bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional Integrals in Stellar Dynamics
Authors: Dagan Eldad
Published: June 2019

In the late 70s, the functional integral formulation equivalent to the Fokker-Planck equation was worked out (Graham). We apply this functional integral formulation to gravitationally interacting systems, whose dynamics may be analyzed by separating the forces operating on a particle into a mean field force and fluctuations due to random collisions at intermediate range (scattering at small angles). In this poster the formalism is presented for short periods (in the stochastical meaning) to systems with isotropic distribution background in velocity space (different spatial densities are possible). Later the functional integral for the local change for the distribution function is evaluated in the steepest descent approximation. In the end we point out the applicability of the method to slowly evolving globular star clusters near thermal equilibrium. In conditions of slow evolution we can express the evolution of the orbits in terms of local deviation from equilibrium.
The Early Stages of Post-Collapse Cluster Evolution
Authors: McMillan Stephen L. W.
Published: June 2019

We present here some recent (and very preliminary) findings from a study of the early stages of the post-core-collapse evolution of an isolated cluster of identical point “stars”. The method used to follow the behavior of the system is the unified N-body/statistical treatment described in detail by McMillan and Lightman (1984a) and by Lightman and McMillan elsewhere in this volume. Briefly, the method combines the standard “large-N” and “small-N” approaches to the problem in the régimes where they are appropriate by treating the inner regions (r < rN) exactly with a regularized Aarseth N-body code (Aarseth, 1972), while permitting stars at greater and greater radii to retain less and less of their individual identities, ultimately treating the outer portions of the system (r > KrN) in an almost purely statistical fashion.
Collisional Relaxation: A New Approach
Authors: Severne G. , Luwel M.
Published: June 2019

Recent numerical simulations for 1-dimensional systems have shown that the relaxation time due to encounters is far shorter than the generally accepted estimate. To account for this, a new approach to the theory is necessary. The analysis of encounters presented here is characterized by the retention of periodic trajectories in the mean field. The kinetic equation obtained yields a relaxation time scale in qualitative agreement with the simulations. The analysis can be extended to the 3-dimensional case, and preliminary results predict here also a reduction of the relaxation time.
Tidal Stripping and Disruption of Globular Clusters
Authors: van Albada T.S. , Bontekoe T. R.
Published: June 2019

Tidal stripping and disruption of globular clusters may be responsible for the absence of low density clusters in the inner region of the Galaxy. We have studied these processes by integrating orbits of stars while the cluster is moving through a spherically symmetric galactic potential with constant circular velocity (Vcir =220 km/s). The response of the cluster to the tidal field of the galaxy is calculated in a selfconsistent manner with a collisionless N-body code with N=5000 (van Albada 1982, van Albada and Bontekoe in preparation).
Space Telescope Observations of Globular Clusters
Authors: Bahcall John N.
Published: June 2019

Six proposed Space Telescope programs involving globular clusters are described. The projects appropriate for galactic clusters are: the detection of white dwarfs, the study of the faint end of the Population II luminosity function, the measurement of mass segregation, and the search for a cusp in the density distribution caused by core collapse or by a massive black hole. The two programs that involve extragalactic globular clusters are: the determination of the luminosity function of clusters around different galaxies and the measurement of tidal radii of clusters surrounding elliptical galaxies.
Equations of motion for isolated bodies with relativistic corrections including the radiation reaction force
Authors: Grishchuk L. P. , Kopejkin S. M.
Published: June 2019

We have derived in an explicit form the equations of motion for two spherically-symmetric non rotating bodies in the slow motion approximation. The equations include relativistic corrections of order (v/c)2, (v/c)4 and (v/c)5 to the newtonian equations of motion. It is shown that the equations depend on the only parameter characterizing each body, namely on its relativistic mass, regardless of its internal structure and degree of compactness. This means that the equations can also be applied to bodies with a strong internal gravity, such as neutron stars and black holes. It is shown that in the (v/c)2 and (v/c)4 approximations the equations can be derived from a Lagrangian. The Lagrangian is given in an exact form. The integration of the equations of motion is performed by the method of osculating elements. The formulae for secular change of the semi-major axis and eccentricity coincide precisely with the standard ones whose derivation is based on a calculation of the energy flux in the outgoing gravitational waves.
A relativistic theory of motion of the inner planets
Authors: Akim E.L. , Brumberg V.A. , Kislik M.D. , Koljuka Ju.F. , Krasinsky G.A. , Pitjeva E.V. , Shishov V.A. , Stepanianz V.A. , Sveshnikov M.L. , Tikhonov V.F.
Published: June 2019

The theory of the motion of Mercury, Venus, Earth and Mars is constructed by numerical integration. The theory takes into account relativistic corrections in the frame of Schwarzschild's space-time metrics. The constants of the theory are determined by discussion of the Soviet and American radar observations of Mercury, Venus and Mars, position astrometric observations of these planets (and the Sun) and observations of the Soviet artificial satellites of Venus. Apart from the planet elements the value AU and corrections to the adopted radii of Mercury, Venus and Mars are determined. Statistics of residuals is given and accuracy of the theory is estimated. The theory presented is an ephemeris base for deep space experiments.
Theoretical and observational efforts in order to obtain high precision positions of the Galilean satellites of Jupiter
Authors: Thuillot W. , Vu D. T. , Arlot J. E.
Published: June 2019

The two manners to improve the knowledge of the motions of the galilean satellites are the elaboration of a new theory and the use of high precision observations. In this paper, we present new results on these subjects.

