bluuebunny/crossref_metadata_2025 huggingface dataset:
Construction of a planetary solution with the help of an n-body program and analytical complements
Authors: Bretagnon P.
Published: June 2019

Up to now we have been dealing with the construction of entirely analytical planetary theories such as VS0P82 (Bretagnon, 1982) and T0P82 (Simon, 1983). These theories take into account the whole of the newtonian perturbations of nine point masses: the Sun, the Earth-Moon barycenter, the planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune. They also take into account perturbations due to some minor planets, to the action of the Moon and the relativistic effects. The perturbations of these last three types are in a very simple way under analytical form but they considerably increase the computations when introduced in the numerical integration programs.
Developing high accuracy numerical theories of motion of outer satellites of Jupiter and Saturn
Authors: Bykova L. E. , Shikhalev V. V.
Published: June 2019

The effect of different perturbing factors on the rectangular coordinates of outer satellites of Jupiter (VI-XII) and Saturn (VI-IX) is investigated by the numerical integration of the equations of motion. The effect of relativistic terms in the equations of motion is considered among other perturbations. The effect of weak perturbations is compared with the accuracy of modern observations of satellites.
Reference frames and gravitational effects in the general theory of relativity
Authors: Ivanitskaya O. S. , Mitskiévič N. V. , Vladimirov Yu. S.
Published: June 2019

In connection with the precision growth in modern astrometry, General Relativity (GR) has become a necessary basis of celestial mechanics and of computations of ephemerides of planets and other space objects, from the point of view of both the laws of motion and the expression of measurable (observable) quantities in terms of Reference Frames (RFs) notions. In this report we summarize the RF theory in GR (in the monad as well as in the tetrad representation) and give examples of specific gravitational effects. In any theory of RFs an important element consists on separation of the RF and system-of-coordinates (SC) notions, with a constructive description of projectors onto the physical temporal and spatial directions, of the observables as invariants (scalars) under SC transformations, as well as of the transformation laws of these observables under transitions between different RFs. For a more detailed though still incomplete synopsis of the monad and tetrad methods of RF representation in GR, see our preprint [1].
System of astronomical constants in the relativistic framework
Authors: Fukushima T. , Fujimoto M. K. , Kinoshita H. , Aoki S.
Published: June 2019

The relation between the units and the readings of time and space coordinates of the terrestrial and the barycentric frames is discussed from the viewpoint of general relativity. Attention is paid to the unit of space coordinates since the International Astronomical Union (IAU) regulates only the unit of time coordinate in the above two frames. Two definitions on unit of length are examined and their effects on the numerical expression of coordinate transformation, equations of planetary motions, and those for light propagation time are discussed. A clear conflict is found between the IAU(1976) recommendation on the definition of the time-scales in different frames and the statement that all constants in the IAU(1976) new system of astronomical constants are defined in terms of the international system of units (SI units). In order to dissolve this conflict, one of the two examined definitions on unit of length is proposed to be adopted, which requests the least alteration on the current procedures to analyze the astrometric observations such as radar/laser rangings, range and range-rate measurements, and very long baseline interferometric observations. An interpretation of numerical values in the IAU(1976) system of astronomical constants is also presented. It is stressed that the definition proposed in this paper requires that a slightly different formula from the current one be used in the numerical transformation of coordinates between the terrestrial and the barycentric frames.
Local measurements and cosmological background
Authors: Teyssandier P. , Tourrenc Ph.
Published: June 2019

The relations between the local measurements achieved in the solar system for testing the metric theories of gravity and the cosmological background are far from being clear. In most cases, some heuristic assumptions are made in order to take into account cosmological boundary conditions. In particular, the light rays from distant stars or extragalactic objects are often believed on the basis of the so-called Mach principle to determine “fixed” directions defining inertial frames. However, it has been already shown in theoretical cosmology that in any anisotropic, inhomogeneous cosmological model, the apparent directions of a distant object varies with respect to locally non rotating inertial frames. Restricting in the first step our attention to some exact anisotropic models obeying to the Einstein equations, we study the order of magnitude of this effect in the context of observational devices such as the HIPPARCOS satellite, the Space Telescope and the gyroscope experiment planned at the Stanford University. Then we try to interpret the effect and more generally the various influences of cosmological terms, within the framework of the parametrized post-newtonian formalism.
Relativistic interpretation of astrometric data
Authors: Pavlov N. V.
Published: June 2019

In papers (Pavlov, 1984 a,b and 1985), a complete and self consistent procedure of relativistic reduction for fundamental and radio-interferometric observations of distant sources has been developed. Relativistic formulae of apparent star positions, time delay and fringe frequency were derived. These formulae include all relativistic corrections due to the gravitational field of the Sun and the observer's motion. In the case of ground observations relativistic corrections are calculated to a relative accuracy of 5.10−9 or 0.001 arcsec.
Techniques for dealing with discordant observations
Authors: Branham Richard L.
Published: June 2019

To test any theory such as theories of motion–Newtonian or relativistic–of solar system objects, one must compare the predictions of theory with observation. But discordant observations habitually plague the reducer of astronomical data. To alleviate the baleful effects, particularly harmful when the observations are reduced by the method of least squares, of discordant data investigators almost invariably reject observations whose corresponding (0-C)'s or post-solution residuals exceed a cutoff. But techniques that are insensitive to the assumption that the observational errors are normally distributed, called robust estimation in the literature, have also been developed.
Relativistic effects in Earth based and cosmic long baseline interferometry
Authors: Cannon W. H. , Lisewski D. , Finkelstein A. M. , Ya Kreinovich V.
Published: June 2019

