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Astrophysics and Astronomy

1990

Articles 1 - 26 of 26

Full-Text Articles in Physical Sciences and Mathematics

Radiative Transfer In Astronomical Masers. I. The Linear Maser, Moshe Elitzur Nov 1990

Radiative Transfer In Astronomical Masers. I. The Linear Maser, Moshe Elitzur

Physics and Astronomy Faculty Publications

This is the first in a series of three papers presenting a comprehensive, unified approach for radiative transfer in astronomical maser sources. This paper provides the general formalism and presents the detailed analytic solution of the linear maser, including the case of a source illuminated by background radiation.

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Four Short-Period Algols, James Bruce Rafert Oct 1990

Four Short-Period Algols, James Bruce Rafert

Aerospace, Physics, and Space Science Faculty Publications

We have analyzed the light curves of four close binary star systems (BV 267, RU UMi, XZ CMi, and VV UMa) using the Wilson-Devinney differential corrections model. The present system geometries of these binaries is that of short-period, semi-detached systems with Roche lobe filling secondaries and main-sequence primaries. Differential coordinates in the mass-luminosity and mass-radius diagrams indicate that the secondary components lie near the main sequence, except in the case of BV 267. It is suggested that these systems are binaries with slightly overluminous and over-sized secondaries which have undergone case A mass transfer. This contention is supported by timing …

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The Effect Of Externally Applied Oscillating Electric Fields On The L=1 And L=2 Diocotron Modes In Non-Neutral Plasmas, Ross L. Spencer Oct 1990

The Effect Of Externally Applied Oscillating Electric Fields On The L=1 And L=2 Diocotron Modes In Non-Neutral Plasmas, Ross L. Spencer

Faculty Publications

A high-frequency oscillating electric field can change the properties of diocotron modes in non-neutral plasmas. The effect depends crucially on the azimuthal mode number, m, of the applied field. For m=0, plus or minus 1 there is no effect, and for applied standing waves there is also no effect. But if the applied field has the form of a traveling wave with the norm of m greater than or equal to 2, the frequency of stable diocotron modes can be modified and for the norm of m greater than or equal to 3, the l=2 instability of hollow density profiles …

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High-Velocity Molecular Gas Associated With Cold Iras Sources, Bruce Wilking, James Blackwell, Lee Mundy Sep 1990

High-Velocity Molecular Gas Associated With Cold Iras Sources, Bruce Wilking, James Blackwell, Lee Mundy

Physics Faculty Works

Maps are presented in the J = 2-1 transition of CO for five molecular outflows associated with deeply embedded far-infrared sources. All of the outflows display lobes of both red- and blue-shifted gas with full velocity extents ranging from 37 to 63 km/s. At least two of the outflows are bipolar but neither is well-collimated. High-velocity C-13O emission is detected in all sources. The data are used to estimate the optical depths, excitation temperatures, masses, momentum supply rates, and energy supply rates for the outflows. A comparison between the properties of IRAS-selected and optically selected molecular outflows is made. The …

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The Luminosities Of Bright H N Regions In Ngc 628 And Its O Star Formation Rate, Ted Von Hippel, Greg Bothun Aug 1990

The Luminosities Of Bright H N Regions In Ngc 628 And Its O Star Formation Rate, Ted Von Hippel, Greg Bothun

Publications

Using narrow band CCD imaging we have identified 183 bright H n regions in the Sc galaxy NGC 628. These H n regions have luminosities which indicate that they are powered by young star clusters which contain ^ 100 ionizing stars. We attempt to reproduce the H ii region LF with and without models including stellar evolution. We find stellar evolution an important parameter in understanding the H n region LF and find that it allows star-forming galaxies to be more robust to star bursting episodes. Ranking the H n regions by luminosity and assuming that luminosity evolution is due …

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Spectroscopic Limits On High-Redshift Lyα Emission, James D. Lowenthal, Craig J. Hogan, Robert W. Leach, Gary D. Schmidt, Craig B. Foltz Jul 1990