We have applied the Sagnier's method in order to get a new theory of the motions and we describe here the second approximation which leads to a third order solution. In this solution appear coupled terms in longitude of the perijoves and longitudes of the nodes. The de Haerdtl's inequalities, which come from the 3-7 commensurability between satellites 3 and 4 are included in this solution. These developments, first computed by de Heardtl, have been improved by Lieske (1973). In our solution we introduce the use of the variables in inclination, and some new terms appear.

In order to get the best precision for the final ephemerides, the accuracy of the observations have to be improved: best results may be obtained with the use of the observations of mutual events. Simulations have shown the interest to take into account the variations of the albedo as a function of geographic longitudes and latitudes on the satellites themselves. So, the theoretical flux of light is closer to the observed one and the accuracy is improved. In 1985, mutual events occur and we have organized a campaign in order to obtain results of high precision.
Relativistic and perspective effects in proper motions and radial velocities of stars
Authors: Stumpff P.
Published: June 2019

The heliocentric motion of stars is investigated by taking into account all effects due to the geometry and due to the finite speed of light. It is shown that the proper motions as given in star catalogues contain the main light retardation term; an additional term of this type modifies Schlesinger's (1917) term but is less significant than a 3rd order perspective term neglected in conventional astrometry. Kapteyn's star serves as a numerical example. The ambiguous relativistic relation between Doppler shifts and radial velocities is discussed and demonstrated in a diagram. The ambiguity is solved with rigorous equations which allow to compute the inertial motion of a star from its proper motion, classical radial velocity, and distance. -
On observations in Schwarzschild background
Authors: Khmil S. V.
Published: June 2019

In the geometrical optics approximation a uniform approach to the description of the influence of strong Schwarzschild field on astronomical observations is given.
Numerical effects of gravitational light deflection on the determination of the equinox and equator
Authors: Hughes J. A. , Scott D. K. , Smith C. A.
Published: June 2019

Observations of the sun and major and minor planets made by transit circle telescopes are used to determine positions of the equinox and the celestial equator and, by repeated observing programs, the motions of these fiducial references. Long series of such absolute observations, when combined into catalogs such as the FK5, yield a fundamental coordinate system which is an observational approximation to an ideal, dynamically defined coordinate system. In such a system the equinox, for example, is defined implicitly by the right ascensions (at mean epoch) and the proper motions of the stars included in the catalog system, together with the adopted constant of precession. It may be noted that independent, highly accurate determinations of the latter quantity thus help to improve the fundamental proper motion system.
Relativistic effects in geodynamics
Authors: Boucher C.
Published: June 2019

Geodesy has now reached such an accuracy in both measuring and modelling that time variations of the size, shape and gravity field of the Earth must be basically considered under the name of Geodynamics. The objective is therefore the description of point positions and gravity field functions in a terrestrial reference frame, together with their time variations.

For this purpose, relativistic effects must be taken into account in models. Currently viable theories of gravitation such as Einstein's General Relativity can be expressed in the solar system into the parametrized post-newtonian (PPN) formalism. Basic problems such as the motion of a test particle give a satisfactory answer to the relativistic modelling in Geodynamics.

The relativistic effects occur in the definition of a terrestrial reference frame and gravity field. They also appear widely into terrestrial (gravimetry, inertial techniques) and space (satellite laser, Lunar laser, VLBI, satellite radioelectric tracking …) measurements.
Application of the Deep Space Network (DSN) to the testing of General Relativity
Authors: Anderson J. D. , Levy G. S. , Renzetti N. A.
Published: June 2019

Over the past two decades, radar and radio observations of planets and spacecraft have been made by stations of the Deep Space Network (DSN), which by the unprecedented nature of their accuracy have produced the most accurate tests of general relativity available. We review the history of the instrumentation and data analysis of the first spacecraft test, the three percent determination of the effect of solar gravity on radio signals between DSN stations and the two spacecraft, Mariner 6 and Mariner 7 (Anderson et al., 1975), as well as later more accurate tests using the Mariner 9 spacecraft anchored to Mars (Reasenberg and Shapiro, 1977; Anderson et al., 1978) and the Viking orbiters and landers (Shapiro et al., 1977; Hellings, 1985). We also review tests of the metric nature of gravity using radar, optical observations, and radio astrometry of the planets (Anderson et al., 1978; Reasenberg, 1985; Hellings, 1985) and the limits placed on the variability of the gravitational constant G (Hellings et al., 1983). Finally, we discuss the prospects for improved accuracy through ongoing upgrades of DSN instrumentation and show the results of covariance analyses for a possible future NASA mission to the Sun (Solar Probe) in the mid 1990's (Mease et al., 1984) and the next NASA mission to Mars, the Mars Observer mission planned for launch in late 1990.
Accuracy estimates for the determination of the solar space-time metric by HIPPARCOS
Authors: Söderhjelm S. , Lindegren L.
Published: June 2019