With present day technology the technique which provides the greatest precision in astrometric and geodetic measurement is Very Long Baseline Interferometry (VLBI) (Robertson, 1975; Dravskykh, 1981; Gubanov, 1983). The precision of present day astrometrical measurements by VLBI exceeds those of the best modern optical observations by an order and a half of magnitude and is capable of further improvement by the future development of phase stable, wide band, global networks and by the future deployment of VLBI antennas in space. Such precision of observation places the technique of VLBI well within the regime of special and general relativity. The present paper presents an analysis of relativistic effects on VLBI measurements with an accuracy of 0.0001 arc seconds.
Spacetime coordinates in the geocentric reference frame
Authors: Fujimoto M. , Grafarend E.
Published: June 2019

A geocentric relativistic reference frame is established which is close to the conventional non-relativistic equatorial frame of reference. Within post-Newtonian approximation the worldline of the geocentre is used to connect points by spacelike geodesics on the equal proper time hypersurface and to establish a properly chosen tetrad reference frame. Points on the earth surface and near the earth-space are coordinated making use of the Frobenius matrix of integrating factors which connects the geocentric orthonormal tetrad with the tangent spacetime of relativistic pseudo-Riemann geometry. The gravity field of the earth and its relative velocity with respect to the solar system barycentre cause coordinate effects of the order of 10 cm for topocentric point positioning.
Relatively Dark Matter: The Local Mass Density of Stellar Remnants
Authors: Green Richard
Published: June 2019

The Palomar-Green Survey produced statistically complete samples of hot white dwarfs and subdwarfs, from which the local mass density of these objects can be determined. The luminosity function of hot hydrogen-atmosphere white dwarfs (DA's) was recently re-determined by Fleming, Liebert, and Green (1985, Ap. J., submitted). The contribution of each of the 353 objects to the local space density was calculated from the ensemble of limiting magnitudes and a spectroscopically or photometrically derived absolute magnitude. The local surface density of white dwarfs with MV < 12.75 (log L/L⊙ > −3.1; TE > 9000 K) is 0.32 ± 0.03 pc−2. Assuming an exponential disk with scale height 250 pc, we derive the differential luminosity function in the figure; the total volume density is 0.65 ± 0.06 per 1000 pc3. He atmosphere degenerates add another 20%.
Kinematics and Warp in NGC 4565
Authors: Casertano S. , Sancisi R. , van Albada T. S.
Published: June 2019

We present preliminary results of the analysis of WSRT observations of the edge-on spiral NGC 4565 (Sancisi 1985). The neutral hydrogen layer of this galaxy extends to 1.3 R25, permitting to trace the rotation curve outside the optical edge of the system, and is warped in the outer parts.
Halo Parameters of Spiral Galaxies
Authors: Athanassoula E. , Bosma A. , Papaioannou S.
Published: June 2019

We have made a rotation curve analysis of a sample of spiral galaxies for which both photometric and kinematical data of reasonable quality are available in the literature. From the photometric radial luminosity profile, assuming constant mass-to-light ratios for bulge and disk separately, we calculate a rotation curve due to the luminous mass in a galaxy. Comparison with the observed rotation velocities allows us to derive a halo rotation curve, which can be used to derive characteristic halo parameters. The decomposition into luminous and dark matter is not unique, with as extremes a “minimum” disk (M/L = 0) and a “maximum” disk (M/L as high as possible while requiring a realistic halo mass distribution without a hollow core).
Some Regularities in the Missing Mass Problem
Authors: Casertano S. , Bahcall J. N.
Published: June 2019

We discuss available information on the distribution of luminous and dark matter in eight galaxies. The galaxies have been chosen according to the following criteria: 1) existence of a good rotation curve, extending well beyond the optical radius; 2) a mass model has been published; 3) valuable constraints can be put on the amount of dark matter inside the optical radius. A full description of the data and reduction procedures is in Bahcall and Casertano (1985).
Are Numerical Simulations Reliable? Proposed Improvements and Tests
Authors: Bouchet F. R.
Published: June 2019

When one builds a code to simulate numerically a process, the first concern is the range of validity of the results. This can be accessed empirically, though the results can be misleading if the tests are too naive. For particle-mesh codes simulating the gravitational clustering, an analytical theory has been proposed in Bouchet et al. 1985. It yields the numerical dispersion relation of the system in the linear regime, and thus describes how the linear growth rate is affected by the discretisation. The theoretical predictions are in agreement with the results of actual numerical experiments: both show that the results of standart particle-mesh codes should not be trusted at distances smaller than 6 to 8 grid-spacing Δx (depending on the detail of the algorithm).
Galaxy Formation
Authors: Silk Joseph
Published: June 2019

Theories of galaxy formation via hierarchical clustering of cold dark matter and by fragmentation of gaseous pancakes or shells are reviewed and compared. Dissipative processes are crucial to all theories of galaxy formation, and are discussed in terms of a simple model involving multiple cloud interactions. Stellar energy input is found to play an important role in protogalaxies, both supporting the gas against collapse, thereby prolonging the duration of the active star formation phase, and driving winds from the less massive galaxies. The significance of such processes is explored both for chemical and dynamical evolution and for biasing galaxy formation towards density peaks in the primordial density fluctuation spectrum.
Disturbance of the CBR by Isothermal Perturbations
Authors: Kodama Hideo , Suto Yasushi , Sato Katsuhiko
Published: June 2019

