bluuebunny/crossref_metadata_2025 huggingface dataset:
X-Ray and UV Emission from VV Puppis
Authors: Patterson J. , Beuermann K. , Fabbiano G. , Lamb D.Q. , Raymond J. C. , Horne K. , Swank J. , White N. E.
Published: March 2016

We have discovered hard and soft X-ray emission from W Puppis, the last of the four classical AM Her stars to be detected in X-rays. The orbital light curves in both soft and hard X-rays are in excellent agreement with the mean optical light curve, indicating that essentially all of the accretion luminosity originates from a very small region at the white dwarf’s magnetic pole. An X-ray dip occurs once per binary period, when the magnetic pole lies closest to our line of sight, and is probably due to absorption. The X-ray data and optical spectroscopy constrain fairly well the geometry of the system, dictating an inclina-tion angle i < 70º and a mass for the white dwarf in excess of 1.1 Mʘ. X-ray and UV observations constrain the temperature of the soft X-ray component to lie in the range 20–45 eV, while the hard X-ray component has a temperature in excess of 6 keV. The observed flux of soft X-rays is much larger than that of hard X-rays. However, when the energy band-passes of the observations are taken into account, the ratio of the soft and hard X-ray luminosities Ls/Lh = 0.5-50. The ratio is unity for Tbb = 30 eV and Tbr = 50 keV; ifc is smaller if Tbb and/or Tbr are larger and is larger in the opposite case. These results, taken together with those for AM Her using the Einstein OGS, suggest that the famous “soft X-ray problem” in the AM Her stars may have gone away.
Dynamical Models for our Virgocentric Deviation from Hubble Flow
Authors: Salpeter E. E.
Published: March 2016

Spherically symmetric models for the dynamic development of a galaxy cluster from an initial overdensity have been carried out numerically, without dissipation or 2-body relaxation but with shell crossings included. The deviation ∆V from pure Hubble Flow of the Local Group, due to the retardation effect of the Virgo cluster and supercluster, has been calculated from a number of different models by Hoffman and Salpeter (Astrophys. J. 263, 1982, in press). The results are somewhat surprising if one takes the point of view of (a) insisting that the dynamic model fit the observed dispersion of galaxy systemic velocities in the core of the Virgo cluster, but (b) allowing the mass to light ratio M/L to be an arbitrary (but smoothly varying) function of distance from the Virgo cluster center. Point (a) essentially fixes the mass density and M/L in the core, but (b) still allows a wide range of values for the cosmological density parameters Ω (proportional to the average M/L far from the Virgo cluster). With this point of view ∆V actually decreases with increasing Ω: If M/L is constant, Ω ≈ 0.3 and ∆V ≈ 250 km s–1 (Hoffman, Olson and Salpeter, Ap. J. 242, 861, 1980); for Ω ~ 0.05, ∆V would exceed 350 km s–1; for Ω = 1, AV could be less than 150 km s–1.
Structure of Atomic Spectra: Some Recent Laboratory Research of Interest for Stellar Spectroscopy
Authors: Martin William C.
Published: March 2016

The data covered are wavelength, line classifications, and energy levels, and the references (numbers in brackets) are mainly supplementary to those supplied by Working Group 4 for the 1982 Report of Commission 14.

New compilations of the energy levels for all the spectra of Fe (Fe I - XXVI) [42] and Co (Co I - XXVII) [43] have been published. Although compilations of the levels for the 235 iron-group spectra (K through Ni) by the NBS AEL Data Center have been published by element during the past five years, the single-volume collection of these levels now under preparation will incorporate fairly extensive additions and revisions for many of the spectra. A compilation of the levels for Si (Si I – XIV) has been completed and should appear early in 1983.
Women in Astronomy in the US and Canada
Authors: Baum S.A.
Published: March 2016

This paper is divided into three sections. In the first, we highlight the results of statistical investigations into the status of women in astronomy in the US. In the second section, we discuss some of the likely reasons for the lack of equal representation by women in astronomy and in the final section, we discuss some the suggestions for how to improve things. Much of the information presented here was taken from the proceedings of the Women in Astronomy meeting held in Baltimore in 1992. Recommendations from that meeting, have been formalized in the Baltimore Charter. The Baltimore Charter has been endorsed by a number of universities and institutions in America, including the NSF, NASA, and the AAS.
Report of the IAU WGAS Sub-group on Electronic Distribution
Authors: Kaplan G.H.
Published: March 2016

The task of the Sub-Group on Electronic Distribution (SGED) of the Working Group on Astronomical Standards (WGAS) is to make recommendations for direct worldwide computer access to astronomical standards of various kinds. Specifically, part of the charter of the WGAS was ”to prepare a draft report on possible electronic access to these units, constants, quantities, and procedures...”

