1995 Research Experiences for Undergraduates Program
National Radio Astronomy Observatory
Research Projects by NRAO Site
Charlottesville students Christopher (`Kester') Allen, David Copeland
and Edward Gray (left to right) examine David Malin's color optical image of
Rho Ophiuchi and the
region of Antares. David produced color radio images of the
same region from data obtained at the NRAO 12m radiotelescope.
There were three students in the 1995 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 were intended to aquaint the students with the research
which various staff members carry out.
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
Semiconductor
Device Laboratory.
. The students had an informal get-together with astronomers from
the University of Virginia at lunch, and from NRAO in the evening, followed
by a visit with graduate students from the
University's Astronomy Department.
Immediately afterward, the Charlottesville students visited Green Bank to
see the NRAO telescopes located there, to meet members of the Green Bank
staff, and to attend the annual picnic.
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.
Later in the summer, the students returned to Green Bank for a session of
observations on the 43m telescope. This was a regularly scheduled program
which Al Wootten, the Charlottesville REU coordinator, runs on the 43m
to monitor the status of water masers in regions where low luminosity stars
are forming. Two new water masers were discovered during the session.
The students also toured the Green Bank Telescope, now about 180 feet high,
the elevation axis assembled and the box structure which supports the surface
being assembled on the ground.
Charlottesville students Christopher (`Kester') Allen
and Edward Gray (left and right) stand on the apex of the elevation axis
tower of the Green Bank
Telescope during their tour of the site.
A Search for Transient Pulsar Signals
Student David Copeland (Reed College) worked on a project to search
for fast (millisecond) dispersed transient signals in rapidly sampled
spectral data from Arecibo Observatory. Such signals could come from
pulsars or possibly other (unknown) Galactic phenomena. Copeland
worked on the analysis routines for this project, both developing and
optimizing the specific algorithm for the search and developing the
overall software system. This involved quite a bit of coding in C,
both reworking old routines and developing a single, coherent package.
The algorithm development included many software runs on test data to
study and fine-tune the search algorithm.
David also processed data to form images taken at NRAO's
12 meter telescope. The
data was taken using a new type of observing. Normally observing is done by
moving the telescope into a specific position, observing for a period of time,
then moving the telescope and observing at another position for a while.
This is very inefficient because most of the time is spent waiting for the
telescope to stop shaking. A new observing mode called OTF or On The Fly
observing is being developed at NRAO. This mode moves the telescope constantly
and records the position of the telescope with very fine precision. No time is
wasted waiting for the telescope to stop moving since it never does. This mode
is subject to a sort of "motion blurring" but such blurring can be removed
mathematically and maps can be constructed that are as good as images made
with the conventional observing mode. David was working on a star
forming region in the constellation Ophiuchus. This
C18O J=1-0 map
of the Ophiuchus Dark Cloud shows a velocity coded image, wich blue
highlighting lower (blueshifted) velocity portions of the cloud, red higher
(redshifted) velocity portions of the cloud, and green showing material lying
near the clouds average velocity. The kinematically disturbed region to the
upper right is known as the Ophiuchus A core, and here the most massive stars
have formed.
Edward Gray
Boston University
Worked with Darrell Schiebel
on
A Graphical Class Browser for AIPS++
Summer student Edward Gray made a lot of good progress on a
graphical class browser. Take a look at it:
Graphical browser
Basically, it first lists the set of
AIPS++
modules; you click
on one, and you end up with a list of the base classes in that
module. From there, you click on the boxes to get documentation
and click on the triangles to descend into the tree.
Water Masers and Cold Gas (Ammonia) in the L1448 Star Formation Region.
At several epochs, observations have been made of the L1448 star-forming region
at the VLA in order to locate pointlike sources of emission in the 22 GHz
line of interstellar water. Collisions in shocks near the forming star
produces brilliant, non-thermal emission from water molecules. The pointlike
sources are known as water masers. Allen reduced these observations for three
epochs in 1994. Several primary centers of star forming activity occur within
a region of about 90" extent in L1448. All of the masers present in 1994
occur near the southernmost of these centers, known as L1448C. The masers
appear segregated by velocity, with those shifted to higher frequency
(blueshifted) relative to ambient gas occurring in one sector, and those
shifted to lower frequency (redshifted) occurring in another sector. The
two clusters of masers lie along a line which is parallel to an outflow
of gas observed on much larger scales toward L1448C. Presumably, the masers
trace shocks near the origin of the flow, within scales of tens of AU from
the young star.
