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Articles 8281 - 8310 of 9205

Full-Text Articles in Physical Sciences and Mathematics

Time-Series Photometric Spot Modeling. Iii. Thirty Years In The Life Of Hk Lacertae., Katalin Oláh, Zsolt Kővári, János Bartus, Klaus G. Strassmeier, Douglas S. Hall, Gregory W. Henry May 1997

Time-Series Photometric Spot Modeling. Iii. Thirty Years In The Life Of Hk Lacertae., Katalin Oláh, Zsolt Kővári, János Bartus, Klaus G. Strassmeier, Douglas S. Hall, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We present a spot modeling analysis of the active late-type giant HK Lac using 30 years of photometry, including 600 new data points from the last six years. We have analyzed folded light curves and, when we had long continuous data sets, applied a new computer code for time-series modeling. The validity of the modeling results was tested as a function of the photometric noise. We have determined the unspotted brightness of HK Lac in the BV(RI)_C_ bandpasses and obtained a spot temperature of {DELTA}T=1200+/-100K. Polar active regions were recovered throughout the modeling because no other scenario was able to …

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Rotational Velocities Of Late-Type Stars, Francis C. Fekel May 1997

Rotational Velocities Of Late-Type Stars, Francis C. Fekel

Information Systems and Engineering Management Research Publications

A calibration based on the results of Gray has been used to determine projected rotational velocities for 133 bright stars with spectral types of F, G, or K, most of which appear in {The Bright Star Catalogue}. The vast majority have {v} sin {i} ≤q 10 km s-1 and, thus, are slow rotators. With the new calibration, projected rotational velocities have been determined for a sample of 111 late-type stars, most of which are chromospherically active. Some of the stars have had their rotational velocities measured for the first time.

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Whole Earth Telescope Observations Of The Helium Interacting Binary Pg 1346+082 (Cr Bootis), Judith L. Provençal, Matt A. Wood May 1997

Whole Earth Telescope Observations Of The Helium Interacting Binary Pg 1346+082 (Cr Bootis), Judith L. Provençal, Matt A. Wood

Aerospace, Physics, and Space Science Faculty Publications

We present our analysis of 240 hr of white-light, high-speed photometry of the dwarf nova-like helium variable PG 1346+082 (CR Boo). We identify two frequencies in the low-state power spectrum, at 679.670 ± 0.004 μHz and 669.887 ± 0.008 μHz. The 679.670 μHz variation is coherent over at least a 2 week time span, the first demonstration of a phase-coherent photometric variation in any dwarf nova-like interacting binary white dwarf system. The high-state power spectrum contains a complex fundamental with a frequency similar, but not identical, to the low-state spectrum, and a series of harmonics not detected in low state. …

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Optical Rotation Curves Of Distant Field Galaxies: Sub-L, Systems, Nicole P. Vogt, Andrew C. Phillips, S. M. Faber, Jesús Gallego, Caryl Gronwall, R. Guzmán, Garth D. Illingworth, David C. Koo, James D. Lowenthal Apr 1997

Optical Rotation Curves Of Distant Field Galaxies: Sub-L, Systems, Nicole P. Vogt, Andrew C. Phillips, S. M. Faber, Jesús Gallego, Caryl Gronwall, R. Guzmán, Garth D. Illingworth, David C. Koo, James D. Lowenthal

Astronomy: Faculty Publications

Moderate-resolution spectroscopic observations from the Keck 10 m telescope are used to derive internal kinematics for eight faint disk galaxies in the fields flanking the Hubble Deep Field. The spectroscopic data are combined with high-resolution F814W Wide Field Planetary Camera 2 images from the Hubble Space Telescope that provide morphologies, scale lengths, inclinations, and orientations. The eight galaxies have redshifts 0.15 ≲ z ≲ 0.75, magnitudes 18.6 ≤ I ≤ 22.1, and luminosities -21.8 ≤ M ≤ -19.0 (H = 75 km s Mpc and q = 0.05). Terminal disk velocities are derived from the spatially resolved velocity profiles by …

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Solar Wind-Magnetosphere Coupling During An Isolated Substorm Event: A Multispacecraft Istp Study, T I. Pulkkinen, D N. Baker, Niescja E. Turner, H J. Singer, L A. Frank, J B. Sigwarth, J Scudder, R Anderson, S Kokubun, R Nakamura, T Mukai, J B. Blake, C T. Russell, H Kawano, F Mozer, J A. Slavin Apr 1997