Following the standard scenario of galaxy formation, density fluctuations with amplitude δ∼10−3 should have been present at the recombination time tR in order that galaxies and clusters of galaxies can be formed. Recent observations of the anisotropy of the cosmic background radiation(CBR), however, indicate that δ is less than 10−4 at tR for adiabatic perturbations in the baryon-dominated universe.
Constraints on the Dark Matter
Authors: Carr B. J.
Published: June 2019

There is evidence for four types of dark matter: (1) the local d.m. in the galactic disc; (2) the d.m. associated with galactic halos; (3) the d.m. in clusters; and (4) a background closure density of d.m. required if the Universe undergoes an inflationary phase. There are three types of explanation: (1) remnants of a first generation of Population III stars, including black holes (SMOs, VMOs or MOs), neutron stars, white dwarfs, or LMOs (M-dwarfs and Jupiters); (2) elementary particle relicts of the Big Bang (inos), usefully classified - according to their mass - as hot, warm, or cold, since this determines the scale on which they can cluster; and (3) primordial black holes, formed from density perturbations or phase transitions in the early Universe. Various constraints on the d.m. candidates are indicated by the shaded regions in the Figure below. The conventional model of cosmological nucleosynthesis precludes Population III remnants providing the closure and perhaps cluster d.m., while stellar nucleosynthesis constraints preclude neutron stars from explaining anything and allow white dwarfs to provide only the local d.m. Source counts exclude M-dwarfs from providing the local or halo d.m., while gravitational lensing effects exclude SMOs larger than 108M⊙ from explaining anything and LMOs or VMOs from having the closure density. Dynamical considerations imply M<2M⊙ for the local d.m., M<106M⊙ for the halo d.m., and M<109M⊙ for the cluster d.m.; they also imply that the local d.m. cannot be inos and that the halo d.m. cannot be a hot ino. The table suggests the following conclusions: (1) no single candidate can explain all four d.m. problems; (2) the best candidate for the closure d.m. is an ino; (3) the best candidates for the local d.m. are white dwarfs or Jupiters; (4) the halo (and possibly cluster) d.m. could plausibly be black holes or Jupiters.
A Cosmologist's Tour through the New Particle Zoo (Candy Shop?)
Authors: Turner Michael S.
Published: June 2019

Recent developments in elementary particle physics have led to a renaissance in cosmology, in general, and in the study of structure formation, in particular. Already, the study of the very early (t ≤ 10−2 sec) history of the Universe has provided valuable hints as to the ‘initial data’ for the structure formation problem — the nature and origin of the primeval density inhomogeneities, the quantity and composition of matter in the Universe today, and numerous candidates for the constituents of the ubiquitious dark matter. I review the multitude of WIMP candidates for the dark matter provided by modern particle physics theories, putting them into context by briefly discussing the theories which predict them. I also review their various birth sites and birth processes in the early Universe. At present the most promising candidates seem to be a 30 or so eV neutrino, a few GeV photino, or the ‘invisible axion’ (weighing in at about 10−5 eV!), with a planck mass monopole, quark nuggets, and shadow matter as the leading ‘dark’ horse candidates. I also mention some very exotic possibilities — unstable WIMPs, cosmic strings, and even the possibility of a relic cosmological term.
A Historical Perspective on Dark Matter
Authors: Tremaine Scott
Published: June 2019

The dominant impression which I carry away from this meeting is that extragalactic astronomy has reached a crisis (‘a state of affairs in which a decisive change for better or worse is imminent’, according to Fowler). The nature, origin and distribution of the dark matter and its role in galaxy formation and dynamics are issues whose resolution is likely to determine the direction of studies in galactic structure and cosmology for decades to come.
On the Radio Emission of Barred Spirals
Authors: Kalloghlian A.T. , Kandalian R.A.
Published: June 2019

It is found that the relation between the presence of radio emission and the degree of central concentration (i.e. the Byurakan class) of spiral galaxies is valid only for barred spirals. Barred spirals are also found to have central radio sources more often than normal spirals which are generally disc radio emitters.
The Thermal Component of the Seyfert Galaxy NGC1275
Authors: Robson E I , Gear W K
Published: June 2019

We have been observing a range of galaxy type over the IR through millimetre region to determine the contribution of thermal emission from heated dust. It is now clear that the ‘Starburst’ phenomenon is widespread and has a range of luminosity. By studying the continuum spectrum of the radio-loud Seyfert galaxy NGC1275 over many years, we have shown that it possesses a thermal component of luminosity comparable to the synchrotron luminosity. We interpret this thermal component as emission from dust heated by stars forming from material in an X-ray cooling accretion flow.
Solar equatorial rotation rate inferred from inversion of frequency splitting of high-degree modes
Authors: Hill Frank , Gough Douglas , Toomre Juri , Haber Deborah A.
Published: June 2019

The equatorial rotation rate has been inferred as a function of depth through the outer 16 Mm of the Sun from observations of high-degree five-minute oscillations. An optimal averaging inversion procedure due to Backus & Gilbert (1970) has been applied to frequency splittings measured from power spectra obtained using Doppler data spanning three and five consecutive days. The resulting rotation curves have proven to be much more stable than the curves obtained from data sets of single days. The results imply that the solar rotation rate increases with depth by 0.023 μHz reaching a maximum at about 2 Mm below the surface, then decreases by 0.037 μHz down to 16 Mm.
Rotation in the solar convection zone inferred from Fabry-Perot observations of the 5-min oscillations
Authors: Hill Frank , Rust David M. , Appourchaux Thierry
Published: June 2019

