# 2000 Research Experiences for Undergraduates Program

## National Radio Astronomy Observatory2000 is the 41st Anniversary of the NRAO Summer Student Program! Research Projects by NRAO Site

The NSF logo denotes those students supported under the NSF Research Experiences for Undergraduates program.

There were five students in the 2000 Charlottesville Summer Student Research Program, four of them under the NSF Research Experience for Undergraduates (REU) program at NRAO-Charlottesville. Highlights of the program included a series of introductory level lectures on aspects of astronomy, particularly radio astronomy, spread over a few weeks. These lectures are intended to aquaint the students with the research which various staff members carry out. The lectures are listed below.

Y2K Summer students from Green Bank and Charlottesville met at a get-together pizza party in Charlottesville.

Skip Thacker, of the Central Development Laboratory, lead the students on a tour of the facility.
Many of the students in the NRAO-Green Bank program visited Charlottesville for a tour of the Central Development Laboratory , and of the University of Virginia's facility for the fabrication of the Semiconductor-Insulator-Semiconductor detectors used in millimeter wave receivers, the Applied Electophysics Laboratory.

Students tour the University's Applied Electophysics Laboratory.

The Y2K students enjoy an informal get-together with astronomers from the University of Virginia's Astronomy Department. and NRAO at the pizza blowout.

Earlier in the summer, the Charlottesville students visited Green Bank to tour the NRAO telescopes located there, to meet members of the Green Bank staff, and to attend the annual picnic. A highlight of the trip was a tour of the nearly completed Green Bank Telescope.

One post-season highlight will be the dedication on 25 August of the Green Bank telescope ( GBT ), the world's largest steerable telescope. It is an offset parabaloid, 110m across the longest axis, incorporating 16 million lbs of steel in the moving structure.

The 40 ft telescope there is a student telescope, open for any project which students would like to carry out on it (though its instrumentation is limited).

We're very excited about the Atacama Large Millimeter Array, which was selected as the top priority for a new astronomical instrument in the 90s back at the beginning of the decade by the Astronomy Survey Committee. Students got to see it take shape as the third year of design and development got underway.

Students also went on several local hikes--to Crabtree Falls, along the Blue Ridge Parkway and to Sugar Hollow Reservoir and falls, below Skyline Drive in Shenandoah National Park. They also visited the Chesapeake Bay.

The students gave a series of 15 minute talks on their projects during a lunch symposium in Charlottesville before they began leaving for the summer. They produced short reports describing their summer research.

## CV Summer Student Schedule, Summer 2000

 Date Person Item Location Time 4 June open Students begin arriving 16 June open Public Night at McCormick Observatory at the Observatory 9pm 22 June All NRAO Summer Picnic 7 Jul open Public Night at McCormick Observatory at the Observatory 9pm 14 Jul Wootten From Antenna Temperature to Science NRAO,Room 317, Stone Hall 9am 18 Jul Turner Interstellar Chemistry NRAO,Room 317, Stone Hall 9am 20 Jul Condon Radio Sources NRAO,Room 317, Stone Hall 9am 21 Jul Wootten ALMA NRAO,Room 317, Stone Hall 9am 21 Jul open Public Night at McCormick Observatory at the Observatory 9pm 21 July All Travel to NRAO Summer Picnic Green Bank TBD 22 July McKinnon Tour of the GBT Lounge, Green Bank 10am 22 July All NRAO Summer Picnic Green Bank Noon 23 July All Return from Green Bank Green Bank TBA 26 Jul van den Bout The Radio Spectrum NRAO,Room 317, Stone Hall 9am 27 Jul Matthews HI in Nearby Galaxies NRAO,Room 317, Stone Hall 9am 1 Aug Hogg Radio Stars NRAO,Room 317, Stone Hall 9am 2 Aug Liszt The Interstellar Medium NRAO,Room 317, Stone Hall 9am 3 Aug Uson Dark Matter NRAO,Room 317, Stone Hall 9am 3 Aug All Pizza Lunch with U. Va. Anna's 12pm 3 Aug All Pizza Extravaganza Edgemont Road 4pm 4 Aug Bradley Central Development Lab NRAO,Room 228, CDL, Ivy Road 9am 4 Aug Bradley Central Development Lab Tour NRAO,Room 228, CDL, Ivy Road 10am 4 Aug Bradley Tour of U. Va. Device Fabrication Facility U. Virginia, T4 lot, Olsson Hall 1:30pm 4 Aug open Public Night at McCormick Observatory at the Observatory 9pm 8 Aug All Summer Student Research Symposium NRAO,Room 317, Stone Hall 12pm 10 Aug Hibbard Weird and Wild Galaxies I Have Known NRAO,Room 317, Stone Hall TBD 18 Aug open Public Night at McCormick Observatory at the Observatory 9pm