Spectroscopic Limits On High-Redshift Lyα Emission, James D. Lowenthal, Craig J. Hogan, Robert W. Leach, Gary D. Schmidt, Craig B. Foltz

Astronomy: Faculty Publications

We have conducted a deep long-slit spectroscopic search for high-redshift (2.7 < z < 4.7) Lyα emission. Four pairs of deep, high-resolution (R ≈ 2000), long-slit CCD frames were taken at the Multiple Mirror Telescope. The "blank sky" in each pair of frames was searched for faint emission features unresolved spatially and spectrally. No emission features were found down to a limiting line surface brightness (1 σ) of 1-4 × 10-18 ergs s-1 cm-2 arcsec-2. The sensitivity of the search was calibrated using simulations with synthetic features added to the data frames. The data set upper limits on the mean space density 〈n〉 and line flux of randomly distributed Lyα-emitting clouds; for example, at z ≈ 4.5 we have a 95% confidence limit of 〈n〉 < 1 Mpc-3 h1003 at a total line flux level of ∼3 × 10-17 ergs s-1 cm-2. These limits approach expected emission levels for fairly conservative published primeval galaxy models. In addition, Lyα emission was searched for, but not detected, from a known Lyα-limit absorption cloud toward QSO 0731+653. Assuming that the gas in this cloud is spatially resolved (size ≳ 4h-1 kpc) we set an upper limit on the diffuse ionizing flux density at z = 2.912 of Jv ≲ 2 × 10-19 ergs s-1 cm-2 sr-1 Hz-1.

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Photometry Of The Young Open Cluster Trumpler 37, Laurence A. Marschall, Neil F. Comins, Gary B. Karshner May 1990

Photometry Of The Young Open Cluster Trumpler 37, Laurence A. Marschall, Neil F. Comins, Gary B. Karshner

Physics and Astronomy Faculty Publications

Photoelectric UBV observations of 120 stars in the young open cluster Trumpler 37 are presented, primarily in the magnitude range 10.0<V

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Hd 43246 And Hd 127208: Two Unusual F-G + B Binary Systems, Robert C. Dempsey, Bernard W. Bopp, Sidney B. Parsons, Francis C. Fekel Mar 1990

Hd 43246 And Hd 127208: Two Unusual F-G + B Binary Systems, Robert C. Dempsey, Bernard W. Bopp, Sidney B. Parsons, Francis C. Fekel

Information Systems and Engineering Management Research Publications

New optical spectroscopic observations along with ultraviolet IUE observations have been obtained for the two interacting F or G III + B V binaries: HD 43246 and HD 127208. Photometric observations indicate random changes superimposed on regular ellipsoidal light variations, the latter probably the result of tidal distortion of the giant primaries. Mass transfer and loss is apparent in inverted mass ratios derived from orbital analysis, strong wind features present in the spectra, and the presence of circumsystem shells. Regular and irregular changes in the spectral features are discussed in this context.

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Sao 23229: A New Double-Lined Spectroscopic Eclipsing Binary, Laurence A. Marschall, Robert P. Stefanik, Harold L. Nations, Robert J. Davis Mar 1990

Sao 23229: A New Double-Lined Spectroscopic Eclipsing Binary, Laurence A. Marschall, Robert P. Stefanik, Harold L. Nations, Robert J. Davis

Physics and Astronomy Faculty Publications

The discovery of eclipses of the bright star SAO 23229 (HD 14384; V=6.9; Spectral Type F5 V) by Indiana observer Dan Kaiser was described in a recent article in Sky and Telescope magazine (MacRobert, 1990). Photoelectric observations by H. Landis and D. Williams, reproduced in that article, show eclipses of 0.55 mag depth and period of 2.111 days. No secondary eclipses are reported, leaving open the question of whether the system contains a very dim secondary or whether it consists of two identical stars with an actual period of 4.2 days. We report here observations that favor the latter interpretation. …

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Photoluminescence Studies In Znxcd1-Xte Single Crystals, David D. Allred, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred Mar 1990

Photoluminescence Studies In Znxcd1-Xte Single Crystals, David D. Allred, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred

Faculty Publications

The crystalline quality of ZnxCd1-xTe single crystals prepared by a modified Bridgman method with 0≤x≤0.05 has been analyzed using photoluminescence. The spectrum of a typical sample is dominated by lines originating from the recombination of free and bound excitons. Lines due to free excitons in their ground and first excited states are observed in both the pure CdTe and the mixed crystals. Excitons bound to Dc vacancies are observed in the pure CdTe crystal but not in the mixed crystal. Weaker and broader features appearing at energies below the exciton emission range were associated with transitions involving free-to-bound and bound-to-bound …

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Hr 1362: A Test Case For Stellar Dynamo Theories, Klaus G. Strassmeier, Douglas S. Hall, William S. Barksdale, Anthony T. Jusick, Gregory W. Henry Feb 1990

Hr 1362: A Test Case For Stellar Dynamo Theories, Klaus G. Strassmeier, Douglas S. Hall, William S. Barksdale, Anthony T. Jusick, Gregory W. Henry

Information Systems and Engineering Management Research Publications

An analysis of 11 yr of photometry of HR 1362 = EK Eri has shown a well-established photometric period of 335 days. This confirms an earlier period determination of about 310 days from 3 yr of APT data and is consistent with a new v sin i determination of 2 + or - 2 km/s. Recent Ca II H and K observations show moderately strong H and K emission lines at a flux level of log F prime (K) of about 6.5 ergs sq m/s. If the photometric period is interpreted as the rotation period, this surface flux is more …

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The Circumstellar Structure Of Iras 16293-2422: C18o, Nh3 , And Co Observations, Lee Mundy, H. Wootten, Bruce Wilking Jan 1990

The Circumstellar Structure Of Iras 16293-2422: C18o, Nh3 , And Co Observations, Lee Mundy, H. Wootten, Bruce Wilking

Physics Faculty Works

Interferometric observations of the (C-18)O and (C-12)O J = 1-0 transitions, and the NH3 (1, 1) and (2, 2) transitions toward the young far-IR source IRAS 16293-2422 are presented. The data reveal elongated gas structures which are aligned perpendicular to the axis of a bipolar outflow and to the local magnetic field direction. By combining the interferometric data with single-dish spectra of the (C-18)O and (C-17)O lines, a comprehensive model for the IRAS 16293-2422 region is developed. In this model, the compact (C-18)O line and 40 K dust emission arise from rotating material within which the central heat source is …

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Supercomputer As Observatory? A Search For Moons In Planetary Rings Using The Cornell National Supercomputer Facility, J A. Burns, Robert A. Kolvoord Jan 1990

Supercomputer As Observatory? A Search For Moons In Planetary Rings Using The Cornell National Supercomputer Facility, J A. Burns, Robert A. Kolvoord

Robert A Kolvoord

No abstract provided.

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Inhomogeneous Broadening In Spectral Bands Of Carbonmonoxymyoglobin: The Connection Between Spectral And Functional Heterogeneity, Todd B. Sauke, P. Ormos, A. Ansari, D. Braunstein, B. R. Cowen, H. Fraunfelder, M. K. Hong, I. E. T. Iben, P. J. Steinbach, R. D. Young Jan 1990

Inhomogeneous Broadening In Spectral Bands Of Carbonmonoxymyoglobin: The Connection Between Spectral And Functional Heterogeneity, Todd B. Sauke, P. Ormos, A. Ansari, D. Braunstein, B. R. Cowen, H. Fraunfelder, M. K. Hong, I. E. T. Iben, P. J. Steinbach, R. D. Young

Todd B. Sauke

The rebinding kinetics of CO to myoglobin after flash photolysis is nonexponential in time below approximately 180 K; the kinetics is governed by a distribution of enthalpic barriers. This distribution results from inhomogeneities in the protein conformation, referred to as conformational substates. Hole-burning experiments on the Soret and IR CO-stretch bands test the assumption that an inhomogeneous distribution of conformational substates results in inhomogeneously broadened spectra. CO was slowly photolyzed at different wavelengths in the Soret band at 10 K. Both the Soret band and the CO-stretch band A1, centered at 1,945 cm-1, shift during photolysis, demonstrating that different wavelengths …

