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Articles 8701 - 8730 of 9199

Full-Text Articles in Physical Sciences and Mathematics

Chromospherically Active Stars. Vii. 39 Ceti=Ay Ceti, Hd185151=V1764 Cygni, And Binary Synchronization, Francis C. Fekel, Joseph J. Eitter Apr 1989

Chromospherically Active Stars. Vii. 39 Ceti=Ay Ceti, Hd185151=V1764 Cygni, And Binary Synchronization, Francis C. Fekel, Joseph J. Eitter

Information Systems and Engineering Management Research Publications

Improved orbital elements have been determined for 39 Ceti and HD 185151.39 Cet has a circular orbit with an orbital period of 56.82 days, which differs substantially from its rotational period of 75-78 days. An observation of the lithium region of 39 Cet shows that the G5 III component has almost no lithium in its outer atmosphere. HD 185151 has a circular orbit with an orbital period of 40.142 days and has a nearly identical rotational period. The large mass function suggests that the secondary is a late A to mid F type star whose continuum should be visible at …

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Semi-Implicit And Fully Implicit Shock-Capturing Methods For Nonequilibrium Flows, Helen C. Yee, Judy L. Shinn Mar 1989

Semi-Implicit And Fully Implicit Shock-Capturing Methods For Nonequilibrium Flows, Helen C. Yee, Judy L. Shinn

United States National Aeronautics and Space Administration: Publications

Some numerical aspects of finite-difference algorithms for nonlinear multidimensional hyperbolic conservation laws with stiff nonhomogeneous (source) terms are discussed. If the stiffness is entirely dominated by the source term, a semi-implicit shock-capturing method is proposed. However, if the stiffness is not solely dominated by the source terms, a fully implicit method would be a more efficient solution procedure. The primary motivation for constructing these schemes was to address large systems of thermally and chemically nonequilibrium flows in the hypersonic regime. Due to the unique structure of the eigenvalues and eigenvectors for fluid flows of this type, the computation can be …

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A Class Of High-Resolution Explicit And Implicit Shock-Capturing Methods, Helen C. Yee Feb 1989

A Class Of High-Resolution Explicit And Implicit Shock-Capturing Methods, Helen C. Yee

United States National Aeronautics and Space Administration: Publications

The development of shock-capturing finite difference methods for hyperbolic conservation laws has been a rapidly growing area for the last decade. Many of the fundamental concepts, state-of-the-art developments and applications to fluid dynamics problems can only be found in meeting proceedings, scientific journals and internal reports. This paper attempts to give a unified and generalized formulation of a class of high-resolution, explicit and implicit shockcapturing methods, and to illustrate their versatility in various steady and unsteady complex shock waves, perfect gases, equilibrium real gases and nonequilibrium flow computations. These numerical methods are formulated for the purpose of ease and efficient …

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On The Size Distribution Of Newly Formed Grains In Red Supergiant Atmospheres, C Gregory Seab, Theodore P. Snow Jan 1989

On The Size Distribution Of Newly Formed Grains In Red Supergiant Atmospheres, C Gregory Seab, Theodore P. Snow

Physics Faculty Publications

Theoretical ultraviolet extinction curves have been calculated for comparison with observed curves for circumstellar dust in M supergiants. The theoretical curves assumed a silicate grain composition, because silicate grains are expected in the oxygen-rich environments that are observed. Calculations were performed with and without the inclusion of scattering into the beam, with largely similar results. A comparison of the computed curves with the observed ultraviolet extinction curve for circumstellar dust in Scorpii indicates that the size distribution of the circumstellar grains must cut off near 800 Å that is, there are few or no grains smaller than this. Our conclusion …

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Predicting Peculiar Interstellar Extinction From Gaseous Abundances, Charles L. Joseph, Theodore P. Snow, C Gregory Seab Jan 1989

Predicting Peculiar Interstellar Extinction From Gaseous Abundances, Charles L. Joseph, Theodore P. Snow, C Gregory Seab

