bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultraviolet Observations of the R Aquarii Jet
Authors: Michalitsianos A.G. , Kafatos M.
Published: March 2016

Observations of the recently discovered jet feature in the symbiotic variable R Aquarii (M7e+pec) were obtained with the International Ultraviolet Explorer (IUE). A comparison of low dispersion UV-spectra reveals important differences between the central ionized source and the jet feature. The UV-continuum flux Fλ between 1200-2000A that rises with decreasing wavelength in the jet feature, essentially is independent with wavelength in the central compact nebula. The prominent emission lines of Si III] λ1892A and Si II λ1817A, evident in the central star, are virtually absent in the jet. The carbon lines of C IV, C III] and C II also suggest the general excitation of the jet is comparatively lower than the central star. This is further indicated by enhanced S II λ1250, 1295A and C II λ1335A emission in the feature. We speculate that material that is ejected from the symbiotic system cools through free-free and nebular recombination emission.
Problems of Jet Physics
Authors: Scheuer P.A.G.
Published: March 2016

What have I learned about jets since the Albuquerque meeting (IAL) Symposium No.97) last summer?

There is where most of the gravitational energy is released, the funnels on the rotation axis of the accretion torus provide the right sort of geometry, and radiation is abundant. But the experts (Sikora & Wilson 1981 and references therein) never can make radiation-driven jets with Lorentz factor γ >> 1. Why? It is because, when an electron moves up through the funnel at a substantial fraction of the speed of light c, it sees as much radiation striking it trom the front as from behind; acceleration then stops. Large γ are attainable only if the source of radiation subtends an angle ≲ 1/γ behind the source.
Introduction of JD 19: Nutation
Authors: Dehant V.
Published: March 2016

Due to both precise time measurements and precise geodetic positioning methods (like Very Long Baseline Interferometry (VLBI), Lunar Laser Ranging (LLR), Satellite Laser Ranging (SLR) and Global Positioning System (GPS)), the position of the instantaneous axis of the Earth’s rotation in space is measured with a precision better than a tenth of milliarcsecond. Simultaneously the amplitudes of the nutations of the Celestial Ephemeris Pole (CEP) deduced from the observations, i.e. the periodic motions in space of the CEP due to the luni-solar attraction or to other planetary attractions, have also been improved. However, these observed nutation amplitudes differ with respect to the computated ones based on an elliptical, uniformly rotating and deformable Earth responding to the lunar and solar attractions, as adopted by the IAU in 1980. The first session on “Observations and data reduction” dealt with Earth’s orientation observations and data analysis for deriving precession and nutations, as well as the associated residuals with respect to the adopted precession constant and nutation series. Comparisons between the different results have been presented including in-phase and out-of-phase components of the prograde and retrograde nutations or of nutations in longitude and in obliquity (see Session 1 of our JD: Newhall et al., McCarthy and Luzum, Herring, and Session 2: Gross). These differences “observed - adopted” nutations achieve several milliarcseconds and exhibit periodic as well as secular characteristics.
New Possibilities in Time-Frequency Standards
Authors: Fliegel H.F.
Published: March 2016

By invitation of Edoardo Proverbio, the President of Commission 31 (Time), this report attempts to summarize “new possibilities in time-frequency standards”. Especially because recent work in this highly specialized field is so diverse and so complex, I appreciate the support of our colleague, Dr. G. Busca, who will survey the extensive progress being made east of the Atlantic. I confine this paper to work that has appeared in the open literature from the United States and Canada.

Since much of this work is proprietary, and since it is difficult to assign credit fairly, I will not attempt to give either a comprehensive or selected bibliography of references in this paper. There are three primary symposia where such work is published: (1) the annual IEEE International Frequency Control Symposia; (2) the more recently organized annual European Frequency and Time Forums; and (3) the (United States) Annual Precise Time and Time Interval (PTTI) Applications and Planning Meetings, organized jointly by the Department of Defense and NASA. The best general review of recent work on frequency standards, which appeared just before our last IAU General Assembly and is not yet outdated, is the special issue of the Proceedings of the IEEE, volume 79, no 7 (July 1991), and especially the papers “An Introduction to Frequency Standards” by Lindon L. Lewis, “Atomic Ion Frequency Standards” by Wayne M. Itano, and “Laser- Cooled Neutral Atom Frequency Standards” by Steven L. Rolston and William D. Phillips.
Internal Structure
Authors: Christensen-Dalsgaard J.
Published: March 2016

In this section I concentrate on the spherically symmetric aspects of solar structure, corresponding to “classical” stellar evolution models. Such models are characterized by a number of simplifying assumptions, as well as by the physical properties of matter in the star, conveniently labeled “micro-physics”. The latter include descriptions of the equation of state, the opacity and the nuclear reaction rates; in addition, molecular diffusion, included in several recent calculations, should be considered as part of the micro-physics. The assumptions in the standard calculations, simplifying what might be called the macro-physics, include the neglect of effects of rotation and magnetic fields (implicit in the assumption of spherical symmetry), as well as the assumption that material mixing occurs only in convectively unstable regions, or possibly as a result of molecular diffusion and settling; also, convective energy transport is treated crudely through some form of mixing-length approximation and the contribution to hydrostatic balance from the turbulent motion in the convection zone, usually called turbulent pressure, is ignored.
Seismic Solar Model
Authors: Goode P.
Published: March 2016

The method of frequency inversion reveals that within the quoted observational errors, it is possible to achieve a precision of ∼ 10−3 in the sound speed determination through most of the Sun’s interior. Only for r < 0.05R⊙ is the precision ∼ 10−2. The accuracy of the density and pressure determinations is only slightly worse. Such restrictions impose significant constraints on the microscopic physical data, i.e. opacities, nuclear reaction cross-sections, and diffusion coefficients as well as on the solar age. The helioseismic age is consistent with that from meteorites.

