NRAO Summer Student Program Project Summaries: 1999

The symbol to the right indicates students who were supported under the National Science Foundation (NSF)'s Research Experiences for Undergraduates (REU) program. All other students were supported under the NRAO Summer Student Research Assistant Program. Follow this link for a list of all student programs at the NRAO. You can also view the student projects titles from 1991-present in tabular form.

These summaries were taken from the Program Reports filed with the NSF. The NSF report include a more detailed discription of the individual summer programs, including itineries, pictures, lectures, and joint student projects.


1999 Summer Students


Cristina M. Murray of University of New Mexico
worked with Jack Gallimore
on

Black Holes in Active Galaxies

Active galaxies (AGNs) are thought to be powered by accretion onto a central, massive black hole. Seyfert galaxies are the nearest AGNs that show all of the classic signs of activity, including radio jets, broad optical line emission, hard X-ray emission, and rapid variability. They are indistinguishable from quasars except that they are nearer and less luminous. Recent VLBA observations have demonstrated that the radio emission from a Seyfert nucleus is, however, peculiar. The nuclear radio properties may owe to thermal processes in gas located very near the massive black hole (i.e., a few light years from the AGN).

I have several projects investigating peculiar radio sources in Seyfert nuclei, two of which are naturally suited for summer student research. One is a VLA survey of high frequency (22 and 43~GHz) emission from Seyfert nuclei. The goal is to locate potential flat-spectrum sources and address the effects of thermal free-free absorption (or possibly emission). There are currently data for 13 sources in hand, and we anticipate having an additional 15 sources this summer (TAC-willing). The other is a VLBI survey of nearby Seyfert galaxies. The main goal of the VLBI project is to investigate the Seyfert radio jets at a spatial resolution of ~ 1 light year. We will be receiving snapshot VLBI data for 8 sources this spring.

Both programs are technically challenging, and the summer student can expect to come away with an advanced understanding of aperture synthesis techniques. The student might choose either to concentrate on complete reduction of the survey data, in which case he or she will receive co-authorship on the survey paper, or to focus on the analysis and interpretation of a specific source and assume lead authorship.


Dustin Bambic, of Western Kentucky University
worked with Michele Thornley
on

NGC 7331: Characterizing the contribution of spiral density waves in flocculent galaxies

My summer with NRAO in Charlottesville began as smoothly as one could hope, even though I was completely unfamiliar with our subject, flocculent galaxies. I had just finished school a week earlier, allowing little preparation time. Michele began the summer with a discussion of our project, data, goals, and motivation. In short, galaxies with large-scale spiral structure are thought to contain spiral density waves. A spiral density wave is a compression wave that is able to organize a galaxys' constituents, forming spiral arms. However, not all galaxies have a large scale spiral design. Another galaxy type, flocculent galaxies, has a disc like the grand-design spirals, but no arms are visible in optical light. Due to their lack of organization, flocculent galaxies have been assumed by some of the astronomical community to not contain spiral density waves. In addition, the topic draws very little attention, and little data is available to those who wish to investigate the matter. So, Michele made this her doctoral thesis topic, investigated several flocculents, including the prototypical flocculent galaxy, NGC 5055, and found conclusive evidence for density wave presence in a few of them. She wished to continue this work, and turned the telescopes toward another flocculent, NGC 7331. Michele was granted 15 hours of observing time with NRAOs Very Large Array, and the data was safe in hand well before the summer. She soon turned her efforts toward new topics, with the NGC 7331 data set unreduced.

I immediately began my background readings, consisting mostly of astrophysical and astronomical journals, spanning the spiral galaxy formation process, spiral form maintenance, galactic surveys, galactic kinematics, galactic interactions and mergers, and of course an introduction to radio astronomy. In addition, the other summer students and I attended a few lectures each week concerning other astronomical topics, each about an hour long, and each by a different NRAO scientist. This introductory time was focused yet unhurried, and perhaps the most learningful period of my life. After only a few weeks, my view of the universe had changed considerably. Suddenly galaxies were dynamical, evolving systems, and the cosmos was much more exciting.