## Water Masers Near Protostars

We studied VLBA images of the water masers in the nearest known rich maser source, IRAS16293-2422 (IR16293 hereafter). Observations were made at four-week intervals in mid-1997. Wootten (1989 ApJ 337, 858; 1993 in {\it Astrophysical Masers}, ed. A. Clegg and G. Nedoluha, p. 315) studied masers in IR16293, showing that the water masers were collimated on scales less than about 40 AU. %These studies were limited by the resolution of the VLA; % structure on finer scales within the maser spots was not reported. Subsequent study of the IRAS16293 masers, using the same data, has revealed that individual masers display structures on scales of a few AU, at the limit of the astrometric resolution of the VLA, and on scales similar to those observed by the Very Long Baseline Array (VLBA) in IR05413. The masers, in addition to being powerful enough to map with the VLBA, might reveal the kinematics of the postshock region on AU scales. Generally speaking, the outflow aligns along position angle 52 degrees on few-AU scales, well-aligned with the large scale CO flow which is thought to emanate from IRAS16293-2422A. The maser velocities are not clearly segregated into redshifted and blueshifted lobes--in fact overall they define a flow sense opposite to that in the larger scale CO flow. One set of features, 0.5 arcsecond to the southwest, suggests that masers there align along a bowshock. Most masers lie quite close to the central object, however. A few masers persist from epoch to epoch, allowing us to estimate the true space velocity of expansion of the maser system.

This project has been described in a paper written at the conclusion of the project.

## Star Formation Rates at 1.4 GHz in the Local Universe

The relationships between SFR determined by optical, radio, and FIR are explored. Using UGC, NVSS, and IRAS catalogs, a SFR at 1.4 GHz was determined for the local universe (within 100 Mpc). This SFR is compared with FIR star formation rates.

This project has been described in a paper written at the conclusion of the project.

## Rotation Curve and Mass Decomposition for the Edge-on Spiral Galaxy UGC711

21-cm HI data from the Very Large Array (VLA) and optical R- and B- band data from the WIYN telescope are presented for the superthin galaxy UGC711. An HI rotation curve is dervied with two different methods, to determine which is the more accurate in the case of an edge-on galaxy. Beam smearing is taken into account and the mass contribtuion from the stars, gas and halo are determined by deriving equations for each of the components (Vtotal)2=(Vgas)2 +(Vhalo)2, and scaling the mass to light ratio and dark halo parameters for a good fit to the observed rotation curve.

This project has been described in a paper written at the conclusion of the project.

## Interpretations of an Observation of an Observed [HCO+]/[HOC+] Ratio

A recent observation indicates that [HCO+]/[HOC+]= 80 pm 26 in the diffuse cloud toward BL Lac. Standard physical models in combination with measured reaction rate coefficients from the UMIST database fail to explain this ratio. The ratio predicts a single formation mechnaism that cannot occur due to the underabundance of the reactants. Other formation mechanisms are ruled out as well, suggesting that a reevaluation of the theory and/or the reaction coefficients is needed, as well as a more accurate measurement of the ratio.

This project has been described in a paper written at the conclusion of the project.

