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Abstracts of Presentations


Research Experiences for Undergraduates (REU)
Abstracts of Presentations
August 6, 2009


2009 REUs


1.3 mm VLBI study of M87
Presentation (PDF)
David Schenck, University of Arizona


The radio galaxy M87 is the largest galaxy in the Virgo cluster located about 16 Mpc away. At its center, M87 is believed to harbour a super massive black hole whose mass estimate was recently doubled to a value of 6.5x109 solar masses. This black hole is the engine for a relativistic jet that extends for kiloparsecs from its base, though the specific mechanism for the jet's formation and structure are unknown. M87 is one of only two radio galaxies to be detected in very-high-energy (VHE) gamma-rays emission. This emission is variable on timescales as low as two days and is believed to originate close to the black hole’s event horizon. Many models have been proposed to explain this emission. Using telescopes in Hawaii, California, and Arizona to conduct a VLBI observation at 1.3 mm (230 GHz), a strict limit was set on the size of the emitting region. The spatial scales predicted by several models were compared to this value to check the validity of the models.


HI as a Tracer of Circumstellar Envelopes
Presentation (PDF)
Marshall Johnson, Wesleyan University


Asymptotic giant branch (AGB) stars are a near-final stage of evolution for approximately solar-mass stars. These stars undergo mass loss, forming circumstellar envelopes of scale ~1 pc and mass ~10-3 M_Sun. These envelopes have previously been detected in a variety of tracers (e.g. CO, SiO, silicate dust). The HI 21-cm line offers a number of advantages for observing these envelopes, such as the ability to detect the envelope at large distances from the star. High-resolution HI observations were taken of three AGBs (X Her, R Peg, and Y UMa) using the Very Large Array. Additionally, low-resolution observations of X Her were made using the Green Bank Telescope. The data indicate that circumstellar envelope morphologies are more complex and varied than previously suspected.


Pioneering Observations with the Murchison Widefield Array: Searching for Radio Transients
Presentation (PDF)
Gregory McGlynn, Northwestern University


The Murchison Widefield Array, currently under construction in Western Australia, will be a wide-field radio telescope operating in a relatively unexplored frequency range. These properties give the MWA a good chance to detect previously unnoticed transient radio signals from high-energy astrophysical events. Transient radio signals will provide clues about the physics of these energetic astrophysical processes, and may reveal previously unknown processes at work in the cosmos. This summer I worked on the All Sky Monitor, a piece of software that will analyze MWA data in real time to detect transient signals. I will present the results of some simulations to test the effectiveness of the transient-detection algorithms and the sensitivity of the MWA to transient signals.


Pioneering Science with the MWA: Observing the Quiet Sun
Presentation (PDF)
Shane Rightley, University of Arizona


The Murchison Widefield Array (MWA) is a 512 element interferometric array designed to operate at radio frequencies from 80 to 300 MHz. It is under construction in the Murchison region of Western Australia, and will feature 512 electronically pointed tiles, each consisting of 16 phased dipole antennas. There is presently a 32 tile (32T) prototype of the array setup on site that is being used to demonstrate the validity of the hardware and software designs, as well as to establish some early science results. One of several targeted science objectives for the MWA is the study of the Sun and the inner heliosphere. The MWA 32T is thus well matched for the study of the solar corona, with the instrument's frequency range corresponding to the local plasma frequency in the corona at heights above the photosphere between approximately 0.1 and 1 solar radii. We present flux calibrated images of the Sun produced by the MWA 32T at 5 frequencies between 85 and 235 MHz. Results for total flux densities and radial brightness temperature profiles are compared to theoretical expectations as well as established results and are found to be in fairly good agreement. It is concluded that the MWA 32T is capable of producing valid and useful data and that further analysis of the solar images may yield information about the large scale electron temperature in the Sun's corona.


Development of an Optimized Antenna for an Ozone Spectrometer
Presentation (PDF)
Sai Tenneti, University of Massachusetts - Amherst


The goal of this project was to optimize the performance of a spectrometer at Haystack that measures the amount of ozone in the mesosphere. This required searching and testing for compact, inexpensive low noise block converters (LNBs) that can perform efficiently in the X-band of the electromagnetic spectrum. Various devices were tested such as the Fortec FSKUVN 0.2 dB, Invacom SNF-031 0.3 dB Horn, Invacom SNF-031 0.3 dB C120 flange, and the Smart 0.1 dB. Software was used to estimate the "sky noise" as a function of azimuth and elevation, and in turn was used to calculate the antenna response. Numerous calibration techniques were used to obtain accurate values for the noise figure, such as the use of various absorbers to measure the "Y-factor", liquid nitrogen calibration, and also calibration with a fluorescent lamp that periodically turns on and off. Some possible solutions to reduce spillover from the ground and further optimize the antenna performance, were also tested.


