ACE Satellite Now In Place Between Earth and Sun; Will Seek To Determine What Sun Is Made Of

PASADENA—Tanning aficionados, beach bums, surfers, and other solar enthusiasts may not realize it yet, but there is a new satellite making a huge looping halo around the sun. And it's a satellite that's going to be a benefit to weather forecasters in predicting solar flares as well as to astrophysicists in understanding the nature of the universe.

The satellite is called the Advanced Composition Explorer, or ACE for short. Launched August 25, the satellite has reached its destination about a million miles from Earth toward the sun at a position known as L1. That's the point at which the gravitational pull from Earth and sun, plus centrifugal effects, exactly balance each other.

"So, a spacecraft can orbit this invisible point, maintaining a fixed distance from Earth as Earth orbits the sun," says Ed Stone, Morrisroe Professor of Physics at Caltech and principal investigator of the ACE science mission.

Stone and Caltech physicist Dick Mewaldt are leading the satellite's science mission at the ACE Science Center at Caltech. There, they obtain spacecraft telemetry from the flight operations team at the Goddard Space Flight Center, and process the data for the astrophysics community.

The satellite is designed to collect a wide range of information on the matter it encounters. Its mission can broadly be classified in two phases:

® The satellite incorporates a real-time solar wind system that will provide around-the-clock coverage of interplanetary conditions that affect Earth. This is especially of benefit to those living at high northern and southern latitudes, because Earth's magnetic field is such that a coronal mass ejection can more easily disrupt power systems close to the poles.

While the ACE can do nothing to prevent this phenomenon from occurring, the satellite can at least provide an hour of warning that a coronal mass ejection may create a magnetic storm. The warning could help minimize and perhaps even eliminate some of the outages.

The National Oceanic and Atmospheric Administration (NOAA) will analyze the data and issue forecasts and warnings of solar storms. According to NOAA, it will be possible to issue geomagnetic storm alerts with virtually 100 percent accuracy.

® The ACE science mission is designed to measure and compare the composition of three samples of matter that can be found in interplanetary space. These are the solar material in the form of the solar wind and energetic particles accelerated by violent eruptions of the sun, the gas from the nearby space between the stars, and high-energy cosmic rays that come from more distant regions in the Milky Way.

Understanding the nature of this matter can help researchers provide answers to fundamental questions about the origin of matter. Additional information on the precise mix of elements in the solar wind, for example, will also serve as a benchmark for understanding the composition of other bodies in the solar system.

The ACE satellite is carrying nine scientific instruments that were developed by a team of scientists representing 10 institutions in the United States and Europe. These instruments are an array of mass spectrometers that measure the mass of individual ions. The satellite is already collecting data, and is expected to do so for at least five years.

"Our first look at the data tells us that the performance of the instruments is excellent," says Stone. "We should be learning what the sun is made of in the months ahead."

[Note to editors: See for more on the ACE science mission. Also, NOAA on Jan. 23 issued a press release on the ACE satellite's space weather forecasting capabilities.]

Robert Tindol

Black Hole That Periodically Ejects Its Inner Disk As Jets Discovered

WASHINGTON—Astronomers observing a disk of matter spiralling into a black hole in our galaxy have discovered that the black hole periodically hurls the inner portion of the disk into space as jets travelling at near the speed of light.

According to Stephen Eikenberry, an astrophysicist at the California Institute of Technology, the superhot gas in the inner disk shines brightly in X-rays, and dramatic dips in the X-ray emission suggest that the inner disk vanishes every 20 to 40 minutes. Infrared and radio observations at the same time show huge flares which indicate that matter is being thrown out of the system.

Eikenberry and colleagues from the Massachusetts Institute of Technology and NASA's Goddard Space Flight Center will discuss their findings at a 9:30 a.m. press conference on Wednesday, January 7, during the winter meeting of the American Astronomical Society.

The scientists observed the disappearance of the inner portion of the disk, known as an accretion disk, at the same time that glowing plasma is ejected from the black hole system. In August, Eikenberry and his collaborators at Caltech observed infrared flares from the black hole system, known as GRS 1915+105, using the Mt. Palomar 200-inch telescope.

