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  • Polymer and Materials Science  (3.049)
  • General Chemistry  (837)
  • ASTRONOMY  (384)
  • 1980-1984  (4.270)
  • 1970-1974
  • 1981  (4.270)
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  • 1980-1984  (4.270)
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  • 101
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    Observational data needs for plasma phenomena (1981)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Bright comets display a rich variety of interesting plasma phenomena which occur over an enormous range of spatial scales, and which require different observational techniques to be studied effectively. Wide-angle photography of high time resolution is probably the best method of studying the phenomenon of largest known scale: the plasma tail disconnection event (DE), which has been attributed to magnetic reconnection at interplanetary sector boundary crossings. These structures usually accelerate as they recede from the head region and observed velocities are typically in the range 50 V km/s. They are often visible for several days following the time of disconnection, and are sometimes seen out past 0.2 AU from the cometary head. The following areas pertaining to plasma phenomena in the ionoshere are addressed: the existence, size, and heliocentric distance variations of the contact surface, and the observational signatures of magnetic reconnection at sector boundary crossings.
    Schlagwort(e): ASTRONOMY
    Materialart: JPL Mod. Observational Tech. for Comets; p 21-32
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  • 102
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    Observational data needs useful for modeling the coma (1981)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: A computer model of comet comae is described; results from assumed composition of frozen gases are summarized and compared to coma observations. Restrictions on relative abundance of some frozen constituents are illustrated. Modeling, when tightly coupled to observational data, can be important for comprehensive analysis of observations, for predicting undetected molecular species and for improved understanding of coma and nucleus. To accomplish this, total gas production rates and relative elemental abundances of H:C:N:O:S are needed as a function of heliocentric distance of the comet. Also needed are relative column densitites and column density profiles with well defined diaphragm range and pointing position on the coma. Production rates are less desirable since they are model dependent. Total number (or upper limits) of molecules in the coma and analysis of unidentified spectral lines are needed also.
    Schlagwort(e): ASTRONOMY
    Materialart: JPL Mod. Observational Tech. for Comets; p 14-18
    Format: application/pdf
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  • 103
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    Plans for Comet Halley (1981)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: The configuration, trajectories, and payloads of a spinning Earth-orbiting satellite designed by ESA for a post-perihelion flythrough (Giotto mission) of Comet Halley are described. Experiments approved for use on two identical three-axis stabilized Venera spacecraft destined to encounter the comet after releasing probes to Venus are listed as well as the instruments to be carried on Japan's Planet-A flyby mission. The main features launch windows are given for each spacecraft.
    Schlagwort(e): ASTRONOMY
    Materialart: JPL Mod. Observational Tech. for Comets; p 277-283
    Format: application/pdf
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  • 104
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    Near perihelion observations of Comet Halley from Shuttle orbiter (1981)
    In:  CASI
    Details
    Publikationsdatum: 2016-06-07
    Beschreibung: Intercept missions and the space telescope will return unique data on Comet Halley, but will leave important gaps in the observational coverage of the comet's activity, especially around the time of perihelion passage. A small package of instruments, which could be scheduled to fly on several shuttle missions, would be an effective means of extending observational coverage of Comet Halley to include the critical part of the apparition near perihelion passage. This approach would certainly be "second best" to a dedicated orbital comet observatory. However, it would be feasible in the sense that payload space appears to be available for at least two flights during the apparition, and instruments exist, or could be modified, or are being developed, which could be integrated into a package of the required size, and which would return useful physical data on the comet.
    Schlagwort(e): ASTRONOMY
    Materialart: Mod. Observational Tech. for Comets; p 241-248
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  • 105
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    Spectropolarimetry of Herbig-Haro objects and the exciting star of HH 30 (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Spectrophotometric and spectropolarimetric observations are presented of three HH objects: HH 11, 30, and 43. Although null polarization results are obtained for HH 11 and 43, the unusually strong continuum of HH 30 is linearly polarized by 3%. The emission lines in this nebula are unpolarized. The electric vector position angle appropriate to the continuum polarization, and the presence of Fe II emission lines apparently from the photosphere of a T Tauri-like star, indicate HL Tau as the exciting/illuminating star for HH 30. Evidence is adduced for a highly anisotropic distribution of circumstellar obscuration around this star.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal; 86; Aug. 198
    Format: text
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  • 106
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    X-ray detection of the symbiotic star AG Draconis (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The detection of the yellow symbiotic star AG Draconis is reported. The star was detected by an imaging proportional counter at a count rate of 0.27 counts/s. The object is an intense source of very soft X-rays, and the X-ray luminosity is estimated to be equal to approximately 10 to the 32nd ergs/s, with a temperature of less than 2,000,000 K. If an interstellar column density of 3 x 10 to the 20th/sq cm is assumed, the emission measure is deduced to be greater than 3 x 10 to the 55th/ cu cm from the X-ray data, and less than 3 x 10 to the 59th/cu cm from the optical data. The observation is discussed in the context of various models of the symbiotic stars.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
    Format: text
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  • 107
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    A spectroscopic, photometric, and magnetic study of the starspot on II Pegasi (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A description is presented of extensive observations of II Peg during 1977 and 1978, taking into account multicolor broad-band photometry, high-dispersion spectroscopy, low-dispersion spectrophotometry, and Zeeman analysis. During this time the star showed periodic light variations in excess of a 0.4 mag range attributable to the presence of a large starspot or an equivalent nonuniform surface brightness distribution. The high-precision multicolor photometry, which differed greatly from previous photometric results, illustrates that the starspots on II Peg are continually evolving on time scales of approximately 1 year or less. A low-dispersion spectrum of the large spot showed pronounced VO and TiO molecular adsorption features. A high-resolution, high signal-to-noise Reticon spectrum at lambda 6707 does not show any compelling evidence of previously reported lithium in this star.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
    Format: text
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  • 108
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    Low energy X-ray emission from five galaxy cluster sources (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: We report the detection of soft (0.2-2.5 keV) X-ray emission from several known cluster X-ray sources using the low energy detectors of the HEAO 1 A-2 experiment. Soft X-ray emission was observed from five clusters - the Centaurus cluster, Abell 2147, SC 1329-314, Abell 2319, and Abell 133. Spectral parameters estimated from the soft X-ray fluxes are inconsistent with those reported at higher energies for the Centaurus cluster, Abell 2147, and SC 1329-314, indicating the presence of more than one spectral component in these clusters. No evidence for more than one component was found for either Abell 2319 or Abell 133. The temperature of Abell 133 is constrained to be less than 2 x 10 to the 7th K, making it the coolest X-ray cluster yet detected.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
    Format: text
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  • 109
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    Infrared reflection nebulae in S 106 and NGC 7538 E (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Two micron linear polarimetry of the S 106 and NGC 7538 E regions reveal the presence of infrared reflection nebulae, which may confuse the count of luminosity sources in a region of star formation. S 106 and NGC 7538/IRS 9 are considered the only luminosity sources in their respective regions, and the polarization of S 106/Source 3 is probably due to absorption by aligned grains. Moreover, the reflection nebula model for NGC 7538 E is best supported if the polarization of NGC 7538/IRS 9 itself is due to the absorption by aligned grains.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics; 99; 1, Ju; June 198
    Format: text
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  • 110
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    Orbital inclination of Iapetus and the rotation of the Laplacian plane (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: This paper explores the possibility that the orbit of Iapetus, with its relatively large inclination but small eccentricity, was generated by a rapid dispersal of a gaseous circumplanetary disk, assumed to be the progenitor of the satellite system. The orientation of the local Laplacian plane is shown to be a sensitive function of the disk's structure. Modification of the disk on a time scale comparable to the precession of the orbit's nodal line can produce a large inclination from one that is initially zero, while leaving the eccentricity unchanged. This time scale is of the same order of magnitude as the viscous evolution time scale for a fully turbulent disk. Hence, Iapetus need not be a captured satellite to account for its curious orbital signature.
    Schlagwort(e): ASTRONOMY
    Materialart: Icarus; 46; Apr. 198
    Format: text
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  • 111
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    IUE spectra of RS Puppis and HD 20722 - Stars in symmetric dusty nebulae (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Spectra obtained by the IUE satellite of the Cepheid variable RS Puppis and the K giant HD 20722, both of which are surrounded by symmetric nebula, are presented. Exposures were made in 1980 with the long wavelength redundant camera and 10 x 20 arcmin focal plane aperture at a spatial resolution of about 5 arcsec and spectral resolution about 6 A. No anomalies are found in the low-dispersion spectra of the stars with nebula with respect to those of apparently similar stars that lack nebulae. It is pointed out, however, that high-resolution studies of the Mg II doublet are still warranted since the doublet profile, which is unresolved in the present studies, is a sensitive indicator of mass loss effects.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Society of the Pacific; vol. 93
    Format: text
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  • 112
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    X-ray bursters and the X-ray sources of the galactic bulge (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: An attempt is made to distill from observational and theoretical information on the galactic bulge X-ray sources in general, and on the X-ray burst sources in particular, those aspects which seem to have the greatest relevance to the understanding of these sources. Galactic bulge sources appear to be collapsed objects of roughly solar mass, in most cases neutron stars, which are accreting matter from low-mass stellar companions. Type I bursts seem to result from thermonuclear flashes in the surface layers of some of these neutron stars, while the type II bursts from the Rapid Burster are almost certainly due to an instability in the accretion flow onto a neutron star. It is concluded that the studies cited offer a new and powerful observational handle on the fundamental properties of neutron stars and of the interacting binary systems in which they are often contained.