## N-body Simulations of Tidal Dwarf Galaxies

Theoretical work (Barnes & Hernquist 1992) suggests that dwarf galaxies may form within the tidal tails of interacting disk galaxies. Recent observational work purports to identify several so-called Tidal Dwarf Galaxies" (TDGs) within tidal debris. However, the observational evidence that these TDGs are distinct dynamical entities is circumstantial or non-existent. The goal of this project was to run numerical N-body simulations of interacting galaxies; to inspect their tidal tails for bound clumps; and to quantify the expected observational signatures of such clumps.
The project involved identifying and downloading software to run the simulations (GADGET and Zeno), to visualize the results (TIPSY, Starsplatter and mpeg_encode), and to identify bound subunits (SKID and Zeno). The N-body results were analyzed and converted into simulated observations (moment maps) by specially written IDL macros.

This project has been described in a paper written at the conclusion of the project.

# NRAO/Socorro 2000 Research Experience for Undergraduates (REU) Program

AOC Summer Students wearing funny hats at the VLA.

The summer REU program at NRAO/Socorro in 2000 consists of 4 main categories of activity:

1 - student research projects, in collaboration with an NRAO advisor
2 - lectures to the students by NRAO staff members
3 - a joint student project, involving observations with the Very Large Array (VLA)
4 - guided tours of the VLA, given by the students on weekends

Yet more mad hattedness amongst the AOC Summer Students.

The 2000 REU program at NRAO/Socorro is under the direction of Chris Fassnacht , Tracy Clarke, and Greg Taylor . Dr Fassnacht and Dr. Clarke are Jansky Postdoctoral Researchers at NRAO/Socorro, and Dr. Taylor is a member of the scientific research staff.

Lectures, etc...

Several lectures about radio astronomy and interferometry will be presented, allowing the students to obtain a good understanding of the technique. Talks were also given on general topics in astronomy, presented by members of the scientific staff. The astronomy talks were designed to give the students an understanding of what sort of research goes on at NRAO, and in radio astronomy in general. The detailed list of lectures and events for the summer is in the following table.

## Weekly Activities

Tuesday - Summer Student Lectures (required -- See lecture schedule below)

Wednesday - Wednesday Lunch (required)

Thursday - Summer Student Lectures (required -- See lecture schedule below)

Friday - Colloquium (required, when scheduled)

Saturday & Sunday - Tours at the VLA site

## Planned Trips

Kitt Peak/Tucson - 28-30 June

## Summer Student Observations

The VLA is in its DnC and D configurations this summer. Some telescope time will be allocated to the summer students to pursue group projects.

The students observed radio emission from the Brown Dwarf LP944-20 and published their results in Nature (Berger et al. 2000 Nature (10 Nov issue).

### Other Stuff

• Check out the picture page for snap-shots from last summer.

# 2000 Summer Student Calendar of Events

## June 2000

June 13: VLA Tour by Dave Finley
June 16: "Magnetic Fields in the Universe" by Tracy Clarke
June 20-27: Seventh Summer School in Synthesis Imaging

## July 2000

July 4: Holiday
July 6: "Cosmic Microwave Background Interferometry" by Steve Myers
July 11: "Star Formation" by Mark Claussen
July 13: "High Luminosity Active Galactic Nuclei" by Greg Taylor
July 18: "The Interstellar Medium" by Miller Goss
July 20: TBD by Michael Rupen
July 25: "Low Luminosity Active Galactic Nuclei and Starbursts" by Jim Ulvestad
July 27: "The Galactic Center" by Geoff Bower

## August 2000

August 1: "Gamma Ray Bursts" by Dale Frail
August 3: "Gravitational Lenses" by Chris Fassnacht
August 8: "Star Formation Regions -- Molecular Clouds and Bipolar Outflows" by Debra Shepherd
August 10: TBD

 cfassnac@nrao.edu

Joint Student Research Project

Discovery of Radio Emission from the Brown Dwarf LP944-20

E. Berger, S. Ball, K. M. Becker, M. Clarke, D. A. Frail, T. A. Fukuda, I. M. Hoffman, S. R. Kulkarni, R. Mellon, E. Momjian, N. W. Murphy, S. H. Teng, T. Woodruff, B. A. Zauderer and R. Zavala

