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01/09/1995 08:00:00

Astronomer John Carlstrom Receives Packard Fellowship

PASADENA—Caltech astronomer John Carlstrom has received a $500,000 Packard Fellowship in Science and Engineering to support his research in radio and submillimeter-wave astronomy. Each year the Packard Foundation recognizes 20 of the most promising young researchers in the nation with these fellowships, which are among the largest research awards in science. Carlstrom is the eighth Caltech faculty member to be so honored, and will receive $100,000 per year for five years.

Carlstrom, a 37-year-old associate professor of astronomy at Caltech, is "the complete astronomer—strong in instrumentation, a critical and innovative observer with an excellent taste in the choice of problem, and with ability to synthesize an overall physical picture," said Charles Peck, chair of Caltech's Division of Physics, Mathematics and Astronomy. He is involved in several projects to create instruments that push the technological frontiers in millimeter- and submillimeter-wavelength astronomy. These innovations are necessary to obtain the extremely high-resolution images needed to pursue his research goals.

In one collaboration, Carlstrom worked with Cambridge University astronomer Richard Hills to build the first submillimeter-wave interferometer by linking two telescopes atop the dormant Hawaiian volcano Mauna Kea, one belonging to Caltech, and one belonging jointly to the United Kingdom, Netherlands, and Canada. An interferometer combines the signals from two separate receivers to obtain a much higher resolution than either instrument could attain alone. In this case the two telescopes are 165 meters apart, so that the resulting image is as sharp as that which would be taken by a 165-meter-diameter dish, or better than one arcsecond resolution (better than 0.0003 angular degrees).

Such sharp images are well-suited to the study of protostellar disks—flat, swirling clouds of gas and dust in orbit around embryonic stars, and one of Carlstrom's main areas of study. Careful measurements with the two telescopes on Mauna Kea have produced the first direct measurements of the size of protostellar disks. The Packard Fellowship will enable Carlstrom to pursue an even more exciting improvement: the inclusion of the 10-meter Keck Telescope to create a three-telescope array.

Carlstrom is also collaborating with NASA astronomer Marshall Joy to use the millimeter-wave array of Caltech's Owens Valley Radio Observatory to measure the Sunyaev-Zel'dovich (SZ) effect in distant clusters of galaxies. In the SZ effect, the cosmic microwave background radiation is scattered by gas within galaxy clusters, causing a lessening of the centimeter-wavelength radiation seen from the center of a cluster compared to its surroundings. In order to make these centimeter-wavelength observations at OVRO, which is a millimeter-wavelength array, they have built five 30-gigahertz receivers and optical systems for the instruments. By combining measurements of this effect with high-sensitivity X-ray observations, astronomers can calculate a value for the Hubble constant and gain new insight into the age and size of the universe.

Carlstrom earned his bachelor's degree at Vassar College in 1981, and his doctorate at the University of California, Berkeley, in 1988, both in physics. He first came to Caltech in 1989 as a Millikan Research Fellow in Astrophysics, and joined the faculty in 1991. In 1992 he received a National Science Foundation Young Investigator Award, an honor given to a selection of the best young scientists in the nation.

Packard Fellowships were first awarded by the David and Lucile Packard Foundation of Los Altos, California, in 1988. The fellowships support basic scientific research being conducted by talented young faculty members, and encourage the recipients to continue productive university careers. Including the 1994 winners, the foundation has awarded a total of 140 fellowships.

Written by John Avery