Recently released low-l solar oscillation data from the BISON network combined with BBSO data yield the most up-to-date solar seismic model of the Sun’s interior. For the core, the solar seismic model from the new data are consistent with the best, current standard solar models. An astrophysical solution to the solar neutrino problem fades away.
OPAL Equation of State Tables
Authors: Rogers F.J.
Published: March 2016

The equation of state of astrophysical plasmas is, for a wide range of stars, nearly ideal with only small non-ideal Coulomb corrections. Calculating the equation of state of an ionizing plasma from a ground state ion, ideal gas model is easy, whereas, fundamental methods to include the small Coulomb corrections are difficult. Attempts to include excited bound states are also complicated by many-body effects that weaken and broaden these states. Nevertheless, the high quality of current observations, particularly seismic data, dictates that the best possible models should be used. The equation of state used in the OPAL opacity tables is based on many-body quantum statistical methods (Rogers, 1994; 1986; 1981) and is suitable for the modeling of seismic data. Extensive tables of the OPAL equation of state are now available. These tables cover the temperature range 5 × 10−3 to 1 × 108 K, the density range 10-14 to 105 g/cm3, the hydrogen mass fraction (X) range 0.0 to 0.8, and the metallicity (Z) range 0.0 to 0.04.
Concluding Remarks
Authors: Landstreet John D.
Published: March 2016

I do not intend to try to summarize the various excellent papers that have been presented in this Joint Discussion on the accuracy of the HR diagram and related parameters. I will content myself with saying that I found them uniformly well-prepared and clear, and all very interesting. I want to thank the various speakers for doing their work so well!

Instead, I propose - since we are in the Netherlands, after all - to assume the role of the good Dutch pastor for a few minutes and draw a few morals from what we have heard and seen. I think the papers presented point to several important recommendations to all of us, and it is these points that I would like to emphasize.

The first moral that I find in this Joint Discussion is a very encouraging one for those of us who are interested in stellar astronomy and astrophysics. It is clear from this JD that our field is alive and well at the 22nd General Assembly of the IAU. This JD drew more poster papers than any of the other 19 JD’s held during this General Assembly, with 54 papers listed in the programme, compared to a mean of about 19 per JD. In addition, these poster papers come from five of the six inhabited continents, and if we allow a paper from New Zealand to stand in for Australia, then we have papers from all six. Not a bad representation, I think.
The Lithium Isotope Ratio In Old Stars
Authors: Nissen P.E.
Published: March 2016

The lithium isotope ratio in stars can be determined from high resolution observations of the profile of the Li I 6707 Å absorption line. Earlier studies of old F and G stars (Andersen et al. 1984, Maurice et al. 1984, Pilachowski et al. 1989) have led to upper limits of 6Li/7Li ranging from 0.05 to 0.10. Recently, Smith, Lambert & Nissen (1993) seem to have detected 6Li in HD 84937 - a metal-poor turnoff star with Teff ⋍ 6200 K and [Fe/H] ⋍ —2.4. An isotope ratio 6Li/7Li = 0.05 ± 0.02 was determined (see Fig. 1) The detection has been confirmed by Hobbs & Thorburn (1994), who derived 6Li/7Li = 0.07 ± 0.03. The main contribution to the quoted (1σ) errors comes from the noise in the spectrum (S/N = 400) and possible errors in the Doppler broadening of the Li line (Nissen 1994). This broadening is due to stellar rotation and macro-turbulent motions in the stellar atmosphere and can be determined from the profiles of unblended metallic absorption lines.

As discussed in detail by Steigman et al. (1993) the presence of 6Li in the atmosphere of HD 84937 is consistent with the measured Be abundance (Boesgaard & King 1993) within the context of i) Standard Big Bang nucleosynthesis, ii) Pop. II cosmic ray nucleosynthesis and iii) standard (non-rotating) models for Li depletion. In particular, Steigman et al. derive D6 > 0.2, where D6 is the depletion factor for 6Li. As shown by Chaboyer (1994) standard stellar evolution models with new opacities predict D6≃ 0.4 for turnoff stars and subgiants with Teff > 5900 K. The same models predict D7 ≃ 1.0, i.e. no 7Li depletion for main sequence stars as well as subgiants with Teff ≥ 5800 K.
Extragalactic Planetary Nebulae
Authors: van den Bergh Sidney
Published: March 2016

It is a great pleasure for me to be able to start off this “Joint Discussion” on Extragalactic Planetary Nebulae. Many astronomers appear somewhat ambivalent in their attitudes towards planetary nebulae. A few of us regard planetaries as the spectacular “last hurrah” before stars slide off into oblivion as white dwarfs. Others think of them as soaring butterflies that evolved from stellar caterpillars. Finally a few less romantic astronomers simply ask “what can planetary nebulae do for us?” Perhaps surprisingly the answer is that they can do a great deal for the progress of various branches of astronomy. At this meeting George Jacoby will, for example, show us how planetary nebulae can be used to measure extragalactic distances. Mike Dopita, Ziaohui Hui and Ken Freeman will tell us that planetaries are powerful probes of the kinematics of galaxies. Furthermore Henry Ferguson will show how planetary nebulae can be used to probe the effects of metallicity on stellar evolution in elliptical galaxies.
Dynamics of the M31 Planetary Nebula System
Authors: Hui Xiaohui
Published: March 2016