At the same time, Ronald Remillard and his collaborators at MIT monitored X-ray dips from the same black hole using NASA's Rossi X-ray Timing Explorer (RXTE) satellite. Jean Swank and her collaborators at NASA/GSFC observed similar dips, antion between the disappearance of the inner disk and the jet ejection has never been seen until now."

"This work is also exciting because it may help us understand many other types of systems with jets," notes Robert Nelson, who works with Eikenberry at Caltech. "Astronomers have found jets in a wide range of objects, from quasars—incredibly powerful objects seen out to the edge of the observable universe—to young protostars."

The half-hour spacing between the ejections may be telling researchers that what they had thought were smooth, continuous outflows may in fact be intermittent explosions.

"There are many fine details in the X-ray dips that we may now seriously investigate to better understand the ejection mechanism," adds Edward R. Morgan, who works with Remillard at MIT. "In particular, there is a very unusual X-ray flash at the bottom of these dips in which the X-ray spectrum changes significantly. This may be the trigger for the rapid acceleration of the disk material."

The black hole in GRS 1915+105 became known to astronomers in 1992 as an X-ray nova, which is believed to signify the sudden flow of hot gases into a black hole from a companion star in a binary system. The black hole in GRS 1915+105 is thought to have a mass equal to ten Suns or more, all crushed by its own gravity into a tiny sphere contained within an "event horizon," which itself has a radius of about 20 km.

When a black hole pulls gas from the atmosphere of a companion star, the matter spirals in toward the event horizon like water going down a drain, and the swirling disk created by the flow is known to astronomers as an "accretion disk." The gas in the disk heats up dramatically due to the large acceleration and friction. Just before entering the event horizon, the gas reaches temperatures of millions of degrees, causing it to glow in X-rays.

In 1994, Mirabel and Luis Rodriguez observed radio emission from jets in GRS 1915+105, and they determined that the speed of the jets was greater than 90 percent of the speed of light, or roughly 600 million miles per hour. Since RXTE began observing the X-ray sky in early 1996, the exceptionally chaotic behavior of GRS 1915+105 in X-rays has been chronicled on many occasions.

The new results gained by Eikenberry's team brings together these phenomena by showing that modest jet ejections and the pattern of X-ray variations are synchronized in an organized way.

"The repeated ejections are really amazing," says Craig Markwardt, a member of the NASA/GSFC team. "The system behaves like a celestial version of Old Faithful. At fairly regular intervals, the accretion disk is disrupted and a fast-moving jet is produced."

"This jet is staggeringly more powerful than a geyser," adds Swank. "Every half hour, the black hole GRS 1915+105 throws off the mass of an asteroid at near the speed of light. This process clearly requires a lot of energy; each cycle is equivalent to 6 trillion times the annual energy consumption of the entire United States."

"Since the disk-jet interaction is so poorly understood, we're hoping that further analysis of these observations will show us more details of what is happening so close to the black hole," Eikenberry says. "We're planning more detailed studies for the coming year which should give us even more clues as to the nature of these incredibly powerful events.

"Right now, we still aren't even sure why these dips and ejections occur every half hour or so—why not every week or every 30 seconds, for instance?

Robert Tindol

Caltech Astrophysicist Charles Steidel Receives $500,000 Packard Foundation Fellowship

PASADENA—A Caltech astrophysicist who searches for the oldest and most distant structures in the universe has been named a recipient of a $500,000 grant from the David and Lucile Packard Foundation.

Charles Steidel, an associate professor of astronomy, is the newest Caltech recipient of the Packard award. He plans to use the money largely for instruments to be fitted onto the 200-inch Hale Telescope at Palomar. These instruments will allow more efficient searches for extremely distant objects in deep space.

"My principal research interests are in the areas of the formation and evolution of galaxies, from the experimental perspective," Steidel says. "The central theme is the history of 'normal' galaxies like our Milky Way."

Nearby galaxies, as well as the stars in the Milky Way, are seen as they appeared when light left them. Thus, a galaxy one million light-years away is observed from Earth as it appeared one million years ago. But since the universe is probably 15 billion years old, astrophysicists must look at galaxies much farther away to learn about the early stages of galactic development. This is Steidel's specialty.