Physics Faculty Publications

Molecular and atomic abundances are examined for 19 lines of sight through dense clouds, each with a peculiar selective extinction curve. The interstellar clouds in the present study appear to fall into two distinct categories: CN-rich, with relatively small amounts of neutral iron, or CN-poor, with large amounts of neutral iron. Lines of sight, having a CN/(Fe i) abundance ratio about two (~ 0.3 dex) or greater, are found to have a shallow (2.57 ± 0.55 mag) 2175 Å feature relative to the underlying extinction, while the strength of the bump is 3.60 ± 0.36 for the other dense clouds …

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A Search For Interstellar And Circumstellar C60, T P. Sno, C G. Seab Jan 1989

A Search For Interstellar And Circumstellar C60, T P. Sno, C G. Seab

Physics Faculty Publications

It has recently been suggested that the diffuse interstellar bands may be formed by ionized polyhedral carbon molecules such as C60(+). While specific laboratory measurements of absorption bands of this molecular ion have not been made, a feature due to the neutral molecule C60 has been discovered at 3860A. Examination of spectra of several reddened stars, as well as one star known to have circumstellar carbonaceous dust, shows no sign of the feature, leading to upper limits of the order of 10 to the 14th/sq cm for the column density of C60. These limits are not yet sensitive enough to …

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Scattering Of Light By Stochastically Rough Particles, J.I. Peltoniemi, K. Lumme, K. Muinonen, William Irvine Jan 1989

Scattering Of Light By Stochastically Rough Particles, J.I. Peltoniemi, K. Lumme, K. Muinonen, William Irvine

William M. Irvine

The single particle phase function and the linear polarization for large stochastically deformed spheres have been calculated by Monte Carlo simulation using the geometrical optics approximation. The radius vector of a particle is assumed to obey a bivariate lognormal distribution with three free parameters: mean radius, its standard deviation and the coherence length of the autocorrelation function. All reflections/refractions which include sufficient energy have been included. Real and imaginary parts of the refractive index can be varied without any restrictions. Results and comparisons with some earlier less general theories are presented. Applications of this theory to the photometric properties of …

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Chromospherically Active Stars. Vi. Hd 136901 = Uv Crb: A Massive Ellipsoidal K Giant Single-Lined Spectroscopic Binary, Francis C. Fekel, J. Davy Kirkpatrick, Xinxing Yang, Klaus G. Strassmeier Jan 1989

Chromospherically Active Stars. Vi. Hd 136901 = Uv Crb: A Massive Ellipsoidal K Giant Single-Lined Spectroscopic Binary, Francis C. Fekel, J. Davy Kirkpatrick, Xinxing Yang, Klaus G. Strassmeier

Information Systems and Engineering Management Research Publications

The variable star HD 136901 = UV CrB is a chromospherically active K2 III single-lined spectroscopic binary with an orbital period of 18.665 days. It has modest-strength Ca H and K emission and UV features, while H-alpha is a strong absorption feature containing little or no emission. The inclination of the system is 53 + or - 12 deg. The v sin i of the primary is 42 + or - 2 km/s, resulting in a minimum radius of 15.5 + or - 0.8 solar. When compared with the Roche lobe radius, this results in a mass ratio of 2.90 …

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The Photometric Variability Of The Chromospherically Active Binary Star Hd 80715, Klaus G. Strassmeier, James T. Hooten, Douglas S. Hall, Francis C. Fekel Jan 1989

The Photometric Variability Of The Chromospherically Active Binary Star Hd 80715, Klaus G. Strassmeier, James T. Hooten, Douglas S. Hall, Francis C. Fekel

Information Systems and Engineering Management Research Publications

Differential UBVRI photometry of the double-lined BY Dra system HD 80715 (K3 V + K3 V) obtained in December 1987 is presented. The star is found to be a variable with a full amplitude of 0.06 mag in V and a period similar or equal to the orbital period of 3.804 days. The mechanism of the variability is interpreted as rotational modulation due to dark starspots. In an attempt to detect chromospheric activity, high-resolution CCD spectra were obtained at Ca II H and K and at Fe I 6430 A and Ca I 6439 A, the photospheric lines normally used …

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Sanduleak's Star (Lmc Anonymous): Its Similarity In The Far-Ultraviolet With The Luminous Object N Carinae And Sn 1987a, A. G. Michalitsianos, Menas Kafatos, S. N. Shore Jan 1989

Sanduleak's Star (Lmc Anonymous): Its Similarity In The Far-Ultraviolet With The Luminous Object N Carinae And Sn 1987a, A. G. Michalitsianos, Menas Kafatos, S. N. Shore