Like the other sub-groups, the SGED operated as a ”committee of the whole”, the whole being the entire Working Group on Astronomical Standards. The scope of interest includes numeric data and software that has some sanction by the IAU or has been validated (in some way) as implementing some IAU-adopted model, set of constants, catalog, ephemeris, or algorithm. Thus, the controversial matters of what defines an IAU standard, whether such standards are still useful, what subject areas are appropriate, what specific standards are to be adopted, how software is to be validated, etc., are addressed by the other sub-groups.
Determination of LC and LB
Authors: Fukushima T.
Published: March 2016

The location-independent part of TCB-TCG, the difference between the two new time scales adopted by the IAU (1992), was integrated numerically for three JPL planetary/lunar ephemerides; DE102, DE200, and DE245. The differences among these three integrations were mostly explained by the difference in the adopted constants of the ephemerides. It was shown that the post-Newtonian correction and the perturbation by asteroids are negligible except for the mean rate, LC. The comparison of these numerical integrations with the analytical formulas of Hirayama et al. (1987) and Fairhead and Bretagnon (1990) as well as their extended versions lead to the best estimate of LC as

Combining this with the recent value of the geoid potential in Bursa et al. (1992), we estimated the value of LB, the scale difference between TCB and TT, as

Table I summarizes these conclusions. These estimates of LC and LB are more reliable than the former values we gave (Fukushima et al. 1986). The new estimate of LB will be useful in converting the numerical values of some precisely determined astronomical constants such as AU measured in meter from those in TDB to those in TCB. Also the numerically integrated TCB-TCG, which are to be called Time Ephemeris, will be useful when converting between TCB and TDB, i.e. the time scales themselves. The full paper will be appeared in A & A with the title of Time Ephemeris.
The IAU Nutation Theory and Perspectives of its Change
Authors: McCarthy D. , Dehant V.
Published: March 2016

The IAU General Assembly has adopted in 1980 a nutation series, on the one hand, based on rigid Earth’s contributions theorically computed from celestial mechanics, and on the other hand, based on non-rigid Earth’s contributions theoretically computed from Earth deformation equations using geophysical parameters.

1.

From the previous papers (see Session 1) of this Joint Discussion, we know that there are differences of this adopted theory with respect to the observations of precession and nutations. These differences can reach several mas, which is well above the present accuracy of the observations.

2.

From previous papers (see Session 2) and from the posters, we also know that there exist new rigid-Earth nutations (Kinoshita-Souchay, Roosbeek, Hartmann) of which the accuracy has increased by one order of magnitude.

3.

From Session 3 papers, we know that there are some additional geophysical effects that are not yet taken into account in Wahr’s nutation theory adopted in 1980 by the IAU which have a contribution at a level above the present precision of the observations. These additional geophysical aspects can be accounted for either from a semi-analytical theory (like Mathews, Herring, Shapiro and Buffett are doing), or from an integration of deformation equations through the whole Earth (Dehant, Wahr).
New Time Scales: Removing Ambiguities
Authors: Brumberg V.A.
Published: March 2016

The new (1991) IAU recommendations on reference systems and time scales are based completely on general relativity. But the metric forms determining the corresponding reference systems are specified in these recommendations not sufficiently definitive to take into account non-geodesic accelerations in the motion of the geocentre or topocentre, to distinguish between relativistic dynamically or kinematically non-rotating systems and to exclude a possible ambiguity in the time scales due to the relativistic coordinate gauge. There is a hidden ambiguity in the relativistic definition of the geocentre due to the difference bewteen Newtonian-type and Blanchet-Damour multipole moments used, respectively, in Brumberg-Kopejkin (Brumberg and Kopejkin, 1989; Kopejkin, 1991a; Brumberg et al., 1993; Klioner, 1993; Klioner and Voinov, 1993) and Damour-Soffel-Xu (1991-1994) approach to construct relativistic hierarchy of reference systems. In using TAI as physical realization of TT one should specify the constant LG(Fukushima, 1994) once for ever not introducing the relativistic ill-defined notion of the geoid (Kopejkin, 1991b). It might be reasonable not to separate this constant at all (as having no sense for moving clocks on the surface of the Earth or in the circumterrestrial space) and to use TAIM as physical realization of TCG itself relating TCG directly with the observer’s proper time avoiding the intermediate scale TT (Brumberg, 1992).
Current Achievements in Time Transfer
Authors: Petit G. , Thomas C.
Published: March 2016

Since early eighties, the introduction of new methods for distant time transfer has led to a major improvement in the precision, accuracy, and coverage of world-wide time metrology. All of these methods are based on the use of satellites. Communication between ground stations and satellites is effected through microwave or optical signals according to a one-way or two-way mode.
Solar Irradiance Variability and Luminosity Changes
Authors: Foukal Peter
Published: March 2016

This review presents a discussion of radiometrie measurements of solar total irradiance variation, ΔS, on time scales of days, to the 15-year extent of present measurements. It does not cover variations in spectral irradiance, particularly the relatively large solar UV and EUV flux variations of great importance in studies of trends in stratospheric ozone, and of upper atmospheric heating variations.

