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Abstracts of Presentations

 

Research Experiences for Undergraduates (REU)
Abstracts of Presentations
August 7, 2014

 

2014 REUs

 

Climatology of Thermospheric Temperature and Oxygen Density during 2002-2013 at Millstone Hill
Presentation (PDF)
Jessica Bozell, Purdue University

 

In recent years, climate change has become an area of increasing importance as researchers strive to better understand the impact of increased greenhouse gas concentrations on earth's atmosphere. Past studies suggest that in the thermosphere and ionosphere, there is a cooling effect which results in a reduction in neutral densities and height dependent changes in electron density. The purpose of this study is to further investigate the long-term changes in the neutral atmosphere by using ground-based incoherent scatter radar (ISR) measurements of the ionosphere and thermosphere. Ion energy balance calculations can be used to estimate exospheric temperature and neutral oxygen density from the radar-measured ionospheric parameters. By using modified versions of existing codes that describe the ion energy balance equations [Nicolls et al.,2006], ionospheric data collected from the Millstone Hill ISR (42.6°N, 288.5°E) between 200 and 600 km from 2002-2013 has been used to calculate exospheric temperature and neutral oxygen density. These results are then used to create a new local empirical model that can describe the climatology of these parameters, varying with local time, season, solar and geomagnetic activities. Comparing the exospheric temperature and neutral oxygen density data measured at Millstone Hill to corresponding MSIS values, there is a possible long-term cooling trend seen in these observed thermospheric parameters at Millstone Hill. These results, based on the most recent solar cycle observations, will be extended to include more solar cycles, and a much improved understanding of the thermospheric long-term trends may be reached.

 

Characterizing the Jet Precession of Quasar 3C273 at 1.3mm with the Event Horizon Telescope
Presentation (PDF)
Michael Calzadilla, Univ. South Florida

 

The Event Horizon Telescope (EHT) is an array of millimeter-wavelength telescopes that observe the nearest supermassive black holes using the technique of very long baseline interferometry (VLBI). The EHT is uniquely capable of resolving structures on angular scales of tens of microarcseconds, corresponding to a few Schwarzschild radii around nearby black holes such as the one in our galactic center, Sgr A*. One of the goals of the EHT is to better understand relativistic outflow processes around black holes, which can be achieved due to its extremely high spatial resolution. To that end, here we present the first high-resolution VLBI observations of 3C273 at 1.3mm. We successfully detected non-zero closure phases, which indicate asymmetric structure that we then fit using simple geometric models. The orientation between model components varied over the range of years that 3C273 was observed, in agreement with multi-epoch data at lower frequencies. Our results suggest that precession can be observed even at sub-parsec scales in 3C273. Furthermore, we demonstrate that polarimetric ratios can be used for relative astrometry between flaring components and discuss the implications of that for future research.

 

Design and evaluation of compact antennae for ionospheric sounding
Presentation (PDF)
Tyler Erjavec, Ohio State University

 

Compact high frequency (HF) antennas are crucial for enabling the use of HF radar sounding for ionospheric remotely sensing using a dense network of sounders. Current ionosonde antennas are too large and expensive. In this study, we investigate two compact HF antenna designs through modeling and prototypes: a folded resistively loaded dipole, and a capacitively tuned small magnetic loop. Both antennas were modeled using FEKO to investigate antenna efficiency and beam patterns. The folded dipole was bought off the shelf, while the compact magnetic loop prototype was built in house. In this study, we present both modeling and measurements of the antenna characteristics. We also present the first ionospheric soundings obtained using the prototype antennas.

 

Investigations of Hemispherical Differences in Geomagnetic Storms
Presentation (PDF)
Katerina Gonzales, Colorado School of Mines

 

The influence of geomagnetic storms on the total electron content (TEC) varies as a function of longitude, season, and hemisphere. None of these differences in TEC are fully understood. Using the TEC data from the ground-based GPS receiver network in the Madrigal database, we analyze the data from 2009 until 2014 in the polar regions from 65 to 90 degrees and -65 to -90 degrees. Our processing started in 2009 due to the better coverage in the GPS ground network in the southern hemisphere in this solar cycle. Case studies are selected from different seasons and longitudes to compare and contrast quiet-time TEC and storm-associated TEC in both hemispheres. We first identify a seasonal dependence of the hourly TEC by analyzing hourly averages in a three-day period around the solstices and equinoxes from 2009 to 2013. Then, we examine storm-time effects on the TEC by examining the hourly averaged TEC in a three day window around a particular storm. We investigate a hypothesis that 1900 UT and 700 UT are favorable times for storm enhanced density (SED) in the northern and southern hemispheres, respectively.

 

Using JVLA Observations of SiO Masers to Probe the Dynamics of an AGB star: W Hydrae
Presentation (PDF)
Patrick Kamieneski, Bowdoin College

 

The Asymptotic Giant Branch star W Hydrae (W Hya) is known to be a strong source of silicon monoxide (SiO) masers. We have used 2014 JVLA observations near 43 GHz to target eleven SiO lines. Those that were successfully detected include the vibrational ground state (v=0) transition for the 28SiO, 29 SiO, and 30 SiO isotopologues, in addition to the v=1, 2, 3 lines for 28 SiO. These detections were used to look into such properties of the J = 1 - 0 maser emission region as shape, size, and intensity. The detection of rare spatially extended ground-state emission in a region located approximately 40 – 80 AU from the center of the photosphere will be discussed. Additionally, a saddle-like distribution in the velocity field for the v=1 case may help to confirm the existence of a weak bipolar outflow in W Hya. The results also indicate that the observed transitions have differing spatial distributions with respect to the star.