Effect of Sudden Stratospheric Warming Event on Low- and Mid-Latitude
Ionospheric Parameters as simulated in the TIMEGCM model
Presentation (PDF)
Allyson Clark, Pennsylvania State University


Ionospheric parameters including temperature, vertical drift, and electron density of the TIME-GCM model were analyzed in this study. The investigation was conducted using model data corresponding to mid- and lower-latitudes during the sudden stratospheric warming event of January 2008. Vertical temperature profiles showed a distinct wave pattern, decreased temperatures and smaller changes in time during the SSW event. The structure of vertical drift profiles were similar between a day during the SSW event and a day without an event. There were similar periodic structures in electron density when comparing profiles during and prior to the SSW event. Decreases in electron density during the SSW event were also seen. Given the model's realistic reproduction of atmospheric conditions in the mid and lower latitudes, the investigation was then focused on a series of large changes in total electron content over the time period. Total electron content was discovered to have a linear dependence on AP Index and had little dependence on solar flux at the mid-latitudes during December to February between 9 and 15 local time, including days during the SSW event.


A Statistical Analysis of Ionospheric Pedersen Conductivity
Presentation (PDF)
Farzan Beroz, Duke University


We will discuss the results of an expanded statistical study on regions of fast flowing plasma in the ionosphere called Sub-Auroral Polarization Streams (SAPS). These events have been sampled many times by the Millstone Hill incoherent scatter radar, and are a consequence of electromagnetic coupling between the upper atmosphere and the overlying magnetosphere. A better understanding of the properties of SAPS is essential to understanding the Sun-Earth system. We will describe efforts to organize Millstone Hill radar measurements of SAPS to examine the events. In particular, our work has produced a Python class-based software data structure that will facilitate future analysis work and that easily allows new parameters to be added. We will describe statistical analysis results of ionospheric Pedersen conductivity, an important quantity for determining the dynamics of SAPS event behavior as a function of season and time of day.


Observing the Earth's Topside Ionosphere with Multiple Atmospheric Instruments
Presentation (PDF)
Gabrielle Tepp, Michigan State University


How can you determine the amount of plasma in the upper ionosphere? Using incoherent scatter radars (ISR), one can only determine the total electron content (TEC) up to an altitude of around 500-800 km. GPS satellites, on the other hand, orbit the Earth some 20,000 km above the ground and can be used to determine the TEC up to that height. By comparing the data from the two types of instruments, the TEC of the upper ionosphere can be determined. Other than the daily cycle of variation, the amount of plasma changes depending on location and time of year as well as other factors such as solar storms. In this project, the plasma contents for two time periods from four different radars with numerous GPS receivers are compared. The time periods are for 1-6 March 2007 and 9-13 July 2008. The radars used are AMISR in Poker Flat, AK; Millstone Hill in Westford, MA; Sondrestrom in Kangerlussuaq, Greenland; and the EISCAT Svalbard ISR in Longyearbyen, Svalbard. From the data, it was found that the GPS data processing still leads to biases. Different elevations and azimuths for the instruments were compared.


Investigation of a Thermo-electrically Cooled UHF Radar Amplifier Module
Poster (PDF)
Michael Shusta, University of Massachusetts - Amherst


In radio instrumentation, the system noise level of a receiver is dominated by the noise added by the first stage after the antenna: the low-noise amplifier (LNA)  . It sets the performance of the receiver in terms of gain, noise figure, stability, and dynamic range. Radar operators working in astronomy and atmospheric science who desire very low system temperatures cool their front-end LNA with cryogenic apparatus. The primary motivation of this engineering project is to achieve a more modest performance gain with simpler, cheaper, and lower-maintenance means: thermoelectric cooling. Thermal simulations of a UHF front end module were performed in the COMSOL Multiphysics environment, which show LNA cooling to 200K. A vacuum housing design and thermal analysis are shown, to be implemented in the Millstone Hill Incoherent Scatter Radar at MIT Haystack Observatory




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