We made a spatially complete and kinematically unbiased survey of M 31 for planetary nebulae (PNs). The survey covers a projected area of 20 by 40 kpc centered on M 31. Subsequently, we measured the radial velocities of over 800 PNs using the Hydra multi-object spectrograph on the KPNO 4-m telescope. With this large dataset, a detailed dynamical study of the stellar disk, bulge and halo populations in M 31 is currently underway. We are focusing on the dynamical transition between the disk, bulge and halo, and a comparison between the kinematics of the PNs and globular clusters.
UV Bright Stars and Planetary Nebulae in Elliptical Galaxies
Authors: Ferguson Henry C.
Published: March 2016

Far UV observations and optical studies of planetary nebula luminosity functions (PNLFs) offer complementary views of the late phases of stellar evolution in elliptical galaxies and spiral galaxy bulges. UV spectroscopy reveals that the hot stellar population is composite, with a mix of temperatures that varies from galaxy to galaxy. This changing mix is most likely due to changes in the relative numbers of stars that channel through the Post-Asymptotic Giant Branch (PAGB), Post-Early-AGB (PEAGB) and Extreme Horizontal Branch (EHB) phases of evolution. EHB stars appear to dominate the integrated λ < 2000 Å flux from galaxies with the strongest far-UV emission, but are too faint to resolve individually in even the nearest galaxies. Far UV images of M31 and M32 reveal a population of hot stars that are much brighter, but do not account for the majority of the far-UV flux. The sources detected are most likely low-mass PAGB stars (0.55 < M/M⊙ < 0.59). In contrast, the PNLF probes the PAGB star mass function at values greater than ∼ 0.6 M⊙. For a given galaxy the relative numbers of stars in these different branches of evolution are determined by the age and chemical evolution of the galaxy and by the physics of mass loss on the red giant branch. We review current constraints on the mass function of hot evolved stars in elliptical galaxies, highlight a few puzzles, and outline where future observations might contribute.
Active Galactic Nuclei in the Extreme Ultraviolet
Authors: Königl Arieh
Published: March 2016

The extreme ultraviolet (EUV) wavelength interval (commonly defined to constitute the range 68 — 912 Å, or 13.6 — 182 eV) hes between the intensively studied FUV (912 - 3000 Å) and X-ray (1 - 68 Å) spectral regimes, but until recently has not been subjected to systematic investigations. This lack of information has been particularly acute in the case of active galactic nuclei (AGNs), where the very ability to carry out successful EUV observations has been seriously questioned. This has stemmed from the fact that, for a Galactic H I column density NG(H I) = 1 × 1020 cm−2, the interstellar transmission factor is 0.42 at 60 Å, but a factor of 10 smaller at 100 Å. In turn, there are no known regions of the interstellar medium (ISM) that have [NG(H I)/1020 cm−2] < 0.6 (resp., 0.8) for positive (resp., negative) latitudes (e.g., Heiles 1991).

There are, however, several reasons why EUV observations of AGNs could provide important information about the nature of these objects. In the case of radio-quiet QSOs, the peak power is known to be emitted in the EUV range (several hundred A). Furthermore, in these sources there is evidence for a distinct soft X-ray component (representing a “soft excess” over an extrapolation of the ISM-absorbed hard X-ray component), whose properties are at present controversial. In particular, the first results of ROSAT PSPC observations of a complete sample of optically selected QSOs (Laor et al. 1994) have pointed to a spectral index αx = 1.50 ± 0.40 in the 0.2 − 2 keV range that flattens by Δαx ≈ 0.5 above ∽ 2 keV. This study has concluded that steep-αx sources are characterized by a week hard component. A similar distribution of αx has been inferred for soft X-ray-bright QSOs and Seyfert 1 galaxies observed in the ROSAT all-sky survey. On the other hand, previous observations (enumerated in Laor et al. 1994) by the Einstein and EXOSAT satellites yielded different soft X-ray spectral slopes and led to an alternative explanation of the steep-αχ objects. These questions could in principle be clarified by EUV measurements, which would then also help determine the soft X-ray emission mechanism.
Molecular Data for Stellar Opacities
Authors: Jørgensen Uffe Gråe
Published: March 2016

In total, 40 neutral diatomic molecules, 2 molecular ions, and 7 polyatomic molecules are known from observed photospheric stellar spectra. Line data for opacity computations (i.e., lists of line frequencies, intensities, and excitation energies) exist for 17 of these molecules, although the data are complete only for a handful of them. A detailed description of stellar photospheric molecules can be found in Tsuji (1986), and the existing opacity data have been reviewed by Jorgensen (1995).

Listed line frequencies in the data bases are either the measured values, or based on computed molecular constants obtained from fits to measured values. Attempts to compute ab initio line frequencies have so far resulted in lower accuracy than what is obtained by use of molecular constants. Published line strengths include measured values as well as ab initio values. For strong bands the ab initio intensities are as accurate as the laboratory values, whereas measured values for weak bands are generally more accurate than the ab initio values. The primary advantage of ab initio computations is therefore that the complete set of all transitions can be obtained. Exploratory studies have shown that completeness of the line data is crucial for the obtained stellar photospheric structure.

