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Articles 8761 - 8790 of 9199

Full-Text Articles in Physical Sciences and Mathematics

The Hydrogen Line Spectra Of Narrow-Line Radio Galaxies, Gary J. Ferland, Donald E. Osterbrock Feb 1985

The Hydrogen Line Spectra Of Narrow-Line Radio Galaxies, Gary J. Ferland, Donald E. Osterbrock

Physics and Astronomy Faculty Publications

We report the results of the first detection of Lyα in a narrow-line radio galaxy. Nearly simultaneous optical and UV observations of 3C 192 and 3C 223 allow the measurement of both Balmer and Lyman decrements. These line ratios are approximate functions of the interstellar reddening and of a parameter which is proportional to the amount of H I collisional excitation present. The reddening of 3C 192 is slightly larger than that due to our Galaxy, although 3C 223 may have a larger value. Both galaxies have intrinsic Balmer and Lyman decrements which are significantly steeper than case B, …

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Example Of A Group Action Determined Phase Transition, Jeffrey W. Felix, Dorian M. Hatch Feb 1985

Example Of A Group Action Determined Phase Transition, Jeffrey W. Felix, Dorian M. Hatch

Faculty Publications

The principles of the group action approach to structural phase transitions are outlined. It is assumed that all properties of the transition are determined by the action of a single physically irreducible represention of the space group of the more symmetric phase. We determine the isotropy groups using the image space of the representation. The free energy minima are determined to fourth order and to all orders using the results of Gufan and then compared. This theory is applied to Calcite (Roverline3c) to determine all possible continuous commensurate phase transitions.

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High Dispersion Untraviolet Spectra Of The Peculiar Star Rx Puppis, Menas Kafatos, A. G. Michalitsianos, R. P. Fahey Jan 1985

High Dispersion Untraviolet Spectra Of The Peculiar Star Rx Puppis, Menas Kafatos, A. G. Michalitsianos, R. P. Fahey

Mathematics, Physics, and Computer Science Faculty Articles and Research

High spectral resolution observations of the peculiar star RX Puppis obtained with the International Ultraviolet Explorer suggest the presence of a complex gaseous ring system which surrounds an accreting hot secondary. The anomalous line intensity ratio of the C IV A.A-1548, 1550 doublet during the observations exceeded the optically thick limit, implying the presence of a high-velocity wind. Additionally, the C IV doublet exhibits about four or five narrow emission components, which are redshifted up to velocities of at least - + 300 km s -I (with respect to the rest wavelength).

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The R Aquarii System At Optical And Radio Wavelengths, J. M. Hollis, Menas Kafatos, A. G. Michalitsianos, H. A. Mcalister Jan 1985

The R Aquarii System At Optical And Radio Wavelengths, J. M. Hollis, Menas Kafatos, A. G. Michalitsianos, H. A. Mcalister

Mathematics, Physics, and Computer Science Faculty Articles and Research

Observations of the symbiotic binary R Aquarii environment were obtained with the Very Large Array (VLA) at 2, 6, and 20 em at the same epoch. The observed spectral index and strong linear polarization reveal that emission from the compact double radio source discovered in previous observations is nonthermal; thus, this source is not associated with R Aquarii but is an extragalactic background object. The spectral index of the compact nebula surrounding R Aquarii indicates that the emission is thermal and the nebula is ionized by an unseen, hot companion to the Mira-like variable R Aquarii. As expected, this region …

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Observations Of Shadow Bands At The Total Solar Eclipse Of 16 February 1980, Laurence A. Marschall, Rita Mahon, Richard C. Henry Dec 1984

Observations Of Shadow Bands At The Total Solar Eclipse Of 16 February 1980, Laurence A. Marschall, Rita Mahon, Richard C. Henry

Physics and Astronomy Faculty Publications

Photoelectric observations of short term light variations (shadow bands) at the 16 Feb. 1980 total solar eclipse have been made using a set of spatially separated PIN diodes. Light variations in a bandpass of 1-500 Hz were detected during the half-minutes preceding and following the total phase. Fourier analysis of the noise spectrum of the variations reveals a sharp drop-off for frequencies about 50 Hz and an overall spectrum quite similar to previously reported power spectra of stellar scintillation. This is consistent with an atmospheric origin for the shadow bands. Cross-correlations between the detector outputs are low, suggesting a short …