    Schlagwort(e): ASTRONOMY
    Materialart: Space Science Reviews; 28; 1, 19; 1981
    Format: text
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  • 113
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    Discovery of a 30.5 day periodicity in LMC X-4 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
    Format: text
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  • 114
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    Evidence for elemental enrichment of Puppis A by a Type II supernova (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
    Format: text
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  • 115
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    Some new results on shock chemistry in IC 443 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: New observations have been made of CO, CO-13, SiO, SO, H2CO, HCO(+), N2H(+), CS, OCS, HCN, and OH in the shocked clouds of IC 443. It is found that at position IC 443 B, (1) the shocked CO is optically thin; (2) the HCO(+)/CO abundance ratio is 4-9 x 10 to the -4 th, representing a tenfold enhancement over that of normal interstellar clouds; (3) there is no enhancement of SO or SIO, as occurs in Orion KL; and (4) there is optically thin preshock OH, confirming a hundredfold enhancement of the OH/CO ratio in the shock.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
    Format: text
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  • 116
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    A survey of X-ray line emission from the supernova remnant Puppis A (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Initial results from the first high-resolution study of the X-ray spectrum of a supernova remnant are reported. The spectrum of Puppis A between 500 and 1100 eV has been surveyed with the Focal Plane Crystal Spectrometer on the Einstein Observatory and the flux in eight lines and three line blends from various transitions of highly ionized nitrogen, oxygen, neon, and iron has been measured. The spectrum resembles that of active regions in the solar corona, but the neon lines seem enhanced relative to the oxygen lines, and both are enhanced relative to iron. The observed line strengths serve as diagnostics of the physical conditions in the emitting material. Without a priori assumptions, the ionization temperatures of O (2.2 million K) and Ne (4 million K) and the dominant ionization stage of Fe (Fe XVII) are deduced. Isothermal equilibrium plasmas or homogeneous nonequilibrium plasmas as descriptions of the source are ruled out. It is concluded that Puppis A must contain plasma over a temperature range 2-million to 5-million K with an intervening absorption column of 4 x 10 to the 21st/sq cm.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
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  • 117
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    Ultraviolet observations of hot stars with circumstellar dust shells (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Absolute fluxes over the wavelength range 1200-3200 A are presented for 13 normal early-type stars and 12 early-type stars known to have large IR excess; the data were obtained to study the UV spectral modifications produced by absorbing circumstellar dust particles. It is found that all the Be/shell stars whose spectral types are later than B6 exhibit greatly enhanced line absorption due to circumstellar Fe II. The circumstellar gaseous line absorption in stars cooler than B6 severely complicates the study of circumstellar dust absorption. However, those B and A stars that exhibit the circumstellar 9.7-micron emission feature have a very large increase in circumstellar absorption for 1800 A; such absorption is expected from circumstellar silicate particles.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
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  • 118
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    Ultraviolet emission of the Vela supernova remnant and the Cygnus Loop (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Ultraviolet emission spectra of several filaments in the Vela supernova remnant and the Cygnus Loop are compared with theoretical models of radiative shocks. Shock velocities range from 85 to 130 km/s. Little or no grain depletion is apparent. Several of the observed filaments deviate from the steady-flow models in the sense that much of the photoionization-recombination zone is absent. It is shown that resonance line scattering within the emitting region can account for the weakness of the C II 1335 and C IV 1550 lines. Evaporation fronts, which are basic to the McKee and Ostriker picture of supernova remnant evolution, do not contribute significantly to the observed emission. Some discrepancies in UV emission predicted by different sets of shock models are traced to differing atomic rates used in the calculations. A fluorescent emission line of H2 may be observable in some supernova remnants.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
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  • 119
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    The amazing X-ray light curve of 2A 0311-227 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The X-ray light curve of the AM Herculis-type binary 2A 0311-227 is presented. A smooth modulation of the X-ray flux at the orbital period is obtained, along with an eclipse feature that is total for 0.1-0.8 keV photons yet not visible for photons above about 3 keV. This strong and smooth dependence on energy suggests an origin in the obscuration of the X-ray emitting region by a column of accreting gas. Furthermore, very strong quasi-periodic pulsations with a period of about 6 min are found in the soft X-ray light curve. This periodicity is also present in the optical and hard X-ray light curves, and in the circular polarization data. It seems likely that the periodicity arises from a modulation of the mass accretion rate onto the white dwarf, and possible that it originates in pulsations of a disk-magnetosphere boundary.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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  • 120
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    The formation of a T Tauri star - Observations of the infrared source in L1551 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Observations at 5 to 25 microns show that the object discovered by Strom et al. (1976) at 2.2 microns within the densest part of the L1551 dark cloud is a strong source of radiation from grains as cool as 130 K. The energy distribution resembles that of infrared objects embedded within other molecular cloud cores, but implies a total luminosity of only 30 solar luminosities. The luminosity of the source and its proximity to the other T Tauri stars suggests that it is a 1-2 solar-mass premain-sequences star still swaddled within the L1551 cloud. The radio and optical evidence for mass motions around IRS 5 may mean that IRS 5 has been flaring in FU Ori-type eruptions within the last 1000 years.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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  • 121
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    Temperatures of galactic molecular clouds showing CO self-absorption (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The CO J = 2-1 line has been observed and, in most cases, mapped in 10 star-forming molecular clouds (W3, NGC 1333, NGC 2071, Mon R2, CRL 961, Rho Oph, W49N, W51A, DR 21, and Cep A). The CO J = 3-2 line has been observed in W3 and DR 21. The CO lines from all these sources are strongly self-absorbed. By comparing the present results with published CO(1-0) line profiles, it is found that large corrections to the temperatures of the cloud cores, as measured by the CO(1-0) lines, are required. The corrections for self-absorption bring the CO brightness temperatures into closer agreement with the grain temperatures inferred from far-IR photometry.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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  • 122
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    Emissivities of strong ultraviolet lines (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Using atomic data published during the last few years for Li to Mg sequence ions, we have carried out multilevel calculations over a range of electron pressures to obtain absolute intensities for spectral lines in the UV and EUV regions of the electromagnetic spectrum. Both the pressure dependence of the ionization balance and the dependence of line emissivities on the populations of metastable levels are taken into account. These line emissivities may be used to obtain plane-parallel model atmospheres for different solar transition region structures, and in general for other late-type stars which have observable lines over a wide range of excitation potentials.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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  • 123
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    Pioneer 10 ultraviolet photometer observations of the interplanetary glow at heliocentric distances from 2 to 14 AU (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: An analysis is presented of the observed Pioneer 10 interplanetary data from 1972 to 1977, taking into account the interplanetary glow intensity observed by the Pioneer 10 UV photometer at sun-spacecraft distances of 2-14 AU. On the basis of the obtained data, it was determined that the background intensity for the 200-1400 A band pass of the photometer channel is about 40 + or - 10 R, and that the nearby interstellar density is 0.04 + or - 0.91 per ccm for hydrogen and about 0.01 + or - 0.002 per ccm for helium. Accordingly, the He/H number density is about 0.25 at large distances from the sun. The Pioneer 10 spacecraft is leaving the solar system in the downwind direction, while both Pioneer 11 and Voyager will leave in the upwind direction. The combined UV observations of the interplanetary glow will provide accurate results on the physical status of the inflowing interstellar gas and the variability of background radiation as well.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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  • 124
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    Continuing changes in the peculiar nebulous object PV Cephei (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Changes in the nebular structure, optical spectrum and stellar brightness of the faint star PV Cephei and the nebulosity associated with it are discussed. Iris photometry of the starlike object at the tip of the fan-shaped nebula reveals irregular variability of approximately 4 magnitudes in the red. Stellar spectra in the region 4300-6750 A taken from December 1976 to April 1980 are similar to the richest emission line spectra of T Tauri stars, while nebular spectra indicate a lack of spherical symmetry. Observations obtained in the infrared reveal a source offset by a few arcsec from the apex of the fan, which is identified with the illuminating star. Radial velocities of CO emission indicate that PV Cep is at the same distance as NGC 7023, and independent estimates lead to an estimated value of 500 pc. Such a distance corresponds to a bolometric luminosity approximately 100 times that of the sun. It is suggested that PV Cep is a T Tauri star that has recently broken through its circumstellar cocoon at a time when highly erratic variability and a strong stellar wind characterize the star.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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  • 125
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    Observations of the giant radio lobes region of Centaurus A with SAS 3 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Observations of the X-ray flux from the extended radio lobes of the galaxy Centaurus A obtained with the SAS 3 observatory are reported. The 15 x 15 deg region that includes the lobes was mapped by superposing data from raster scans with the horizontal tubular collimator detectors, which have a 1.7 deg FWHM circular field of view. Data obtained is consistent with the presence of superposed emission from the point sources NGC 5128 and MX 1312-42, a previously unreported source detected by the Einstein Observatory IPC. Fluxes of 4.63 + or - 0.14 x 10 to the -10th and 4.6 + or - 0.6 x 10 to the -11th ergs/sq cm per sec were measured for NGC 5128 and MX 1312-42, respectively, with best fit power law spectra of indices 0.83 + or - 0.04 and 0.62 + or - 0.10 and hydrogen column densities of 1.23 + or - 0.10 x 10 to the 23rd and 9.7 + or - 15.0 x 10 to the 21st atoms/sq cm. Results imply an upper limit of 2.9 x 10 to the 11th for the X-ray emission from the extended radio lobes of Cen A between 2 and 10 keV, which indicates a lower limit to the magnetic field in the lobes of 1.6 x 10 to the -6th gauss.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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  • 126
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    Simultaneous X-ray, ultraviolet, optical, and radio observations of the flare star Proxima Centauri (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Results of coordinated program of observations in the X-ray, UV, optical and radio regions of the dM5e flare star Proxima Centauri are presented. Simultaneous observations of the star were obtained on March 6 and March 7, 1979, by the Einstein Observatory IPC, the IUE SWP and LWR cameras at low dispersion, three ground-based optical telescopes in Australia and the Parkes 64-m radio telescope. A total of 10 radio bursts and six optical flares was detected during three nights of simultaneous radio and optical observations, which appear to be broadly correlated. A major X-ray flare event was detected with temperatures of 1.7 x 10 to the 7th and 1.2 x 10 to the 7th K during the rise and decay phases, respectively, respective X-ray fluxes of 3.0 x 10 to the -11th and 3.7 x 10 to the -11th ergs/sq cm per sec, and changes in spectral flux distribution. No radio, optical or UV flare emission corresponding to the X-ray flare was detected. The X-ray flare is interpreted in terms of an arch model with cooling predominantly by X-ray radiation, with an electron density of 1.0 x 10 to the 11th/cu cm during the decay phase and a total arch length comparable to the size of the star itself. The X-ray flare observed is thus more similar to a typical strong solar flare than heretofore seen on a flare star.
