Open Access. Powered by Scholars. Published by Universities.®

Astrophysics and Astronomy Commons™

Open Access. Powered by Scholars. Published by Universities.®

1997

Discipline
Institution
Keyword
Publication
Publication Type

Articles 61 - 90 of 93

Full-Text Articles in Astrophysics and Astronomy

Optical Polarimetry, High–Resolution Spectroscopy And Ir Analysis Of The Chamaeleon I Dark Cloud, E. Covino, E. Palazzi, Bryan E. Penprase, H. E. Schwarz, L. Terranegra Jan 1997

Optical Polarimetry, High–Resolution Spectroscopy And Ir Analysis Of The Chamaeleon I Dark Cloud, E. Covino, E. Palazzi, Bryan E. Penprase, H. E. Schwarz, L. Terranegra

Pomona Faculty Publications and Research

We present optical polarimetry and high resolution spectroscopy of a sample of stars toward the Chamaeleon I dark cloud. We use our polarimetry which includes 33 stars to study the wavelength dependence of the degree and position angle of polarization.

From our data we found, by interpretation of the various correlations between the polarimetry, photometry and IRAS fluxes, the following:
the probable presence of shocked molecular gas; a warm molecular CH component; small dust grains at the edges of the cloud, and larger grains in the central parts, which are causing the polarization.

Our results provide a consistent picture of …

Go to article

Semiclassical Effects In Black Hole Interiors, William A. Hiscock, Shane L. Larson, Paul R. Anderson Jan 1997

Semiclassical Effects In Black Hole Interiors, William A. Hiscock, Shane L. Larson, Paul R. Anderson

All Physics Faculty Publications

First-order semiclassical perturbations to the Schwarzschild black hole geometry are studied within the black hole interior. The source of the perturbations is taken to be the vacuum stress-energy of quantized scalar, spinor, and vector fields, evaluated using analytic approximations developed by Page and others (for massless fields) and the DeWitt-Schwinger approximation (for massive fields). Viewing the interior as an anisotropic collapsing cosmology, we find that minimally or conformally coupled scalar fields, and spinor fields, decrease the anisotropy as the singularity is approached, while vector fields increase the anisotropy. In addition, we find that for massless fields of all spins, the …

Go to article

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 …

Go to article

A Search For Gamma-Ray Flares From Black-Hole Candidates On Time Scales Of ∼1.5 Hours, R Vandijk, K Bennett, H Bloemen, R Diehl, W Hermsen, Mark L. Mcconnell, James M. Ryan, V Schonfelder Jan 1997

A Search For Gamma-Ray Flares From Black-Hole Candidates On Time Scales Of ∼1.5 Hours, R Vandijk, K Bennett, H Bloemen, R Diehl, W Hermsen, Mark L. Mcconnell, James M. Ryan, V Schonfelder

Space Science Center

Strong short-lived flares from black-hole candidates have been detected in the hard X-rayregime and possibly also at γ-ray energies. Here we present a search for short-lived flares in the 0.75–30 MeV COMPTEL data. No flares are found during the 5 viewing periods considered, with typical upper limits of a few times the Crab flux.

Go to article

Reassessment Of The 56co Emission From Sn 1991t, D Morris, K Bennett, H Bloemen, R Diehl, W Hermsen, G G. Lichti, Mark L. Mcconnell, James M. Ryan, V Schonfelder Jan 1997

Reassessment Of The 56co Emission From Sn 1991t, D Morris, K Bennett, H Bloemen, R Diehl, W Hermsen, G G. Lichti, Mark L. Mcconnell, James M. Ryan, V Schonfelder

Space Science Center

The detection of 56Co emission from SN 1991T has been previously reported at a level near the COMPTEL sensitivity threshold. The spectral analysis method, fitting the count spectrum to a background model plus a 56Co emission template, is subject to possible systematic effects which had not been thoroughly studied at that time. To better evaluate the significance of that ∼3.3σ detection, the same method has been applied to a grid of points with 5° spacing, out to 35° from the pointing direction, in each of 103 observing periods from phases 1 through 3. A dozen instances were found with a …

Go to article

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.

