Previous NRAO Summer Student Research Project Summaries
For descriptions of the individual summer programs,
including itineries, pictures, lectures, and joint student projects,
see the previous
Program Reports.
Select a date range, student program, and site below:
Alexander Grichener, of Tufts University,
worked with John Effland on
ALMA Band 6 SIS Mixer Test System
Alex's summer project consisted of writing software to synchronize power meter readings to a spinning chopper wheel. The chopper wheel was placed between a cold load (a liquid nitrogen bath) and the receiver. As the chopper spun, if the receiver was looking at the cold load (chopper was not blocking the liquid nitrogen) the meter would measure a lower power level coming out of the receiver than if the chopper was looking at a hot load (chopper was blocking the liquid nitrogen). Alex wrote software to keep synchronize the spinning chopper wheel to a continuous record of hot load and cold load power meter measurements. At the same time a stream of Y factors was computed as well (Y factor directly relates to the amount of noise the receiver system is contributing), which is simply the hot load power level divided by the cold load power level. The program also calculated statistics on this stream of Y factors and would return with the final Y factor only after its standard error had fallen below a certain threshold. The software was written in Visual Basic .NET and some effort went into porting previously programmed code in VB 6.0 to VB .NET. All software was documented using UML class, sequence and activity diagrams.
John Kelly, of University of Virginia,
worked with Matt Lister on
Investigating Jet Bending and Projection Effects in Active Galactic Nuclei
To study jet bending and projection effects, John modelled the curving jet in the quasar CTA 102 (2230+114), assuming the jet followed a helical path. To quantify the jet he used eight epochs of 15 GHz VLBA images and ridgeline mapping code to create a base ridgeline for comparison. The helix used was based on the model in Gomez et al. (1994), with an additional parameter added to convert the conical helix into a cylindrical helix at a specified distance from the origin. To determine the best fit parameters, John wrote code for a genetic algorithm search, which tested model ridgelines against the base ridgeline determined from the VLBA data. He placed additional limits on the parameter ranges using the lack of a counterjet in the source, and the ratio of bright to dim areas in the continuous jet. A unique answer was not found, and to place further constraints on the parameters, further epochs of high resolution images will be necessary.
Mehreen Mahmud, of Whittier College,
worked with Ken Kellermann on
Superluminal Motions in Quasars and AGN
This summer, Mehreen compared the apparent speeds of jet components of 29 quasars and active galactic nuclei that were common to the 2 cm survey (15 GHz) and the Radio Reference Frame Image Database (4cm or 8 GHz). A plot of speeds measured from the 4 cm data against those measured at 2 cm showed that a few points (components) disagree at the 2sigma level. The disagreement can be attributed to the differences in imaging, whereby model-fitting was done in the UV plane for the 8 GHz sample and in the image plane for the 15 GHz.
Although we did see components near the core at the higher frequency, and did trace out the outer components at the lower frequency for some cases, very close to the core a common feature in the plots showed a blend of components near the core. Observing at different frequencies can lead to a 'core shift' (not more than 1 milli-arcsecond) which can cause these differences. This is because the jet is optically thin and the core is optically thick and the 'VLBI' core may be different at different frequencies and not the actual core. Eight quasars from the sample were also common to the sample studied by Jorstad et al. at 43 and 22 GHz. Close to the core, more components were observed at these higher frequencies, as expected. However, further out from the core, components that were detected at 15 GHz and 8 GHz were unresolved at 22 and 43 GHz, and hence there were no measured speeds for the unresolved components. Speed comparison was therefore not possible with this sample.
Jodie Martin, of University of Virginia,
worked with John Hibbard on
The HI Environment of Ellipticals with Anomalous Light Profiles
This summer, Jodie looked for evidence of a gaseous merger history in two samples of early type galaxies (17 test galaxies and 19 controls), using 21cm neutral hydrogen spectral line observations taken with the GBT Spectral Processor. The test sample consisted of early type galaxies with central spikes in their surface brightness profiles which may indicate a former dense star formation region. The control sample consisted of early type galaxies without central spikes (and presumably without as recent or as densely located star formation events). Both samples covered a similar range of distances and sizes and were chosen to be free of dust and active galactic nuclei.
The spectra were reduced by removing the radio frequency interference, calibrating via the noise diode and position switching, averaging the multi-integrated spectra, baselining, and calibrating the flux via the observation of a standard source (3C295). The spectra of three galaxies were contaminated by continuum sources in the beam. The spectra of nine more galaxies displayed one or more 21cm lines. Three of these galaxies are members of the test sample and 6 are controls. After comparing the positions and velocities of neighboring galaxies which may also contribute to the observed spectral features, the probability that environmental gas can be associated with early type galaxies with central spikes is slightly higher. However, the numbers are too low for an adequate statistical analysis and mapping may be required to isolate the location of the detected gas.