"Our goal for the next five years is to study galaxies, and their distribution in space, as they appeared when the universe was less than about 15 percent of its current age," Steidel says. "The hope is that this will tell us a lot about how and when the galaxies and large clusters of galaxies we see in the nearby universe came to be."

The success of the searches for these extremely distant galaxies depends on a vital combination of the Hale Telescope and the 10-meter W.M. Keck Telescopes on the island of Hawaii. The Hale can identify candidates based upon very deep images of relatively large areas of sky, and the W.M. Keck 10–meter telescopes can obtain the spectra of the very faint candidates, to allow more precise distances to be measured.

"It should be quite feasible, within the next few years, to trace the galaxies back to the point where they have not yet coalesced, and where the large-scale structures of galaxies we see today were just beginning to come together," he says.

The Fellowships in Science and Engineering were first awarded by The David and Lucile Packard Foundation of Los Altos, California, in 1988. The goals of the fellowship program are to support outstanding faculty as they build productive research programs and to help attract and retain faculty of the highest quality for our universities. With the announcement of the 20 awards for 1997, the foundation has awarded a total of 200 fellowships.

Founded in 1891, Caltech has an enrollment of some 2,000 students, and a faculty of about 280 professorial members and 284 research members. The Institute has more than 19,000 alumni. Caltech employs a staff of more than 1,700 on campus and 5,300 at JPL.

Over the years, 26 Nobel Prizes have been awarded to faculty members and alumni; and two faculty members and one alumnus have been awarded the Crafoord Prize. Forty-three Caltech faculty members and alumni have received the National Medal of Science; and eight alumni (two of whom are also trustees), two additional trustees, and one faculty member have won the National Medal of Technology.

Robert Tindol

Astronomers Detect Relativistically Expanding Clouds Around the May 8 Gamma-Ray Burst

PASADENA—Astrophysicists still don't know what caused the gamma-ray burst of May 8, but they now have a size and rate of expansion for its remnant "fireball" to add to the location and distance.

New measurements by researchers at the California Institute of Technology and the National Radio Astronomy Observatory (NRAO) indicate that the fireball is now 85 times larger in diameter than our own solar system.

Further, the researchers have determined that the fireball is expanding at an extremely high rate of speed—perhaps as fast as 99.99 percent of the speed of light when the explosion first occured, and currently about 85 percent of light speed.

"This has all helped us to understand the mechanics of gamma-ray bursts once they take place," said Shrinivas Kulkarni, a Caltech astrophysicist who is coprincipal investigator of the work, which is reported in the September 18 issue of the journal Nature.

A few months ago the Caltech team, using the Palomar and the Keck telescopes, decisively showed that this gamma-ray burst occurred in a distant galaxy, settling one of the major controversies about the origin of these enigmatic objects.

Coprincipal investigator Dale Frail of NRAO added, "If you ask me what caused the burst, I'd still have to say it's pure speculation. It could have been a black hole smothering a neutron star, or maybe two neutron stars colliding, or perhaps even two black holes colliding.

"What we do know is that this was a spectacular cosmic event—far more energetic than a supernova explosion."

Gamma-ray bursters were first discovered by military satellites almost 30 years ago. The field has advanced rapidly, thanks to the precise localization of the bursts offered by the Italian-Dutch satellite BeppoSAX. Astrophysicists have now found, rapidly in succession, that gamma-ray bursts occur at cosmological distances and are probably the most energetic events in the universe.

This particular burst was first reported by BeppoSAX on May 8, 1997. Before the advent of BeppoSAX, astrophysicists had no idea whether gamma bursts originated in our own galaxy or across the universe, and, in fact, had formulated competing theories accounting for either scenario.

The measurements were obtained at the Very Large Array, a radio telescope array operated by NRAO with funding from the National Science Foundation. Other authors of the paper include Greg Taylor of NRAO and two BeppoSAX team members, Luciano Nicastro and Marve event."