Abstract

Brown dwarfs are classified as object which are not massive enough to sustain nuclear fusion of hydrogen and are distinguished from planets by their ability to burn deuterium for a period of 107 years. They are expected to possess short-lived, dynamo-powered magnetic fields, and weak radio and X-ray emitting coronae. Several efforts have been undertaken in the past to detect chromospheric activity from the brown dwarf LP944-20 at X-ray and optical wavelengths, but only recently an X-ray flare from this object was detected with the Chandra X-ray Observatory. Here we report on the discovery of strong quiescent and quasi-periodic flaring radio emission from this source, which represents the first example of persistent radio emission from a brown dwarf, with luminosities that are several orders of magnitude larger than predicted from an empirical relation between the X-ray and radio luminosities of coronal active stars. We show that the fluence in the flares is approsimately constant, and that in the context of synchrotron emission, the unusually bright emission possibly results from a combination of weak magnetic fields and highly relativistic electrons.

Submitted to Nature

Student Research Projects

Each of the REU students will work with one or more advisors on one or more projects throughout the summer. This is the main focus of the program, and the majority of the students' time will be spent on these research endeavors. These projects involved observing, data reduction and analysis, equipment development, and theoretical studies. At the end of the program, each student gave a lunch talk explaining the main project(s) he or she worked on during the summer. The possibility exists for the students to present their original research at scientific meetings deemed appropriate by their advisor(s).

## An Optical Telescope for Antenna 23

Steve Ball worked on outfitting an optical telescope on antenna 23 for use in pointing error diagnostics.

Operation of the VLA at higher frequencies have made it necessary to improve upon the pointing accuracy of the antennas. Currently at the VLA a pointing error of 10 seconds is acceptable, but higher accuracy would benefit the observer. Antenna 23 has a larger error. An optical telescope mounted to the antenna will allow the actual tracking of the radio telescope to be analyzed in real time. The error in the pointing can then be quantified and remedied.

This project is described in a paper written at the conclusion of the project.

## Gamma Ray Burst Radio Afterglows

This project involved three main components: searching for radio afterglows of gamma ray bursts, writing a computer program to analyze the effect of interstellar scattering on gamma ray burst (GRB) afterglows, and helping to design and code a program, called autoObserve, which will automatically create files to direct VLA observations in response to electronic GRB alerts.

No radio afterglow was found during the duration of the project. However, observations were made of the error box of the first localized short-duration burst at L, C and X bands on the VLA. No evidence of an afterglow was found.

This project is described in a paper written at the conclusion of the project.

## A Jet Model for the Afterglow Emission from GRB000301C

Broadband radio observations of the afterglow of GRB000301C spanning from 1.4 to 350 GHz for a period of 3 to 130 days after the burst were studied with a host of collaborators. These radio data, in combination with measurements in optical bands, suggest that the afterglow arises from a collimated outflow, i.e. a jet. To test this hypothesis in a self-consistent manner, we employ a global fit and find that a model of a jet expanding into a constant density interstellar medium (ISM + jet) provides the best fit to the data.

This project is described in a paper written at the conclusion of the project.

## Automating the Analysis of Photogrammetric Meaurements

Knowing the surface accuracy of a radio telescope is important for the optimal use of a telescope, for improving the telescope and for the upgrading of the telescope. Holography has shown itself to be a good way to measure a reflector's main surface but it is not in general accurate enough to measure the subreflector. In addition, from an engineering perspective, if the measurements are to be used to correct a subreflector, holography is inconvenient, since it requires that the subreflector be mounted on an antenna to take the measurement. A more appealing option for measuring subreflectors is photogrammetry. A method was developed to employ this. The method worked, but was unappealingly slow. Further developments were suggested to improve the method.

This project is described in a paper written at the conclusion of the project.

## The Sizes of 1720 MHz OH Masers in the Supernova Remnant IC443

Two observations of the 1720 MHz maser emission from the OH molecule in the supernova remnant IC443 (G189.1+3.0) were investigated, with M. J. Claussen and A. Richards. We present separate results from the VLBA + phased VLA and from six antennas of the MERLIN radio telescope array. The MERLIN array was able to resolve some of the maser emission regions showing imaged sizes of 115 mas < theta < 230 mas. The visibility data from the VLBA + phased VLA indicate sources sizes ~180 mas. Since interstellar image scatter-broadening is expected to be minimal towards IC443, near the Galactic anticenter, these measured sizes are likely the intrinsic sizes of the maser regions. Based on the assumption that the IC443 OH sources are not scatter-broadened at the relatively small distance of 1.5 kpc, these data are the the most reliable determination of the intrinsic size of OH (1720 MHz) masers in supernova remnants. These measurements indicate that 1720 MHz OH maser regions in supernova remnants have, in general, linear sizes approaching ~300 AU.

