bluuebunny/crossref_metadata_2025 huggingface dataset:
Novae as Local Thermonuclear Runaways
Authors: Orio Marina , Shaviv Giora
Published: July 2016

Accretion occurs from a disc or possibly from polar caps in the case of magnetic novae: it is doubtful whether a spherically symmetric and homogeneous envelope configuration is eventually reached. A number of works (see in particular Kippenhahn & Thomas, 1978, King & Shaviv, 1978, Livio & Truran, 1988) adressed to this problem. Even if the matter can be almost homogeneously distributed - at least for high accretion rates - it is very likely that the chemical composition would not be uniform because of the shear mixing in the equatorial belt. Moreover, there can be temperature gradients. These and several non spherically symmetric factors (see the discussion of Tutokov & Yungelson, 1974, on the effects of rotation and magnetic fields) could lead to runaway only in a portion of the envelope. Instead of having a spherically symmetric explosion there would be a local thermonuclear runaway (LTNR). Estimates of Shara (1982) indicate that, with certain sets of parameters, the time for thermalization of the envelope would be much longer than the time to reach the conditions for the runaway and the outburst in such a case would occur only in a certain portion of the envelope. A non-spherically symmetric outburst could be the cause for the peculiar equatorial belts - polar caps geometry of the shells of many novae. There are other explanations (for instance interaction of the secondary with the expanding shell, like suggested by Livio and by Shankar et al. in this colloquium), but bidimensional spectroscopy seems to favour also difference in chemical composition in the envelope and in the polar caps (Duerbeck 1987) and high resolution Hα spectroscopy of Nova Cen 1986 hints that the blobs in the shell have formed at the time of the outburst (Bandiera & Focardi 1989) and cannot be explained by a spherically symmetric TNR model.
HM Sge still evolving
Authors: Nussbaumer H. , Vogel M.
Published: July 2016

In their study on C/N/O abundances in red giants, planetary nebulae, novae and symbiotic stars Nussbaumer, Schild, Schmid and Vogel (1988: Astron.Astrophys.198, 179) pointed out that among symbiotic stars HM Sge is quite exceptional, in that its C/N/O abundance ratios rather resemble those of novae and not of symbiotic stars.

In 1975 HM Sge brightened within a few months by at least 4m. The object has been observed in radio, visual, X-ray, and since 1978 with IUE. Here we show the changing level of activity in the UV. Figure 1 gives the FES (IUE fine error sensor) counts, representing an integrated flux at visual wavelengths. This flux shows a general decline with a secondary maximum in 1982. – Our mFES is at variance with the visual magnitude estimates given by Munari and Whitelock (1989: Mon.Not.Roy.astr.Soc. 237, 45p). They report high brightness up to at least the end of 1984.
Structure and Appearance of Envelopes around Protostars
Authors: Yorke Harold W.
Published: July 2016

The existence of material in the immediate vicinity of young main sequence stars or even younger objects, protostars, still contracting and evolving towards the main sequence, is related closely to the details of star formation. Although a number of individual idealized problems related to star formation have been well studied, our overall understanding of how interstellar matter evolves into full fledged hydrogen-burning stars can be deemed qualitative at best. The emerging picture is neither complete nor should it be considered the final answer as to how stars form. Let us summarize this picture by a list of “axioms”, valid for star formation (SF) in the plane of our Galaxy.
Post-Outburst Spectroscopy of Classical Novae
Authors: Wyckoff S. , Wehinger P.A.
Published: July 2016

SIT Vidicon spectra (3500 - 5100 Å) with time resolutions of several minutes and spectral resolutions of 6 Å have been obtained of a sample of old novae at minimum light. For comparison, spectra of SCO X-1 (V818 Sco) are also presented. Velocity-resolved image-tube spectra of RR Pic 1925 indicate Doppler variations in the He II λ4686 emission line with a period ~ 3 hours, thus confirming the binary nature of RR Pic.
Maser Line Profiles and Mass Outflow of Long-Period Variable Stars
Authors: Olnon Friso M.
Published: July 2016

The long-period variable giants with maser emission (maser/LPV stars) can be divided into two groups. The stars in group 1 have color indices I (0.84μ) - K (2.2µ) < 6, those in group 2 have I - K≥6. Fig. 1 gives the velocity structure of the maser lines for both groups. I have included only those maser /LPV stars for which the radial velocity of the star is known. In most cases this is the mean velocity of the outer OH peaks (Winnberg, this Colloquium), but for R Leo and R Cas the stellar velocity is found from the ground-vibrational state SiO emission (Reid and Dickinson, 1976). The abscissa of fig. 1 gives the velocity relative to the stellar velocity and the verticale scale gives the number of stars that show emission in a specific line at the relative velocity indicated. Note that the “line profiles” obtained in this way are not real mean profiles, because I only counted the presence of emission, weak or strong.
Masses of Classical Cepheids and Mass Loss Rate at Pre-Cepheid Stage
Authors: Takeuti M.
Published: July 2016

The mass-luminosity relation for single-mode Cepheids obtained by Saio, Kobayashi, and Takeuti (1977) indicates that the masses of classical Cepheids seem to be less than those that result from evolutionary calculations without substantial mass loss. The mass loss rate at the red giant phase should be 10−5 solar masses per year. Some of the beat Cepheids seem to form a group among the variable stars.
Is There Mass Loss in B Canis Majoris Stars?
Authors: Lesh Janet Rountree , Karp Alan H.
Published: July 2016