Full disk observations of the 5-min solar oscillations have been obtained with a lithium niobate Fabry-Perot filter. The equatorial solar rotation rate as a function of depth has been inferred from the sectoral modes of oscillation using the Backus-Gilbert optimal averaging inversion method. The results show a rotation rate that slowly decreases over the depths of 15 to 56 Mm below the photosphere. The results are in agreement with the previous Duvall-Harvey observations.
Limb darkening oscillations: the discrepancy with Doppler data and the 160-minute period
Authors: Yerle Raymond
Published: June 2019

The amplitude discrepancy between solar limb darkening and Doppler measurements in the five-minute range, suggests the possible existence of Earth's atmosphere oscillations. Recent aeronomical observations add strong evidence to this point of view. A possible explanation of the mysterious 160-min period is presented as a direct consequence. Short period oscillations are another one. Slight discrepancies between Doppler data and between those with theoretical calculations could be also explained in the same way.
An attempt to determine the structure of the solar core from observed g-mode frequencies
Authors: Kosovichev A.G.
Published: June 2019

The purpose of this investigation is to estimate how well the structure of the solar core might be inferred by inverting g-mode frequencies.

Delache and Scherrer (1983), Isaak et al. (1984), Severny et al. (1984) reported detection and identification of solar g modes. Although the results seem not to be complete it is helpful to invert the available data in order to understand what new information on the structure of the solar core can be obtained from g-mode frequencies.
On the implications of the symmetric component of the frequency splitting reported by Duvall, Harvey and Pomerantz
Authors: Gough D.O. , Thompson M.J.
Published: June 2019

The component of the frequency splitting of solar five-minute oscillations observed by Duvall, Harvey and Pomerantz that is even in azimuthal degree measures latitudinal and depth variations in the structure of the sun. We indicate how the data hint that there is a shallow perturbation, possibly associated with a magnetic field, that is concentrated at low latitudes.
Oscillations in sunspot umbra, -penumbra and the surrounding photosphere
Authors: Balthasar H. , Fangmeier E. , Küveler G. , Wiehr E.
Published: June 2019

Doppler shifts of the nonsplit line Fe I 7090Å have been measured simultaneously in the sunspot umbra, penumbra and the photosphere using a 100 × 100 diode array. The power in the range 2.5–4.5 mHz is found to decrease from the photosphere towards the umbra. Besides the minimum at the center of the umbra, further power minima occur at the transition region between umbra and penumbra. No significant power is found in the range 5.0–6.0 mHz.
Radial and non-radial oscillations of spherically symmetric stellar systems
Authors: Sobouti Yousef
Published: June 2019

In an expansion scheme in velocity space, the first order perturbations of a stellar system bear close resemblance to those of a fluid. This feature is exploited to study the structure of the Hilbert space of the linear perturbations of a stellar system, to provide a classification for the modes, and to construct ansatz for variational calculations. The first order non-radial modes appear to be trispectral in that they are predominantly derived from a scalar potential, a toroidal vector potential, or a poloidal vector potential. The eigenfrequencies and the eigenfunctions of radial (ℓ = 0) and non-radial (ℓ, = 1) modes of polytropes and of truncated isothermal distributions are calculated. The density waves associated with these modes are also reported.
Time variations of the frequencies of low-degree solar p-modes
Authors: Woodard Martin F. , Noyes Robert W.
Published: June 2019

A comparison of three separate years (1980, 1984, 1985) of SMM/ACRIM solar total irradiance data reveals small but significant changes in the frequencies of low-degree solar p-modes. Specifically, a decrease in the mean frequency of the nine strongest ℓ = 0 and 1 oscillation peaks was observed between 1980 and 1984 such that
The 13 day period oscillation and the solar cycle
Authors: Jiménez A. , Pallé P.L. , Régulo C. , Cortés T. Roca , Isaak G.R. , McLeod C.P. , van der Raay H.B.
Published: June 2019

From the analysis of radial velocity measurements of the Sun, obtained at Izaña during long observing seasons covering ten years, from 1976 to 1985, stable periods longer than 1 day, have been found in the observed signal. In particular the appearance of an oscillation with a 13 day period, discovered by Claverie et al (1982), has been confirmed. The comparison, for 1981 - 82 - 83 and 84, of the observations with a calibrated numerical model of the passage of inhomogeneities (spots and plages) on the solar surface, shows that the signal is not only due to this effect. The obtained signal from the model has a phase lag of almost two days relative to the observed one. So, it is believed that another velocity field, probably related to the surface inhomogeneities, contributes to the observed signal.
Study of long period global oscillations of Sun through spherical harmonic Fourier analysis of sunspot activity
Authors: Gokhale M.H.
Published: June 2019

A spherical-harmonic-fourier analysis of the maximum areas of sunspot groups listed in Ledgers I and II of Greenwich photoheliographic results for 1933–1954 yield significant peaks at the 11y periodicity for some spherical harmonic modes: especially the mode (ℓ = 6, m = 0). A similar analysis of the daily areas of the spotgroups during 1944–1954 yields 11y periodicity peaks only for some non-axisymmetric modes. These results suggest that the sunspot activity may be physically related to long period global oscillations of the sun.
A spectroscopic search for oscillations in the 769.9 nm potassium line of Procyon
Authors: Isaak G.R. , Jones A.R.
Published: June 2019