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Civilian Space Stations And The U.S. Future In Space, U.S. Office Of Technology Assessment Nov 1984

Civilian Space Stations And The U.S. Future In Space, U.S. Office Of Technology Assessment

Space Law Documents

After the expenditure of some $200 billion (1984$) since the launch of its first spacecraft in early 1958, the United States has obtained the scientific knowledge and developed the technological capability and professional expertise to succeed in virtually any theoretically possible civilian space venture that it may choose to undertake, But America’s second quarter-century of space activities promises to differ markedly from the first, almost wholly exploratory, era. If space is to be successfully developed in roughly the same fashion as have other, more familiar natural resources and environments, the next stage will be characterized by establishing and securing the …

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Cosmic Rays And The Emission-Line Regions Of Active Galactic Nuclei, Gary J. Ferland, R. F. Mushotzky Nov 1984

Cosmic Rays And The Emission-Line Regions Of Active Galactic Nuclei, Gary J. Ferland, R. F. Mushotzky

Physics and Astronomy Faculty Publications

We discuss the effects that the synchrotron emitting relativistic electrons, which are known to exist throughout many distance scales in active nuclei, could have on the emission-line regions that characterize these objects. Detailed models of both the inner, dense, broad-line region and the outer, lower density, narrow-line region are presented, together with the first models of the optically emitting gas often found within extended radio lobes. We show that, in all cases, if the relativistic gas that produces the synchrotron radio emission is mixed with the gas in the emission-line region, then significant changes in the emission-line spectrum will result. …

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Radiation Pressure And The Stability Of Broad-Line Region Clouds, Gary J. Ferland, Moshe Elitzur Oct 1984

Radiation Pressure And The Stability Of Broad-Line Region Clouds, Gary J. Ferland, Moshe Elitzur

Physics and Astronomy Faculty Publications

We discuss two constraints on the existence and stability of quasar emission-line gas. The case of a constant pressure photoionized cloud in pressure equilibrium with a surrounding hot gas is considered. We show that the radiation pressure of the internally generated line emission makes a significant contribution to the total pressure in standard broad-line region models, and that models with either a higher ionization parameter or lower gas density are dominated by radiation pressure and hence unstable. Further, clouds with ionization parameters lower than the standard value cannot be supported by any hot gas which is heated only by the …

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The Adsorption Of Atmospheric Xenon And Inert Gas Measurements In Size Separates Of The Allende Meteorite, Russel L. Palma Aug 1984

The Adsorption Of Atmospheric Xenon And Inert Gas Measurements In Size Separates Of The Allende Meteorite, Russel L. Palma

Physics and Astronomy Department Publications

No abstract provided.

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Iue Observations Of Dq Herculis And Its Nebula, And The Nature Of The Cold Nova Shells, Gary J. Ferland, R. E. Williams, D. L. Lambert, G. A. Shields, M. Slovak, P. M. Gondhalekar, J. W. Truran Jun 1984

Iue Observations Of Dq Herculis And Its Nebula, And The Nature Of The Cold Nova Shells, Gary J. Ferland, R. E. Williams, D. L. Lambert, G. A. Shields, M. Slovak, P. M. Gondhalekar, J. W. Truran

Physics and Astronomy Faculty Publications

The nebula ejected in the 1934 outburst of the classical nova DQ Her is remarkable for its unprecedentedly low temperature of Te 500 K as measured by Williams et al. (1978). In this paper, IUE observations are combined with Steward optical spectra. It is confirmed that the gas is quite cold. It is further shown that the gas is ionized by the radiation field of the central object. X-ray, ultraviolet, optical and infrared observations of the underlying binary are combined with the extreme-ultraviolet continuum deduced from the level of ionization of the nebula to obtain a composite energy …

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Isotropy Group Description Of A Phase Transition In Nano3, W. Scott Stornetta, Dorian M. Hatch Jun 1984

Isotropy Group Description Of A Phase Transition In Nano3, W. Scott Stornetta, Dorian M. Hatch

