Showing papers by "European Southern Observatory published in 1978"

On the number of isolating integrals in Hamiltonian systems

Abstract: In a Hamiltonian system of three degrees of freedom we have found a large stochastic region (the "big sea"), some other stochastic regions, apparently separated from the above ("small seas"), and some ordered regions. In the ordered regions the maximal Lyapunov characteristic number vanishes, while it has finite values in the stochastic regions. However, these values are different in the big sea and the small seas. Three formal integrals were constructed and they were truncated at orders 2,3,...,11. The numerical values of the truncated integrals along several orbits were calculated. The variations of all three integrals decrease with order in the ordered region, while they remain large in the big sea. In a small sea two integrals have large relative variations, while one integral seems to be well conserved. This indicates that in the ordered region there are two integrals, in the big sea none, and in the small seas one integral beyond the energy.

IUE observations of extragalactic objects

Abstract: During the commissioning phase of IUE several extragalactic objects were observed spectrally at low dispersion in the UV range lambda lambda 1150-3200: the Seyfert galaxies NGC4151 and NGC1068, the QSO 3C273, the BL Lacertae object B2 1101+38, the giant elliptical galaxy M87 and the spiral galaxy M81. The results obtained are presented and a preliminary analysis given for all six objects, discussing the continuous spectrum, extinction, emission line spectrum and absorption line spectrum, where possible for each case. Several new or confirmatory astrophysical results are obtained.

Dust from periodic comet Encke - Large grains in short supply

Abstract: A photographic observation of periodic comet Encke is analyzed which reveals the emission of large dust grains from the comet. Photometric reduction of the photographic plate is described, and a two-dimensional isodensitometer scan of P/Encke is presented. An analytical expression is obtained for the average mass-loss rate of the dust over the revolution period of about 1200 days. A comparison of the results for P/Encke with previous results for P/d'Arrest indicates that both comets shed dust at just about equal average rates. It is concluded that the current contribution of P/Encke to the interplanetary dust is quite negligible if the dust particles reflect more than 1% of light and that smaller dust grains probably tend to contribute more mass than larger grains.

Meteoroids from periodic comet d'Arrest

Abstract: The predicted anomalous tail of periodic comet d'Arrest was photographed and photometrically studied. The derived particle-size distribution function varies inversely according to slightly higher than the 4-th power of the size. Particle dimensions span a few orders of magnitude, the mean size being in the general range of 0.01 to 0.1 cm depending on the assumed bulk density. The determination of the amount of the ejected dust is complicated by large uncertainties in the particle albedo. The product of the particle albedo and of the production rate of meteoroids that remain gravitationally bound to the solar system is found to be about 3000 g/s at the time of maximum activity and some 200 g/s when averaged over the comet's revolution period. The contribution of the comet to the interplanetary dust cloud is insignificant, unless the albedo of the debris from the comet is as low as 0.1 percent.

Higher order resonances in dynamical systems

Abstract: It is shown that the appearance of higher order resonances (that produce higher order islands on a surface of section), is not an indication of non-integrability. Examples are given and a method is described for constructing integrable Hamiltonians with higher order resonances.

Discovery and optical identification of 2S0921 – 630

Abstract: The discovery of a faint X-ray source at approximately 282 deg galactic longitude, -9 deg galactic latitude with the rotation modulation collimator X-ray detectors aboard SAS 3 is reported. The source is designated 2S 0921-630 and is tentatively identified, on the basis of an optical search, with a 17th magnitude star exhibiting the He II line at 4686 A and H-beta in emission. The optical spectrum of this star is shown to be similar to those of the optical counterparts of Sco X-1 and other such galactic X-ray sources. It is suggested that 2S 0921-630 may belong to the class of low-luminosity galactic X-ray binaries.

Disappearance of Integrals in Systems of More Than Two Degrees of Freedom

Abstract: The disappearance of some integrals of motion when two or more resonance conditions are approached at the same time is explained. As an example a Hamiltonian of three degrees of freedom is considered in action-angle variables which in zero order represents three harmonic oscillators, while the perturbation contains two trigonometric terms. One integral disappears if two appropriate resonant conditions are approached sufficiently closely.

Three Dimensional Analysis of Groups of Galaxies

Abstract: A systematic and automatic classification of groups of galaxies has been made only in two dimensions up to now (Turner and Gott, 1976). They investigated the projected density of galaxies at the sky. In this analysis one can correct for foreground and background galaxies and superimposed groups only statistically. The properties of the groups and their member galaxies will often not be recognized correctly. Therefore, a three dimensional analysis is proposed.

Physical properties of Cepheids and RR Lyrae stars

Abstract: At the Leiden Southern Station a large program on galactic pulsating variables has been carried out with the Walraven five-channel photometer For 170 Cepheids and 100 RR Lyrae stars south of δ =+15° there are now available 30000 VBLUW measurements (Walraven et al, 1964; Pel, 1976; Lub, 1977b) These data are used to derive physical properties of the variables A general discussion of the VBLUW system and its calibration for A-G stars by means of the theoretical fluxes of Kurucz (1975) has been given by Lub and Pel (1977) Following this calibration, reddening and blanketing corrections, as well as effective temperatures, gravities, and their cyclical variations were determined, and luminosity and radius curves were derived (Cepheids: Pel, 1977; RR Lyrae stars: Lub, 1977a) We will present here some interesting results that have been obtained from these data A more detailed discussion is in preparation

On the Effects of Inhomogeneities in High Excitation H II Regions

Abstract: We discuss the effects of inhomogeneities in HII regions. It is shown that some emission lines are strongly affected when the filling factor is substantially smaller than 1.

Photoelectric Surface Photometry of the Coma Cluster

Abstract: A photoelectric search is presented for light from a smooth intergalactic background in the Coma cluster of galaxies.