Solar Wind-Magnetosphere Coupling During An Isolated Substorm Event: A Multispacecraft Istp Study, T I. Pulkkinen, D N. Baker, Niescja E. Turner, H J. Singer, L A. Frank, J B. Sigwarth, J Scudder, R Anderson, S Kokubun, R Nakamura, T Mukai, J B. Blake, C T. Russell, H Kawano, F Mozer, J A. Slavin

Physics and Astronomy Faculty Research

Multispacecraft data from the upstream solar wind, polar cusp, and inner magnetotail are used to show that the polar ionosphere responds within a few minutes to a southward IMF turning, whereas the inner tail signatures are visible within ten min from the southward turning. Comparison of two subsequent substorm onsets, one during southward and the other during northward IMF, demonstrates the dependence of the expansion phase characteristics on the external driving conditions. Both onsets are shown to have initiated in the midtail, with signatures in the inner tail and auroral oval following a few minutes later.

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Accurate Hydrogen Spectral Simulations With A Compact Model Atom, Jason W. Ferguson, Gary J. Ferland Apr 1997

Accurate Hydrogen Spectral Simulations With A Compact Model Atom, Jason W. Ferguson, Gary J. Ferland

Physics and Astronomy Faculty Publications

Many large-scale numerical simulations of astrophysical plasmas must also reproduce the hydrogen ionization and the resulting emission spectrum, in some cases quite accurately. We describe a compact model hydrogen atom that can be readily incorporated into such simulations. It reproduces the recombination efficiency and line spectrum predicted by much larger calculations for a very broad range of densities and temperatures. Uncertainties in hydrogen collision data are the largest source of differences between our compact atom and predictions of more extensive calculations and underscore the need for accurate atomic data.

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Resolution And Kinematics Of Molecular Hydrogen In The Cloverleaf Gravitational Lens, Min S. Yun, N Z. Scoville, J J. Carrasco, R D. Blandford Apr 1997

Resolution And Kinematics Of Molecular Hydrogen In The Cloverleaf Gravitational Lens, Min S. Yun, N Z. Scoville, J J. Carrasco, R D. Blandford

Min S. Yun

Gravitational lenses have long been advertised as primitive telescopes, capable of magnifying cosmologically distant sources. In this Letter we present new, 0"9 resolution CO (7– 6) observations of the z 5 2.56 Cloverleaf quasar (H14131117) and spatially resolved images. By modeling the gravitational lens, we infer a size scale of 0"3 (11 kpc) for the molecular gas structure surrounding the quasar, and the gas has a kinematic structure roughly consistent with a rotating disk. The observed properties of the CO-emitting gas are similar to the nuclear starburst complexes found in the infrared luminous galaxies in the local universe, and metal …

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Using Fundamental Plane Distances To Estimate The Total Binding Mass In Abell 2626, Joseph J. Mohr, Gary Wegner Apr 1997

Using Fundamental Plane Distances To Estimate The Total Binding Mass In Abell 2626, Joseph J. Mohr, Gary Wegner

Dartmouth Scholarship

We use fundamental plane (FP) distance estimates to the components of the double cluster A2626 (cz ~ 17,500 km/s) to constrain cluster kinematics and estimate total binding mass. We employ deep R band CCD photometry, multi-object spectroscopy, and software designed to account for seeing effects to measure the FP parameters R_e, sigma , and for 24 known early type and S0 cluster members. The FP coefficients from this sample (alpha =1.30+/-0.36 and beta =0.31+/-0.06) are consistent with others reported in the literature. We examine the Mg_b equivalent width distributions within both subclusters and find them to be indistinguishable. Lacking evidence …

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The Extremely Active Single Giant 1e 1751+7046 = Et Draconis: Revised Properties And A Reevaluation Of Its Evolutionary Status, Carol W. Ambruster, Francis C. Fekel, Edward F. Guinan, Bruce J. Hrivnak Apr 1997