Robert Tindol

Possible Planet-Forming Disk imaged by Caltech Radio Astronomers

PASADENA—A giant disk of gas and dust over 10 times the size of our own solar system has been detected rotating around a young star in the constellation of Auriga. The star is both more massive and brighter than our sun, and appears to be a young version of another star called Beta Pictoris, where astronomers have long suspected the presence of planets.

The new discovery was made by radio astronomers at the California Institute of Technology using the millimeter-wave array at Caltech's Owens Valley Radio Observatory in central California. The results appear in the current issue of the journal Nature, and concern a relatively massive star known as MWC480, which is about 450 light-years from Earth.

How prevalent is planet formation around young stars? Past work had shown that stars similar to our own sun possess protoplanetary disks in their youth, disks we believe will form planets, perhaps as our own solar system did. However, little was known about the propensity of disks to form planets around stars that are more massive than our sun.

According to Vince Mannings, the paper's first author, the new results provide unprecedentedly clear evidence for the presence of a rotating disk of gas surrounding MWC480, and support earlier indications of rotating disks encircling some less massive and young sunlike stars. Not only is the gas around MWC480 clearly discernible at radio wavelengths, he says, but the orbital rotation of the entire disklike cloud is also unambiguously observed.

The presence of rotation suggests that, as for the disks around the young sunlike stars, the disk structure around MWC480 is long-lived. Indeed, this massive reservoir of orbiting material could last long enough to form new planets. "Families of planets, perhaps resembling our own solar system, are thought to originate in such disks," says Mannings. "Our sun, when very young, possibly had a disk similar to that around MWC480."

The star in the middle of the MWC480 disk resembles a much older star called Beta Pictoris, which is surrounded by a comparatively lightweight "debris disk," probably composed in part of dust-grain remnants from processes connected with an earlier phase of planet building. The new results imply that, in its youth, Beta Pictoris may have possessed a massive disk comparable to that now identified around MWC480. Beta Pictoris might have been, effectively, a "planetary construction site," says Mannings.

Other members of the research team are David Koerner, an astronomer at the Caltech/NASA Jet Propulsion Lab, and Anneila Sargent, who is executive director of Caltech's Owens Valley Radio Observatory.

Mannings says, "We believe that the amount of material in this disk is sufficient to produce a system of planets. We detect enough gas and dust to build planets with the same total mass as that of the nine planets in our own solar system. But we emphasize that the possibility of planet building within this particular disk is speculation only."

The radio image is sufficiently detailed to show that the large disk of gas and dust is tilted about 30 degrees from face-on. A tantalizing aspect of the image is that the rotation of the disk can be detected by measuring the velocities of the gas, most of which is in the form of molecular hydrogen. About 1 percent of the disk is dust grains, and just a trace amount of the material is carbon monoxide. The hydrogen is not detected directly, but the gas velocities can be probed using spectral-line radio waves emitted by the carbon monoxide. The Caltech measurements demonstrate that gas south of the star travels approximately toward us, and away from us when north of the star. From our vantage point, the disk is inferred to be rotating roughly from south to north.

For the first time, astronomers have identified clearly a young massive disk that could gradually evolve into a debris disk such as that surrounding the older star Beta Pictoris, perhaps building planets along the way. By studying stars like MWC480, say Mannings, Koerner and Sargent, we can hope to learn not only about the origins of the Beta Pictoris debris disk, but perhaps about the beginnings of our own solar system too. Astronomers have targeted nearby sunlike stars for searches for new planets, but this discovery shows that brighter stars should also be included.

Big Bear Observatory Telescopes and Dome To Be Named In Honor of Longtime Director Hal Zirin

PASADENA—Renowned solar astronomer Harold Zirin will be honored Wednesday when the solar telescopes and dome at Big Bear Solar Observatory are named for him.

The ceremony, set for 11 a.m. Wednesday, July 2, at the observatory near Big Bear City, Calif., also marks the official transfer of operations of the observatory management from the California Institute of Technology to the New Jersey Institute of Technology. Zirin, a longtime member of the astrophysics faculty at Caltech, has been the sole director of the facility since its founding in 1969.

