Showing papers in "The Astronomical Journal in 1975"

Dynamical models of elliptical galaxies.

Abstract: To represent observed features of elliptical galaxies on the basis of a simple dynamical theory, Poisson's equation is solved for the development of self-consistent models provided with rotational symmetry and differential rotation. The density is calculated by integrating over all the velocities a near-Gaussian distribution function dependent on energy and angular momentum with two free parameters. Observable properties are predicted by projecting the models onto the plane of the sky. The models give radial intensity profiles and isophote shapes in good agreement with observations of NGC 3379, predict a rotation curve consistent with the one observed, however they all show the same general trend of isophote flattening with radius while in real galaxies there is an enormous variety.

Encounters between binary and single stars and their effect on the dynamical evolution of stellar systems

Abstract: More than 1.4times10$sup 4$ computer-simulated encounters between binaries and field stars have been run for various preencounter relative velocities V/subf/ and impact parameters p. At low values of V/subf/, the encounter causes the binary orbit to shrink and become more tightly bound with the two more massive of the three stars involved in the encounter remaining in the binary and the third being ejected from the binary at a relatively high velocity. As V/subf/ increases, the amount of orbit shrinking decreases until, for V/subf/ greater than a well-defined velocity V/subE/, the encounter tends to increase the semimajor axis of the binary and eventually to break it apart. We find that about 10% of the binaries with semimajor axes a$sub 0$>10$sup 3$ au have broken apart in the solar neighborhood. In globular clusters almost all primordial binaries with a$sub 0$>35 au have broken apart; this is true for binaries with a$sub 0$>100--1000 au in open clusters and a$sub 0$>1--2 au in galactic nuclei. The breakup of these loosely bound binaries has relatively little effect on the dynamical evolution of the stellar system. However, the shrinking of the more tightly bound binary orbits, which feeds kinetic energy into the cluster, will destroymore » an open cluster in a few times 10$sup 8$ y unless it is either unusually massive or unusually deficient in binaries. While the lifetime of a globular cluster due to this mechanism is about 10$sup 11$ y, it is likely that binary stars limit the maximum density attainable in the nucleus of a globular cluster. The presence of the binaries transforms the familiar instability leading to a rapid shrinking of the core of the cluster and to the buildup of a high-density central cusp into one which causes an accelerated rate of decrease in the semimajor axes of the binaries in the core. Binaries are not likely to have any significant effect on the dynamical evolution of a dense galactic nucleus.« less

Empirical calibrations of the uvby, beta systems. II. The B-type stars.

Abstract: Photoelectric photometric four-color and H..beta.. indices have been calibrated for A-type stars (stars with 2.890 >..beta..>2.720 and deltac/sub 1/<0.28 that are not B-type stars) in terms of intrinsic color and absolute magnitude by using data for bright stars and stars in several open clusters. Intrinsic color indices should be predictable to about +- 0.01 mag and absolute magnitude to +- 0.3 mag. Systematic effects can exist in the absolute magnitude calibration due to rotational velocity. Am-type stars appear to fit the calibration well. There is quite a good agreement between the photometric classification and MK spectral classification.

Tidal friction and generalized Cassini's laws in the solar system.

Abstract: The tidal drift toward a generalized Cassini state of rotation of the spin axis of a planet or satellite in a precessing orbit is described. Generalized Cassini's laws are applied to several solar system objects and the location of their spin axes estimated. Of those considered only the moon definitely occupies state 2 with the spin axis near to the normal of the invariable plane. Most objects appear to occupy state 1 with the spin axis near to the orbit normal. Iapetus could occupy either state depending on its oblateness. In addition, the resonant rotation of Mercury is found to have little effect on the tidal drift of its spin axis toward state 1.