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Inhomogeneous Broadening In Spectral Bands Of Carbonmonoxymyoglobin: The Connection Between Spectral And Functional Heterogeneity, Todd B. Sauke, P. Ormos, A. Ansari, D. Braunstein, B. R. Cowen, H. Fraunfelder, M. K. Hong, I. E. T. Iben, P. J. Steinbach, R. D. Young Jan 1990

Inhomogeneous Broadening In Spectral Bands Of Carbonmonoxymyoglobin: The Connection Between Spectral And Functional Heterogeneity, Todd B. Sauke, P. Ormos, A. Ansari, D. Braunstein, B. R. Cowen, H. Fraunfelder, M. K. Hong, I. E. T. Iben, P. J. Steinbach, R. D. Young

Faculty Publications

The rebinding kinetics of CO to myoglobin after flash photolysis is nonexponential in time below approximately 180 K; the kinetics is governed by a distribution of enthalpic barriers. This distribution results from inhomogeneities in the protein conformation, referred to as conformational substates. Hole-burning experiments on the Soret and IR CO-stretch bands test the assumption that an inhomogeneous distribution of conformational substates results in inhomogeneously broadened spectra. CO was slowly photolyzed at different wavelengths in the Soret band at 10 K. Both the Soret band and the CO-stretch band A1, centered at 1,945 cm-1, shift during photolysis, demonstrating that different wavelengths …

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Evolution Of The Starspots In V478 Lyrae From 1980 To 1988, Douglas S. Hall, Gregory W. Henry, James R. Sowell Jan 1990

Evolution Of The Starspots In V478 Lyrae From 1980 To 1988, Douglas S. Hall, Gregory W. Henry, James R. Sowell

Information Systems and Engineering Management Research Publications

Differential UBV photometry of V478 Lyrae from 1980 to 1988 is given and analyzed as 22 separate light curves, each spanning an average of a dozen rotation cycles. It is shown that spots on V478 Lyr appear to have lifetimes on the order of several months to a year. The amplitude of the light loss produced by a spot can change by a factor of 2 within 20 days. In the only four determinate cases, a spot came into existence at one of the two conjunctions, that is, in the middle of the hemisphere facing (or opposing) the companion star. …

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Chromospheric Ca Ii H And K And H Alpha Emission In Single And Binary Stars Of Spectra Types F6--M2, Klaus G. Strassmeier, Francis C. Fekel, Bernard W. Bopp, Robert C. Dempsey, Gregory W. Henry Jan 1990

Chromospheric Ca Ii H And K And H Alpha Emission In Single And Binary Stars Of Spectra Types F6--M2, Klaus G. Strassmeier, Francis C. Fekel, Bernard W. Bopp, Robert C. Dempsey, Gregory W. Henry

Information Systems and Engineering Management Research Publications

New observations of the Ca II H and K and H-epsilon region and/or the Balmer H-alpha line are presented for 100 mostly very active stars but also for weak or inactive stars with suspected activity. Correlations between chromospheric activity at Ca II H and K and H-alpha and effective surface temperature and rotation are identified, and several new stars with chromospheric Ca II H and K emission are discovered. No single activity-rotation relation can be derived for all luminosity classes, and there is clear evidence that evolved stars are generally more active than main-sequence stars of the same rotation period. …

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Annealing Behavior Of The Photoluminescence Lines In Cdte And Znx Cd1-X Te Single Crystals, David D. Allred, A. Reyes-Mena, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred Jan 1990

Annealing Behavior Of The Photoluminescence Lines In Cdte And Znx Cd1-X Te Single Crystals, David D. Allred, A. Reyes-Mena, Jesus González-Hernández, Elías López-Cruz, Worth P. Allred

Faculty Publications

The main lines in the photoluminescence spectra of Zn1Cd1-xTe single crystals grown by a modified Bridgman method in the compositional range of 0≤X≤0.25 have been identified. All crystals show only near-band-edge emission. To assist in the identification, various samples with different compositions were annealed under a Cd atmosphere. In the pure crystals, the prominent (A°, X) bound exciton line, as well as the doublet at longer wavelengths, disappear after the annealing. In contrast, the treatments do not change significantly the PL spectra of the mixed crystals.