Analysis of the pyrheliometry of ΔS carried out from the Solar Maximum Mission, Nimbus-7 and ERB S satellites has shown that a) the sun brightens by 0.05 - 0.1% around activity maximum and; b) it dims by up to approximately 0.2% when large sunspot groups cross the disc. Empirical models of ΔS based on areas and photometric contrasts of sunspots, and on proxies of facular area, are remarkably successful in matching the observed record of ΔS, on time scales between days and the full 15- year record available since 1978. These models indicate that the opposite contributions of sunspots and faculae in active regions roughly balance over time scales of years, and the net solar brightening observed around peak activity is caused by increased emission from the photospheric magnetic network.
Magnetohydrodynamical Phenomena in the Solar Corona as revealed by Yohkoh
Authors: Uchida Yutaka
Published: March 2016

In the talk, some of the new findings about the magnetodynamical phenomen a in the inner corona obtained by the satellite Yohkoh were reviewed. Here we give a very brief summary of it. (The long list of references has been omitted due to the limitation of space here.)

One of the most remarkable findings by Yohkoh is that the corona is quite a dynamic entity. Such a dynamicity was recognized in its full form by the wide-dynamic range, high cadence imaging from Yohkoh-Soft X-ray Telescope (SXT) with the use of the video-movie presentation. It turned out that the background corona formed quite a dynamic system with the active regions (Uchida 1992, Tsuneta and Lemen 1992), and many examples of interesting dynamic interplay between them were found. It may well be said that the corona is not an “atmosphere” of the usual sense, but is an entity highly electromagnetic in character.
Atomic Data and Coronal Diagnostics
Authors: Mason Helen E.
Published: March 2016

Spectroscopic diagnostics play an important role in determining the electron density and temperature structure, element abundances and dynamic nature of different features in the solar atmosphere. To ensure that these techniques are accurate it is necessary to interface solar analysis programs with the best available atomic data calculations. Recent progress in this work is presented and applications to planned space observations are discussed. In particular, the CDS and Sumer instruments, on the Solar Heliospheric Observatory, will make extensive use of spectroscopic diagnostics to study the heating processes for the solar corona and the acceleration mechanisms for the solar wind.
Particle Acceleration in the Heliosphere
Authors: Vlahos Loukas
Published: March 2016

The heliosphere could be divided in three major acceleration Laboratories, the solar surface (Laboratory 1), the interplanetary medium (Laboratory 2) and Earth and Planetary magnetospheres (Laboratory 3). Our understanding of the acceleration process depends strongly on the nature of the drivers and the energy dissipation process. The energy gain by a particle with velocity where is the variation of the electric field in space and time. All three Laboratories mentioned above share a common characteristic, the drivers and the energy dissipation processes are closely connected to fully developed MHD turbulence. We can show that our understanding of particle acceleration depends strongly on the interaction of particles with fields resulting from fully developed MHD turbulence.
The solar interior and BISON observations
Authors: Elsworth Y.
Published: March 2016

The data taken by the Birmingham Solar Oscillation Network (BISON) forms an interesting link between the twin themes of this session: solar and stellar seismology. Like stellar astronomers, we view the Sun as a star without spatial resolution. There are clearly disadvantages in this, in that we lose information about oscillations which vary rapidly across the Sun. But we are not limited to just the simple radial mode which has l=0; because of Doppler imaging we see modes with a range of l from 0 to 4. Unlike stellar astronomers, our star is near to us and the photon flux is high enough that we need not be limited by photon shot noise. We detect the modes by measuring the integrated surface velocity of the Sun. With long integration times, and for the coherent modes, the smallest amplitudes that we can measure are between 1 and 0.1 cm s−1.
Observations of deep-seated structure in the stellar winds of OB stars
Authors: Prinja R. K.
Published: March 2016

High-resolution, time-resolved spectroscopy in both optical and UV wavebands has shown that the outer layers of luminous OB stars vary on time scales of hours-days. Spectroscopic monitoring with the IUE satellite provides evidence that the stellar winds of luminous, hot stars are not smooth and steady, but are frequently disrupted by the presence of time-dependent structures. In addition, variability is often present in optical photospheric line profiles; these variations are likely due to the influence of photospheric velocity fields, especially those from one or more modes of nonradial pulsation (NRP). The process (or processes) responsible for the formation of time-dependent wind structure is (are) not known. Issues concerning potential connections between NRPs, variations at the base of the outflow, and the development of wind structure pose some of the greatest challenges to our understanding of mass-loss via radiatively driven stellar winds.
Link to the Physical Modelling with an Emphasis on Chemical Peculiarities
Authors: Mathys G.
Published: March 2016

Frequently, the atmospheres of stars of spectral types B to F, on which the attention is particularly focussed in this Joint Discussion, are characterized by non-standard physical conditions: non-solar abundance patterns, surface in homogeneities, strong magnetic fields. The most extreme anomalies are found in the chemically peculiar (CP) stars but more moderate departures from standard atmospheres are observed in many stars in the considered temperature range. This can affect the derivation of fundamental stellar parameters in a number of ways, some of which will be presented in this contribution. The emphasis is set on those physical processes which are specific to CP stars. Due to lack of space, this review is necessarily incomplete: a selection of recent results of interest will be pointed out and some directions of investigation will be suggested.

