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Articles 8251 - 8280 of 8894

Full-Text Articles in Astrophysics and Astronomy

The Design Of A Gamma‐Ray Burst Polarimeter, Mark L. Mcconnell, D J. Forrest, K Levenson, W T. Vestrand Jan 1993

The Design Of A Gamma‐Ray Burst Polarimeter, Mark L. Mcconnell, D J. Forrest, K Levenson, W T. Vestrand

Space Science Center

The study of the polarization properties of the gamma‐ray bursts is the one remaining unexplored avenue of research which may help to answer some of the fundamental problems regarding the nature of these mysterious objects. We have designed an instrument to measure linear polarization in cosmic gamma‐ray bursts at energies ≳50 keV. Here we describe the design of this instrument, which we call the Gamma‐ray Burst Polarimeter Experiment (GRAPE).

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Comptel Observations Of The Inner Galaxy, H Bloemen, H Deboer, R Van Dijk, J W. Den Herder, W Hermsen, L Kuiper, B Swanenburg, C De Vries, W Collmar, R Diehl, G G. Lichti, V Schonfelder, H Steinle, A W. Strong, Mark L. Mcconnell, A Connors, D Morris, G Stacy, K Bennett Jan 1993

Comptel Observations Of The Inner Galaxy, H Bloemen, H Deboer, R Van Dijk, J W. Den Herder, W Hermsen, L Kuiper, B Swanenburg, C De Vries, W Collmar, R Diehl, G G. Lichti, V Schonfelder, H Steinle, A W. Strong, Mark L. Mcconnell, A Connors, D Morris, G Stacy, K Bennett

Space Science Center

This paper presents a first global study of COMPTEL observations of the inner Galaxy in the energy range 0.75–10 MeV. Preliminary findings demonstrate COMPTEL’s capabilities for mapping the observed gamma radiation and disentangling the contributions from point sources and diffuse emission.

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Comptel Gamma Ray And Neutron Measurements Of Solar Flares, James M. Ryan, D J. Forrest, J Lockwood, M Loomis, Mark L. Mcconnell, D Morris, W Webber, G Rank, V Schonfelder, B Swanenburg, K Bennett, L O. Hanlon, C Winkler, H Debrunner Jan 1993

Comptel Gamma Ray And Neutron Measurements Of Solar Flares, James M. Ryan, D J. Forrest, J Lockwood, M Loomis, Mark L. Mcconnell, D Morris, W Webber, G Rank, V Schonfelder, B Swanenburg, K Bennett, L O. Hanlon, C Winkler, H Debrunner

Space Science Center

COMPTEL on the Compton Gamma Ray Observatory has measured the flux of x‐rays and neutrons from several solar flares. These data have also been used to image the Sun in both forms of radiation. Unusually intense flares occurred during June 1991 yielding data sets that offer some new insight into of how energetic protons and electrons are accelerated and behave in the solar environment. We summarize here some of the essential features in the solar flare data as obtained by COMPTEL during June 1991.

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Comptel Observations Of Cygnus X‐1, Mark L. Mcconnell, A Connors, D J. Forrest, James M. Ryan, W Collmar, R Diehl, V Schonfelder, H Steinle, A W. Strong, H Bloemen, R Van Dijk, W Hermsen, L Kuiper, B Swanenburg, C Winkler Jan 1993

Comptel Observations Of Cygnus X‐1, Mark L. Mcconnell, A Connors, D J. Forrest, James M. Ryan, W Collmar, R Diehl, V Schonfelder, H Steinle, A W. Strong, H Bloemen, R Van Dijk, W Hermsen, L Kuiper, B Swanenburg, C Winkler

Space Science Center

We report on the latest results from an analysis of data on Cygnus X‐1 as collected by the COMPTEL experiment on the Compton Gamma‐Ray Observatory (CGRO). COMPTEL detected the source around 1 MeV during two separate one‐week observations in 1991. The measured flux levels indicate variability on a time scale of weeks. The results also indicate flux levels which are well below the levels reported by some investigators for an excess of emission in the energy range ≥1 MeV.