Parallel to the determination of astrometric parameters for some 100,000 stars, the HIPPARCOS data may also be used to study the light deflection produced by the sun. Cowling (1983 thesis) has calculated the light deflection observable by HIPPARCOS for a general space-time metric, and we have included his list of fifteen metric coefficients as “global” parameters in simulated HIPPARCOS reductions. The estimated covariance matrices show that only 7–9 linear combinations of the Cowling parameters may be determined with some accuracy (~10−10). The value for the standard GR light deflection may be determined if the thermal effects on the satellite are small, but not to better than about 0.5%.
Proposals for an experiment to detect the Earth's gravitomagnetic field
Authors: Polnarev A. G.
Published: June 2019

Some experiments are discussed for measuring the earth's gravitomagnetic field, using a pendulum or an oscillator rather than a gyroscope.
Galaxy Luminosity Functions, M/L Ratios, and Closure of the Universe
Authors: Felten James E.
Published: June 2019

Data on the luminosity function (LF) of galaxies are reviewed and compared on a common magnitude system and with common assumptions. The result of Kirshner et al. (Astron. J. 88, 1285, 1983) is chosen as a best guess. Departures from this “standard LF” for specific galaxy types and environments (clusters, groups, field) are discussed briefly. If the Galactic absorption is AB = 0.2 csc|b| and the solar absolute magnitude is MB⊙ = 5.48, this LF leads to a mean luminosity density on the BT system, or about 1.4 × 10−2 h “Galaxies” Mpc−3. The mean M/L ratio needed to give critical cosmological density (Ω0 = 1) is then 920h in solar units on the BT0 (face-on) system. [The latter number can be larger by a factor ∼2 if a different LF is used, and larger still on different systems and with different assumptions (see Table).] The “weighed” M/L on this system is in clusters, but it is smaller in binaries and small groups. Estimates of the weighed (clumped) Ω0 vary, but it is definitely < 1. Comparison with constraints imposed by inflation and nucleosynthesis suggests that we distinguish at least two “dark-matter” problems: (1) What is the weighed mass, and how is it distributed? It contributes an Ω0 ∼ 0.1–0.5 and could be all baryonic if at the lower end of this range. (2) Is there additional matter, more smoothly distributed and probably nonbaryonic, which brings Ω0 up to unity? For details see Comments on Astrophys., in press.
Do Baryon Structures Survive after the Decay of Unstable Particles?
Authors: Suto Yasushi , Noguchi Masafumi
Published: June 2019

A possibility of a universe dominated by unstable particles has been suggested recently as an interesting solution to various cosmological problems. In this scenario, however, nonlinear structures may be disrupted or even smoothed out during the decay of unstable particles. In order to obtain the survival condition of baryon structures, we studied evolution of systems composed of baryon and unstable particles by the numerical integration of the Vlasov equation.
Morphology of Galaxies with UV-Continuum
Authors: Jôeveer Mihkel
Published: June 2019

The purpose of this contribution is to compare the morphology of galaxies with UV-continuum (Markarian galaxies) found in the First Byurakan Survey with normal galaxies. We use only data from general surveys.
The Excitation Mechanism of Metastable Levels and Variability of Oxygen Forbidden Lines 4959+5007 Å [OIII] in the Seyfert Nuclei
Authors: Pronik V. I. , Pronik I. I.
Published: June 2019

In high density gas n(H) ~ 107cm−3 the electron impact and charge transfer OIV+HI→OIII+HII secure high emissivity of gas in [OIII] lines only with low hydrogen and helium ionization, when ne~ n(OIII) ~ 106−107 cm−3. Such condition is possible in HI-zones where oxygen is ionized by soft X-ray (Auger effect). It is shown, that the observed luminosity of NGC 1275 nucleus in 4959+ 5007 Å [OIII] lines can be explained by the electron impact in gas with hydrogen concentration n(H) ~ 1012 cm−3 and does not contradict to a possibility of lines variations within several days.
A Probable Model of Compact Variable Radio Sources with a “Superluminal” Motion of VLBI-Components
Authors: Komberg B.V.
Published: June 2019

“Ballistic” models are now put in doubt on the strength of the observed properties of “superluminal” components, and preference is given to “screen” models. It is suggested that active nuclei are supermassive systems, such as SS-433, with two precessing relativistic plasma jets, which flow from opposite directions into the same precession cone. In this case “superluminal” components can manifest themselves as displacements of the interaction between these jets and inhomogeneities in the circum-nuclear medium (clouds). Thus, due to isotropic production of relativistic particles in the interaction area and/or magnetic field distortions, bursts of emission may be observed not only along flows, as would be the case for BL Lacertae objects, but also at appreciable angular distances from the jets. Moreover, one may understand the observed one-sidedness of VLBI-jets on parsec scales and the symmetrical VLA-structures on kiloparsec scales as a result of random cloud hits by the precessing flows. We suggest that the observed repetition of active cycles of different objects may be caused by several cloud hits by the precessing flows of a complex multibeam structure once every 50–100 years.
Helioseismic Observations at Stanford, 1977–1986
Authors: Henning Harald M. , Scherrer Philip H.
Published: June 2019

Observations of low degree modes of solar oscillation have been made at The Wilcox Solar Observatory at Stanford University for more than a decade. We are presently re-examining the set of observations from 1977 through 1986. We have first tested the stability of the p-mode frequencies for modes of degree l=2–5 in each year. We find a marginally significant trend of a decrease in p-mode frequencies of 0.06 μHz per year. We have also examined the continuity of the observed signal at 160.01 minutes. We find that the previously reported phase stability is no longer present. However, due to uncertainties in calibration we can not exclude the reality of the reported signal.
Observations of solar global oscillations (1983–1985) and potential influence of terrestrial sources of errors
Authors: Severny A.B. , Kotov V.A. , Tsap T.T.
Published: June 2019