Mathematics, Physics, and Computer Science Faculty Articles and Research

Spectra obtained in the far UV wavelength range 1200-2000 A with the International Ultraviolet Explorer (IUE) of the peculiar emission object LMC Anonymous, or Sanduleak's Star in the Large Magellanic Cloud, indicate the presence of circumstellar-high-excitation gas, which is rich in CNO processed material. Although LMC Anonymous is a field star whose nebular line-forming region can not be resolved, and whose mass may be considerably smaller than the massive-luminous galactic object η Carinae, the far-UV spectrum of LMC Anonymous closely resembles that of the S Condensation of η Carinae. The similarity between LMC Anonymous and the S Condensation is apparent …

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R Aquarii: Evidence For A Two-Sided Radio Jet And A Circumbinary Sio Maser, Menas Kafatos, J. M. Hollis, F. Yusef-Zadeh, A. G. Michalitsianos, M. Elitzur Jan 1989

R Aquarii: Evidence For A Two-Sided Radio Jet And A Circumbinary Sio Maser, Menas Kafatos, J. M. Hollis, F. Yusef-Zadeh, A. G. Michalitsianos, M. Elitzur

Mathematics, Physics, and Computer Science Faculty Articles and Research

We have detected collimated 4.86 GHz (~6 cm) radio continuum emission southwest (SW) of the symbiotic vanable R Aquarii by combining data corresponding to different configurations of the Very Large Array (VLA). In the xontext of a previously reported northeast (NE) 6 cm jet structure, the orientation of the newly found SW radto structure suggests bipolar symmetry, extending to distances of ~2500 AU on either side of the central H II region. The amorphous morphology of the new collimated SW structure is distinct from the discrete radio knots NE of the central object. Further, we have determined the radio spectral …

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Rx Puppis: Detection Of Asymmetrical Radio Structure, J. M. Hollis, F. Yusef-Zadeh, T. J. Cornwell, R. J. Oliverson, A. G. Michalitsianos, Menas Kafatos Jan 1989

Rx Puppis: Detection Of Asymmetrical Radio Structure, J. M. Hollis, F. Yusef-Zadeh, T. J. Cornwell, R. J. Oliverson, A. G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Subarcsecond ( ~0':3 x ~0':1) observations of the RX Puppis symbiotic system with the Very Large Array (VLA) have resolved 2 cm continuum emission which deviates from a previously reported circularly symmetric radio distribution. The radio structure is comprised of at least three nearly colinear components. Under the assumption that the strongest feature is coincident with the hot star, the other two features lie 230 and 590 AU distant. These radio features are reminiscent of small-scale radio structure detected toward R Aquarii, another symbiotic star system, and probably represents material ejected from the RX Puppis system at an earlier epoch.

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An Assessment Of Potential Hazards To The Cassini Spacecraft From Debris Along Satellite Orbits, Robert A. Kolvoord Dec 1988

An Assessment Of Potential Hazards To The Cassini Spacecraft From Debris Along Satellite Orbits, Robert A. Kolvoord

Robert A Kolvoord

No abstract provided.

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Parenago 1540: A Pre-Main-Sequence Double-Lined Spectroscopic Binary Near The Orion Trapezium, Laurence A. Marschall, Robert D. Mathieu Dec 1988

Parenago 1540: A Pre-Main-Sequence Double-Lined Spectroscopic Binary Near The Orion Trapezium, Laurence A. Marschall, Robert D. Mathieu

Physics and Astronomy Faculty Publications

Spectroscopic and photometric observations of the star Parenago 1540 (V = 11.3), located 10 arcmin west of the Trapezium in Orion, have shown the star to be a pre-main-sequence double-lined spectroscopic binary. Thirty-seven radial-velocity measurements were obtained from which the orbital elements of the binary were determined, in particular an orbital period P = 33.73 + 0.03 days and an eccentricity of e = 0.12 + 0.01. High-dispersion spectra reveal strong Li 6707 A absorption lines in each of the components of P1540. A spectrum at lower dispersion also shows strong Ca II H and K emission lines, not …

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Chromospherically Active Stars. V. Hd 91816=Lr Hya: A Double-Lined By Draconis Type Binary, Francis C. Fekel, Kim Gillies, John L. Africano, Robert Quigley Oct 1988

