Showing papers in "The Astronomical Journal in 1968"

Comets and nongravitational forces. IV.

Abstract: Orbital elements and nongravitational parameters are derived from observations at every apparition of the periodic comets Honda-Mrkos-Pajdusakova, Faye, Tempel 2, Biela, Brorsen, and Tempel-Swift. For all except the first comet, the observations go back a century and more, although the last three comets have failed to reappear for some considerable time. The circumstances of the splitting of P/Biela are studied, and it is shown that the motion of the primary component was scarcely affected; it is also demonstrated that, if the primary still exists, it may pass only 0.05 AU from the earth in November 1971. An up-to-date list of mass-loss rates from comets is presented. It is found that, while most of the reliable determinations indicate that the cometary nongravitational effects decrease with time, there are a few cases where the effects increase slightly. The former situation is discussed in terms of a nuclear core-mantle model, implying that these comets will eventually evolve into inert, asteroidal objects, while the nuclei of the other comets are interpreted as coreless, eventually to disappear completely (or almost completely).

Motions and structure of the filamentary envelope of the Crab Nebula

Abstract: Proper motions have been measured for 132 line-emitting filaments in the Crab Nebula on direct plates taken with the 100 and 200-inch telescopes. These motions, if assumed constant and extrapolated backwards in time, converge toward a point about 12" southeast of the double star near the center of the nebula. The filaments approach, on the average, most closely to that point or expansion center in about the year 1140, indicating that the expansion has been somewhat accelerated. Proper motions and radial velocities were measured for an additional 126 features on the same direct plates and Mt. Wilson and Palomar spectra. These, along with other, nondynamical data, indicate a most probable distance to the object of 2.02 kpc. Two projections of the nebula perpendicular to the one seen in the plane of the sky are constructed and do not differ significantly from that presented to us. The proper motion and radial velocity of the nebula as a whole are found and converted into galactic coordinates. This requires several assumptions of questionable validity. The nebula seems to be moving about 112 km/sec faster than the galactic rotation at its position. The proper motion of the so-called central star translates into an equally unlikely space motion, but this is also extremely uncertain. The likelihood of a physical connection between the star and the nebula is discussed. The line-emitting filaments are shown to be distributed throughout the nebula rather than being confined to a thin outer envelope. The motions are largely radial, each filament having a velocity approximately proportional to its distance from the expansion center. The deviations from this proportionality are as large as .032"/yr or 300 km/sec and have mean values near .010"/yr or 70 km/sec. These deviations are correlated with the scatter of the filaments around the expansion center in 1140. Photographic materials on pp. 99 and 101 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.

Multicolor photoelectric photometry of the brighter planets. III - Observations from Boyden Observatory.

Abstract: Multicolor photoelectric photometry of Venus, Mars, Jupiter and Saturn, noting phase curves and monochromatic geometric albedos of Mars and Jupiter

Change in Total Energy of Comets Passing Through the Solar System

Abstract: Over 180.000 hypothetical long-period comets with orbits of random orientation are sent through a solar system havmg but on~ planet~ Alon~ ea~h o:bit is computed the chang/" in the comet's total energy caused by. the ~Ianet-comet.mt~rac~lOn. DlstnbutlOns of this quantity are presented wherein the comets' peri­ helion distances and mchnatlOns are both specified. These changes for retroo-rade comets are found to be largest when their perihelion distance is near zero, but for direct comets the~e is a ma;;imum effect wben ~he come~s' pe?heli~n distances are comparable with the orbital radius of the planet. The one-planet case ~s solved m.a dlmenslO?les~ w~y. so that s~mple scaling factors allow the solution to be applied to any number f planets m calculatl.ng mdlvldual orbIts. However, the distribution in changes of energy with planets !"ferc~ry .to ~eptune mcluded. is shown to be practically the same as when Jupiter alone is considered. The dlstnbutlOns are symmetrIcal about zero but are clearly non-Gaussian in shape. At moderately large values of the .energy change U, the number of such changes falls off as 1/ I u 13• The predicted distribution agrees well With the values found for known long-period comets.

Supernovae and Supernova Remnants

Abstract: Supernovae remnants evolution, properties and galactic distribution, discussing criteria for catalog listing and remnants as X ray sources

Statistical mechanics of a collisionless self- gravitating system.

Abstract: Computer experiments with one dimensional model, determining self gravitating system approach to Lynden-Bell distribution

Outer satellites of Jupiter.

Abstract: Jupiter outer satellites orbits determination with computer program based on modified Cowell/Moulton methods for adjusting initial conditions

Classical Cepheids and Galactic Structure

Abstract: In this review I consider recent results on the space distribution of classical Cepheids, first dealing with their Z-distribution normal to the galactic plane, and second considering their X,Y components in the plane. In doing so, use is made of a new database of 505 stars known to be or likely to be classical Cepheids which has recently been compiled by Fernie et al. (1995) and which is available electronically on the World Wide Web at the URL http://ddo.astro.utoronto.ca/cepheids.html , and by anonymous ftp at perseus.astro.utoronto.ca (128.100.77.18) in the directory pub/cepheids. Following the discussion of space distribution, a review of recent work on Cepheid kinematics and the resulting determination of the distance to the galactic centre will be given.

A statistical ray analysis of the scattering of radio waves by the solar corona.

Abstract: Radio ray scattering resulting from traversing anisotropically turbulent solar corona, noting refraction effect on signal pulse arrival time