This project has not yet been described in a paper written at the conclusion of the project.

## Polarization in Low Luminosity AGNs

Recent observations of Sagittarius A* (SgrA*) have revealed interesting polarization properies. These properties help us to understand the accretion regions in the innermost parsecsof Sgr A*, and help us to understand other low luminosity AGNs (LLAGNs). We present a search for linear and circular polarization with the Very Large Array (VLA) at 8.4 GHz in 11 LLAGNs. Due to the high phase stability of the VLA, and our careful data reduction, we can detect linear and circular polarization to 0.1 per cent. We detect linear polarization in all but two of these sources, M81 and NGC6500, with circular polarization only detected in M81. The detection of circular polarization shows that M81 has very similar polarization properties as Sgr A* at this frequency.

This project has been described in a paper written at the conclusion of the project.

## Global VLBI Observations of High Velocity HI Absorption toward 3C84

Early optical emission and HI 21cm absorption studies toward NGC 1275 (Perseus A), showed a velocity component 3000 km/s higher than the systemic velocity of the Perseus cluster. For this project, 21cm global VLBI observations of the high velocity HI absorption were reduced and analyzed. The results revealed the existence of several HI absorption lines seen against the compact core of NGC 1275, 3C84. These components appear to arise in "interstellar" type HI clouds within a gas-rich galaxy falling toward NGC 1275 at 3000 km/s. The velocity widths of these HI lines are between 1.5 and 5 km/s, with optical depths ranging from 0.1 to 0.45.

This project has been described in a paper written at the conclusion of the project.

## Deep Field Sources

Optical data was used to map the star formation regions of the galaxies within the cluster Abell 2124, which will later be compared with VLA radio observations of this cluster. The observations were mosaic images in nine optical bands toward five pointing positions for each band. The five pointings were combined into a single band during the course of the summer. Further analysis is planned.

This project has been described in a paper written at the conclusion of the project.

## Parsec-Scale Cores in Seyfert Galaxies

A study was conducted on 21 Seyfert galaxies, part of a complete sample of 75 galaxies selected by 60 micron emission. Observations were made with the VLBA at 1.6 GHz in November and December 1999. Due to trouble with phase referencing only 6 out of 14 galaxies were imaged (the last 7 are in preparation). Out of the 6 galaxies, MCG8-11-11 was found to have curvature or warping on parsec-scales compared to VLA-scales (40-100 pc). A VLBA/VLA flux density ratio was also measured and ranged from 1.7 to 42.5 per cent. The loss in flux could be due to various possibilities discussed in detail in the paper.

This project has been described in a paper written at the conclusion of the project.

## Starburst in NGC3690

NGC3690 has been studied over the years because it is a merger in progress and also because of its optical supernovae, the most recent being in 1999. Because NGC3690 is a system of interacting galaxies and has active star formation, it is a good candidate for the study being conducted by Ulvestad and Neff on an age-ordered sequence of interacting starburst galaxies to determine the period of maximum star formation in the merger process. For this project, imaging of NGC3690 was performed using archived VLA data in all array configurations at both 4cm and 6cm. Thus we created an image with highest possible spatial resolution and lowest possible noise levels. An interesting source was found which must possess a very high stellar density with a large concentration of ionized gas. This source may be a super HII region.

This project has been described in a paper written at the conclusion of the project.

## Space VLBI and the Inner Parsec of NGC1052

NGC1052 is an elliptical galaxy that has been classified as a LINER. Very luminous water maser emission has been found near the nucleus. The masers lie along the nuclear jet, rather than perpendicular to it as in NGC4258. In that galaxy, the masers lie in a Keplerian disk around its nucleus. We have created a 5 GHz image of the central region for comparison to the maser structures. Jet structures were found to move at a speed of about 0.36c very close to the peak. Owing to this variability, it cannot be determined if the masers are related to the jet structures.