Chromospherically Active Stars. V. Hd 91816=Lr Hya: A Double-Lined By Draconis Type Binary, Francis C. Fekel, Kim Gillies, John L. Africano, Robert Quigley

Information Systems and Engineering Management Research Publications

Observations of HD 91816=LR Hya obtained between 1982 and 1988 show it to consist of two nearly identical K0 dwarfs and to have an orbital period of 6.866 days and an orbital eccentricity of 0.014 + or - 0.003. The results suggest that the system has an age equal to or greater than that of the Hyades cluster. A spectroscopic parallax of 0.027 is obtained, and individual minimum masses of 0.55 solar masses each are found, implying an inclination of 61 + or - 3 deg.

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A Working Catalogue Of Herbig Haro Objects, Ted Von Hippel, S.J. Bell Burnell, P.M. Williams Sep 1988

A Working Catalogue Of Herbig Haro Objects, Ted Von Hippel, S.J. Bell Burnell, P.M. Williams

Publications

We present a catalogue of 184 Herbig Haro objects from a literature search complete to 1987.5. It is intended to update the 1974 catalogue of Herbig. The catalogue contains accurate co-ordinates, proper motions, radial velocities and spectral information for these objects. A cross-reference to the two best finding charts is included. A grouping of Herbig Haro objects into is also listed.

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A New Search For Interstellar C3, Charles L. Joseph, Theodore P. Snow, C Gregory Seab Jan 1988

A New Search For Interstellar C3, Charles L. Joseph, Theodore P. Snow, C Gregory Seab

Physics Faculty Publications

A new, very sensitive search for interstellar triatomic carbon has resulted in upper limits for a few diffuse clouds of order 1010 cm – 2, or about 10 – 11 with respect to hydrogen. These limits are consistent with recent cold diffuse cloud chemistry models, but may be in conflict with shocked cloud models such as those invoked to explain CH + abundances. Our results may also be argue against linear carbon-chain molecules as carriers of the diffuse interstellar bands.

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Numerical Simulations Of Narrow Planetary Rings: An Animation, Robert A. Kolvoord, J A. Burns Jan 1988

Numerical Simulations Of Narrow Planetary Rings: An Animation, Robert A. Kolvoord, J A. Burns

Robert A Kolvoord

No abstract provided.

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Microcomputer In An Introductory College Astronomy Laboratory: A Software Development Project, D D. Meisel, K F. Kinsey, Charles H. Recchia Jan 1988

Microcomputer In An Introductory College Astronomy Laboratory: A Software Development Project, D D. Meisel, K F. Kinsey, Charles H. Recchia

Charles H Recchia

No abstract provided.

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Chromospherically Active Stars. Iv. Hd 178450=V478 Lyr: An Early-Type By Draconis Type Binary, Francis C. Fekel Jan 1988

Chromospherically Active Stars. Iv. Hd 178450=V478 Lyr: An Early-Type By Draconis Type Binary, Francis C. Fekel

Information Systems and Engineering Management Research Publications

The variable star HD 178450 = V478 Lyr is a chromospherically active G8 V single-lined spectroscopic binary with a period of 2.130514 days. This star has strong ultraviolet emission features and a filled-in Hα absorption line which is variable in strength. It is classified as an early-type BY Draconis system and is similar in many respects to the BY Dra star HD 175742 = V775 Her. The unseen secondary of HD 178450 has a mass of about 0.3 M_sun; and is probably an M2-M3 dwarf. The inclination of the system is 67°±12°. The lithium abundance of the G8 dwarf results …

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Nonlocal Symmetries And Backlund Transformations For The Self-Dual Yang-Mills System, C. J. Papachristou, Kent B. Harrison Jan 1988

Nonlocal Symmetries And Backlund Transformations For The Self-Dual Yang-Mills System, C. J. Papachristou, Kent B. Harrison

Faculty Publications

The observation is made that generalized evolutionary isovectors of the self-dual Yang–Mills equation, obtained by "verticalization'' of the geometrical isovectors derived in a previous paper [J. Math. Phys. 28, 1261 (1987)], generate Bäcklund transformations for the self-dual system. In particular, new Bäcklund transformations are obtained by "verticalizing'' the generators of point transformations on the solution manifold. A geometric ansatz for the derivation of such (generally nonlocal) symmetries is proposed.