CP stars have an anomalous continuous energy distribution. Fitting this distribution by standard model atmospheres can only be achieved using models corresponding to different effective temperatures to represent different spectral ranges (e.g., Leone & Catalano 1991). This is obviously not physically meaningful: the effective temperature characterizes the total flux of a star, thus is unique. “Realistic” models must incorporate the anomalous elemental abundances. Such models are presently being developed by Kurucz (ATLAS12) and by the Vienna group (Weiss 1994, private communication). The latter is adapted from Muthsam’s (1979) code. One important result obtained by Muthsam is that the relation T(τ) appears steeper in magnetic Ap stars than in normal stars. This view recently received support from observations of rapid oscillations (Matthews et al. 1990). But even such realistic models may not represent satisfactorily CP star atmospheres, as some potentially important opacity sources may still be unknown. For instance, the broad continuum depressions observed in many magnetic CP stars have not been fully explained yet.
Tests of Evolution Models Using Eclipsing Binaries
Authors: Andersen J.
Published: March 2016

Stellar models are the means by which we describe and understand the distribution of stars in the HR diagram. A stellar model is, in principle, completely specified by the three fundamental parameters mass, chemical composition, and age. Comparing the properties of models and real stars with the same parameters will tell us if our recipe for constructing stellar models is realistic. Unfortunately, the only star for which all three are known independently of stellar models is the Sun. For stars of other masses and ages we must devise observational tests in which at least one fundamental parameter is unknown. Two such popular test objects are double-lined eclipsing binaries and star clusters.

In suitable eclipsing binaries we can determine both masses and chemical composition; the absolute age is unknown, but the same for both stars. Since evolution depends most sensitively on the mass, eclipsing binaries provide a very direct test of the models, but only for two points on a single isochrone. In star clusters, neither ages nor individual masses are known, but the detailed shape and population of a well-observed cluster sequence in the HR diagram provide a number of additional probes into the models.
Tests of Evolution Models Using Star Clusters
Authors: Mermilliod J.-C.
Published: March 2016

The fitting of isochrones over star-cluster colour-magnitude diagrams is a favourite test of stellar evolution models because it seems to be the easiest and most evident one: the star distribution in the colour-magnitude diagram represents a constant age locus, provided the clusters are old enough and the internal age dispersion is negligible. The ratios of evolved to main-sequence stars in open clusters, or of population along the red giant branch in globular clusters, could provide valuable tests, but it is difficult to estimate these ratios with small enough uncertainties. Furthermore the detailed surface chemical composition (element abundances and isotope ratios) is not known for many cluster stars and model predictions cannot be tested in various environments.

Tests have been mostly devoted to the main sequence and the long debate between canonical precepts and core overshooting is still active. St others (1991) has argued that the use of the new opacities (Rogers & Iglesias 1992) reduces the necessity of adding overshooting to the models. Castellani et al (1992) computed extensive grids of models with canonical precepts. However, recent papers (Carraro et al. 1993; Meynet et al. 1993; Demarque et al. 1994) show that a moderate core overshooting (about 0.2 Hp) is still necessary. Basically, cluster observations call for more massive cores, whatever process is at work. An excellent review of the various ingredients included in models (equation of state, nuclear rates, opacities, convection) and the effects of their changes has been presented by Vandenberg (1991).
Joint Discussion 11: The Lithium Problem Introduction
Authors: Spite F.
Published: March 2016

The exact title of the JD 11 was: “stellar and interstellar lithium and primordial nucleosynthesis”. The large amount of work recently done about lithium provided an incentive for a discussion among the members of several commissions of the IAU. Lithium is a peculiar element. Since it is not produced in supernovae (at least such a production is not proven and would be quite different from the production of the other elements) its presence in old material is a legacy of the primordial nucleosynthesis. But lithium is a fragile element, and from a theoretical point of view, there are arguments tending to conclude that, in old stars, this legacy has been depleted. This difficult problem is areal challenge, an has been the motivation for many different works. The analysis of the lithium behavior in well known stars, of all kind of ages, metallicities, structures, peculiarities etc. is therefore extremely useful in order to understand the physicalprocesse at work for lithium depletion, and the reader will find here many up-to-date data. The analysis of lithium in interstellar material provides an essential information. Many works about lithium are in progress throughout the world on the different points of interest, so that the General Assembly of the IAU was an excellent occasion to have a review of the recent progresses made in different areas. A summary of (nearly) each communication made during the Joint Discussion 11 may be found hereafter. Longer summaries of the talks, and summaries of the posters will be published in a forthcoming volume of the Memorie of the Società Astronomica Italiana.
Lithium In Population II Stars
Authors: Thorburn J.A.
Published: March 2016

Since the work of Spite & Spite (1982), halo main sequence turn-off stars have usually been considered a site where Li synthesized in the Big-Bang is wholly preserved and uncontaminated by other Li sources. However, the interpretation of halo dwarf Li abundances has become more complex as new samples of halo star Li I observations have become available. Linking the Li plateau abundance identically with the cosmological Li fraction is no longer warranted. At present, observational evidence favors a scenario where most—but not all—of the plateau abundance is cosmological in origin and a non-negligible amount is contributed subsequently by Galactic nucleosynthesis; severe, uniform Li depletion is constrained but not yet completely ruled out.
Lithium Abundance of Halo Stars With New Teff
Authors: Molaro P.
Published: March 2016

The lithium observed in the atmospheres of unevolved halo stars is believed to be an essentially unproccessed element which reflects the primordial yields. The primordial nature of Li is inferred from the presence of a constant Li abundance for all the halo dwarfs where convection is not effective (Teff ≥ 5600 K). Such an uniformity is taken as evidence for the absence of any stellar depletion during the formation and the long life of the halo stars and also as evidence for the absence of any production mechanism acting either before or at the same time of the formation of the halo population. The existence of a real plateau has been recently questioned by Thorburn (1994), Norris et al (1994) and Deliyannis et al (1993). These results open the possibility of substantial depletion by rotational mixing where a certain degree of dispersion is foreseen for different initial angular momenta of the stars and/or to a significant Galactic Li enrichment within the first few Gyrs.