The purpose of this communication is to show that one possible explanation for the asymmetric line profiles observed in β Canis Majoris stars may be the presence of a stellar wind superimposed on a radial or nonradial pulsation.
1. The Pristine Nature of Comets
Authors: Delsemme A. H.
Published: July 2016

Abundance considerations suggest that comets are likely to be the most pristine minor bodies in the solar system. In proportion to solar abundances, the present scanty data suggest that cometary oxygen is not depleted, whereas carbon is by a factor of 4 and hydrogen, by a factor of 2000. This implies that comets are less depleted in H, C, N, O than CI chondrites, namely 10:1 in hydrogen, 4:1 in carbon and 3:1 in oxygen. These results have been obtained by using dust-to-gas ratios in comets, to measure the relative abundance of silicon and metals to volatile material, and the spectra of atomic lines, mainly from the vacuum ultraviolet, to determine the H/O and C/O ratios of the mixture of volatile molecules.
3. Chemical Composition of Meteoric and Meteoritic Matter
Authors: Yavnel’ A. A.
Published: July 2016

A comparison has been made of the data of Millman’s (1972) work on the relative content of Na, Mg, Ca and Fe in Draconids (Giacobinids) with corresponding data for carbonaceous chondrites of type CI, CII, CIIIV, and CIIIO and ordinary chondrites of type H, L and LL. The correlation of values Fe/Mg, Na/Mg and Ca/Mg in Draconids agrees with their successive change in carbonaceous chondrites from CIIIV to CI. By its composition, meteoric substance is more distant from CIII than from CI. This result agrees with the idea that cometary matter condensed farther away from the sun and contains lighter volatile components, than CI chondrites.
6. From Dust to Comets
Authors: Greenberg J. M.
Published: July 2016

The growth and chemical evolution of a typical interstellar dust grain are followed starting from average interstellar conditions to the dense cloud and contraction phase. Based on the theory of cometary accretion directly from cold interstellar dust it is shown that the bulk material of a primordial comet would consist mostly of an icy conglomerate of complex organic molecules and frozen radicals in which are imbedded approximately equal volumes (10% each) of small grains in two different sizes - one variety being the order of 0.05 μ and the other ~0.005 μ in size - consisting mostly of silicates
2. Catalytic Reactions in the Solar Nebula
Authors: Anders E. , Hayatsu R. , Studier M. H.
Published: July 2016

Organic compounds in meteorites seem to have formed by Fischer-Tropsch-type, catalytic reactions of CO, H2, and NH3 in the solar nebula, at 360-400 K (and 4-10) x 10-6 atm. The onset of these reactions was triggered by the formation of catalytically active grains of magnetite and serpentine at these temperatures.

Laboratory experiments show that the Fischer-Tropsch reaction gives a large kinetic isotope fractionation of C12/C13, duplicating the hitherto unexplained fractionation in meteorites. All of the principal compound classes in meteorites are produced by this reaction, or a variant involving a brief excursion to higher temperatures. (1) normal, mono-, and dimethylalkanes; (2) arenes and alkylarenes; (3) dimeric isoprenoids from Cg to C14; (4) purines and pyrimidines, such as adenine, guanine, uracil, thymine, xanthine, etc.; (5) amino acids, including tyrosine and histidine; (6) porphyrin-liJce pigments; (7) aromatic polymer with -OH and -COOH groups.

These reactions may also have played a major role in the evolution of life: first, by converting carbon to a sufficiently non-volatile form to permit its accretion by the inner planets; second, by synthesizing organic compounds on the primitive planets whenever CO, H2, NH3, and clay or magnetite particles came together at the right temperature. Similar reactions in other solar nebulae may be the source of interstellar molecules, as first suggested by G. H. Herbig. Ten of the twelve polyatomic interstellar molecules have in fact been see in these synthesis or in meteorites.
1. Comets, Asteroids and Meteorites: Unsolved Problems about their Relationships, Evolution and Origin
Authors: Delsemme A. H.
Published: July 2016

A few of the questions proposed earlier to the contributors are reviewed to identify some of the unsolved problems related to the different interfaces between comets, asteroids, and meteorites and their evolution and origin.
Observations of the Local Interstellar Cloud
Authors: Lallement R.
Published: July 2016

Constraints on the ambient (circumsolar) interstellar medium can be derived from observations of interstellar neutrals or their derivatives in the heliosphere. New results have been recently obtained which, when combined with optical and UV observations of the nearby stars (HST-GHRS, EUVE), remove long-standing contradictions and allow us to infer for our local cloud, pressure, ionization and limits on the magnetic field. The electron density in the circumsolar gas is found to be between 0.04 and 0.15 cm−3. Its total thermal pressure is within the interval 1700 – 2600 cm−3 K. If the local magnetic field is nearly perpendicular to the interstellar wind flow, which is likely, then its intensity is smaller than 3.6 μG. Our Sun is located very close to the edge of the local cloud (the volume of gas which has the same physical properties as the circumsolar gas), while there are at least 5 other cloudlets within 10 pc. Abundances vary from cloudlet to cloudlet. How they are located and whether they are separated by tenuous gas or shock discontinuities is not clear yet. Semi-hot (105 K) gas has been detected in absorption towards nearby stars (Wood et al, 1996), which probably originates in the “H walls” surrounding our heliosphere and other asterospheres. This shows that semi-hot gas is not necessarily linked with cloud interfaces with the hot gas of the Local Bubble.
The Intrinsic Properties of the Local Interstellar Medium
Authors: Puyoo Olivia , Ben Jaffel Lotfi
Published: July 2016

