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 12 educational and research institutions in the northeast. Wellesley College joined NEROC in the past year. The Observatory receives financial support primarily from federal agencies including the NSF, NASA, and the USAF through MIT Lincoln Laboratory.
INSTRUMENTATION
The Haystack Observatory instrumentation consists of the following facilities:
Highlights of the radio astronomy program using the 37m-diameter radio telescope in the past year include the discovery of ethylene oxide, the fourth cyclic molecule detected in the interstellar medium. The detection of complex organic compounds is important in the study of chemistry in molecular clouds. Observations of comet Hale-Bopp led to the detection of hydrogen cyanide and methanol, and the measurements are being used to better constrain the chemical production rates in the comet. Monitoring of the water vapor megamaser in the galaxy NGC 4258, which is thought to arise in a circumnuclear torus orbiting a supermassive black hole in the nucleus of the galaxy, led to the detection in March 1997 of a spectacular flare in its radio emission. Some of the possibilities being studied to explain the occurrence of such a bright flare include an exceptionally hot spot in the jet behind the maser that supplies seed radiation, or chance alignment of separate maser clumps in the disk around the galaxy center. Finally, a survey for infall motions in a large number of starless dense clouds was completed and led to discovery of an asymmetry in the distribution of velocities, particularly for the youngest stars in the sample. Further investigation of this asymmetry is planned as part of addressing a fundamental problem in astrophysics, namely how stars form.
During the past observing season, a total of 45 observing projects were conducted at Haystack by 80 members of the astronomical community, including 12 graduate students. A majority of the observing projects were carried out in the 85-115 GHz and in the 35-49 GHz frequency bands where the telescope provides excellent angular resolution and sensitivity. A new technique has been developed during the past year to allow the acquisition of continuum data in a fast-scanning mode needed to search for radio counterparts to gamma-ray bursts. A drift-scan procedure was also developed to enable the measurement offlux densities of small-diameter radio sources and the mapping of extended sources. Progress has also been made in the replacement of the control computer for the telescope, which is a necessary step towards the goal of remote control of the telescope. Our initial goal is to provide a capability to monitor observations remotely. To that end, a modernization of the servo and data acquisition systems has been completed in the past year, with much of the analog hardware replaced with digital units that enable the interfacing of the hardware with computer control through the Internet.
The astronomy program at Haystack is planned in the next year to shift its orientation from that of a facility supporting a broad collection of research projects to science-driven, in-depth investigations, consistent with the Observatory's university-based charter. The research will focus on two key projects: (1) a survey of point radio sources to aid in foreground subtraction for cosmic microwave background experiments and a search for radio counterparts to gamma-ray bursters and X-ray transients, to be led by Professor Jacqueline Hewitt (MIT Physics Department) with the collaboration of the Haystack staff, and (2) an extensive survey for infall motions in star-forming dense cores to be led by Dr. Philip Myers (Harvard-Smithsonian Center for Astrophysics) with the assistance of Haystack staff. On a smaller scale, the telescope will also participate in VLBI experiments at mm-wavelengths led by Alan Rogers (Haystack). The goal is to focus the resources of the Observatory on programs that are well suited to the capabilities of the telescope, and hence insure that the Observatory will play a unique and valuable role in contributing to the solution of important astrophysical problems driven by the interests of its MIT and active NEROC communities. The proposal is now pending at NSF.
VERY LONG BASELINE INTERFEROMETRY
VLBI applied to astronomical observations at 3mm-wavelength, the Coordinated Millimeter-VLBI Array (CMVA) has operated successfully during the past year under Haystack's leadership. In the latest experiment in April 1997, eleven radio telescopes, globally distributed in the US, Europe, and South America, successfully participated in the largest array configuration to date to study the central region of our galaxy and to map quasars at the center of external galaxies with an unprecedented angular resolution of less than 50 microarcseconds. Recent scientific highlights include the mapping of a ring structure of silicon monoxide masers in a thin spherical shell within 1.5 stellar radii around the late-type star VXSgr. The measurements allowed the surprising discovery of a large scale linear velocity gradient among the masers, the first such gradient to be observed in any silicon monoxide maser source. If this observation is interpreted as an indication of rigid rotation, an accurate measure of the rotation rate of the star is obtained. In other important mm-VLBI experiments, the evolving structure of bright active galactic nuclei was mapped, tracing the ejection and expansion speed of material in the jet ejected from the core of galaxies such as 3C 111,3C273 and 3C279. In the blazar, NRAO 530, which underwent a large radio flare during the past year, the observations led to modeling of the flare structure in terms of a core, two shocks and a large halo, and revealed a distinct asymmetry in the structure which was not evident in previous observations. All recent scientific results from the CMVA were reviewed at a special workshop convened at MIT in November 1996 and attended by 40 astronomers and graduate students. Future scientific thrusts in mm-VLBI are aimed at high-resolution studies of the polarization structure in galaxies to determine magnetic field patterns, and at extending the observations to 1- and 2 mm-wavelength which will further increase the angular resolution of the observations.