    Schlagwort(e): ASTRONOMY
    Materialart: PB81-248957 , Astrophysical Journal; vol. 245
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    The Ophiuchus cluster - A bright X-ray cluster of galaxies at low galactic latitude (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The discovery of an extended X-ray source identified with a cluster of galaxies at low galactic latitude is reported. The source, designated the Ophiuchus cluster, was detected near 4U 1708-23 with the HEAO 1 Scanning Modulation Collimator, and identified with the cluster on the basis of extended X-ray size and positional coincidence on the ESO/SRC (J) plate of the region. An X-ray flux density in the region 2-10 keV of approximately 25 microJ was measured, along with an X-ray luminosity of 1.6 x 10 to the 45th ergs/sec and an X-ray core radius of approximately 4 arcmin (0.2 Mpc) for an assumed isothermal sphere surface brightness distribution. The X-ray spectrum in the range 2-10 keV obtained with the HEAO 1 A-2 instrument is well fit by a thermal bremsstrahlung model with kT = 8 keV and a 6.7-keV iron line of equivalent width 450 eV. The steep-spectrum radio source MSH 17-203 also appears to be associated with the cluster, which is the closest and brightest representative of the class of X-ray clusters with a dominant central galaxy.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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    Infrared spectrophotometry of three Seyfert galaxies and 3C 273 (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: Spectrophotometry in the range 2.1-4.0 microns is presented for the Seyfert galaxies NGC 1068, NGC 4151 and Mrk 231 and the quasar 3C 273, together with broadband and narrowband observations of the Seyfert galaxies in the range 8-13 microns. The spectra of NGC 1068 and NGC 4151 are found to contain a significant component due to starlight, especially at shorter wavelengths. The nonstellar component in NGC 1068 is observed to fall off rapidly at wavelengths shorter than 4 microns, consistent with the interpretation of the excess beyond 5 microns as thermal reradiation by dust. Observations confirm the variability of NGC 4151, and indicate the presence of two components of the flux other than starlight: a nonthermal variable component predominant at shorter wavelengths and a constant, probably thermal component at wavelengths greater than 3 microns. Mrk 231 and 3C 273 exhibit no discernable stellar component and were not observed to vary by more than 10%. Evidence is obtained for a broad minimum in the 8 to 13 micron spectrum of Mrk 231, as well as possible structure between rest wavelengths of 2.8 and 2.9 microns, and the spectrum is not a power law. The spectrum of 3C 273 is consistent with a power law from 1.2 to 10 microns, with small but significant deviations.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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    Periodic solutions about the collinear Lagrangian solution in the general problem of three bodies (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: The article describes the solutions near Lagrange's circular collinear configuration in the planar problem of three bodies with three finite masses. The article begins with a detailed review of the properties of Lagrange's collinear solution. Lagrange's quintic equation is derived and several expressions are given for the angular velocity of the rotating frame. The equations of motion are then linearized near the circular collinear solution, and the characteristic equation is also derived in detail. The different types of roots and their corresponding solutions are discussed. The special case of two equal outer masses receives special attention, as well as the special case of two small outer masses. Finally, the fundamental family of periodic solutions is extended by numerical integration all the way up to and past a binary collision orbit. The stability and the bifurcations of this family are briefly enumerated.
    Schlagwort(e): ASTRONOMY
    Materialart: Celestial Mechanics; 24; May 1981
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    Observations of strong ultraviolet absorptions in the spectrum of the DC white dwarf LDS 678 B (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Evidence from spectroscopic observations that LDS 678 B has strong ultraviolet lines of neutral carbon in its spectrum is presented. The spectra are found to contain strong lines of C I in the ultraviolet and weak He I lines in the visible. The appearance of the star's spectrum and published photometry are consistent with its having an effective temperature near 10,600 K with a helium-dominated atmosphere and a carbon abundance lower than C:He = 0.001. The star's spectra are compared with those of the white dwarfs L879-14 and L145-141, which are cooler than LDS 678B, have C2 bands in the visible and also show strong evidence of strong ultraviolet C I lines. It is concluded that LDS 678 B has a temperature intermediate between the DB and C2 band white dwarfs and that the ultraviolet C I lines can be a useful means for finding carbon in the atmosphere of the cooler white dwarfs.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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    SC 2059-247 - An unusual radio/X-ray source in a distant cluster of galaxies (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The X-ray, optical and radio properties of a high redshift, Bautz-Morgan type I cluster of galaxies, namely SC 2059-247, are examined. This cluster is optically dominated by a cD galaxy with a powerful flat-spectrum radio source coincident with the possibly stellar nucleus. Two possible interpretations are suggested for the apparently soft X-ray spectrum of the extremely luminous cluster. Either the intracluster gas is much cooler in high-redshift clusters because they are less relaxed, or the X-ray and radio emissions from SC 2059-247 are the result of a nonthermal QSO/BL Lac type object in the nucleus of the cD. If the latter, it would be the first time that an X-ray source similar to a quasar or BL Lac object has been discovered in a previously identified galaxy.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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    HR 4511 - A probable Cepheid with a supergiant-like hot companion (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: IUE observations have shown HR 4511 to have an early B-type companion with a strong stellar wind. Fitting the energy distribution of the system from far-UV to middle-IR yields a difference of about 3.2 mag at the V passband. Since HR 4511 is in the small cluster Stock 14 and has M(V) = -7.8, M(V) for the secondary is about -4.6, which is only slightly more luminous than the known BO.5 III and B1 stars at the turnoff point. This implies an inconsistency between the deduced luminosity of the secondary and the nature of its UV spectrum, which mimics stars of considerably greater luminosity. It is suggested that the secondary may have been observed in a brief stage between core and shell H burning.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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  • 133
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    Pointed soft X-ray observations of AM Herculis from HEAO 1 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Extensive soft X-ray (0.1-1.5 keV) observations of AM Herculis are reported. The data, acquired during two pointed observations by HEAO 1 in 1978, span four binary cycles and reveal considerable detail in the 3.09 hour light curve. Rapid X-ray flickering is evident throughout the bright section of the light curve and is characterized by an average e-folding autocorrelation time of about 10 s. Analysis of the spectral data indicates a 30% variability; on occasion the X-ray spectrum becomes softer as the source intensity decreases. The current understanding of AM Her as an accreting magnetic white dwarf is discussed, and various models are related to the present HEAO-1 data.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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    Far-infrared observations of globules (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: Observations of far-infrared emission from nine globules are presented. The intensity and uniformity of the emission confirm that the heat source is the interstellar radiation field. Spectra of B133 and B335 are presented; they are consistent with optically thin thermal emission from dust with temperature 13-16 K. The temperature and intensity of B335 are used to calculate the ratio of visual extinction to far-infrared emission frequency.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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    Results from an extensive Einstein stellar survey (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: The preliminary results of the Einstein Observatory stellar X-ray survey are presented. To date, 143 soft X-ray sources have been identified with stellar counterparts, leaving no doubt that stars in general constitute a pervasive class of low-luminosity galactic X-ray sources. Stars along the entire main sequence, of all luminosity classes, pre-main sequence stars as well as very evolved stars have been detected. Early type OB stars have X-ray luminosities in the range 10 to the 31st to 10 to the 34th ergs/s; late type stars show a somewhat lower range of X-ray emission levels, from 10 to the 26th to 10 to the 31st ergs/s. Late type main-sequence stars show little dependence of X-ray emission levels upon stellar effective temperature; similarly, the observations suggest weak, if any, dependence of X-ray luminosity upon effective gravity. Instead, the data show a broad range of emission levels (about three orders of magnitude) throughout the main sequence later than F0.