Lithium abundances in a sample (39) of halo dwarfs have been redetermined by using the new Teff derived by Fuhrmann et al (1994) from modelling of the Balmer lines. These Teff are reddening independent, homogeneous and of higher quality than those based on broad band photometry. The sample represent a significant fraction of the presently available Li determinations, and form an unique sample with a good and homogeneous Teff Fuhrmann et al are also able to provide errors in the Teff for individual stars and in most cases they are as good as ± 50 K, which is a factor 2 smaller than the grossly estimated errors for photometric-based Teff. The Li equivalent widths have been taken from the literature and the theoretically derived random errors from Deliyannis et al (1993) or computed following their prescriptions. Abundances have been derived by generating new atmospheric models by using the ATLAS-9 code by Kurucz (1993) with enhanced α-elements and without the overshooting option. If we use the Kurucz 1993 grid which includes overshooting the Li abundance is increased by ≈ 0.08 dex.
The Rotational History of Solar-Type Stars: Does It Affect Lithium Abundances?
Authors: Bouvier J.
Published: March 2016

Recent studies of lithium abundances in solar-type stars suggest that second order effects, such as rotation and/or mass-loss, might affect the rate at which lithium is depleted at the surface of cool stars. This conclusion mainly stems from the dispersion of lithium abundances observed in late-type stars with otherwise similar mass and age. The dispersion of lithium abundances is relatively small in pre-main sequence (PMS) stars [1], reaches a maximum of about 2 dex in ZAMS stars (Soderblom, this volume), and decreases later during main sequence evolution, although significant dispersion may still be present by the age of the Sun [2], and perhaps even during the giant stage (Balachandran, this volume).

Such a pattern of lithium dispersion is difficult to understand in the framework of conventional models in which lithium burning occurs at the base of the convective zone of non-rotating, non-mass losing stars. That two stars of the same age and mass can exhibit different lithium content strongly suggests that other, so far neglected, mechanisms play a role in lithium depletion.

In this context, it may be relevant to stress that the pattern of lithium dispersion varies with age in much a similar way than does the dispersion of stellar rotation, namely: the dispersion in both rotation rates and lithium abundances is relatively small in the PMS stage, then strongly increases from the PMS to the ZAMS, and subsequently decreases on the main sequence. The parallel evolution of the range of lithium abundances and of rotation rates observed in solar-type stars is strongly suggestive of a physical link between rotation and lithium depletion.
From AGB to PN in External Galaxies
Authors: Chiosi Cesare
Published: March 2016

We present new results from spectro-photometric models for elliptical galaxies in which detailed descriptions of the star formation history and chemical enrichment are taken into account. In particular, we focus on the important role played stars of different chemical composition evolving along the red giant branch (RGB), horizontal branch (HB), asymptotic giant branch (AGB), and finally planetary nebula (PN) stages in relation to the sources of UV flux in elliptical galaxies. A few important applications of these new galaxy models are briefly outlined.
The Planetary Nebula Luminosity Function (PNLF) of Our Galaxy Compared to those of other Galaxies
Authors: Méndez R. H.
Published: March 2016

Nowadays it is possible to detect planetary nebulae, and measure their [O III] λ5007 fluxes, in many galaxies. Given this information it is relatively straightforward to build the [O III] λ5007 PNLF for any galaxy, because we can always assume all its PNs to be essentially at the same distance from us.

Of course the situation is much more difficult for PNs in the solar neighborhood. We have two problems here: (1) the individual PN distances are poorly known, except for ∼ 25 objects; (2) in the literature there is no agreement on which are the 25 PNs with reliable distances. Clearly it was a wise decision to calibrate the PNLF method of extragalactic distance determinations using the distance to M 31 (Ciardullo et al. 1989, Jacoby et al. 1992). In these short notes I review if it may be possible to build a PNLF for our Galaxy (the answer is: yes, probably more than one) and discuss if it would be worth the trouble (the answer is: yes, it would) and what can be done to achieve that elusive goal.
Planetary Nebulae and the Cosmic Distance Scale
Authors: Jacoby George H.
Published: March 2016

Planetary nebula luminosity functions provide very accurate distances to galaxies as judged by comparisons with other techniques, including Cepheids; systematic effects cannot be significant. The method is empirical and is a consequence of the shallow initial-final mass relationship predicted by stellar evolution and directly measured. From distances to ∼ 30 galaxies, the PNLF yields H0 = 79, in excellent agreement with recent Cepheid discoveries in Virgo.
Chromospheric and Coronal Spectra
Authors: Jordan Carole
Published: March 2016

The interpretation of chromospheric and coronal spectra requires accurate ionization and recombination rates, collision strengths and transition probabilities. Recent projects to improve calculations of opacities in stellar interiors have led to a large amount of new atomic data. Some current and potential applications of atomic data to chromospheric and coronal spectra are mentioned below.