"Hal Zirin's achievements in solar physics are recognized throughout the world," says Philip R. Goode, director of the Center for Solar Research at NJIT, in a special resolution. "It is fitting for his friends and associates to express deep admiration and respect for him as a scholar, a teacher, and a colleague."

Goode, the new director of Big Bear Solar Observatory, also said that, based on BBSO observations, Zirin had established BearAlerts, a service for forecasting solar activity and issuing flare warnings. Solar flares, if sufficiently powerful, can cause communication satellites to malfunction and can also cause electrical disturbances on Earth.

Zirin, a member of the Caltech faculty since 1963, is a leading authority on solar flares. He discovered the role of emerging flux regions in rearranging magnetic fields and triggering solar flares, as well as the role of delta sunspots in producing solar flares. He also established a chromosphere atmospheric reference model for the study of the solar atmosphere.

Speakers at the Wednesday ceremony, in addition to Zirin and Goode, will include Dr. Thomas E. Everhart, president of Caltech; and Saul K. Fenster, president of NJIT. The media are invited. For directions and to schedule tours of the facilities, please call in advance.


Caltech Astronomers Crack the Puzzle of Cosmic Gamma-Ray Bursts

Additional Images can be obtained on the Caltech astronomy web site at

PASADENA—A team of Caltech astronomers has pinpointed a gamma-ray burst several billion light-years away from the Milky Way. The team was following up on a discovery made by the Italian/Dutch satellite BeppoSAX.

The results demonstrate for the first time that at least some of the enigmatic gamma-ray bursts that have puzzled astronomers for decades are extragalactic in origin.

The team has announced the results in the International Astronomical Union Circular, which is the primary means by which astronomers alert their colleagues of transient phenomena. The results will be published in scientific journals at a later date.

Mark Metzger, a Caltech astronomy professor, said he was thrilled by the result. "When I finished analyzing the spectrum and saw features, I knew we had finally caught it. It was a stunning moment of revelation. Such events happen only a few times in the life of a scientist."

According to Dr. Shri Kulkarni, an astronomy professor at Caltech and another team member, gamma-ray bursts occur a couple of times a day. These brilliant flashes seem to appear from random directions in space and typically last a few seconds.

"After hunting clues to these bursts for so many years, we now know that the bursts are in fact incredibly energetic events," said Kulkarni.

For team member and astronomy professor George Djorgovski, "Gamma-ray bursts are one of the great mysteries of science. It is wonderful to contribute to its unraveling."

The bursts of high-energy radiation were first discovered by military satellites almost 30 years ago, but so far their origin has remained a mystery. New information came in recent years from NASA's Compton Gamma-Ray Observatory satellite, which has so far detected several thousand bursts. Nonetheless, the fundamental question of where the bursts came from remained unanswered.

Competing theories on gamma-ray bursts generally fall into two types: one, which supposes the bursts to originate from some as-yet unknown population of objects within our own Milky Way galaxy, and another, which proposes that the bursts originate in distant galaxies, several billion light-years away. If the latter (as was indirectly supported by the Compton Observatory's observations), then the bursts are among the most violent and brilliant events in the universe.

Progress in understanding the nature of ters had to make an extra effort to identify this counterpart quickly so that the Keck observations could be carried out when the object was bright. The discovery is a major step to help scientists understand the nature of the burst's origin. We now know that for a few seconds the burst was over a million times brighter than an entire galaxy. No other phenomena are known that produce this much energy in such a short time. Thus, while the observations have settled the question of whether the bursts come from cosmological distances, their physical mechanism remains shrouded in mystery.

The Caltech team, in addition to Metzger, Kulkarni, and Djorgovski, consists of professor Charles Steidel, postdoctoral scholars Steven Odewahn and Debra Shepherd, and graduate students Kurt Adelberger, Roy Gal, and Michael Pahre. The team also includes Dr. Dale Frail of the National Radio Astronomy Observatory in Socorro, New Mexico.

Robert Tindol

Caltech Astronomer Obtains Data That Could Resolve the "Age Problem"

PASADENA — A California Institute of Technology astronomer has obtained data that could resolve the "age problem" of the universe, in which certain stars appear to be older than the universe itself.