    Schlagwort(e): ASTRONOMY
    Materialart: PB81-236309 , Astrophysical Journal; vol. 245
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    Anomalous extinction in the planetary nebula Abell 30 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The stellar continuous energy distribution from 8000 to 1250 A in Abell 30 is quite peculiar. The observed flux can be understood if a hot central star (approximately 200,000 K) is immersed in an absorbing dust cloud which has anomalous absorption with its peak near 2470 A. The dust nebula is a strong infrared source, maintained by conversion of the stellar UV flux. The internal reddening is E(B - V) = 0.30 mag and reaches 2.5 mag at 2470 A; it is best matched not by graphite but by laboratory observations of carbon smoke. Intense P Cygni lines show that a strong stellar wind exists. The central star may be an O subdwarf, approaching more nearly a helium-carbon degenerate DO.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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    Ultraviolet slit spectroscopy in the core of 30 Doradus with the International Ultraviolet Explorer (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Low resolution (about 7 A) IUE observations of the core of the 30 Doradus Nebula in the Large Magellanic Cloud are presented. Data were obtained through the large entrance aperture at 11 different positions in both the long wavelength (1900-3200 A) and short wavelength (1150-2000 A) cameras. The aperture was stepped in 10-arcsec intervals, in the direction of the long axis of the aperture, effectively yielding a 2-arcmin long slit with the central object, R136, close to the center. The brightness distribution is strongly peaked at the position of R136, but it is found that the far-ultraviolet fluxes are dominated by luminous early-type stars at any position along the slit. The behavior of the ultraviolet colors along the slit implies that the core of 30 Dor lies behind a cloud of dust extending over at least 2 arcmin = 30 pc and suggests that the reddening law changes with distance from R136.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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    A statistical study of radio emission in E and S0 galaxies (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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    Polarization of the cosmic background radiation (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: The technique and results of a measurement of the linear polarization of the cosmic background radiation at a wavelength of 9 mm are discussed. Data taken between 1978 May and 1980 February from both the Northern Hemisphere (Berkeley latitude 38 deg N) and the Southern Hemisphere (Lima latitude 12 deg S) over 11 declinations from -37 to +63 deg show the radiation to be essentially unpolarized over all areas surveyed. Fitting all data gives the 95% confidence level limit on a linearly polarized component of 0.3 mK for spherical harmonics through third order. A fit of all data to the anisotropic axisymmetric model of Rees (1968) yields a 95% confidence level limit of 0.15 mK for the magnitude of the polarized component. Constraints on various cosmological models are discussed in light of these limits.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 245
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  • 140
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    VLA search for radio emission from stars with solar-type structures (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Results are presented of a high-sensitivity search for 6-cm radio emission from stars with evidence of active chromospheric or coronal regions. The data indicate that many of these stars have radio luminosities much less than those that have been found for known radio stars.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal; 86; Apr. 198
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    The ultraviolet spectrum of the magnetic degenerate star GD229 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The ultraviolet spectrum obtained with the IUE satellite of the magnetic degenerate white dwarf star GD 229 is presented. The ultraviolet energy distribution measured by the short- and long-wavelength cameras covering the range 1170-3200 A, when combined with optical data, indicates a best fit blackbody temperature of 16,000 K, which is significantly lower than previous estimates. A broad absorption trough in the 2000-3000 A region is observed which may be produced by opacity in the fundamental cyclotron frequency for surface magnetic fields from 3.2 to 5 x 10 to the 8th gauss. The absence of a strong Lyman-alpha sigma + component suggests that the primary atmospheric constituent is not hydrogen, with various absorption features probably attributable to Zeeman components of neutral helium, or possibly Mg II, C II and other metal lines. The superposition of many strong Zeeman features is also an alternative interpretation of the absorption in the 2000-3000 A interval.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Society of the Pacific; vol. 93
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    The ultraviolet spectrum of the peculiar A star HD 51418 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: High-dispersion observations of the peculiar A star HD 51418 have been carried out in the ultraviolet by the IUE satellite. Atomic resonance lines observed in the regions 1800-2000 and 2500-3000 A include those of Mg II, Ti II, Cr I, Cr II, Mn II, Fe II and Zn II, and possibly Si II, S I, V II, Fe I, Co II, Y II, Ce II, Ce III, Eu II, Eu III and Tb III. The Mg II 2796 and 2803 A resonance lines exhibit definite variations in equivalent width with orbital phase, which can be attributed to changes in the local atmospheric structure due to the patchy distribution of other elements. In addition, the observations confirm the well known trend for a light-heavy asymmetry in iron peak spectra similar to that observed in the rare earths.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Society of the Pacific; vol. 93
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    Spectrophotometry of AM Herculis at minimum (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Spectrophotometric observations of AM Her during its 1980 minimum are reported. The M dwarf in the system is revealed by its TiO bands and domination of the spectrum longward of 6000 A. The blue region of the spectrum reveals a hot, magnetic white dwarf with Zeeman-split hydrogen absorption lines, and emission lines of H, He I, and Fe II. The inferred surface magnetic field of roughly 10 to the 7th gauss permits the presence of an accretion disk in the system. Velocities and intensities of the H emission lines indicate an origin in the X-ray-heated atmosphere of the M dwarf. The continuum light variation in the red appears to result from the heating of the secondary, while the blue light variation probably results from the rotation of the bright spot at the white dwarf's magnetic pole. A self-consistent geometrical model is proposed, in which the minimum state is interpreted as a lull in the rate of accretion onto the white dwarf.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Society of the Pacific; vol. 93
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    The oxygen I depletion in the diffuse interstellar medium (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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    4U 1626-67 - A prograde spinning X-ray pulsar in a 2500 s binary system (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The binary period of 4U 1626-67 was found from an analysis of its optical pulsations. A single lower frequency sideband of the 2.4% amplitude 7.68-s optical pulsations from this X-ray pulsar was detected on at least three different nights in Fourier transforms of high-speed photometry obtained with the CTIO 4 m telescope. The 0.42% sidelobe pulsations have a frequency which is 0.4011(2) mHz lower than the frequency of the direct pulsations near 130.26 mHz. The weaker sidelobe pulsations are interpreted as arising from X-ray to optical reprocessing on the companion star and are shifted to the lower frequency by the rotation frequency of the binary orbit because the X-ray pulsar spins in the same sense as the orbital motion (direct or prograde).