Go to article

The Mev Spectrum Of Cygnus X-1 As Observed With Comptel, Mark L. Mcconnell, K Bennett, H Bloemen, W Collmar, W Hermsen, L Kuiper, R Much, James M. Ryan, V Schonfelder, H Steinle, A W. Strong, R Vandijk Jan 1997

The Mev Spectrum Of Cygnus X-1 As Observed With Comptel, Mark L. Mcconnell, K Bennett, H Bloemen, W Collmar, W Hermsen, L Kuiper, R Much, James M. Ryan, V Schonfelder, H Steinle, A W. Strong, R Vandijk

Space Science Center

The COMPTEL experiment on the Compton Gamma-Ray Observatory (CGRO) has observed the Cygnus region on several occasions since launch. These data represent the most sensitive observations to date of Cygnus X-1 in the 0.75–30 MeV range. The spectrum shows significant evidence for emission extending out to several MeV. These data alone suggest a need to modify the thermal Comptonization models or to incorporate some type of non-thermal emission mechanism. Here we report on the results of an analysis of selected COMPTEL data collected during the first three years of the CGRO mission. These data are then compared with contemporaneous data …

Go to article

The Total Cosmic Diffuse Gamma-Ray Spectrum From 9 To 30 Mev Measured With Comptel, S C. Kappadath, James M. Ryan, K Bennett, H Bloemen, R Diehl, W Hermsen, Mark L. Mcconnell, V Schonfelder, M Varendorff, G Weidenspointer, C Winkler Jan 1997

The Total Cosmic Diffuse Gamma-Ray Spectrum From 9 To 30 Mev Measured With Comptel, S C. Kappadath, James M. Ryan, K Bennett, H Bloemen, R Diehl, W Hermsen, Mark L. Mcconnell, V Schonfelder, M Varendorff, G Weidenspointer, C Winkler

Space Science Center

A preliminary COMPTEL Cosmic Diffuse Gamma-Ray (CDG) spectrum from 800 keV to 30 MeV was presented earlier at the 3rd Compton Symposium. The COMPTEL results represent the first significant detection of the CDG radiation in the 9 to 30 MeV range. Using high-latitude data from the first 5 years of the mission we have performed a new detailed measurement of the 9 to 30 MeV spectrum with finer energy binning. The new improved results are in good agreement with our previous estimates and are compatible with power-law extrapolations from higher energies. The measured 9–30 MeV spectra from the Virgo and …

Go to article

A Time Dependent Model For The Activation Of Comptel, M Varendorff, U Oberlack, G Weidenspointer, R Diehl, R Vandijk, Mark L. Mcconnell, James M. Ryan Jan 1997

A Time Dependent Model For The Activation Of Comptel, M Varendorff, U Oberlack, G Weidenspointer, R Diehl, R Vandijk, Mark L. Mcconnell, James M. Ryan

Space Science Center

The structure of the CGRO satellite is irradiated by cosmic rays and trapped particles fromradiation belts. These incident particles produce radioactive nuclei in nuclear reactions with the satellite structure. Most of the radiation dose can be attributed to the passages through the South Atlantic Anomaly. The incident particle flux on the COMPTEL instrument is estimated from the event rate of a plastic scintillation detector. This event rate is modeled with a Neural Network simulation. The increase of the event rate during SAA passages is taken as a measure for the amount of induced radioactivity. A Neural Network Model is used …

Go to article

Comptel All-Sky Imaging At 2.2 Mev, Mark L. Mcconnell, S Fletcher, K Bennett, H Bloemen, R Diehl, W Hermsen, James M. Ryan, V Schonfelder, A W. Strong, R Vandijk Jan 1997

Comptel All-Sky Imaging At 2.2 Mev, Mark L. Mcconnell, S Fletcher, K Bennett, H Bloemen, R Diehl, W Hermsen, James M. Ryan, V Schonfelder, A W. Strong, R Vandijk

Space Science Center

It is now generally accepted that accretion of matter onto a compact object (white dwarf, neutron star or black hole) is one of the most efficient processes in the universe for producing high energy radiations. Measurements of the γ-ray emission will provide a potentially valuable means for furthering our understanding of the accretion process. Here we focus on neutroncapture processes, which can be expected in any situation where energetic neutrons may be produced and where the liberated neutrons will interact with matter before they decay (where they have a chance of undergoing some type of neutron capture). Line emission at …

Go to article

Diffuse Galactic Continuum Emission: Recent Studies Using Comptel Data, A W. Strong, R Diehl, V Schonfelder, K Bennett, Mark L. Mcconnell, James M. Ryan Jan 1997

Diffuse Galactic Continuum Emission: Recent Studies Using Comptel Data, A W. Strong, R Diehl, V Schonfelder, K Bennett, Mark L. Mcconnell, James M. Ryan

Space Science Center

COMPTEL full sky maximum entropy maps using 5 years of data have been produced using background estimates based on high-latitude observations. The Galactic diffuse emission can be studied using latitude and longitude profiles from these maps. Direct comparison of profiles with theoretical models is illustrated for the 10–30 MeV range. We demonstrate the presence of a broad latitude component, consistent with results from model-fitting studies. The method is also used to obtain model-independent broad-band spectra of the Galactic emission.

