The Haystack Observatory, located in Westford, MA, is an interdisciplinary research center engaged in radio astronomy, geodesy, atmospheric sciences, and radar applications. The radio astronomy program is conducted under the auspices of the Northeast Radio Observatory Corporation (NEROC), a consortium of 11 educational and research institutions in the northeast (Boston University, Brandeis University, Dartmouth College, Harvard University, Harvard-Smithsonian Center for Astrophysics, MIT, State University of New York at Stony Brook, Tufts University, University of Massachusetts, University of New Hampshire, and Yale University.) The Observatory receives financial support primarily from federal agencies including the NSF, NASA, and the USAF through MIT Lincoln Laboratory.
The Observatory instrumentation consists of the following facilities: a 37m-diameter radio telescope used for astronomical observations at wavelengths from 2.6 mm to 13 cm, as well as for wideband radar measurements at 3 cm; an 18m-diameter radio telescope involved in geodetic measurements of the earth's plate motions using very long baseline interferometry (VLBI) techniques; a VLBI correlator to process global geodetic experiments and astronomical observations at millimeter-wavelengths; and a high-power radar that utilizes two large antennas, 46 m and 67 m in diameter, to study the earth's upper atmosphere using incoherent backscatter techniques. The radar is operated in conjunction with an optical observatory to measure airglow emission and determine upper atmospheric winds.
Highlights of the radio astronomy program using the 37m-diameter radio telescope in the past year include the detailed observations of the speed of gravitational infall in dense molecular clouds which is fundamental to the star formation process. Due to the high spectral and angular resolution of the upgraded Haystack radio telescope at millimeter wavelengths, observations of the spectral shape of tracer molecules such as C3H2 and H2CO and CS have allowed Dr. Philip Myers and colleagues at the Harvard-Smithsonian Center for Astrophysics to determine the infall rates in different core types such as embedded clusters, isolated protostars and starless cores. MIT Professor Jacqueline Hewitt and nine graduate and undergraduate students utilized the telescope to search for radio emission at 35 GHz from gamma-ray bursts in order to clarify their emission mechanisms, improve their position determination, and measure their distance. The search was conducted over a two week period without detection of new radio sources at the 1-sigma emission limit of 0.5 Jy. This search is expected to be continued when MIT's High Energy Transients Experiment (HETE) satellite is launched. HETE is expected to provide improved positional accuracies of the gamma-ray bursts which will facilitate the radio observations at Haystack.
During the past observing season, a total of 38 observing projects were conducted at Haystack by members of the astronomical community, including 12 graduate students. A majority of the observing projects were carried out in the 85-115 GHz frequency range which takes advantage of the newly-upgraded telescope, and were conducted successfully using the recently installed digital servo control system and a renovated console that allows future connection to the Internet for remote control of the telescope. Our plans are to continue the automation of the radio telescope for remote operation, and to encourage its utilization by undergraduates for research. Through radio astronomical observations with the Haystack telescope and a smaller 3m-telescope that can be constructed and installed at small colleges, we believe that we can contribute to our national goal to strengthen the linkage between undergraduate education and research.
During the past year, we have completed conceptual studies for the installation of a new surface on the Haystack antenna that will enhance the aperture efficiency of the radio telescope at frequencies of 100-150 GHz. The surface will consist of lightweight panels that are aligned using actuators, and a laser measurement system that determines the distortions from a parabolic surface. Efficiencies of 45% are expected from the new antenna, roughly 3 times better than can be achieved at present, and telescope operations will be possible under all thermal conditions. Applications in radio astronomy and planetary radar research will benefit from such a capability at Haystack. These studies have been conducted in collaboration with Lincoln Laboratory which is pursuing radar projects at 35 and 95 GHz using the improved antenna surface.