Dr. Neill Reid, using information collected by the European Space Agency's Hipparcos satellite, has determined that a key distance measure used to compute the age of certain Milky Way stars is off by 10 to 15 percent. The new data leads to the conclusion that the oldest stars are actually 11 to 13 billion years old, rather than 16 to 18 billion years old, as had been thought.

The new results will be of great interest to cosmologists, Reid says, because estimates of the age of the universe, based on tracking back the current rate of expansion, suggest that the Big Bang occurred no more than about 13 billion years ago. Therefore, astronomers will no longer be confronted with the nettling discrepancy between the ages of stars and the age of the universe.

"This gives us an alternate way of estimating the age of the universe," says Reid. "The ideal situation would be to have the same answer, independently given by stellar modeling and cosmology."

Reid's method focuses on a type of star (known as subdwarfs) found in globular clusters, which are spherical accumulations of hundreds of thousands of individual stars. These have long been known to be among the earliest objects to form in the universe, since the stars are composed mainly of the primordial elements hydrogen and helium, and because the clusters themselves are distributed throughout a sphere 100,000 light-years in diameter, rather than confined, like the sun, within the flattened pancake of the galactic disk. Astronomers can determine quantitative ages for the clusters by measuring the luminosity (the intrinsic brightness) of the brightest sunlike stars in each cluster. Those measurements require that the distances to the clusters be known accurately.

Reid looked at some 30 stars within about 200 light-years of Earth. Using the Hipparcos satellite, he was able to obtain very accurate distances to these stars by the parallax method. Parallax is a common method for determining relatively nearby objects. Just as a tree 10 feet away will seem to shift its position against the distant background when an observer closes one eye and then the other, a nearby star will shift its position slightly if the observer waits six months for Earth to reach the opposite side of its orbit. And if the distance between the two observing sites (the baseline) is known very accurately, the observer can then compute the distance to the object by treating the object and the two observing sites as a giant triangle.

Reid chose the 30 stars for special study (out of the 100,000 for which Hipparcos obtained parallax data) because they, like the globular cluster stars, are composed primarily of hydrogen and helium. Thus, these stars also can be assumed to be very old, and may indeed themselves once have been members of globulars that were torn apart as they orbited the galaxy.

Once distances have been measured, these nearby stars act as standard candles whose brightness can be compared to similar stars in the globular clusters. While this is a well-known technique, older investigations were only able to use lower-accuracy, pre-Hipparcos parallaxes for 10 of the 30 stars.

Reid's conclusion is that the clusters are about 10 to 15 percent farther from Earth than previously thought. This, in turn, means that the stars in those clusters are actually about 20 percent brighter than previously thought, because luminosity falls off as distance increases. Brighter stars have shorter lifetimes, so this means that the clusters themselves must be younger than once assumed.

British astronomers Michael Feast and Robin Catchpole recently arrived at very similar conclusions, also based on new data from Hipparcos, but using a different, and less direct, line of argument. They used new measurements of a type of variable known as Cepheids to determine a revised distance to the Large Magellanic Cloud, a galaxy orbiting the Milky Way.

Feast and Catchpole used another type of variable star, the RR Lyrae variables, to bridge between the LMC and globular clusters. The fact that these two independent methods give the same answer makes that answer more believable, says Reid. "Most people previously believed that 14 billion years was the youngest age you could have for these stars," Reid says. "I think it's now accurate to say that the oldest you could make them is 14 billion years.

"No longer are we faced with the paradox of a universe younger than its stellar constituents," says Reid.

The work is set to appear in July in the Astrophysical Journal.

Robert Tindol

Renowned Physicist Robert B. Leighton Dies

PASADENA—Robert B. Leighton, a longtime physicist and astronomer at the California Institute of Technology, died Sunday, March 9, 1997, after a long illness. He was 77.

Widely known for his innovative design of scientific instruments such as the Caltech Submillimeter Observatory on Mauna Kea, Hawaii, Leighton was active in many areas of physics and astronomy during his career. His work over the years spanned solid state physics, cosmic ray physics, the beginnings of modern particle physics, solar physics, planetary photography, infrared astronomy, and millimeter- and submillimeter-wave astronomy.