In geodetic VLBI, applied to the study of the earth's plate motions and its orientation parameters such as rotation and precession rates, the main emphasis has shifted towards studying the short-term variations in the orientation parameters. An internationally-coordinated initiative called CORE (Continuous Observations of the Rotation of the Earth), has been organized to address this objective under NASA's leadership and with the participation of the Haystack Observatory. Seven VLBI networks, each consisting of five radio telescopes around the world including MIT's Westford 18m-telescope, will operate serially to observe changes in the earth's rotation rate and will identify changes on time scales of one hour. This research program was enabled by the development at Haystack of the next generation VLBI correlator, the Mark IV system, which will provide high processing throughput and enhanced sensitivity through increased recording bandwidth. Pilot observations have started in 1997 and the observing program will be at full capacity in 1999 when the Mark IV correlator becomes operational.
INSTRUMENTATION DEVELOPMENT
The Mark IV correlator subsystems designed at Haystack have been successfully tested during the past year and have met all specifications. Production of a large number of these subsystems is now in progress using local area industries, and the assembly of several correlators will be carried out over the next year. In addition to the Haystack correlator, copies will be constructed for the US Naval Observatory, the Smithsonian Institution, the Joint Institute for VLBI in Europe, the Netherlands Westerbork Array, and the Max Planck Institute in Bonn, Germany. Completion of the correlators to be used for VLBI data processing has been delayed due to difficulties in the station units that prepare the recorded data from the telescopes prior to their correlation. These units have been designed by an industrial firm in England and have not successfully passed the acceptance tests. The difficulties should be resolved by the end of the year. Haystack resources are being applied to assist with the solution of the problems.
An important element of the Mark IV system is the data acquisition electronics and recorders operating at the telescopes. The data acquisition technology, developed at Haystack, has now been transferred successfully to industry where various components have been reproduced for installation at various telescopes around the world. Our collaboration with Seagate Tape Technology Division continues towards the adaptation of thin-film recording head-array technology to high data rate recording of VLBI data. These head-arrays will enable magnetic tape recording at rates in excess of 2 Gb/s and will lower the cost of recorder head replacements compared to the present ferrite headstacks. A digital read-channel subsystem is also being developed at Haystack to increase the linear track density. Such enhancements in recording rates and capacity are important for both geodetic and astronomical VLBI since they lead to enhanced interferometer sensitivity through the increase of the recorded signal bandwidth. Other advanced initiatives in recording technology are being developed with industrial groups at Kodak, Quantum and Hewlett-Packard Laboratories.
The ability of the VLBI technique to determine precisely the time delay in the arrival of a radio signal from a quasar has resulted in a spin-off that has societal benefits, namely a system that can provide the accurate location of a cellular phone issuing a 911 emergency call. In collaboration with and 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 various locations. At present an operational prototype system is being exercised on the New Jersey Turnpike and has been shown to locate cellular phones to an accuracy better than 200m. Improvements in the digital signal processing system and the applicability of the technique to digital cellular phones are presently being explored.
The installation of a new surface on the Haystack antenna has been pursued in collaboration with Lincoln Laboratory. The new surface will triple the aperture efficiency of the radio telescope at frequencies of 85-115 GHz and open an observing window at frequencies of 150-160 GHz. The primary goal is to use the new antenna as part of a radar system at 95 GHz in order to enhance the resolution with which small satellites can be imaged and to increase the radar sensitivity so that asteroids can be tracked and imaged. The surface will consist of lightweight panels that are aligned using actuators. A laser interferometer measurement system will be used to determine the distortions from a parabolic surface that need to be corrected using the actuator system. Tests of this laser system are in progress at Lincoln Laboratory using a Haystack antenna panel in order to ascertain the accuracy of the measurements under various conditions. It is expected that detailed design studies for the new antenna surface and for the radar will begin in the next year. With this new surface, the Haystack radio telescope will become more competitive at short wavelengths.
ATMOSPHERIC SCIENCE
In the past year, the Millstone Hill ionospheric radar and the Observatory's optical instrumentation have gathered data during two major geomagnetic events triggered by coronal mass ejections on the Sun. In response to alerts received from satellites observing the Sun and measuring the energetic particles in the solar wind, the radar and optical instruments recorded the effects of geomagnetic substorms and storms as the energetic particles penetrated the earth's magnetosphere. These data sets have revealed large perturbations in the ionospheric plasma density and temperature, as well as enhancement in the plasma drift and neutral winds as the perturbations travelled from the magnetic pole towards the equator, passing over Massachusetts. The optical instruments imaged enhancements in the nightglow and auroral particle precipitation. Such observations are expected to receive increased emphasis as the solar cycle continues to increase towards a maximum in 2001. The measurements will be important to the study of the geomagnetic effects on satellite communications, satellite orbital changes, and ground induced currents, as part of our National Space Weather Program.