Faculty Publications

Predictions of the possible post-transition symmetries of an R 3c zone center continuous phase transition are made using recent extensions of the Landau theory. The Landau theory is summarized and direct group theoretical methods are applied to the R 3c phase. General techniques for solving systems of nonlinear polynomial equations are reviewed and these techniques are applied to the minimization of the free energy F for the aforementioned possible symmetries. The results of the direct methods and the minimization procedures are shown to be compatible. It is shown that the transition to R 3c in NaNO3 is consistent with the …

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Spectroscopic Studies Of 4u1735 – 44; Evidence For Binary Motion, A. P. Smale, P. A. Charles, I. R. Tuohy, J. R. Thorstensen Mar 1984

Spectroscopic Studies Of 4u1735 – 44; Evidence For Binary Motion, A. P. Smale, P. A. Charles, I. R. Tuohy, J. R. Thorstensen

Dartmouth Scholarship

We have obtained optical spectroscopy of the X-ray burst source 4U1735 – 44 with spectral resolution of ∼ 1.6 Å and a time resolution of ∼ 30 min. There is strong evidence for cyclic He II velocity variations, but we are unable to confirm or deny either of the previously reported possible binary periodicities in the source. However, kinematic arguments suggest that the companion can be classified as being of spectral type F0–K5 V and the presence of the Ca II K interstellar absorption line at λ 3933 leads to a lower limit on the distance of the source of …

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The Effect Of Viscosity On Impact Cratering And Possible Application To The Icy Satellites Of Saturn And Jupiter, Jonathan H. Fink, Donald Gault, Ronald Greeley Jan 1984

The Effect Of Viscosity On Impact Cratering And Possible Application To The Icy Satellites Of Saturn And Jupiter, Jonathan H. Fink, Donald Gault, Ronald Greeley

Geology Faculty Publications and Presentations

Impact experiments in Newtonian fluids with a range of viscosities of 10-3 to 60 Pa s demonstrate that transient prater volume and shape (depth-to-diameter: ratio) depend on target viscosity as well as on gravity. Volume is reduced, and depth-to-diameter ratio is increased for cratering events in which viscosity plays a dominant role. In addition to being affected by target kinematic viscosity, viscous scaling is most strongly influenced by projectile diameter, less strongly by projectile velocity, and least strongly by gravity. In a Planetary context, viscols effects can occur for craters formed by small or slow moving impacting bodies, low …

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Variable Ultraviolet Emission In Sy Muscae, A. G. Michalitsianos, Menas Kafatos Jan 1984

Variable Ultraviolet Emission In Sy Muscae, A. G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Following the enhancement in ultraviolet flux which we reported previously, we have continued monitoring the symbiotic variable SY Muscae with the International Ultraviolet Explorer (JUE). Over the course of one year, the prominent emission lines of N v, 0 v, C rv, He II appear to be gradually decreasing in absolute intensity. This appears to coincide with a steady decline in electron density in the emission line forming region, as suggested from the Sim] :\1892 and Cm] :\1909 intensity ratio. Our data is consistent with a sudden ejection event in which material expelled from the surface of a hot Teff …

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Stimulated Emission And The Flat Balmer Decrements Of Cataclysmic Variable Stars, Moshe Elitzur, Gary J. Ferland, W. G. Mathews, G. A. Shields Sep 1983

Stimulated Emission And The Flat Balmer Decrements Of Cataclysmic Variable Stars, Moshe Elitzur, Gary J. Ferland, W. G. Mathews, G. A. Shields

Physics and Astronomy Faculty Publications

Balmer emission lines from cataclysmic variables often have nearly equal intensities rather than the rapid decrement predicted by simple nebular theory. Traditionally, this has been interpreted in terms of local thermodynamic equilibrium emission from a dense gas with small volume located just above the accretion disk. In this Letter we show that the intense radiation field within a close binary system can affect excited-state populations and optical emission in ways which allow a relatively low density gas to closely mimic the high-density situation. In at least one case, the old nova V603 Aql, the emitting gas has a low density …

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Development Of A Mass Spectrometer System For The Measurement Of Inert Gases In Meteorites, Russel L. Palma Sep 1983

Development Of A Mass Spectrometer System For The Measurement Of Inert Gases In Meteorites, Russel L. Palma

Physics and Astronomy Department Publications

No abstract provided.