As an alternative to the ab initio computations of the line intensities, fits to experimental data have been attempted. The most promising method seems to be to fit the dipole function by use of a Padé approximant. Combined with a potential fitted to experimental energy levels, such a dipole function can in principle be used to predict the complete list of band intensities and line intensities for all bands with energies up to the molecular dissociation energy. The part of the dipole function which corresponds to the largest stretching (or bending) of the molecule is the most uncertain in such fits as well as in ab initio computations. This part is responsible for most of the many weak transitions, and large uncertainties are therefore to be excepted in the computed intensities of the weak spectral bands. As these are of major importance for the stellar photospheric structure (due to their huge number and their pseudo continuous appearance in the spectrum), a particularly large effort is desirable in comparing computed intensities with laboratory data for a representative sample of weak bands. Unfortunately, only few measurements of weak bands exist.
Cepheids: Pulsation, Evolution, Opacity
Authors: Simon Norman R.
Published: March 2016

With the advent of new radiative opacities, the gross discrepancies in period ratio between observed stars and theoretical models have been eliminated in both the “beat” and “bump” Cepheid regimes (Moskalik, et al. 1992; Kanbur & Simon 1994). This paves the way for detailed modeling of the beat and bump stars.

We begin here by summarizing one such effort, the full description of which is given by Simon & Kanbur (1994). In this study, the slope of the evolutionary luminosity-mass relation is taken to be dlogL/dlogM = 4.0 (Stothers and Chin 1991) and the intercept determined by forcing models which follow this slope to also conform with the bump Cepheid resonance condition P2/P0 = 0.50 at P0 = 10d (Simon & Schmidt 1976; Buchler =et al. 1990). We then model separately each of the dozen known galactic beat Cepheids, subject to the just mentioned evolutionary constraint imposed by the 10-day resonance. We find masses and luminosities, ranging from M = 4Mʘ, log L = 3.0 at P0 = 3d to M = 6Mʘ, log L = 3.5 at P0 = 1Od. Furthermore, a range of metallicity, 0.01<Z<0.02, is required among the beat stars, whose period ratios, P1/P0,are predicted to decrease as the metallicity rises. This trend has been observed (Andrievsky et al. 1993). However, “standard” evolutionary tracks for Z = 0.02 [e.g., the Geneva calculations (Schaller, et al. 1992) or the Padua calculations (Bressan, et al. 1993)] cannot produce Cepheids with parameters as given above - first because the models are somewhat underluminous at given mass, and second because the calculated blue loops do not reach the instability strip for M = 7Mʘ. On the other hand, the models described by El Eid (1994) do penetrate the strip at masses as low as 4 or 5 Mʘ, but display a luminosity-to-mass ratio considerably too small to satisfy the resonance condition for bump Cepheids. Possible resolutions to these problems include a deep Fe convection zone whose effect would be to lower the period ratios (Cox 1993), and/or an opacity increase near 1 × 106K, which could extend the blue loops (Stothers & Chin 1994). Each of these schemes require more research.
Infrared Observations of Interstellar Ices — Laboratory Needs
Authors: Boogert A.C.A.
Published: March 2016

A selection of recent highlights in the area of infrared observations of interstellar ices is presented. The essential role that laboratory astrophysics plays in the interpretation of the data, and current problems and expected future needs are discussed.
Water in Comets: Observations and Models
Authors: Crovisier Jacques
Published: March 2016

Cometary water, the main constituent of nucleus ices, is difficult to observe directly. Breakthroughs were made recently using new ground based infrared instruments and space techniques (ISO and SWAS) on comets C/1996 B2 (Hyakutake), C/1995 01 (Hale-Bopp), 103P/Hartley 2, and C/1999 H1 (Lee): observations of water hot bands, of water rotational lines, and measurements of the [D]/[H] ratio and ortho-to-para ratio of water. We discuss the laboratory data necessary to model the water spectrum and to interpret these observations.
Chemistry in the Envelopes around Massive Young Stars
Authors: van Dishoeck Ewine F. , van der Tak Floris F.S.
Published: March 2016

Recent chemical studies of high-mass star-forming regions at submillimeter and infrared wavelengths reveal large variations in the abundances depending on evolutionary state. Such variations can be explained by freezing out of molecules onto grains in the cold collapse phase, followed by evaporation and high-temperature chemical reactions when the young star heats the envelope. Thus, the chemical composition can be a powerful diagnostic tool. A detailed study of a set of infrared-bright massive young stars reveals systematic increases in the gas/solid ratios and abundances of evaporated molecules with temperature. This ‘global heating’ plausibly results from the gradual dispersion of the envelopes. We argue that these objects form the earliest phase of massive star formation, before the ‘hot core’ and ultracompact H II region phase.
The New Generation of Ionization and Recombination Fronts
Authors: Dyson J.E. , Hartquist T.W. , Williams R.J.R. , Redman M.P.
Published: March 2016

We summarize previous work on hydrodynamic ionization fronts and new work where magnetic fields are incorporated into their structures. We describe recent work on recombination front structures and outline refinements which need to be made to both them and ionization fronts.
Spectrophotometry of Trans-Neptunian Objects
Authors: Romon Jennifer , Doressoundiram Alain , Barucci Maria Antonietta
Published: March 2016

The Trans-Neptunian Objects (TNOs) are very difficult to observe due to their faintness. Spectra can be obtained for only few objects. For this reason, broad band photometry is the only available technique to study their physical properties from a statistical point of view. To improve the knowledge about the physical nature of the Kuiper Belt, we have obtained several observing runs at different four-meter class telescopes (NTT - Chile; CFHT - Hawaii).