Soon, however, it was back to earth and into the world of AIPS and LINUX. UNIX is an operating system. Prior to NRAO, I may have thought the whole world was either Windows or Mac. However, my eyes were shown additional operating systems, UNIX/LINUX and SUN OS, and my digital adventure was underway. But, not before I was shown AIPS, and opened to what real radio astronomy consists of. AIPS is the data reduction program used for reduction of data collected by NRAO telescopes. Data from observations is stored onto DAT tape, and AIPS enters when you're ready to read and/or edit the data. AIPS consists of tasks and verbs used to configure your data, and with AIPS, bytes are turned into actual images of your object. Initially, I was very intimidated by both AIPS and LINUX, but as my stay at NRAO advanced, I became much more confident in my understanding of both, or at least the parts of each we used.

The data set came in three main sets, each corresponding to a different antenna configuration used to obtain the data. Different configurations provide information on different size scales. However, the reduction process is basically the same for each. Michele and I went through the first data set together, taking notes the entire time so that I could repeat the process by myself. However, it was not thoughtless replication. Each data set is different, almost taking on a character. Each had its own problems, requiring data interpretation and troubleshooting until the final image was satisfactory. The first eight of my twelve week stay at NRAO consisted of this reduction process, until three final images were obtained, one from each configuration.

These three images served as the base of all our further investigations. The three images were combined to create one "mother image." From this image, we were able to create velocity maps, density maps, major and minor axis velocity slices, and zooms of each, corresponding to different regions of NGC 7331. Again, we used each to look for density wave signatures in NGC 7331. We were not the first to look at NGC 7331 with density wave detection in mind. A previous group had used optical means to search for density waves, and claimed to detect density wave perturbations along the western side of the galaxy. We investigated the same region, and the rest of the galaxy. Interestingly, we could not confirm the wave detection along the western side of NGC 7331, but found more significant perturbations along the southeastern side of the galaxy. This final analysis process, along with my preparation for the final presentation of our research to the NRAO staff, occupied the last four weeks of my stay in Charlottesville, and before I knew it, the summer was over.

My summer at NRAO was as pleasing an experience as I could have imagined. I formed great friendships during my stay. I experienced the reality of astronomical research. I saw what astronomers do all day, what they eat, what they talk about, and even how they drive. My plans before NRAO included attending an astronomical graduate program. After my summer at NRAO, these plans have solidified. In fact, I plan to pursue astronomy more than ever. Perhaps I'll have a summer student working under me some day.


Porter Mason , of Duke University

worked with Barry Turner
on

The 2mm Spectral Survey

Mr. Mason worked on preparing Turner's 2mm survey for presentation on the WWW. The input to the problem is (i) the observed spectra in tabular form (the form to be determined); (ii) and catalog of computed spectral lines including Lovas, JPL, and my own calculations; (iii) tables of spectral line parameters measured by me from the spectra. The problem will be to provide a WEB setup that allows the user to click on a given spectrum, and obtain several features including (i) a plot which with cursor control may be scaled in both axes, over a chosen frequency range; (ii) may be linked to the atlas of computed lines with which any selected line on the plot may be searched and labelled if a match is found; (iii) contain most of the elementary features of Unipops or AIOS++ such as rms (requiring designation of baseline parameters); perhaps gaussian fitting; 0th moment measures, etc.

The result may be viewed here.


Jonathan Durbin , of
Valdosta State University
worked with Richard Bradley
on

Wideband Balanced Amplifiers

Mr. Durbin helped to design wideband balanced amplifiers for operation in the 1-6 GHz band. Specifically, we need to develop multi-octave hybrid couplers. The student will learn about the operation of such components and then use computer-aided design tools to simulate their performance. Test structures will be fabricated and evaluated.


Chris Power, of Trinity College, Dublin
worked with John Hibbard on

N-body Simulation of "The Antennae"

Collisions between galaxies can be dealt with analytically only in very specific cases. Unfortunately, the conditions that are prevalent in the bulk of galaxy interactions rarely satisfy these idealisations and so, when considering such situations, the researcher must make use of N-Body simulations to model the encounters. In general, pictorial representations of the time evolution of such encounters is desired.

In this report, I will discuss my work in this area; in particular I will concentrate on how I developed a means to convert observational and simulation data into a form that is readable by the interactive 3 dimensional visualization tool, Geomview. I will also describe my work on the matching of simulation and observational data for the case of NGC 4038/9, the "Antennae", as well as the motivation for such model matching and the characteristic features of a system that are particularly suited to such fitting.