A double magneto optical filter attached to the Cassegrain focus of the 1.9 m reflector of the South African Astronomical Observatory was used to observe Procyon in the 769.9 nm line of potassium during all clear hours of six nights. Velocity calibration was provided by the rotational and orbital velocity changes of the observer as well as by a continuous magnetic modulation.
A survey for Doppler-shift oscillations in K giants
Authors: Smith Peter H. , McMillan Robert S. , Merline William J.
Published: June 2019

A survey of K giants is being conducted to search for both short- and long-term oscillations. Our radial velocity spectrometer has a short-term precision on bright stars of 4 m/s after an exposure of 3 minutes on the CCD detector. Extensive sets of observations have been reduced for Arcturus, Pollux, and Aldebaran. Power spectra show no apparent oscillations within these data sets for frequencies between 0.15 and 2.0 mHz. However, the nightly averages over a 4 month time base show a three-fold increase in variance for Arcturus when compared to Pollux. A periodogram reveals a period of 1.844 0.005 days (or its alias of 2.174 days).
Helium diffusion in rapidly oscillating Ap stars
Authors: Dolez N. , Gough D. O. , Vauclair S.
Published: June 2019

Suppression of convection near the poles of magnetic A stars and inhibition of winds near the equator influence chemical composition gradients resulting from diffusion, leading to appreciable horizontal variation in the equilibrium configurations of the stars. We conjecture that it is this variation which is responsible for the apparent alignment of non-radial pulsations with the magnetic axes of the stars, and also for a possible previous misidentification of the modes. We suggest that nonadiabatic excitation can be sufficient to overcome energy leakage into the atmosphere.
Pulsations of White Dwarf Stars with Thick Hydrogen or Helium Surface Layers
Authors: Cox Arthur N. , Starrfield Sumner G. , Kidman Russell B. , Pesnell W. Dean
Published: June 2019

In order to see if there could be agreement between results of stellar evolution theory and those of nonradial pulsation theory, calculations of white dwarf models have been made for hydrogen surface masses of 10−4M⊙. Earlier results by Winget et al. (1982) indicated that surface masses greater than 10−8M⊙ would not allow nonradial pulsations, even though all the driving and damping is in surface layers only 10−12 of the mass thick. We show that the surface mass of hydrogen in the pulsating white dwarfs (ZZ Ceti variables) can be any value as long as it is thick enough to contain the surface convection zone.
What do the observations tell us about the excitation of solar oscillation modes?
Authors: Libbrecht Ken G.
Published: June 2019

Present theories suggest two different classes of excitation mechanisms which may be responsible for the observed amplitudes of solar p-mode oscillations—self-excitation of the modes (e.g. the κ mechanism), and stochastic excitation by turbulent convection. I discuss here the agreement and disagreement between the predictions of these two mechanisms and the observed mode amplitudes and linewidths.
Influence of the perturbation of the Reynolds tensor on the stability of the solar 5 minute oscillations
Authors: Gabriel M.
Published: June 2019

The excitation mechanism of the 5 min. oscillations is not yet understood. So far two mechanisms have been discussed. The first one is the linear vibrational instability. The second one is the non linear coupling between convection and pulsation discussed by Goldreich and Keeley (1977) and Goldreich and Kumar (1986).
The evolution to steady nonlinear pulsation in stellar models
Authors: Kovács G. , Buchler J. R.
Published: June 2019

The numerically generated dynamical evolution of an RR Lyrae model from different initial conditions is subjected to a time-dependent Fourier analysis, which yields the temporal behavior of the amplitudes and phases of the few longlived transient modes in addition to the ultimate winner. It is shown that the amplitude equation formalism of Buchler and Goupil gives an almost perfect fit to the observed transient behavior of the amplitudes and phases of the excited modes. Prospects and applications are discussed.
The critical mass for the overstability of massive zero-age main sequence stars
Authors: Klapp J. , Langer N. , Fricke K.J.
Published: June 2019

The linear stability of massive extreme Pop I stars at the main sequence is investigated with a full nonadiabatic treatment. Contrary to earlier beliefs these stars become vibrationally unstable only beyond a critical mass as high as 440 M⊙ at the main sequence.
Chromospheric seismology
Authors: Gouttebroze Pierre
Published: June 2019

The aim of the present study is to examine whether seismologic diagnostic techniques may be used to improve the models of the solar chromosphere. We are mainly concerned by oscillations observed in the cores of strong lines such as the resonance lines of Ca II or Mg II. It is intuitive, and confirmed by numerical simulations (Gouttebroze and Leibacher, 1980), that the displacements of the cores of these lines are strongly correlated with the vertical velocity of the atmospheric layer where the line center optical depth is equal to 1. With classical atmospheric models such as those of Vernazza et al. (1981) (hereafter VAL), these line cores are formed in the chromospheric plateau, around 1500 km for the Ca II lines and 1900 km for the Mg II ones.
Variation of the generalized Compton red shift in the Sun
Authors: Missana M.
Published: June 2019