The data presented here were obtained at NTT (ESO - Chile) during three observing runs from 1997 to 2000. We used the SUSI and SUSI 2 CCD cameras with the Bessel B, V, R, and I filters.
Chemical Abundances in Main Sequence Stars
Authors: Landstreet John D.
Published: March 2016

This talk reviews recent results relevant to identifying and constraining the processes that mix and transport specific elements in the envelopes of main sequence stars.
Observations of Chemical Abundances in Stars: Globular Cluster Stars
Authors: Kraft Robert P.
Published: March 2016

The chemical composition of globular cluster stars is briefly reviewed, attention being given principally to the following problems: (1) primordial and evolutionary abundance variations among globular cluster stars, and (2) abundance differences between cluster and halo field giants.
Scientific Interpretation of Historical Auroral Records
Authors: Willis David M. , Stephenson F. Richard
Published: March 2016

Recent research on the scientific interpretation of historical auroral records is summarised, with special emphasis on topics that provide physical insight into possible variations in geomagnetic disturbance and solar activity during the past two millennia.
Particle Acceleration and Diffusion in Fossil Radio Plasma
Authors: Enβlin Torsten A.
Published: March 2016

The strong activity of radio galaxies should have led to a nearly ubiquitous presence of fossil radio plasma in the denser regions of the inter-galactic medium as clusters, groups and filaments of galaxies. This fossil radio plasma can contain large quantities of relativistic particles (electrons and possibly protons) by magnetic confinement. These particles might be released and/or re-energized under environmental influences as turbulence and shock waves. Possible connections of such processes to the formation of the observed sources of diffuse radio emission in clusters of galaxies (the cluster radio halos and the cluster radio relics) are discussed.
Jupiter’s Aurora: Solar Wind and Rotational Influences
Authors: Waite J. Hunter , Clarke John T. , Walker R.J. , Connerney John E.P. , McComas D. , Riley P. , Lewis William S.
Published: March 2016

Jovian auroral emissions are observed at infrared, visible, ultraviolet, and x-ray wavelengths. As at Earth, pitch-angle scattering of energetic particles into the atmospheric loss cone and the acceleration of current-carrying electrons in field-aligned currents both play a role in exciting the auroral emissions. The x-ray aurora is believed to result principally from heavy ion precipitation, while the ultraviolet aurora is produced predominantly by precipitating energetic electrons. The magnetospheric processes responsible for the aurora are driven primarily by planetary rotation. Acceleration of Iogenic plasma by rotationally-induced electric fields results in both the formation of the energetic ions that are scattered and the formation of strong, field-aligned currents that communicate the torques from the ionosphere. In addition to rotation-driven processes, solar-wind-modulated processes in the outer magnetosphere may lead to highly, time-dependent acceleration and thus also contribute to jovian auroral activity. Observational evidence for both sources will be presented. See Waite et al. (2001, Nat., 410, 787).
MGS TES Results: Atmospheric Structure, Aerosols, and Dynamics
Authors: Conrath Barney J. , Pearl John C. , Smith Michael D. , Christensen Philip R.
Published: March 2016

Thermal emission spectra from the MGS TES instrument permit retrieval of atmospheric properties that are of interest in the study of Martian meteorology, including temperature, dust, and water ice. Examples of analyses of zonal mean meridional thermal sructure for equinox and solstice conditions are presented.
A Single Resolved Ground-Based Observation of Mercury
Authors: Ksanfomality Leonid V.
Published: March 2016

Short–exposure images of Mercury were recorded at the Abastumany astrophysical observatory. A single image, with low distortion, is shown and discussed with respect to Mariner 10 observations.
Variable and Constant Features on Titan from HST
Authors: Lorenz Ralph D. , Lemmon Mark T. , Smith Peter H.
Published: March 2016

Observations with HST WFPC-2 from 1994 to 1997 show a number of features which can be attributed to the surface (notably the large as-yet-unnamed bright region, several smaller bright areas and a number of dark regions). The delineation of these features in several datasets is presented. Other features are variable and are due to atmospheric phenomena: these include the total brightness of Titan (drop by 5% 1994-1997 at 350 nm; increase by 7% at 889 nm), the hemispheric north-south asymmetry, and the hint of a south polar hood.