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An Overview Of First Results From Comptel, V. Schonfelder, H Aarts, K Bennett, H Bloemen, H Deboer, M Busetta, W Collmar, A Connors, R Diehl, J W. Den Herder, W Hermsen, L Kuiper, G G. Lichti, J Lockwood, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, G. Simpson, J G. Stacy, H Steinle, A W. Strong, B Swanenburg, B G. Taylor, M Varendorff, C De Vries, W Webber, C Winkler Jan 1993

An Overview Of First Results From Comptel, V. Schonfelder, H Aarts, K Bennett, H Bloemen, H Deboer, M Busetta, W Collmar, A Connors, R Diehl, J W. Den Herder, W Hermsen, L Kuiper, G G. Lichti, J Lockwood, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, G. Simpson, J G. Stacy, H Steinle, A W. Strong, B Swanenburg, B G. Taylor, M Varendorff, C De Vries, W Webber, C Winkler

Space Science Center

COMPTEL is the first imaging telescope to explore the MeV gamma-ray range (0.7 to 30 MeV). At present, it is performing a complete sky survey. Targets of special interest in the COMPTEL energy range are radio pulsars, X-ray binaries, novae, supernovae, supernova remnants, mulecular clouds, the interstellar medium within the Milky Way, active galactic nuclei, and the diffuse cosmic background radiation. The data from the first half year of the mission have demonstrated that COMPTEL performs as expected. The Crab is clearly seen at its proper position in the first images of the anticenter region of the galaxy. The Crab …

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Comptel Detections Of The Quasars 3c 273 And 3c 279, W Hermsen, H Aarts, K Bennett, H Bloemen, H Deboer, W Collmar, A Connors, R Diehl, R Vandijk, J W. Den Herder, L Kuiper, G G. Lichti, J Lockwood, John R. Macri, Mark L. Mcconnell, D Morris, James M. Ryan, V. Schonfelder, G. Simpson, H Steinle, A W. Strong, B Swanenburg, C De Vries, W Webber, O R. Williams, C Winkler Jan 1993

Comptel Detections Of The Quasars 3c 273 And 3c 279, W Hermsen, H Aarts, K Bennett, H Bloemen, H Deboer, W Collmar, A Connors, R Diehl, R Vandijk, J W. Den Herder, L Kuiper, G G. Lichti, J Lockwood, John R. Macri, Mark L. Mcconnell, D Morris, James M. Ryan, V. Schonfelder, G. Simpson, H Steinle, A W. Strong, B Swanenburg, C De Vries, W Webber, O R. Williams, C Winkler

Physics & Astronomy

The COMPTEL experiment aboard the Compton Gamma Ray Observatory, sensitive in the energy range from about 0.7 to 30 MeV, observed the high-latitude region containing 3C 273 and 3C 279 during a 2-week period in June, 1991. A search for sources using a maximum likelihood analysis revealed two statistically significant point-like excesses, the positions of which are consistent with those of 3C 273 and 3C 279. These sources are the first QSOs detected at MeV energies. In the COMPTEL energy domain their spectra appear to be greatly different. A comparison with earlier and simultaneous measurements in neighboring energy ranges indicates …

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Comptel Observations Of The Crab And Vela Pulsars, K Bennett, H Aarts, H Bloemen, R Buccheri, M Busetta, W Collmar, A Connors, A Carramiñana, R Diehl, H Deboer, J W. Den Herder, W Hermsen, L Kuiper, J Lockwood, G G. Lichti, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, V. Schonfelder, G. Simpson, J G. Stacy, H Steinle, A W. Strong, B Swanenburg, B G. Taylor, M Varendorff, C De Vries, W Webber, C Winkler Jan 1993

Comptel Observations Of The Crab And Vela Pulsars, K Bennett, H Aarts, H Bloemen, R Buccheri, M Busetta, W Collmar, A Connors, A Carramiñana, R Diehl, H Deboer, J W. Den Herder, W Hermsen, L Kuiper, J Lockwood, G G. Lichti, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, V. Schonfelder, G. Simpson, J G. Stacy, H Steinle, A W. Strong, B Swanenburg, B G. Taylor, M Varendorff, C De Vries, W Webber, C Winkler

Physics & Astronomy

The COMPTEL gamma-ray telescope, sensitive in the range 0.7-30 MeV, has viewed the Crab and Vela Pulsars. The light curves observed from both objects have been derived in several energy bands. Features of these light curves and some spectral details are discussed.