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Unification Of Ernst-Equation Backlund Transformations Using A Modified Wahlquist-Estabrook Technique; Wahlquist-Estabrook, B. Kent Harrison Aug 1983

Unification Of Ernst-Equation Backlund Transformations Using A Modified Wahlquist-Estabrook Technique; Wahlquist-Estabrook, B. Kent Harrison

Faculty Publications

The three known Backlund transformations for the Ernst equation are derived using a modification of the Wahlquist-Estabrook prolongation procedure. The modification requires that the equation to be studied be cast into a set of differential forms and their exterior derivatives, such that all coefficients are constant (a "CC ideal''). Analysis of the resulting equations produces 16 solutions composed of the three basic transformations combined with identity and other essentially trivial transformations. The group structure of the transformations is discussed. A Backlund transformation (already known) for the Ernst-Maxwell equations can be found by the same method. Promising generalizations are mentioned.

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Photometric And Spectroscopic Observations Of An Optical Candidate For The X-Ray Source H 0544 - 665, M. Van Der Klis, J. Van Paradijs, P. A. Charles, J. R. Thorstensen Jun 1983

Photometric And Spectroscopic Observations Of An Optical Candidate For The X-Ray Source H 0544 - 665, M. Van Der Klis, J. Van Paradijs, P. A. Charles, J. R. Thorstensen

Dartmouth Scholarship

We present the results of spectroscopic and UBV observations of the brightest star in the error box of the X-ray source H 0544–665. This object is a B0–1 V star and a member of the LMC. It shows correlated variations in brightness and colour indices. We suggest that it is a Be-type star observed during a stage of low emission strength. Although a relation between this star and the X-ray source has still to be proven the present data add considerable support to the proposed identification.

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Colonial Astronomers In Search Of The Longitude Of New England, Richard F. Rothschild Apr 1983

Colonial Astronomers In Search Of The Longitude Of New England, Richard F. Rothschild

Maine History

This article deals with aspects of progress made between 1755 and 1785 to identify the longitude of New England and the reasons for the failure of the Harvard-American Academy of Arts and Sciences expedition to Penobscot to see the totality of the solar eclipse of October 27 1780.

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Extreme Variability In The Be-Type, Periodic Recurrent X-Ray Transient A0538 - 66: A Highly Eccentric Interacting Binary, P. A. Charles, L. Booth, R. H. Densham, G. T. Bath, J. R. Thorstensen Mar 1983

Extreme Variability In The Be-Type, Periodic Recurrent X-Ray Transient A0538 - 66: A Highly Eccentric Interacting Binary, P. A. Charles, L. Booth, R. H. Densham, G. T. Bath, J. R. Thorstensen

Dartmouth Scholarship

We present optical spectroscopy and photometry and IUE spectroscopy of the counterpart of the extremely powerful LMC recurrent X-ray transient A0538 – 66. During one 16.6 day outburst cycle at the end of 1980 December the optical spectra show steadily increasing Balmer and He I emission (indicative of an expanding envelope) superposed on a B2 III–IV spectrum. There is a substantial optical brightness increase of 2 mag at the peak, accompanied by the sudden turn-on of He IIλ 4686. These and other optical spectra show significant radial velocity changes but we can find no clear correlation with the 16.6 …

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Mm Herculis: An Eclipsing Binary Of The Rs Cvn Type, James R. Sowell, Douglas S. Hall, Gregory W. Henry, Edward W. Burke Jr., Eugene F. Milone Jan 1983

Mm Herculis: An Eclipsing Binary Of The Rs Cvn Type, James R. Sowell, Douglas S. Hall, Gregory W. Henry, Edward W. Burke Jr., Eugene F. Milone

