MIT Reports to the President 1999–2000
The Haystack Observatory, located in Westford, MA, is an interdisciplinary research center whose mission is to advance research and technical developments in radio science with applications to astronomy, geodesy, and atmospheric physics. The astronomy program emphasizes the use of radio interferometry for high-resolution imaging of galaxies and is carried out under the auspices of the Northeast Radio Observatory Corporation (NEROC), a consortium of eleven educational and research institutions in the northeast. An important component of the Observatory’s mission is to support the training of students with particular emphasis on instrumentation technology and to provide opportunities for students to link their education with research. The Observatory receives financial support primarily from federal agencies including the National Science Foundation, the National Aeronautical and Space Administration, and the Department of Defense, as well as from industrial sources.
The Haystack Observatory instrumentation consists of the following facilities:
In astronomical research, Haystack Observatory concentrates on the application of Very Long Baseline Interferometry (VLBI) at millimeter wavelengths using an global array of radio telescopes to make high resolution observations of radio sources and study their structure and evolution. In the past year, Dr. Sheperd Doeleman and Dr. Colin Lonsdale have pursued a study of SiO masers in the Orion K-L region through measurements of the emission in various transitions of this molecule. They discovered numerous maser spots in the transitions that occur at 7 mm and 3 mm wavelengths and found a systematic spatial distribution of the spots relative to the central star, indicating the presence of an ambient temperature and density gradient in the circumstellar environment. Similar observations by Dr. Robert Phillips and collaborators of SiO masers in the shells of the supergiant stars R Cas and Mira reveal a nearly complete ring of maser spots with strong velocity structures and suggest the presence of turbulent or convective cells in the extended stellar atmosphere.
Other mm-VLBI projects include the study of the polarization of active galactic nuclei that provide information about the structure of the magnetic field in these synchrotron-emitting sources. In addition, the high angular resolution observations by mm-VLBI allows new outbursts feeding the radio jets of these galaxies to be probed near their point of origin. Calibration of the data has proven to be very challenging and the results have been found to be very sensitive to telescope calibration. To date, the radio source 3C273 has been found by Dr. Joanne Attridge to be unpolarized, and studies of source 3C279 reveal some polarization although a quantitative measure is not yet available.
Technical developments to explore VLBI observations at wavelengths shorter than 3 mm have continued with the development of a radiometer at 2-mm wavelength for the Heinrich Hertz radio telescope on Mt. Graham in Arizona. A hydrogen maser and a VLBI data acquisition system have been installed at the telescope and the first test experiment led by Dr. Sheperd Doeleman is planned for Fall 2000, using the Hertz telescope and the 12-m telescope on Kitt Peak. Maser emission from radio sources in our galaxy will be used as the primary emitters for the experiments. In preparation for the improvement of the VLBI sensitivity at these short wavelengths, development and tests of water vapor radiometers have continued by Dr. Alan Rogers and MIT graduate student David Tahmoush. Results to date indicate that the phase coherence has been extended by roughly a factor of two under relatively poor weather conditions.
In collaboration with Professor Jacqueline Hewitt, Physics Department, Haystack Observatory has continued its efforts to study the design of large radio-telescope arrays. Emphasis has been placed during the past year on the scientific and technical considerations for a low frequency array (called LOFAR) that covers the frequency range from about 10 MHz to 220 MHz. This project is being pursued in collaboration with the Netherlands Foundation for Research in Astronomy and the Naval Research Laboratory. Under the leadership of Dr. Colin Lonsdale at Haystack, the various tradeoffs of array configuration, sensitivity and resolution have been conducted to optimize the scientific yield of the instrument. The scientific projects of interest to the MIT group involve measurements of the structure of the universe at the early epoch of reionization and the detection of transients such as gamma ray bursts and gravitational wave events through their radio emission. It is anticipated that the studies conducted to date will result in a funded project to construct the array, particularly since the project was endorsed recently by the National Academy of Sciences review of astrophysics and astronomy for the next decade.
The VLBI Mk IV correlator system, designed at Haystack by a team led by Dr. Alan Whitney, has achieved operational status during the past year. Copies of the system have been successfully installed at the Haystack Observatory, the U.S. Naval Observatory in Washington, DC, the Max-Planck Institute in Bonn, Germany, the Joint Institute for VLBI in Europe in Dwingeloo, Netherlands, and the Smithsonian Sub-millimeter Array (SMA) atop Mauna Kea, Hawaii. The new system allows the processing of wide-bandwidth VLBI signals up to 1 Gbits/sec thus improving observational sensitivity. The new system also results in a substantial increase in the throughput of interferometric data processing for geodesy.