Go to article

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 …

Go to article

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 …

Go to article

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 …

Go to article

The Panchromatic Starburst Intensity Limit At Low And High Redshift, Gerhardt R. Meurer, Timothy M. Heckman, Matthew D. Lehnert, Claus Leitherer, James D. Lowenthal Jan 1997

The Panchromatic Starburst Intensity Limit At Low And High Redshift, Gerhardt R. Meurer, Timothy M. Heckman, Matthew D. Lehnert, Claus Leitherer, James D. Lowenthal

Astronomy: Faculty Publications

The integrated bolometric effective surface brightness S distributions of starbursts are investigated for samples observed in (1) the rest frame ultraviolet (UV), (2) the far-infrared and Hα, and (3) 21 cm radio continuum emission. For the UV sample we exploit a tight empirical relationship between UV reddening and extinction to recover the bolometric flux. Parameterizing the S upper limit by the 90th percentile of the distribution, we find a mean S = 2.0×10 L⊙kpc for the three samples, with a factor of 3 difference between the samples. This is consistent with what is expected from the calibration uncertainties alone. We …

Go to article

The Nature Of Compact Galaxies In The Hubble Deep Field. Ii. Spectroscopic Properties And Implications For The Evolution Of The Star Formation Rate Density Of The Universe, Rafael Guzmán, Jesús Gallego, David C. Koo, Andrew C. Phillips, James D. Lowenthal, S. M. Faber, Garth D. Illingworth, Nicole P. Vogt Jan 1997

The Nature Of Compact Galaxies In The Hubble Deep Field. Ii. Spectroscopic Properties And Implications For The Evolution Of The Star Formation Rate Density Of The Universe, Rafael Guzmán, Jesús Gallego, David C. Koo, Andrew C. Phillips, James D. Lowenthal, S. M. Faber, Garth D. Illingworth, Nicole P. Vogt

Astronomy: Faculty Publications

We present a spectroscopic study of 51 compact field galaxies with redshifts z < 1.4 and apparent magnitudes I < 23.74 in the flanking fields of the Hubble Deep Field. These galaxies are compact in the sense that they have small apparent half-light radii (r ≤ 0″.5) and high surface brightnesses (μ ≤ 22.2 mag arcsec ). The spectra, taken at the Keck telescope, show emission lines in 88% of our sample, and only absorption lines in the remaining 12%. Emission-line profiles are roughly Gaussian with velocity widths that range from the measurement limit of σ ∼ 35 km s to 150 km s . Rest frame [O II] λ3727 equivalent widths range from 5 to 94 Å, yielding star formation rates (SFRs) of ∼0.1 to 14 M yr . The analysis of various line diagnostic diagrams reveals that ∼60% of compact emission-line galaxies have velocity widths, excitations, Hβ luminosities, SFRs, and mass-to-light ratios characteristic of young star-forming H II galaxies. The remaining 40% form a more heterogeneous class of evolved starbursts, similar to local starburst disk galaxies. We find that, although the compact galaxies at z > 0.7 have similar SFRs per unit mass to those at z < 0.7, they are on average ∼10 times more massive. Our sample implies a lower limit for the global comoving SFR density of ∼0.004 M yr Mpc at z = 0.55, and ∼0.008 M yr Mpc at z = 0.85 (assuming Salpeter IMF, H = 50 km s Mpc , and q = 0.5). These values, when compared to estimates for a sample of local compact galaxies selected in a similar fashion, support a history of the universe in which the SFR density declines by a factor ∼10 from z = 1 to today. From the comparison with the SFR densities derived for magnitude-limited samples of field galaxies, we conclude that compact emission-line galaxies, though only ∼20% of the general field population, may contribute as much as ∼45% to the global SFR of the universe at 0.4 < z < 1. © 1997. The American Astronomical Society. All rights reserved. 814 1/2 I814 ⊙ ⊙ ⊙ 0 o -2 -1 -1 -1 -1 -3 -1 -3 -1 -1

