MIT Reports to the President 1998-99
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. Its 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 Aeronautics and Space Administration, and the Department of Defense, as well as from industrial sources.
INSTRUMENTATION
The Haystack Observatory instrumentation consists of the following facilities:
RADIO ASTRONOMY
In astronomical research, Haystack Observatory concentrates on the application of Very Long Baseline Interferometry (VLBI) at 3mm—wavelength to study the structure of galaxies with angular resolutions of 50—100 microarcseconds. The Coordinated Millimeter-VLBI Array (CMVA) used for these observations consists of twelve radio telescopes, globally distributed in the US, Europe, and South America. Haystack researchers schedule these telescopes for their own observations as well as for the astronomical community at large, process the data using Haystack's VLBI correlator, and analyze and interpret the scientific results. Emphasis at Haystack has been placed on spectral-line observations of SiO masers that are used as tracers of the galactic structure.
The most significant highlight of the past year's astronomical research program at Haystack has been the discovery of molecular outflow in the Orion KL nebula by Drs. Shep Doeleman, Colin Lonsdale and collaborators. Previous models of this region based on lower resolution observations than achieved with VLBI suggested that it consisted of an expanding and rotating protostellar disk, but the VLBI measurements pointed convincingly to the maser emission tracing a bipolar outflow from the protostar.
Challenging experiments aimed at advancing VLBI observations at wavelengths shorter than 3 mm have been carried out in February 1999 using a set of four telescopes in the western U.S. operating at a wavelength of 1.3 mm. Due to marginal sensitivity of the array, interferometric fringes have not yet been detected and the next set of observations will be made at a wavelength of 2 mm. To help with the improvement of the VLBI sensitivity at these short wavelengths, water vapor radiometers have been constructed and successfully tested by Dr. Alan Rogers and MIT graduate student David Tahmoush. The instruments will be used operationally in the next set of planned experiments as a method to correct for atmospheric phase fluctuations and increase the coherence time for integration of the signals.
In partnership with the MIT Physics Department and under the leadership of Professor Jacqueline Hewitt, Haystack Observatory has joined the international team of astronomers to develop the next generation radio telescope. This is planned to be an array of telescopes with an unprecedented sensitivity represented by a collecting area of 106 m2, called the Square Kilometer Array (SKA). With such sensitivity, it is predicted that the very early structures in the universe can be observed through detection of inhomogeneities in primordial neutral hydrogen. The sensitivity and resolution of the planned array, which will operate over a wide frequency range spanning 30 MHz to 20 GHz will yield opportunities for achieving major advances in astronomical research, particularly the processes of galaxy and star formation and detection of planetary systems.
Internationally, the SKA involves Australia, Canada, China, Europe and India. The U.S. consortium of universities that has been organized under MIT's leadership to contribute to this project so far includes Caltech, Cornell, University of California at Berkeley, Ohio State, and the SETI Institute, with other institutions expected to join in the future. The project is currently being reviewed by the Decadal Survey of Astrophysics and Astronomy that we expect to endorse the effort. The MIT-Haystack contributions to the development of the array are planned to be in the area of configuration and system trade-off studies, architectural studies of the massive parallel processor needed to reduce the data, and investigations of the calibration and high dynamic range imaging techniques. In particular, our team is concentrating on the configuration of a large-N array, consisting of 1000 or more telescope stations, each with 5—10 small parabolic antennas, installed in a log-spiral configuration over roughly 500 km. Overall cost of the array is expected to be around $600M to be shared by the various countries. The plan is to develop a detailed design and test key elements of the approach through prototypes in the next five years, followed by a phased construction effort over the 2005—2015 period.
The relationship between NEROC and the Observatory is presently undergoing review now that the focus of the Observatory has shifted from that of a user facility through the 37-m telescope to a mission emphasizing radio interferometry. A subset of the NEROC institutions are associated with the interferometry work, while the majority find closest synergy with Haystack's role in undergraduate and graduate education. Efforts to redefine and strengthen the NEROC program are being planned.
GEODESY AND VLBI INSTRUMENTATION DEVELOPMENT
The study of Earth's orientation using VLBI techniques has continued as part of the international program aimed at continuous observations of the rotation of the Earth (CORE), using a globally-distributed network of radio telescopes including the MIT 18-m telescope at Westford. Processing of the data for CORE has been conducted using the Mk IIIA VLBI correlator at Haystack, which will be soon replaced by the more powerful Mk IV system. The Mk IV correlator, designed at Haystack by a team led by Dr. Alan Whitney, is now close to operational status, and copies of the system will also be installed over the next year at various processing centers around the world, including the U.S. Naval Observatory in Washington, DC, the Max-Planck Institute in Bonn, Germany, and the Joint Institute for VLBI in Europe in Dwingeloo, Netherlands. In addition, the same correlator board design will be used for connected element interferometers, including the Smithsonian Sub-millimeter Array (SMA) currently under construction atop Mauna Kea, Hawaii.
The Global Positioning System (GPS) is also used for geodetic measurements, and by virtue of the low cost of its receivers, has been successfully applied to monitor the Earth's plate motions and orientation parameters. The VLBI technique which uses quasar radio emission for its measurements serves to provide a reference to GPS accuracy and yields unique information on the Earth's orientation in the inertial frame uncontaminated by satellite motions. GPS and VLBI have common problems in geodesy to overcome such as compensation for atmospheric errors. Dr. Arthur Niell has developed atmospheric compensation methods to correct the observations in both systems. In addition, a special calibration system for multipath errors is being developed and tested at Haystack by Dr. Brian Corey to improve GPS geodetic accuracy at low elevations, and uses a 3-m antenna that provides a stable reference source for the omnidirectional antennas used in GPS measurements.