We propose a new method to constrain the actual state of the interstellar cloud that surrounds the solar system. Using Voyager UVS Lyman-α sky maps and the powerful principle of invariance, we derive the H distribution all along the spacecraft path. Provided current models of the heliopause interface between the solar and the interstellar winds, we extrapolate this distribution to farther distances from the Sun and infer in a self consistent way key parameters of the local cloud. Our findings are a high interstellar hydrogen density of ~ 0.24 cm−3 and a weak ionization .
EURD: An Extreme Ultraviolet Spectrograph to Probe the Hot Interstellar Medium
Authors: Morales C. , Trapero J. , Gómez J.F. , Bowyer S. , Edelstein J. , Lampton M.
Published: July 2016

The EURD instrument has been designed to measure diffuse emission in the extreme ultraviolet (350–1100 Å). This new design provides an unprecedented 4–5 Å spectral resolution and 200 photons/sec/cm2/sr sensitivity after only 100 hours of observations. One of the goals of this project is to search for spectral lines of highly ionized species from the high temperature component (105 – 106 K) of the interstellar medium that fills the Local Bubble. It is expected that EURD will detect lines due to a thermalized hot component of the interstellar medium, and it will also provide critical diagnostics of the physical properties of this gas. With EURD data we could also detect a spectral line due to the decay of massive neutrinos as well as study oxygen lines from the upper atmosphere airglow. EURD is on board the Spanish MINISAT-01 satellite.
The Thermal Pressure of the Interstellar Medium Derived from Cloud Shadows in the Extreme Ultraviolet
Authors: Berghöfer Thomas W. , Bowyer Stuart , Lieu Richard , Knude Jens
Published: July 2016

We have used the Deep Survey telescope of EUVE to investigate shadows in the diffuse EUV/Soft X-ray background cast by clouds in the interstellar medium. We confirm the existence of a shadow previously reported, and provide evidence for two new shadows. We used IRAS data to identify the clouds producing these shadows and to determine their optical depth to EUV radiation. The EUV-absorbing clouds are optically thick in the EUV, and all EUV emission detected in the direction of these shadows must be produced from material in front of the clouds. We obtained new optical data to determine the distance to these clouds. We use a new differential cloud technique to obtain the pressure of the interstellar medium. These results do not depend on any zero level calibration of the data. Our results provide evidence that the pressure of the hot interstellar gas is the same in three different directions in the local interstellar medium, and is at least 8 times higher than derived for the local cloud surrounding our Sun. This provides new evidence for large thermal pressure imbalances in the local ISM, and directly contradicts the basic assumption of thermal pressure equilibrium used in almost all present models of the interstellar medium.
Thin Layer Approximation in 3-D
Authors: Bisnovatyi-Kogan G.S. , Silich S.A.
Published: July 2016

Equations are derived which describe the propagation of strong shocks in the interstellar matter, without any restrictions for symmetry, in a thin layer approximation (2.5 dimensions). Using these equations permits to calculate the propagation of shock waves from nonsymmetric supernovae explosions in a medium with arbitrary density distribution and the formation of superbubbles in galaxies.
Magnetorotational Mechanism: 2D Simulation
Authors: Ardeljan N.V. , Bisnovatyi-Kogan G.S. , Moiseenko S.G.
Published: July 2016

In the paper we present results of numerical simulations of magnetorotational model of explosion of magnetized cloud. For the simulation we used a specially developed 2D implicit numerical scheme on Lagrangian triangular grid with grid reconstruction. Our results show that due to the amplification of toroidal magnetic field component and transfer of angular momentum, a compression wave in the envelope of the cloud appears and moves through rapidly decreasing density background. This wave turns into a shock wave and pushes out part of the envelope of the star. Quantitative estimates of mass and energy carried away are given.
Imaging Polarimetry of Nearby Molecular Clouds
Authors: Ramaprakash A.N. , Tandon S.N. , Gupta R.
Published: July 2016

In order to study the role played by the magnetic fields in the dynamics of the interstellar medium (ISM) a two-channel imaging polarimeter (IMPOL) has been constructed. The instrument is capable of multi-wavelength observations in the visible and very near infrared (IR) wavelengths, has a sensitive CCD detector and a built-in acquisition and guidance unit. When used with a 1.2m, f/13 telescope IMPOL gives a field of view of 6 × 6 arcmin with an angular resolution of 2" so that it is well-suited to observe both faint extended objects and moderately crowded stellar fields. The instrumental polarization is less than 0.05% and the accuracy of the measurements is primarily limited by photon noise in a typical observation. In this paper, we present a brief description of the instrument and observational techniques, as well as the results of a successful observation of a molecular cloud close to the open cluster IC 5146.
ORFEUS-I Observations of Molecular Hydrogen in the Galactic Disk
Authors: Van Dyke Dixon W. , Hurwitz Mark , Bowyer Stuart
Published: July 2016