On much larger scales, thermal emission from ammonia molecules has been
mapped using the VLA by Wootten and Mangum. Allen investigated the ammonia
images for evidence of thermal gas in proximity to L1448C.
The intensity maps show a pronounced ridge surrounded by several knots of bright
gas around the location of the masers.
Disk-like, the ridge is symmetrical around the maser positions, and has a "tied-
off" pinched appearance in the section closest to the maser.
This feature is oriented approximately 65 degrees E of N, and is approximately
20'' or 5000 AU across; since this is perpendicular to the observed angle
that a line between the blue- and red-shifted masers forms, this suggests that
the ridge is related to a possible accretion disk for the hypothetical
protostar within. Strong ammonia emission was also observed from the IRS3
protostars to the north.
Socorro, New Mexico (NRAO Array Operations Center)
Students conducting their research at the NRAO Array Operations Center (AOC)
in New Mexico included John Barthelmes, James Brauher, Christopher Carpenter,
Amy Hronek, Audress Johnson, Allison Nugent, and Ngan Ying Lui. The
program at the AOC is under the direction of Dr. Claire Chandler and Dr.
Bryan Butler.
Claire wrote a report on the summer student program at the AOC:
This year the VLA held its regular Synthesis Imaging Summer School
in Socorro. Since many of the lecturers who we usually invite to give
talks to our summer students were already speaking for the Summer
School, we asked the summer students to arrive in time for the School
so that they could attend. After this, and several lectures about radio
astronomy and
interferometry presented by Bryan and myself, many of them showed a
good understanding of the technique. We also gave talks on general
topics in astronomy, and invited other members of the scientific staff
to do the same. The astronomy talks went down well with the students.
I took the summer students on a field trip to visit the observatory at
Kitt Peak, including the instruments of
NOAO, the
NRAO 12-m ,
and the
VLBA antenna. We also visited the
Mirror Lab at
Steward Observatory.
This trip was a big hit, and the students requested more like it in the
future. The students from NOAO visited us in Socorro on their way to
the
National Solar Observatory at
Sac Peak , and I gave
them a tour of the
VLA.
Our students were given a couple of hours of their own VLA time, which
was used for an OH maser search toward supernova remnants, a project
supervised by Dale Frail.
Our students also gave guided tours of the VLA every weekend, and at
the end of their time here, each student gave a short lunch talk (about
15 minutes) about their summer project.
John Barthelmes
State University of New York
Worked with Ruth Milner
on
From SunOS 4 to Solaris
John Barthelmes worked with Ruth Milner assisting with various aspects
of the migration of our Sun workstations to the new Solaris 2 operating
system. John's tasks began with obtaining and compiling the source
code for a number of public-domain packages we use on our systems. He
inventoried both our SunOS 4 and Solaris systems to determine which
programs were missing in the new environment, and then located and
retrieved the source code for everything he could find. He then
successfully built about fifty packages. His next major task was to
learn the "perl" language and use it to write scripts which would
enhance the usefulness of the system software installation log that is
kept at all NRAO sites. The scripts he produced will be used to search
the log and print information about the package specified by the user,
and he also wrote an
HTML front end (including a perl CGI script) for
updating the log file. John then took the plain TeX copies of the
UNIX Introduction and the
AOC Guide to Computing (nearly eighty
pages of documentation) and retypeset them in LaTeX, and using
"latex2html" he then produced HTML files from the LaTeX versions, which
will allow users access to HyperText versions of these documents from
the
Socorro Computing WWW pages. John also updated several sections of
these documents, including the diagrams of our public computers. The
results of his work should be useful to us for a long time to come.
Jim Brauher
University of Michigan
Worked with Huib van Langevelde
on
Measuring Stellar Proper Motions Via OH Masers
Jim Brauher worked with on the analysis of
spectral line VLBA data. The main goal of this project was to
measure the proper motions and annual parallaxes of two Mira
variables, U Her and R LMi. The OH masers associated with both
objects were observed with the VLBA for two epochs in phase
referencing mode. Jim used the
AIPS reduction package to map the
circumstellar main-line OH masers with both phase referencing and
self-calibration, and compared the results. He also constructed
moment maps of the large data cubes. His analysis revealed
discrepancies with the standard model, in which the brightest maser
should line up with the stellar position and coincide with the most
blue-shifted component in the spectrum. A publication on this
subject is in preparation. Short
VLA
observations of the same
objects were made and processed to measure the amount of flux
resolved out by the
VLBA . Finally, Jim completely recalibrated the
data from one of the epochs, in order to correct for a missing
component in the correlator model. This will enable us to use the
data for astrometry.
