Showing papers in "The Astronomical Journal in 1980"

The resonance overlap criterion and the onset of stochastic behavior in the restricted three-body problem

Abstract: The resonance overlap criterion for the onset of stochastic behavior is applied to the planar circular-restricted three-body problem with small mass ratio (mu). Its predictions for mu = 0.001, 0.0001, and 0.00001 are compared to the transitions observed in the numerically determined Kolmogorov-Sinai entropy and found to be in remarkably good agreement. In addition, an approximate scaling law for the onset of stochastic behavior is derived.

On the Method of Least-Squares

Abstract: A method for fitting models to observed data by least squares when the data appear nonlinearly in the equations of condition, where there are nonlinear constraints among model parameters, and where the observations may be correlated, is described. The method is independent of the form in which the equations of condition are expressed, and is a generalization of the classical technique. The method is nearly as simple to apply in practice as the classical method of least squares.

Inclination effects on the recognition of Seyfert galaxies

Abstract: Axial ratios have been measured from images of 91 Seyfert galaxies thought to be disk systems, and their distribution as a function of axial ratio compared to that of field spirals similarly distributed in distance. There is a deficiency of nearly edge-on Seyfert 1 galaxies relative to the comparison sample. Examination of the visibility of nuclei in a sample of nearby spirals indicates that the effect is too large to be caused by absorption in the disks of normal spiral galaxies, while no absorption other than that expected from such disks is found in non-Seyfert Markarian spirals with bright, condensed nuclei.

Red and nebulous objects in dark clouds - A survey

Abstract: A search on the NGS-PO Sky Survey photographs has revealed 150 interesting nebulous and/or red objects, mostly lying in dark clouds and not previously catalogued. Spectral classifications are presented for 55 objects. These indicate a small number of new members of the class of Herbig-Haro objects, a significant number of new T Tauri stars, and a few emission-line hot stars. It is argued that hot, high-mass stars form preferentially in the dense cores of dark clouds. The possible symbiosis of high and low mass stars is considered. A new morphology class is defined for cometary nebulae, in which a star lies on the periphery of a nebulous ring.

Infrared reflectance spectra of asteroids - A search for water of hydration

Abstract: Infrared reflectance spectra have shown the presence of an absorption feature in the 3-4 micron region for seven C and U asteroids. By comparison with laboratory spectra of terrestrial silicates and meteorites, it is concluded that this band is probably due to water in the form of hydrated salts and silicates (clay minerals), implying that the surface material of these asteroids may be analogous to the CI and CM carbonaceous chondritic meteorites. The presence of other hydrated minerals, however, cannot be ruled out. The depths of the water bands in the spectra vary from asteroid to asteroid, though no asteroid spectrum shows a band as deep as was detected on 1 Ceres. On four other C asteroids, no water band was detected. The implications of these observations for the mineralogy of these asteroids are discussed

Computer simulations of close encounters between single stars and hard binaries

Abstract: We have simulated 5175 close encounters between hard binaries and single stars having masses M/sub 3/ ranging from 0.01 to 100 times the mass M/sub 1/ of the binary components. For all mass ratios the encounters lead to a net average fractional increase in the binding energy of the binary. For M/sub 3//M/sub 1/ approx. =0.7(M/sub 3//M/sub 1/). For M/sub 3//M/sub 1/> or approx. =3, approx. =3.1. The average recoil velocity of the single star after a close encounter increases from 0.84 of the initial orbital velocity of the binary for M/sub 3/ M/sub 1/. About two-thirds of the total recoil energy released in encounters at all impact parameters is produced by encounters in which the recoil velocity is less than the average recoil velocity at zero impact parameter. The probability that the impacting star will be a member of the post-encounter binary after a close encounter is virtually nonexistent if M/sub 3//M/sub 1/ 1.6. Except for a resonance-like peak in the transition zone between M/sub 3//M/sub 1/=0.2 and 1.6, the average post-encounter eccentricity increases monotonically with increasing values of M/sub 3//M/sub 1/. We usemore » the results of the computer simulations to compute improved cross sections governing the rate at which binaries feed kinetic energy into their parent star clusters. We compare these to earlier work.« less

Rotation and outbursts of comet P/Schwassmann-Wachmann 1

Abstract: The paper examines rotation and outbursts of comet P/Schwassmann-Wachmann 1. The observations of the P/Schwassmann-Wachmann 1 show this comet to flare above its quiescent level from before perihelion q=5.5 AU, to after aphelion Q of about 7AU. Cometary 'afternoon' activity suggests counterclockwise rotation of aphelion pole as seen near lambda=100 deg; outburst dates were derived from observed coma diameters, and the rotation was found to be direct with pole near lambda=280 deg. Usually one large area of the comet is active during one opposition, although two were observed concurrently in four very active oppositions; old active areas persist near the East limb of the comet and new areas resist development toward the West limb.