We present measurements of interstellar H2 absorption lines in the continuum spectra of seven early-type stars in the Galactic disk at distances between 1 and 4 kpc. The spectra, obtained with the Berkeley EUV/FUV spectrometer on the ORFEUS telescope in 1993 September, have a resolution of 3000 and statistical signal-to-noise ratios between 20 and 80. We determine column densities for each observed rotational level and derive mean excitation temperatures and proton density limits for the H2 clouds along each line of sight. The gross properties of the H2-bearing clouds (e.g., column density, spatial density, cloud size) are consistent with those derived from Copernicus observations, though our lines of sight are much longer, with lower average reddenings and neutral gas densities. We find that the molecular fraction of the neutral hydrogen remains ~ 0.1 out to distances of 4 kpc in the Galactic disk.
Physical Association Between the Southern Coalsack and Chamaeleon-Musca Dark Clouds
Authors: Wagner Corradi J.B. , Franco Gabriel A.P. , Knude Jens
Published: July 2016

To investigate a possible physical association between the Southern Coalsack and the Chamaeleon-Musca (SCCM) dark clouds we have obtained uubyβ photometry for 1017 stars covering the connecting area: 308° ≥ l ≥ 294° and –20° ≤ b ≤ 5°. Analysis of the various colour excess E(b – y) vs. distance diagrams has indicated the presence of a local low absorption volume limited at 150 ± 30 pc from the Sun by an extended interstellar dust sheet-like feature, that is followed by a region where almost no additional reddening is measured for the next 350 pc. Combined with other data on the local ISM the existence of the dust sheet at an identical distance of the SCCM dark clouds have suggested that these clouds could be higher density regions associated to the diffuse lane of dust of the Local-Loop I bubbles’ interface.
The Influence of the Local Bubble on the Ionization of the Local Interstellar Cloud
Authors: Slavin Jonathan D. , Frisch Priscilla C.
Published: July 2016

The ionization of the the Local Interstellar Cloud (LIC) is quite unusual compared with most warm (T ~ 104 K) interstellar gas. Hydrogen and helium are both partially ionized with helium surprisingly more ionized than hydrogen. Directly observed ionization sources including nearby stellar EUV sources and the diffuse emission of the Soft X-ray Background (SXRB), do not provide enough ionization and heating to account for both the ionization state and temperature of the LIC. We propose that an evaporative boundary between the LIC and the hot gas of the Local Bubble can provide the necessary ionizing radiation. Results of detailed models of the emission from the interface are presented and shown to be adequate to explain the observations.
Modeling the Galactic ¾ keV X-ray Background
Authors: Freyberg M.J. , Schmitt J.H.M.M.
Published: July 2016

We have analyzed the ROSAT PSPC all-sky survey maps of the soft X-ray background (SXRB) in the ¾ keV band. One approach was to study the large-scale distribution of the X-ray emission with a multipole analysis. Here a significant dipole toward the galactic center region was found. This is interpreted in terms of variation of distant X-ray emission, e.g. galactic halo. Also a smallscale structure analysis of the ¾ keV X-ray sky has been performed and a new analytic fluctuation probability distribution has been derived. No significant excess over the expected extragalactic point source contribution has been found. Finally, X-ray colours have been used to investigate spectral variations of the SXRB.
Equilibrium Ionization and Non-Equilibrium Ionization Plasma Models
Authors: Böhringer Hans
Published: July 2016

This paper provides a brief review on ionization and radiation models of an optically thin, hot plasma and their application to the interpretation of observations of the Local Bubble. The basic structure and atomic physics ingredients of the models are outlined. Some general characteristic results of ionization equilibrium and non-equilibrium calculations are shown. Recent progress in plasma model codes is reviewed. The interpretation of the observations of absorption lines and emission spectra from the Local Bubble is discussed in the framework of ionization equilibrium and non-equilibrium ionization models with particular reference to the fast adiabatic cooling model of Breitschwerdt and Schmutzler.
Dust Composition in the Low Density Medium Around Spica
Authors: Zagury F. , Jones A. , Boulanger F.
Published: July 2016

Dust grains in low density gas are subjected to sputtering and shattering in fast supernovae shocks. Although there has been extensive modelling of the dust destruction, still little is known about the grains which survive. Jones et al. (1996) have modeled the effect of the destruction processes on the size distribution of grains. They predict that fast J shocks are efficient in grinding large dust grains into smaller particles. We present observations of the dust emission around the nearby star Spica. Comparison of the observations to the infrared emission of ’standard’ cirrus suggest that the abundance of very small grains is significantly enhanced.
New Measurements of the 4He Abundance in Galactic HII Regions
Authors: Cioni M.R. , Cortiglioni S. , Orsini M. , Palazzi E. , Palumbo G.G.C. , Sorochenko R.L. , Tsivilev A.P.
Published: July 2016

Preliminary results of the 4He relative abundance determination from Radio Recombination Lines observations at different frequencies in the Orion, Rosette and W3 HII regions are presented. The Orion HII region has been mapped at both 22 GHz and 36 GHz with the same beamwidth (2 arcmin) using the Medicina and Puschino radio telescopes respectively. The RRLs parameters, together with their variation with frequency and with distance were determined by centering the map on the star θ1OriC. Three positions were observed in the Rosette HII region at 8.3 GHz leading to the first detection in this region of the transition He92α. The derived 4He relative abundance is considerably greater than the ones obtained from previous measurements. The W3 HII region was observed at 36 GHz and the 4He/H value derived was compared with previous measurements performed with higher spatial resolution.
Ultraviolet Absorption Line Studies of Halo Gas
Authors: de Boer Klaas S.
Published: July 2016