The most accurate measurements of red shifts in the solar spectrum, made in different epochs by different astronomers, show a systematic difference, in the average 2 mA° (0.2 pm), that seems quite independent on the wavelengths. Such a result can be explained, at least from a qualitative point of view, by the Compton effect. Indeed a variation of the normalized width U of the spectral lines causes a consequent variation of the Compton red shift: increasing U of the 50%, also the red shift increases of about 0.1 pm. Besides that a variation of the average depth h for the formation of the spectral lines in the reversing layer, may cause, in some model atmospheres a change of the red shift: an increase of about 90 Km for h may induce an increase of about 0.4 pm in the Compton red shift.
Performance of a stabilized Fabry-Perot solar analyzer
Authors: Rust D. M. , Appourchaux T. , Hill F.
Published: June 2019

A unique solar lineshift analyzer described by Rust, Burton and Leistner (1986) has been used at the Sacramento Peak Observatory to study solar oscillations. Operation of this “Stablized Solar Analyzer” (SSA) depends on the electro-optic effect in crystalline lithium niobate, the substrate of the solid Fabry-Perot etalon. Voltage on the etalon shifts the passband by ∼ 4.5 × 10−4 Å/V. The etalon has a passband of 0.175 Å at 6102.7 Å. The stabilization system uses a tunable diode laser to relate the Fabry-Perot passband to the D2 line of atomic Cs 133, at 8521.46 Å. This system reduced instrumental noise to less than Δλ/λ = 10−9 over a six-hour interval.
The discovery of late twentieth century mød man
Authors: Phåknø Dyån , Rhødz Edwød
Published: June 2019

Greetings! We who now salute you from the year 2986 are members of the species Homo tachyones, the first human generation to learn how to use the tachyon. Naturally, following this discovery, the immediate question arose, “To what great purpose shall we put this knowledge?” After much deliberation, we decided on the interesting experiment of communicating about some of our more puzzling archaeopsychological discoveries with the subjects of those discoveries themselves, back in the distant and hitherto inaccessible past.
Temperatures of Central Stars of Planetary Nebulae
Authors: Preite-Martinez A.
Published: June 2019

The temperature of Central Stars of Planetary Nebulae (CSPN) is one of the most important parameters for a better understanding of their evolution, their properties and those of the surrounding photoionized nebula. It is an elusive quantity to derive though, because CSPN are generally faint objects and their spectrum is often heavily contaminated by nebular continuum emission.
Ultraviolet and Optical Spectra of Central Stars of Halo Planetary Nebulae
Authors: Peña M. , Torres-Peimbert S. , Ruiz M. T.
Published: June 2019

Optical and UV spectrophotometric data are analyzed for the central stars of the known Population II planetary nebulae. From this, we derive visual magnitudes, spectral classification, color temperatures, luminosities and masses of the objects. It is found that all the stars show absorption type spectrum and most of them have normal H and He photospheric abundances, the only possible exceptions are M 2–29 and GJJC-1 which seem to be H-deficient stars.
On the Distances to Galactic Planetary Nebulae
Authors: Zhang C.Y.
Published: June 2019

The distances are determined for 142 Galactic planetary nebulae, using two methods. Method A is based on the stellar mass and surface gravity, while Method B makes use of the stellar luminosity. These properties of the central star are inferred from the modeling of the distance-independent parameters (Zhang and Kwok 1992). The results from the two methods used in this paper are consistent with each other. A distance of 10.8 kpc is found for K648 using Method A of this work. This is in excellent agreement with the distance of 10 kpc of its hosting globular cluster M15. The distances obtained in this work are in good agreement with the distances of Mendez et al. (1992), based on the recently developed non-LTE model atmospheres including spherical extension and stellar winds. The agreement of our distances with the individually determined distances of Gathier et al. (1986a, 1986b), using the extinction-distance method and the HI 21 cm absorption method, is worse than that found between ours and Mendez et al.'s. The distances obtained by Gathier et al. are likely often to be underestimated. The various statistical distance scales, except for Cudworth's (1974) distance scale, show no agreement with the distances determined in this work. CYZ was supported by the NASA grant NAG 2–67.
A Twodimensional Ionisation Model of NGC 2440
Authors: Bässgen M. , Diesch C. , Grewing M.
Published: June 2019

NGC 2440 is one of the most prominent butterfly- shaped nebula in the sky. It has a very rich spectrum up to high ionic species. Its central star is handled as one of the hottest central stars. We present a 2-dimensional cylindrically symmetric ionisation model of this nebula. Under the assumption that the main nebula axis lies perpendicular to the line of sight and achieving the inverse Abel∗∗∗transformation, the density distribution could be calculated using a monochromatic Hα-CCD-image. The gridsize of the model was chosen to 0.38 arcsec (=pixel size of the image). Due to the fact that in a cylindrically symmetric model only a half plane has to be calculated, the total grid has a size of (−100‥100, 0‥100). The procedures determining the ionisation state is principally the same we used for our 3D-model of NGC 3132 (Bässgen et al 1990). If the ionic densities and the electron temperatures in all volume elements are known, emission line strengths and artificial monochromatic images can be calculated. These can be compared with “real” monochromatic images.
Near- and Mid-Infrared Imaging of the PN IC 418
Authors: Hora J. L. , Deutsch L. K. , Hoffmann W. F. , Fazio G. G. , Shivanandan K.
Published: June 2019