The Extremely Active Single Giant 1e 1751+7046 = Et Draconis: Revised Properties And A Reevaluation Of Its Evolutionary Status, Carol W. Ambruster, Francis C. Fekel, Edward F. Guinan, Bruce J. Hrivnak

Information Systems and Engineering Management Research Publications

New spectroscopic observations have resulted in significant revisions to several of the orginally published properties of the X-ray bright, chromospherically active star 1E 1751+7046: the spectral classification has been revised from K5 IV to K0 III, v sin i from 30-40 km s-1 to 23 km s-1, and the reported nondetection of the Li I 6707 Å line to a significant log epsilon(Li) = 1.8. Chromospheric and transition region surface fluxes from IUE observations and the coronal surface flux from earlier Einstein data are close to saturation levels, and comparable only to very active binaries, pre-main-sequence stars, and FK Comae …

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Peculiar Velocities Of Clusters In Cold Dark Matter Models, Stefano Borgani, Luiz N. Da Costa, Wolfram Freudling, Riccardo Giovanelli, Martha P. Haynes, John Salzer, Gary Wegner Mar 1997

Peculiar Velocities Of Clusters In Cold Dark Matter Models, Stefano Borgani, Luiz N. Da Costa, Wolfram Freudling, Riccardo Giovanelli, Martha P. Haynes, John Salzer, Gary Wegner

Dartmouth Scholarship

Recently, peculiar velocity measurements became available for a new sample of galaxy clusters, hereafter the SCI sample. From an accurately calibrated Tully-Fisher relation for spiral galaxies, we compute the rms peculiar velocity, Vrms, and compare it with the linear theory predictions of COBE-normalized low-density and open cold dark matter models (ΛCDM and OCDM, respectively). Confidence levels for model rejection are estimated using a Monte Carlo procedure in order to generate a large ensemble of artificial data sets for each model. Following Zaroubi et al., we express our results in terms of constraints on the (Ω0, …

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Grains In Ionized Nebulae. Ii. Heavy-Element Depletion, J. B. Kingdon, Gary J. Ferland Mar 1997

Grains In Ionized Nebulae. Ii. Heavy-Element Depletion, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

The presence of grains in gaseous nebulae can have significant effects on the thermal balance and radiative line transfer in these objects. The depletion of condensable elements onto grains provides evidence that dust exists in the ionized regions of nebulae. In this paper, we consider the elements Sc, Ti, V, and Cr, all of which are strongly depleted in the general interstellar medium. We construct simple three-level atoms for several ions of these elements, and incorporate them into our photoionization code CLOUDY. For both a model planetary nebula and a model H II region, we find that several lines of …

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The Spectroscopic Orbit Of Pi Ceti, Claud H.S. Lacy, Francis C. Fekel, Robert D. Mathieu, Nidia I. Morrell, J. A. Morse, Guillermo Torres, Daryl W. Willmarth Mar 1997

The Spectroscopic Orbit Of Pi Ceti, Claud H.S. Lacy, Francis C. Fekel, Robert D. Mathieu, Nidia I. Morrell, J. A. Morse, Guillermo Torres, Daryl W. Willmarth

Information Systems and Engineering Management Research Publications

π Ceti (HR 811, B7 V) has been known to be variable in its radial velocity for almost a century, but its relatively long period and small amplitude have conspired against a determination of its orbit. We have combined in an optimal fashion observations from early in this century with modern measurements to find the spectroscopic orbit with high accuracy. The orbit has a period of 7.45 years and a semiamplitude of 4.3 km/s. The measured eccentricity of e=0.00±0.07 is indistinguishable from circular, surprising for such a long period. The 76 radial velocity observations available extend over 12 cycles of …

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New And Improved Parameters Of Hd 202908=Ads 14839: A Spectroscopic-Visual Triple System, Francis C. Fekel, Colin D. Scarfe, David J. Barlow, Antoine Duquennoy, Harold A. Mcalister, William I. Hartkopf, Brian D. Mason, Andrei A. Tokovinin Mar 1997

New And Improved Parameters Of Hd 202908=Ads 14839: A Spectroscopic-Visual Triple System, Francis C. Fekel, Colin D. Scarfe, David J. Barlow, Antoine Duquennoy, Harold A. Mcalister, William I. Hartkopf, Brian D. Mason, Andrei A. Tokovinin