The Earth atmospheric pressure fluctuations in the 5-min range of periods are analysed and their influence on observations of solar 5-min oscillations are briefly discussed. New series of observations confirmed the oscillations of the Sun with period of 160.010 min.
Solar 5-min Oscillation Amplitude Anisotropy and Doppler Velocity Systematics
Authors: Kuhn J.R. , O'Neill C.M. , Gilliam L.B.
Published: June 2019

Several measurements of 5-min velocity amplitudes have yielded confusing and conflicting information on the l and m dependence of the modal excitation (Kuhn and O'hanlon, 1983 – henceforth KO; Deubner, 1985; and Hill et al. 1985). We have obtained considerably more data than was described in KO using similar observing techniques. Additional analysis has illuminated a systematic effect related to the finite spatial resolution, and line asymmetry of the data that can lead to errors in inferred velocity amplitudes. Even though Doppler shifts are calculated from the Fraunhofer line center positions the effect can lead to 5-min oscillation amplitude errors at the 10 percent or greater level. Line wing observations should be more susceptible, and comparable resolution 2-dimensional data may be less sensitive to this systematic.
Sensitivity of solar p-modes to solar envelope structure
Authors: Demarque P. , Guenther D. B.
Published: June 2019

We present a study of the effects of diffusion of helium and heavy elements from the convection zone into the radiative layer immediately below the convection zone, on the structure of the solar envelope. A comparison is made of the p-mode oscillation spectrum and the run of the speed of sound in a model with diffusion, in a standard model, and with observation.
Constraints on central solar conditions from helioseismology and neutrino counts
Authors: Faulkner John
Published: June 2019

Interesting joint constraints are placed on central solar conditions by the solar neutrino detection rate and the frequency separations of high-order, low-degree p-modes of pulsation. A new form of diagnostic diagram is introduced that illustrates the difficulty in standard theories of simultaneously satisfying these joint constraints. A model employing WIMPs (= weakly interacting massive particles) appears to be the only model extant capable of fitting both kinds of data. Unambiguous identification and fitting of g-modes can provide a further test of the WIMP model provided a certain caution is exercised.
The study of oscillations localized near a layer of density discontinuity in an example of solar model
Authors: Vandakurov Yu. V.
Published: June 2019

If at some radius r = rj there is a jump of the density and composition then a simple asymptotic formula can be derived which gives ω, the oscillation frequency for large degree modes (ℓ ≫ 1). Using relations of Gabriel and Scuflaire (1979) and taking into account the fact that the oscillation amplitude at R < rj or R > rj is equal to rℓ or r−ℓ multiplied by some functions only weakly dependent on ℓ, we obtain
where g is the gravitational acceleration, and ρi(ρe) are the densities at the lover (upper) sides of the layer in question. The comparison with the exact ω-values considered below shows that the asymptotic values are larger by 13, 8.8, and 6 percents for ℓ equal to 5, 7, and 10, respectively. Because ω should be less than the maximum value of the Brunt - Väisälä frequency, we have for a finite thickness Δ of the jump layer and for finite ℓ that ℓ ≪ 2rj/Δ. We have performed numerical study of the above modes which may be called interior modes. The equilibrium model was similar to that studied by Vandakurov (1984 a,b) but now we assume that a small iron-like core (as in Rouse's (1983) model) is present. We assume the hydrogen content in the core to be large enough for convection to occur. Above the core, there are the inhomogeneous convectively neutral zone (rj ≤ r ≤ rj1), the homogeneous radiative zone (rj1 ≤ r ≤ ru), and the convective envelope (ru ≤ r ≤ R), whose structure have been taken from Spruit's (1974) paper.
Inertial modes trapped in the solar convective envelope
Authors: Dziembowski W. , Kosovichev A. , Kozlowski. M.
Published: June 2019

Due to their efficient trapping in the outer layers such modes may reach observable amplitudes of the order of 1–10 m/s, even if their energies are as those of the “five minute” oscillations. The modes that are most likely to be seen correspond to the lowest radial orders.

The paper will be published in Acta Astronomica.
Non-newtonian forces and the observed solar oscillation spectrum
Authors: Kuhn J. R.
Published: June 2019

Motivated by recent interest in the possibility of a long range gravitation-like force we have considered the effects a deviation from the Newtonian force law would have on the solar normal mode spectrum. Observations of low order and degree modes provide the most interesting limits to possible new physics. The constraint from solar oscillation observations is distinct from other planetary data in that it provides an integral bound on force law deviations on spatial scales between roughly 2×104 km and planetary scales. This limit is −0.02 ≤ δG/G ≤ 0.3 and is presently limited by systematic differences between the low-l observations and uncertainty in the solar model.
Stellar acoustic ray patterns
Authors: Perdang J.
Published: June 2019