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Deposition Of Zinc Selenide By Atomic Layer Epitaxy For Multilayer X-Ray Optics, J.K. Shurtleff, David D. Allred, R. T. Perkins, J. M. Thorne Jan 1990

Deposition Of Zinc Selenide By Atomic Layer Epitaxy For Multilayer X-Ray Optics, J.K. Shurtleff, David D. Allred, R. T. Perkins, J. M. Thorne

Faculty Publications

Thin film deposition techniques currently being used to produce multilayer x-ray optics (MXOs) have difficulty producing smooth, uniform multilayers with d-spacings less than about twelve angstroms. We are investigating atomic layer epitaxy (ALE) as an alternative to these techniques. ALE is a chemical vapor deposition technique which deposits an atomic layer of material during each cycle of the deposition process. The thickness of a film deposited by ALE depends only on the number of cycles. Multilayers deposited by ALE should be smooth and uniform with precise d-spacings which makes ALE an excellent technique for producing multilayer x-ray optics. We have …

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Advanced Infrared Optically Black Baffle Materials, David D. Allred, Ronald D. Seals, C. M. Egert Jan 1990

Advanced Infrared Optically Black Baffle Materials, David D. Allred, Ronald D. Seals, C. M. Egert

Faculty Publications

Infrared optically black baffle surfaces are an essential component of many advanced optical systems. All internal surfaces in advanced infrared optical sensors that require stray light management to achieve resolution are of primary concern in baffle design. Current industrial materials need improvements to meet advanced optical sensor systems requirements for optical, survivability, and endurability. Baffles are required to survive and operate in potentially severe environments. Robust diffuse-absorptive black surfaces, which are (1) thermally and mechanically stable to threats of x-ray, launch, and in-flight maneuver conditions, with specific densities to allow an acceptable weight load, (2) handleable during assembly, (3) cleanable, …

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Diffuse Absorbing Beryllium Coatings Produced By Magnetron Sputtering, David D. Allred, C. M. Egert Jan 1990

Diffuse Absorbing Beryllium Coatings Produced By Magnetron Sputtering, David D. Allred, C. M. Egert

Faculty Publications

Beryllium coatings with varying thicknesses and columnar grain sizes were deposited by low temperature magnetron sputtering and wet chemically etched to enhance diffuse absorption of light. After etching these coatings exhibited a matte black surface finish and low specular reflectance (below 2%) in the IR up to a critical wavelength dependent upon the original grain size of the coating. Extremely thick coatings (350 µm) with original grain sizes of 10 to 12 µm were produced which exhibited specular reflectances below 0.5% up to 50 µm wavelength and a Lambertian BRDF at 10.6 µm averaging 4.3x10-3 ster-1. Scanning electron micrographs are …

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Moderate-Resolution Spectroscopy Of The Lensed Quasar 2237+0305: A Search For Ca Ii Absorption Due To The Interstellar Medium In The Foreground Lensing Galaxy, P. Hintzen, S. P. Maran, A. G. Michalitsianos, C. B. Foltz, F. H. Chafee, Menas Kafatos Jan 1990

Moderate-Resolution Spectroscopy Of The Lensed Quasar 2237+0305: A Search For Ca Ii Absorption Due To The Interstellar Medium In The Foreground Lensing Galaxy, P. Hintzen, S. P. Maran, A. G. Michalitsianos, C. B. Foltz, F. H. Chafee, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

The gravitational lens system 2237 + 0305 consists of a low-redshift barred spiral galaxy (z = 0.0394) centered on a more distant quasar (z = 1.695). Because the lensing galaxy is nearly face on, spectroscopy of the background quasar affords a unique opportunity to study the interstellar medium in the galaxy's center and buW:. We report moderate-resolution spectroscopy of QS02237 + 0305 yielding a 3u upper limit of 72 rnA forthe rest equivalent width of Ca II K absorption d);le to gas in the intervening galaxy. Since gas in the Milky Way "thick disk" typically produces 220 mA Ca II …