Information Systems and Engineering Management Research Publications

Differential photoelectric photometry in V, B, and U has been obtained for the eclipsing binary MM Her, a member of the RS Canum Venaticorum class. The light outside eclipse was Fourier-analyzed to study the wave. The migration and amplitude of the wave and the mean light level of the system now have been monitored from 1976 through 1980. The phase of wave minimum has decreased from 0P.80 to 0P.25, the wave amplitude has varied between 0m.06 and 0m.12, and the mean light level has fluctuated between 0.94 and 0.99. Observations …

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Implicit Total Variation Diminishing (Tvd) Schemes For Steady-State Calculations, H. C. Yee, R. F Warming, A. Harten Jan 1983

Implicit Total Variation Diminishing (Tvd) Schemes For Steady-State Calculations, H. C. Yee, R. F Warming, A. Harten

United States National Aeronautics and Space Administration: Publications

We examine the application of a new implicit unconditionally-stable high-resolution TVD scheme to steady-state calculations. It is a member of a one-parameter family of explicit and implicit second-order accurate schemes developed by Harten for the computation of weak solutions of one-dimensional hyperbolic conservation laws. This scheme is guaranteed not to generate spurious oscillations for a nonlinear scalar equation and a constant coefficient system. Numerical experiments show that this scheme not only has a fairly rapid convergence rate, but also generates a highly-resolved approximation to the steady-state solution. A detailed implementation of the implicit scheme for the one- and two-dimensional compressible …

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Are There Any Shock-Heated Galaxies?, Gary J. Ferland, Hagai Netzer Jan 1983

Are There Any Shock-Heated Galaxies?, Gary J. Ferland, Hagai Netzer

Physics and Astronomy Faculty Publications

We study the spectroscopic characteristics of low ionization nuclear emission-line regions (Liners) in galaxies, and compare them with other active galactic nuclei. We show the results of new, extensive photoionization model calculations and use them to investigate line ratio diagrams, such as [O III] λ5007/Hβ versus [O II] λ3727/[O III] λ5007, and [O I] λ6300/[O III] λ5007 versus [O III] λ3727/[O III] λ5007. On the diagrams broad line objects, Seyfert 2 galaxies, and Liners form a continuous smooth sequence of decreasing ionization parameter. This suggests a common origin for line excitation in …

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High Spatial Resolution Vla Observations Of The R Aquarii Jet, Menas Kafatos, J. M. Hollis, A. G. Michalitsianos Jan 1983

High Spatial Resolution Vla Observations Of The R Aquarii Jet, Menas Kafatos, J. M. Hollis, A. G. Michalitsianos

Mathematics, Physics, and Computer Science Faculty Articles and Research

High spatial resolution observations (~1") of the jet feature associated with the symbiotic variable R Aquarii were obtained with the Very Large Array (VLA). The peak radio intensity of the jet lies at a 29~3 P.A. with respect to the radio emission from R Aquarii itself. If the line defined by the jet and star is extended ~196", it intercepts a previously reported and heretofore unresolved radio source. In our high spatial resolution 6 cm map, this feature is resolved into a compact double radio source, whose peak intensity lies on an axis defined by the jet and star. The …

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The High-Energy Spectrum Of Hot Accretion Disks, J. A. Eilek, Menas Kafatos Jan 1983

The High-Energy Spectrum Of Hot Accretion Disks, J. A. Eilek, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

A hot, two-temperature accretion disk can be a strong γ-ray and relativistic particle source. This occurs when the accretion rate is high enough -- M/ M ≥ 3 X 10^-9 α γr^-1 for a canonical Kerr black hole-due to the high ion temperature in the inner disk. We present detailed photon and particle spectra for specific disk models. The predicted γ-ray flux is as high as 10% of the bolometric luminosity in sub-Eddington models. Most of the γ-radiation is continuous, due to the π^0 decay, emitted around 100 MeV but degraded to a few MeV in optically thick models. Spectral …

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Observations Of Two Peculiar Emission Objects In The Large Magellanic Cloud, Menas Kafatos, A. G. Michalitsianos, D. A. Allen, R. E. Stencel Jan 1983

Observations Of Two Peculiar Emission Objects In The Large Magellanic Cloud, Menas Kafatos, A. G. Michalitsianos, D. A. Allen, R. E. Stencel