Go to article

Keck Spectroscopy Of Redshift Z ∼ 3 Galaxies In The Hubble Deep Field, James Lowenthal, David C. Koo, Rafael Guzmán, Jesús Gallego, Andrew C. Phillips, S. M. Faber, Nicole P. Vogt, Garth D. Illingworth, Caryl Gronwall Jan 1997

Keck Spectroscopy Of Redshift Z ∼ 3 Galaxies In The Hubble Deep Field, James Lowenthal, David C. Koo, Rafael Guzmán, Jesús Gallego, Andrew C. Phillips, S. M. Faber, Nicole P. Vogt, Garth D. Illingworth, Caryl Gronwall

Astronomy: Faculty Publications

We have obtained spectra with the 10 m Keck telescope of a sample of 24 galaxies having colors consistent with star-forming galaxies at redshifts 2 ≲ z ≲ 4.5 in the Hubble deep field (HDF). Eleven of these galaxies are confirmed to be at high redshift (z = 3.0), one is at z = 0.5, and the other 12 have uncertain redshifts but have spectra consistent with their being at z > 2. The spectra of the confirmed high-redshift galaxies show a diversity of features, including weak Lyα emission, strong Lyα breaks or damped Lyα absorption profiles, and the stellar and …

Go to article

The Nature Of Compact Galaxies In The Hubble Deep Field. I. Global Properties, Andrew C. Phillips, Rafael Guzmán, Jesús Gallego, David C. Koo, James D. Lowenthal, Nicole P. Vogt, S. M. Faber, Garth D. Illingworth Jan 1997

The Nature Of Compact Galaxies In The Hubble Deep Field. I. Global Properties, Andrew C. Phillips, Rafael Guzmán, Jesús Gallego, David C. Koo, James D. Lowenthal, Nicole P. Vogt, S. M. Faber, Garth D. Illingworth

Astronomy: Faculty Publications

We present 10 m Keck spectroscopy and photometry for a sample of 61 small (r1/2 ≤ 0″.5), faint (I814 ≤ 23.74), high-surface brightness (μI814 < 22.2 mag arcsec-2) galaxies in fields flanking the Hubble Deep Field. The majority of this empirically defined sample of compact galaxies lies at redshifts 0.4 ≲ z ≲ 1 (88% completeness in redshift identifications), ruling out a large component of low-redshift galaxies. The number of such galaxies in the range 1.4 ≲ z ≲ 2.2 is also constrained to ≲ 10%. The majority of the observed galaxies are emission-line systems, while a significant fraction (23%-34%) appear to be normal ellipticals or otherwise early-type systems. One object is an active galactic nucleus, and two are at high redshift (z > 2). The Keck redshift and photometric data are combined with Hubble Space Telescope images to derive luminosities and physical sizes. We also use emission-line widths, where available, to estimate masses. About two-thirds of the emission-line galaxies, or roughly one-half the sample, are small, low-mass, relatively luminous systems with properties resembling those of local H II galaxies. We compare the properties and numbers of these galaxies to the "bursting dwarf" model of Babul & Ferguson. Our sample …

Go to article

Design Considerations For A Small Ultraviolet-Visible Space Telescope For Amateur And Professional Use, Donald Platt Jan 1997

Design Considerations For A Small Ultraviolet-Visible Space Telescope For Amateur And Professional Use, Donald Platt

Aerospace, Physics, and Space Science Faculty Publications

Presented is a preliminary design for a small ultraviolet- visible (uv-vis) sensitive space telescope. Included will be optical, sensor, and spacecraft subsystem design considerations. With recent advances in charge coupled device (CCD) technology it is now possible to build a space telescope system with wavelength sensitivity from 200 to 1000 nm. A main objective of this design is to keep costs to a minimum and use commercial off the shelf (COTS) components wherever possible. Such a low-cost system could provide a platform for studying such untested techniques as small space-based optical interferometry. The observatory could be open to a guest …

Go to article

Magnetic Field Decay In Single Radio Pulsars: A Statistical Study, Soma Mukherjee, Ajit Kembhavi Jan 1997

Magnetic Field Decay In Single Radio Pulsars: A Statistical Study, Soma Mukherjee, Ajit Kembhavi