Additionally, small variable features, apparently due to clouds, are documented. As well as variability from one year to the next, these show anomalous center-to-limb brightness behaviour, and a 673/940 nm color much bluer than the large surface feature, consistent with clouds in the troposphere.
Hipparcos Luminosities and Asteroseismology
Authors: Bedding Timothy R.
Published: March 2016

Asteroseismology involves using the resonant frequencies of a star to infer details about its internal structure and evolutionary state. Large efforts have been made and continue to be made to measure oscillation frequencies with both ground- and space-based telescopes, with typical precisions of one part in 103–104. However, oscillation frequencies are most useful when accompanied by accurate measurements of the more traditional stellar parameters such as luminosity and effective temperature. The Hipparcos catalogue provides luminosities with precisions of a few percent or better for many oscillating stars. I briefly discuss the importance of Hipparcos measurements for interpreting asteroseismic data on three types of oscillating stars: δ Scuti variables, rapidly oscillating Ap stars and solar-like stars.
Numerical Simulations of Turbulent Dynamos
Authors: Brandenburg Axel
Published: March 2016

Using a periodic box calculation it is shown that, owing to helicity conservation, a large scale field can only develop on a resistive timescale. This behaviour can be reproduced by a mean-field dynamo with α and ƞt quenchings that are equally strong and ‘catastrophic’.
MeV Neutrino Sources: The Sun and the Supernovae
Authors: Turck-Chièze Sylvaine
Published: March 2016

The two sources of MeV neutrinos, the Sun and the Supernovae are very interesting to study nowadays. Seismology aboard SoHO has properly constrained the solar emitted neutrino fluxes and consequently contributes to an unambiguous evidence of the solar neutrino oscillations. The main role of seismology stays nevertheless the description of the magneto-hydrodynamic processes and this progress provokes a renewal of the stellar discipline. Important results are noticed these three years, for the Sun. Future will be richer implying a large number of stars with an evident impact on supernovae and solar neutrino properties.
Plasma Dynamics in Mercury’s Magnetosphere
Authors: Ip Wing-Huen
Published: March 2016

Mercury is in all sense of the words still Terra Incognito, its magnetosphere is hence little known. The only source of knowledge came from the in-situ measurements by the Mariner 10 close encounters in 1974. This has been complemented since by ground-based observations of the atomic sodium and potassium emissions in the vicinity of the planetary disk. This series of optical observations has produced intriguing evidence of magnetospheric and/or solar wind effects on the surface-plasma interaction processes. In this review we will describe the current theories of the corresponding space weather effects.
Space Studies of the Black-Drop Effect at a Mercury Transit
Authors: Schneider Glenn , Pasachoff Jay M. , Golub Leon
Published: March 2016

Transits of Mercury and Venus across the face of the Sun are rare. The 20th century had 15 transits of Mercury and the 21st century will have 14, the two most recent occurring on 15 November 1999 and 7 May 2003. We report on our observations and analysis of a black-drop effect at the 1999 and 2003 transits of Mercury seen in high spatial resolution optical imaging with NASA’s Transition Region and Coronal Explorer (TRACE) spacecraft. We have separated the primary contributors to this effect, solar limb darkening and broadening due to the instrumental point spread function, for the 1999 event. The observations are important for understanding historical observations of transits of Venus, which in the 18th and 19th centuries were basic for the determination of the scale of the solar system. Our observations are in preparation for the 8 June 2004 transit of Venus, the first to occur since 1882. Only five transits of Venus have ever been seen – in 1639, 1761, 1769, 1874, and 1882. These events occur in pairs, whose members are separated by 8 years, with an interval between pairs of 105 or 122 years. Nobody alive has ever seen a transit of Venus.
Twist and writhe of δ active region magnetic fields
Authors: Tian Lirong , Yang Jing
Published: March 2016

Twist is a parameter to measure turning of the field lines around axis of the flux tube. Observations show that each active region (AR) has a pronounced overall twist, following hemispheric helicity rule (Pevtsov et al. 1995; Bao & Zhang 1998). αbest, best-fit single value for a whole AR, is used to characterize the overall twist. Writhe is a measure of the spatial turning of the axis of the flux tube. It is described by systematic tilt angle of an AR, an angle of joined line of opposite main polarities with respect to the equator. Observations show that most ARs follow Joy’s Law. The relationship between the twist and writhe is important to studying origin of the twist and solar activities. Canfield & Pevtsov (1998) found the same handedness of the twist as that of writhe, using 99 ARs observed at MSO. However, Tian et al. (2001) found opposite handedness of them for 286 ARs taken at HSOS, among which only 19% have δ magnetic configuration. López Fuentes et al. (2003) also obtained opposite handedness for 22 ARs measured again at MSO, among which 41% have δ magnetic class. Most recently, Tian & Liu (2003) found that the twist and the writhe have same handedness for major flare-producing ARs.
The Fundamental Plane of Globular Clusters
Authors: McLaughlin Dean E.
Published: March 2016

The fundamental plane of globular clusters can be expressed as a particular scaling of cluster energy vs. mass: Eb ~ M2. New calculations of energy and mass for a large sample of young clusters in the Magellanic Clouds may shed light on the origins of this scaling.
Formation of ω Centauri from an Ancient Nucleated Dwarf Galaxy
Authors: Bekki Kenji , Freeman K. C.
Published: March 2016

We present a self-consistent dynamical model in which ω Cen is formed from an ancient nucleated dwarf galaxy merging with the first generation of the Galactic thin disc in a retrograde manner with respect to the Galactic rotation. Our numerical simulations demonstrate that during merging between the Galaxy and the ω Cen’s host dwarf with MB ⋍ ‒14 mag and its nucleus mass of 107M⊙, the outer stellar envelope of the dwarf is nearly completely stripped whereas the central nucleus can survive from the tidal stripping because of its compactness. The developed naked nucleus is orbiting the young Galactic disc in a retrograde manner with its apocenter and pericenter distances of ~ 8 kpc and ~ 1 kpc, respectively, and thus have orbital properties similar to those of ω Cen. The Galactic tidal force can induce radial inflow of gas to the dwarf’s center and consequently triggers moderately strong nuclear starbursts in a repetitive manner. This result implies that efficient nuclear chemical enrichment resulting from the later starbursts can be closely associated with the origin of the observed relatively young and metal-rich stars in ω Cen. Dynamical heating by the ω Cen’s host can transform the young thin disc into the thick one during merging.
Perhaps They are not Globular Clusters After All
Authors: Karick A. M.
Published: March 2016