In VLBI applied to astronomical observations at 3mm-wavelength, the Coordinated Millimeter-VLBI Array (CMVA) which has been organized under MIT Haystack's leadership has begun successful formal operations. Ten radio telescopes, globally distributed in the US, Europe, and South America, have participated in 12 experiments during the past year, which have yielded images of quasars with a resolution of 50 uarcsec. A survey of sources available for such imaging has been completed, and observations of the center of our galaxy have been made. Haystack has been responsible for the coordination and planning of the observations at the various telescopes, technical improvements at the participating telescopes, processing of observations on the Mark IIIA correlator at the Observatory, development of post-processing software, and scientific analysis of some of the observations.
Work has continued during the past year on VLBI technological developments, both in high data rate recording and in high speed data processing. Thin-film recording head-arrays are being developed by Seagate Tape Technology Division for application to VLBI and the interface electronics design has been initiated at Haystack. These head-arrays will enable magnetic tape recording at rates in excess of 2 Gb/s and high data storage capacity (1 TB) at a much reduced cost compared to the present ferrite headstacks. In data processing, the VLSI chip designed specially for the advanced VLBI correlator, the Mark IV system, has been successfully produced in large quantities, and the correlator boards that utilize these chips have been fully tested and are in the production phase. Several correlators will utilize this design for national and international programs. This includes the NASA/GSFC geodesy program, the US Naval Observatory time services program in Washington, DC, the Smithsonian Institution Submillimeter-Array project, the Joint Institute for VLBI in Europe for astronomical data processing, the Netherlands Westerbork array, and the Institute of Applied Geodesy for data processing at the Max Planck Institute in Bonn, Germany.
Our VLBI research program has resulted in a spin-off that is beneficial to the nation, namely a system that can provide the accurate location of a cellular phone issuing a 911 emergency call. Under the sponsorship of the Associated Group, Inc., a system based on precise range determination using the time delay of signals received at various cellular sites has been designed and tested in the city of Philadelphia and elsewhere. The most challenging aspect of this application has been the accounting for multipath effects in order to realize location accuracies in the 200m range. At present, production systems are in development by industry for implementation, while Haystack engineers are examining the application of such a location system to digital cellular phones.
In our atmospheric science research program at Millstone Hill, the prime emphasis has continued on the specification of the coupling of the Earth's upper atmosphere with the lower atmosphere through tidal wave propagation from the stratosphere and mesosphere. Measurements of tidal wave parameters in experiments involving as many as 15 radars distributed globally have been conducted to characterize these oscillations and to calibrate general circulation models. The Observatory's atmospheric sciences group has continued to lead studies of the effects of geomagnetic storms on the earth's ionosphere, with particular emphasis on "space weather" phenomena caused by coronal mass ejections on the sun that propagate in the solar wind and perturb the earth's upper atmosphere. These effects result in communication problems, satellite orbital changes, and ground induced currents, and the prediction of these effects is the subject of a newly-formed National Space Weather Program.
In our optical aeronomy program, the effort has been concentrated on observing winds from nighttime airglow spectra measured using Fabry-Perot Interferometry at the oxygen and hydroxyl lines in the 85-100 km altitude region, and at the oxygen line above 250 km at night and in the daytime. Most recently, a 24 watt Nd-Yag laser has been installed at the Lincoln Laboratory Firepond 1.2m telescope to observe Rayleigh scatter from the mesosphere and stratosphere, in collaboration with Clemson University. The objective is to measure density and temperature at 30-100 km altitude, in order to characterize the inversion layers that are seen in the mesosphere and investigate their relationship to tidal wave variability observed with the Millstone Hill radar at higher altitudes.
Finally, our graduate and undergraduate educational programs have continued successfully during the past year. In addition to students using the Haystack instrumentation for observing projects, an undergraduate summer internship program involving 13 students has been conducted this year. The students are provided with research experiences and mentored by our staff. In addition, our Young Scholars program aimed at pre-college outreach involves 56 students and four science teachers from the local area in a three-week summer program. This will be followed by individual student projects and special mentorship by our staff during the academic year.
Joseph E. Salah
MIT Reports to the President 1995-96