the present spectral lines data. The main results are the following: 1, Lithium abunances of 76 RS CVn components for 57 RS CVn systems are obviously reduced with the the effective temperatures gradually decreasing. 2, Li abundance has staistically decreasing trend in RS CVn stars with the rotational velocities vsini increasing. 2, The position of 168 RS CVn stars in the (U-B, B-V) Figure show that they can be devided into two groups. The most of them seem to be not poor-metal stars. Li abundances of these stars seem to have no obious correlations with their stellar chromosphery activity levels, but 7 RS CVn systems, in which cool component is more active show that the more active component has a lower Li abundance.