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Abstracts of Presentations

Research Experiences for Undergraduates (REU)
Abstracts of Presentations
August 10, 2006


2006 REU students


Maser Emission and Outflow in the Orion KL Nebula
Presentation (PDF)
Christopher Beaumont, Calvin College

We present new maps of the v=1,2 J=1–>0 transitions of silicon monoxide masers in the Orion KL nebula. These masers are centered on Source I - a continuum source thought to mark the position of a massive young star - and thus probe the physical environment of massive star formation at scales of tens of AUs. These new data provide a bridge between previous high resolution VLBI maps of high surface brightness emission and low resolution VLA maps of low surface brightness emission. I discuss what implications these new data have on proposed models for outflow and accretion around Source I.


OH Megamaser Emission Toward Radio Supernovae in Arp 220
Presentation (PDF)
Katherine de Kleer, Massachusetts Institute of Technology

We have used VLBI data and resulting images from two time epochs separated by 15 months to study the radio supernovae and compact masers in the two colliding nuclei of Arp 220 (IC 4553), an Ultra-Luminous Infrared Galaxy (ULIRG) located at a distance of 76 Mpc (z = 0.018). As one of the closest and brightest ULIRGs, Arp 220 is an ideal candidate for study to understand both the properties of these dynamic galaxies and the characteristics of the OH megamasers often associated with them. Arp 220 has confirmed OH megamaser emission at both the 1665 and 1667 MHz frequencies, with two-thirds of the 1667 MHz emission arising from high-gain compact masers, and the rest of the emission assumed to come from diffuse, low gain OH masers spread over the two-nucleus region. Such emission is resolved out by VLBI and is therefore not observed in our data set. Arp 220 also has 49 confirmed radio supernovae in its two nuclei, and we have discovered spectral features that are attributed to OH megamaser amplification of the supernovae emission in both the 1665 and 1667 MHz lines. The question we seek to investigate is whether such features represent a new type of physical maser that is local to the supernovae, or whether they can be explained as amplification along lines of sight through the diffuse OH medium. We have used spectral line cubes to extract individual and comparison spectra for each of the radio supernovae in the eastern and western nuclei of Arp 220, and have identified and verified numerous spectral features. We approach the question of the physical properties of these masers by looking at the associated velocity widths, amplification factors, and time variability of the spectral features. We thus present in this paper the spectral and physical properties of the OH megamasers toward the radio supernovae in Arp 220, and introduce the possibility of a third type of supernovae-associated megamaser emission.


Web Interface development for the Millstone Hill Incoherent Scatter Radar
Presentation (PDF)
Brandon Scott Fines, University of Missouri, Columbia

The Madrigal Database provides access to data from several different Incoherent Scatter Radars. While powerful and robust, the associated interface is also limited in that a user cannot group experiments by geographic region, nor can the user see all experiments of a given type at one time. However, if one were to build an interface on top of Madrigal which only searched data from a specific institution, it would be possible to make a simple, easy-to-use interface which does not require prior knowledge to operate. Making use of the Common Gateway Interface and the Madrigal Python library, a web-based interface was created, allowing a user to search Millstone Hill data using any combination of three search methods — Date, Experiment type, and Geographic region.


Class I Methanol Masers in DR21N and W75N
Poster (PDF)
Samantha Hoffmann, Texas Lutheran University

New class I methanol masers were discovered during a previous survey of several molecular clouds with the Haystack 37m Telescope at the 36 and 44 GHz frequencies. Two systems were chosen for their methanol maser activity, W75N and DR21N. In order to study the environments of these masers, accurate positions were needed, so observations were made with the Very Large Array at the 44 GHz frequency. The maser features were then compared with Spitzer Space Telescope images. The Spitzer images showed no infrared source in the W75N region, which could indicate a very young star in which the infrared radiation from the young star has not yet emerged from the dense material surrounding it. The DR21N masers were grouped around an infrared source. Study of data previously taken by the Haystack 37m Telescope of the DR21N masers revealed short term variability in these masers on a timescale of days. Further observation of the DR21N region with both the Haystack Telescope and the Spitzer Space Telescope is proposed for November to explore this short term variability and its cause in greater depth.


The South Atlantic Anomaly and its Effects on the Equatorial Ionosphere
Presentation (PDF)
Ann Kapusta, Dartmouth College

One of the more significant space weather effects that occurs during geomagnetic storms is a disturbance that moves plasma from the equatorial region of Earth's ionosphere into the mid-latitudes. This effect is manifested when the peaks in the total electron content (TEC), normally located approximately ± 15 degrees from the magnetic equator, move further north and south. During some large storms, greatly enhanced TEC values are observed as far north as Florida. Recently there has been evidence that the longitude sector close to the South Atlantic Anomaly (SAA) shows more significant effects in the TEC disturbance during geomagnetic storms. The SAA is a well known irregularity in the Earth's magnetic field. In the SAA, the magnetic field is much weaker than all surrounding areas allowing charged particles to enter further into Earth's atmosphere. With the help of the Haystack Observatory's Madrigal database, our study evaluated the effects of the SAA on TEC values in the northern and southern hemispheres over a variety of longitude sectors during both quiet and storm times.