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First Results From Comptel Measurement Of The Al-26 1.8 Mev Gamma-Ray Line From The Galactic Center Region, R Diehl, K Bennett, H Bloemen, H Deboer, M Busetta, W Collmar, A Connors, J W. Den Herder, C. Devries, W Hermsen, J Knodlseder, L Kuiper, G G. Lichti, J Lockwood, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, V. Schonfelder, G. Simpson, J G. Stacy, H Steinle, A W. Strong, B Swanenburg, M Varendorff, P. Von Ballmoos, W Webber, C Winkler Jan 1993

First Results From Comptel Measurement Of The Al-26 1.8 Mev Gamma-Ray Line From The Galactic Center Region, R Diehl, K Bennett, H Bloemen, H Deboer, M Busetta, W Collmar, A Connors, J W. Den Herder, C. Devries, W Hermsen, J Knodlseder, L Kuiper, G G. Lichti, J Lockwood, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, V. Schonfelder, G. Simpson, J G. Stacy, H Steinle, A W. Strong, B Swanenburg, M Varendorff, P. Von Ballmoos, W Webber, C Winkler

Physics & Astronomy

The COMPTEL instrument on GRO is designed to image celestial gamma radiation in the approximately 0.7-30 MeV region of nuclear lines. Within a large field of view of about 1 sr its angular resolution of about 1 deg enables mapping of extended emission and location of (strong) point sources to an accuracy of better than 0.5 deg. The Galactic center region was observed by COMPTEL for a 2-week period in July 1991. Here we report the detection of the line at 1.8 MeV attributed to Al-26, addressing in particular the extent of the emission and the 1.8 MeV line flux.

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The Crab And Galactic Anticentre Region Observed By Comptel, A W. Strong, K Bennett, H Bloemen, H Deboer, R Buccheri, M Busetta, W Collmar, A Connors, R Diehl, J W. Den Herder, W Hermsen, L Kuiper, J Lockwood, G G. Lichti, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, V. Schonfelder, G. Simpson, J G. Stacy, H Steinle, B Swanenburg, M Varendorff, C Winkler, C De Vries Jan 1993

The Crab And Galactic Anticentre Region Observed By Comptel, A W. Strong, K Bennett, H Bloemen, H Deboer, R Buccheri, M Busetta, W Collmar, A Connors, R Diehl, J W. Den Herder, W Hermsen, L Kuiper, J Lockwood, G G. Lichti, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, V. Schonfelder, G. Simpson, J G. Stacy, H Steinle, B Swanenburg, M Varendorff, C Winkler, C De Vries

Physics & Astronomy

The Galactic anticenter region including the Crab nebula has been observed with the COMPTEL gamma-ray telescope on the Gamma Ray Observatory. A map of the region in the 1-30 MeV energy range is presented. The total spectrum of the Crab is derived as well as that of the pulsed and unpulsed components. Upper limits on the pulsar Geminga are also presented.

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Comptel Observations Of The 1.809 Mev Gamma-Ray Line From Galactic 26al, R Diehl, C. Dupraz, K Bennett, H Bloemen, H Deboer, W Hermsen, G G. Lichti, Mark L. Mcconnell, D Morris, James M. Ryan, V. Schonfelder, H Steinle, A W. Strong, B Swanenburg, M Varendorff, C Winkler Jan 1993

Comptel Observations Of The 1.809 Mev Gamma-Ray Line From Galactic 26al, R Diehl, C. Dupraz, K Bennett, H Bloemen, H Deboer, W Hermsen, G G. Lichti, Mark L. Mcconnell, D Morris, James M. Ryan, V. Schonfelder, H Steinle, A W. Strong, B Swanenburg, M Varendorff, C Winkler

Physics & Astronomy

No abstract provided.

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Preliminary Results From Comptel On A Search For Gamma-Ray Line Emission From Sn 1991t, G G. Lichti, K Bennett, H Bloemen, H Deboer, M Busetta, W Collmar, A Connors, R Diehl, R Van Dijk, J W. Den Herder, W Hermsen, L Kuiper, J Lockwood, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, V. Schonfelder, G. Simpson, J G. Stacy, H Steinle, A W. Strong, B Swanenburg, M Varendorff, C De Vries, C Winkler Jan 1993

Preliminary Results From Comptel On A Search For Gamma-Ray Line Emission From Sn 1991t, G G. Lichti, K Bennett, H Bloemen, H Deboer, M Busetta, W Collmar, A Connors, R Diehl, R Van Dijk, J W. Den Herder, W Hermsen, L Kuiper, J Lockwood, John R. Macri, Mark L. Mcconnell, D Morris, R Much, James M. Ryan, V. Schonfelder, G. Simpson, J G. Stacy, H Steinle, A W. Strong, B Swanenburg, M Varendorff, C De Vries, C Winkler

