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Research Experiences for Undergraduates (REU)
Abstracts of Presentations
August 8, 2002


LOFAR Simulator Development: Design Parameters, Accuracy Tests, and Imaging Limits
Tanja Bode
Cornell University

The Low Frequency Array (LOFAR) is a step into a new technological and observational arena as a low frequency, highly digital, highly sensitive, low-cost instrument for radio interferometry. While the array is still in its early stages of development, the simulator is a vital tool in the designing of the instruments and processing/post-processing algorithms for LOFAR. The simulator will expand in capability in the next two years to allow members of ASTRON, the Naval Research Laboratory (NRL), and MIT Haystack Observatory to explore different array design parameters, the effect of ionospheric turbulence and noise on array performance, and effectiveness of post-processing algorithms in achieving the desired high dynamic ranges of the resulting images.Recently, explorations were conducted into the effect of various design parameters for logspiral configurations on the point response function of the array. Debugging and accuracy tests created confidence in existing areas of simulator code before adding new functionality such as inserting simulated phase errors due to the ionosphere. Tests were also performed on the limitations of existing imaging packages. This talk focuses on the preliminary array design parameter exploration, current simulator capabilities, and limitations found.


VLBI Study of Jet Proper Motions in Blazars
Elyse A. Casper
Dickinson College

Because of its high angular resolution, Very Long Baseline Interferometry (VLBI) is useful for the study of extragalactic sources, such as blazars. Both polarization information and kinematic constraints derived from analyses of proper motions are useful tools with which to study the structure of blazars. Very Long Baseline Array (VLBA) data taken at 5 GHz have been calibrated, and intensity and linear polarization maps of seven blazars have been completed. Proper motion measurements of the seven blazars have also been made; these results are tabulated with two previous epochs. Ultimately, the data will be analyzed to detect circular polarization among the thirty-nine sources observed.


Acoustic Monitoring and Signal Identification for Steerable Radar Antennas
Rex E Cook
University of Arizona

The Millstone Hill Steerable Antenna (MISA), weighing about 150 tons, could be severely damaged if a mechanical problem occurred and was not detected immediately or in a short period of time. A previous project researched the feasibility of acoustic monitoring of this antenna and found usable signals. The current project extends this work using electronically programmable analog circuits for signal acquisition. Significantly larger quantities of data were also collected. The programmable circuits were used as amplifiers or filters whose response can be reprogrammed easily. This improved the quality of the signals from the sensors significantly. Accelerometer sensors detected a definite spike when brakes released and engaged. Another signature was produced with the motor moving at a constant rate. Frequency patterns observed by the 40-kHz ultrasonic sensor could be used in the future to determine the speed of the antenna. Placement of sensors and how they are affixed to the antenna impacts the quality of the measured signal. Recommendations for affixing the sensors are discussed. Results of this project indicate a monitoring system is feasible and would be very useful.


Observations of Class I Methanol Masers Towards Regions of Star Formation
Adrienne Schwartz
University of Minnesota Morris

Methanol masers have been detected in galactic molecular clouds and regions of known star formation. They are classified in two categories dependent on their pumping mechanisms and relative positions. Class II methanol masers are radiatively pumped. They are often found near OH and H2O masers, compact HII regions and appear to be associated with the formation of young massive stars. Class I masers result from collisional excitation, which is followed by spontaneous radiative decay. They arise at the interface between outflows and the interstellar medium, separated from centers of star formation. We have conducted our observations to detect the existence of class I methanol masers. Since these masers are often offset from compact HII regions and strong infrared sources, they have been overlooked in traditional searches. To prevent restricting detection of outlying class I masers, our observations were conducted systematically over an entire molecular cloud. Our source, NGC 7538, is a known region of star formation located in the arm of Perseus. Observations were made with the 37-meter radio telescope at Haystack with frequencies of 24, 36, and 44 GHz, as well as with the Very Large Array at 44 GHz. Analysis of the VLA data provided us with positions, velocities, intensities and widths of the emission detected. A new maser was identified near infrared source IRS 9. Also, two masers were detected near IRS 11 with velocities of roughly –57 km/s and –53 km/s. These velocities are shifted from the systemic velocity of –56 km/s detected by ammonia emission. These masers may possibly indicate lobes of bipolar outflow created by a very young embedded star. This could imply that class I methanol masers are associated with very early star formation. Data received from the Haystack Antenna will also be presented. A comparison will be made between the line spectra widths and intensities of corresponding offsets at the 36 and 44 GHz frequencies.


Madrigal Global Query Web Interface
Ezinne Uzo-Okoro
Montgomery College, MD

I describe the Madrigal Global Query Web Interface, a web-based search engine designed to allow users to run global queries against a Madrigal database. Unlike other on-line systems for accessing data from upper-atmosphere research instruments, Madrigal Global Search does not just allow the user to analyze data one experiment at a time. Rather, users select a set of instruments, precise dates, and parameter filters that describes the report they wish to generate. This type of global query requires no knowledge of any programming language, only an ability to formalize desired search criteria appropriately. The search mechanism of the Madrigal Global Query Interface balances two conflicting needs – the need for ease of use and understanding, and the need for flexibility to allow complex queries.


Direct Digitization Receiver for Incoherent Scatter Radar
Timothy Walsh
Villanova University

The Millstone Hill Radar currently captures data with an intermediate frequency receiver which down converts from 440 MHz in order to digitize the radio frequency signal. Using a high speed analog to digital converter, it is possible to directly digitize the incoming signal without mixing it. The goal of this project is to design, fabricate, and test a prototype direct RF sub-sampling digital receiver for use with the Millstone Hill UHF radar system. This project has focused on the analog portion of the receiver, from the output of the antenna to the analog to digital converter. The components of the prototype receiver include amplifiers, RF switches and a noise diode for calibration, attenuators, and bandpass filters. The prototype receiver has been constructed from these components in a modular fashion. This allows for testing of the components separately as well as for experimenting with different receiver configurations. Some early tests of the receiver will be described.


Simultaneous 86 and 43 GHz VLBI Observations of LPV R Cas near SiO Maximum
Lisa Winter
Villanova University

Following the inaugural April 2001 simultaneous 3mm and 7mm VLBI observations of SiO masers around R Cas, the 3mm and 7mm v=1 shells of a red giant star were registered for the first time (Straughn et al. 2001). The initial VLBI run occurred during stellar SiO minimum, when R Cas exhibiting anomalously weak 3mm masers. In order to study the R Cas masers more effectively, the second set of observations were scheduled to take advantage of a predicted SiO maximum. The new observations, consisting of three epochs spaced between late February and March 2002, provide a valuable tool in examining the extended atmosphere of R Cas. Imaging of the three epochs, spaced approximately ten days apart, revealed rings in the v=1 and v=2, J=1->0 (7mm) transitions and partial rings in the v=1, J=2->1 (3mm) transition. For the first time, all three bright transitions have been registered spatially, using an original algorithm I developed, based on individual maser component correlations within velocity planes. This allowed for comparison of changing behavior from epoch to epoch. From this comparison, a general trend in the epochs seems to have emerged, where the maser components towards the west end of the rings overlap in all transitions and the eastward components exhibit a separation of the rings, where the 7mm transitions lie within the 3mm transition.


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