We present high-resolution near- and mid-infrared images of the planetary nebula IC 418 at 1.2 (J), 1.6 (H), 2.2 (K), 9.8, and 11.7 μm. The near-IR images were obtained with a 64×64 pixel Hg:Cd:Te array camera, and the mid-IR images were obtained using the new 20×64 pixel Mid-Infrared Array Camera (MIRAC). The size of IC 418 in the near-IR is seen to vary with wavelength, being largest at K and smallest at J. Differences in the morphology of the nebula are seen between the J and K images. There is excess near-IR emission in the center of the nebula, after subtracting out the emission from the central star. Faint halo emission is detected at H and K, extending to a total diameter of approximately 40″. The 9.8 μm emission is distributed nonsymmetrically, with the peak in the NE lobe.
CO Line Emission in Planetary and Proto-Planetary Nebulae: The Molecular Envelope
Authors: Silvestro G. , Porro I.
Published: June 2019

Planetary nebulae (PNe) are believed to form when the envelope of gas and dust, ejected at the end of the AGB phase of stellar evolution, is heated by the hot stellar nucleus, left after mass loss due to the “superwind” is terminated. The presence of residual molecular gas in PNe should therefore be important for understanding the formation and subsequent evolution of the nebulae. Observations (Bachiller et al. 1988) of CO line radiation in proto-planetary nebulae (PPNe), the transition phase from AGB stars to PNe, allowed to set very low upper limits on the molecular gas mass and to predict almost complete dissociation of the molecular envelope at the end of the PPN stage. On the other hand, observations (Huggins & Healy 1989; Healy & Huggins 1990) of CO lines detected intense signals from several PNe, including some evolved sources.
Molecular-Line Observations of the Remnant AGB Envelopes Around Planetary Nebulae
Authors: Sahai R. , Wootten A. , Clegg R.E.S.
Published: June 2019

We present recent results from a “search and mapping” program of molecular line emission (mainly CO) from remnant AGB envelopes around planetary nebulae (PNe), using the SEST (La Silla, Chile). New detections in CO J=2−1 include NGC2899 (0.02K), NGC6369 (0.14K) & NGC7009 (0.08K). In many of the detected PNe, notably NGC3132, IC4406, NGC6302, M1-16, and CPD-56°8032, the molecular envelopes contain 2 kinematically distinct outflows. Mapping of the strongest of these shows (1) that the fast (e.g. Vexp≳40–60 km s−1 in NGC3132, IC4406) outflows have bipolar spatial structure, and (2) there exists an equatorial density enhancement in the slower, more massive [· (M⊙yr−1)>5 10−6(NGC3132), >2 10−5(IC4406)] outflows, which presumably collimates the fast outflow (e.g. Sahai et al. 1990, A & A, 234, L1; Sahai et al. 1992, A & A, 251, 560). The fractional CO abundance in the envelope, f(CO), is probably rather low (<10−4), as a result of photodissociation by the stellar and interstellar UV radiation [e.g. f(CO)≲10−5 in IC4406]. HCN, HCO+, and 13CO have also been detected in several PNe, and sensitive upper limits set on CS, C18O, & C17O (in M1-16), and SO (in NGC3132). Some results are tabulated below, and calculations to estimate the molecular masses, mass-loss rates and molecular abundances are in progress.
Near IR-Photometry of Semiregular Variables
Authors: Kerschbaum F. , Hron J.
Published: June 2019

During the past decade much effort has been spent also on observation and theoretical modelling of AGB stars. However, the Semiregulars have been almost neglected. Kerschbaum & Hron (1992) used GCVS- and IRAS-data to define samples of SRa and SRb stars. These were compared with optical Miras with respect to their pulsational properties, effective temperatures, mass loss rates, luminosities, scale heights and galactic volume densities.
UKIRT CGS3 Observations of New IRAS 21 Micron Sources
Authors: Kwok Sun , Hrivnak Bruce J. , Geballe Tom R. , Langill Phillip L.
Published: June 2019

An unidentified emission feature at 21 μm has been detected in the IRAS Low Resolution Spectra (LRS) of 5 IRAS sources (Kwok, Volk, and Hrivnak 1989, Hrivnak and Kwok 1991). The sources are generally found to be F and G supergiants with cool, detached dust shells. We have searched for additional 21 μm sources in the LRS database and have obtained ground-based UKIRT spectra at 10 and 20 μm in an attempt to confirm the LRS feature.
High Velocity Outflows in IRAS 17423-1755
Authors: Riera A. , García-Lario P. , Manchado A. , Pottasch S.R.
Published: June 2019

IRAS 17423-1755 is a new transition object between the post-AGB phase and the planetary nebula (PN) stage included in an observational program of IRAS sources with infrared colours similar to those of PNe. We have taken B, V, R, I, Z, Hα and [OIII] CCD images at the 1m JKT (Roque de los Muchachos, La Palma), where a clearly marked bipolar structure with a total extension of about 10″ can be seen, and long slit (low and high resolution) optical spectra at the 4.2m WHT, 2.5m INT (RM, La Palma) and ESO 1.5m (La Silla) telescopes.
Is there a Connection Between Thermal Pulses and PNe Halos: An Approach to an Answer
Authors: Frank Adam , Balick Bruce , Van Der Veen Will
Published: June 2019

We wish to explore the hypothesis that the shells and halos of planetary nebulae are formed during the thermal pulsing of progenitor AGB stars. Using published data and model results we compare the AGB interpulse time ΔtT and the time between shell ejections ΔtD for a sample of PNe with halos. ΔtT is derived from the Paczynski relation using the PNe central star luminosity. ΔtD is calculated using the radii and velocity of PNe shells and halos.
Spherically Symmetric Kinematic Modelling of Planetary Nebulae
Authors: Diesch C. , Grewing M.
Published: June 2019

High resolution two-dimensional long slit spectra of NGC 7009, NGC 3242, IC 2448 and TC 1 in the Hα(6565 Å), OIII(5007 Å) and NII(6584 Å) emission lines have been used as input to determine radial velocity gradients in PNe by fitting calculated high resolution spatially resolved spectral structures of single emission lines. Contributions to the Doppler structure of emission lines taken into account are the global expansion of the PN shell and thermal line broadening due to temperatures of some 104 K. This model is based on two parametrized empirically chosen spherical symmetric functions:

1.