Information Systems and Engineering Management Research Publications

HD 202908=ADS 14839 is a spectroscopic-visual triple system consisting of three solar-type stars. Eighteen years of spectroscopic observations including coverage of the recent periastron of 1987 January plus visual and speckle observations, the latter covering roughly the same interval as the radial velocities, have been used to obtain a simultaneous three-dimensional orbital solution. The short-period pair, Aa and Ab, has an orbital period of 3.9660465 days and a small but real eccentricity of 0.0033. The visual pair, A and B, has an orbital period of 78.5 yr and an eccentricity of 0.865. The solution yields masses for all three stars …

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The Elemental Composition Of Stony Cosmic Spherules, D. E. Brownlee, Beeway Bates, L. Schramm Mar 1997

The Elemental Composition Of Stony Cosmic Spherules, D. E. Brownlee, Beeway Bates, L. Schramm

SIAS Faculty Publications

Five hundred stony cosmic spherules collected from deep-sea sediments, polar ice, and the stratosphere have been analyzed for major and some minor element composition. Typical spherules are products of atmospheric melting of millimeter sized and smaller meteoroids. The samples are small and modified by atmospheric entry, but they are an important source of information on the composition of asteroids. The spherules in this study were all analyzed in an identical Manner, and they provide a sampling of the solar system's asteroids that is both different and less biased than provided by studies of conventional meteorites. Volatile elements such as Na …

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The Tully-Fisher Relation And H0, Riccardo Giovanelli, Martha P. Haynes, Luiz N. Da Costa, Wolfram Freudling, John Salzer, Gary Wegner Mar 1997

The Tully-Fisher Relation And H0, Riccardo Giovanelli, Martha P. Haynes, Luiz N. Da Costa, Wolfram Freudling, John Salzer, Gary Wegner

Dartmouth Scholarship

The use of the Tully-Fisher (TF) relation for the determination of H0 relies on the availability of an adequate template TF relation and of reliable primary distances. Here we use a TF template relation with the best available kinematical zero point, obtained from a sample of 24 clusters of galaxies extending to cz ~ 9000 km s-1, and the most recent set of Cepheid distances for galaxies fit for TF use. The combination of these two ingredients yields H0 = 69 ± 5 km s-1 Mpc-1. The approach is significantly more accurate than …

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The Peculiar Motions Of Early‐Type Galaxies In Two Distant Regions. Iv. The Photometric Fitting Procedure, R. P. Saglia, Edmund Bertschinger, G. Baggley, David Burstein, Matthew Colless, Roger L. Davies, Robert K. Mcmahan Jr., Gary Wegner Mar 1997

The Peculiar Motions Of Early‐Type Galaxies In Two Distant Regions. Iv. The Photometric Fitting Procedure, R. P. Saglia, Edmund Bertschinger, G. Baggley, David Burstein, Matthew Colless, Roger L. Davies, Robert K. Mcmahan Jr., Gary Wegner

Dartmouth Scholarship

The EFAR project is a study of 736 candidate early-type galaxies in 84 clusters lying in two regions toward Hercules-Corona Borealis and Perseus-Cetus at distances cz ≈ 6000-15,000 km s-1. In this paper we describe a new method of galaxy photometry adopted to derive the photometric parameters of the EFAR galaxies. The algorithm fits the circularized surface brightness profiles as the sum of two seeing-convolved components, an R1/4 and an exponential law. This approach allows us to fit the large variety of luminosity profiles displayed by the EFAR galaxies homogeneously and to derive (for at least a …

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Far-Ultraviolet Absorption Lines In The Remnant Of Sn 1006, Chi-Chao Wu, D. Michael Crenshaw, Andrew J. S. Hamilton, Robert A. Fesen Mar 1997

Far-Ultraviolet Absorption Lines In The Remnant Of Sn 1006, Chi-Chao Wu, D. Michael Crenshaw, Andrew J. S. Hamilton, Robert A. Fesen

Dartmouth Scholarship

We have obtained a far-ultraviolet spectrum (1150-1600 Å) of a hot subdwarf star behind the remnant of supernova 1006 with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope. The high-quality spectrum is used to test previous identifications of the strong absorption features discovered with the International Ultraviolet Explorer. These features have FWHM = 4000 (±300) km s-1 and are not at the rest wavelengths of known interstellar lines, as opposed to the broader (~8000 km s-1 FWHM) Fe II lines from the remnant centered at 0 km s-1 in near-UV FOS spectra. We …