We have analysed and attempted to classify the acoustic ray patterns in stars whose equilibrium figure is globally deformed. We discuss here the effect of distortions of ellipsoidal and pear-shaped structure. Under ellipsoidal symmetry all ray patterns remain ‘regular’. For arbitrarily small pear-shaped deformations our numerical results indicate the occurrence of ‘chaotic’ ray patterns arising out of the unstable longest diameter ray. These chaotic rays cover the whole configuration space.
The effect of toroidal magnetic fields in the overshoot layer on the eigenfrequencies of stellar oscillations
Authors: Belvedere Gaetano
Published: June 2019

The overshoot layer in stellar convection zones is slightly subadiabatic and can be considered as a stable region for storage of magnetic flux. Belvedere, Pidatella and Stix (1986) estimated the size of the overshoot layer and computed the magnetic field strength, beyond which toroidal flux tubes become unstable to buoyancy, for a number of main sequence spectral types ranging from F5 to K0. Here we estimate the relative frequency perturbation of high order acoustic modes due to the presence of a non-oblique axisymmetric magnetic field in the overshoot layer. We find that increases with the advancing spectral type, the predicted frequency splitting being large enough to be detected by observations, at least for the Sun.

We conclude that magnetic field induced frequency splitting of high order acoustic modes may well be due to a toroidal field of relatively moderate strength just beneath the bottom of the convection zone.
Long periods in diameter, irradiance and activity of the Sun
Authors: Delache Ph. , Laclare F. , Sadsaoud H.
Published: June 2019

Long periods have been detected in solar diameter measurements obtained during the past 10 years. The same periodicities are also present in other global Sun parameters such as the 10 cm radio flux, the total irradiance, and possibly the neutrino flux. Special attention is paid to periods corresponding to the solar cycle (“C”), 1000 days (“P”) and 320 days (“W”). Studying the respective phases of the signals give some insight to the possible physical origins of these variations.
Evidence for global pressure oscillations in Procyon and α Centauri
Authors: Gellt B. , Grec G. , Fossat E.
Published: June 2019

Helioseismology bas proved to be a powerful tool to probe the internal structure of the sun. With a new adapted optical resonance spectrophotometer, an extension has been attempted to two bright stars, namely α Centauri Å and Procyon. Results obtained from two observing runs on α Centauri Å in May 1983 and May 1984 at La Silla, and one observing run on Procyon in February 1984 at Hawaii are presented. In both cases, solar-like pressure oscillations have been detected. The complete analysis is presented, which leads to determine essentially five parameters: the frequency range, the amplitudes, the mean equidistance Δν, the departure around this equidistance (curvature of the echelle-diagram) and the fine frequency spacing between modes of degree 0 and 2. For Procyon, all results are consistent with theoretical predictions, including excitation of oscillations, mass, radius, and age of the star. For α Centauri, all the results are consistent together and are confirmed by the 1984 observations. They suggest that α Cen might be younger than estimated, consistent with a zero age main sequence star.

This is the abstract of a paper recently published in Astronomy and Astrophysics. We have selected here under some parts of this paper. For more detail, it is recommended to refer to this journal.
A search for rapidly oscillating Ap stars in the northern hemisphere
Authors: Kreidl Tobias J.
Published: June 2019

Since 1984, efforts have been underway at Lowell Observatory to monitor Ap stars for rapid oscillations utilizing a photoelectric photometer on 0.6- to 1.8-meter telescopes. These variables, first discovered and designated as a subgroup of Ap stars by D.W. Kurtz, pulsate with periods between 4 and 15 minutes and light variations less than about 0.m016 in B. This strongly suggests high overtone p-mode oscillations as the cause of rapid variability. To attempt to increase the known number, Ap stars of spectral type B9 and later are being monitored. As members currently span the range A5 to F0, it is important to establish within what limits rapid oscillations are present. So far, only one new member has been found at Lowell (HD 134214), bringing the known total to eleven. The coordination of observations for known members has proved to be useful; no fewer than five rapidly oscillating Ap stars have been observed via multi-site, coordinated photometry. In this context, the status of this observing program and its future goals are presented.
A Hertzsprung-Russell diagram for stellar oscillations
Authors: Christensen-Dalsgaard Jørgen
Published: June 2019

I present evolutionary tracks and curves of constant central hydrogen abundance in diagrams based on frequencies of high-order, low-degree p modes. For stars with masses between 0.7 and 1.5 M⊙, a clean separation is obtained between the effects of varying mass and varying evolutionary state.
The stellar seismology of the hot white dwarf star PG1159-035
Authors: Kawaler Steven D.
Published: June 2019

Asymptotic analysis of the equations of nonradial adiabatic oscillation shows that there is a “characteristic period spacing” for g-modes with the same degree (l) and consecutive values of the radial wavenumber (n). If modes with the same l but different n are present in a pulsating star, then comparison of the characteristic period spacing in appropriate stellar models with period differences between the observed pulsation periods can provide mode identifications, and thereby constrain other physical properties of the star. A simple empirical model of the observed period spectrum of the hot white dwarf star PG1159-035 yields two statistically significant mean period intervals of 21.0±0.3 or 8.8±0.1s. We also evaluate the period interval for models of hot white dwarfs that are representative of PG1159 stars. The observed intervals correspond very closely to those derived from the theoretical models. This analysis indicates that the mass of PG1159-035 is 0.60M⊙ and that it is either a dipole (l=1) or l=3 pulsator (or both!), pulsating in high radial overtone g-modes.
Diagnosis of the solar atmosphere using solar oscillations
Authors: Frandsen Søren
Published: June 2019