Strong chromospheric lines are optically thick, and the solution of the radiative transfer equations can depend on atomic data for other species contributing to the background opacity. Many lines in the spectra of stars with hot coronae are excited by electron collisions, but in the cooler non-coronal giants radiative processes involving the H Lyman α and β lines become more important (see Jordan 1988a). Photo-ionization rates from ground configuration excited terms and oscillator strengths to high levels are still needed.

Fe II is an important ion producing emission lines in stellar chromospheres. Several excitation mechanisms contribute to the observed spectra (Jordan 1988b). Permitted lines to the ground term and low lying metastable terms have high optical depths and transfer photons to spin forbidden lines sharing a common upper level (e.g. mults. uv 1 and uv 3 transfer photons to mults. uv 32 and 61). Line intensity ratios yield the optical depth in the optically thick lines. The strong H Ly α line in cool giants and supergiants excites high levels in Fe II, resulting in strong decays in multiplets such as uv 391 and 399. A large number of f-values are required to interpret the lines formed by these radiative processes. Nahar & Pradhan (1994) have published some results from the Opacity Project, calculated by using the close coupling method and observed energy levels (which introduce some allowance for relativistic effects). In most cases these f-values agree with experimental results and the calculations by Kurucz (1988) to within 10%. The latter are still needed for the interpretation of stellar uv spectra because of the treatment of spin-forbidden lines.
Interpreting the Spectra of Chemically Peculiar Stars
Authors: Lanz Thierry
Published: March 2016

Similarly to many astrophysical studies, a spectroscopic analysis of chemically peculiar (CP) stars requires extensive, accurate sets of atomic data. Our purpose is to show here that the CP stars can also serve as a laboratory for checking the accuracy of the atomic data. Despite additional challenges toward modeling the atmospheres of the CP stars, they have a definite advantage as laboratories for atomic physics: their strong chemical anomalies make some spectral features especially prominent in their spectra, which can be better checked against theoretical predictions. This statement may be applied to both to stars exhibiting large over- or under- abundances. We discuss several examples how CP stars can be used along this idea.

We will focus here on the chemically peculiar stars of the upper main-sequence, which encompass the classical Am and Ap stars. Chemical anomalies are widespread on the main sequence for spectral types B. to F. These stars mostly show weak helium lines, and abnormally strong lines from iron-peak and heavier (e.g. the lanthanides) elements. A classical characteristics of Am stars in their weak Ca lines, while Ap stars may exhibit either strong Si or Hg lines. CP stars can be grouped according to the most obvious line strength anomalies, which are related to the effective temperature and to the presence or the absence of a magnetic field. In magnetic CP stars, the chemical elements are not uniformly distributed over the stellar surface, but they seem to be concentrated (or depleted) in rings or polar caps following the magnetic geometry. Magnetic CP stars have also broad absorption features in their ultraviolet and visible spectra that can used photometric peculiarity criteria. Using the new extensive photoionization data from the Opacity Project (OP), the UV absorption features can be identified and the UV spectrum can be well reproduced.
Opening Remarks
Authors: Batten Alan H.
Published: March 2016

Only five countries in Africa have resident members of the 1AU, and in some there are, quite literally, only one or two. They are isolated (communication with other countries is often difficult), poorly equipped and poorly financed --some have no current journals at all. Most of Africa faces terrible problems, so it is hardly surprising that our colleagues there have their difficulties. Astronomers are useful in developing countries, however, especially as educators, so we can help the whole continent by helping our own colleagues.
Astronomy in Saudi Arabia
Authors: Al-Malki M.B.
Published: March 2016

In the last twenty-five years, more than 100 astronomers have graduated from two astronomical departments in the Kingdom: one at King Saud University (KSU) in Riyadh and the other in King Abdulaziz university (KAU) in Jeddah. About 15% to 20% of those graduated are now working in fields related to astronomy, among them five with Ph.D. degrees and three with M.Sc. degrees. Most of the other astronomy graduates are teaching mathematics, physics or general science in schools.

The total number of academic staff in the two universities is ten Ph.Ds (five Saudis and five from abroad) and five research assistants, with no post-graduate students. Each department has a Celestron 14-inch (approx. 0.35m) with photo-counters, a 15-cm coudé refractor, solar laboratory, small planetarium and astronomical measuring instruments. In addition, KAU has a CCD camera, while KSU has a double telescope with 45cm Ritchey-Chrétien optics and a 24cm Schmidt telescope. All these observational facilities are located near the universities, where light pollution is very high and limits the observations. There is a plan to move the KSU double telescope away from Riyadh. Because of a lack of students and Saudi teaching staff, and cuts in the budget for universities, it is planned to turn the two astronomy departments into groups in the respective physics departments.
Laboratory Analogues of Cosmic Dust
Authors: Mutschke H. , Clément D. , Dorschner J. , Fabian D. , Jäger C. , Henning Th.
Published: March 2016