Chris Carpenter
Harvard University
Worked with Dale Frail
on
A Search for Radio Counterparts of Gamma Ray Bursters.
Chris Carpenter worked with Dale Frail on a long term monitoring effort
to look for the radio counterparts of gamma ray bursters. Gamma ray
bursts are brief flashes of energetic emission from random directions
in space whose origin is completely unknown. It is expected that some
fraction of this radiation should come out at radio wavelengths,
resulting in a time-variable radio source. Chris reduced and analyzed
VLA
data taken over several epochs toward 9 gamma ray burst error
boxes. A total of 50 images were made and a variability analysis was
done on the 112 sources cataloged from the images. Three unusual
time-variable sources were found in the error boxes of the gamma ray
bursters. Follow-up optical observations are planned.
Amy Hronek
Occidental College
Worked with Craig Walker
on
Behavior of VLBA Antennas and VLBA Dynamic Range Tests
Amy Hronek worked with Craig Walker on two projects during the summer
of 1995. The first was an effort to characterize the system
temperature, gain, and overall sensitivity of the
VLBA antennas as a
function of frequency across the full range that can be observed in
each band. This project involved several sessions of single dish
observing using all of the VLBA antennas and reduction of the monitor
data using both standard VLBA software and a new program that she and Walker
wrote. The project will result in a VLBA Test Memo which she wrote and
Walker is in the process of finishing. The second project was a test of the
ability to make high dynamic range images using VLBA data recorded in
the 2 bit mode. All previous high dynamic range tests had been done in
1 bit mode. This project involved one session of VLBA interferometric
observing, correlation on the VLBA correlator, and reduction of the
data in AIPS
and SDE. Amy did most of the data reduction. The test
was successful and Walker will write a very short memo to that effect based
on her work.
Audress Johnson
The University of Texas at Austin
Worked with Rick Perley
on
An Update to the VLA Calibration Scheme.
Audress Johnson worked with Rick Perley on a project aimed at updating
the VLA's calibration scheme. After mastering the intricacies of
calibrating radio interferometer data she went on to determine accurate
flux density ratios for various
standard VLA calibrators. Her work
will be vital in maintaining the high quality of data coming out of the
VLA.
Ngan Ying Lui
Polytechnic University
Worked with Clint Janes
on
Interference Protection.
NGAN YING LUI
Ngan Ying "Annie" Lui worked with Clint Janes in the Electronics
Division at NRAO Socorro. Her assignments were to support the
Interference Protection Group in its efforts to identify and mitigate
radio frequency interference to radio astronomy observations. NRAO has
had in place for some time a procedure to measure interference in the
20 cm observing band at the VLA, and recently those
plots
were made accessible via the World Wide Web. Ms. Lui added an overlay to the
plotting procedure so that now Web browsers can find specific frequency
and other helpful information to better interpret the amplitude vs.
frequency information on the plots. In the process, she improved
understanding of the overall procedure so that she could copy the
entire interference measuring procedure to the VLA 90 cm band, and make
interference plots available on the Web for that band as well. The
project involved writing an
Observe File for the
VLA and modifications
to existing AIPS (Advanced Image Processing System), Fortran, and Unix
routines. She also supported one of the scientists, Dr. Vivek Dhawan,
in his efforts to translate the VLA interference measuring procedures
to VLBA bands. Using her work, data were successfully observed. To
spot check Dhawan's measurements, she used a VLBA remote operating
procedure called SPAN to find and plot interfering signals at VLBA
sites. In the process she improved the understanding of SPAN plotting
procedures. Finally, Ms. Lui prepared a recommendation for the VLBA
Field Group Leader on displaying graphs at the remote VLBA sites of
data gathered from a central VLBA data monitor in Socorro.
Allison Nugent
Southwest Missouri State University
Worked with Mark Holdaway
on
Radio Images of Large Supernova Remnants.