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Characterization Of Metal/Carbon Multilayers By Raman Spectroscopy, David D. Allred, Qi Wang, Jesus González-Hernández Jan 1990

Characterization Of Metal/Carbon Multilayers By Raman Spectroscopy, David D. Allred, Qi Wang, Jesus González-Hernández

Faculty Publications

Laser Raman spectroscopy has been found to be useful for characterizing amorphous semiconductor multilayers, especially the interfaces of multilayers. Recently, we have extended this technique to the characterization of magnetron sputtered multilayers commonly used as reflectors in soft x-ray optics. Unlike the multilayers previously studied which contained only semiconductors and dielectrics, these are generally semiconductor/metal multilayers. We report here on the Raman characterization of the most common class of multilayers used in soft x-ray optics, those that contain a high density metal like tungsten interspersed with layers of carbon. In all of the metal/carbon multilayers the dominate feature in the …

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Photoconductive Characterization Of Znxcd1-Xte (0≤X≤0.25) Single Crystal Alloys, David D. Allred, Elías López-Cruz, Jesus González-Hernández, Worth P. Allred Jan 1990

Photoconductive Characterization Of Znxcd1-Xte (0≤X≤0.25) Single Crystal Alloys, David D. Allred, Elías López-Cruz, Jesus González-Hernández, Worth P. Allred

Faculty Publications

Large grain polycrystalline and single crystals of ZnxCd1-xTe grown by a modified Bridgman method were studied using the photoluminescence and photoconductivity techniques. The temperature dependence of the band gap, as determined by photoluminescence, follows the Varshni equation for measuring temperature in the range of 15-290 K. One of the fitted parameters, the Debye temperature, monotonically decreases with the increase of the atomic zinc concentration. A close correlation between the photoluminescence and photoconductivity measurements is also found. Samples in which the photoluminescence spectra exhibit emission bands associated to cadmium vacancies and other structural defects, show a photoresponse curve which includes, in …

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Design Of High Performance Soft X-Ray Windows, Raymond T. Perkins, David D. Allred, Larry V. Knight, James M. Thorne Jan 1990

Design Of High Performance Soft X-Ray Windows, Raymond T. Perkins, David D. Allred, Larry V. Knight, James M. Thorne

Faculty Publications

X-ray windows are used in sources and detectors to separate the neighborhood of the x-ray generation or detection from the use environment. While each use has its own requirements, there are some principles that should be used in designing an optimal x-ray window. Because x-rays are absorbed to some extent by all materials, minimizing absorption is one criterion in preparing windows. Also, for most uses there is a pressure difference across the window so that ensuring pinhole-free structure and sufficient mechanical strength to support the differential is another criterion for window design. Traditionally, absorption is minimized by fabricating the window …

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Comparisons Of Sio Maser And Long-Period Variable Positions In The Aquarii And Omicron Ceti Binary Systems, J. M. Hollis, M. C. H. Wright, W. J. Welch, P. R. Jewell, H. E. Crull, Menas Kafatos, A. G. Michalitsianos Jan 1990

Comparisons Of Sio Maser And Long-Period Variable Positions In The Aquarii And Omicron Ceti Binary Systems, J. M. Hollis, M. C. H. Wright, W. J. Welch, P. R. Jewell, H. E. Crull, Menas Kafatos, A. G. Michalitsianos

Mathematics, Physics, and Computer Science Faculty Articles and Research

We have determined that the absolute position of the centroid of SiO maser-emitting spots toward both R A~r ~nd o Cet are coincident with the position of the long-period variables (LPVs) in these binary systems to within the errors of measurement. The SiO positions were determined with the Hat Creek interferometer while the LPV positions were determined with the 8 inch (20 em) transit circle of the US Naval Observatory: These results contradict an earlier report of a circumbinary SiO maser far removed from the LPV in the R Aqr binary system, and we suggest statistical reasons for the discrepancy. …

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