Physical Sciences and Mathematics Commons^™

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 …

Solar Infrared Relative Intensity Data From The Halogen Occultation Experiment, Philip Todd Spickler

Dissertations, Theses, and Masters Projects

Solar data from the Halogen Occultation Experiment (HALOE) were analyzed to determine the center-to-limb relative intensity and the vertical temperature profile for the quiet and active Sun over wavelengths from 2.4 to 10 {dollar}\mu{dollar}m. An algorithm that incorporated a nonlinear least squares procedure was developed that modeled the HALOE instrument during data acquisition. Data obtained from limb-to-limb scans along the solar equator on days of very low activity in May 1994 were analyzed to obtain coefficients of a function describing the relative intensity from center to limb. The relative intensities produced were precise to 0.1% (2{dollar}\sigma{dollar}) from the center to …

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

Physics and Astronomy Faculty Publications and Presentations

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.

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.

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 …

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

Physics and Astronomy Faculty Publications and Presentations

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 …

Lower And Upper Bounds On Internal-Wave Frequencies In Stratified Rotating Fluids, Benoit Cushman-Roisin

Dartmouth Scholarship

According to classical theories, the frequencies of internal-gravity waves in stratified rotating fluids must lie between the Brunt-Väisälä frequency (a measure of the vertical density stratification) and the Coriolis frequency (equal to twice the rotation rate about the vertical axis). It is shown here that, in the case of the Earth's rotation where the pole-to-pole axis of rotation is almost everywhere not parallel to the local vertical, the range of realizable frequencies is broader. New formulas are derived for the lower and upper bounds of the frequencies.

Gamma-Ray Observations Of Gro J1655-40, R Kroeger, Mark Strickman, J E. Grove, Philip Kaaret, E. Ford, B A. Harmon, Mark L. Mcconnell

Physics & Astronomy

The bright transient X-ray source GRO J1655-40 = XN Sco 1994 was observed by the OSSE instrument on the Compton Gamma Ray Observatory (GRO). Preliminary results are reported here. The initial outburst from GRO J1655-40 was detected by BATSE on 27 Jul 1994. OSSE observations were made in five separate viewing periods starting between 4 Aug 1994 and 4 Apr 1995. The first, third, and fifth observations are near the peak luminosity. In the second observation, the source flux had dropped by several orders of magnitude and we can only set an upper limit. The fourth observation is a weak …

Macrophage-Mediated 15-Lipoxygenase Expression Protects Against Atherosclerosis Development, Jianhe Shen, Ed Herderick, J. Fredrick Cornhill, Eva Zsigmond, Han Seob Kim, Hartmut Kühn, Natalia V. Guevara, Lawrence Chan

Physics and Astronomy Faculty Publications and Presentations

Oxidative modification of LDL increases its atherogenicity, and 15- lipoxygenase (15-LO) has been implicated in the process. To address this issue, we generated transgenic rabbits that expressed 15-LO in a macrophage- specific manner and studied their susceptibility to atherosclerosis development when they were fed a high-fat, high-cholesterol (HFHC) diet (Teklad 0533 rabbit diet 7009 with 10% corn oil and 0.25% cholesterol) for 13.5 wk. Transgenic and nontransgenic rabbits developed similar degrees of hypercholesterolemia and had similar levels of triglyceride, VLDL, LDL, and HDL. Quantitative morphometric analysis of the aortic atherosclerosis indicated that the transgenic animals (n = 19) had significantly …

Performance Of Cdznte Strip Detectors As Sub-Millimeter Resolution Imaging Gamma Radiation Spectrometers, M Mayer, V Boykin, M L. Cherry, J F. Courville, F P. Doty, A Drake, T G. Guzik, L A. Hamel, K Larson, John R. Macri, Mark L. Mcconnell, James M. Ryan, O Tousignant

Space Science Center

We report & gamma;-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for & gamma;-ray astronomy measurements in the range of 20-200 keV. The prototype is a 1.5 mm thick, 64×64 orthogonal stripeCdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8×8 stripe region of the prototype we measured good spectroscopic uniformity and sub-pitch (~0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative …

On The Orbital Period Of The New Cataclysmic Variable Euve J2115-586, Stephane Vennes, Dayal T. Wickramasinghe, John R. Thorstensen, Damian J. Christian, Michael S. Bessell

Dartmouth Scholarship

We have obtained phase-resolved spectroscopy (3660-6040 Å) of the recently discovered cataclysmic variable EUVE J21 15-586 using the 74-inch telescope at Mount Stromlo Observatory. The radial velocity is modulated over a period of 110.8 min with a possible one-cycle-per-day alias of 102.8 min, and a semiamplitude of ≍270 km s^-1 at Hβ and ≍390 km s^-1 at He II λ4686. The spectroscopic appearance (H I Balmer, Ca II, He I, He II emission lines), the orbital period, and the velocity amplitude indicate that this cataclysmic variable is probably an AM Her type; the absence of cyclotron humps indicates …