Physics & Astronomy

The COMPTEL experiment aboard the Compton Gamma-Ray Observatory is designed to image celestial gamma-radiation in the energy range from 0.7-30 MeV. With a field of view of 1 sr it is capable of locating strong point sources with an accuracy of better than 0.5 deg. From June 15 to 28, 1991 and a second time from October 3 to 17, 1991 the region containing the supernova SN 1991T was observed by COMPTEL. Here preliminary results from these observations are presented, with special attention to a search for gamma-ray line emission from the supernova.

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The Production And Escape Of Nitrogen Atoms On Mars, Jane L. Fox Jan 1993

The Production And Escape Of Nitrogen Atoms On Mars, Jane L. Fox

Physics Faculty Publications

We have computed the production rates and densities of odd nitrogen species in the Martian atmosphere using updated rate coefficients and a revised ionosphere-thermosphere model. We find that the computed densities of NO are somewhat smaller than those measured by Viking 1, but reasonable agreement can be obtained by assuming that the rate coefficient for loss of odd nitrogen in the reaction of N with NO is smaller at temperatures that prevail in the lower Martian thermosphere (about 130–160 K) than the standard value, which applies to temperatures of 200–400 K. We have also modeled the escape fluxes of N …

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On The System Of Diffuse Interstellar Bands At 5844 And 5850 Å, J Krelowski, Theodore P. Snow, J Papaj, C G. Seab, B Wszolek Jan 1993

On The System Of Diffuse Interstellar Bands At 5844 And 5850 Å, J Krelowski, Theodore P. Snow, J Papaj, C G. Seab, B Wszolek

Physics Faculty Publications

Two neighboring diffuse interstellar bands (DIBs) at 5844 and 5850 Å are shown to be of different origin. The presence or absence of the 5844 DIB is related to the ratio of the two prominent DIBs at 5780 and 5797 Å as well as to the nature of the ultraviolet extinction curve. The 5844 Å DIB is very sensitive to the extinction, being completely absent in cases where the far-UV extinction is low. This suggests that the carrier is destroyed by photons having energies above 11 or 12 eV. The 5850 Å DIB correlates very well with the well-studied DIB …

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Extended Variability Of The Symbiotic Star Ag Draconis, Menas Kafatos, S. R. Meier Jan 1993

Extended Variability Of The Symbiotic Star Ag Draconis, Menas Kafatos, S. R. Meier

Mathematics, Physics, and Computer Science Faculty Articles and Research

We have analyzed the complete set of available IUE (International Ultraviolet Explorer) spectra for the symbiotic star AG Draconis covering the period from 1979 to 1989. All absolute line fluxes and wavelengths have been obtained for the prominent emission lines in the λλ1200-3200 wavelength range. These spectra contain observations which were taken before, during and after the two extended outbursts which occurred on 1980 November to 1981 November and 1985 February to 1986 January. These two outburst events have two maxima that are separated by ~1600 days, a time scale not known to be associated with the star, but which …

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Monte Carlo Director Modeling And Display, Using The Cern Laboratory, Christine A. Byrd, Charles M. Byrd, Wilfred J. Braithwaite Jan 1993

Monte Carlo Director Modeling And Display, Using The Cern Laboratory, Christine A. Byrd, Charles M. Byrd, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

Detectors for high energy nuclear physics experiments are being modeled using programs developed and maintained at CERN, the European Organization for Nuclear Research. These programs include data handling and display routines, as well as those using random-sampling Monte Carlo techniques to calculate energy depositions for high energy particles as they pass through the various parts of the detector system. The complete CERN library has been imported for use with our Workstation computers in a multiple user environment. The enormous CERN Monte Carlo program GEANT(French for GIANT) tracks the progress of a particle through a detector on a simulated event-by-event basis. …

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Radiative Lifetimes, Branching Ratios, And Absolute Transition Probabilities In Cr Ii And Zn Ii, Scott D. Bergeson, J. E. Lawler Jan 1993

Radiative Lifetimes, Branching Ratios, And Absolute Transition Probabilities In Cr Ii And Zn Ii, Scott D. Bergeson, J. E. Lawler

Faculty Publications

New absolute atomic transition probability measurements are reported for 12 transitions in Cr II and two transitions in Zn II. These transition probabilities are determined by combining branching ratios measured by classical techniques and radiative lifetimes measured by time-resolved laser-induced fluorescence. The measurements are compared with branching fractions, radiative lifetimes, and transition probabilities in the literature. The 206 nm resonance multiplets in Cr II and Zn II are included in this work. These multiplets are very useful in determining the distribution of the elements in the gas versus grain phases in the interstellar medium.