Effect of binary stars on the dynamical evolution of stellar clusters. II. Analytic evolutionary models

Abstract: We use analytic models to compute the evolution of the core of a stellar system due simultaneously to stellar evaporation which causes the system (core) to contract and to its binaries which cause it to expand by progressively decreasing its binding energy. The evolution of the system is determined by two parameters: the initial number of stars in the system N$sub 0$, and the fraction f/subb/ of its stars which are binaries. For a fixed f/subb/, stellar evaporation initially dominates the dynamical evolution if N$sub 0$ is sufficiently large due to the fact that the rate of evaporation is determined chiefly by long-range encounters which increase in importance as the number of stars in the system increases. If stellar evaporation initially dominates, the system first contracts, but as N/subc/, the number of remaining stars in the system, decreases by evaporation, the system reaches a minimum radius and a maximum density and then it expands monotonically as N/subc/ decreases further. Open clusters expand monotonically from the beginning if they have anything approaching average Population I binary frequencies. Globular clusters are highly deficient in binaries in order to have formed and retained the high- density stellar cores observed in most of them.more » We estimate that for these system f/subb/ < or = 0.15. (AIP)« less

5-GHz survey of bright galaxies.

Abstract: The 1135 galaxies in the Reference Catalogue of Bright Galaxies with declinations between +10degree and +70degree were surveyed at 6-cm wavelength with a 3-sigma detection limit of about 30 mf sun/usun; of these 149 were detected For 90 of these galaxies, spectral indices were obtained There is a suggestion that the elliptical galaxies have flat spectra more often than the spiral galaxies

Observed properties of 147 pulsars

Abstract: The principal parameters of all known pulsars have been compiled and listed in tabular form, together with references to the sources of information. A number of quantities derived from the observations are also tabulated, including distance, height above the galactic plane, spectral index, radio luminosity, rate of kinetic energy loss, characteristic age, and surface magnetic field. (auth)

26.3-MHz radio source survey. II - Radio source positions and fluxes

Abstract: The results of the Clark Lake 26.3-MHz Sky Survey are presented. Data concerning the apparent fluxes and positions of 471 radio sources in the declination range 3-63 deg are given. Almost all of these sources are identified with 3CR or 4C sources, and upper limits are placed on the fluxes of all 3CR sources which could not be found. The flux scale for this survey is based upon the absolute flux determinations of Viner (1975, Paper I of this series). The procedures employed and the errors are discussed. Low-frequency flux scales are discussed and comparisons are made with other workers. The Kellermann, Pauliny-Toth, and Williams (1969) scale should be raised by 11% to agree with the Clark Lake scale. The Penticton scale (Roger, Bridle, and Costain 1973) and the Clark Lake scale agree very well. The Grakovo scale (Bruk et al. 1968; Braude et al. 1969a) appears to be highly nonlinear and about 30% above the Clark Lake scale.

Molecular production rates in Comet Kohoutek

Abstract: Narrow-band photometry was carried out on Comet Kohoutek over a moderately wide range of heliocentric distances (0.66--1.77 au). Production rates for C$sub 2$ and CN seem to vary as r$sup -3$.$sup 5$/sup plus-or-minus// sup 0//sup .5/. C$sub 3$ abundance is comparable to that for CN and C$sub 2$. The comet was very dustry at large, preperihelion distances and, for comparable heliocentric distances, was less dusty after perihelion than before. There was a major outburst of both dust and molecules on 1 and 2 December.

Do comets play a role in galactic chemistry and gamma-ray bursts

Abstract: This paper explores the plausibility of the assumption that enough material from interstellar space is locked up in comets to reduce significantly the apparent growth rate of 'heavy' elements (mass greater than He) and, therefore, the present abundance of heavy elements in the interstellar medium and in the disk stars. A related suggestion concerns the influx of comets on neutron stars as a source of gamma-ray bursts. Although no interstellar comets have been observed, reasonable upper limits to the observed numbers and masses do not rule out the first suggestion. The gamma-ray-burst suggestion appears unlikely. A surprisingly large total mass of comets could be gravitationally bound to the sun and, of course, to other stars, but remain undetected. The nature of the 1908 Tunguska explosion is discussed briefly. It was probably not an encounter with an active comet.