Development of a high data-rate (1—2 Gbits/s) recording system is continuing with the goal of enhancing the bandwidth, hence sensitivity, of the VLBI arrays used in geodesy and astronomy. Prototype thin-film recording head-arrays developed by Seagate Tape Technology Division have been successfully tested by Dr. Hans Hinteregger in the past year, and specifications have been developed for production of these head-arrays. Dr. Sinan Muftu continues to work closely with various industrial firms such as Quantum Corporation and Kodak in the study and modeling of tape and head interactions applicable to VLBI as well as to industrial interests.
In a successful spin-off program from VLBI to radio location of E911 calls from cellular phones, Haystack engineers led by Dr. Alan Rogers under support of TruePositionTM, a subsidiary of the Associated Group, have supported the testing of the algorithms for this system and analyzed the results from field operations. Emphasis in the past year has been placed on design of new equipment to support the use of the CDMA digital cellular phone system for radio location.
ATMOSPHERIC SCIENCE
With the increasing occurrence of geomagnetic storms as the solar cycle climbs towards its maximum phase, the efforts of the atmospheric sciences group at Haystack have been on the use of the radar to detect and understand the effects of these storms on the structure and dynamics of the Earth's upper atmosphere. The response of the ionospheric plasma to these storms is manifested in enhanced ion convection that propagates from the polar regions to middle latitudes. The MIT incoherent scatter radar is used in a rapid response mode to observe the enhanced plasma convection, monitor the depletions of ionospheric density, and infer the effects of the storms on the neutral atmosphere. These studies, conducted under the leadership of Drs. John Foster and Michael Buonsanto, are serving as an important input to the investigation of space weather effects on satellite systems and their orbits, and for the calibration of models that predict the effects of these storms.
In the past year, major progress has been achieved at Haystack Observatory in characterizing the structure of the Earth's lower thermosphere, defined to exist at altitudes between 100 and 150 km. This region is not as well understood as other regions of the atmosphere due to the complex interactions that take place at this boundary between the lower and upper parts of the atmosphere. There is also a paucity of data covering this region since few instruments can probe the atmosphere at these altitudes. Using the incoherent scatter radar at Millstone Hill, Dr. Joseph Salah and Larisa Goncharenko have measured winds and temperatures in the lower thermosphere and developed a climatological description of the region. Semidiurnal tidal fluctuations were detected with amplitudes larger than predicted by theoretical models, and a large variability was found amongst the observations. Some of this variability has been traced to systematic seasonal variations, and some to the variation of the propagating waves from the lower atmosphere.
Common volume experiments with the nearby University of New Hampshire meteor wind radar at Durham, NH, reveal the presence of small scale variations at mesospheric altitudes, just below the lower thermosphere. Additional observations to characterize this source of variability in the lower atmosphere will be made with the Firepond lidar at Millstone Hill, which continues to be under development. Finally, we have studied the effects of geomagnetic storms as another potential source of the variability and found that at midlatitudes the lower thermosphere responds only to intense storms where the largest effects are exhibited in sustained enhancements of zonal motions. Additional experiments are planned to address this topic on a global basis using the network of incoherent scatter radars and the NASA TIMED satellite scheduled for launch in May 2000.
EDUCATIONAL PROGRAMS
In an effort to contribute to the strengthening of undergraduate education, Haystack has successfully implemented a program to allow students to link their education with research using the MIT radio-astronomical facilities at Haystack. Under NSF funding, pilot projects led by Dr. Preethi Pratap at Haystack have involved 116 students at 12 colleges and universities in the northeast who have used the 37-m telescope to conduct observations as part of courses, laboratory exercises, and independent research projects. Evaluation of the impact of this project has been most favorable, and we have proposed to provide similar research opportunities to students nationwide. To facilitate access, we have developed a capability that allows full remote control and monitoring of the 37-m telescope through the Internet, and the system has been tested successfully by the students. During the past year, we have also tested the use of radio astronomy observations in a large class at Brandeis University composed of 190 non-science majors. Working with Professor John Wardle, the real-time demonstration of astronomical observations with the 37-m telescope proved to be very effective in exciting the students about science, and we plan to further exploit such activities in the future.
In order to provide students with a direct experience in radio observational techniques, a small radio telescope (SRT) with a 2-m antenna has been developed as an engineering kit capable of some basic measurements of solar emissions and hydrogen in our galaxy. There has been a great demand for this kit from colleges and institutions nationwide, and we now seek to commercialize the kit so that others can use it as a learning tool prior to the use of the 37-m telescope for research projects. Replication of the SRT was carried out by students at the University of Massachusetts at Lowell (UML) in a collaborative effort between Haystack researchers and faculty in the Physics Department. The SRT was installed at UML and used by the students as part of their educational program. Continuation of the successful education program, using both the 37-m telescope and the SRT, is contingent on continued NSF support.
Haystack Observatory also hosts a successful summer research internship program for undergraduates, supported by the NSF. Recruited from across the nation, nine students have participated in the program during the past year, and were augmented by eleven additional students supported by our various research programs. The students are mentored by members of the Haystack staff and participate in the staff's research projects in astronomy, atmospheric science and instrumentation development.
Finally, we have undertaken an effort to explore the applicability at the pre-college level of our small radio telescope project in astronomy and the space weather project in atmospheric physics. We are hosting two high-school teachers from the local area to learn about our research disciplines, and develop lesson plans that will be tested in their classes during the next academic year. We expect that this initiative will be successful and will be expanded further in the future.
More information about the Haystack Observatory can be found on the World Wide Web at http://www.haystack.mit.edu/, and information about our educational research project for undergraduates can be found directly at http://web.haystack.mit.edu/education/education.html.
Joseph E. Salah
MIT Reports to the President 1998-99