Chaitali Parashare, of Chalmers University Of Technology,Sweden,
worked with Rich Bradley on
The Low Frequency Component of the Solar Burst Monitoring Station
Tim Bastian and I are proposing to build a broadband solar burst monitoring station to be deployed in Green Bank. This instrument will serve as a basic research tool in solar radiophysics for use by the wider community, it remedies the lack of an important component to the US Space Weather effort, and it provides a platform for R&D work on broadband antennas, feeds, and receivers operating from decimeter to decameter wavelengths. Hardware for the low frequency component of the Station, operating from about 20 MHz to 80 MHz, is being provided by the Navel Research Laboratory (NRL) and is essentially a copy of the system developed by Bill Erickson. The summer student will be responsible for assembling this system, upgrading and expanding its capabilities where appropriate, and deploying the system in Green Bank.
Christine Roark, of University of Iowa,
worked with Rachel Osten on
The UV Spectrum of the Flare Star EV Lac
This project is part of a multi-wavelength survey using UV time-tagged data from four orbits of the HST to study the flare star EV Lacertae. By extracting the data in 60s intervals, Chrissy was able to create light curves, determine the quiescent and flaring times and make respective spectra ranging from 1140 to 1735 Angstroms. These spectra contain ionic transitions with formation temperatures between about 104 and 105 K, which probe the choromosphere and transition region in the outer atmosphere of EV Lac. While fitting both the quiescent and flare spectral emission lines with Gaussian curves, broad wings were discovered in the high formation temperature lines of the quiescent stages, thus requiring multiple Gaussians. The peak flare count rates were enhanced approximately 2-3 times the quiescent count rate and lasted a few minutes at most. The average continuum was determined to be 6E-16 ergs/cm2/s for the quiescent times and 2E-15 ergs/cm2/s for the flaring, which are both relatively small compared to the line fluxes and didn't need to be taken into account during line fitting. Using Chianti, Chrissy was able constrain a viable range (2.3E11 to 3.8E11) to the electron density of OV by calculating the line ratio of 1218 to 1371 Angstroms.
Richard Thomsen, of Duke University,
worked with Skip Thacker on
The Design and Test of LO sources for ALMA
Porter helped with the final design and test of Local Oscillator (LO) sources for ALMA. he learned about the test and characterization of servo loops (phase lock loop), mechanical design and layout of microwave components, and had an opportunity to assist with research in low phase noise fiber optic transmission systems. His major project was to assist in the gathering and reduction of data taken to test the noise and stability of the new digitally tuned YIG LO which is intended to be used in ALMA. The purpose of the experiment was to generate a method of comparing the YIG LO to the Gunn LO, which is already in use in radio astronomy and has known excellent working charateristics already. The YIG was untested until these experiments, so the hope is to show that its characteristics are as favorable as the Gunn, but with the advantage of being digitally tuned instead of analog. Porter did preliminary comparisons of the data that helped to generate some intial speculations; however, the data reduction is just getting started and ALMA scientists are looking at it now. In addition to this experiment, Porter was given the task of designing a portable box to set the bias voltages for amplifier chains that will go in the LO circuit. This portable box has the same capabilities as the desk top computer which set the amplifiers before, but will be able to move from lab to lab and out to the site in Chile where ALMA will be built. The box was wired together and in use by the summer's end.
Lauren Wye, of University of Virginia,
worked with Rich Bradley on
Low Frequency Component of the Green Bank Solar Radio Burst Spectrometer
NRAO is building a broadband solar burst monitoring station to be deployed in Green Bank. This instrument will serve as a basic research tool in solar radiophysics for use by the wider community. It remedies the lack of an important component to the US Space Weather effort, and it provides a platform for R&D work on broadband antennas, feeds, and receivers operating from decimeter to decameter wavelengths. Hardware for the low frequency component of the Station, operating from about 20 MHz to 80 MHz, was provided by the Navel Research Laboratory (NRL) and is essentially a copy of the system developed by Bill Erickson. Lauren Wye was responsible for simulating and understanding the properties of the NRL-provided dipole antenna, using CST Microwave Studio software, and assembling the data acquisition portion of this system, adapting the NRL control software to operate in a Linux environment. With the help of NRAO employees Dan Boyd and Chaitali Parashare, a prototype of the Low Frequency Spectrometer (consisting of a dipole antenna, active balun preamplifier, spectrum analyzer receiver, data acquisition card, and control software) was successfully tested and deployed on the roof of the NRAO Ivy Road building, paving the way for future upgrades and deployment at Green Bank.