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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    The ultraviolet energy distributions of late A stars (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: Observed late A star energy distributions for the wavelength range 1400-2500 A are compared. No difference is found between energy distributions of Am stars and those of normal slowly rotating A stars. The fluxes of rapidly rotating stars, however, appear to be increased for wavelengths smaller than 1530 A; this cannot be understood as an effect of pole heating or reduced gravity. In addition, the comparison of the UV energy distributions with model atmosphere energy distributions of Kurucz indicates some problems with the theoretical Si I absorption edges at 1530 A.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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    Molecular hydrogen and the 2 micron spectrum of NGC 7027 (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: The spectrum of the planetary nebula NGC 7027 in the range 1.6-2.5 microns was obtained with a resolution of 1.2 per cm. The presence of molecular hydrogen emission in the v = 1-0 S(1), Q(1), and Q(3) lines is confirmed, and the detection of H2 lines v = 1-0 Q(2), Q(4), S(0), and S(2) is reported. The H2 line strengths, with upper limits for the v = 2-1 band, suggest a model in which the emitting gas is confined to clumps heated by a shock front accompanying an expanding H II region. Emission lines are also detected from atomic hydrogen (Pfund and Brackett series) and from He I and He II.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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    A comparison of quasar absorption line systems with absorption by the galactic halo (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Milky Way halo and quasar absorption spectra contain a number of remarkable similarities which include mixed ion absorption, a general absence of excited fine structure levels with the possible exception of excited C II, similar column densities, and similar multicomponent line profiles. The extreme sensitivity of UV lines to small amounts of gas is well illustrated in a comparison of 21-cm H I emission with UV absorption toward the Large Magellanic Cloud. This sensitivity shows that galaxies are likely to appear significantly larger in UV absorption than in 21-cm emission and that the size problem for galactic halos is probably not a serious one. It is concluded that many of the absorption line systems seen in the spectra of quasars are probably produced in the gaseous halos of intervening galaxies.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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    The triple quasar Q1115+080A, B, C - A quintuple gravitational lens image (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Spectroscopy and direct imaging of Q1115+080A, B, C with a CCD camera support the hypothesis that they are gravitational images of a single object. Spectroscopy of the semiforbidden C III 1909-A emission line shows all the images to have identical spectra and redshifts (to within 100 km/s), except that B is slightly redder. Gravitational lens imaging by a massive spiral galaxy is investigated, and a quintuple image model resembling Q1115+080A, B, C is found. In this model, Q1115+080A is a highly magnified close pair of images oriented in the position angle 23 deg. An elongation Q1115+080A at this angle is seen in the CCD pictures.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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    VLBI observations of the jet near the core of M87 (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: VLBI observations of M87 with four antennas at 13 cm wavelength indicate that the large-scale jet extends inward to the core. The presence of the jet within several light-years of the currently inactive core indicates that either the source has been active in the recent past or that the core supplies energy to the jet even in the quiescent phase.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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    Interstellar absorption in the Mg II resonance line k2 and h2 emissions (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: High-resolution (0.2 A) IUE spectra for the long wavelength range (1800-3000 A) have been studied. It is shown that narrow interstellar Mg II lines are seen in the center of the k2 and h2 emissions from nearby stars with large rotational velocities. For all observed stars, the radial velocity of the central k3 absorption component in the rest system of the star is strongly correlated with the mirror image of the radial velocity of the stars; this shows that a major fraction if not all of the k3 absorption is due to interstellar absorption in the solar neighborhood. The violet to red asymmetry of the k2 emission also correlates with the radial velocities of the star; this shows that the shift of k3 is due to the velocity shift of the local interstellar cloud with respect to the star.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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    IUE high-dispersion spectrum of R Aquarii (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Emission-line spectra of several ions were observed in R Aqr in the wavelength range 1900-3000 A. C II diagnostics gives an electron density of about 400,000/cu cm and an electron temperature of about 10,000 K. The Mg II doublet profiles are grossly asymmetric, of a P Cygni type with terminal ejection velocity of at least 200 km/s. This is like Mg II behavior in Omicron Cet, Zeta Aur, and 32 Cyg, but unlike smaller UV shifts of the Mg II self-absorptions reported so far in other red giants and supergiants.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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  • 153
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    Spectroscopy, surface photometry, and three-dimensional models for NGC 596 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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  • 154
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    Centaurus A /NGC 5128/ at 2 keV-2.3 MeV - HEAO 1 observations and implications (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The active-nucleus galaxy Centaurus A has been studied at 2 keV-2.3 MeV using data from the UCSD/MIT hard X-ray and low-energy gamma-ray instrument and the GSFC/CIT cosmic X-ray experiment on HEAO-1. It is found that an E exp -1.60 + or - 0.03 power law spectrum breaking to E exp -2.0 + or - 0.2 at 140 keV best describes the January and July 1978 data. The average intensity was 50% higher during the January observations. Upper limits to unresolved lines at 511 keV and 1.6 MeV were found to be 6.5 x 10 to the -4th photons/sq cm-s and 2.2 x 10 to the -4th photons/sq cm-s, respectively, at the 90% confidence level. The present data are consistent with the detailed calculations of the synchrotron self-Compton mechanism; they may also agree, marginally, with the predictions of emission from spherical accretion onto black holes.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 244
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  • 155
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    The Sun among stars. IV - Albedos of Uranus and Neptune and the solar color (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Geometric albedos in 48 adjacent 50 A bands from 3250 to 5600 A have been derived from observations of Uranus and Neptune. The solar analog found in earlier papers (Hardorp 1978, 1980) was chosen for these reductions, so these albedos are more reliable systematically than earlier ones and allow a choice among the scattering models of Savage et al. (1980). Green methane bands are stronger on Neptune. Strong solar absorption lines are found to be partially filled in by Raman-scattering. Neglect of this effect caused Croft et al. (1972) to find a solar color that is too blue. It probably also affected the classification of G-type stars in the Michigan Spectral Catalogue as well as Garrison's (1979) interpretation of IUE observations.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics; 96; 1-2,; Mar. 198
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  • 156
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    Pulsar statistics and their interpretations (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: It is shown that a lack of knowledge concerning interstellar electron density, the true spatial distribution of pulsars, the radio luminosity source distribution of pulsars, the real ages and real aging rates of pulsars, the beaming factor (and other unknown factors causing the known sample of about 350 pulsars to be incomplete to an unknown degree) is sufficient to cause a minimum uncertainty of a factor of 20 in any attempt to determine pulsar birth or death rates in the Galaxy. It is suggested that this uncertainty must impact on suggestions that the pulsar rates can be used to constrain possible scenarios for neutron star formation and stellar evolution in general.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics; 95; 2, Ma; Mar. 198
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  • 157
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    Implications of photometric and spectroscopic periods of SS433 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: It is suggested that a comparison of the periodicities inferred from spectroscopic and photometric observations of SS433 may help clarify its structure. The interaction between the orbital and beam motions may produce sideband periods in the photometry. It is found that Lense-Thirring and slaved disk models make differing predictions.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics; 95; 2, Ma; Mar. 198
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  • 158
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    The very soft X-ray transient H1853 + 60 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The detection of a new soft X-ray transient, H1853 + 60, using data from the Low Energy Detectors (LEDs) on the HEAO 1 A-2 experiment, is reported. Although the solar flare hypothesis cannot be ruled out, the similarity between this X-ray transient's temporal and spectral characteristics and those of several other transients observed by HEAO 1 LEDs, suggest a common emission mechanism for these events. It is unlikely that more transients as strong as these will be discovered, except on an individual scan basis.
    Schlagwort(e): ASTRONOMY
    Materialart: Nature; 290; Apr. 16
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  • 159
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    Interference-filter photometry of periodic comet Ashbrook-Jackson (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal; 86; Mar. 198
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  • 160
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    Orbits of nine Uranian rings (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Observations of a stellar occultation by Uranus and its nine rings are presented and used to examine the structures and kinematics of the rings. The observations of the occultation of the K giant star KM 12 were obtained in the K band with the 4-m CTIO telescope at a signal-to-noise ratio higher than any previously obtained. Ring occultation profiles reveal the alpha ring to possibly have a double structure and less abrupt boundaries than the gamma ring, which exhibits diffraction fringes, while the eta ring is a broad ring with an unresolved narrow component at its inner edge. The present timing data, as well as previous occultation timings, are fit to a kinematic model in which all nine rings are treated as coplanar eclipses of zero inclination, precessing due to the zonal harmonics of the Uranian gravitational potential to obtain solutions for the ring orbits. Analysis of the residuals from the fitted orbits reveals that the proposed model is a good representation of ring kinematics. The reference system defined by the orbit solutions has also been used to obtain a value of 0.022 + or - 0.003 for the ellipticity of Uranus and a Uranian rotation period of 15.5 h.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal; 86; Mar. 198
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  • 161
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    A note on the statistics of early-type close binaries (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: A degree of contact index (I sub c) is defined, and its frequency diagram is given for 16 early-type close binaries. The objective is to determine whether the numbers of such systems are continuous or discontinuous across marginal contact. Data for four of the systems (TU Mus, V499 Sco, Delta Pic, and SZ Cam) derive from new photometric analyses, the results of which are also given. Present results indicate that there is continuity in frequency across marginal contact, although it would be desirable to include more binaries as further observations become available. It is noted that the only two systems in the bin of largest I sub c are known to be in the rapid phase of mass transfer.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysics and Space Science; 76; 1, Ma; May 1981
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  • 162
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    The spectra and light curves of two gamma-ray bursts (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Observations made by the Hard X-ray and Low Energy Gamma-Ray Experiment on board HEAO-1 of the spectra and light curves of two gamma-ray bursts for which localized arrival directions will become available are presented. The burst of October 20, 1977 is found to exhibit a fluence of 0.000031 + or - 0.000005 erg/sq cm over the energy range 0.135-2.05 MeV and a duration of 38.7 sec, while that of November 10, 1977 is found to have a fluence of 0.000021 + or - 0.000008 erg/sq cm between 0.125 and 3 MeV over 2.8 sec. The light curves of both bursts exhibit time fluctuations down to the limiting time resolution of the detectors. The spectrum of the October burst can be fit by a power law of index -1.93 + or -0.16, which is harder than any other gamma-burst spectrum yet reported. The spectrum of the second burst is softer (index -2.4 + or - 0.7), and is consistent with the upper index in the double power law fit to the burst of April 27, 1972.