A empirical two parameter density function ρ(r).

2.

A linear radial velocity component function ν(r).
High-Dispersion Spectroscopy of IC 351 and NGC 3242, Planetaries by High Internal Motion
Authors: Yadoumaru Y. , Tamura S.
Published: June 2019

We made high-dispersion spectroscopic observations of IC 351 = PK 159 − 15°1, a compact high-excitation planetary nebula. We found the expansion velocity from Hα, [OIII] and HeII line, of 45.1kms−1, 38.7kms−1, and 33.3kms−1, respectively. Moreover, for the Hα line we detected an additional faint blue-shifted component escaping from the center of expansion with high velocity of 120kms−1. This value is larger than the usual expansion velocity (< 50kms−1) but considerably smaller than that of stellar wind. This faint blue-shifted component of Hα is also coincidently identified as the helium line, HeIIλ6560 (Pickering 6). Using the emission coefficients of recombination lines (Case B, T= 10,000K; Osterbrock 1989), and the intensity ratio, I(HeIIλ4686)/I(Hβ)=0.56±0.05 (Aller&Czyzak 1979), we can estimate the expected line intensity ratio, I(HeIIλ6560)/I(Hα)=0.026±0.002. On the other hand, the intensity ratio of faint component to Hα in the present observations is estimated as Ifaintcomp./I(Hα)=0.064±0.013, based up the Hα profile in 1988. Comparing these two estimated intensity ratios it is clearly unable to emit the all intensity of the observed faint component by HeIIλ6560 line only. Therefore, even if this component is partly polluted by HeIIλ6560 line, we can consider the rest part as an emission from high velocity component of Hα. We can also recognize the bumped feature of [OIII]λ5007 line around the same velocity to the blue-shifted component of Hα. This fact supports the idea that these components can be attributed to the high velocity flow. We discuss the three ideas for the interpretation of such component; (a) colliding winds, (b) unresolved bipolar flow, and (c) secondary formation of an expanding shell. We have investigated whether the colliding winds model gives such high velocity or not. As the results of the calculation, if we use the usual mass-loss rate, the model can not give such high velocity. Therefore, it is doubtful that we can take this model as an explanation of the high velocity components. The high velocity component of IC 351 is not uncommon; such large internal motions are reported for other planetaries by Weinberger(1989) and compiled by Grewing(1989). The article on the results of IC 351 is submitted to PASP (Yadoumaru & Tamura 1992). We also report the other analysis on NGC 3242.
Simulations of a Population of Planetary Nebulae
Authors: Stasinska G. , Tylenda R.
Published: June 2019

We present a simulation of the population of Galactic bulge planetary nebulae (GBPN), which matches the diagrams obtained from VLA radio observations. This simulation may not be the only one fitting the observed data, but it helps understanding the role of observational uncertainties and selection effects in the interpretation of observational diagrams.
Variable Spectra of IC 4997 and NGC 6572
Authors: Hyung Siek , Aller Lawrence H. , Feibelman Walter A.
Published: June 2019

Variability of the [OIII]4363/4340 H γ ratio in IC 4007 was established in 1956 by William Liller and L.H. Aller who attributed the changes to a gradual decrease of electron density with time. Subsequent 4363/4340 ratio fluctuations negated this explanation. Ferland pointed out that small changes in the radiative flux of the Planetary nebula nucleus (PNN) could explains the variations. Our pervious study emphasized IUE observations, here we compare high dispersion spectra obtained with the Hamilton Echelle Spectrograph with previous measurements to asses line intensity variations. Emission line variability in PNN spectra as noted by Mendez et al. (1988) and by other for HeII 4686 in NGC 6572 may offer significant clues. PNN 4686 appeared by 1990 in IC 4997. Possibly both of these PNN may be evolving into Wolf-Rayet objects, but this development does not necessarily imply that the nebular excitation will increase with time.
Clumps in the Planetary Nebulae
Authors: Kholtygin A.F. , Feklistova T. Kh.
Published: June 2019

The effect of density and temperature fluctuations on the intensity of the recombination and collisionally excited lines is investigated.
Chemical Abundances of Planetary Nebulae in the LMC
Authors: De Freitas Pacheco J.A. , Costa R.D.D.
Published: June 2019

We report new spectroscopic data on a sample constituted of 21 well observed planetary nebulae in the LMC. The observations were performed at the National Laboratory for Astrophysics (Brazópolis — Brasil) using the 1.6m telescope and a CCD detector. Extinction, electron temperature and densities were derived for all the planetaries and a comparison is made with results obtained by other surveys, including common objects. Chemical abundances of helium, nitrogen, oxygen, sulphur and argon were also derived for all sample objects. Enrichment of the progenitor stars in He and N due to mixing episodes as well as the relation with the chemical evolution of the LMC are discussed in terms of our data and other observations.