The status of halo studies using UV absorption lines is assessed. Sin absorption is essentially only seen from gas with z ≤ 1 kpc, and shows a modest flow toward the galactic disk. CIV shows diffuse absorption in general only from gas with z ≥ 1 kpc with predominantly negative velocities. Three exceptional cases of gas showing CIV absorption without absorption by neutral components are discussed. Outflowing gas has not been detected thusfar.
The High-Velocity Clouds: Galactic or Extragalactic?
Authors: van Woerden Hugo , Wakker Bart P. , Schwarz Ulrich J. , Peletier Reynier F. , Kalberla Peter M.W.
Published: July 2016

We present firm evidence that one of the major high velocity clouds (HVCs), Complex A, lies in the Milky Way Halo, at a vertical distance z = 3 - 7 kpc from the Galactic plane. For clouds MII/MIII, Danly et al. and Keenan et al. had already found z < 5 kpc. We further report that the metallicity in the largest HVC, Complex C, is at least 0.1 solar. Call/Hi ratios in 6 HVCs, ranging from 0.002 to 0.07 times solar, set lower limits to their metallicities.

Blitz et al. have recently suggested that most of the HVCs are relatively unprocessed, extragalactic remnants of the gas which formed the Local Group of galaxies. However, the results mentioned above indicate that several major HVC complexes are neither primordial nor extragalactic. For the smaller HVCs, some of which have much higher velocities, a location in the Local Group remains a possibility.
The Galactic Halo in Hydrostatic Equilibrium
Authors: Kalberla P.M.W. , Pietz J. , Kerp J.
Published: July 2016

The large scale distribution of gas, magnetic field and cosmic rays in the Galaxy is explored. We analyze recent all-sky surveys of HI gas (Leiden/Dwingeloo survey), soft X-ray radiation (ROSAT) and high energy gamma-rays (EGRET > 100 MeV) in combination with the 408 MHz survey. Prom these observations we derive a Galactic halo model consistent with hydrostatic equilibrium conditions.

The large scale equilibrium configuration consists of two separate domains with different properties and scale sizes:

1)

The gaseous halo consists of collisionally ionized gas at T=106.2K as well as HI and has an exponential scale height hz ~ 4.4 kpc. The radial distribution is characterized by the galactocentric scale length A1 ~ 15 kpc. All components of the halo – gas, magnetic field and cosmic rays – contribute equally to the pressure. The magnetic field in the halo is oriented parallel to the Galactic plane.

2)

The disk extends up to a scale height of hz ~ 1 kpc and is associated with irregular magnetic fields. Here the pressure of the magnetic field is only ⅓ of the gas pressure. The cosmic rays are only weakly coupled to the disk.
A Ring of X-rays from the Cartwheel Galaxy
Authors: Trinchieri Ginevra , Wolter Anna , Iovino Angela
Published: July 2016

ROSAT HRI observations of the Cartwheel galaxy indicate that there is X-ray emission from the outer ring in connection with the strongest HII regions in the southern portion of the ring. No significant emission is detected from the nucleus or from the inner ring. This implies a strong connection between star formation activity and X-ray emission in this ring galaxy.
Radiative Fluxes and Forces in Non-spherical Winds
Authors: Wehrse Rainer , Kanschat Guido
Published: July 2016

For the modelling of the radiation fields in stellar winds and the resulting forces new efficient algorithms are presented. In the first one, the radiative transfer equation for moving 3D media is solved analytically with the assumption that the source function is known, eg. from the solution of the NLTE rate equations. For a wind with inhomogeneities an a-posteriori error controlled finite element code is described that takes scattering explicitly into account. Finally, we present possibilities for the accurate inclusion of an arbitrary number of spectral lines in a deterministic and in a stochastic way.
Variability and Evidence of Non-spherical Stellar Winds in A-Type Supergiants
Authors: Verdugo Eva , Talavera Antonio , de Castro Ana I. Gómez
Published: July 2016

The profiles of the Hα and uv lines and the observed variability suggest deviations from spherical symmetry for the envelope of A-type supergiants.
Short-Term Variations of LBV’s
Authors: Stahl Otmar
Published: July 2016

LBV’s are variable on many different time scales from weeks to years or even decades. The typical LBV variations on timescales of years or longer are covered in the paper by Humphreys (this volume). Here I discuss variations of LBV’s on timescales from weeks to years.

Most classes of stars are little studied on these timescales. This also holds true for LBV’s. Therefore the hot star group of the Landessternwarte Heidelberg Started a monitoring program of a few bright LBV’s (and other objects) using the 70cm-telescopes at the Landessternwarte and later the ESO 50cm-telescope at La Silla. For more details about the project see the paper by Kaufer (this volume).
The Line-Driven Instability
Authors: Feldmeier Achim
Published: July 2016

The line-driven instability may cause pronounced structure in winds of hot, luminous stars, e.g., fragments of dense shells, strong reverse shocks, and fast cloudlets. We discuss the linear stability theory, including the line-drag effect, phase reversal due to the diffuse radiation field, and the relevance of so-called Abbott waves. Recent hydrodynamic simulations focuss on the influence of a time-dependent source function on the flow structure, and on the X-ray emission from wind shocks and cloud collisions.
Non-radial Pulsations of BA Supergiants and Be Stars
Authors: Baade Dietrich
Published: July 2016

If observing time and number of photons are not the limit, it will probably be very difficult to find any Be star or BA supergiant that is not variable. Moreover, there is hardly any major set of observations that is not tempting to explain at least partly in terms of nonradial (g-mode) pulsations. Since a few years ago, such conjectures are also theoretically permissible because improved opacity calculations have established the classicalк-mechanism as a viable source of pulsation driving (cf. Pamyatnykh, these proceedings).