Mathematics, Physics, and Computer Science Faculty Articles and Research

Ultraviolet and visual wavelength spectra were obtained of two peculiar emission objects, Henize S63 and Sanduleak.'s star in the Large Magellanic Cloud. Previously not observed in the near- or far-ultraviolet, both objects exhibit strong permitted and semiforbidden line emission. Estimates based on the absolute continuum flux of the hot companion star in Hen S63 indicate that it rivals the luminosity of the carbon star primary. The emission-line profile structure in both objects does not suggest Wolf-Rayet type emission. Carbon in Sanduleak.'s star (LMC anonymous) is conspicuously absent, while N v, N IV], and N III] dominate the UV emission-line spectrum. …

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The Mystery Of The Missing Boundary Layer, Gary J. Ferland, S. S. Langer, J. Macdonald, G. H. Pepper, G. Shaviv, J. W. Truran Nov 1982

The Mystery Of The Missing Boundary Layer, Gary J. Ferland, S. S. Langer, J. Macdonald, G. H. Pepper, G. Shaviv, J. W. Truran

Physics and Astronomy Faculty Publications

The question of the nature of the ultraviolet and X-ray radiation field of cataclysmic binaries is addressed. The spectrum and luminosity of this radiation are important in determining the mass transfer rate and energy budget of the system and in studies of the ejecta surrounding novae. In many systems, the soft X-ray luminosity is ~ 102-104 times weaker than predicted by simple accretion models. We discuss several possible solutions to this discrepancy. The most likely are either that the optical luminosity of a typical old nova is produced partly by reprocessed ultraviolet light from the white dwarf, …

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Broad Line Region Clouds And The Absorbing Material In Ngc 4151, Gary J. Ferland, R. F. Mushotzky Nov 1982

Broad Line Region Clouds And The Absorbing Material In Ngc 4151, Gary J. Ferland, R. F. Mushotzky

Physics and Astronomy Faculty Publications

The constraints imposed by X-ray, ultraviolet, and optical observations on the absorbing material in the Seyfert 1.5 galaxy NGC 4151 are discussed. These observations are compared to the predictions of photoionization models of both broad line region clouds, which Holt et al. identify as the source of the extinction, and to models of the narrow line region gas. The weakness of both C III] 1909 and the broad component of Hα relative to C IV 1549, together with the absence of an absorption Balmer jump, indicate that the ionization parameter for the broad line region is a factor …

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Membership Of The Rosette Nebula Cluster, Ngc 2244, Laurence A. Marschall, William F. Van Altena, Liang-Tai George Chiu Nov 1982

Membership Of The Rosette Nebula Cluster, Ngc 2244, Laurence A. Marschall, William F. Van Altena, Liang-Tai George Chiu

Physics and Astronomy Faculty Publications

Relative proper motions for 287 stars in the region of the young open cluster NGC 2244, located in the Rsette Nebula, have been determined from plates taken with the Yerkes 40-in. and the Allegheny 30-in. refractors. Probabilities of membership based on these proper motions are derived. Because probable members are chosen primarily from kinematic considerations, the sample should show a minimum photometric bias. Differential extinction across the cluster, however, is identified as a complication in the immediate interpretation of the sample in terms of color-magnitude diagrams or luminosity functions.

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Physical Conditions In The Accretion Disk Of V603 Aquilae, Gary J. Ferland, D. L. Lambert, M. L. Mccall, G. A. Shields, M. Slovak Sep 1982

Physical Conditions In The Accretion Disk Of V603 Aquilae, Gary J. Ferland, D. L. Lambert, M. L. Mccall, G. A. Shields, M. Slovak

Physics and Astronomy Faculty Publications

Ultraviolet and optical spectra of the old nova V603 Aql are discussed. The UV-optical continuum is dominated by emission from the accretion disk. Emission lines from ions of H, He, C, N, and 0 are identified. These lines are probably formed in a circumstellar shell with radius comparable to the binary separation, density ~1010 cm-3, and a roughly solar chemical composition. This corona is probably heated by radiation emitted by the underlying accretion disk. Photoionization calculations of the structure and emission-line spectrum of the corona are presented, and the effects of this gas on the X-ray continuum …

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