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  • 163
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    Optical studies of the regions of the gamma-ray bursts of 19 November, 1978 and 5 March, 1979 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Optical studies were made of two well-located gamma-ray burst regions in the Southern Hemisphere using the 1.5 m telescope at the Cerro Tololo Inter-American Observatory in Chile. Multi-filter image tube plates and UBV photometry surveys were made of both regions. The field of the 19 November, 1978 gamma-ray burst shows no early star or star with unusual colors out to several diameters of the nominal error box. The region of the 5 March, 1979 gamma-ray burst, which includes N49, contains several blue giants in the LMC, two of which deserve further study.
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  • 164
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    Negative ions in comets (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Negative ion sources in comets are identified and cometary plasma effects caused by negative ions are examined. The primary negative ion sources are shown to be: (1) for the inner coma - photodissociation of HCN, electron attachment of OH, and collision with alkalis; (2) in the vicinity of the nucleus - interplanetary dust collisions with the nucleus; and (3) for both the contaminated solar wind region and sporadic discharges in the nonhomogeneous inner coma plasma - dissociative electron attachment and charge inversion during keV positive ion scattering by cometary dust. Negative ion abundance for Halley's Comet has been estimated to be 10 to the -6th - 10 to the -10th of electron densities.
    Schlagwort(e): ASTRONOMY
    Materialart: Moon and the Planets; 24; Apr. 198
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  • 165
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    The far-ultraviolet energy distribution of two globular cluster blue horizontal-branch stars in M13 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The far-UV energy distribution of two blue horizontal-branch (BHB) stars detected in the nucleus of M13 is presented. Their continua can be characterized by a model atmosphere of an effective temperature of 15,000 to 20,000 K and log g = 4.5, and it follows that V is in the range 15.9-16.7 for these stars. Comparison with integrated photometry by OAO 2 and by ANS indicates that, at wavelengths smaller than 1800 A, the integrated light is from BHB stars only, of which M13 contains about 200. For these far-UV wavelengths, the color of the BHB stars is also very similar to the integrated color of the elliptical galaxy M87.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 243
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  • 166
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    Observations of fast oscillations in SS Cygni (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: High-speed photometric observations of the dwarf nova SS Cygni have been made using an ultraviolet and blue sensitive photomultiplier. Rapid oscillations were detected over an interval of 7 days. The period of the oscillations passed through a minimum of 7.29 s, the shortest period yet observed in a dwarf nova. The signal was spread in frequency by an amount larger than required by the slow evolution of the period. The data are considered from the viewpoint of several models.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 243
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  • 167
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    Far-infrared emission line and continuum observations of NGC 7027 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The first observation of a fine-structure transition in NGC 7027 at wavelengths greater than 30 microns is reported. The flux in the 63.2-micron line is found to be approximately 10 to the -16th W/sq cm. It is noted that if NGC 7027 lies at 1 kpc, this corresponds to a luminosity, in the line, approximately 30 times greater than the solar luminosity. The flux of the 88.35-micron line is less than 10 to the -17th W/sq cm, and the upper limit to the line flux at 51.8 microns is found to be 10 to the -16th W/sq cm. These upper limits imply an electron density that is less than 1.6 x 10 to the 5th/cu cm. It is noted that the continuum measurements obtained support a dust temperature of 90 K with an emissivity approximately equal to the reciprocal of the square of the wavelength. The data exclude grain materials whose wavelength-dependent emissivity (the reciprocal of the wavelength raised to nth power) requires n to be outside the range between 1.6 and 2, unless the temperature varies drastically across the dust cloud
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 243
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  • 168
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    The diameter of Juno from its occultation of AG + 0 deg 1022 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The occultation on Dec. 11, 1979, of AG + 0 deg 1022 by Juno was observed photoelectrically from 15 sites distributed across the occultation track. The observations are well represented by a mean elliptical limb profile having semimajor and semiminor axes of 145.2 + or 0.8 and 122.8 + or - 1.9 km, respectively. The corresponding effective diameter of Juno is 267 + or - 5 km, where the uncertainty has been conservatively increased to reflect the presence of limb irregularities clearly seen in the observations. Published radiometric and polarimetric diameters for Juno are 6% to 7% smaller than the occultation result. No secondary occultations attributable to possible satellites of Juno were recorded at any of 23 photoelectrically equipped observing sites.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal; 86; Feb. 198
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  • 169
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    A spectrophotometric search for the halo of Markarian 10 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Observations of a faint halo around the Mk 10 galaxy nucleus with the Palomar multichannel spectrophotometer reveal blue continuum emission forbidden lines of O II and O III, the hydrogen Balmer series, and stellar absorption series. The flux is detected at the surface brightness of 27.2 + or - 0.2 mag arc/sq sec at wavelengths of 5000 A at the radial distance of 27 kpc from the nucleus. The surface photometry of the inner parts of Mk 10 are depicted, and the radial brightness profile is decomposed into disk and bulge components. No evidence of a halo component was observed; the extended bulge is sufficient for the stabilization of the disk against bar-like instabilities.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal; 86; Feb. 198
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  • 170
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    Transformation from proper time on earth to coordinate time in solar system barycentric space-time frame of reference. I. II (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: It is noted that in order to obtain accurate computed values of earth-based range and Doppler observables of a deep space probe, an expression is required for the difference between coordinate time (t) in the solar system barycentric space-time frame of reference and proper time (tau) recorded on a fixed atomic clock on earth. This is part 1 of a two-part article which obtains an expression for the coordinate time/proper time difference that can be used in deriving computed values of observations of a spacecraft or celestial body located anywhere in the solar system. The expression can also be used in computing Very Long Baseline Interferometry data types. In part 1, expression for the coordinate time/proper time difference is obtained that is a function of position and velocity vectors of the major celestial bodies of the solar system and the atomic clock on earth which reads proper time. This expression is transformed in part 2 to a function of time and the earth-fixed coordinates of the atomic clock.
    Schlagwort(e): ASTRONOMY
    Materialart: Celestial Mechanics; 23; Jan. 198
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  • 171
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    Documentation for the machine-readable version of the thirteen color photometry of 1380 bright stars (1981)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The magnetic tape version of the catalogue of thirteen-color photometry of 1380 bright stars, containing data on the 13 color medium narrow band photometric system is described. Observations of essentially all stars brighter than fifth visual magnitude north of delta = -20 deg and brighter than fourth visual magnitude south of delta = -20 deg are included. It is intended to enable users to read and process the tape without the common difficulties and uncertainties.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-TM-84018 , NSSDC/WDC-A-R/S-81-02
    Format: application/pdf
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  • 172
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    Documentation for the machine-readable character coded version of the SKYMAP catalogue (1981)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The SKYMAP catalogue is a compilation of astronomical data prepared primarily for purposes of attitude guidance for satellites. In addition to the SKYMAP Master Catalogue data base, a software package of data base management and utility programs is available. The tape version of the SKYMAP Catalogue, as received by the Astronomical Data Center (ADC), contains logical records consisting of a combination of binary and EBCDIC data. Certain character coded data in each record are redundant in that the same data are present in binary form. In order to facilitate wider use of all SKYMAP data by the astronomical community, a formatted (character) version was prepared by eliminating all redundant character data and converting all binary data to character form. The character version of the catalogue is described. The document is intended to fully describe the formatted tape so that users can process the data problems and guess work; it should be distributed with any character version of the catalogue.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-TM-84019 , NSSDC/WDC-A-R/S-81-05
    Format: application/pdf
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  • 173
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    Test results of Spacelab 2 infrared telescope focal plane (1981)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The small helium cooled infrared telescope for Spacelab 2 is designed for sensitive mapping of extended, low-surface-brightness celestial sources as well as highly sensitive investigations of the shuttle contamination environment (FPA) for this mission is described as well as the design for a thermally isolated, self-heated J-FET transimpedance amplifier. This amplifier is Johnson noise limited for feedback resistances from less than 10 to the 8th power Omega to greater than 2 x 10 to the 10th power Omega at T = 4.2K. Work on the focal plane array is complete. Performance testing for qualification of the flight hardware is discussed, and results are presented. All infrared data channels are measured to be background limited by the expected level of zodiacal emission.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-TM-80456 , REPT-280-2
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  • 174
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    CCD photometry of 1218+304 1219+28 and 1727+50: Point sources, associated nebulosity and broadband spectra (1981)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: Visual and far red surface photometry were obtained of two X-ray emitting BL Lacertae objects, 1218+304 (2A1219+305) and 1727+50 (Izw 187), as well as the highly variable object 1219+28 (ON 231, W Com). The intensity distribution for 1727+50 can be modeled using a central point source plus a de Vaucouleurs intensity law for an underlying galaxy. The broad band spectral energy distribution so derived is consistent with what is expected for an elliptical galaxy. The spectral index of the point source is alpha = 0.97. Additional VLBI and X-ray data are also reported for 1727+50. There is nebulosity associated with the recently discovered object 1218+304. No nebulosity is found associated with 1219+28. A comparison of the results with observations at X-ray and radio frequencies suggests that all the emission from 1727+50 and 1218+304 can be interpreted as due solely to direct synchrotron emission. If this is the case, the data further imply the existence of relativistic motion effects and continuous particle injection.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-TM-82090