Our 2dF Fornax Cluster Spectroscopic Survey (FCSS) and follow-up work in the Virgo Cluster have shown that the cores of both galaxy clusters contain a previously-unknown class of object, ultra-compact dwarf (UCD) galaxies. We present high resolution spectroscopy and deep multicolor imaging to show that these enigmatic objects are dynamically distinct from both globular clusters (GCs) and nucleated dwarf galaxies (dE,Ns). Our hypothesis for their origin may explain the observed high “specific frequency” of GCs in central cluster galaxies.
Search for Formation Criteria of Globular Cluster Systems
Authors: Nuritdinov S. N. , Mirtadjieva K. T. , Tadjibaev I. U.
Published: March 2016

The research of early evolution stages and formation of galaxies requires creation of appropriate non-linear theory. The formation process of globular cluster systems (GCS) covers the long period of time as probably one begins from a dark matter state. So far it is difficult to simulate formation of GCS and galaxies ab initio. That’s why it is necessary to construct exact analytically solvable models of non-linear non-stationary early stages of evolution of self-gravitating systems and revealing the instabilities on a background of non-equilibrium states. The formation and evolution of GCS at early stage of collapsing dark matter (or protogalaxy) can be explained by instability of the modes of the high oscillation degrees (Nuritdinov et al., 2000), which corresponds to rather small-scale perturbations of the density of collapsing system. The mode degree defines on the average the number of clusters.
JD 7: The Sun and the Heliosphere as an Integrated System
Authors: Poletto Giannina , Suess Steven T.
Published: March 2016

We summarize here the oral contributions given at the Joint Discussion (JD) 7The Sun and the Heliosphere as an Integrated System, held on July 17, 2003, in Sydney, as part of IAU XXV and give a list of posters presented at the JD.
X-ray Cavities and Cooling Flows
Authors: Nulsen Paul E. J. , McNamara Brian R. , David Laurence P. , Wise Michael W.
Published: March 2016

Recent data have radically altered the X-ray perspective on cooling flow clusters. X-ray spectra show that very little of the hot intra-cluster medium is cooler than about 1 keV, despite having short cooling times. In an increasing number of cooling flow clusters, the lobes of a central radio source are found to have created cavities in the hot gas. Generally, the cavities are not overpressured relative to the intra-cluster gas, but act as buoyant bubbles of radio emitting plasma that drive circulation as they rise, mixing and heating the intra-cluster gas. All this points to the radio source, i.e., an active galactic nucleus, as the heat source that prevents gas from cooling to low temperatures. However, heating due to bubbles alone seems to be insufficient, so the energetics of cooling flows remain obscure. We briefly review the data and theory supporting this view and discuss the energetics of cooling flows.
Mass Loss, Kinematics, & Evolution of Super Star Clusters in the Antennae
Authors: Gilbert Andrea M. , Graham James R.
Published: March 2016

The youngest super star clusters (SSCs) in the merging Antennae Galaxies (NGC 4038/39) drive supersonic mass-loaded outflows from the HII regions in which they are embedded. High-resolution K-band Keck/NIRSPEC spectroscopy reveals broad, spatially extended Brγ emission in 16 targets. Simple wind models for the line profiles provide good fits and imply cluster mass-loss rates of up to 1.5 M⊙/year and terminal velocities of up to 205 km s−1. The emission-line clusters (ELCs) that drive these outflows constitute at least 15% of the star formation rate in the Antennae, and their high star formation efficiencies imply that they will probably evolve into bound SSCs. The youngest ELC outflows, which are driven primarily by stellar winds, very efficiently entrain ambient matter. The cluster winds transfer or dissipate a large fraction of their energy and momentum in a hot or cool medium that does not emit Brγ. ELCs are the individual engines that power galactic-scale superwinds, viewed in their earliest evolutionary stage.
Helio- and Asteroseismic Analysis Methods
Authors: Schou Jesper
Published: March 2016

Over the past couple of decades increasingly sophisticated analysis algorithms have been developed in helioseismology. Here I will describe some of these with an emphasis on those most relevant to asteroseismology and some of the lessons learned. I will also discuss some of the properties of stellar oscillations and how those affect the analysis.
Local Helioseismology – What Does It Really Tell Us?
Authors: Hill Frank
Published: March 2016

The three major local helioseismology methods of time-distance, ring diagrams, and acoustic holography are briefly summarized along with their advantages and disadvantages. Useful tests with artificial data are outlined, and current data comparisons briefly described.
Seeing Double in the Local Group: Extragalactic Binaries
Authors: Guinan Edward F.
Published: March 2016

