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Hyron Spinrad (1934–2015)

Published onDec 01, 2015
Hyron Spinrad (1934–2015)

Hyron Spinrad, emeritus professor of astronomy and former chair of the Department of Astronomy at the University of California, Berkeley, died on 7 December 2015 at age 81, in Walnut Creek, California, after a long illness.

Hy (as we and the worldwide astronomical community knew him) was born on 17 February 1934 in Brooklyn, New York, to Manny and Ida Spinrad. His Brooklyn roots showed through his lifelong love of the Dodgers Major League baseball team. His family moved to San Francisco in 1946, and Hy attended UC Berkeley, playing baseball and graduating in 1955. After serving in the U.S. Army, he came back to Berkeley for graduate school, earning his Ph.D. in astronomy in 1961. He passed three years in Pasadena as a senior scientist at the Jet Propulsion Laboratory (JPL), before returning once and for all to Berkeley in 1964, when he joined the astronomy faculty. He served as department chair from 1980 to 1984, and retired in 2004. Spinrad published more than 300 scientific articles during his career. He was an elected member of the National Academy of Sciences and the 1986 recipient of the Dannie Heineman Prize for Astrophysics, awarded by the American Astronomical Society and the American Institute for Physics. Asteroid 3207 is named after him.

Spinrad’s research career spanned an unusual range of interests, from planetary atmospheres and comets to the most distant objects in the universe. A unifying thread was his interest and expertise in making challenging spectroscopic measurements, often using new instrument technologies and observing techniques.

Planetary atmospheres and comets

Hy’s expertise in near-infrared spectroscopy with hyper-sensitized photographic plates was particularly important for his earliest work. From 1962 through 1969, Hy observed the atmospheres of Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Neptune’s satellite Triton. In 1963, Spinrad, Guido Münch, and Lewis Kaplan reported the first detection of water vapor in the Martian atmosphere. Hy then demonstrated that seasonal variations of water vapor correlate with changes in the sizes of the polar caps. This was the first substantial evidence that water is an important component of the Martian polar caps. He also showed that the Martian atmosphere is very tenuous and consists primarily of carbon dioxide.

Hy studied the temperature and pressure of atmospheric CO2 on Venus and set limits on the abundance of molecular oxygen there, as well as limits on CO2, O2, and H2 O in the atmosphere of Mercury. He discovered that ammonia and methane in the atmospheres of Jupiter and Saturn showed anomalous rotational velocities compared to that of the cloud layer that reflects optical sunlight. He also studied molecular hydrogen in the atmospheres of Saturn, Uranus, and Neptune, and set limits on methane in Triton’s atmosphere.

From 1968 onward, Spinrad extensively observed comets. As an expert in faint-object spectroscopy, he made many observations of comets at very large solar distances, including the first spectra of an exceedingly faint and inactive Comet Halley when it was eight astronomical units from the Sun, two years before its 1986 perihelion. With Ray L. Newburn (JPL), Hy worked out an early understanding of the compositional variability of comets, and in 1987 he published an important review article on comets and their composition.

Stars and stellar populations of nearby galaxies

Much of Hy’s early work on stars in nearby galaxies focused on their chemical abundances. His Ph.D. thesis, published in May 1962 (Astrophysical Journal, 135 (1962): 715-735), concerned stellar populations in the nuclei of nearby galaxies, using spectroscopy of their integrated light. His observation that some metal lines were unexpectedly strong led to his long-term interest in unusual stellar populations and abundance patterns, especially the surprising “super metal-rich” stars (and star clusters, and galactic nuclei). Later in the 1960s, he made early attempts to interpret galaxies through “population synthesis,” deriving plausible solutions for the mix of individual stellar types whose light combines to produce the integrated spectrum. In this way, astronomers can constrain the ages and past evolutionary histories of galaxies through observations of their spectra.

As with his planetary work, much of Hy’s stellar research featured then-difficult near-infrared spectroscopy, which is particularly important for studying absorption from water, H2, CO, CN, and other molecules. Together with colleagues, he wrote papers in the late 1960s on observations of “infrared stars,” bright and very red objects then being discovered in the first infrared sky surveys. Hy and his first Ph.D. student, Robert Wing, summarized the field of infrared stellar spectroscopy in a 1969 review article.

Galaxies at high redshift

At the dawn of the 1970s, Hy began his long push outward, into the distant universe, motivated by an interest in using galaxies to test cosmology. In the 1960s, Allan Sandage had outlined a program to test the expected deceleration (as was then believed to be the case) of cosmic expansion using the “Hubble diagram” — the relation between galaxies’ observed brightness (a measure of their distance) and their recession velocities or redshifts (a measure of cosmic expansion, whose value is denoted by the variable z). This requires: (1) identifying a population of galaxies with a small dispersion in luminosity, (2) understanding how their luminosities might evolve with time as their stellar populations age, and (3) actually finding and studying galaxies at distances large enough that changes in the rate of universal expansion lead to observable effects on the Hubble diagram. Sandage envisioned this as a quest for the Palomar Observatory 5-meter telescope, then the world’s largest. Spinrad, with sympathy for the underdog perhaps motivated by his love of the Dodgers, and with access only to smaller telescopes like the Lick Observatory 3-meter, made this challenge his own.