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  • 175
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    Optical spectral variability of the N galaxies 3C 382 and 3C 390.3 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Multichannel spectrophotometry data acquired from 1969 to 1980 are used to study the absolute energy distribution and emission line variability of the N galaxies 3C 382 and 3C 390.3. It is shown that: (1) the continuum spectra can be decomposed into a nuclear nonthermal component of constant spectral shape and a constant elliptical galaxy component; (2) apparent visual magnitudes within a 10 arcsec aperture are derived for underlying galaxies, 3C 382 being 15.27 and 3C 390.3, 16.04; (3) forbidden lines and narrow Balmer lines do not change with the central continuum, but (4) the intensity variations of the broad Balmer lines are correlated nonlinearly with changes in the luminosity of the central continuum source. This correlation can be explained by a time-lag effect if there are two components of broad-line emission, one varying on a time scale of a few months and the other over a few years.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 248
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  • 176
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    The FK Comae stars (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The paper presents IUE observations of three very rapidly rotating G-K giants (v sin i = 100 km/s). The UV spectra show strong chromospheric and transition region emission lines similar to (and in excess of) the RS CVn binaries. These stars show no evidence for radial velocity variations in excess of plus or minus 3 to plus or minus 20 km/s, arguing against duplicity. As a class, they lend support to the rotation-activity hypothesis. Coalesced W UMa binaries, rather than single stars, are the possible progenitors for these FK Com variables.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 177
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    Observations of six flat spectrum sources from the 5 GHz survey (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Observations at radio, optical, and X-ray wavelengths of six sources from the Bonn-NRAO 5 GHz survey are reported. The sources were selected on the basis of their flux densities and spectral indices at 5 GHz. All have been shown to contain compact radio cores and to emit strongly at X-ray wavelengths; five are strongly polarized at optical wavelengths. The measured flux densities suggest that the sources are of comparable luminosity (per fractional bandwidth) in the X-ray and optical regions. The interpretation of these results in terms of a synchrotron-self-Compton mechanism is briefly discussed.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 178
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    IUE observations of eight dwarf novae - A study of the outburst cycle from 0.12 to 3.5 microns (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The dwarf novae are a class of close binary systems with a G-M star transferring mass to a white dwarf. The transferred material accumulates in a disk and accretes onto the white dwarf. Dwarf novae are characterized by outbursts on time scales of weeks to months possibly triggered by instabilities in the disk. To test the steady state models and the behavior of the disk at various stages of the outburst cycle, IUE observations were conducted for eight dwarf novae. Selected UV continuum points were joined to nonsimultaneous optical and IR spectrophotometry and broad-band photography to yield flux distributions over a large wavelength range. These flux distributions are discussed in terms of available accretion disk models.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 179
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    Outer atmospheres of cool stars. IX - A survey of ultraviolet emission from F-K dwarfs and giants with IUE (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Low-dispersion ultraviolet spectra (1150-2000 A) of a representative sample of cool stars, including dwarfs and giants of spectral types F-K, obtained with the IUE, are examined. The observation and the absolute calibration procedures are described. Correlation diagrams are constructed that compare chromospheric and transition-region emission line strengths and broadband coronal soft X-ray fluxes. The transition-region and coronal emission in the G-K dwarfs and G giants is well correlated with the Mg II (wavelength 2800) doublet emission strength, which is symptomatic of chromospheric energy losses. The power-law slopes are steeper than unity, particularly for soft X-rays. The implications of the correlations are discussed with respect to the weakening or disappearance of transition regions and hot coronae in the cool half of the red-giant branch and possible chromospheric and coronal heating mechanisms. It is proposed that the weakness of outer atmospheres in the red giants compared with the yellow giants can be understood as a consequence of stellar evolution, since it is possible that stars of slightly different spectral type in the giant branch have very different main-sequence progenitors.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 180
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    A planetary nebula with high oxygen abundance in the galactic bulge (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Extensive photoelectric spectra of the planetary nebula H1-55 in the galactic bulge are obtained, and indicate that the object is overabundant in oxygen and nitrogen. Temperature and density are estimated, and chi-square tests are used to place confidence limits on the result. The logarithmic oxygen abundance is found to be 9.50, and the abundance of other heavy elements are also enhanced, such as N = 8.87, S = 7.4, and Ar = 7.4. Helium, sulfur, and argon abundances are affected by uncertainties in the corrections for unobserved ions, which remains consistent with the exceptionally low electron temperature of less than 5600 K. Results agree with the usual models of planetary nebula formation; and therefore, if H1-55 is formed like most planetary nebulae, there must be some very metal-rich stars in the galactic bulge.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 181
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    An extended far-infrared emission complex at IC 1318b and IC 1318c (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: A map of extended 90 micron emission with 15 arcmin resolution is presented for sources centered on IC 1318b and c. A strong correlation is found between far-infrared emission and radio continuum emission, although a comparison of far-infrared and CO molecular line maps shows no similarity. Extended far-infrared sources have inferred gas densities, which implies that far-infrared emitting dust is mixed with the ionized gas. Far-infrared emission from dust is also observed in the nonthermal radio source DR 4 which is part of a supernova remnant, and the data are compatible with a core-halo model for the compact source DR 7.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 182
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    Concurrent radio, infrared, optical and X-ray observations of the nucleus of the Seyfert galaxy NGC 4151 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The nucleus of the Seyfert galaxy NGC 4151 was observed during May and June 1977 at X-ray energies from 20 to 200 keV using the high-energy X-ray spectrometer on OSO 8 at radio frequencies of 2695 and 8085. Data were also taken in the visual, and at infrared wavelengths of 1 to 2 microns, and from 2 to 6 keV using the OSO 8 proportional counter. Optical data showed variability by a factor of 2 within the observing period, which is comparable to the variability in the 2 to 6 keV X-ray flux. No variability, however, was measured at infrared or radio frequencies. The composite spectrum from radio to gamma-ray is plotted, and it is found that the optical and X-ray fluxes varied during the observing period, although it is not known if they varied concurrently.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 183
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    The C IV 1550 profile in type 1 Seyfert galaxies (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The paper presents C IV 1550 A line profiles for the type 1 Seyfert galaxies NGC 5548, Mrk 509, NGC 7469, and MCG-2-58-22. Several line broadening mechanisms and theoretical line profiles are considered, and random motion of discrete clouds is ruled out. A spherical ensemble of discrete clouds with steady outflow or inflow produces a logarithmic profile, but does not account for the highly extended wings. A spherical ensemble with ballistic outflow produces a profile of the first exponential integral function, and fits the observed profile to the continuum level. Although C IV profiles favor the ballistic model, both Mrk 509 and NGC 7469 have significant asymmetry, and Balmer lines with a higher optical depth show higher asymmetry and redshift than all four galaxies.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 184
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    Discovery of X-ray emission lines from the RS CVn binary sigma CrB (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: X-ray observations of the RS CVn binary sigma CrB were carried out with a solid state spectrometer on board the Einstein Observatory in 1979. X-ray emission lines due to Mg XI, Si XIII, S XV and a blend of L-transition lines due to Fe XVII and Fe XVIII were detected in the sigma CrB spectrum. The observed X-ray spectrum is described by a two-temperature coronal X-ray emission model: the dominant low temperature component originates in a plasma at a temperature of 5.9 + or 0.5 x 10 to the 6th K; the weaker higher temperature arises from a plasma of not less than 35 x 10 to the 6th K. Intensity variations over a period of a few hours are also recorded and thought to be due to a variation in the number of loops concentrated around active regions on the star surface. Implications of the results are discussed in terms of the constant-pressure coronal loop model (Rosner, Tucker, Vaiana, 1978).
    Schlagwort(e): ASTRONOMY
    Materialart: Royal Astronomical Society; vol. 196
    Format: text
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  • 185
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    Tidal evolution of the Galilean satellites - A linearized theory (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The Laplace resonance among the Galilean satellites Io, Europa, and Ganymede is traditionally reduced to a pendulum-like dynamical problem by neglecting short-period variations of several orbital elements. However, some of these variations that can now be neglected may once have had longer periods, comparable to the 'pendulum' period, if the system was formerly in deep resonance (pairs of periods even closer to the ratio 2:1 than they are now). In that case, the dynamical system cannot be reduced to fewer than nine dimensions. The nine-dimensional system is linearized here in order to study small variations about equilibrium. When tidal effects are included, the resulting evolution is substantially the same as was indicated by the pendulum approach, except that evolution out of deep resonance is found to be somewhat slower than suggested by extrapolation of the pendulum results. This slower rate helps support the hypothesis that the system may have evolved from deep resonance.