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Pulsations And Accretion Geometry In Yy Draconis: A Study Based On Hubble Space Telescope Observations, Carole A. Haswell, Joseph Patterson, John R. Thorstensen, Coel Hellier Feb 1997

Pulsations And Accretion Geometry In Yy Draconis: A Study Based On Hubble Space Telescope Observations, Carole A. Haswell, Joseph Patterson, John R. Thorstensen, Coel Hellier

Dartmouth Scholarship

We present 1 Å resolution fast ultraviolet spectroscopy of YY Dra, coordinated U, B, V, R, and I photometry, and Hα spectroscopy. The UV continuum is strongly pulsed: we found 16% semiamplitude pulses with period 264.7(1) s; there was no evidence for power at twice this period. The UBV pulses are in phase with the UV continuum pulsation. A color temperature of 105 K was found for the pulse spectrum, with a corresponding area 0.5% of the white dwarf surface. We refine the white dwarf spin period, obtaining Pspin = 529.31 ± 0.02 s. Optical pulses at …

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An Atlas Of Computed Equivalent Widths Of Quasar Broad Emission Lines, Kirk Korista, Jack Baldwin, Gary J. Ferland, Dima Verner Feb 1997

An Atlas Of Computed Equivalent Widths Of Quasar Broad Emission Lines, Kirk Korista, Jack Baldwin, Gary J. Ferland, Dima Verner

Physics and Astronomy Faculty Publications

We present graphically the results of several thousand photoionization calculations of broad emission-line clouds in quasars, spanning 7 orders of magnitude in hydrogen ionizing flux and particle density. The equivalent widths of 42 quasar emission lines are presented as contours in the particle density-ionizing flux plane for a typical incident continuum shape, solar chemical abundances, and cloud column density of N(H) = 1023 cm-2. Results are similarly given for a small subset of emission lines for two other column densities (1022 and 1024 cm-2), five other incident continuum shapes, and a gas …

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On Protostellar Disks In Herbig Ae/Be Stars, Anatoly Miroshnichenko, Željko Ivezić, Moshe Elitzur Jan 1997

On Protostellar Disks In Herbig Ae/Be Stars, Anatoly Miroshnichenko, Željko Ivezić, Moshe Elitzur

Physics and Astronomy Faculty Publications

The spectral shape of IR emission from Herbig Ae/Be stars has been invoked as evidence for accretion disks around high-mass protostars. Instead, we present here models based on spherical envelopes with an r-1.5 dust density profile that successfully explain the observed spectral shapes. The spectral energy distributions of eight primary candidates for protostellar disks are fitted in detail for all wavelengths available, from visual to far-IR. The only envelope property adjusted in individual sources is the overall visual optical depth, and it ranges from 0.3 to 3. In each case, our models properly reproduce the data for IR excess, …

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Molecular Gas And Infrared Emission In Hcg 31 And Hcg 92 (Stephan's Quintet) And Tidal Interactions In Compact Group Environment, Min S. Yun, L Verdes-Montenegro, A Del Olmo, J Perea Jan 1997

Molecular Gas And Infrared Emission In Hcg 31 And Hcg 92 (Stephan's Quintet) And Tidal Interactions In Compact Group Environment, Min S. Yun, L Verdes-Montenegro, A Del Olmo, J Perea

Min S. Yun

We present the interferometric measurements of 2.6 mm CO (J 5 13 0) emission (uFWHM 1 50) and the analysis of IRAS HIRES images of two Hickson compact groups HCG 31 and HCG 92 (“Stephan’s Quintet”). The far-infrared (FIR) emission is concentrated to a single region in HCG 31 while it is clearly extended and peaks near the group center in HCG 92. CO emission is weak in HCG 31, and the brightest peak occurs in the overlap region between the galaxies A and C. CO emission is detected only in galaxy C (NGC 7319) in HCG 92, and the …

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[Fe Iv] In The Orion Nebula, R. H. Rubin, R. J. Dufour, Gary J. Ferland, P. G. Martin, C. R. O'Dell, J. A. Baldwin, J. J. Hester, D. K. Walter, Z. Wen Jan 1997