I present a review of the art of using acoustic and gravity waves as a tool to probe the structure of the solar atmosphere. The principle ideas behind the technique are discussed and a small bouquet of results is presented. The current discrepancies are pointed out, and in the last section a few thoughts are let loose about the inversion of data to deduce the physical state of the atmosphere.
On the energy of short period acoustic waves in the solar atmosphere
Authors: Deubner F.-L. , Reichling M. , Langhanki R.
Published: June 2019

The amount of energy carried in the solar atmosphere by short period acoustic waves is particularly uncertain in the range of frequencies (ν ≥ 10mHz) which is potentially relevant for acoustic heating.
Techniques for observing solar oscillations
Authors: Brown Timothy M.
Published: June 2019

There is currently a wide range of methods for observing the properties of solar oscillations. It is generally true, however, that the means used to analyze the data are just as important to the final result as the instrumentation. I discuss first the instrumental techniques used to observe solar p-modes, with attention given both to low- and no-resolution systems, and to systems with spatial resolution. Then I describe the reduction techniques that are used to convert the raw observations into useful form.
Infrared heterodyne spectroscopy: a tool for helioseismology
Authors: Glenar D.A. , Käufl H.U. , Deming D. , Kostiuk T. , Mumma M.J.
Published: June 2019

Heterodyne spectroscopy at infrared (IR) wavelengths is a technique well suited for measuring small velocities in the solar atmosphere. An IR heterodyne spectrometer for solar oscillation measurements has been located at the McMath Solar Telescope of the Kitt Peak National Solar Observatory. It is now being used for single point Doppler shift measurements of 11 micron OH absorption features formed in the upper photosphere, with sampling rates as high as 33 mHz. The instrument employs a stabilized CO2. laser permitting absolute velocity measurements with an uncertainty of < 10 ms−1.
A Bayesian approach to ridge fitting in the ω-kdiagram of the solar five-minute oscillations
Authors: Morrow Cherilynn A. , Brown Timothy M.
Published: June 2019

The acoustic oscillation modes of the Sun cluster along ridges of power in the ω-kplane. Fitting curves to these ridges provides input for methods that reveal information about the Sun's interior. This curve-fitting task is difficult due to noise in the data, close spacing between ridges at lowk, and heuristic approaches to the fitting problem. The procedure we are investigating employs a simple but powerful rule from Bayesian decision theory in an effort to minimize the impact of such problems. This Bayesian approach allows one to make systematic use of prior physical and phenomenological information to assign a prior probability that a candidate curve gives the best fit to a ridge. Bayes' rule then permits one to update this probability using the new ridge power data. The maximally probable candidate curve given both new and prior information is chosen as the best fit.
Automated p-mode identification using Bayes' theorem
Authors: Brown Timothy M.
Published: June 2019

The task of interpreting p-mode spectra is complicated by the presence of a very large number of oscillation modes, each of which may appear (because of aliasing) in the power spectra corresponding to several values oflandm.Identifying peaks in a power spectrum with particular modes in an interactive fashion thus quickly becomes impractical. Here I describe an automated method for doing this identification. The method is based on an application of Bayes' theorem, which provides a simple way to use prior knowledge about the oscillation spectrum. The method takes as input the observed power spectra, and a model of the amplitudes and frequencies one expects to see.
Techniques for observing stellar oscillations
Authors: Harvey J. W.
Published: June 2019

Although stellar oscillations have been observed for more than two centuries, the demands of asteroseismology require new observations of substantially higher precision. Two major techniques are reviewed: Doppler spectroscopy and photometry. Fundamental limitations are described using the sun as a representative stellar target. The current state of the art is limited by lack of light in the case of Doppler methods and by atmospheric noise in the case of photometry. Prospects for improvements in both of these techniques are good and we may expect someday to be able to detect solar-like oscillations of stars as faint as 10th magnitude.
Space observations of solar and stellar oscillations
Authors: Noyes Robert W.
Published: June 2019

Space observations offer many advantages for helio- and asteroseismology, due principally to the absence in space of transparency fluctuations, image blurring, and absorption by the Earth's atmosphere, and to the possibility of long-term continuous observations by a single spaceborne instrument. Helioseismology from space has already shown that stars produce a measurable oscillation signal through photometric variations at the micromagnitude level; this leads to the near-term possibility of simple spaceborne instruments for both helio- and asteroseismology. For the Sun, where photon flux is not a serious problem, doppler analyzer instruments also show great promise. A number of space investigations in helio- and asteroseismology presently under definition or development are briefly discussed.
Overview of the conference: implications of seismological data for astrophysics
Authors: Cox Arthur N.
Published: June 2019

This review of the conference will necessarily consider the seismological data implications for only stellar astrophysics. While there are some aspects of this conference that interface with subjects like relativity, gravity, stellar systems, studies of chaos, etc., these will not be discussed here. What we are doing here is discussing the interiors of stars. We want to learn about their masses and composition structures. Pulsation periods can be used to measure stellar mean densities. Further details that seem accessible are the solar rotation speed versus depth and latitude and the structure of both solar and stellar atmospheres.