Balloon-Borne Coded Aperture Telescope For Arc-Minute Angular Resolution At Hard X-Ray Energies, Mark L. Mcconnell, V Boykin, R M. Kippen, K Larson, John R. Macri, M Mayer, James M. Ryan, P P. Altice, M L. Cherry, S B. Ellison, B Price, T G. Guzik, R Lockwood, M B. Barakat, K Johnston, N Zotov, M Elaasar

Space Science Center

We are working on the development of a new balloon-borne telescope, MARGIE (minute-of-arc resolution gamma ray imaging experiment). It will be a coded aperture telescope designed to image hard x-rays (in various configurations) over the 20 - 600 keV range with an angular resolution approaching one arc minute. MARGIE will use one (or both) of two different detection plane technologies, each of which is capable of providing event locations with sub-mm accuracies. One such technology involves the use of cadmium zinc telluride (CZT) strip detectors. We have successfully completed a series of laboratory measurements using a prototype CZT detector with …

Charge-Coupled Devices With Fast Timing For Astrophysics And Space Physics Research, M L. Cherry, P P. Altice, S B. Ellison, T G. Guzik, John R. Macri, Mark L. Mcconnell, G Y. Mclean, James M. Ryan, Paul P. Suni

Space Science Center

A charge coupled device is under development with fast timing capability (15 millisecond full frame readout, 30 microsecond resolution for measuring the time of individual pixel hits). The fast timing CCD will be used in conjunction with a CsI microfiber array or segmented scintillator matrix detector to detect x rays and gamma rays with submillimeter position resolution. The initial application will be in conjunction with a coded aperture hard x ray/gamma ray astronomy instrument. We describe the concept and the readout architecture of the device.

Physical Conditions In Low-Ionization Regions Of The Orion Nebula, J. A. Baldwin, A. Crotts, R. J. Dufour, Gary J. Ferland, S. Heathcote, J. J. Hester, K. T. Korista, P. G. Martin, C. R. O'Dell, R. H. Rubin, A. G. G. M. Tielens, D. A. Verner, D. K. Walter, Z. Wen

Physics and Astronomy Faculty Publications

We reexamine the spectroscopic underpinnings of recent suggestions that [O I] and [Fe II] lines from the Orion H II region are produced in gas where the iron-carrying grains have been destroyed and the electron density is surprisingly high. Our new observations show that previous detections of [O I] 5577 were dominated by telluric emission. Our limits are consistent with a moderate density (≈ 10⁴ cm^-3) photoionized gas. We show that a previously proposed model of the Orion H II region reproduces the observed [O I] and [Fe II] spectrum. These lines are fully consistent with formation …

Rate Coefficients For Charge Transfer Between Hydrogen And The First 30 Elements, J. B. Kingdon, Gary J. Ferland

Physics and Astronomy Faculty Publications

We present analytic fits to charge exchange rate coefficients over the full range of temperatures which occurs in photoionized or shock-heated plasmas. We consider reactions between neutral hydrogen and all elements with parent ion charge q = 1-4 up to Z = 30. Many rates were obtained from various sources in the literature. For reactions for which no data were available, we calculated rates using the Landau-Zener formalism. For these new reactions, we tabulate both total and state-specific rate coefficients. Ml are fitted with a consistent, accurate formula. These fits may be incorporated easily into spectral synthesis codes, and we …

Bringing The Moon Into The Classroom, Laurence A. Marschall

Physics and Astronomy Faculty Publications

Understanding the phases of the Moon is a perennial stumbling block in introductory astronomy classes. In the film, "A Private Universe," for instance, both Harvard graduates and gifted high-school students display serious misconceptions about the Moon's phases, believing, among other things, that the Earth's shadow on the Moon is the cause of it all. Part of the problem may stem from textbook illustrations that show a view of the Moon in orbit around the Earth with the Sun of to one side. Students have trouble converting mentally from this "God's eye" perspective into the "geocentric" perspective we experience as observers …

Experimental Results Of Neutron Fluence Outside An Iron Shield In The Forward Direction, M. M.C. Torres, A. J. Elwyn, D. Fein, E. James, K. Johns, W. Davis, D. P. Ciampa, E. Mierkiewicz

Publications

This work represents the first systematic study at a high energy accelerator of the depth dependence of neutron fluence in longitudinal shielding.

