Astrophysics and Astronomy Commons^™

Superstring Cosmology: An Investigation Into Low Temperature Effective Gauss-Bonnet Corrections To The Einstein Field Equations In An Inflationary Scenario, David Dressel

Masters Theses

Several problems with the inflationary cosmological model and the force coupling constants are addressed in the context of superstring theory. In order to simplify the field equations slightly, vacuum solutions are attempted. The solutions for several field equations are analyzed in order to obtain an inflationary universe that leads to a nearly static internal space. A solution is found when Gauss-Bonnet terms, as well as the Einstein terms, are used in the field equations, along with an exponential radii function for a ten dimensional product space. The solutions lead to a three-phase universe that might describe our very early universe. …

Characterization Of Cosmic Microwave Background Temperature Fluctuations For Cosmological Topologies Specified By Topological Betti Numbers, Troy Gobble

Masters Theses

The cosmic microwave background explorer, COBE, and the Balloon Observations of Millimetric Extragalactic Radiation and Geophysics, BOOMERanG, have collected data from the universe and detected relic anisotropies indicative of one of the earliest events of the universe, decoupling. Hidden in the correlation between these temperature fluctuations is the signature of the global shape, or topology, of the early universe. It is possible to calculate the temperature fluctuations as due to primeval adiabatic density temperature fluctuations from the Sachs-Wolfe effect, which contains a topological term. Here we investigate some of the spaces and how they affect the microwave background.

A large …

The Age Of The Inner Halo Globular Cluster Ngc 6652, Brian Chaboyer, Ata Sarajedini, Taft E. Armandroff

Dartmouth Scholarship

Hubble Space Telescope (V, I) photometry has been obtained for the inner halo globular cluster NGC 6652. The photometry reaches ~4 mag below the turnoff and includes a well-populated horizontal branch. This cluster is located close to the Galactic center, at R_GC 2.0 kpc, with a reddening of E(V-I) = 0.15 ± 0.02, and has a metallicity of [Fe/H] -0.85. Based upon ΔV, NGC 6652 is 11.7 ± 1.6 Gyr old. Using ΔV, precise differential ages for 47 Tuc (a thick disk globular cluster), M107, and NGC …

Magnetic Confinement, Magnetohydrodynamic Waves And Smooth Line Profiles In Active Galactic Nuclei, M. C. Bottorff, Gary J. Ferland

Physics and Astronomy Faculty Publications

In this paper, we show that if the broad-line region clouds are in approximate energy equipartition between the magnetic field and gravity, as hypothesized by Rees, there will be a significant effect on the shape and smoothness of broad emission-line profiles in active galactic nuclei. Linewidths of contributing clouds or flow elements are much wider than their thermal widths, because of the presence of non-dissipative magnetohydrodynamic waves and their collective contribution produce emission-line profiles broader and smoother than would be expected if a magnetic field were not present. As an illustration, a simple model of isotropically emitting clouds, normally distributed …

A Substorm Onset Observed By The Polar Spacecraft In Conjunction With The Image Chain, P K. Toivanen, D N. Baker, W K. Peterson, A Viljanen, Niescja E. Turner, X Li, C A. Kletzing

Physics and Astronomy Faculty Research

We present observations of the Polar spacecraft of magnetospheric substorm signatures in the plasma sheet midway along auroral field lines between the ionosphere and the equatorial plasma sheet. An isolated substorm on October 17, 1997, is studied in detail. The onset time at 2040:42 UT was defined to be almost simultaneous (within 20 sec) on the ground and at Polar altitude (~ 4R_E. At Polar, the onset was manifested as strong magnetic field variations and plasma flow bursts with amplitudes exceeding 20 nT and 100 km/s, respectively. Bursts of parallel Poynting flux of ~ 0.5 ergs/cm^{2 …}

Evaluation Of The Tail Current Contribution To Dst, Niescja E. Turner, D N. Baker, T I. Pulkkinen, R L. Mcpherron

