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Abstracts of Presentations

Research Experiences for Undergraduates (REU)
Abstracts of Presentations
August 11, 2005


2005 REU students

OH Masers in Arp 220
(2.2 MB PDF)
Andrew Bialecki, Harvard University

When two galaxies merge together their interaction can produce significant activity in the form of star formation, supernova explosions, and even possibly the development of supermassive black holes and quasars. By far the closest and most easily observable example of an intergalactic merger is Arp 220, an ultra luminous infrared galaxy (ULIRG), only 76 megaparsecs away. By observing Arp 220 in radio bands using global VLBI techniques, high-resolution measurements of compact continuum sources and associated spectral line emission and absorption due to hydroxyl have been taken. This presentation explains the data analysis techniques and derived results of observations of the 1667 and 1665 MHz hydroxyl transition lines in the two merging nuclei of Arp 220. Among those results is evidence of hydroxyl emission and absorption in the direction of at least 25% of the sources which is, in some cases, related between several sources. The properties of these emission and absorption features along with possible explanations of the physical circumstances producing them and what future observations might help reveal are also explored.

Using Small Radio Telescopes for VLBI Interferometry
(0.4 MB PDF)
Eric Evarts, Brandeis University

Throughout the summer development has continued on the next generation of the Small Radio Telescope for use as a VLBI type interferometer. The presentation will include a discussion of difficulties encountered with setting up this interferometer and an examination of a couple potential uses for the SRT interferometer. We used 3 SRTs to form one short baseline of about 5m and two long baselines of about 1.4 km. We observed consistent strong fringes on the Sun using the short baseline and an occasional "microburst" on the long baseline. The extragalactic source Cygnus A was observed on the long baselines and a double source model was fit to the data. These test observations were carried out while developing software to make VLBI observations with the SRT easier.

Analysis of the neutral temperature and composition based on Incoherent Scatter Radar Observations
(5.0 MB PDF)
Tanya Gertzen, University of Texas, Dallas

Previously developed ISR models generate local electron temperature, electron density and ion temperature data for the Millstone Hill, Arecibo and St. Santin locations as inputs for the ion energy balance equation to determine profiles of neutral temperature and oxygen density in the thermosphere. This method generates four parameters used for the profile determination, temperature at 120km, exosphere temperature, shape factor and oxygen density at 400km, which are the focus of this research. The change in these derived parameters with season, local time, F107 or ap are compared to those produced by the MSIS model. Trends are observed highlight local variations not well picked up on a global scale, such that the local models are asymmetric in their annual variation when the MSIS model is symmetric. However, the derived exosphere temperature does follow the global model closely with a less than ten percent difference. Investigation into the ratio of the local oxygen density over the global oxygen density produced results which varied between the values of one and two when F107 was restricted to a maximum of 190. Such a ratio gives an estimate on the O+ - O collision frequency modification factor, the Burnside factor, if we assume that the MSIS oxygen density and our energy equation are valid. Averaging Millstone Hill data over the year, during daytime hours for median solar activity and quiet magnetic conditions produces a ratio of 1.25 with an error of 0.0022.As F107 and ap also are considered at different values the ratio for Millstone Hill increases slightly to 1.42 with an error of 0.010. These values have many implications which require further analysis by comparing them with other techniques used in obtaining the Burnside factor.

A Multi-transition search for Class I methanol masers
(3.3 MB PDF)
Reimi Hicks, Brown University

Using the Haystack 37m telescope and positional information from the Spitzer Infrared Telescope data, we have conducted a survey of the W5 molecular cloud for Class I methanol masers. Observations at 44 GHz were made of four regions in W5, three of which were densely packed with protostars. Additional observations at 44.069 GHz, 36.169 GHz, and 24.933 GHz were made of an area in the source M8E that had previously been found to contain a 44.069 GHz methanol maser. Though multiple integrations of the regions in W5 were performed, questionable system temperatures and aperture efficiencies made the results inconclusive. The spectra retrieved from W5 seemed to be only noise, but further investigation of these regions is necessary to rule out the existence of masers. Results from M8E showed clearly identifiable masing in both the 44.069 GHz and 36.169 GHz transitions but none in the 24.933 GHz transition. These results were then compared to multi-transitional observations of class I methanol masers in S255 and S235 made by former REU students at Haystack. Future multi-transitional searches and studies like this one will better our general understanding of masers and perhaps lead to the formation of an adequate structural and energetic model.

Automated Detection of SED Plumes Using GPS TEC Data
(0.9 MB PDF)
Brandon Taylor, University of Texas, Austin

The effects of Storm Enhanced Density (SED) structures with high level of and sharp changes in total electron content (TEC) must be compensated for in order to ensure stability of trans-ionospheric communications. The Madrigal database's collection of TEC data from the World-Wide GPS Receiver Network offers a new tool for identifying and studying these structures.With over 10 years of continuous GPS TEC data that will soon be available on the database, an automated system for detecting when these SED structures are present will greatly assist in the study of them. Two Matlab methods that will be made available on the Madrigal server at MIT Haystack Observatory will provide such a system. The first method downloads and formats the GPS TEC data over a specified time period. The second method accepts this formatted data and returns a structure characterizing any SED structures that were detected. This program not only offers an indication whether an SED structure exists, but also returns information about its location and magnitude which can be used to study the movement and evolution of the SED structure in time.

Simulating the Effects of the Ionosphere on MWA Measurements
(1.2 MB PDF)
Sean Ting, Stanford University

The epoch of reionization (EOR), a period in the early universe during which the formation of the first stars and/or active galactic nuclei ionized the surrounding intergalactic medium, has become a hot topic in astrophysics and cosmology.Presently, telescopes cannot take accurate readings at the frequencies necessary for probing the structure of the universe during this era. However, there is an effort to build an array in Western Australia, the Mileura Widefield Array, which should have the required sensitivity, precision, and frequency range. In order to test this, a simulation has been built at Haystack that mimics the measurements the MWA will take. This summer I have examined the effects of inserting an ionosphere into this simulation. This has included testing preexisting code, creating a model of the ionosphere, and exploring different methods for correcting distortions of the data due to the ionosphere.

The effects of Geomagnetic Storms on Ion Temperatures in the Lower Thermosphere
(1.6 MB PDF)
Robert Yatteau, Oberlin College

With E-region observations from 1970 through July, 2005, Millstone Hill has acquired a considerable amount of temperature data for this region of the atmosphere. Using this dataset, we examine how the temperature varies during geomagnetically quiet times in response to changing altitude, UT, season, and solar flux (F10.7). The temperatures remain roughly constant over all altitudes (100 km to 150 km) during night (0 to 11 UT) and for all hours at altitudes below 120 km. During the day, temperatures increase by 200 K and 500 K at 125 km and 150 km, respectively. Summer median temperatures are higher than winter by approximately 20 K and 40 K at 125 km and 150 km, respectively. Median temperatures during periods of high solar activity (F10.7 > 150) are 10 K and 20 K higher at 125 km and 150 km, respectively, than during periods of low solar activity (F10.7 < 150). Knowing this, the effect of geomagnetic storms on E-region temperatures can be analyzed. Millstone Hill's data shows that even at sub-auroral latitudes, the median temperatures during geomagnetically active periods are increased over quiet-time levels by as much as 100 K for 3 < Kp < 5, as much as 150 K for 5 < Kp < 7, and as much as 200 K for 7 < Kp < 9. The effect is most pronounced during spring and summer seasons, and it is stronger than seasonal or solar cycle effects for every season except winter.



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