"In the latter four fields, his pioneering work opened up entirely new scientific areas of research that subsequently developed into vigorous scientific communities," said Charles Peck, professor of physics and chair of the Division of Physics, Mathematics and Astronomy. "All of us who knew Bob Leighton deeply admired him and miss him greatly."

In addition, he was a renowned teacher, having edited "The Feynman Lectures in Physics" into their printed form, and authored a highly influential text, "Principles of Modern Physics," and, for his contemporaries, set a high standard of teaching quality. In addition, he co-authored, with Caltech physics professor Robbie Vogt , a set of problems to accompany the Feynman Lectures.

In 1948, Leighton's first scientific publication concerned the specific heat of face-centered cubic crystals, but he had already been drawn into Caltech's strong cosmic ray group under Nobel laureate Carl Anderson's leadership. He played a key role in 1949 in showing that the mu-meson decay products are two neutrinos and an electron, and he made the first measurement of the energy spectrum of the decay electron (at the time, low statistics experiments suggested that only one neutrino was involved). In 1950 he made the first observation of strange particle decays after the initial discovery of two cases in England in 1947. Over the next seven years, he elucidated many of the properties, e.g., mass, lifetime, decay-modes and energies, of several of the new strange particles, in particular, the lambda, the xi, and what were then called the theta particles (K-mesons).

In the mid-1950s, Leighton became interested in the physics of the outer layers of the Sun. With characteristic imagination and insight, he devised Doppler-shift and Zeeman effect solar cameras. They were applied with striking success to the investigation of magnetic and velocity fields on the sun. With the Zeeman camera, Leighton and his students mapped complicated patterns of the sun's magnetic field with excellent resolution. Even more striking were his discoveries of a remarkable five-minute oscillation in local surface velocities and of a "super-granulation pattern" of horizontal convection currents in large cells of moving material. These solar oscillations have subsequently been recognized as internally trapped acoustic waves, opening up the field of solar seismology, subsequently pursued by Caltech physics professor Ken Libbrecht.

In the early 1960's, Leighton developed and fabricated a novel, inexpensive infrared telescope. He and Caltech physics professor Gerry Neugebauer used it to produce the first survey of the sky at 2.2 microns. This survey revealed an unexpectedly large number of relatively cool objects. Some of these have been found to be new stars still surrounded by their dusty pre-stellar shells, while others are supergiant stars in the last stages of their evolution, embedded in expanding dusty shells of matter ejected by the stars themselves. During the middle 1960's Leighton was the Team Leader at JPL for the Imaging Science Investigations on the Mariner 4, 6, and 7 missions to Mars. As Team Leader and an experienced experimental physicist, Leighton played a key role in forming and guiding the development of JPL's first digital television system for use in deep space. He also contributed to the first efforts at image processing and enhancement techniques made possible by the digital form of the imaging data.

Leighton also designed and built equipment earlier in his career that was used to make images of the planets. These were considered the best images of the planets until the era of space exploration with probes began in the 1960s.

In the 1970's, Leighton's interest shifted to the development of large, inexpensive dish antennae which could be used to pursue millimeter-wave interferometry and submillimeter-wave astronomy. Once again, his remarkable experimental abilities opened a new field of science at Caltech which continues to be vigorously pursued at the Owens Valley Radio Observatory (OVRO) and the Caltech Sub-millimeter Observatory (CSO) on Mauna Kea using the "Leighton Dishes."

Born in Detroit, September 10, 1919, Dr. Leighton received his B.S. in 1941, his M.S. in 1944, and his Ph.D. in 1947, all from Caltech. He continued here as a Research Fellow (1947-1949), Assistant Professor (1949-1953), Associate Professor (1953-1959), Professor (1959-1984), Valentine Professor of Physics (1984-1985), and Valentine Professor, Emeritus (1985-1997). Bob served as Division Chair of Physics, Mathematics and Astronomy from 1970 to 1975. He was a member of the American Physical Society, Sigma Xi, the American Astronomical Society, the American Association of Arts and Sciences, and the National Academy of Sciences.