Minor planets and related objects. XVIII - UBV photometry and surface composition

Abstract: New photometric observations on the UBV system are presented for 45 asteroids, bringing the total to 91 for which complete UBV colors are available. The reduced magnitudes B (1, 0) scatter about the adopted catalog values by + or - 0m, 25, with negligible systematic difference. The UBV colors fall into three distinct groups which correspond almost perfectly to the S (silicaceous or stony), C (carbonaceous), and U (unclassifiable) asteroid types recently identified from polarimetry, infrared radiometry, and narrow-band spectrophotometry. It becomes possible to classify asteroids from UBV observations alone. The S asteroids have colors very similar to those of L and LL ordinary chondrites, and some of the U objects are consistent in color with nickel-iron or enstatite-rich meteorites, but no meteorites appear to have the UBV colors of the C asteroids. The asteroid C and S compositional types have no exact counterparts among the surfaces of natural satellites.

Minor planets and comets in libration about the 2:1 resonance with Jupiter

Abstract: We examine the orbits of minor planets in a search for objects librating about the 2:1 mean-motion resonance with Jupiter. Some 30 candidates are found among the Palomar-Leiden Survey and other unnumbered minor planets. Although almost all the orbits are very uncertain, there does seem to be an indication that librators of low orbital eccentricity do exist, contrary to the hypothesis by Giffen. We also tabulate data describing 12 comets that are temporarily librating about the 2:1 resonance. Finally, we present a discussion of what are apparently 'apocentric' librations. This type of libration, of which we find seven representatives among the numbered minor planets, can occur only for sufficiently small eccentricity. For such bodies, the role of Jupiter's eccentricity is vital; it is associated with a continuing alternation between apocentric libration and an oscillation of the line of apsides.

Low-frequency radio maps and spectra of supernova remnants.

Abstract: Low-frequency radio maps of 18 supernova remnants have been constructed from observations made at the Arecibo Observatory. The integrated flux densities have been combined with others in the literature to show that most of the sources have simple power-law spectra. None of the sources show features which would suggest changes in the spectrum spatially across the given source.

Optical behavior of 20 violently variable extragalactic radio sources

Abstract: A 7-yr photometric study of nearly 200 extragalactic radio sources has confirmed 20 of these objects as violent optical variables. Light curves and photometric data are given for these 20 sources, which are placed in one of four categories according to the type of variablitity displayed. (AIP)

Reformulation of the relativistic conversion between coordinate time and atomic time

Abstract: The relativistic conversion between coordinate time and atomic time is reformulated to allow simpler time calculations relating analysis in solar system barycentric coordinates (using coordinate time) with earth-fixed observations (measuring 'earth-bound' proper time or atomic time). After an interpretation in terms of relatively well-known concepts, this simplified formulation, which has a rate accuracy of about 10 to the minus 15th, is used to explain the conventions required in the synchronization of a worldwide clock network and to analyze two synchronization techniques - portable clocks and radio interferometry. Finally, pertinent experimental tests of relativity are briefly discussed in terms of the reformulated time conversion.

Spectrophotometry of Comet Kohoutek /1973f = 1973XII/

Abstract: Spectrum scans have been obtained of Comet Kohoutek with a Fourier spectrometer at heliocentric distances from 0.55 to 1.05 AU. The useful spectral range is roughly 3800-8400 A and the resolution is about 10-15 A at 5000 A. Large variations occurred in the gas-to-dust ratio (pre- versus postperihelion) and in the relative strength of the NH2 bands (with heliocentric distance). There is a smaller change in the ratio of CN to C2 emission. The Swan bands of C2 show the customary anomaly in strengths implying highly non-Boltzmann distributions among vibrational levels. The red and violet CN system fluxes are in slightly better agreement with laboratory data on oscillator strengths than results on previous comets. Other species measured include Na, (O I), CH, and C3.