Understanding the properties and the evolution of cosmic dust requires laboratory experiments for measuring basic physical and chemical data and simulating the interaction of dust grains with their cosmic environments. We give a short review of such laboratory experiments using analogue materials of cosmic dust.
Probing the Nature of Grain Surface- and Photo-Chemistry by Laboratory Simulation
Authors: Schutte W.A.
Published: March 2016

The experimental results that have been obtained in simulation experiments of grain surface- and photochemistry are reviewed, and ways to include these in models of dense cloud chemistry are indicated.
H2 in Space
Authors: Flower D.R.
Published: March 2016

Molecular hydrogen may be excited by collisions with other particles (as in shock waves), by ultraviolet pumping (as in photon-dominated regions), through its formation on the surfaces of dust grains (in interstellar clouds), or by absorption of the cosmic background radiation (in the primordial gas). We consider the adequacy of our knowledge of H2, from the viewpoint of being able to reliably predict the spectrum arising from these excitation mechanisms.
Atomic Data Needs for X-ray Astronomy
Authors: Brickhouse Nancy S.
Published: March 2016

With the launches of the Chandra X-ray Observatory and XMM-Newton, high resolution X-ray spectra of cosmic sources are broadening our understanding of the physical conditions, such as temperature, density, ionization state, and elemental abundances. X-ray emitting astrophysical plasmas can be generally classified by their dominant ionization mechanism, either collisional ionization or X-ray photoionization. The atomic data needs are significantly different for these two cases; however, for both cases it is important that we identify robust and accurate diagnostics and that we verify completeness of the broadband models. We discuss the status of the atomic data currently used in atomic databases for X-ray astronomy, in view of theoretical and experimental atomic physics considerations.
Laboratory Chemical Dynamics in Hydrocarbon Rich Atmospheres of Outer Planets
Authors: Kaiser Ralph I. , Lee Yuan Tse
Published: March 2016

Investigating the formation of organic molecules in hydrocarbon rich atmospheres of planets and their moons is of paramount importance to understand the chemical composition, mixing ratios, and the future evolution of carbon bearing species in Solar System environments. The diacetylene molecule (C4H2) as detected in the stratosphere of Saturn and its moon Titan is the largest polyatomic organic species observed so far in the outer Solar System. In addition the methyl radical (CH3) together with methane (CH4), acetylene (C2H2), ethylene (C2H4), ethane (C2H6), methylacetylene (CH3CCH), propane (C3H8) and the CN bearing species hydrogen cyanide (HCN), dicyan (NCCN), methykyanide (CH3CN), cyanoacetylene (HCCCN), and presumably solid state dicyanoacetylene (NCC-CCN) were detected as well. Photochemical models of Jupiter, Saturn, Uranus, Neptune, Pluto and their satellites Titan and Triton predict further the presence of even more complex hydrocarbons up to triacetylene (C6H2) and tetraacetylene (C8H2). Previous experiments attempting to unravel the formation of these molecules in planetary environments employed and open reactors subjecting gas mixtures to high energy discharges or electron bombardments; often products were analyzed via gas chromatography coupled to a mass spectrometer (GS-MS). This approach can match the existence of major trace constituents. However, no information on radical intermediates could be supplied; further, possible open shell products and extremely labile products cannot be identified; hence involved reaction mechanism can only be guessed. However, the explicit identification of reaction intermediates, ALL reaction products, and the mechanism are a top priority to give a systematic picture on the chemistry in hydrocarbon rich atmospheres and to predict the formation of hitherto unobserved molecules.
Report on Astronomical Constants
Authors: Fukushima Toshio
Published: March 2016

Given was additional information to a previous report on the recent progress in the determinations of astronomical constants (Fukushima 2000), including the revision of Lg, Δp and the offsets of CEP. As a summary, presented was the (revised) IAU 2000 File of Current Best Estimates of astronomical constants, which is to replace the former 1994 version (Standish 1995).
Dynamical Evolution of Trans-Neptunian Objects in High-Eccentricity Orbits
Authors: Emel’yanenko V.V.
Published: March 2016

The evolution of near-parabolic orbits with perihelia in the trans-neptunian region has been studied, considering the action of planetary, Galactic and stellar perturbations for the age of the Solar System. This investigation has led to the conclusion that the observed trans-neptunian objects in high-eccentricity orbits might originate from the inner core of the Oort cloud.
Statistical Ranging of Orbits for Trans-Neptunian Objects
Authors: Virtanen J. , Muinonen K. , Bowell E.
Published: March 2016

We consider initial determination of orbits for trans-neptunian objects (TNOs), a topical theme because of the rapidly growing TNO population and the challenges in recovering lost TNOs. We apply the method of initial phase-space ranging of orbits to the poorly observed TNOs. The rigorous a posteriori probability density of the TNO orbital elements is examined using a Monte Carlo technique by varying the TNO topocentric ranges corresponding to the observation dates. We can optionally adopt a Bayesian approach to select the region of phase space containing the most plausible orbits. This is accomplished by incorporating semimajor axes, eccentricities, inclinations, and absolute magnitudes of multi-apparition TNOs as a priori information. The resulting a posteriori distributions permit ephemeris and ephemeris uncertainty prediction for TNO recovery observations.
Photometric Evidence for Mixing and Diffusion in GC Stars
Authors: Grundahl Frank
Published: March 2016