Contrary to Be stars, it can for any given BA supergiant nevertheless be arbitrarily difficult to diagnose nonradial pulsations (NRP’s) with certainty because they need to be detected against considerable background ‘noise’ of other physical processes, most of which are related to mass loss and/or rotation. To make things worse, there is some evidence that NRP’s can have some effect on the dynamics of the mass loss. On the other hand, variable and non-spherical winds is the subject of this Colloquium, and this paper is accordingly biased towards the interplay between pulsation and mass loss.
Rotation and Anisotropic Losses of Mass and Angular Momentum
Authors: Maeder André
Published: July 2016

The expressions of the radiative flux at the surface of a non-uniformly rotating star are revised and this leads to a small extra-term in the von Zeipel theorem. The Eddington factor needs also to be carefully defined in a rotating star, as well as the critical break-up velocity. This leads us to reconsider the so-called Ω–limit. The most massive stars reach the Ω and Г limits almost simultaneously.

We also examine the latitudinal dependence of the mass loss rates Ṁ(υ) in rotating stars and find two main effects: 1) the “geff” effect which enhances the polar ejection; 2) the “opacity effect” (or “к–effect”), which favours equatorial ejection. In O–stars, the geff effect is expected to largely dominate. In B– and later type stars the opacity effect should favour equatorial ejection and the formation of equatorial rings. Possible relations with η Carinae and the inner and outer rings of SN 1987 A are mentioned. Opacity peaks produce some extrema in Ṁ(υ) and this may also lead to the formation non-equatorial symmetrical rings.

Anisotropic stellar winds remove selectively the angular momentum. For example, winds passing through polar caps in O–stars remove very little angular momentum, an excess of angular momentum is retained and rapidly redistributed by horizontal turbulence. These excesses may lead some Wolf–Rayet stars, those resulting directly from O–stars, to be fast spinning objects, while we predict that the WR–stars which have passed through the red supergiant phase will have lower rotation velocities on the average. We also show how anisotropic ejection can be treated in numerical models by properly modifying the outer boundary conditions for the transport of angular momentum.
Trojans in Stable Chaotic Motion
Authors: Pilat-Lohinger E. , Dvorak R. , Burger Ch.
Published: July 2016

The orbits of 13 Trojan asteroids have been calculated numerically in the model of the outer solar system for a time interval of 100 million years. For these asteroids Milani et al. (1997) determined Lyapunov times less than 100 000 years and introduced the notion “asteroids in stable chaotic motion”. We studied the dynamical behavior of these Trojan asteroids (except the asteroid Thersites which escaped after 26 million years) within 11 time intervals - i.e. subintervals of the whole time - by means of: (1) a numerical frequency analysis (2) the root mean square (r.m.s.) of the orbital elements and (3) the proper elements. For each time interval we compared the root mean squares of the orbital elements (a, e and i) with the corresponding proper element. It turned out that the variations of the proper elements ep in the different time intervals are correlated with the corresponding r.m.s.(e); this is not the case for sin Ip with r.m.s.(i).
Simple Periodic Orbits in Elliptical Galaxies Modelled by Hamiltonians in 1-1-1 Resonance
Authors: Palacián J. , Yanguas P. , Ferrer S.
Published: July 2016

We consider elliptical galactic models, whose dynamical system consists of a three-dimensional isotropic harmonic oscillator plus a potential given by a homogeneous polynomial of degree four with an additional discrete symmetry. We identify families of simple periodic orbits by studying the reduced phase space.
A New Model of Mars Rotation from Pathfinder Data
Authors: Bouquillon Sebastian , Souchay Jean
Published: July 2016

Following efforts to construct an accurate modelisation of Mars rotation starting from canonical equations in an Hamiltonian theoretical frame (Bouquillon and Souchay, 1996), we use recent results from radio tracking data of the Mars Pathfinder mission (Folkner et al., 1997) to modelize in the best way the motion of precession and nutation of the planet. A complete set of coefficients related to these two motions is presented, including the main effect due to the Sun and also those due to the two satellites Phobos and Deimos as well as to the planets. Morever, Oppolzer terms are calculated and included.
Lommel Functions in some Drag-Perturbed Problems
Authors: Sławomir Breiter  , Jackson Albert A.
Published: July 2016

Let us consider the orbital problem in which a particle is subject to the force (per unit mass)

The force consists of the Newtonian two body attraction term and a drag part which is linear in both components of velocity (radial vr and transverse vt). Depending on a physical interpretation of the parameters μ and α, as well as on the particular choice of the dimensionless constant γ, the model (1) can match various two body problems with dissipation. They include the classical Poynting-Robertson effect (Robertson, 1936) with γ = 1, Poynting’s (1903) version with γ = ½ and the two body drag cases recently studied by Mittleman and Jezewski (1982) and by Mavraganis and Michalakis (1994) under the name of Danby’s drag.
Three-Body Stability Criteria
Authors: Donnison J.R.
Published: July 2016