He is survived by his wife, Marge Leighton of Pasadena; his former wife, Alice Leighton of Seattle, Washington; their two sons, Alan of Bochum, Germany and Ralph of Tiburon, California; and two grandchildren, Ian and Nicole, both of Tiburon. Memorials may be made to the Los Angeles Library Foundation at 630 West 5th Street, Los Angeles, California 90071.

Robert Tindol

Caltech Astronomers Obtain the Most Detailed Infared Image of the Environment of an Active Black Hole

TORONTO — Sophisticated imaging techniques applied on the Keck Telescope have uncovered a new structure in a nearby active galaxy.

The image and associated research are being presented today at the semiannual meeting of the American Astronomical Society. Alycia Weinberger, a doctoral student in physics at the California Institute of Technology, and her collaborators have used the computer-intensive technique of speckle imaging and the 10-meter W. M. Keck Telescope atop Mauna Kea, Hawaii, to image the nucleus of NGC 1068.

This galaxy, found in the constellation Cetus at a distance of about 50 million light years, reveals a a bright active nucleus at infrared wavelengths. This nucleus has long been thought to harbor a black hole as its central engine and, because it is bright and nearby, has been intensely studied by astrophysicists.

The accompanying false color image shows an elongated structure, which is over 100 light-years across, centered on a bright point-like infrared nucleus. In contrast, the bright disk of the galaxy NGC 1068 is over 30,000 light-years across at visual wavelengths.

Made at a wavelength of 2.2 microns, Weinberger's near-infrared image has the capability to reveal structures which are only 12 light years across. This is an extremely small distance by galactic standards, as small as about three times the distance between the Sun and its nearest stellar neighbors. Although taken from a ground based observatory, this image has resolution as fine as what the Hubble Space Telescope achieves in the visual part of the spectrum. The space telescope does not currently have an infrared camera, but is scheduled to receive one in 1997. The elongated feature discovered by the Caltech group has not been seen in Hubble's optical images.

There are two very interesting aspects of this image. First, the image is elongated, and second the axis of the emission points in a different direction than previously observed visual emission. The near-infrared light used to make this picture typically traces the distribution of hot dust and cool stars.

However, in NGC 1068, it is very unlikely that there could be dust 100 light-years from the central black hole which would be hot enough to produce the observed emission. Rather, Weinberger says, it is likely that the observed extended near-infrared light is from stars. Furthermore, since it points in a different direction, this newly resolved infrared emission is likely to come from an entirely different source than previously observed visual emission.

It has long been proposed that stellar bars are a way of funneling material to an active nucleus. As gas moves in a non-circular distribution of stars, such as what may be seen in Weinberger's image, it is forced into orbits likely to take it near the central black hole. This provides a continuous mechanism for "feeding" the central engine.

"The significance of this research is that it finds a brand-new feature in this galaxy. And even more, this new feature may provide observational evidence for a theoretically predicted means of channelling material to the black hole on very small scales," Weinberger says. The image is by no means detailed enough to show the in-fall of the matter itself, Weinberger stresses. For this, one would need a resolution of less than a light-year, and there is currently no way to make such finely detailed pictures.

Nonetheless, the quality of this image is unparalleled because it relies on the unique resolving power of Caltech's 10-m Keck Telescope and the technique of speckle interferometry to remove the distorting effects of Earth's atmosphere. With this technique, a series of very rapid exposures are made of the object, freezing the atmospheric distortions that cause stars to "twinkle." Then the distortions are removed in computer post-processing. As the largest infrared telescope in the world, the Keck Telescope provides the best obtainable resolution.

Weinberger is currently completing work on her doctorate. She will continue doing observations to support this research, a part of her thesis. "It will be exciting to look at NGC 1068 with similar resolution in other infrared wavelengths," she says. "The more information we have across the spectrum the more we'll understand about the nature of this extended emission."

Also collaborating in this research are her thesis supervisor, Gerry Neugebauer and Keith Matthews both of the Caltech physics department.

Robert Tindol


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