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Oscillator Strengths Of The Si Ii 181 Nanometer Resonance Multiplet, Scott D. Bergeson, J. E. Lawler Jan 1993

Oscillator Strengths Of The Si Ii 181 Nanometer Resonance Multiplet, Scott D. Bergeson, J. E. Lawler

Faculty Publications

We report Si II experimental log (gf)-values of –2.38(4) for the 180.801 nm line, of –2.18(4) for the 181.693 nm line, and of –3.29(5) for the 181.745 nm line, where the number in parenthesis is the uncertainty in the last digit. The overall uncertainties (~10%) include the 1 σ random uncertainty (~6%) and an estimate of the systematic uncertainty. The oscillator strengths are determined by combining branching fractions and radiative lifetimes. The branching fractions are measured using standard spectroradiometry on an optically thin source; the radiative lifetimes are measured using time-resolved laser-induced fluorescence.

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Ti-Ii Transition Probabilities And Radiative Lifetimes In Ti+ And The Solar Titanium Abundance, A. Bizzarri, M.C.E. Huber, A. Noels, N. Grevesse, Scott D. Bergeson, P. Tsekeris, J. E. Lawler Jan 1993

Ti-Ii Transition Probabilities And Radiative Lifetimes In Ti+ And The Solar Titanium Abundance, A. Bizzarri, M.C.E. Huber, A. Noels, N. Grevesse, Scott D. Bergeson, P. Tsekeris, J. E. Lawler

Faculty Publications

Transition probabilities of 100 Ti-II emission lines, originating from 7 different atomic levels, have been determined by combining branching fractions with radiative lifetimes. The branching fractions were meaures using Fourier transform spectroscopy on a hollow cathode. The radiative lifetimes of these 7 – and 35 additional – levels were measured using time resolved laser-induced fluorescence on a slow Ti ion beam. The transition probabilities of 21 very weak lines have been used to derive a solar titanium abundance of aTi=log(NTi/NH)+12=5.04±0.04 dex, which is insensitive to the solar model. This value is in …

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Transition Probabilities For The 3s23p(2PO)–3s3p2(4P) Intersystem Lines Of Si Ii, Anthony G. Calamai, Peter L. Smith, Scott D. Bergeson Jan 1993

Transition Probabilities For The 3s23p(2PO)–3s3p2(4P) Intersystem Lines Of Si Ii, Anthony G. Calamai, Peter L. Smith, Scott D. Bergeson

Faculty Publications

Intensity ratios of lines of the spin-changing "intersystem" multiplet of Si II (4P → 2Po) at 234 nm have been used to determine electron densities and temperatures in a variety of astrophysical environments. However, the accuracy of these diagnostic calculations have been limited by uncertainties associated with the available atomic data. We report the first laboratory measurement, using an ion-trapping technique, of the radiative lifetimes of the three metastable levels of the 3s3p2 4P term of Si II. Our results are 104 ± 16, 406 ± 33, and 811 ± 77 µs for …

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Modeling Sio Maser Emission From Late-Type Stars, Philip B. Lockett, Moshe Elitzur Nov 1992

Modeling Sio Maser Emission From Late-Type Stars, Philip B. Lockett, Moshe Elitzur

Physics and Astronomy Faculty Publications

We have performed a thorough study of both radiative and collisional pumping of the SiO masers around late-type stars, carefully considering the combined and separate actions of each type of pump in order to gauge its effectiveness. We find that collisional pumping is severely underestimated when the model calculations use a small number (less than about 18) of rotational levels in each vibrational state. We have developed a procedure that corrects this problem and gives results that are nearly independent of the number of levels utilized in the calculations. We recognize, but do not solve, an important problem that afflicts …

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Two New Spotted Variables-Hd 191262 And Hd 191011, Douglas S. Hall, Gregory W. Henry Nov 1992

Two New Spotted Variables-Hd 191262 And Hd 191011, Douglas S. Hall, Gregory W. Henry

Information Systems and Engineering Management Research Publications

New 1988-1990 photometry in V and B with a 16 inch automatic telescope shows that both HD 191262, a previously known chromospherically active binary, and its comparison star HD 191011 are variable, with starspots judged to be the mechanism in both. In HD 191262 and 191011, respectively, spot rotation periods of 5d.4 < P < 5d.7 and 1 7d.4 < P < 23d.0 were found and differential rotation coefficients of k=0.054 and 0.28 were estimated. HD 191011, shown to be a KS giant about 475 parsecs away, had eight different spots present during the 2.5 years of observation.