Most of the contributions at this conference dealt with the hard problems of our understanding oscillations of the sun. As we shall see in many cases, the problems in understanding the stars by observing their pulsation periods are even more difficult. Similarities and differences between helioseismology and asteroseismology will be a principal theme of this review.
Results from Space
Authors: Heap Sara R.
Published: June 2019

Space astronomy has made major and ever increasing contributions to planetary nebula research. Three astronomical satellites – Rosat, Hubble, and EUVE – have been launched since our last meeting five years ago. In addition, SpaceLab experiments flying on the NASA Shuttle have now observed a planetary nebula. After fourteen years, the IUE satellite is still going strong, and IRAS data continue to provide new results on planetaries and their antecedents.

With such a large volume of space data and a broad range in research topics, it is impossible to describe all the results from these instruments. Fortunately, other reviews at this conference by Perinotto (IUE observations of stellar winds) and Zhang (broadband flux distributions) will cover some of these topics. I will limit this review to five topics: (1) the first far-UV spectrum of a planetary, (2) new observations concerning the interaction of a stellar wind and the nebula, (3) the first high-resolution pictures of planetaries made by Hubble, (4) new observational evidence on the masses of planetary nuclei, and (5) recent advances in UV spectroscopy of central stars.
The Southern Deep Near Infrared Survey (DENIS) a Prospect of PN Exploration
Authors: Kimeswenger Stefan , Kienel Christoph
Published: June 2019

The near infrared light is important for the exploration of proto-planetary nebulae as well as for the planetary nebulae in early phases (Persi et. al. 1986, in Planetary and Proto-Planetary Nebulae: From IRAS to ISO, ed A. P. Martinez). Numerous work on the fluxes of the well known planetary nebulae was already done in the late 80's, but a sky survey will give a large sample of data to provide more detailed statistics.

The present work presents an overview of the data on planetary nebulae expected from the European project of a deep near infrared survey of the southern sky (denis) (IAP and DESPA Paris, Heidelberg, Leiden, IAC Tenerife, Grenoble, Lyon, Frascati, Innsbruck, Vienna) in the I, J and K band with a limiting magnitude of 14.5 to 15 for point sources and 17 mag arcsec−1 for the surface brightness. The angular resolution for identification of non–point source objects will be about 5″.
Planetary Nebulae by the Strong [NII] Emission Lines
Authors: Kondratjeva L. N.
Published: June 2019

The sample of planetaries with the strong [NII] emission lines are analysed. All available parameters are discussed. The enrichments of all elements and the tendency to rather low surface brightness of ne bulae in Hβ flux are remarked. The deficiency of hydrogen in envelopes is proposed as the possible reason of observational spectra.
Spectrophotometry and Multicolour Imagery of the Planetary Nebula Around the P Cygni Star AG Carinae
Authors: Rossi C. , Altamore A. , Costa R.D.D. , Neto A. Damineli , De Freitas Pacheco J.A. , Cassatella A. , Marenzi A.R. , Persi P. , Polcaro V.F. , Viotti R.
Published: June 2019

Some of the high luminosity stars in our Galaxy are surrounded by planetary-like nebulae formed by material ejected from the central star. The most interesting case is that of the ring nebula PK 289-0° 1 around the P Cygni star AG Car. Long slit spectroscopy shows that nitrogen is overabundant and oxygen underabundant in the nebula. The Hα/[NII] ratio is lower in the nebula with respect to the surrounding H II region, possibly as a result of the N overabundance in the stellar wind. The emission line peak separation confirms a model of a distorted spherical shell expanding at 66 km s−1. The scattered star's spectrum is observable near the star, suggesting the presence of circumstellar dust grains. A nebular mass of at least 2.7 M⊙ is derived. While the nebula in the Hα imagery reveals the ring-like shape with many structures, in the blue it is much fainter and smoother. No nebular emission was detected in the JHK bands, suggesting a low dust temperature.
First Results of a Near IR Monitoring Program of OH/IR Stars
Authors: García-Lario P. , Engels D. , Manchado A.
Published: June 2019

We present the first results of a long-term monitoring program of observations in the near infrared of a selected sample of OH/IR stars included in the IRAS Point Source Catalogue. The observations have been made using the 1.5m Sanchez Magro Telescope (SMT) at Izaña (Tenerife, Spain) since the beginning of 1991 and are still in progress. They are being complemented with observations made using the 1m ESO photometric telescope (La Silla, Chile). The sample includes 30 OH/IR stars with a variety of infrared and OH maser luminosities, expansion velocities, LRS classes and position in the IRAS two-colour diagram.
Near-Infrared Spectroscopy of Proto-Planetary Nebulae
Authors: Hrivnak B.J. , Kwok S. , Geballe T.R.
Published: June 2019

Sixteen candidates for proto-planetary nebulae have been observed with low-resolution infrared spectroscopy in the H and K bands, and 6 in the L band, using the United Kingdom Infrared Telescope. In the H band, the objects show hydrogen Brackett lines in absorption. In the K band, absorption bands (del v=2) of CO were observed, and in three cases the CO bands are in emission. The CO spectrum of IRAS 22272+5435 was found to change from emission to absorption over a three-month interval. This CO emission can be interpreted as an indication of some recent episodes of mass loss in these objects. Four of the objects were found to possess an emission feature at 3.3 um, usually associated with PAHs, and two of these show an unusually strong 3.4 um emission feature (Geballe, Tielens, Kwok, & Hrivnak 1992, ApJ, 387, L89).
The Chemical Composition of Post AGB Stars
Authors: Parthasarathy M. , Lario P. Garcia , Pottasch S.R.
Published: June 2019