The Mass Distribution In The Nearby Universe, Luiz N. Da Costa, Wolfram Freudling, Gary Wegner, Riccardo Giovanelli

Dartmouth Scholarship

We present a new reconstruction of the mass density and the peculiar velocity fields in the nearby universe using recent measurements of Tully-Fisher distances for a sample of late spirals. We find significant differences between our reconstructed fields and those obtained in earlier work: overdensities tend to be more compact while underdense regions, consisting of individual voids, are more abundant. Our results suggest that voids observed in redshift surveys of galaxies represent real voids in the underlying matter distribution. While we detect a bulk velocity of ~300 km s^-1, within a top-hat window 6000 km s^-1 in …

The Peculiar Motions Of Early-Type Galaxies In Two Distant Regions. I. Cluster And Galaxy Selection, Gary Wegner, Matthew Colless, Glenn Baggley, Roger L. Davies

Dartmouth Scholarship

The EFAR project is a study of 736 candidate elliptical galaxies in 84 clusters lying in two regions, toward Hercules-Corona Borealis and Perseus-Pisces-Cetus, at distances cz ~ 6000-15,000 km s^-1^. In this paper (the first of a series), we present an introduction to the EFAR project and describe in detail the selection of the clusters and galaxies in our sample. Fundamental data for the galaxies and clusters are given, including accurate new positions for each galaxy and redshifts for each cluster. The galaxy selection functions are determined by using diameters measured from Schmidt sky survey images for 2185 galaxies in …

New Promise For Electron Bulk Energization In Solar Flares: Preferential Fermi Acceleration Of Electrons Over Protons In Reconnection-Driven Magnetohydrodynamic Turbulence, Ted La Rosa, Ronald L. Moore, James A. Miller, Steven N. Shore

Faculty Articles

The hard X-ray luminosity of impulsive solar flares indicates that electrons in the low corona are bulk energized to energies of order 25 keV. LaRosa & Moore pointed out that the required bulk energization could be produced by cascading MHD turbulence generated by Alfvénic outflows from sites of strongly driven reconnection. LaRosa, Moore, & Shore proposed that the compressive component of the cascading turbulence dissipates into the electrons via Fermi acceleration. However, for this to be a viable electron bulk energization mechanism, the rate of proton energization by the same turbulence cannot exceed the electron energization rate. In this paper …

Structural Phase Transition And Tc Distribution In Hf-Doped Lamno3 Investigated Using Perturbed-Angular-Correlation Spectroscopy, William E. Evenson, David D. Allred, Gary L. Catchen

Faculty Publications

Using perturbed-angular-correlation (PAC) spectroscopy, via the Hf-->Ta probe, we have measured Mn-site electric-field gradients (EFG's) at Ta nuclei in ceramic samples of LaMnO3. Two crystallographic phases coexist over a temperature interval of ≈16 K near the orthorhombic-to-rhombohedral transition at ≈724 K, which shows a thermal hysteresis of ≈1.7±0.2 K. Concurrently, in the two phases, we determined the temperature dependence of the EFG parameters, Vzz, ƞ, and δ, and the ratio of the probe concentrations A1/A2. To explain the apparent coexistence of two phases in this weakly first-order transition, we present a model that assumes a spatial distribution of Tc …

Design Of A Device Independent Computer Graphic Software Package, An-Shyang Chu

Physics & Astronomy ETDs

The fabrication and optical analysis of well-defined Si quantum walls (periodic slabs) are presented. Using a unique combination of interference lithography and wet-­chemical KOH etching, vertically-standing, periodic Si rectangular slabs are fabricated with a slab thickness ranging from a few nm to ~ 200 nm. Each slab has its three principal axes in the <110>, <112> and <111> direction, and each slab surfaces is extended in the <110>-<112> plane and normal to the <111> direction. These samples are used to study the effects of the size confinement on the crystal properties of Si. Raman scattering experiment is carried out because the scattering of …

Silcom Quantum Walls: Fabrication And Opticla Analysis, An-Shyang Chu

Physics & Astronomy ETDs

The fabrication and optical analysis of well-defined Si quantum walls (periodic slabs) are presented. Using a unique combination of interference lithography and wet-­chemical KOH etching, vertically-standing, periodic Si rectangular slabs are fabricated with a slab thickness ranging from a few nm to ~ 200 nm. Each slab has its three principal axes in the,anddirection, and each slab surfaces is extended in the-plane and normal to thedirection. These samples are used to study the effects of the size confinement on the crystal properties of Si. Raman scattering experiment is carried out because the scattering of the phonons is highly dependent on …

Atomic Data For Astrophysics. Ii. New Analytic Fits For Photoionization Cross Sections Of Atoms And Ions, D. A. Verner, Gary J. Ferland, K. T. Korista, D. G. Yakovlev

Physics and Astronomy Faculty Publications

We present a complete set of analytic fits to the nonrelativistic photoionization cross sections for the ground states of atoms and ions of elements from H through Si, and S, Ar, Ca, and Fe. Near the ionization thresholds, the fits are based on the Opacity Project theoretical cross sections interpolated and smoothed over resonances. At higher energies, the fits reproduce calculated Hartree-Dirac-Slater photoionization cross sections.