 

The Martian Climate Using HDO/H2-180
Presentation (PDF)
Miranda Kephart, Yale University

 

Isotopes of common molecules (especially water) are often used on Earth as a probe of climatic variations, both geographically and with time. This is possible because we have a good 'standard' for the abundances of various isotopes due to our large oceans. In order to obtain the same information about the Martian climate, we need to determine the 'standard' distribution of these isotopes on Mars. In April 2014, SMA observations of two water isotopes - HDO and H2-18O - were obtained, allowing the relative abundances of deuterium and hydrogen to be compared. The resulting D/H ratios decrease as a function of latitude, being highest at the Martian north pole and lowest in the southern hemisphere.

 

Connecting Stratospheric and Ionospheric Anomalies
Presentation (PDF)
Mary Spraggs, Western Kentucky University

 

This study investigates any relationship between lunar phases and ionospheric anomalies that appear at low latitudes concurrently with sudden stratospheric warmings (SSWs). The study utilizes World-wide GPS Receiver Network Total Electron Content (TEC) data spanning 13 years (2001-2014) and focuses on the changes in the equatorial ionization anomaly the Western hemisphere. TEC is highly variable due to the influences of solar flux, geomagnetic activity, and seasonal variation and these influences are removed by the use of model. This empirical TEC model is a combination of linear dependencies of solar flux (F10.7) and geomagnetic activity (Ap3) with a third degree polynomial dependency for day-of-year (DOY). With such dependencies removed, the remaining TEC variation could be resolved and attributed to an appropriate mechanism. Lunar phase and apside was investigated in particular, especially the new and full moon phases during perigees when tidal forcing would be most powerful. Lunar tidal forcing on planetary waves is also examined as being physically responsible for setting up conditions that may give rise to SSWs and ionospheric anomalies. Preliminary results suggest that such anomalies may be enhanced in intensity during the full or new moon and even more so during perigee by different amounts depending on whether the SSW is a major (40-60%) or minor (20-45%) event.

 

The Birth of Quasars
Presentation (PDF)
Rachel Thorp, California Institute of Technology

 

Little is known about the nature of luminous quasars with young radio emissions, yet active galactic nuclei (AGNs) play an important role in the properties of almost any large-scale structure in the universe. We take VLBA data of 90 unique, distant (1.4 < z < 3), luminous quasars with young jets and image their structures. This sample has been selected from the WISE mid-infrared survey with a preference towards the most heavily obscured sources (believed to be the youngest). By studying these objects, we attempt to better understand the nature of radio emission interactions with interstellar medium (ISM), and AGN formation and evolution.

 

Automated Discovery of Short Duration Solar Radio Bursts in Murchison-Widefield Array (MWA) Data
Presentation (PDF)
Brian Timar, University of California, Berkeley

 

Low-frequency radio observations of the Sun with the MWA have revealed a previously unknown class of weak radio events, with durations on the order of 1 second or less, and frequency widths of a few MHz. This radio phenomenon is not well-understood, and insight generation is difficult due to the large volume of data produced by the MWA at rates of several terabytes per hour. To address this situation, we developed a new approach for the detection, characterization, and classification of such events, as well as for the well-known Type III flares. Our technique consists of a pipeline of processing steps that starts with background noise estimation and subtraction. Radio events are then isolated algorithmically using region-growing techniques, wavelet decompositions, and thresholding. Physical parameter metadata for each event are then extracted and stored in a database. Scientists can query these data, filter events based on specified properties, and generate statistics and plots for exploratory studies. Our toolset is the first to empower MWA solar scientists with such computational intelligence in order to enhance their ability to interpret large numbers of short-lived events in voluminous MWA data. Computer vision approaches on solar images obtained from optical, x-ray, and infrared instruments are thus complemented by detections of phenomena in the radio frequency domain.

 

Development of a Low Cost Multichannel Spectrometer for the Study of Ozone in the Mesosphere
Presentation (PDF)
Emily True, University of Maryland College Park

 

Previously, Haystack Observatory has developed a low cost spectrometer for detecting ozone in the mesosphere using satellite TV dishes and a low noise block down converter feed (LNBF). While these spectrometers have contributed greatly to our understanding of the ozone at 100 km altitude, they require at least twelve hours to attain a significant signal-to-noise ratio (SNR). By using three dual polarization LNBFs, we are able to decrease the time to obtain a significant SNR by a factor of √6 or to about two hours. The increased sensitivity also can provide a fine enough resolution to provide data about wind speeds and the temperature of the ozone in the mesosphere. The modest cost of the system is maintained by using inexpensive digital TV tuners and demodulators. This system will enable scientists to gain continued understanding of the atmosphere at a fraction of the cost of other methods.

 

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