The F-type supergiant HD 56126 (F5I) is an IRAS source with detached cold dust shell with characteristics similar to the dust shells around planetary nebulae. From an analysis of high resolution and high signal to noise ratio spectra metal and CNO abundances have been determined. It is found that in HD 56126 [C/H] =−0.01, [N/H]=+0.17, [O/H] = −0.02, [S/H]=+0.01 and [Fe/H]< −1.0. The C/N/O abundance ratios and CNO abundances relative to Fe of HD 56126 and related post AGB stars suggest that they have on their photospheres the material processed by triple alpha, CN and ON cycles.
Effects of New Opacity on the Post-AGB Evolution
Authors: Kato M. , Hachisu I.
Published: June 2019

Using the OPAL opacity, we have calculated the post-AGB evolutions of low mass stars. It is newly found that optically thick wind occurs for Mcore > 0.55M⊙ and the evolutionary time scale is drastically shortened.
Evolution of Planetary Nebulae Envelopes: An Empirical Approach
Authors: Golovaty V.V. , Malkov Yu. F.
Published: June 2019

We carried out the empirical investigation of the evolution of gas density distribution in the envelopes of planetary nebulae (PN). For this purpose we analysed the isophotal maps of 10 PN in the lines H alpha, H beta or in the optically thin radio continuum. To obtain the spatial radial distribution of gas density n(r) (where n = n(H)+n(He)) we used Abell's integral equation in the simplest, spherically-symmetric case. We found that n(r) for all PN envelopes in our sample can be described by an approximative expression:
SN 1987A Deconvolved by Mim
Authors: Gratl H. , Pfleiderer J.
Published: June 2019

Modelling of PNs from blurred images, as from the Hubble Space Telescope, needs good deconvolution, and the better that is, the more reliable are the results. As an example, we have MIM-deconvolved the HST image of SN 1987A taken in August 1990 by the FOC in [O III] λ5007 Å (F501N). MIM (minimum information method) is a linear deconvolution method with a local smoothness constraint (Pfleiderer 1991). Our results are similar to those already published (Jakobson et al. 1991, Panagia et al. 1991) but we were able to decrease some of the uncertainties. The ring, centered on the SN, has diameter 1680 ± 20 mas (≡ 1.3 ly) and tilt 44.5°±1.5° (Fig 1.). The lumps deviate from the ellipse by up to ≤ 0.05 ly, the ratio of brightest to faintest knots being ≈ 10 (Fig.3). The SN is resolved (Fig.2), being not a uniformly illuminated disk but brighter in the center. Its FWHM is 100 ± 10 mas, i.e. an average expansion velocity since the explosion of v ≈ 3 500 km s−1.
Time-Resolved CCD-Photometry of Planetary Nebula Nuclei
Authors: Roth M. M. , Soffner T. , Mitsch W.
Published: June 2019

The enormous potential of direct imaging CCDs with respect to stellar photometry was soon discovered after these detectors became available for standard instrumentation at modern telescopes. Among favourable properties like high quantum efficiency, linearity, and large dynamic range the multiplexing advantage of the 2-dimensional detector has permitted to perform quantitative work that otherwise would have been impossible with classical photoelectric photometry. Striking examples for this are the progress in constructing colour magnitude diagrams for globular clusters (see e.g. Hesser et al. 1987, their Fig.9) or the high precision (down to the mmag level) achieved in differential photometry on ensembles of stars (Gilliland and Brown 1988). Several groups have also used CCDs for time series measurements employing specialized instruments and/or proper observing strategies (Dunham et al. 1985, Howell and Jacoby 1986, Stover and Allen 1987). If high time resolution (on the order of seconds or less) is required, however, the photoelectric method is still superior to CCDs mainly because of problems like data rates and readout time overhead (Barwig 1987).
O, S, Ar from Planetary Nebulae Data and the Chemical Evolution of the Galactic Disk
Authors: De Freitas Pacheco J.A.
Published: June 2019

The O, S, Ar abundances for a sample of 122 planetary nebulae (merging LNA data and those by Köppen, Acker and Stenholm 1991) were analysed. Average abundances were calculated for progenitors having different metallicities (ages). Our study suggests that type I planetaries, whose progenitors are not older than 1–2 Gyr, have average oxygen abundances 0.2 dex lower than the solar value. This agrees with O-abundance determinations in HII regions, intermediate mass supergiants and B stars in young associations. S and Ar show a different behaviour. We suggest that such a paucity of O in the ISM is produced by recent infalling gas from the halo, having abundance ratios similar to those expected from type Ia supernovae.
High Resolution Millimeter Wave Images of HL Tau Reveal a Companion in the Disk
Authors: Welch William J. , Webster Zodiac , Mundy Lee , Volgenau Nikolaus , Looney Leslie.
Published: June 2019

An image of the disk of the TTauri star HL Tau at 1.4 mm wavelength at an angular resolution of 0.25 arcsec shows a secondary peak in the disk at a radius of 70 AU and position angle of −40°. This secondary peak is evidently a small unresolved nebulosity which may surround a star or planet or may not yet have formed such a body. The nebulosity could have formed as a result of a density wave instability in the disk.