Allison Nugent worked with Mark Holdaway on reducing and analyzing VLA
data on a sample of large supernova remnants. This sample was poorly
studied because of the large angular size of the remnants, most of
which required adding total power from the
Effelsberg 100 meter
antenna and mosaicing several VLA pointings together. Allison responded
well to the technical challenges of mosaicing the VLA and Effelsberg
data. Allison found that a number of sources were polarized, and some
had interesting rotation measure structure. Since only two frequencies
were used in these observations, unambiguous rotation measure results
could not be obtained, so these objects require more observations. In
addition to creating beautiful images of these impressive radio
sources, Allison looked into correlations with images at other emission
bands such as the infrared and X-ray. We found that some sources which
were presumed to be supernova remnants may actually be HII regions
based on the infrared emission.
Green Bank, West Virginia (NRAO 43m and 100m Telescopes)
Students conducting their research at the NRAO Green Bank Site
in West Virginia included Katrina Koski, Daniel McCoy, D. J. Pisano,
Douglas Williams and Thomas Wilson. The
program at Green Bank is under the direction of Dr. Ron Maddalena.
Daniel J. Pisano
Yale University
Worked with Jay Lockman
on
A Recombination Line Survey of Inner Galaxy Diffuse HII Regions.
D.J. Pisano, a junior from Yale, worked with Jay Lockman. He helped
finalize the data from a recombination line survey of diffuse HII regions in
the inner Galaxy. They then analyzed the data to derive the distribution of
diffuse nebulae and to compare them with compact HII regions. Finally,
they tried to estimate the distance to each object and derive the total
luminosity that each contributes to the Galaxy. Interesting results were
found. A
paper
is available.
Thomas J. Wilson
The University of Nevada at Las Vegas
Worked with Dana Balser
on
Combining Interferometer and Single-dish Continuum maps.
The data consisted of two sets of 11 continuum maps of classical
HII regions at 8.7 GHz. The high resolution maps were obtained at the
VLA
in the D-array configuration. The single-dish maps were taken by
the
MPIfR 100 meter telescope to recover the zero-spacing flux. Tom
Wilson made two major contributions: (1) he improved the
signal-to-noise ratio of the VLA maps by self-calibrating the data;
and (2) he combined the interferometer data with the single-dish data
using the AIPS
task VTESS, which uses the maximum entropy method. The
results are much more sensitive and accurate maps of these regions.
The primary goal is to use these maps to constrain models of the
density and ionization structure of these HII regions.
Daniel McCoy
West Virginia Institute of Technology
Worked with Mike Stennes
on
An LO Reference Distribution System for Green Bank.
During the summer we designed, built, and (partially) tested an LO reference
distribution system. The system provides transmission of precision
reference frequencies to various points on the Green Bank site via phase
monitored optical fiber. Daniel was given full responsibility of the
round trip phase monitor module, and the clock synchronization circuit.
The round trip phase monitor uses a mixture of digital and analog
technology to measure the two-way propagation delay of a signal with an
accuracy of much less than 1 picosecond. The clock synchronization
circuit is a high speed (500 MHz) digital circuit. This circuit was
designed by Daniel from scratch, and was particularly challenging as it
required careful attention to layout on microstrip transmission line media.
During Daniel's stay at Green Bank, he became familiar with all aspects
of hardware development. Parts procurement, circuit design/fab/test,
scheduling milestones, and cost estimating were all part of Daniel's
assigned tasks.
Doug Williams
Stanford University
Worked with Rich Lacasse
on
GBT Active Surface Computer Design and Status Monitor.
Doug Williams worked for me this past summer and produced a great deal of very
useful software. First he put together a status monitor for the GBT open loop
active surface. It consists of a color coded display of all the actuators with
the colors indicating their status. The package also actively queries the
actuators to update the status and provides the ability to command all
actuators. In addition, Doug produced a design for the master computer
controlling the active surface, and implemented a fair amount of software for
it.
David Ward
San Francisco State University
Worked with Mike Holstine
on
Plant Engineering
Katrina Koski
Lake Forest College
Worked with Glen Langston
on
Sky Survey at X-Band and with the Janksy Antenna.
Katrina worked on two projects this summer, analyzing the raw
X band (3.6 cm) Green Bank Earth Station (GBES) Survey data,
and helping with the experiments to test the Jansky Antenna.