Progress has been made in understanding the stability of hierarchical three-body systems where the third body moves on an approximately Keplerian orbit about the centre of mass of the binary, at a distance large compared to the binary separation. Harrington (1968,1969) showed analytically that provided the third body was sufficiently distant from the binary no secular terms appeared in the semi-major axis and the system was stable. Harrington (1972,1975,1977) established numerically a critical minimum separation distance (or period) for a stable system in terms of the masses, unaffected by the relative inclinations of the orbits, except for angles close to 90°. Most subsequent investigations have therefore used planar configurations. Graziani & Black (1981), Black (1982) and Pendleton & Black (1983) again using long-term integration of the orbits obtained a criterion for high and low mass binaries. Donnison & Mikulskis (1992,1994,1995) carried out numerical integrations on prograde, retrogade, planetary and stellar triple systems and found for prograde systems very good quantitative agreement with the c2H method. Eggleton & Kieselva (1995) suggested a critical distance ratio approximation determined by the masses in the system. Systems with eccentric orbits are covered using the period ratio determined by Kepler’s third law.
Nekhoroshev Stability in Quasi-Integrable Degenerate Hamiltonian Systems
Authors: Guzzo Massimiliano
Published: July 2016

Many classical problems of Mechanics can be studied regarding them as perturbations of integrable systems; this is the case of the fast rotations of the rigid body in an arbitrary potential, the restricted three body problem with small values of the mass-ratio, and others. However, the application of the classical results of Hamiltonian Perturbation Theory to these systems encounters difficulties due to the presence of the so-called ‘degeneracy’. More precisely, the Hamiltonian of a quasi-integrable degenerate system looks like

where (I, φ) є U × Tn, U ⊆ Rn, are action-angle type coordinates, while the degeneracy of the system manifests itself with the presence of the ‘degenerate’ variables (p, q) є B ⊆ R2m. The KAM theorem has been applied under quite general assumptions to degenerate Hamiltonians (Arnold, 1963), while the Nekhoroshev theorem (Nekhoroshev, 1977) provides, if h is convex, the following bounds: there exist positive ε0, a0, t0 such that if ε < ε0 then if where Te is the escape time of the solution from the domain of (1). An escape is possible because the motion of the degenerate variables can be bounded in principle only by , and so over the time they can experience large variations. Therefore, there is the problem of individuating which assumptions on the perturbation and on the initial data allow to control the motion of the degenerate variables over long times.
Zonal Harmonics of the Gravity Field in Def-Variables
Authors: Aparicio Ignacio , Floría Luis
Published: July 2016

To take advantage of thelinear and regularformulation and treatment of Celestial Mechanics problems (Kustaanheimo & Stiefel 1965; Stiefel & Scheifele 1971; Deprit, Elipe & Ferrer 1994), Sharaf & Saad (1997) have given an analytical expansion of the Earth’s gravitationalzonal potentialin terms of Kustaanheimo-Stiefel (KS) regular elements (Stiefel & Scheifele 1971, §19), with special emphasis on its application toelliptic-type two-body orbitsand, consequently, using a generalized (elliptic) eccentric anomaly as the independent variable.

Motivated by these and other considerations based on the definition and use of KS elements, and following a treatment similar to that of Stiefel & Scheifele (1971, §19), we developelement equations corresponding to a DEF-formulationof the satellite problem under the effect of the zonal potential.
On The Stability of Stationary Solutions of the Twice-Averaged Hill’s Problem Taking Into Account The Planet Oblateness
Authors: Vashkovyak M.A.
Published: July 2016

The problem of satellite orbital evolution with the combined influence of a distant perturbing body and the planet oblateness is well known (Laplace, 1805; Lidov, 1962, 1973; Kozai, 1963; Kudielka, 1994, 1997). The case of near-circular orbits is investigated in more details in (Sekiguchi, 1961; Allan and Cook, 1964; Vashkovyak, 1974).
Theoretical Problems of Beta Cephei Stars
Authors: Osaki Yoji
Published: July 2016

The Beta Cephei (or Beta Canis Majoris) stars are a small group of pulsating variables of early spectral type. There are some 20 “classical” β Cephei stars, and several new or suspected variables in this group. The classical β Cephei stars are confined in a narrow “instability strip” which lies about 1 mag above and nearly parallel to the zero-age main-sequence of massive stars (M~10-20 M⊙). They are thus located far away from other well-known pulsating variables such as classical Cepheids and RR Lyrae stars in the HR diagram.
The current Hamburg Program of precise optical positions of radio sources in the FK4 System
Authors: de Vegt Chr. , Gehlich U. K.
Published: July 2016

In 1975 an observational program for the determination of precise positions of optical counterparts of extragalactic radio sources in the FK4 system has been started at the Hamburg Observatory. The sources have been selected from the recent radio lists by Elsmore and Ryle (1976), Wade and Johnston (1977) and Clark et al. (1976) to perform a comparison between the radio- and independent optical positions in the FK4 system. The results from a pilot program to be reported here partly, which includes 17 sources (de Vegt and Gehlich, 1978), encouraged us to extend the program to at present 34 extragalactic sources and 14 radio stars on the northern hemisphere; a list of these sources is given in the appendix.
Astrometric work at the Max Planck Institute for Radioastronomy
Authors: Witzel A.
Published: July 2016

Two sets of experiments with primarily astrometric and/or geodetic goals are presently under way at the Max-Planck-lnstitut fur Radioastronomie. Both observing programs use the 100-m telescope in Effelsberg as an element of an intercontinental Very Long Baseline Interferometer.
The Bordeaux Automatic Meridian Circle
Authors: Requième Y.
Published: July 2016