Physics & Astronomy Faculty Publications

We report on an extensive statistical study of single radio pulsar properties, which we undertook to estimate the decay timescale of pulsar magnetic fields. We synthesized a population of pulsars using assumed theoretical distributions of age, initial magnetic field, period of rotation, position, luminosity, and dispersion measure, taking into account the new distance model for pulsars as well as new velocity estimates. We also took into account the selection effects that characterize pulsar observations. We compared the simulated population with the observed single pulsar population using one- and two-dimensional Kolmogorov-Smirnov tests to obtain a lower bound of ∼160 Myr on …

Go to article

Scattering From Stellar Acoustic-Gravity Potentials: Ii. Phase Shifts Via The First Born Approximation, J. A. Adam, I. Mckaig Jan 1997

Scattering From Stellar Acoustic-Gravity Potentials: Ii. Phase Shifts Via The First Born Approximation, J. A. Adam, I. Mckaig

Mathematics & Statistics Faculty Publications

Using the first Born approximation, properties of the scattering phase shift are investigated for waves that are scattered by a schematic representation of a large-scale “stellar potential,” i.e., one for which the star itself is viewed as the potential inducing a phase shift in an incoming wave. In particular, the phase shift properties are examined as functions of the relative wavenumber (α) and the azimuthal wavenumber (l), high l-values being of interest in helioseismology.

Go to article

Contemporaneous Iue, Euve, And High-Energy Observations Of 3c 273, E. Ramos, Menas Kafatos, A. Fruscione, F. C. Bruhweiler, I. M. Mchardy, R. C. Hartman, L. G. Titarchuk, C. Von Montigny Jan 1997

Contemporaneous Iue, Euve, And High-Energy Observations Of 3c 273, E. Ramos, Menas Kafatos, A. Fruscione, F. C. Bruhweiler, I. M. Mchardy, R. C. Hartman, L. G. Titarchuk, C. Von Montigny

Mathematics, Physics, and Computer Science Faculty Articles and Research

We present the results of our 1994 January and 1995 January observations of the quasar 3C 273 obtained with the International Ultraviolet Explorer (IUE) and the Extreme-Ultraviolet Explorer (EUV E). These observations were part of a large multiwavelength campaign to observe 3C 273 from radio through γ-rays. Our 1995 January photometric observations with the EUV E Lexan/B Deep Survey (DS) instrument indicate strong evidence for variability, at a 99% confidence level, during the 12 day observing period. We have utilized ROSAT PSPC soft X-ray power-law models to correlate with EUV E count rates. Besides variations in the normalization level between …

Go to article

Correlation Of Changes In The Outer-Zone Relativistic-Electron Population With Upstream Solar Wind Measurements, J B. Blake, D N. Baker, Niescja E. Turner, K Ogilvie, R P. Lepping Jan 1997

Correlation Of Changes In The Outer-Zone Relativistic-Electron Population With Upstream Solar Wind Measurements, J B. Blake, D N. Baker, Niescja E. Turner, K Ogilvie, R P. Lepping

Physics and Astronomy Faculty Research

A study has been made of the correlation of the population of relativistic electrons in the outer-zone magnetosphere with the properties of the solar wind (speed, density, magnetic field) during a solar minimum period. The study is based upon observations made in the Spring of 1995 with sensors aboard 1994-026 and WIND. It is found that a large relativistic electron enhancement depends upon a substantial solar-wind speed increase associated with precursor solar-wind density enhancement, and, in particular, upon a southward turning of the interplanetary magnetic field

Go to article

The Rosat Hri X-Ray Survey Of The Cygnus Loop, N. A. Levenson, J R. Graham, B. Aschenbach, W. P. Blair, W. Brinkmann, J. U. Busser, R. Egger, R. A. Fesen, J. J. Hester, S. M. Kahn, R. I. Klein, C. F. Mckee, R. Petre, R. Pisarski, J. C. Raymond, S. L. Snowden Jan 1997

The Rosat Hri X-Ray Survey Of The Cygnus Loop, N. A. Levenson, J R. Graham, B. Aschenbach, W. P. Blair, W. Brinkmann, J. U. Busser, R. Egger, R. A. Fesen, J. J. Hester, S. M. Kahn, R. I. Klein, C. F. Mckee, R. Petre, R. Pisarski, J. C. Raymond, S. L. Snowden

Dartmouth Scholarship

We describe and report progress on the joint U.S. and German campaign to map the X-ray emission from the entire Cygnus Loop supernova remnant with the ROSAT High Resolution Imager. The Cygnus Loop is the prototype for a supernova remnant that is dominated by interactions with the interstellar medium and supplies fundamental physical information on this basic mechanism for shaping the interstellar medium. The global view that these high-resolution observations provide emphasizes the inhomogeneity of the interstellar medium and the pivotal nature of cloud-blast wave interactions in determining the X-ray morphology of the supernova remnant. While investigating the details of …