Based on Strömgren uvby CCD photometry, and UVES spectroscopy we present evidence that possibly all globular clusters show large variations in their abundances of nitrogen, aluminium and sodium, which are not only due to internal mixing processes. Furthermore the evidence for radiative levitation among hot horizontal branch stars is briefly discussed.
Mixing in Magnetized Interiors of Solar-Type Stars: Frequently Asked Questions
Authors: Charbonneau Paul
Published: March 2016

This short paper discusses various issues pertaining to the redistribution of angular momentum and mixing of chemical species in the radiative interior of solar-type stars. Results obtained to date indicate that models combining magnetically-mediated angular momentum transport with turbulent mixing of chemical species offer the best hope of explaining the observed rotation and light element evolution in open clusters, without doing excess violence to seismic measurements of the solar internal differential rotation.
Babylonian Observations
Authors: Brown D.R.
Published: March 2016

Cuneiform tablets from Babylonia record lunar and solar eclipses, the presence and movement of comets, meteors and meteor showers. These have provided historical astronomers with much valuable data, but caution must be exercised when using such records, for accuracy of observation often ceded to astrological intent. In the future, texts from Assyria may also provide useful data for historical astronomers.
Ancient Eclipses and the Earth’s Rotation
Authors: Morrison L.V. , Stephenson F.R.
Published: March 2016

The analysis of historical eclipses shows that the length of the day is increasing on the average by 1.8 milliseconds per century, as distinct from the value of 2.3 milliseconds per century expected from tidal friction. The difference may be accounted for by the response of the Earth to post-glacial uplift following the end of the last ice-age.
About Some Astronomical Instruments from Batthyanian Observatory in Alba Iulia
Authors: Botez Elvira , Oproiu Tiberiu
Published: March 2016

Built toward the end of the 18th century on the last floor of a former Trinitarian church, the Astronomical Observatory in Alba Iulia (Romania) was equipped with instruments brought from Vienna and it was in activity until 1860. A description of the astronomical instruments of those existing at present is given.
Seismic Forecasting of Solar Activity
Authors: Braun D.C. , Lindsey C.
Published: March 2016

Computational seismic holography, applied to Solar Oscillations Investigation -Michelson Doppler Imager (SOI-MDI) data from SOHO, has recently given us the first images of an active region on the far side of the Sun(Lindsey & Braun 2000). The advent of phase-coherent seismic imaging is now allowing us quite literally to look into the solar interior from a local perspective, indeed to see through the solar interior acoustically to its far surface. Solar activity is critical to near-Earth space weather. A great deal of effort has been invested towards the prediction of flares and CMEs, based on the formidable presence of active regions on the near solar surface. Active regions can emerge rapidly from beneath the photosphere or appear on the east limb with relatively little warning. Because of this, the ability to anticipate the appearances of active regions will contribute substantially to forecasts of space weather on time scales of more than about a day. In collaboration with Dr. Phil Scherrer and the MDI team at Stanford University we are currently deriving far-side images from the lower resolution “medium-l” SOI-MDI Dopplergrams, which are obtained continuously through the year and arrive at MDI headquarters within 24 hours of their acquisition by the SOHO spacecraft. We are therefore already capable of locating large far-side active regions and predicting their appearance on the east solar limb to within a few hours more than a week in advance. In addition, ground-based networks such as GONG will soon have the capability for “real-time helioseismology”, and will be routinely monitoring the far surface of the Sun, and perhaps beneath the near surface, for emerging solar activity.
Characteristics of Flare-Productive Sunspot Groups
Authors: Ishii Takako T. , Kurokawa Hiroki , Takeuchi Tsutomu T.
Published: March 2016

The mechanism of flare energy build-up is one of the most fundamental questions in the solar flare study, but is still to be solved. From the review of the previous studies, we notice that the formation process of the magnetic shear in an active region should be essential for the flare energy build-up mechanism. Based on this idea, we make detailed studies of the active region evolutions using high resolution Hα images obtained with the 60 cm Domeless Solar Telescope at Hida Observatory, Kyoto University.

We study sunspot proper motions and evolutionary changes of Hα fine structures and magnetic fields in active regions NOAA 5395 (Ishii et al. 1998) and NOAA 4201 (Ishii et al. 2000). To explain the evolutionary characteristics found from the analysis of these two active regions, we propose schematic models of twisted flux bundles emerging from the convection zone. We also found that the occurrence of high flare activity in each active region was restricted to the rapidly emerging region of the twisted flux bundle. In conclusion, we suggest that the emergence of the twisted flux bundle should be the key to high flare-productivity of the sunspot group, or the flare energy build-up mechanism.
Solar Flare Prediction and Magnetic Field Evolution in Solar Active Region
Authors: Wang H.N. , Zhang G.Q. , Zhu C.L. , Sun J.L.
Published: March 2016

The authors propose a number of empirical criteria for prediction of solar flares based on many years of observations at Huairou Solar Observing Station of Beijing Astronomical Observatory.