As an interesting aside, I indulged myself and present brief discussions on The History of Mergers and previous attempts to model the "Antennae" in Numerical Models of NGC 4038/9. My work may be reviewed here.


Darrell Osgood of New Mexico Institute of Mining and Technology
worked with Frazer Owen
on

Evolution of Populations of Radio Galaxies in Clusters

Using the existing deep VLA radio images for 6 clusters of galaxies with z between 0.25 and 0.41 and existing optical imaging (ground-based and HST),the student would make the optical identifications. The student would use these data, along with existing optical spectroscopy to estimate size of the radio populations in each of these clusters and whether the radio galaxies were likely star-formation driven or AGN's. These data would then be compared with lower redshift results to evaluate the evolution of these populations with redshift and other cluster properties.


Teddy Cheung of Brandeis
worked with Jim Ulvestad
on

ARISE Imaging

Space VLBI missions have unique imaging requirements relative to ground VLBI. For the highest resolutions, there typically are large holes in the (u,v) plane, both due to the high spacecraft orbit and to intermittent tracking. Also, high sensitivity is required, but the space telescope cannot nod back and forth between sources due to a limited slewing capability, making phase referencing impossible for the space element. These two issues should be addressed in order to provide better imaging for the future ARISE mission. Either problem is reasonably well-defined, and could be completed in a summer term, assuming a well-prepared student with some AIPS and radio interferometry background. The proposed approaches are outlined below, with the final selection to be made based on the student's and advisor's negotiation. Item (1) is probably a more tractable problem for a summer, although item (2) might also be possible.

(1) Explore techniques in AIPS and/or DIFMAP for imaging of ARISE data having large holes in the (u,v) plane. The approach would be to take on-hand VSOP data from my projects or other observations, then create (u,v) holes of varying sizes by deleting antennas giving long ground spacings (e.g., use the southwestern VLBA stations plus HALCA). The data would be used to examine techniques for fringe-fitting, self-calibration, and data weighting in order to find the best range of parameters, the limitations to dynamic range, and the inflection points at which the images begin to degrade rapidly. Simulated data might also be used.

(2) Investigate the possibility of phase-referencing the ground telescopes at high frequencies, while keeping ARISE pointed at the program source, in order to increase the coherent integration time and the detection threshold. There are two possible approaches, either through the acquisition of VLBA test data with most (but not all) of the antennas phase referencing, or by generation of simulated data with such an observing strategy. Currently, the latter strategy is favored, because real test data would still have an atmosphere above the VLBA antenna that is not phase referencing; the whole point of the project would be to test phase referencing for an antenna that cannot slew, but also has NO atmosphere.


Colleen Schwartz of Colby College
worked with Joan Wrobel
on

PROPER MOTIONS IN THE FR~I RADIO GALAXY M84

Evidence is accumulating that jets in FR I radio galaxies are relativistic from pc to kpc scales. The strongest evidence is based on measurement of apparent superluminal motions of features about 100~pc along the jet in the FR~I radio galaxy M87. As convincing as these important M87 results are, it would be reassuring to find direct evidence for relativistic speeds in other, more traditional FR~I radio galaxies. We therefore began a search for moving features less than 7 arcsec (550pc) along the northern jet of the FR I radio galaxy M84. Our preliminary results for M84, based on two VLA A-configuration runs 8 years apart, offer some evidence for relativistic motions. We conducted a cross-correlation analysis of features a-d in the northern jet. We were unable to obtain reliable results for features a and c, probably because those features lack maxima with steep brightness gradients, but we did obtain credible results for the other features. Feature b, located 3.8 arcsec (300 pc) from the core, moved 11+/-2 mas East and 15+/-2 mas South, for a net motion of 19 mas in 8 years or 0.58+/-0.06c toward PA 144 degrees. Feature d, located 6.1 arcsec (480 pc) from the core, moved 2+/-3~mas East and 25+/-4 mas North, for a net speed of 0.80+/-0.14c toward PA 5 degrees. The formal errors from the cross-correlation fits do not reflect systematic uncertainties. These measurements are being refined with a third A-configuration run that extends the time baseline for this proper motion study from 8 to 20 years.