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Galactic Structure From Faint Stromgren Photometry: The Catalog Of Observations, Ted A. Von Hippel Nov 1992

Galactic Structure From Faint Stromgren Photometry: The Catalog Of Observations, Ted A. Von Hippel

Publications

We have initiated the faint photometric survey in the Stromgren system covering about 1 square degree and including 1238 objects in order to develop samples which best probe the thick disk population. The catalog of observations are presented here. They were acquired without kinematic or metallicity biases and are complete to V=17.3-18.5, depending on the field, for 810 early to relatively late type stars. Photometric metallicities were derived for 508 stars and indicate a metal-poor stellar population, consistent with a mixture of thick disk and halo stars. While the Stromgren u-band was not part of the survey, follow-up u-band observations …

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Linear Theory Of Non-Neutral Plasma Equilibrium In A Tilted Magnetic Field, Ross L. Spencer, Grant W. Hart Nov 1992

Linear Theory Of Non-Neutral Plasma Equilibrium In A Tilted Magnetic Field, Ross L. Spencer, Grant W. Hart

Faculty Publications

A linear perturbation expansion has been found that allows the rapid and accurate calculation of the response of a non-neutral plasma to a tilted magnetic field. The results of the calculation have been found to agree with previous three-dimensional equilibrium calculations, and also to agree with Keinigs' [Phys. Fluids 24, 860 (1981)] calculation of zero-frequency resonances caused by magnetic field errors. This expansion also allows the perturbed velocity to be calculated. It is speculated that this perturbed flow may be related to the enhanced radial transport in a non-neutral plasma with a tilted magnetic field.

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Use Of Raman Spectroscopy In Characterizing Soft X-Ray Multilayers: Tools In Understanding Structure And Interfaces, Ming Cai, Qi Wang, David D. Allred, Larry V. Knight, Dorian M. Hatch, A. Reyes-Mena, Guizhong Zhang Oct 1992

Use Of Raman Spectroscopy In Characterizing Soft X-Ray Multilayers: Tools In Understanding Structure And Interfaces, Ming Cai, Qi Wang, David D. Allred, Larry V. Knight, Dorian M. Hatch, A. Reyes-Mena, Guizhong Zhang

Faculty Publications

Our group is studying the structure and interfaces of soft x-ray multilayers by various techniques including x-ray diffraction and Raman spectroscopy. Raman spectroscopy is particularly useful since it is sensitive to the identity of individual bonds and thus can potentially characterize the abruptness of interfaces in multilayers. Blocking interfacial mixing is very important in achieving and maintaining high reflectivity. We report our studies of the as-deposited and postannealed structure of Mo/Si and W/C multilayers. The Mo/Si system is probably the most widely studied multilayer currently because of its potential applications for soft x-ray projection lithography for the range of 13 …

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An Interacting Galaxy Pair In The Bootes Void, D. Weistrop, P. Hintzen, R. C. Kennicut, C. Liu, James Lowenthal, K. P. Cheng, R. Oliversen, B. Woodgate Sep 1992

An Interacting Galaxy Pair In The Bootes Void, D. Weistrop, P. Hintzen, R. C. Kennicut, C. Liu, James Lowenthal, K. P. Cheng, R. Oliversen, B. Woodgate

Astronomy: Faculty Publications

We report the first identified pair of interacting galaxies in the Bootes void. The galaxies, CG 692 (IRAS 1519 + 5050) and CG 693, have redshifts 0.0572 and 0.0575, respectively, and a mutual separation of ∼34 kpc. CG 692 is experiencing widespread star formation, at a rate estimated to be 18.4 M ⊙ yr-1. CG 693 is a Seyfert 1, the third AGN found in the Bootes void, with a small amount of extranuclear star formation. The pair is another example of interacting galaxies displaying starburst and Seyfert activity apparently triggered by the interaction.