Hy pinned his hopes on radio galaxies, which in the local universe are giant elliptical galaxies with massive black holes at their centers. These black holes produce powerful plasma jets and lobes that generate bright radio emission, allowing the galaxies to be pinpointed at cosmological distances. The most distant galaxy known in the early 1970s was the powerful radio galaxy 3C 295 at redshift z = 0.46. Many more radio sources were known that were too faint to be seen in the Palomar Sky Survey, suggesting that they were more distant still. Hy launched a quest to find ever more distant galaxies that would continue for four decades.

From 1975 to 1985, Hy and his students monopolized the redshift records, pushing the limits from z = 0.47 out to z = 3.2. For many years, his motto was “ z = 5 or bust!,” which one of his students had emblazoned onto T-shirts. Other astronomers got into the game and set their own records, too, but Hy stayed at or near the forefront. When the new W. M. Keck Observatory’s 10-meter telescopes became operational, Hy and his colleagues achieved his motto by discovering the first galaxies at redshifts greater than 5. In 2012, eight years after retiring, Hy participated in the discovery of a galaxy at z = 7.22, a new record for its time.

Besides setting records, Hy and his colleagues made important discoveries along the way. He painstakingly completed identification and spectroscopy for the 3CR catalog of radio sources, a resource that has been valued by many astronomers ever since. Studying these 3CR sources, he was the first to demonstrate that giant radio galaxies do indeed evolve over time. That discovery complicated their use for testing cosmology, and by the late 1990s other methods were setting more powerful constraints on cosmological parameters. But it opened a new line of investigation to understand just how galaxies evolve, and when they first formed. Hy’s students and colleagues discovered that radio jets have dramatic effects on the gas and stars in young radio galaxies at high redshifts, producing spectacularly elongated and clumpy morphologies that are far different from those of today’s “red, dead” elliptical galaxies. He did, however, help to discover that “red, dead” galaxies exist even at high redshift, when the universe was young; they must have formed very early indeed. He returned repeatedly to his beloved hydrogen Lyman-alpha emission line, a strong ultraviolet feature that first enabled spectroscopic confirmations of redshifts z > 2, and now even z > 7. With his students, he observed giant Lyman-alpha nebulae around powerful radio galaxies, whose origins and significance are still somewhat uncertain, but which suggested that some of these objects might be very young proto-galaxies in their first phase of formation.

Serendipity, Oddballs, and Persistence

Hy took masterful advantage of serendipity. For example, in 1977, Hy and (then-) graduate student John Stauffer were observing a distant radio galaxy with the Lick 3-meter telescope when a tremendously bright meteor exploded overhead, illuminating their spectrograph. They dutifully reported their very high signal-to-noise ratio bolide spectrum in a journal article.

Throughout his career, Hy was fond of investigating “oddball” objects or phenomena. In one notorious example, he and his colleagues investigated the mysterious occurrence of intense, transient potassium emission features in otherwise ordinary stars, which had been reported by astronomers at the Haute-Provence Observatory in France. With colleagues, he initially failed to detect the potassium features under ordinary conditions at Lick Observatory. However, they discovered that matches struck in the vicinity of the telescope produced potassium spectral lines. The authors diplomatically refrained from stating definitive conclusions, but implied that smoking might have caused the phenomena observed by the French astronomers.

In further pursuit of astronomical oddities, Hy observed two faint, fuzzy objects detected in 1968 near the Galactic plane, and showed that they are previously unknown galaxies quite nearby, but heavily obscured by the dust in our own Milky Way. He tried some unusual and extremely challenging spectroscopic gymnastics, such as measuring chemical abundances in elliptical galaxies far out in their faint halos, and set limits on the intensity of the (hypothesized) extragalactic background light by comparing spectra of blank sky to that of a dark dust cloud in the Milky Way.

Hy’s persistence was legendary. Struggling in poor weather at underdog Lick Observatory, he would wait until long after midnight for the rain to stop or the fog to clear, glued to a weather radio “squawk box,” and optimistically musing “Maybe we’ll get the second half…” Hy would see “ghost lines” of emission in noisy spectra that only he could love, but then return to the telescope to observe those galaxies again and again until their redshifts were either confirmed or disproven. Indeed, he helped to debunk some erroneous claims of record-setting redshifts, but was also generous about offering his own observing time to help confirm discoveries made by other teams. He and his students discovered some remarkable and occasionally record-setting high-redshift objects entirely by accident, when Lyman-alpha emission lines would pop up like mushrooms in deep spectra of other objects observed for entirely different reasons.

During his 40 years as a professor at Berkeley, Hy inspired and supervised several generations of Ph.D. students and a few postdoctoral fellows, most of whom continued with successful research careers, chasing after their own high-redshift oddballs and records. He passed along a sense of determination for making tough observations (“You’ve got to be a bulldog,” he would say), but also a spirit of adventure for pushing boundaries and horizons. Colleagues worldwide remember him fondly for his sheer enthusiasm, his wry humor, and his good sense about what problems were worthwhile and which others might be largely a waste of time. During his tenure as department chair, Hy was proud to have hired the first woman on the Berkeley astronomy faculty (Imke de Pater). Many people now or previously at Berkeley can fondly recall their experiences and discussions with Hy, scientific or otherwise.

In addition to his wife, Bette (Abrams) Spinrad, Hy is survived by his sons, Mike and Robert, his daughter, Tracy, his sons-in-law, Harry Joel and Grant Shapiro, and his seven grandchildren.

— Hy Spinrad’s grateful former students and colleagues, including Mark Dickinson, Imke de Pater, and Alex Filippenko; and the Academic Senate of the University of California, Berkeley.

Photo credit: Jane Scherr

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