This project has been described in a paper written at the conclusion of the project.

## Time Variations in the Small-Scale Galactic Netural Hydrogen Structure towards Quasar 3C138

The QSO 3C138 lies behind galactic neutral hydrogen and has proven a useful way to probe the small scale structure of that gas. The canonical interpretation of the data was that the clouds lay in small spheres. However, there are a number of reasons for suspecting that the true geometry is filamentary or sheet-like. by studying how the small scale structure changes with direction, either the filament or sheet model can be supported.

The goal of this project was to start with the raw visibility data as collected over 12 hours by ten VLBA antennas and the phased VLA and reduce it completely. The data is still in the reduction stages.

This project has been described in a paper written at the conclusion of the project.

## VLBA Polarimetric Observations of 3C273 and 3C279

VLBA polarimetric observations of 3C273 and 3C279 were reduced and analyzed. Seven from eight quasars observed witht he VLBA show Rotation Measures (RM) greater than 1000 rad/m2 within their central 20 pc. Beyond this, the RM drops to 100 rad/m2. Such a dramatic change over such small scales could not be the result of cluster scale features which vary o length scales of ~1 kpc. The observations also show a temporal variation of the RM on a timescale of 3 years. This variation serves to rule out cluster or galactic-scale mechanisms to explain the RM preperties. Furthermore, the RM samples the magnetic field along the line of sight, weighted by the electron density. Therefore the RM probes physical conditions within the core of the Active Galactic Nucleus (AGN) of the quasar itself. Such changes are exemplified by our observations of 3C273. A uniform -2000 rad/m2 RM three years ago has changed to a more complex structure ranging in |RM| by 2500 rad/m2 over little more than 10 pc.

This project has been described in a paper written at the conclusion of the project.

## Green Bank, West Virginia (NRAO 43m and 100m Telescopes)

Students conducting their research at the NRAO Green Bank Site in West Virginia included the students in the list below, along with others. The program at Green Bank is under the direction of Dr. Ron Maddalena.

2000 Summer Students (l to r) Gabe Prochter, Sara Petty_Powell, Emily Mercer, Charlie Fulton, and Scott Zastoupil below Seneca Rocks.

2000 Summer Students explore the Sinks of Gandy



2000 Calendar of Events -- West Virginia


Amy Shelton : Intro to Unix : 11 AM July 11 - Auditorium

Rich Lacasse : GBT Active Surface: 11 AM July 14 - Auditorium

Gary Anderson : History of Radio : 11 AM July 18 - Conference Room

Dana Balser : Radiative Processes : 11 AM July 21 - Conference Room

Jay Lockman : Milky Way & ISM : 11 AM July 25 - Conference Room

Anish Roshi : Spectrometers/Correlators : 11 AM July 28 - Auditorium

Galen Watts : OVLBI : 11 AM August 1 - Conference Room

Dave Parker : GBT Metrology : 11 AM August 4 - Conference Room

## A Random Search for Galactic Neutral Hydrogen High-Velocity Clouds: Preliminary Results

This paper is the continuation of the Murphy, Lockman & Savage (1995) analysis. A sensitive search was conducted in the direction of approximately 275 quasars to detect neutral hydrogen high-velocity clouds above and below the galactic plane using the 43 m telescope at the Green Bank National Radio Astronomy Observatory. Preliminary results indicate a 14% high-velocity cloud detection. A table of the objects and their analysis is included.

This project has been described in a paper written at the conclusion of the project.

## CLEO Messages

CLEO Messages is an application that receives all incoming messages from M&C Control regarding the events that are continuously being monitored. These events may occur due to any number of reasons or combinations of errors or information. Some of these events might be as harmless as some incoming information about a Manager being on source or as Fatal as a message regarding a Device that is not responding to its Manager. All of these types of message, as well as anything in between, need to be constantly monitored. To try to make sense of the data that is constantly coming in, an attempt to make a user friendly application to display this data was made. We call this CLEO Messages. CLEO Messages is a way of organizing all of the data being received and displaying it in a user friendly application. Many of the aspects about this application are dynamic and can be specified and changed by the user, over and over again. Others cannot be changed due to their being color coordinated for meaning and clarity. There are different icons, row colors, tab names and colors, width of columns, etc. This application has the ability to create up to ten tabs with user specified names, descriptions, and foreground colors for the tabs, delete any number of tabs after you have created them, to have multiple tabs that can be viewed at one time, copies of messages going to different tabs for different reasons, hiding and resizable columns, extended text, sorting, filtering, drag 'n drop, users input as to suggestions for any changes, as well as many more enhancements that can, and hopefully will, be used. I hope you enjoy the application and that it enhances the readability of the incoming data and makes it more understandable to the common user.