Photographic surveys of the Magellanic Clouds and the M31 carried decades ago discovered ~200 close binaries. In most cases the photographic light curves are good enough only to identify the stars as close (mostly eclipsing) binaries and to estimate orbital periods and binary type. Except for a few cases, little useful information may be obtained from these stars except to be reassured that eclipsing binary (EB) systems are present in other galaxies. However a major advance occurred with the advent of high quantum efficient CCDs. Because of this an explosion in the number of known extragalactic binaries occurred during the 1990s as offshoots of photometric microlensing surveys such as EROS, MACHO, and OGLE. Now over 10 000 extragalactic EBs have been identified. Also, photometric surveys of M31 and M33 (e.g. DIRECT) are discovering many more 19-20th mag eclipsing/close binaries. Over the next decade it is expected that ~1 million new binary systems will be identified in these galaxies. In this overview I will discuss recent advances and future expectations in the studies of extragalactic binaries
Eclipsing Binaries as Precise Standard Candles and Distance Indicators
Authors: Clausen Jens Viggo
Published: March 2016

Double-lined eclipsing binaries are (still) our main source for accurate information on stellar masses, radii, and luminosities. Also, they offer very direct distance determinations, useful within the Milky Way and for Local Group Galaxies. I will briefly review the methods involved and discuss critically their advantages and limitations. Furthermore, past and recent highlights will be presented.
Processed and Unprocessed Ices in Circumstellar Disks
Authors: Pontoppidan Klaus , Dishoeck Ewine van , Dartois Emmanuel , Thi Wing-Fai
Published: March 2016

We present 3-5 µm VLT-ISAAC spectroscopy showing the presence of methanol ices in edge-on disks of young embedded stars. Examples include the disks of L1489 IRS in Taurus and CRBR 2422.8-3423 in Ophiuchus, the last of which has the highest column density of solid CO known toward a YSO. Several additional low-mass sources in the Serpens and Chameleon molecular clouds exhibit abundant solid methanol although it is not clear if the ice is associated with a disk or with the envelope. These are the first detections of solid methanol in the disks and circumstellar environments of embedded young low-mass stars providing evidence that complex molecular species previously observed only in the solid state toward high-mass star forming regions are also present near solar-type young stars. The constraints on the formation mechanisms of methanol and the chemical evolution of ices as the material is incorporated into circumstellar disks are discussed.
Disk Chemistry and Cometary Composition
Authors: Markwick A. J. , Charnley S. B.
Published: March 2016

We describe a theoretical study of protoplanetary disk chemistry. By considering physical conditions similar to that of the protosolar nebula, we attempt to assess the contribution made by material from the cooler nebular regions to cometesimal composition. Calculations are presented which determine the spatial and temporal chemistry of the gas and dust within the 5-40 AU comet-forming region of the nebula. We show that there is little radial variation in the solid-state distribution of some molecules which could potentially be parents of the carbon-chain species observed in comets. We conclude that the apparent variation in abundance of C2 and C3 between long- and short-period comets is the result of chemical processing during their lifetimes and not differences in composition at the time of formation.
Crystallization of Silicate Particles By Shock Waves
Authors: Nakamoto Taishi , Miura Hitoshi
Published: March 2016

Crystalline silicate dust particles have been found in some comets, though progenitors of those dust particles are thought to be amorphous. Here, the origin of the crystalline particles was investigated based on the shock-wave heating mechanism. We find that appropriate shock waves can crystallize amorphous dust particles and conditions of these shock waves (shock velocity and pre-shock gas density) are clarified.

The gas density in the solar nebula and the shock velocity that may be induced in comet forming regions by some mechanisms were discussed. It was suggested that comets formed in a region closer than about 20 AU to the Sun can contain the crystalline particles, whereas comets formed in a further region can hardly have them.
Atomic Spectral Tables for the Chandra X-ray Observatory
Authors: Podobedova L. I. , Kelleher D. E. , Reader J. , Wiese W. L.
Published: March 2016

Tables of wavelengths, line classifications, and transition probabilities have been critically compiled for ionized spectra of neon (Ne V-VIII), magnesium (Mg V-X), silicon (Si VI-XII), and sulfur (S VIII-XIV) in the 20 Å-170 Å region. The tables provide basic atomic data for about 3300 transitions in support of astronomical studies from the Chandra X-ray Observatory.
The Astrophysical Plasma Emission Database: Progress and Plans
Authors: Smith Randall K. , Brickhouse Nancy S. , Liedahl Duane A.
Published: March 2016

The Astrophysical Plasma Emission Database (APED) contains atomic data for the 14 most abundant astrophysical elements, collected from the literature. Although APED was originally designed for use in calculating a collisional-equilibrium X-ray spectrum suitable for analysis of high-resolution data, it is in a general format which can be efficiently used to calculate absorption spectra, photoionization models, and non-equilibrium collisional models. We emphasize original sources; each transition, rate, and energy level in APED contains a bibliographic reference. The APED can be downloaded from http://cxc.harvard.edu/atomdb/, or our website WebGUIDE (http://obsvis.harvard.edu/WebGUIDE/) can be used to search for individual lines or transitions. We are continually working to expand APED (current version 1.3.1) and regularly issue updated collections.
Comet Halley Observed During the ESA Giotto Fly-By
Authors: Keller H. U.
Published: March 2016

The major observational results of the detection of the nucleus of Comet Halley will be summarized with some emphasis on the images. A comparison to or context with ground based observations will be discussed. The paradigm set by the first observations of a cometary nucleus should be critically reviewed. The results of the VEGA missions and the recent observations of the nucleus of Comet Borrelly by DS-1 will also be considered.