Andreea Petric, of Columbia University and NMIMT
worked with Frazer Owen
on

Multi-object Spectroscopy of the Cluster CL0939+47

Multi-object spectroscopy of objects in this z=0.4 cluster was undertaken to determine how important dust extinction is in moderate redshift clusters, and to clarify galaxy type in clusters at redshifts between 0.3 and 0.5. The data were from the HYDRA imstrument of NOAO reduced with IRAF. The optical data suggested that significant extinction was, in fact, present. Comparison to reddening-free radio images should prove useful. A complete written report is available.


Niruj Mohan , of Raman Research Institute, Bangalore
worked with K. Anantharamiah
on

Recombination Line Emission from Starbursts

Niruj will work mainly on VLA spectral line data from two proposals AN81 and AM614. This will form the basis of his Ph.D. thesis. If time permits, he will also work on VLBA continuum data on PKS 1830-211 (at 90 and 50 cm) from the project BA031.

AN81 is a VLA proposal to study Recombination line emission near 8.5 GHz from a variety of starburst galaxies: a Wolf-Rayet Galaxy (He 2-10), a blue compact Dwarf (NGC 5253), an interacting system (NGC 1808) and two merging systems (NGC 4038 and VV 114). This proposal was awarded a total of 38 hours of VLA time (14 hrs in CnB, 4 hrs in C, 16 hrs in DnC and 4 hrs in D configurations). The CnB and C array observations were made in Nov/Dec 98 and is awaiting data reduction. The remaining obsevations will be made sometime during during Mar-Jun 99. These proposals were prepared by Niruj and the observe files were also made by him.

AM614 is a VLA proposal that Niruj wrote to followup our earlier detection of RRLs from two well known starburst systems, IC694 and NGC 3628. Models for line emission that were made based on the detections at 8.5 GHz, predicted a strong variation of line strength with frequency. It is crucial to study higher frequency RRLs to constrain the models. This proposal is for observations of RRLs at 2 cm and has been awarded a total of 16 hours of VLA time in the D-configuration. I expect that these observations will be made when Niruj is visiting Socorro and thus he will take care of all aspects of these observations.

Another project that Niruj is involved in, and which is only peripherally related to the main theme of his thesis, is search for RRLs at 20cm from the gravitational lens system PKS1830-211 (VLA proposal AA220). To study the effect of intervening ionized gas (due to free-free absorption and scattering) on the continuum structure of PKS 1830-211, we have obtained a 10 hr VLBA observation (Program BA031) at 90 cm and 50 cm. If time permits, I will ask Niruj to work on this data as well while he is here. This will provide him (and me) valuable experience with low-frequency VLBA data.


Crystal Brogan , of The University of Kentucky
worked with Dale Frail
on

1720 MHz Zeeman Observations of OH Masers Toward SNRs

Ms Brogan will be working with Drs D. A. Frail and W. M. Goss on an effort to perform 1720 MHz Zeeman observations of OH masers toward galactic supernova remnants. The 1720 MHz transition has proven to be a powerful probe of supernova remnant interactions with molecular clouds. The 1720 MHz line also exhibits the Zeeman effect, allowing for the magnetic field strength to be measured in these regions for the first time. The goal of this project will be to increase significantly the small number of such measurements in order to accurately model the role of magnetic fields in molecular shocks.


Chad Young of Mississippi State University,
worked with Dale Frail
on

Afterglows from Gamma-ray Bursters

The goal is the detection of long-lived afterglows from gamma-ray bursters at radio wavelengths. The study of these afterglows in the radio yields unique diagnostics not obtainable by any other means. In particular radio observations give the size and allow one to infer the expansion of the relativistic fireball that is produced in the burst.

A student might be expected to work on several things including (1) the monitoring of known radio afterglows (2) searching for radio emission from new bursts, (3) modeling the flux evolution of the synchrotron-emitting fireball, (4) developing observing/reduction code to simplify the process of obtaining radio data on GRBs. Depending on the student's talents I can see this as a pure observing project, a theory project or a partial software project. The detection of an afterglow would almost certainly involve the publication of paper.