Spectral Analysis of Neutral Wind Tides in the Lower Thermosphere
Presentation (PDF)
Amrita Masurkar, Massachusetts Institute of Technology

Lower thermospheric neutral wind data taken with the Millstone Hill ISR during the September 2005 30-day campaign was used to investigate atmospheric tides. Lomb-Scargle spectral analysis was utilized, and 8-hour, 12-hour, 24-hour, quasi-2-day, quasi-5-day, and quasi-10-day waves were observed. Spectral analysis was carried out for the zonal and meridional winds. Several techniques were employed to verify the authenticity of the spectral peaks in order to determine whether the tides were a result of physical phenomena or an effect of data truncation and nighttime gaps.


Advanced Radio Imaging Techniques
Presentation (PDF)
Dylan Nelson, University of California Berkeley

The science requirements of next-generation radio telescope arrays present a new set of challenges to traditional imaging and data processing techniques. Instruments such as the MWA, SKA, and other arrays implementing large numbers of small diameter dishes have a naturally large field-of-view due to the small diameter of individual telescopes. In order to achieve high image fidelity and dynamic ranges, noise contributions from off-center sources must be reduced — a task traditionally requiring imaging of the full field-of-view. However, implementation of this subtraction requires unreasonable computational speeds while also generating unmanageable volumes of data. One approach to this problem involves dynamic control over the field-of-view, implemented in software as a weighting function internal to the integration routine of the correlator. Using this technique one can effectively reduce the noise contribution levels from sources outside the region of interest, and in some cases dramatically reduce the volume of data exiting the correlator for post-processing. In this paper we focus on verifying the effectiveness of this technique, implemented through the MIT Array Performance Simulator (MAPS) using simulated data sets. Additionally, several dimensions of possible parameter space are explored in order to test limitations and determine design requirements of this approach, including the impact of variable levels of radio frequency interference (RFI) excision on image fidelity and off-center source signal rejection.


Analysis of Limb Brightening on the Quiet Sun at 21 cm
Using a Three-Element Interferometer
Poster (PDF)
Jonathon Oiler, University of Wisconsin, Madison

During the summer, three small radio telescopes (SRTs) were used for observing the Sun during the Sun's Quiet Phase almost daily over a two month period. We used the three SRTs as a 3-element interferometer to observe the entire Sun. The baselines used were 7.77 meters, 20.12 meters, and 26.67 meters. Data from the Sun were taken and software was used to calculate the visibility amplitudes and closure phase. A modeling program was used to replicate the Sun and a comparison of closure phases between the SRT data and the modeling data was performed with a weighted least-squares fit. We found evidence for limb brightening around the equatorial region of the Sun and determined that the modeling software fit the data better with limb brightening (the outer 20 percent of the solar disk's diameter) used in conjunction with a translatable sunspot of varying brightness. The equatorial limb brightening was found to contribute 30 ± 10 percent of the total solar radio flux.


Variability of Wind in the Lower Thermosphere
Poster (PDF)
Kevin Reed, University of Michigan

Neutral winds in the lower thermosphere were measured by the ground based incoherent scatter radar at Millstone Hill during a thirty day campaign in September 2005. This data was used to investigate the long term and short term tidal variations of the northward and eastward winds over the altitude range of 100 – 136 km for the whole thirty day campaign. Analysis shows that a semi-diurnal (12 hour) tide is the most dominate variation, with evidence of a less dominate diurnal (24 hour) tide, and perhaps an 8 hour wave present on some days during the campaign. There is much variability in the amplitude and mean wind of the semi-diurnal and diurnal tide, and strong consistency in the variation of the semi-diurnal and diurnal phase with altitude.


Prototype Tension Stabilized Mesh Antenna for UHF Radar Applications
Presentation (PDF)
Debra Rich, University of Rochester

Incoherent Scatter Radar systems are very powerful and provide a variety of observational data for the study of the Earth's ionosphere and near space environment. Recent pursuits have been made by Millstone Hill for the implementation of a low cost, large aperture antenna design known as the Zenith Incoherent Profiler. The purpose of this project was to investigate the cost and various engineering components necessary to design a prototype tension-stabilized mesh antenna operating at optimal efficiency. Computer simulations were used to develop the reflector geometry, analyze different UHF feeds, and to evaluate the structural as well as mechanical elements of construction. Considerations were also taken into account for these engineering aspects in order to make it easier to scale the design to a much larger aperture.



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