Physics and Astronomy Faculty Research

The Dst index is produced using low-latitude ground magnetic field measurements and frequently is used as an estimate of the energy density of the ring current carried mainly by energetic (∼10-200 keV) ions relatively close to the Earth. However, other magnetospheric current systems can cause field perturbations at the Earth's surface: for example, dayside magnetopause currents are known to contribute to the Dst index. It has also been suggested that the nightside tail current sheet can significantly affect the Dst index during high magnetic activity periods when the currents are intense and flow relatively close to the Earth. In this …

Correlation Analysis Of Sfi Peculiar Velocities, Stefano Borgani, Luiz N. Da Costa, Idit Zehavi, Riccardo Giovanelli, Martha P. Haynes, Wolfram Freudling, Gary Wegner, John J. Salzer

Dartmouth Scholarship

We present results of a statistical analysis of the SFI catalog of peculiar velocities, a recently completed survey of spiral field galaxies with I-band Tully-Fisher distances. The velocity field statistic utilized is the velocity correlation function, ψ₁(r), originally introduced by Górski et al. The analysis is performed in redshift space so as to circumvent potential ambiguities connected with inhomogeneous Malmquist bias corrections. The results from the SFI sample are compared with linear-theory predictions for a class of cosmological models. We generate a large set of mock samples, extracted from N-body simulations, which are used …

Robust Test For Detecting Nonstationarity In Data From Gravitational Wave Detectors, Soumya Mohanty

Physics & Astronomy Faculty Publications

It is difficult to choose detection thresholds for tests of nonstationarity that assume a priori a noise model if the data are statistically uncharacterized to begin with. This is a potentially serious problem when an automated analysis is required, as would be the case for the huge data sets that large interferometric gravitational wave detectors will produce. A solution is proposed in the form of a robust time-frequency test for detecting nonstationarity whose threshold for a specified false alarm rate is almost independent of the statistical nature of the ambient stationary noise. The efficiency of this test in detecting bursts …

Detection Of Co And Dust Emission In Near-Infrared Spectra Of Sn 1998s, Christopher L. Gerardy, Robert A. Fesen, Peter Höflich, J. Craig Wheeler

Dartmouth Scholarship

Near-infrared spectra (0.95 – 2.4 μ m) of the peculiar Type IIn supernova 1998S in NGC 3877 from 95 to 355 days after maximum light are presented. K -band data taken at days 95 and 225 show the presence of the first overtone of CO emission near 2.3 μ m, which is gone by day 355. An apparent extended blue wing on the CO profile in the day 95 spectrum could indicate a large CO expansion velocity (≈ 2000 – 3000 km s − 1). This is the third detection of infrared CO emission in nearly as many Type II …

The Recent High State Of The Bl Lacertae Object Ao 0235 And Cross-Correlations Between Optical And Radio Bands, M. Roy, I. E. Papadikis, E. Ramos-Colon, R. Sambruna, K. Tsinganos, J. Papamastorkis, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

We present new optical (B, V , R, I) and radio (at 14.5, 8.5, and 4.8 GHz) observations of the γ-ray- loud blazar AO 0235+164 obtained during the high state of 1997 December-1998 January. The data were combined with historical light curves from the literature to study correlated optical and radio variations over a time span of more than 20 years. Flux variability with large and energy-dependent amplitude is observed at both wave bands, with the source varying over all timescales sampled (years-months- days), in agreement with previous reports. We have performed a cross-correlation analysis of optical and radio light …

A Wide Field 90 Cm Vla Image Of The Galactic Center Region, Ted La Rosa, Namir E. Kassim, Joseph W. Lazlo, Scott B. Hyman

