Jackie Must
The University of Toledo
Dust in Galaxies
 Spiral galaxies show color gradients across their disks, appearing redder in the center and bluer in the outer regions. These color gradients may be caused by an age gradient of the stars within the disk, a metallicity gradient across the disk, dust in the disk, or a combination of these factors. The present work focuses on how dust extinction affects the color gradient across the disks of non-active and of Seyfert galaxies. We modeled the scalelengths in galactic disks in the B, V, R, I, J, H, and K photometric bands. The scalelength is defined as the distance from the photometric center of a galaxy for which the surface brightness drops by a factor of 1/e. We examined the variation of this parameter as a function of wavelength with dust optical depth and galactic ellipticity for a homogeneous and for a clumpy dust distribution. Our model parameters included a number of inclination angles simulating the widely variable observing geometries, optical depths between 0.25 and 8.00, and wavelength-dependent dust scattering properties. Our model results were tested against observations of galaxies with a variety of ellipticities. It was found that the current models can account for only a small fraction of the observed range of the variation of the scalelength with wavelength. We conclude that metallicity gradients and age gradients, in addition to dust attenuation, must play a major role in producing the observed variation of the scalelength with wavelength in the range covered by the photometric band from B to K.

Josh Thomas
The University of Toledo
Gravitational Microlensing of Stars With Circumstellar Envelopes
 According to Einstein's theory of general relativity mass bends space-time, since light travels in straight lines through curved space the path of a light ray is altered. A gravitational microlensing event occurs when a massive object passes between the observer and a distant source, in this case a star with an extended atmosphere. The massive object acts as a lens bending more light toward the observer than the observer normally receives from the star. A useful analogy is as follows: take a magnifying glass and pass it between you and a light bulb. In a microlensing survey the light from a star is monitored. When the intensity of light shows a significant wavelength independent increase it is called a microlensing event. The maximum magnification of the light occurs when the microlens is at is smallest separation from the star on the sky. A few studies have measured this light curve as a function of time for a number of stars, but these studies have only looked at the intensity of the light. We plan to show, through modeling, that polarization data would allow one to determine various properties of the atmosphere. When the microlens is far away from the star the polarization is at a minimum. As the microlens approaches the star the polarization increases to a maximum then falls off as it passes from the edge of the atmosphere to the star.

Noel Richardson
The University of Toledo
H alpha Periodicities in the Spectrum of Alpha Cygni
 Alpha Cygni, also known as Deneb, is a very luminous class A2Iae star. Some estimates show it to be the brightest star of its spectral class with 160,000 times the luminosity of the Sun. The H alpha feature has a weak P Cygni profile, telling us that Deneb exhibits mass loss. However, the H alpha profile is not static. The 1997 observing season shows enhanced absorption events occurring approximately every 40 days. Not all of these events are the same. We are analyzing 71 spectra taken at Ritter observatory with the échelle spectrograph in 2001. In order to remove telluric water vapor lines from the spectra, we employed line templates constructed from spectra of rapidly rotating hot stars. After removing telluric lines, we Doppler corrected the spectra for the movement of the Earth around the Sun, and then normalized the continuum radiation to unity. We will construct a dynamical spectrum from the normalized spectra to look for periodic behavior. One currently favored interpretation is spiral shaped density enhancements in the stellar wind, which would travel with the rotation of the star. The dynamical spectrum should allow theoreticians to create models for these density enhancements in the stellar wind.

Nick Sperling
The University of Toledo
Magnetic Nanostructures
 Scanning Probe Microscopy is a useful tool in the magnetic characterization of features of magnetic nanostructures. The research presented here has the goal of the creation of a Spin Polarized Scanning Tunneling Microscope (SPSTM) and the analysis of simulations done in the Object Oriented MicroMagnetic framework (OOMMF), released by NIST, to build an understanding of domain-wall formation in magnetic nanostructures. The project includes analysis of images from other Scanning Probe Microscopy sources, and highlights the usefulness of a SPSTM over other measuring techniques for this application.

Chuck Borener
Eastern Michigan University
Demonstrations for Acoustics
 Many concepts in acoustical physics are hard for beginning students to grasp. Good demonstrations are an invaluable tool teachers can use to help students learn through active rather than passive methods. My presentation will introduce a variety of exciting demonstrations that will help students learn acoustical physics.

Steve Chapman
University of Michigan
Development of a Pair-Production Based Slow Positron Beam
 We constructed a beam of slow (~1eV) positrons obtained via pair-production. Such beams are used to study material properties by exploiting the variable behavior of positrons in matter. Our preliminary results indicate that rates justifying the choice of such a beam over more traditional radioactive source based beams are attainable.

Alex Povilus
University of Michigan
Combined Ion-Neutral Trapping
 The ability to contain both ions and neutral particles simultaneously in an electromagnetic trap would allow for large advances in the field of antimatter generation and spectroscopy. More specifically, this form of trapping may be used to test for fundamental quantities in physics and CPT violation. We will discuss the basic mechanics of trapping and cooling as well as current experiments that utilize the ion-neutral construction.

Michael Borysow
University of Michigan
Instrumentation and procedures for the characterization of HgCdTe detectors for SNAP
 We have adapted a spot projection system originally developed at LBL for use in the visible to project several micron diameter spots. We have adapted this system for use in the near infrared and have mounted it on a motorized three dimensional translation stage. We have also written software to automate focusing and scanning. Our "spot-o-matic" system will be used to measure interpixel, as well as intrapixel variations on HgCdTe detectors. These detectors will be used for near infrared photon detection on the SNAP focal plane. I will be presenting proof of concept of our system as demonstrated with the characterization of the CCD on a consumer level webcam.

Zone Home