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Comparison Of Effective Medium Procedures For Optical Modeling Of Laminar Structures, David D. Allred, Robert F. Edgerton Jan 1988

Comparison Of Effective Medium Procedures For Optical Modeling Of Laminar Structures, David D. Allred, Robert F. Edgerton

Faculty Publications

This study addresses the question, "How can the optical properties of matter in ultrathin amorphous nonmetallic films in multilayers best be determined from reflectance (R) and transmission (T) measurements?" A blue shift in the band gap of plasma CVD a-Si:H/a-SiNx:H multilayers was reported several years ago. It was suggested that the shift in the band gap, Eg, Relative to bulk a-Si:H as given by the Tauç plot was due to quantum confinement effects. The purpose of this study is to evaluate the usefulness of various effective media theories (EMT) for determining the optical constants of materials in a multilayer and …

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The C Iv Doublet Ratio Intensity Effect In Symbiotic Stars, A. G. Michalitsianos, Menas Kafatos, R. P. Fahey, R. Viotti, A. Cassatella, A. Altamore Jan 1988

The C Iv Doublet Ratio Intensity Effect In Symbiotic Stars, A. G. Michalitsianos, Menas Kafatos, R. P. Fahey, R. Viotti, A. Cassatella, A. Altamore

Mathematics, Physics, and Computer Science Faculty Articles and Research

The first successful high-resolution ultraviolet spectra in the λλ 1200-2000 wavelength range of the symbiotic variable R Aquarii and its nebular Jet were obtained in 1987 July with the International Ultraviolet Explorer (IUE). The line profile structure of the C IV λλ1548, 1550 doublet in the jet indicates multicomponent velocity structure from an optically thin emitting gas. The C IV doublet profiles in the compact H II region engulfing the Mira and hot companion binary also suggest multicomponent structure, in which the radial velocities range up to ~ -100 km s^- 1. The value of the doublet intensity ratio in …

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The Energy-Dependence Of Polarization Observables In The ²H(D,Γ)⁴He Reaction, H. R. Weller, R. M. Whitton, J. Langenbrunner, Evans Hayward, W. R. Dodge, S. Kuhn, D. R. Tilley Jan 1988

The Energy-Dependence Of Polarization Observables In The ²H(D,Γ)⁴He Reaction, H. R. Weller, R. M. Whitton, J. Langenbrunner, Evans Hayward, W. R. Dodge, S. Kuhn, D. R. Tilley

Physics Faculty Publications

Measurements of the tensor and vector analyzing powers, Ayy(130°) and Ay(130°), have been obtained for the 2H(d,γ )4He reaction for energies ranging from Ed(lab) = 0.3 MeV to Ed(lab) = 50 MeV. The Ayy(130°) data are sensitive to the D-state present in the ground state of 4He and are observed to have their maximum value near Ed = 30 MeV. The vector analyzing power data show a maximum near Ed = 3 MeV. The data are compared to the results of a microscopic …

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R Aquarii: The Large-Scale Optical Nebula And The Mira Variable Position, A. G. Michalitsianos, R. J. Oliverson, J. M. Hollis, Menas Kafatos, H. E. Crull, R. J. Miller Jan 1988

R Aquarii: The Large-Scale Optical Nebula And The Mira Variable Position, A. G. Michalitsianos, R. J. Oliverson, J. M. Hollis, Menas Kafatos, H. E. Crull, R. J. Miller

Mathematics, Physics, and Computer Science Faculty Articles and Research

The R Aquarii symbiotic star system is surrounded by a large-scale optical nebula. We present observations of the nebular [O III] structure and discuss its morphological significance in context with previously observed small-scale radio-continuum features, which may be related. We suggest that a precessing accretion disk may explain the global features of both the large-scale optical emission and the small-scale radio emission. Moreover, we have determined an accurate position of the system's Mira, which suggests that a recent theoretical model, yielding an egg-shaped central H II region for symbiotic systems with certain physical parameters, may apply to R Aquarii. The …

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Gamma-Ray Observations Of The Crab Region Using A Coded-Aperture Telescope, Mark L. Mcconnell, P. P. Dunphy, D J. Forrest, E. L. Chupp, A Owens Oct 1987