In spite of important delays in the initial planning, the full automation of the Bordeaux meridian circle is progressing well and will be ready for regular observations by the middle of the next year. It is expected that the mean square error for one observation will be about ±0.”10 in the two coordinates for declinations up to 87°.
Parallaxes and detection of dark companions: atmospheric limitations
Authors: Connes P.
Published: July 2016

We have proposed elsewhere a photoelectric technique for narrow field astrometry which is potentially far more accurate than photography. In this paper the atmospheric limitations, particularly those arising from anomalous refraction are studied. The conclusion is that considerable improvements are indeed feasible from the ground.
Catalogue reduction techniques
Authors: de Vegt Chr.
Published: July 2016

Reduction techniques as applied to astrometric data material tend to split up traditionally into at least two different classes according to the observational technique used, namely transit circle observations and photographic observations. Although it is not realized fully in practice at present, the application of a blockadjustment technique for all kind of catalogue reductions is suggested. The term blockadjustment shall denote in this context the common adjustment of the principal unknowns which are the positions, proper motions and certain reduction parameters modelling the systematic properties of the observational process. Especially for old epoch catalogue data we frequently meet the situation that no independent detailed information on the telescope properties and other instrumental parameters, describing for example the measuring process, is available from special calibration observations or measurements; therefore the adjustment process should be highly self-calibrating, that means: all necessary information has to be extracted from the catalogue data themselves. Successful applications of this concept have been made already in the field of aerial photogrammetry.
Systematic errors Δαcosδ by magnitude in the FK 4 Catalogue
Authors: Loyola P.
Published: July 2016

Systematic errors Δαcosδ by magnitude of the FK4 Catalogue in the zone -20° to -52° of declination are presented. A comparison with the Perth 70 Catalogue and First Astrolabe Catalogue of Santiago is given.
First accuracy estimates of the stellar positions in the “Preliminary Catalogue of the NPZT Program Stars” compiled on the basis of observations with the Belgrade Meridian Circle
Authors: Sadzakov S. , Saletic D. , Dacie M.
Published: July 2016

A brief review is presented of the works under way on the elaboration of a catalogue of the NPZT program stars with the Belgrade Meridian Circle, as well as accuracy estimates of the stellar positions in the “Preliminary catalogue of the NPZT program stars”, compiled on the request of Prof. Yasuda on the basis of about 80% of the planned observations. This catalogue was dispatched to as private communication Prof. Yasuda and Prof. Gliese for use in their respective current undertakings.
SRS Observations: Future US Naval Observatory Meridian Programs
Authors: Hughes J. A.
Published: July 2016

The purpose of these brief remarks is twofold; on the one hand it is to inform you of the activities and plans at the U.S. Naval Observatory (USNO), and on the other hand to make a few comments regarding our mutual astrometric interests.
Concluding Summary
Authors: Blaauw A.
Published: July 2016

The title of this colloquium suggests that it deals with techniques rather than with their fields of application, but in fact, we have dealt with both and covered virtually the whole range of problems to which current astrometric work contributes. Of the topics covered, I cannot but select a few for these concluding remarks - not necessarily the most prominent ones.
Extending the Fourier Transform – The Positivity Constraint
Authors: Komesaroff M.M. , Lerche I.
Published: July 2016

In radio astronomy it is often necessary to estimate a brightness distribution from a limited number of samples of its Fourier transform. The manifest requirement that the brightness distribution be everywhere positive imposes definite constraints on its Fourier transform which yield information about unmeasured Fourier components. Here we discuss the question: given the first n+1 values, p0, P1 … pn, of a uniformly sampled Fourier transform of a real positive function, what can we say about Fourier terms of higher order?
The Height Dependence of Granular Motion
Authors: Nesis Anastasios
Published: July 2016

Spectrograms of Mg I-absorptions lines have been registrated at different positions of the damping wings. The corresponding heights within the atmosphere have been approximated by the Eddington-Barbier approximation. We calculated the coherence between the intensity fluctuations in the continuum and those of the higher layers. We found a rather flat gradient up to a height of 100 km and above this a steep decrease of coherence. From this result we can conclude that above a height of 100 km any fluctuations of intensity are not due to ordinary convective processes. However, up to a height of 400 km we found a coherence between the velocity of granulation and its intensity fluctuations.
Differential Rotation in Stars with Convection Zones
Authors: Gilman Peter A.
Published: July 2016

The topic I was originally assigned for this colloquium was “Generation of Non Thermal, Non Oscillatory Motions”. Being basically a fluid dynamicist, at first I thought this meant I was supposed to talk about the origin of motions which are not thermally driven, i.e., I should not talk about convection. But then I realized all that was meant was that I was to talk about bulk fluid motions, rather than the molecular “thermal” motion of stellar gas that defines its temperature. Obviously the original question was posed by a stellar spectroscopist! Having surmounted that small semantic hurdle, I began to think about all the ways circulatory motions might be generated in a star. All manner of fluid dynamical instabilities come to mind--not only convective instability, but also barotropic or inertial, baroclinic, Kelvin-Helmholz, Rayleiqh-Taylor, Goldreich-Shubert, Solberg-Hoiland, etc. The list is large, overlapping, I am sure confusing to an observer (and to many a theoretician). Then there are Eddington-Sweet currents, and several additional motions arising from the presence of magnetic fields--fields which give rise to magnetic buoyancy of flux tubes, and large collection of magnetohydrodynamic instabilities.