    Schlagwort(e): ASTRONOMY
    Materialart: Icarus; 46; June 198
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  • 186
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    The positions of secular resonance surfaces (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The surfaces for the three strongest secular resonances have been located as a function of proper semimajor axis, eccentricity, and inclination for semimajor axes between 1.25 and 3.5 AU. The results are presented graphically. The nu5 resonance only occurs at high inclinations (approximately greater than 23 deg). The nu6 resonance passes through both the main belt and Mars-crossing space. The nu16 resonance starts near the inner edge of the belt and, at low inclinations at least, folds around a portion of the Mars-crossing space until it runs nearly parallel with the earth-crossing boundary.
    Schlagwort(e): ASTRONOMY
    Materialart: Icarus; 46; June 198
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  • 187
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    The ultraviolet spectrum of the O-type subdwarf HD 49798 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The O-type subdwarf (O6p) single-lined spectroscopic binary HD 49798, with an orbital period of 1.5477 d, has been observed by the International Ultraviolet Explorer satellite, to aid in analyses of O type photospheres. Four high resolution (0.1A) spectra are found in the far-ultraviolet region, and two high resolution (0.2A) spectra are found in the mid-ultraviolet region. Numerous absorption lines are identified in the spectra of the star, most of which are attributable to Fe V lines at wavelengths of 1270 to 1500 A. Fe IV lines are also identified at wavelengths of 1500 to 1860 A. The strong Fe V features are found to have no corresponding analogs in the Kurucz and Peytremann (1975) list, and the total line blanketing for stars of spectral type O6 to B0 is discovered to be underestimated by at least a factor of four. In addition, mass loss from the subdwarf observed in the N V resonance doublet at wavelengths of 1238 A and 1242 A is discussed, indicating the existence of a hot stellar wind.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal Supplement Series; 46; July 198
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  • 188
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    Sco X-1 - A galactic radio source with an extragalactic radio morphology (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: VLA observations of radio emissions at 1465 and 4885 MHz, of Sco X-1 confirm the existence of a colinear triple structure. Evidence that the three components of Sco X-1 are physically associated is presented, including the morphology, spectrum, variability, volume emissivity and magnetic field strength. The possibility of a physical phenomenon occurring in Sco X-1 similar to that occurring in extragalactic radio sources is discussed, and two galactic sources are found having extended emission similar to that in extragalactic objects. The extended structure of Sco X-1 is also observed to be similar to that of the hot spots in luminous extragalactic sources, and a radio source 20 arcmin from Sco X-1 is found to lie nearly along the radio axis formed by the components of Sco X-1.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal; 86; July 198
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  • 189
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    Time elements in rectangular coordinates (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: In a paper by the second author (Nacozy, 1981), various time elements are presented for use with the Sundman time transformation. In that paper, the time elements are given in terms of Keplerian orbital elements. We give here the corresponding time elements in terms of rectangular coordinates. Extensive references are given in the previous paper and will be omitted here. We present additional numerical experiments comparing the use of time elements and time transformations together with the use of time transformations alone. The results indicate a reduction in computational error when time elements are used.
    Schlagwort(e): ASTRONOMY
    Materialart: Celestial Mechanics; 24; July 198
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  • 190
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    The hard X-ray spectrum of X Persei (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Results of observations of 3U 0352 + 30, the source associated with the X Persei system, in the energy range 12-180 keV are reported. The measurements were made on 1978 August 22 with the UCSD/MIT High-Energy X-ray and Low-Energy Gamma-ray Experiment on HEAO 1. Data taken simultaneously in the energy range 2-50 keV indicate that, in addition to a 7 keV thermal bremsstrahlung component, there is a second component of higher energy. It is found that this higher energy component fits a power law of photon index 1.3 (+0.4, -0.5) and is pulsed at the 13.95 minute period of the lower energy component.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
    Format: text
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  • 191
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    NGC 1097 - The structure of the central 3 kiloparsecs at 10 microns (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: It is found that the central, optically bright region of the spiral galaxy NGC 1097 is a strong 10 micron source. A striking correlation is seen between the optical and infrared surface brightnesses. The properties of these sources imply that young stars power the infrared emission. It is inferred that the central 30 arcsec of NGC 1097 has a large bolometric luminosity of about 10 to the 11th solar luminosities, most of which originates in a ring approximately 2 kpc in diameter. These observations strongly support the hypothesis that the infrared emission from galaxies is often associated with bursts of star formation.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 192
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    X-ray temperatures of distant clusters of galaxies (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The first X-ray temperature measurements of clusters of galaxies at high redshifts (z greater than 0.1), have been made using the Einstein X-ray Observatory. Evidence is found for decreasing X-ray temperature with increasing redshift. Results are consistent with the gravitational instability hypothesis for cluster formation and growth.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 247
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  • 193
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    The 1966 observations of the coorbiting satellites of Saturn, S10 and S11 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Most of the positions of faint satellite images obtained during the 1966 Saturn ring plane crossing fit the period of the coorbital satellites 1980 S1 and 1980 S3. In 1966 the satellites were separated by 137 deg in orbital longitude. Until the mutual interaction of the satellites is understood and applied to derive the precise orbital motion, the 1966 and 1980 observations cannot be linked.
    Schlagwort(e): ASTRONOMY
    Materialart: Icarus; 46; May 1981
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  • 194
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    On the computation of acceleration parallaxes (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: Rigorous formulas are derived with which one can compute from three observed (coplanar) directions the proper-motion components and the product of parallax and radial velocity of an object (star) which moves uniformly with respect to the observer (earth). The errors of the determination of distance by parallactic acceleration are analyzed and the possibility of determining distances by this method is discussed.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal; 86; June 198
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  • 195
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    Apsidal precession of orbits about an oblate planet (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: It is noted that expressions for the apsidal precession rates to second order on J2 appear in the literature in at least three apparently mutually contradictory forms. The expressions are reconciled by accounting for subtle differences in the definitions of orbital elements.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal; 86; June 198
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  • 196
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    HM Sagittae - Symbiotic cousin of the RS CVn stars (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: In the brief time since its brightening in 1975, the optical spectrum of HM Sagittae has shown considerable variation in both its general characteristics and relative line intensity ratios. The observations place HM Sagittae in a small class of objects which are thought to be proto-planetary nebulae, of which V 1016 Cygni is the prototype. Attention is given to derived density and temperature, helium abundance and nebular mass, and an evolutionary scenario. The considered observations show a decrease in the intensity of the continuum and a continuation of the trend toward higher excitation in the spectrum of HM Sagittae. Parallels are seen in the development of this object and V 1016 Cygni, with the implication that the trend toward higher excitation is expected to continue.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics; 99; 1, Ju; June 198
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  • 197
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    Low-energy X-ray line emission from IC 443 (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: HEAO 1 observations of the spectrum of the supernova remnant IC 443 in the energy range of 0.4-3 keV reveal the presence of a complex structure suggestive of emission from Fe XVIII-XX, S XV-XVI, and Si XIII-XIV ions. The best electron temperature in the band for simple model fits is about (6-11) x 10 to the 6th K. Raymond and Smith collisional equilibrium emission models do not adequately fit the data. These results are discussed in terms of possible nonequilibrium effects in the remnant.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
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  • 198
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    A high-resolution study of the gas flow in barred spirals (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The considered investigation is concerned with conditions in that type of spiral galaxy which is known as a 'barred spiral'. The lack of star formation and the smoothness of the dark dust lanes may indicate that the bar region is pervaded by a more homogeneous interstellar medium with a lower viscosity than that characteristic of the outer regions. The effects of such a reduced viscosity are investigated on the basis of high-resolution time-dependent gasdynamical equations. Calculations modeling the gas flow in a given bar potential are presented. The calculations were performed on grids with various mesh sizes and consequently had different resolutions and numerical viscosities. A reduction in the numerical diffusion and viscosity was accompanied by changes in the flow pattern, including the appearance of a strong shock in the bar region and the occurrence of postshock outflow.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
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  • 199
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    Ultraviolet extinction curves derived from IUE data (1981)
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    Publikationsdatum: 2019-06-28
    Beschreibung: Data from the International Ultraviolet Explorer (IUE) have been used to derive extinction curves for several stars chosen because of unusual diffuse band strength or location within dense clouds. Both the strength and position of the 2200 A extinction maximum were assessed, as well as the level of extinction in the far-ultraviolet. A variety of combinations of these features were found, ranging from near or complete absence of a 2200 A bump (HD 29647), to low far-ultraviolet extinction (Rho Oph), to unusually steep, far-ultraviolet extinction (HD 169454). Anomalous extinction apparently shows up frequently in stars associated with nebulosity or dense clouds. The apparent independence of 2200 A and far-ultraviolet extinction supports earlier suggestions that these two features are created by distinct populations of grains.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
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    High energy X-ray observations of the 38-second pulsar (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The results of observations of the 38-second pulsar obtained at high X-ray energies (13-180 keV) with the UCSD/MIT instrument aboard HEAO 1 are reported. The results include a measurement of the source location, measurement of the pulse profile, and determination of the average intensity and spectrum during each of three time intervals spanning a baseline of 1 year. The total intensity of the pulsar is seen to vary on a 6-month time scale. The spectrum is hard but, like other X-ray pulsars, steepens at energies above 20 keV.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal; vol. 246
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