Faculty Articles

We present a wide-field, high dynamic range, high-resolution, long-wavelength (lambda = 90 cm) VLA image of the Galactic center region. The image is centered on Sgr A, covers an area of 4 degrees x 5 degrees with an angular resolution of 43 ", and has a rms sensitivity of approximate to 5 mJy beam-l. The image was constructed from archival (1989 and 1991) VLA data of Pedlar et al. and Anantharamaiah et al. using new three-dimensional image restoration techniques. These three-dimensional imaging techniques resolve the problem of non-coplanar baselines encountered at long wavelengths and yield distortion-free imaging of far-field sources …

Star Formation And Tidal Encounters With The Low Surface Brightness Galaxy Ugc 12695 And Companions, Stacy S. Mcgaugh

Faculty Scholarship

We present VLA H I observations of the low surface brightness (LSB) galaxy UGC 12695 and its two companions, UGC 12687 and a newly discovered dwarf galaxy 2333 + 1234. UGC 12695 shows solid-body rotation but has a very lopsided morphology of the H I disk, with the majority of the H I lying in the southern arm of the galaxy. The H I column density distribution of this very blue LSB galaxy coincides in detail with its light distribution. Comparing the H I column density of UGC 12695 with the empirical (but not well-understood) value of Σc = 1021 …

The Hî² Index As An Age Indicator Of Old Stellar Systems: The Effects Of Horizontal-Branch Stars, Hyun Chul Lee, Suk Jin Yoon, Young Wook Lee

Physics & Astronomy Faculty Publications

The strength of the Hβ index is computed for the integrated spectra of model globular clusters from the evolutionary population synthesis. For the first time, these models take into account the detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity. Our models show that the Hβ index is significantly affected by the presence of blue HB stars. Because of the contribution from blue HB stars, the Hβ does not monotonically decrease as metallicity increases at a given age. Instead, it reaches a maximum strength when the distribution of HB stars is centered around 9500 K, the temperature at …

Critical Adsorption On Defects In Ising Magnets And Binary Alloys, Andreas Hanke

Physics & Astronomy Faculty Publications

Long-range correlations in a magnet close to its critical point or in a binary alloy close to a continuous order-disorder transition can substantially enhance the effect of local perturbations. It is demonstrated using a position-space renormalization procedure that quasi-one-dimensional defects which break the symmetry of the order parameter have pronounced effects: They cause long-range critical adsorption profiles and give rise to new universal critical exponents, which are identified and calculated using field-theoretical methods.

A Solar Comparison, Larry Weinstein

Physics Faculty Publications

[First paragraph] Gilbert Ward [Phys.Teach 38, 333 (Sept. 2000)] states, "You emit more than 7000 times as much heat per unit mass as the Sun does." This difference was pointed out to me much more graphically by Brian Quinn many years ago as, "If the sun were made out of gerbils, the Earth would be incinerated."

Time Step Truncation Error In Direct Simulation Monte Carlo, Alejandro Garcia, W. Wagner

Faculty Publications

No abstract provided.

Book Review: The Birth Of Time: How Astronomers Measured The Age Of The Universe, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of The Birth of Time : How Astronomers Measured the Age of the Universe by John Gribbin. Yale, 2000 237p, 0-300-08346-7 $22.50.

The Wiyn Open Cluster Study: A New Color-Magnitude Diagram For M35 - A Twin Of The Pleiades, Ted Von Hippel, Vera Kozhurina-Platais, Imants Platais, Pierre Demarque, Ata Sarajedini

Publications

M35 (NGC 2168) is rich, young, and in some regards a bet­ter laboratory for stellar cluster research at 100 million years than the Pleiades. Yet, while M35 has been the subject of intriguing photometric, astrometric, and theoretical studies, to the best of our knowledge no pub­lished CCD-based photometry exists for this cluster. We have obtained relatively wide-field (23' x23') precise UBVRJ CCD photometry for M35 as part of the WIYN Open Cluster Study (WOCS) at the 0.9m telescope at Kitt Peak National Observatory. The photometry extends from the main sequence turn off to beyond V = 19. We find that …