Gas flow above an alpha disk

Abstract: The flow of particles and of gas above an alpha disk is studied by solving the equations of their motion when acted upon by the radiation pressure from the disk and by the gravitational attraction of its central object. When the disk luminosity is 0.4 times the Eddington luminosity, almost all material is ultimately accepted by the central object. Between Eddington numbers 0.4 and 1.2, some gas streams away along the rotation axis of the disk. When 1.2

Internal Faraday rotation effects in transparent synchrotron sources

Abstract: Calculations of the polarization properties of transparent synchrotron sources subject to internal Faraday rotation are presented and discussed. Effects when sources are fully, partially, or not resolved are included. In particular, the characteristics of unresolved spherical and cylindrical sources are compared. In addition, the effects of partial resolution and inhomogeneity are considered for spherically symmetric sources. The calculations emphasize that accurate estimates of Faraday depth are difficult to make unless one is confident that the polarized emission and the Faraday dispersion are homogeneous within the source. To estimate correctly the intrinsic polarization direction when the source Faraday rotation is large, the source must be sufficiently resolved, so that there is little variation in Faraday depth across the telescope beam at any wavelength examined.

Spectrophotometric observations of P/Schwassmann-Wachmann 1 during outburst

Abstract: Spectra of Comet Schwassmann-Wachmann 1 were obtained on November 26-27, 1978 and February 15, 1979 using the Cassegrain Digicon spectrograph, and on February 21-23, 1979 using the IDS spectrograph of McDonald Observatory. All spectra were obtained while the comet was in an extended series of outburst (12th-13th mag). The spectra were predominantly reflected solar light, indicating the outburst was very rich in dust. Weak emission between 4000 and 4050 A, and between 4240 and 4290 A was detected in November 1978 and is probably due to CO(+). These outbursts, and the detection of CO(+), indicate that comets are not inactive at distances as great as 6 AU.

The striated dust tail of Comet West 1976 VI as a particle fragmentation phenomenon.

Abstract: The motions of 16 striae in the dust tail of Comet West are studied. It is found that all 16 striae have originated from particle ejections, and that the particles responsible for the formation of a discrete striae must be emitted simultaneously, be subjected to the same repulsive acceleration in the tail, and break up simultaneously. A strong correlation is found between the ejection times and the times of known explosive events. The repulsive accelerations of particle fragments in the striae vary from 0.6 to 2.7 times the solar attraction, indicating submicron grains of strongly absorbing materials. The repulsive acceleration of parent particles range from 0.55 to 1.10, which is only slightly smaller than those of their fragments and suggests highly nonspherical shapes of parents. The mass of dust in an average striae is estimated to be one-billion grams. Rotational bursting is discussed as a possible fragmentation mechanism. The absence of measurable effects of the Lorentz force indicate an upper limit of a few volts for the electric charge of the fragments.

Abundance correlations among comets.

Abstract: Results of narrowband filter photometry are presented for comets 1977g, 1978b, 1978f, 1978j, 1979c, and 1979i. There appears to be a remarkable homogeneity among comets with regard to the relative production rates for those species which are readily measured, specifically C2, CN, C3, and OH. Most comets appear to show identical relative abundances, except for a rather well-defined variation with heliocentric distance. Molecular production rates appear to be unrelated to either the emission-to-continuum (gas-to-dust) ratio or the dynamical age of the comet. The correlation with visual magnitudes is excellent, though the slope is not what could be intuitively expected.

The measurement of magnetic fields in stars.

Abstract: A review is presented of techniques of measuring magnetic fields in nondegenerate stars. The strengths and limitations of the classical photographic field measurement technique are compared to those of various photoelectric methods developed during the past decade, particularly the Balmer-line Zeeman analyzer technique. The problem of modeling magnetic data to infer the magnetic field geometry of an observed star is discussed. In the few cases where sufficient data are available to test the centered dipole geometry, it is found to be inadequate. It appears that most magnetic stars have field geometries at least as complex as the oblique decentered dipole (or dipole plus parallel linear quadrupole) model.