Go to article

Dynamical Stability And Environmental Influences In Low Surface Brightness Disk Galaxies, Stacy S. Mcgaugh Jan 1997

Dynamical Stability And Environmental Influences In Low Surface Brightness Disk Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

Using analytic stability criteria we demonstrate that, because of their low surface mass density and large dark matter content, low surface brightness (LSB) disks are quite stable against the growth of global nonaxisymmetric modes such as bars. However, depending on their (poorly constrained) stellar velocity dispersions, they may be only marginally stable against local instabilities. We simulate a collision between an LSB and a high surface brightness (HSB) galaxy and find that, while the HSB galaxy forms a strong bar, the response of the LSB disk is milder, manifesting weaker rings and spiral features. The lack of sufficient disk self-gravity …

Go to article

Gas Mass Fractions And The Evolution Of Spiral Galaxies, Stacy S. Mcgaugh Jan 1997

Gas Mass Fractions And The Evolution Of Spiral Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

We show that the gas mass fraction of spiral galaxies is strongly correlated with luminosity and surface brightness. It is not correlated with linear size. Gas fraction varies with luminosity and surface brightness at the same rate, indicating evolution at fixed size. Dim galaxies are clearly less evolved than bright ones, having consumed only ∼1/2 of their gas. This resolves the gas consumption paradox, since there exist many galaxies with large gas reservoirs. These gas-rich galaxies must have formed the bulk of their stellar populations in the last half of a Hubble time. The existence of such immature galaxies at …

Go to article

Lateral Shock Of The R Aquarii Jet, J. M. Hollis, J. A. Pedelty, Menas Kafatos Jan 1997

Lateral Shock Of The R Aquarii Jet, J. M. Hollis, J. A. Pedelty, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

The R Aqr jet was observed with the VLA B-configuration at two epochs separated by ~13.2 yr. Comparison of the resulting 6 cm continuum images show that the radio jet has undergone a lateral counterclockwise rotation of ~6-12 on the plane of the sky. The model of jet parcels on independent trajectories is difficult to reconcile with these observations and leads us to consider a path-oriented jet (i.e., younger parcels follow the same path as older parcels). Comparison of the most recent radio image with a nearly contemporaneous HST /FOC ultraviolet image at ~2330 A suggests that the ultraviolet emission …

Go to article

Multiwavelength Blazar Studies, Menas Kafatos Jan 1997

Multiwavelength Blazar Studies, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

The present report concerns the following projects 'High energy emission from hot accretion disks from active galactic nuclei'; 'OSSE spectral timing and monitoring observations of Cygnus X- 1'; 'OSSE observations of blazars'; and 'Search for correlated time variations of bright EGRET blazars'. The most favored model for the central engine inAGNs is the supermassive black hole hypothesis (Rees 1978). The observed luminosities range from approx. 10 logical and 44-45 erg /s for objects such as Mk 421 and Seyferts to as much as approx. 10logical and 47 for powerful QSOs such as 3C 273 and 3C 279, a large fraction …

Go to article

Large-Amplitude Solitary Waves In Finite Temperature Dusty Plasma, R. Roychoudhury, S. Mukherjee Jan 1997

Large-Amplitude Solitary Waves In Finite Temperature Dusty Plasma, R. Roychoudhury, S. Mukherjee

Physics & Astronomy Faculty Publications

Large-amplitude solitary waves in dusty plasma are investigated, taking into account the dusty particle temperature. It is shown that finite dusty temperature restricts the region for the existence of solitary waves.

Go to article

Multifrequency Studies, Menas Kafatos Jan 1997

Multifrequency Studies, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

The present report concerns the following projects 'Multifrequency observations of the BL Lacertae object MK 421"; "EUVE and multifrequency observations of the quasars 3C 273 and 3C 279"; "EUVE observations of the symbiotic star RAquarii"; and "Morphology of the local HI void and ionization of He in the local ISM". The common theme of the above projects is UV observations and analysis of a wide range of astrophysical classes or objects, from the diffuse interstellar medium, to symbiotic stars (R Aqr), to active galactic nuclei (AGNs). Understanding the local (primarily neutral hydrogen or HI) interstellar medium is of great importance …

Go to article

First Prev Next Last