Hall was an accomplished astronomer and instrumentalist who led the development and use of high-resolution infrared spectrometers and large format infrared arrays. The latter had an enormous impact on both ground- and space-based telescopes.
Donald N. B. Hall, Astronomer at the University of Hawaiʻi Institute for Astronomy (IfA), passed away on the morning of March 18th, 2020, after suffering a heart attack. He was 75.
After graduating from the University of Sydney with a B.Sc. in Physics in 1966, Hall was admitted to Harvard University, where he studied with Robert Noyes and received his Ph.D. in astrophysics in 1970. His dissertation involved infrared studies of sunspots. Thereafter, he worked as a member of the scientific staff at Kitt Peak National Observatory (KPNO) from 1970 to 1981. During this period he developed advanced infrared spectroscopic instrumentation and detectors for the McMath Solar Telescope and later, the Mayall 4-meter telescope. He led the construction of a high-spectral-resolution Fourier Transform Spectrometer and the development of the InSb detector for 1-5 μm nighttime observations. The InSb detector had a huge impact in advancing infrared astronomy leading up to the development of large infrared arrays.
Don had wide knowledge of optical technology, and excellent instincts for matching technology with application. He committed himself fully to a series of very high-resolution infrared spectrometers, first grating-based, and then interferometric. His observing programs were diverse and opportunity driven, pursuing the most exciting measurements enabled by the instruments and detectors that he deployed. He welcomed collaborators and visiting astronomers, took pleasure in facilitating their successes, and was generous with credit.
While at KPNO he served as project scientist for the KPNO Next Generation Telescope study of concepts for achieving a 25-meter ground-based telescope. This facilitated the wave of development of 10 meter class telescopes at the turn of the century and anticipated the coming generation of 30-40 meter class telescopes. One of Don’s lesser known activities was the KPNO grating laboratory. When MIT surplussed the Harrison grating engine, Don, seemingly cavalierly, offered to take it on. It was shipped to Tucson, installed, and operated for a number of years. Don became an expert in the technology and the machine, producing excellent gratings that significantly enhanced the performance of the Mayall echelle and other spectrographs.
In addition to working hard, Don knew how to enjoy life. He was a sensational host, splurging when still young on a magnificent Tucson foothills home where he and his wife Sandy hosted wall-to-wall eclectic crowds, and often welcomed visiting astronomers with free lodging. He loved the outdoors, organizing backpacking outings to the national forests. He was locally renowned for roasting a whole pig for the annual observatory picnic.
In 1981, Don was recruited to the position of deputy director of the newly created Space Telescope Science Institute (STScI) in Baltimore. While there, he worked closely with Riccardo Giacconi, helping to build the STScI into a world-renowned research institution which went on to successfully conduct the science program of the Hubble Space Telescope.
In 1984, Don took up the Directorship of the Institute for Astronomy (IfA) at the University of Hawaiʻi , a position which he held for thirteen years. During this time he led the development of major observatories on Maunakea and Haleakala as well as the growth of the IfA into one of the leading international astronomical centers. He negotiated tirelessly with national and international agencies as they sought to build observatories on Maunakea and Haleakala. At the same time he pursued technological advancement in charge-coupled devices and infrared detectors. He brought in expertise to develop and use large format charge-coupled device arrays while leading a group to develop infrared array technology. His work on infrared detector arrays helped astronomers to progress from laboriously scanning a single semiconductor detector across the sky in the 1980s to today’s sensor chips with 16 megapixels, each with sensitivity improved a thousand-fold. This 16 billion-fold increase in observing efficiency has reshaped infrared astronomy from a technology-constrained field into a powerful tool for the study of the universe.