Chromospherically Active Stars. Xv. Hd 8357=Ar Piscium, An Extremely Active Rs Cvn System, Francis C. Fekel

Information Systems and Engineering Management Research Publications

One of the first x-ray sources optically identified as a chromospherically active star, HD 8357=AR Piscium, is a double-lined binary consisting of a K1 IV primary and G7 V secondary. Careful examination of the Ca II H and K lines indicates that only the primary is active, having strong Ca II H and K, Hɛ, and Hα emission. The system has an orbital period of 14.3023 days and an eccentricity of 0.185. Such an eccentricity is not particularly unusual for chromospherically active stars with periods between 10 and 20 days. An assumed mass of 0.92Msun for the secondary results in …

The Metallicity Dependence Of The Stellar Luminosity And Initial Mass Functions: Hst Observations Of Open And Globular Clusters, Ted Von Hippel, Gerard Gilmore, Nial R. Tanvir, David Robinson, Derek H.P. Jones

Publications

Using HST and the WFPC2 we have acquired very deep V- and I-band photometry of stars in NGC 2420 and NGC 2477 to study cluster luminosity functions at approximately solar metallicity. We have determined these cluster luminosity functions down to MI = 10.5 (0.2 M⊙) and find that the luminosity function of NGC 2420 turns over at MI ≈ 9.0, and possibly stops altogether by MI ≈ 9.5. The luminosity function of NGC 2477 may flatten at MI ≥ 9.5. We compare our open cluster luminosity functions to the solar neighborhood field star luminosity function of Kroupa, Tout \& Gilmore …

A Test Of The Lauer-Postman Bulk Flow, Riccardo Giovanelli, Martha P. Haynes, Gary Wegner, Luiz N. Da Costa

Dartmouth Scholarship

We use Tully-Fisher distances for a sample of field late spiral galaxies to test the Lauer & Postman result suggestive of a bulk flow with respect to the cosmic microwave background reference frame, of amplitude of +689 km s^-1 in the direction l = 343°, b = +52°. A total of 432 galaxies are used, subdivided between two cones, of 30° semiaperture each and pointed toward the apex and antapex of the LP motion, respectively. The peculiar velocities in the two data sets are inconsistent with a bulk flow of the amplitude claimed by Lauer & Postman. When combined …

Flare Energetics: Analysis Of A Large Flare On Yz Canis Minoris Observed Simultaneously In The Ultraviolet, Optical And Radio., G. H. J. Van Den Oord, John G. Doyle, M. Rodono, D. E. Gary, Gregory W. Henry, Patrick B. Byrne, Jeffrey L. Linsky

Information Systems and Engineering Management Research Publications

The results of coordinated observations of the dMe star YZ CMi at optical, UV and radio wavelengths during 3-7 February 1983 are presented. YZ CMi showed repeated optical flaring with the largest flare having a magnitude of 3.8 in the U-band. This flare coincided with an IUE exposure which permits a comparison of the emission measure curves of YZ CMi in its flaring and quiescent state. During the flare a downward shift of the transition zone is observed while the radiative losses in the range 10^4^-10^7^K strongly increase. The optical flare is accompanied with a radio flare at 6cm, while …

Discovery Of A White Dwarf Companion (Ms0354.6-3650 = Euve J0356-366) To A G2v Star, Damian J. Christian, Stephane Vennes, John R. Thorstensen, Mihalis Mathioudakis

Dartmouth Scholarship

We present x-ray, ultraviolet, and optical observations of the mysterious EUV/soft x-ray source EUVE J0356-336 (= MS0354.6-3650). Initial Einstein observations identified this source with a cluster of galaxies, but the relatively high source count rate in the Extreme Ultraviolet Explorer (EUVE) 100 Å band and the lack of variability hinted that EUVE J0356-3650 might be a white dwarf; the UK Schmidt plate of the field surrounding this object found a 12.45 magnitude G2V star that could hide a compact companion. This hypothesis was confirmed in an IUE ultraviolet spectrum that shows the definite signature of a hydrogen-rich white dwarf (DA). …

Is The Universe Expanding?: An Historical And Philosophical Perspective For Cosmologists Starting Anew, David A. Vlosak

Masters Theses

This study addresses the problem of how scientists ought to go about resolving the current crisis in big bang cosmology. Although this problem can be addressed by scientists themselves at the level of their own practice, this study addresses it at the meta-level by using the resources offered by philosophy of science.

There are two ways to resolve the current crisis. Either cosmologists can continue working on big bang theory or they can start anew. For those who choose to start anew, this study argues it would be a mistake for them to assume any new cosmological theory would have …