Hanna Smith , of Smith College,
worked with Greg Taylor
on

Compact Symmetric Object 1946+708

The Compact Symmetric Object 1946+708 was the first extragalactic source in which bi-directional motions were directly observed (Taylor & Vermeulen 1997, ApJL, 485, L9). This offers a unique chance to measure H$_0$. Along with Rene Vermeulen, I have obtained multi-epoch VLBA observations of 1946+708 at 8 and 15 GHz. Our program will also measure the advance speeds of the hot spots, from which we will obtain the age of the source. The past year has seen the first such direct measurements of the hotspot advance speed in extragalactic radio sources (Owsianik, Conway & Polatidis 1998, A&A, 336, L37; Owsianik & Conway 1998, A&A, 337, 69). The high reported velocities (0.25 c) in the Compact Symmetric Objects 0108+388 and 0710+439, give ages of order 1000 years, reinforcing the idea that these objects are compact by virtue of their youth and are not confined ("frustrated") by a dense environment. A velocity of 0.25 c (0.06 mas/yr) will be readily detectable by our monitoring observations. The basic work for a summer student would be to calibrate and image four VLBA epochs at 8 and 15 GHz on 1946+708 and to determine the motions of the jet components and especially the hot spots. A summer student working on this project would learn about the physics of Compact Symmetric Objects, and about the reduction and analysis of phase-referenced VLBI data. The goal for the student would be the publication of a paper in the ApJ and presentation of the results at a AAS meeting or other suitable conference.


Elizabeth McGrath of Vassar
worked with Miller Goss
on

Water and HII in the Giant HII Region W49

Miller Goss: Chris De Pree and I have started a program to determine the relative positions of H2O and continuum components in the giant HII regions Sgr B2 and W49. The observing technique is to do simultaneous continuum and H2O observations ( both IF's ). We self cal on the strong H2O masers and then can detect the weak 1.3 cm continuum components at high resolution ( 0.2 arc sec or so in the B array). The data reduction is complete for Sgr B2 and just started for W49. The relative positions can be determined at the level of 0.001 arc sec or so due to the favorable signal to noise. An REU student can bring this program to completion.


Makenzie Lystrup of Portland State University
worked with Craig Walker
on

Phase Referencing with the VLBA: Structure and Motion of 3C120

The compact radio source 3C120 was one of the first in which superluminal motions were observed. VLBI monitoring observations at 5 GHz were made three times per year between 1979 and 1988 with the Global VLBI Network to study the superluminal motions on parsec scales. Other VLBI monitoring were made at 1.7 GHz using large global arrays between 1982 and 1997 (and are being continued) to study the motions out to about 100 parsecs. The summer student project is to help produce the final images from the monitoring observations and to begin writing the paper that presents the observations.


Bryan Jones, of Northern Arizona University
worked with Rick Perley
on

Ionospheric Correction Using A Dual Frequency GPS Unit

I think I have a cool project for an REU student -- working with our brand new dual frequency GPS unit. It looks as though the software support promised by the software group will be a little late in showing up. We could probably use a student to help us learn how to use the device. It is run from a PC running Windows NT, and does lots of cool things. Once we get the receiver up, and the software loaded, more experiments with polarized pulsars will be needed to finish the project.


Scott Zmerick, of West Virginia University
worked with Ron Maddalena and Sue Ann Heatherly
on

A 40 Foot Upgrade


We are currently updating the control interface and receiver system for the 40-ft educational telescope. A programming student is needed to complete the graphical user interface to the telescope system.


Steve Hicks, of University of Memphis
worked with Dan Pedtke
on

An OVLBI Controller

OVLBI and NRAO is to complete the design of our new Peltier controller. This is a 90% hardware and 10% software project, so it would be good to have an EE as opposed to a CE. I think it could be finished in a summer and would help all on the site. There are a few other small things as well, one would be capturing schematics, updating our documentation.


Christopher S Deyoung , of University of Houston
worked with Steve White
on

Test Dewars for Radioastronomy Instrumentation

A project in the cryogenics lab. An automated system for characterizing and logging the cooling capacity of the various refrigerator needs to be designed built and tested. This would be a nice summer long project which could be carried through form design to completion during the summer months. What I have in mind is a test dewar(s) with variable loads on the first and second stages of the refrigerators. A computer controls the energy applied to each load and graphs a load diagram for the particular refrigerator. This project entails thermodynamics, electrical engineering and writing code for the PC.