VLBI recording systems to support data acquisition at 1 Gbit/sec rates compatible with the Mk IV correlator system have focused in the past year on a design that utilizes commercial off-the-shelf components. Under the leadership of Dr. Whitney, a design and proof-of-concept phase has been started and a demonstration of the design approach is expected in the next year.
Tests of an E911 radio location system from cellular phones using CDMA digital phones have been successfully conducted under the leadership of Dr. Rogers, with support from TruePosition™. Current plans call for operational tests to be conducted in Manhattan in the next year to demonstrate the readiness of the system to meet the FCC requirements for cellular phone location in emergency situations.
With the approach of the maximum in the solar cycle in 2001, the number of solar coronal mass ejections and ensuing geomagnetic storms have increased during the past year. This has provided excellent opportunities for the MIT incoherent scatter radars at Millstone Hill to observe the effects of disturbances in the Earth’s ionosphere as a result of these storms. A novel correlation between ionospheric electric fields enhanced by the storms and coherent backscatter echoes has been detected by Drs. John Foster and Phil Erickson and will serve as an important diagnostic of ionospheric disturbances. Plans for coordinated global observations of geomagnetic storm effects in the Earth’s lower thermosphere (90 to 150 km altitude) have been developed by Dr. Joseph Salah and Larisa Goncharenko, using a global array of incoherent scatter radars and the NASA TIMED satellite which will be launched in March 2001. Such measurements are expected to clarify the response of the Earth’s upper atmosphere to geomagnetic storms at altitudes that have been hitherto unexplored by direct observations.
The most important accomplishment in the atmospheric sciences program at Haystack in the past year has been the successful implementation of a Rayleigh lidar technique using the Firepond 1.2-m optical telescope. Under the leadership of Dr. Thomas Duck, observations of lidar scatter have been recorded at altitudes from about 30 km to 100 km. Such measurements complement radar observations that extend from 100 km to 500 km and allow the study of wave propagation from the Earth’s lower atmosphere into the upper atmosphere. The narrow field-of-view of the telescope has also allowed unprecedented daytime observations of density and temperature fluctuations to be made, thereby providing unique measurements of temperature inversion layers to be made. A systematic observational schedule has been developed to provide the database necessary to understand the causes of these inversion layers.
A program to strengthen undergraduate education through research in radio astronomy has been successfully demonstrated during the past year using the MIT facilities at Haystack. Based on this success, support has been obtained from the NSF for an expanded program during the next three years. The program, led by Dr. Preethi Pratap, has involved 155 students from NEROC institutions and elsewhere as part of courses, laboratory exercises and special projects. Some projects have been conducted using the internet to access and control the 37-m telescope remotely. Projects from MIT have involved Professor Leslie Rosenberg and his students in attempts to detect radio emission from axions.
Great interest has been expressed by various colleges and universities in a small radio telescope (SRT) kit developed at Haystack to allow students to enjoy a hands-on experience in radio observational techniques. A beta-version of the telescope with a 2-m antenna has been constructed using industrial involvement and is being shipped to 15 colleges and national astronomy centers for tests. This is a first step in the commercialization of this telescope so that colleges nationwide can acquire it for education. The SRT provides an excellent teaching tool for faculty and students prior to the use of the 37-m telescope for research projects. Examples of research projects that can be conducted with the SRT and the 37-m telescope have been provided on the Web, together with tutorials on radio astronomy.
Haystack Observatory has continued to host successful summer research internship programs for undergraduates and for pre-college science teachers, with support from the NSF. Nine students recruited from across the nation and three teachers recruited locally have participated in the program during the past year. The students and teachers are mentored by members of the Haystack staff and participate in the Observatory’s research projects in astronomy, atmospheric science and instrumentation development.
Finally, Haystack was pleased to participate in the MIT artists-in-residence program which resulted in an exhibit in the Compton Gallery in Spring 2000 by Michael Wenyon and Susan Gamble. The exhibit of Haystack facility photographs was complemented by displays on the research and education programs underway at Haystack, thus providing an opportunity to communicate the Observatory’s mission, instrumentation capabilities, and scientific results to MIT faculty, students and staff.
More information about the Haystack Observatory research and education programs can be found on the World Wide Web at http://www.haystack.mit.edu/.
Joseph E. Salah
MIT Reports to the President 1999–2000