Soon after arriving at the IfA, Don led a small team to exploit the United Kingdom Infrared Telescope (UKIRT) and NASA Infrared Telescope Facility (IRTF) spectrometers to determine a mass limit of the proposed black hole at the very center of the Milky Way. They successfully observed the 2.3 μm CO band head and obtained by far the best mass limit at that time. A few years later he realized the great advantage of using IR arrays and adaptive optics to measure the proper motions of individual stars to determine the mass or mass limit of the central black hole. This idea was compelling and enabled two groups at the University of California at Los Angeles and Max Planck Institute for Extragalactic Physics in Garching to discover a 4 million solar mass black hole at the center of the Milky Way. This gives a glimpse of the extraordinary intellect of Don which was always evident in working with him as a scientific colleague, a technical innovator, and an administrator.
Don loved to travel, and his positions enabled a lot of it. Often commuting between Baltimore and Hawaiʻi , he was so well known to American Airlines that the agents and attendants held a full row of seats in back for him to sleep. Don tried to be widely in touch, to feel the pulse of the community, in later years traveling to conferences for just the face time in hallway chats. In his later years as Director, he faced alcohol-related challenges. After stepping down as Director and after much effort he was able to overcome this disease and was able to resume his long term interest in advancing infrared detector technology.
Don usually had an outrageously positive attitude. He encountered failure and road blocks with smiles and optimism. Faced with difficult or even obnoxious people, his response was brief perplexity. Don had great ambitions and energetically pursued them with quiet determination - he did so by means of talent, dedication, hard work, and immense personal charm. He waited to be called to serve rather than indulge in self-promotion. He was an effective team leader, a friendly and affirmative critic, always well prepared, not hesitating to labor invisibly at thankless tasks. He greatly preferred for decisions to be made by consensus and was remarkably reluctant to rely on the authority of his positions.
Upon returning to his research career in 1997 as a member of the IfA’s tenured faculty, Don established an infrared detector lab at IfA’s Hilo facility where he concentrated on development of very large array detectors for infrared astronomy both from the ground and in space. His work led to the development of the HAWAIʻI series of infrared arrays that are used in almost all current ground-based infrared instruments as well as space missions and observatories. Most notable are the infrared arrays on the Wide Field Camera 3 on the Hubble Space Telescope. HAWAIʻI -1R arrays were also used on the NASA Deep Impact comet mission and the Wide Field Survey Explorer.
A University of Hawaiʻi -Teledyne Technologies (formerly Rockwell) team led by Don developed the near infrared HAWAIʻI -2RG 4 megapixel array detectors and also the on-chip controller selected by NASA for the James Webb Space Telescope. Fifteen 4 megapixel HAWAIʻI 2RG sensors totaling over 60 megapixels are used in three scientific instruments on the James Webb Space Telescope which is now transforming every field of astronomy. For this work Don and his team were honored with a NASA Congressional Space Act award. The next major NASA astrophysics mission, the Roman Space Telescope, is based on a camera with 18 HAWAIʻI 4RG arrays for a total of over 300 megapixels. HAWAIʻI arrays are also in use in ground-based observatories around the world, including all eight optical/infrared telescopes on Maunakea.
At the time of his death, he and his close collaborators in Europe were working on developing new near-infrared detector technology utilizing avalanche photodiode detectors. He pushed the development of fast high gain avalanche photodiode (APD) sensors to be used in adaptive optics wavefront sensors and fringe trackers in interferometry, as well as lower APD gain, low dark current large format science grade detectors that are essentially noiseless large format science arrays.
Don received numerous awards for both his research and instrumentation work, including the American Astronomical Society (AAS) Newton Lacy Pierce Prize in 1977 for outstanding work in instrumentation and observational astrophysics under the age of 35 and the AAS Joseph Weber Award for Astronomical Instrumentation in 2010 for the design, invention, or significant improvement of instrumentation leading to advances in astronomy. In 2013 he was elected as a fellow of the American Association for the Advancement of Science.
He is survived by his wife, Pat Tummons, his first wife, Sandra Kimberley Hall of Honolulu, mother of son Andrew Hall and daughter Katherine Gonsalves, both of Portland, Oregon; and two grandsons, Malcolm and Theo Gonsalves.