About this ArticleAlex Fullerton (fullerton[at]stsci.edu)
Nolan R. Walborn, one of the original members of the research staff at STScI and a renowned expert on the spectral classification of hot, massive stars, died on February 22. His passing marks the end of an era for both the Institute and the hot-star community.
Walborn was born in Bloomsburg, PA, but moved with his family to Argentina when he was 8 years old. He attended local schools, and—as a result—was fluent in Spanish; something that often caught other Spanish speakers off guard upon their first meeting! He maintained a deep affection for South America throughout his life and retained close ties with the astronomical community there.
Walborn returned to the U.S. for undergraduate studies in physics at Gettysburg College, PA and graduated summa cum laude in 1966. He moved to the Yerkes Observatory of the University of Chicago for graduate work in the field of stellar spectroscopy with W. W. Morgan—the "M" in "MK spectral classification." Larry Marschall of Gettysburg College, who was also a graduate student at Yerkes at the time, remembers Walborn as a clear, logical thinker who wasn't hesitant to offer a fresh, and sometimes contrarian, view on the issues. "We discussed these topics informally at the Yerkes Observatory or at Friday fish-fries in the local restaurants."
In his dissertation, Walborn established precise luminosity criteria for early O‑type spectra and clarified details of the temperature classification for late O- and early B‑type stars. This work launched his career as a pre-eminent classifier of the spectra of early-type stars. Nolan's keen eye and fastidious attention to detail were perfectly suited to this type of work, which lead to numerous discoveries over the course of his 50-year research career.
After completing his dissertation in 1970, Walborn held a postdoctoral position at the David Dunlap Observatory, University of Toronto, during which he helped inaugurate the University of Toronto Southern Observatory on Las Campanas, Chile. He was hired as a staff astronomer at the Cerro Tololo Inter-American Observatory in 1973, which positioned him to continue his research into early-type stars in the Galaxy and Magellanic Clouds, and to widen his interests to include explorations of the ejecta of η Carinae, the interstellar medium of the Carina region, and the properties of massive young star clusters.
Walborn's long association with the Institute began in 1979 when he was seconded from CTIO to the AURA corporate office to help draft the AURA/JHU proposal to NASA to manage the Space Telescope Science Institute. He was especially involved with drafting the "science management" section, and later recalled: "After AURA won the competition, I heard that one of the winning points of the AURA proposal was the Science Management section, which gave me a warm feeling." Following a stint as a NASA/NRC Senior Research Associate at NASA's Goddard Space Flight Center, he joined the research staff of the fledgling Institute in 1984.
Walborn held a variety of roles during his 34-year career at the Institute. He was a founding member of the General Observer Support Branch, which established the Institute's core commitment to serving the Hubble user community. After Hubble's launch in 1990, Nolan provided dedicated support for multiple generations of spectroscopic instruments—Goddard High-Resolution Spectrograph, Space Telescope Imaging Spectrograph (STIS), Cosmic Origins Spectrograph—with the particular aim of enabling complicated, "impossible" programs to be scheduled and their scientific goals achieved, while also ensuring the health and safety of the delicate UV detectors. "Nolan unfailingly had the best interests of both the science and the workings of Hubble at heart," said John Debes, the current STIS Branch Manager.
Above all else, Walborn was a classifier of stellar spectra. He championed the morphological approach that underlies spectral classification and thought deeply about the role the method plays in scientific investigations. In his view, the search for similarities, differences, trends, and relationships provided the informational framework that is a prerequisite for meaningful investigation of the physical origin of a new phenomenon. In his own words: "Of course, morphology does not explain anything; rather, it properly formulates the phenomenon to be explained." His philosophical perspective on the linkage between "Nature," our imperfect but ever-improving "Image of Nature," and the ultimate goal of "Understanding of Nature" is articulated in the Walborn Diagram, which he spoke about frequently and defended fiercely.
Walborn's own work to study shapes, patterns, and trends in the line spectra of O‑type stars lead to the recognition of a wide variety of new phenomena, many of which are still awaiting adequate physical explanations. By-products of this work include landmark atlases of the spectra of early-type stars in the ultraviolet (International Ultraviolet Explorer, Hubble), far-ultraviolet (Copernicus, Hopkins Ultraviolet Telescope, Far Ultraviolet Spectroscopic Explorer), and X‑ray (Chandra) wavebands. Although he championed the spectroscopic explorations provided by these new windows on the universe, he always came back to the optical region of the spectrum. He was an early convert to classification with high S/N digital data obtained with modern detectors, and was particularly proud of his recent work to classify all the O‑type spectra in the Galactic O‑Star Spectroscopic Survey (GOSSS; 590 stars) and VLT-Flames Tarantula Survey (VFTS; 213 stars) with newly refined criteria. He was continuing to work on a variety of projects until the very end of his life.
Walborn was happy to engage in the "cut and thrust" of spirited debates, whether on details of stellar spectra, the necessity of the morphological approach to research, or the political and sociological issues of the day. In the context of their work on η Carinae, Roberta Humphreys, Professor Emeritus at the University of Minnesota recalls that "he could be both insightful and critical, but with a twinkle in his eye and a sly grin afterwards." Nolan was also a tireless raconteur, who would happily entertain gatherings with stories of astronomy and astronomers, as well as his many experiences in different places and times. His more playful side would often emerge after the banquet dinner at an astronomical conference. Linda Smith, head of the STScI Instruments Division, attended many of the same conferences as Nolan over the years, and noted that along with scientific discussions, "his biggest joy at conferences, however, was to dance the Macarena. He also taught the dance to many conference attendees over the years."
Nolan Walborn was a unique individual with a rich legacy of achievements. His colleagues at the Institute and many friends around the world mourn his passing, and express sincere condolences to his family. Though the loss of his insights and mentorship will be keenly missed, his accomplishments will continue to guide massive star research for years to come.