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Planar H2O Masers In Star-Forming Regions, Moshe Elitzur, David J. Hollenbach, Christopher F. Mckee Jul 1992

Planar H2O Masers In Star-Forming Regions, Moshe Elitzur, David J. Hollenbach, Christopher F. Mckee

Physics and Astronomy Faculty Publications

The planar geometry of shocked material is the key property in enabling the high brightness temperatures of H20 masars in star-forming regions. We solve for the brightness temperature, the beaming angle, and the maser spot size for thin, saturated planar masers under the assumption that the velocity change across the maser due to ordered motions is small compared with the thermal or microturbulent line width. For a given set of physical parameters, the brightness temperature is essentially fully determined by the length of the velocity-coherent region in the shocked plane along the line of sight. The geometry in the transverse …

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Sic Particles From Asymptotic Giant Branch Stars: Mg Burning And The S-Process, Lawrence E. Brown, Donald D. Clayton Jun 1992

Sic Particles From Asymptotic Giant Branch Stars: Mg Burning And The S-Process, Lawrence E. Brown, Donald D. Clayton

Publications

The question of whether isotopically anomalous SiC particles found in meteorites originate in AGB stars is addressed. It is shown that if the peak helium shell flash temperatures of massive (6-9 solar masses) stars are about 10 percent larger than they are normally assumed to be, alpha particle reactions with the magnesium will become significant. Then the (Mg-29)(alpha, n)Si-29 reaction produces a large excess of Si-29. With a light element nuclear reaction network, the evolution of the silicon isotopic composition during AGB evolution is calculated. It is found that the experimentally determined correlation between excess Si-29 and excess Si-30 in …

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Line Profile Asymmetries In Chromospherically Active Stars, Robert C. Dempsey, Bernard W. Bopp, Klaus G. Strassmeier, Arno F. Granados, Gregory W. Henry, Douglas S. Hall Jun 1992

Line Profile Asymmetries In Chromospherically Active Stars, Robert C. Dempsey, Bernard W. Bopp, Klaus G. Strassmeier, Arno F. Granados, Gregory W. Henry, Douglas S. Hall

Information Systems and Engineering Management Research Publications

A powerful, new probe of chromospheric activity, cross-correlation, has been developed and applied to a variety of stars. In this particular application, an entire CCD spectrum of an active star is correlated with the spectrum of a narrow-line, inactive star of similar spectral type and luminosity class. Using a number of strong lines in this manner enables the detection of absorption profile asymmetries at moderate resolution (lambda/Delta lambda about 40,000) and S/N 150:1. This technique has been applied to 14 systems mostly RS CVn's, with 10 not greater than nu sin i not greater than 50 km/s and P not …

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Speckle And Spectroscopic Orbits Of The Early A-Type Triple System In Virginis, William I. Hartkopf, Harold A. Mcalister, Xinxing Yang, Francis C. Fekel Jun 1992

Speckle And Spectroscopic Orbits Of The Early A-Type Triple System In Virginis, William I. Hartkopf, Harold A. Mcalister, Xinxing Yang, Francis C. Fekel

Information Systems and Engineering Management Research Publications

Eta Virginis is a bright (V = 3.89) triple system of composite spectral type A2 IV that has been observed for over a dozen years with both spectroscopy and speckle interferometry. Analysis of the speckle observations results in a long period of 13.1 yr. This period is also detected in residuals from the spectroscopic observations of the 71.7919 day short-period orbit. Elements of the long-period orbit were determined separately using the observations of both techniques. The more accurate elements from the speckle solution have been assumed in a simultaneous spectroscopic determination of the short- and long-period orbital elements. The magnitude …

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Water Masers In W49n - The Youngest Stellar Jet?, Mordecai-Mark Mac Low, Moshe Elitzur Jun 1992

Water Masers In W49n - The Youngest Stellar Jet?, Mordecai-Mark Mac Low, Moshe Elitzur

Physics and Astronomy Faculty Publications

Observations by Gwinn, Moran, and Reid of the proper motions of water masers in W49N show that they have an elongated distribution expanding from a common center. Features with high space velocity only occur far from the center, while low-velocity features occur at all distances. It is proposed that water masers in star-forming regions occur in expanding shells swept up by high-velocity winds from young, massive stars during the early phases of the expansion. In W49N, confinement of the bubble by a density distribution with an axial cavity can explain both the velocity field and the shape of the maser …

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