[Fe Iv] In The Orion Nebula, R. H. Rubin, R. J. Dufour, Gary J. Ferland, P. G. Martin, C. R. O'Dell, J. A. Baldwin, J. J. Hester, D. K. Walter, Z. Wen

Physics and Astronomy Faculty Publications

Using the Goddard High-Resolution Spectrograph on the Hubble Space Telescope, we measured the flux of [Fe IV] (3d5 4P5/2 --> 3d5 6S5/2) λvac = 2836.56 Å in the Orion Nebula, the first detection of an [Fe IV] line in an H II region. A useful upper limit is set on the sum of fluxes of [Fe IV] (3d5 4D5/2, 3/2 --> 3d5 6S5/2) λvac = 2568.4, 2568.2 Å. By comparing these observations with predicted fluxes from simply ``retrofitting'' our two previous photoionization models, …

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Progress In The Study Of Cdznte Strip Detectors, O Tousignant, L A. Hamel, J F. Courville, P Paki, John R. Macri, K Larson, M Mayer, Mark L. Mcconnell, James M. Ryan Jan 1997

Progress In The Study Of Cdznte Strip Detectors, O Tousignant, L A. Hamel, J F. Courville, P Paki, John R. Macri, K Larson, M Mayer, Mark L. Mcconnell, James M. Ryan

Space Science Center

We report new performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector under study as a prototype imaging spectrometer for astronomical x-ray and gamma-ray observations. The prototype is 1.5 mm thick with 375 micron strip pitch in both the x and y dimensions. Previously reported work included demonstrations of half-pitch spatial resolution (approximately 190 microns) and good energy resolution and spectral uniformity. Strip detector efficiency measurements have also been presented. A model that includes the photon interaction, carrier transport and the electronics was developed that qualitatively reproduced the measurements. The new studies include measurements of the CdZnTe …

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Galactic Black Hole Binaries: High-Energy Radiation, J E. Grove, J E. Grindlay, B A. Harmon, X M. Hua, D Kazanas, Mark L. Mcconnell Jan 1997

Galactic Black Hole Binaries: High-Energy Radiation, J E. Grove, J E. Grindlay, B A. Harmon, X M. Hua, D Kazanas, Mark L. Mcconnell

Space Science Center

Observations of galactic black hole candidates made by the instruments aboard the Compton GRO in the hard X-ray and γ-ray bands have significantly enhanced our knowledge of the phenomenology of the emission from these objects. Understanding these observations presents a formidable challenge to theoretical models of the accretion flow onto the compact object and of the physical mechanisms that generate high-energy radiation. Here we summarize the current state of observations and theoretical interpretation of the emission from black holecandidates above 20 keV. The all-sky monitoring capability of BATSE allows, for the first time, nearly continuous studies of the high-energy emission …

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5 Years Of Crab Pulsar Observations With Comptel, R Much, K Bennett, C Winkler, R Diehl, G G. Lichti, V Schonfelder, H Steinle, A W. Strong, M Varendorff, W Hermsen, L Kuiper, R Van Der Meulen, A Connors, Mark L. Mcconnell, James M. Ryan, R Buccheri Jan 1997

5 Years Of Crab Pulsar Observations With Comptel, R Much, K Bennett, C Winkler, R Diehl, G G. Lichti, V Schonfelder, H Steinle, A W. Strong, M Varendorff, W Hermsen, L Kuiper, R Van Der Meulen, A Connors, Mark L. Mcconnell, James M. Ryan, R Buccheri

Space Science Center

Using the COMPTEL data of the first 5 years of the CGRO mission we have derived the average pulsed spectrum of the Crab Pulsar, as well as phase-resolved spectra of the pulsed emission of the Crab Pulsar. The spectra in the COMPTEL energy range (0.75 to 30 MeV) are compared to those in the neighboring energy bands. The pulsed flux has been examined for its stability. Pulsed lightcurves have been derived for different energy intervals. Preliminary results of this analysis are presented.