Gamma-Ray Observations Of The Crab Region Using A Coded-Aperture Telescope, Mark L. Mcconnell, P. P. Dunphy, D J. Forrest, E. L. Chupp, A Owens

Physics & Astronomy

The region of the Galactic anticenter, including the Crab Nebula, was observed during a balloon flight of the University of New Hampshire Directional Gamma-Ray Telescope employing the coded-aperture imaging technique to image celestial gamma-radiation between 160 keV and 9.3 MeV. The background systematics are treated with a simple and relatively straightforward correction procedure. The results demonstrate that the coded-aperture procedure is a viable approach for imaging not only point sources of radiation, but also extended sources of emission. The results for the Crab's photon spectrum are consistent with a power-law spectrum. Upper limits on the flux levels of line emission …

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Chromospherically Active Stars. Iii. Hd 26337 = Ei Eri: An Rs Cvn Candidate For The Doppler-Imaging Technique, Francis C. Fekel, Robert Quigley, Kim Gillies, John L. Africano Sep 1987

Chromospherically Active Stars. Iii. Hd 26337 = Ei Eri: An Rs Cvn Candidate For The Doppler-Imaging Technique, Francis C. Fekel, Robert Quigley, Kim Gillies, John L. Africano

Information Systems and Engineering Management Research Publications

The variable star HD 26337 = EI Eri is a chromospherically active G5 IV single-lined spectroscopic binary with a period of 1.94722 days. It has moderate strength Ca II H and K emission and strong ultraviolet emission features, while Hα is a weak absorption feature that is variable in strength. The inclination of the system is 46°±12°, and the unseen secondary is most likely a late K or early M dwarf. The v sin i of the primary is 50±3 km s-1, resulting in a minimum radius of 1.9±0.1 R_sun;. A mass ratio of M1/M2 ≥ 2.6 and a mass …

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Optical Variability Of The Black Hole Candidate Gx339-4 (X1659-487, V821 Ara) - Limits On Periodic Modulation, R. H. D. Corbet, J. R. Thorstensen, P. A. Charles, W. B. Honey Aug 1987

Optical Variability Of The Black Hole Candidate Gx339-4 (X1659-487, V821 Ara) - Limits On Periodic Modulation, R. H. D. Corbet, J. R. Thorstensen, P. A. Charles, W. B. Honey

Dartmouth Scholarship

We present results of extensive CCD optical photometry (over 1000 frames representing ~150 hr of integration time) of the optical counterpart of the X-ray source GX339–4 obtained during the high (soft) state. The source was seen to be significantly variable. We do not, however, detect any periodic modulation with semi-amplitude greater than ~0.03 mag for periods less than ~0.5 day or semi-amplitude greater than ~0.07 mag for longer periods. An optical spectrum obtained shortly after GX339–4 made a transition from a ‘low’ to a ‘high’ state is also presented and compared with previous results. The width of the He II …

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Membership In The Young Cluster Trumpler 37, Laurence A. Marschall, William F. Van Altena Jul 1987

Membership In The Young Cluster Trumpler 37, Laurence A. Marschall, William F. Van Altena

Physics and Astronomy Faculty Publications

Astrometric positions for 1387 stars and proper motions for a subset of 1135 stars brighter than V=15 in a 1.5 degree surrounding the young open cluster Trumpler 37 are presented. Membership probabilities are presented for those stars with measured proper motions, and 486 stars with probabilities of >80% are identified.

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Surface Conductance Of A Copper Wire In A Fluid At High Pressure, Daniel L. Decker Jul 1987

Surface Conductance Of A Copper Wire In A Fluid At High Pressure, Daniel L. Decker

Faculty Publications

The three-dimensional flow of heat in a wire carrying a current and immersed in a liquid is solved in detail. Using this exact result the surface conductance of copper in petroleum ether has been measured as a function of pressure to 40 kbars. The measured surface conductance for copper in a fluid is very small, justifying approximations which yield results that are in agreement with a simplified one-dimensional heat-flow problem. Surprisingly, even at 40 kbars pressure a very large fraction of the joule heating within a wire with a length-to-diameter ratio of ~100 is dissipated through the ends of the …

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