The astrophysical context of diffusion in stars

Abstract: Chemical separation of the elements is shown to solve a number of puzzling astrophysical problems. Diffusion naturally explains the low abundance of helium in the Ap-Bp stars and in some horizontal branch stars, but it simultaneously predicts a low helium abundance in Am stars which naturally explains the near exclusion of the Am and delta-Scuti phenomena. Similarly the low helium abundance in the solar wind is explained by diffusion. Many other observed phenomena in the solar particle outflux imply chemical separation. That the sun should lead to a chemically differentiated outflux is surprising, given the high turbulence observed in the atmosphere. Those stars of the upper main sequence that are slow rotators and have strong magnetic fields presumably are more stable than the sun. It is not too surprising, then, that chemical differentiation should appear on their surfaces. It is shown that for the observed abundance ''spots'' to last on Ap stars for more than 10/sup 2/--10/sup 3/ yr the convection zones must disappear on those stars. For the spots to last 10/sup 8/ yr or more, the turbulent diffusion coefficient must be small enough to allow vertical separation of the elements by diffusion. This probably rules out accretion, andmore » many other models, as the main source of the abundance anomalies. The creation of spots or, rather, rings by diffusion is finally discussed and is shown to depend sensitively on a number of poorly known parameters that probably vary from star to star. This explains the variety of observed abundance patterns. Even though the emerging picture is consistent, the diffusion model still has not answered all the questions that observations suggest. There might be a missing parameter. A possible one is suggested here.« less

The young open cluster NGC 3293 and its relation to CAR OB1 and the Carina nebula complex.

Abstract: On the basis of visible evidence, NGC 3293 appears to be associated with a number of objects in the Carina Nebula complex. UBVRI photoelectric photometry and MK-spectral specifications are presented for a large number of stars in this cluster and its surroundings (Car OB1). Over 70 cluster members with spectral types earlier than B9 are identified. Star counts indicate that the expected number of members brighter than V = 18 is 297 plus or minus 9. The cluster appears to be situated just in front of a dense dust lane, which itself appears to be part of the dust complex emanating from the center of the Carina Nebula.

Simultaneous radio spectra of sources with strong millimeter components

Abstract: Simultaneous radio spectra (within a 36-day period) are presented for 136 sources with flat or inverted spectra at centimeter wavelengths. Flux densities were measured at up to 11 frequencies ranging from 318 MHz to 90 GHz. At low frequencies ( 1 Jy had variations only a little larger at 90 GHz than at 5 GHz. This latter result seems inconsistent with either simple inhomogeneous or relativistic Maxwellian models. Models with relativistic jets close to the line of sight can probably account for most of our results.

Starspots and the rotation of the flare star EV Lac

Abstract: Sinusoidal variations in the magnitude of EV Lac outside of flares are interpreted as due to intensity modulations from a photospheric spot group No variations are detected in the color indices An upper limit set by observational uncertainties indicates that the temperature difference between the photosphere and the spot region is only a few hundred degrees The period of the cyclic magnitude variations is determined for the first time for EV Lac, and my best estimate is P=4378 days This implies an equatorial rotational velocity of 42 +- 05 km s/sup -1/ The equivalent width of the Hbeta emission line does not vary, as measured through a set of interference filters A larger scatter is evident in the measurements of the Hcap alpha emission, however, but the variations in this line do not correlate clearly with the rotation of EV Lac The variation in the equivalent width of the Hcap alpha line is about one hundred percent We are led to the conclusion that the prominent emission seen in the Hcap alpha line is formed partly in the chromosphere of EV Lac and partly in flare-associated regions of the atmosphere, and with a possible contribution also from analogs to solarmore » plage areas« less

An investigation of previously derived Hyades, Coma, and M67 reddenings

Abstract: New Hyades polarimetry and field star photometry were obtained to check the Hyades reddening, which was found to be nonzero in a previous study (Taylor, 1978). The new Hyades polarimetry implies essentially zero reddening. Four photometric techniques which are assumed to be insensitive to blanketing are used to compare the Hyades to nearby field stars and are found to yield essentially zero reddening. A simultaneous solution for the Hyades, Coma, and M67 reddenings is made, and the results are E(B-V) = 3 plus or minus 2(sigma) mmag, -1 plus or minus 3(sigma) mmag, and 46 plus or minus 6(sigma) mmag, respectively.

Radio emission in the directions of cD and related galaxies in poor clusters. III - VLA observations at 20 cm

Abstract: VLA radio maps and optical identifications of a sample of sources in the directions of 21 Yerkes poor cluster fields are presented. The majority of the cluster radio sources are associated with the dominant D or cD galaxies (approximately 70 percent). Our analysis of dominant galaxies in rich and poor clusters indicates that these giant galaxies are much more often radio emitters (approximately 25 percent of cD's are radio active in the poor clusters), have steeper radio spectra, and have simpler radio morphologies (i.e., double or other linear structure) than other less bright ellipticals. A strong continuum of radio properties in cD galaxies is seen from rich to poor clusters. It is speculated that the location of these dominant galaxies at the cluster centers (i.e., at the bottom of a deep, isolated gravitational potential well) is the crucial factor in explaining their multifrequency activity. Galaxy cannibalism and gas infall models as fueling mechanisms for the observed radio and X-ray emission are discussed