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Evidence For Γ-Ray Flares In 3c 279 And Pks 1622-297 At ∼10 Mev, W Collmar, V Schonfelder, H Bloemen, J J. Blom, W Hermsen, Mark L. Mcconnell, J G. Stacy, K Bennett, O R. Williams Jan 1997

Evidence For Γ-Ray Flares In 3c 279 And Pks 1622-297 At ∼10 Mev, W Collmar, V Schonfelder, H Bloemen, J J. Blom, W Hermsen, Mark L. Mcconnell, J G. Stacy, K Bennett, O R. Williams

Space Science Center

The EGRET experiment aboard the Compton Gamma-Ray Observatory (CGRO) has observed at energies above 100 MeV strong gamma-ray flares with short-term time variability from thegamma-ray blazars 3C 279 [1] and PKS 1622-297 [2]. During these flaring periods both blazarshave been detected by the COMPTEL experiment aboard CGRO at photon energies of ∼10 MeV, revealing simultaneous γ-ray activity down to these energies. For both cases the derived fluxes exceed those measured in previous observations, and 3C 279 shows an indication for time variability within the observational period. Both sources show evidence for ‘hard’ MeV spectra. In general the behaviour of both …

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Improved Comptel 10–30 Mev Event Selections For Point Sources From Inflight Data, W Collmar, U Wessolowski, V Schonfelder, G Weidenspointer, S C. Kappadath, Mark L. Mcconnell, K Bennett Jan 1997

Improved Comptel 10–30 Mev Event Selections For Point Sources From Inflight Data, W Collmar, U Wessolowski, V Schonfelder, G Weidenspointer, S C. Kappadath, Mark L. Mcconnell, K Bennett

Space Science Center

After several years in orbit the COMPTEL experiment aboard the COMPTON Gamma-RayObservatory has collected a substantial amount of data from the MeV sky. We have used the inflight event data collected from the Crab, which is the brightest point source at MeV energies, to optimize our event selections for point sources. For the COMPTEL 10–30 MeV range we have derived a set of improved parameter selections, which leads to a reduction of background events and—at the same time—increases the number of source events, resulting in an obvious improvement in the signal-to-background ratio for point sources. Due to a revised cut …

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The Prompt Cosmic-Ray-Induced Background In The Orbiting Compton Telescope Comptel, James M. Ryan, S C. Kappadath, Mark L. Mcconnell, D Morris, V Schonfelder, M Varendorff, G Weidenspointer, W Hermsen, K Bennett Jan 1997

The Prompt Cosmic-Ray-Induced Background In The Orbiting Compton Telescope Comptel, James M. Ryan, S C. Kappadath, Mark L. Mcconnell, D Morris, V Schonfelder, M Varendorff, G Weidenspointer, W Hermsen, K Bennett

Space Science Center

The authors report the spectrum of background events that the COMPTEL instrument on ComptonGamma Ray Observatory experiences due to the instantaneous effects of cosmic rays. Otherbackgrounds are present in the data of this Compton telescope, but the components that closely follow the instantaneous flux of cosmic rays are the most identifiable. The background varies approximately linearly with the cosmic-ray intensity and exhibits a broad feature from about 1 to 10 MeV suggestive of the nuclear nature of the events. Above 10 MeV there is a marked change in the nature of thebackground that is not understood. It appears that the …

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Nonlinear Dependence Of Lb On Lfir And Mh2 Among Spiral Galaxies And The Effects Of Tidal Interaction, J Perea, A Del Olmo, L Verdes-Montenegro, Min S. Yun Jan 1997

Nonlinear Dependence Of Lb On Lfir And Mh2 Among Spiral Galaxies And The Effects Of Tidal Interaction, J Perea, A Del Olmo, L Verdes-Montenegro, Min S. Yun

Min S. Yun

Through the study of a carefully selected sample of isolated spiral galaxies, we have established that two important global physical quantities for tracing star-forming activities, LFIR and MH2, have a nonlinear dependence on another commonly cited global quantity, LB. Furthermore, we show that simple power-law relations can effectively describe these nonlinear relations for spiral galaxies spanning 4 orders of magnitude in FIR and MH2, and nearly 3 orders of magnitude in LB. While the existence of a nonlinear dependence of MH2 (assuming a constant CO-to-H2 conversion) and LFIR on optical luminosity (LB) has been previously noted in the literature, an …

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Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras Jan 1997

Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras

Faculty Publications

No abstract provided.

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