This project has been described in a paper written at the conclusion of the project.

## Hydrogen Wings

Melanie analyzed extended wings on extragalactic HI profiles. Model fitting was employed to estimate essential parameters. Two of the parameters were found to be not independently determinable.

Melanie also worked with Mark McKinnon on "The Sign-Changing Circular Polarization in Pulsar Radio Emission"

## 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.

## GBT Single-board Control and Reset Box

Please see this document for a description of the work Lacasse and Shelton accomplished.

This project has been described in a paper written at the conclusion of the project.

## Interstellar Scintillation of Galactic and Extragalactic Water Masers

Observations of water maser sources at 22 GHz are made to investigate rapid flux variability. An analysis of archival data confirms the result of Greenhill et al. (1997), who show that the masers in the Circinus galaxy are variable on a 5-minute timescale. The effect is likely caused by interstellar scintillation, but intrinsic variability has not been ruled out. New observations of galactic water masers were made with the Haystack telescope to search for similar variability. The modulation index of galactic masers ($\le$ 0.1) is found to be smaller than that of the Circinus galaxy ($\simeq$ 0.5), probably because the angular size of the galactic masers is large enough to dampen the effect of scintillation. The modulation index of the galactic sources seems to increase with distance. This may reflect either that the angular size of the masers decreases with distance, making them more susceptible to scintillation, or that the intrinsic variability of maser sources depends on their luminosity.

This project has been described in a paper written at the conclusion of the project.

## Faraday Rotation Measurements of Extragalactic Sources

We calculate the Faraday rotation measurements of 40 extragalactic sources in a ten degree square region of the sky. The particular region, centered on (l,b) = (185,+20), is also mapped in HAlpha emission and lacks any HII emission. Due to this unique area of the sky observed, it is possible to study the turbulent fluctuations of magnetized plasma via Faraday rotation measurements.

This project has been described in a paper written at the conclusion of the project.

### Scott Zastoupil , of North Dakota State University worked with Rick Fisher on

The Green Bank RFI Montitoring Station project is an evolving project to study interference affecting NRAO Green Bank. This project is in the prototyping stages begun in May of 2000. The goal for the system is first to be implemented as a tool for a certain few astronomers to study interference and propagation characteristics on site. Eventually the findings from this study will then be applied for developement towards an active cancellation of interference in telescope observing. From ideas and basic specifications from advisors, the beginning of the realization of this task was performed by the student. Due to time constraints, the third part of the project, implementation of the spectrum analyzer control and data capture, was not started.

This project has been described in a paper written at the conclusion of the project.

### Charles Fulton , of Ohio University worked withSue Ann Heatherly on

Charles Fulton worked to build the SRT (a small education-oriented radio telescope ala Haystack) and test it.

The MIT designed Small Radio Telescope (SRT) is a fully steerable 2.3 or 3 meter radio telescope intended for use as an educational tool. The SRT is available in a ready to assemble kit or, for the more adventurous, in a somewhat more assembly required package. NRAO Green Bank pursued the less evolved prospect. Parts were sourced from their respective manufacturers and assembled entirely in house. The finished produce saw use with the final Radio Astronomy Enhancing Coordinated And Thematic Science (RARECATS) teacher institute held in summer 2000. The observations of the group assigned to the SRT are included, along with my own, in order to evaluate the usability of the SRT hardware/software in advanced secondary and post-secondary teaching situations.

This project has been described in a paper written at the conclusion of the project.

## Tucson, Arizona (NRAO 12m, ALMA and VLBA Telescopes)

There were no REU activities at the NRAO Tucson site during the summer of 2000.