The GBES Surveys are intended to be full northern sky surveys
at X and Ku (2 cm) bands. The surveys will monitor the sky,
searching for short term variable sources, and monitor all the
bright variable radio soruces. These surveys will be repeated at
two week intervals. During the summer of 1995, the modifications
were being made to the tracking station, which did not allow
full Ku band data to be collected.
Katrina wrote parts of a C program to edit the X band data, remove solar
system objects and convert from Kelvins to Janskys. She used AIPS
to grid the data into images, then identify radio sources.
Some of the
gridded images
can be viewed. For example
the galactic center region , covers
right ascension range 16 to 20 hours, declination -30 to 33
degrees.
Tucson, Arizona (NRAO 12m and VLBA Telescopes)
Students conducting their research at the NRAO Tucson Site
in Arizona included Frank Kolor, Larissa Bowles and James Wren. The
program in Tucson is under the direction of Jeff Hagen. As the
NRAO offices are across the street from KPNO/NOAO offices, the REU
group shares in the activities of the NOAO REU program there.
Tucson summer students
Jim Wren, Kelsey Johnson, Regina Jorgenson, Remy Indebetouw, Rain
Winebarger, Reed Riddle, Larissa Bowles, Elena Neagu, Nadege Meunier,
and Scott Clingenpeel (left to right) watch a (terrestrial) fireworks display
from a vantage point above Tucson. Wren and Bowles were NRAO summer
students, the others in the picture were from the
NOAO summer student program.
Photo courtesy Larissa Bowles.
Frank Kolor
Stanford University
Worked with Matt Waddel
on
Thermal Characteristics of the 12m Radiotelescope.
Frank Kolor labored intensively
on a new sytem for monitoring thermal characteristics of the backup structure
on the 12 meter telescope. This project included a circuit design and
analysis, component specification and test, assembly, and installation. He
was able to almost complete the project in the time alloted. There were only
a couple of thermistors left to install and the circuit card needed to be
programmed and installed. All of these tasks have now been completed and
the system is functional.
Molecular Clouds and Star Formation in Different Galactic Environments.
Though it is generally understood that massive star formation takes
place in giant molecular clouds (GMCs), there is still no clear picture
of how these clouds are formed or under what conditions star formation
is initiated. We can help address these questions by studying molecular
clouds and star formation in different galactic environments. To do
this, we can study different parts of our own Galaxy or look at other
galaxies. In studying other galaxies, telescope resolution limits us
to ones in the Local Group: the Large and Small Magellanic Clouds and
the Andromeda Galaxy, M31.
This project involved observations of CO(J=2-1) (1.3mm) emission from a
section of M31 believed to have strong magnetic fields (to tell us
something about the relationship between magnetic fields and star
formation). The observations were carried out in May 1995 on the
12m
telescope, located on Kitt Peak. A 4' x 4' region was mapped using a
new technique, On the Fly (OTF) mapping. In OTF mapping, data are
taken continuously as the telescope is scanned across the source
(rather than simply stopping the telescope at each position to be
observed). OTF produces higher quality images, and takes less
observing time, but provides some challenges in data reduction.
Ms. Bowles used the
Astronomical Image Processing System
(AIPS) to
process the data. The major tasks involved combining the 70 maps of
the region into a single map, detecting and deleting bad data,
arranging all of the observed points onto a regular grid and collecting
the results into a data cube that could be further analyzed. For
example, by picking out emission in different velocity ranges, she
could isolate emission from different parts of the region. The results
of this work will be presented as a poster at the next
AAS Meeting.
Ms. Bowles wrote a beginners handbook for anyone using AIPS to do OTF
mapping for the first time. This handbook will be useful to anyone
with no or limited prior knowledge of AIPS. This handbook will be
incorporated in more extensive NRAO documentation.
Pointing Characteristics of the 12m Radiotelescope.
This summer I worked with Phil Jewell and Darell Emerson on the analysis
of structural tilt and pointing offsets of the 12-m radio telescope on
Kitt Peak. Most of my project consisted of writing routines in PV-Wave
for analysis of the data coming from the tilt meters and pointing
calibration files. PV-Wave is a mathematical analysis package similar to
IDL. Over the summer I used it to write many routines to reduce and display
the data. Using these tools it may be possible to determine any periodic
offsets in the pointing of the 12-m not compensated for in the current
model. It may then be possible to add additional terms to the pointing
equations that will be able to adjust the pointing model to obtain a
better fit and therefore reduce pointing error.
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