Two major initiatives have been the focus of our atmospheric science program in the past year. The first is the development of a lidar system as part of the atmospheric instruments clustered around the Millstone Hill incoherent scatter radar to allow the study of the coupling between the Earth's middle atmosphere(30-100 km altitude) and the upper atmosphere. The lidar would utilize the Lincoln Laboratory Firepond 1.2m-aperture telescope together with a 25 Watt Nd:Yag laser obtained through a collaborative effort with Clemson University. The combination of these two systems provides a lidar with the highest power-aperture product of any atmospheric lidar in the US. A Rayleigh-scattering capability was successfully demonstrated at Firepond during the past year leading to atmospheric density profiles up to 90 km. Design of a Doppler capability to be used with the fully-steerable Firepond telescope has been completed, and this would provide measurements of the vector winds in the middle atmosphere. Grant requests have been made to the NSF Major Research Instrumentation program and the CEDAR (Coupling, Energetics, Dynamics of Atmosphere Regions) program in order to implement the Doppler capability and to operate the lidar system to study the effects of tidal and gravity wave propagation from the Earth's lower atmosphere into the upper atmosphere
The second initiative in atmospheric science is the participation of the Haystack Observatory in the design and development of the Polar Cap Observatory (PCO) at Resolute Bay, North West Territories, Canada, in response to an NSF solicitation. The PCO is one of the major NSF initiatives under the Major Research Equipment program for FY98. MIT/Haystack, SRI, Boston University and the University of Michigan pre planning the submission of a joint proposal to NSF for this important development. MIT/Haystack's responsibility will be the design and development of the data acquisition system for the incoherent scatter radar that is the central element of the PCO. This system will remotely control the radar, monitor its data output and analyze its observations in real time. The radar is planned to be a phased array system capable of rapid electronic steering (responsibility of the PI institution, SRI). A suite of optical instruments will also be placed at the PCO consisting of imagers and photometers (Boston University) and Fabry-Perot Interferometers and lidars (University of Michigan). The overall PCO development is expected to take three years, and will become operational in 2001, near the peak of the solar cycle when important geomagnetic effects will occur. The study of such effects at the Earth's polar cap is crucial to understanding the phenomena that couple the Earth's ionosphere and magnetosphere to solar perturbations that drive the dynamics of the Earth's upper atmosphere at all latitudes. The PCO will form an important element in the chain of observatories from the equator to the pole, including MIT's Millstone Hill radar at midlatitude, which are dedicated to the study of the structure and dynamics of the Earth's upper atmosphere.
EDUCATIONAL PROGRAMS
Haystack Observatory programs and facilities present an excellent opportunity to link education and research by undergraduates. Accordingly, a new initiative was undertaken at Haystack during the past year to encourage undergraduate students to practice radioastronomical observations as part of their study curriculum. In pilot projects at MIT (IAP), Harvard University, Boston University and Connecticut College, 40 undergraduates utilized the Haystack telescope to design experiments, gather data and analyze the observations. A grant request has been submitted to the NSF Education and Human Resources and the Division of Astronomical Sciences to formalize this initiative and provide access to the telescope for undergraduates in the region. MIT and the University of Massachusetts at Lowell will be initial test sites for new projects and software development that will enable students to control the telescope remotely to gather data, once hands-on training has been completed. In addition to the use the 37m-telescope, a small radio telescope, 3m in diameter, will be made available for construction and use by undergraduates, based on a prototype that has been developed at Haystack. The project has been approved for funding by NSF for the next two years, and the development of projects at Haystack has begun. After the initial testing phase, we expect to expand the research projects to undergraduates in colleges and universities in the northeast, in preparation for national access.
Our graduate educational programs have also continued successfully during the past year. Twelve graduate students have used the telescope for observations used in thesis research. The Haystack undergraduate summer internship program involves 12 students this year, recruited from across the nation. 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. The pre-college outreach effort, called the Haystack Young Scholars program, has also continued this year and involves 56 students and three science teachers from 20 towns around Haystack. Following a three-week summer program, each student carries out an individual project during the academic year under special mentorship by our staff. This effort represents our educational contribution to our neighboring communities.
More information about the Haystack Observatory can be found on the World Wide Web at the following URL: http://www.haystack.edu/
Joseph E. Salah
MIT Reports to the President 1996-97