Jill C. Kamienski , of University of Colorado, Boulder
worked with Frank Ghigo
on

Green Bank Interferometer Upgrades

The project will involve programming in C or C++ for the Green Bank Interferometer project. It can involve either
1. Developing software for control of two 85-foot telescopes, in a vxWorks environment. The software would generate commands for moving the telescope to desired positions, would monitor the positions and other status information, and would write the status data in a log file.
or
2. Developing a system for on-line editing and analysis of data from the Interferometer. Perhaps this will include an automated way of identifying radio sources that are flaring or exhibiting unusual behavior, and of identifying hardware problems.


David Sand, of UCLA,
worked with Jim Braatz
on

Distant Megamasers

The student and I will address the question of whether water megamaser sources are preferentially detected in AGNs with highly inclined galactic disks. Such a trend was detected at early stages of the maser surveys, and it can now be updated with survey results from the past two years, and the question addressed more confidently. The project will involve collecting, cataloguing, and analyzing properties of galaxies which have been observed for water. Statistical comparisons of the detected and undetected populations will then be pursued.


Jeanine Wilson , of The University of Washington,
worked with Dana Balser and Toney Minter
on

Diffuse Ionized Gas in Galaxies

The summer student will work on modelling the diffuse ionized gas of galaxies. Models of ionization levels of different atoms will be computed using the program CLOUDY for many different types of stars and differing ISM characteristics around these stars. The results from the CLOUDY models will then be used to model a galactic disk. These models will then be compared to the galactic disk of the Milky Way and other galaxies with extended emission from diffuse ionized gas such as NGC 891.


Sean Andrews, of Northwestern University
worked with Jonathan Williams
on

Molecular Clouds and Star Formation in the Outer Galaxy

My project was a study of star formation and molecular clouds using data from the Five College Radio Astronomy Observatory's CO Outer Galaxy Survey (Heyer et al. 1998, ApJ Suppl,115,241) and the IRAS point source catalog. The CO survey contains more than 2 million spectra and is the most detailed millimeter spectral line map ever made. It covers approximately 300 square degrees of sky in the outer Perseus arm of the Galaxy.

The beginning of the project consisted of a general overview of the properties of molecular clouds in the outer Galaxy, including analysis of their masses, volume densities, sizes, dynamics, and temperatures. As a familiarity with these characteristics was developed, the project shifted into an examination of star formation within the clouds of the survey.

Using the IRAS point source catalog, I created images of the clouds and embedded stars using IDL. After thorough analysis of the IRAS sources' spectra, two samples of clouds were compiled: one of clouds with embedded stars and the other of clouds without embedded stars. Many comparisons between these two samples were made to bring out any characteristics that are indicative of star formation. Specifically, I found a relationship between the samples that suggests that most of the integrated mass of clouds with embedded stars is in a much higher mass range than that of the clouds without embedded stars. Additionally, comparing the column densities of the two samples revealed signs that clouds with embedded stars are more compact than those clouds without stars. These results affirm that molecular clouds that are more massive and compact are likely to have greater star formation efficiencies.


Andria Schwortz , of Alfred University
worked with Jeff Mangum
on

Methyl Cyanide as a Probe of Kinetic Temperature in Dense Molecular Clouds

Historically, the inversion transition of ammonia (NH3) has been used as the primary temperature indicator in dense molecular clouds. However, the physical approximation typically used for this method assumes that only three energy levels are populated. This model breaks down when the temperature becomes high enough, about 50K. Recent investigations designed to determine the temperatures of the cores of molecular clouds have found that many of them to be at about 70-150K. As these temperatures are beyond the range of accuracy of the NH3 inversion transition method, these numbers have significant inaccuracies. We propose a different temperature probe which retains its accuracy at higher temperatures than the probes previously used. This probe uses the rotational transitions of methyl cyanide (CH3CN), a symmetric rotor. Using measurements of the J=6-5, 8-7, and 12-11 rotational transitions of CH3CN obtained with the IRAM 30m Telescope, we have derived the kinetic temperature within a sample of molecular cloud cores. The analysis of these data used two separate analysis methods; a statistical equilibrium technique which compared the intensities of the different K-transitions within a given J-ladder, and a rotational temperature diagram analysis. The results of this analysis has yielded good temperature and column density figures for some 24 molecular cloud cores within our galaxy. The results of this work will be presented at the AAS meeting in Atlanta, Georga in January 2000.


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