Parkinson’s research helped establish the field of “laboratory astrophysics.” He contributed fundamental UV spectral atomic and molecular data and lead space-based observational studies of the Sun.
With great sadness, we report that William H. (Bill) Parkinson, a former leader of laboratory astrophysics and solar space research projects at the Harvard College Observatory (HCO) and the Harvard-Smithsonian Center for Astrophysics (CfA), and loving husband and father, died on January 19, 2022. He was 89.
Bill was born in Trenton, New Jersey on June 26, 1932. When he was two years old, his family moved to Port Dover, Ontario, Canada, where his father owned a service station. Teenaged Bill thrived in the rural community, raising a hawk and an owl and reading science fiction. In 1952, he married Phyllis T. Smith, who he had met on a double date with his best friend. They switched dates, and each couple later married. Bill and Phyllis were married for 68 years until Phyllis’s death in 2020, and raised two delightful and successful sons, Richard, of New York City, and Dougald of Newport, Rhode Island. Summer trips back to Port Dover occurred regularly for decades.
Bill did his undergraduate and graduate studies at the University of Western Ontario (UWO), receiving a Ph.D. in 1959 for his work with Ralph Nicholls in atomic and molecular physics. The publication resulting from his thesis was titled “The Laboratory Excitation of Meteoritic Spectra in Shock Tubes.”
This was followed by two years of postdoctoral research in molecular spectroscopy with A. G. Gaydon at Imperial College, London, England, studying, in part, some bands of BaO. About two decades after Bill’s work there, he and one of us (PLS) met Bob Field at his lab at MIT. “Are you the Parkinson of the ‘Parkinson Bands’?”, Bob asked of Bill. Bill demurred, claiming that he’d never heard of the Parkinson Bands. To his delight, Bill learned that Huber & Herzberg’s definitive work on diatomic molecules associates Bill, and only Bill, with a band of BaO.
In 1961 Bill was hired at the HCO by Leo Goldberg, who realized that space astronomy with spectroscopic observations in the vacuum ultraviolet (VUV; wavelengths less than 200 nm) would soon be possible, and that there was a dearth of spectroscopic data at VUV wavelengths for atoms and molecules that were expected to be seen by astronomers. Such data — spectral line identifications, line strengths (or transition probabilities), photoexcitation and photoionization cross sections, and autoionization and predissociation parameters for atoms and molecules — are essential for astrophysicists to determine and model abundances, pressures, temperatures, and rate constants in planetary and stellar (including the Sun) atmospheres and the interstellar medium.
At the HCO, in association with Goldberg, Bill created and led the HCO Atomic and Molecular Physics Laboratory, colloquially known as the “Shock Tube Laboratory”, for making such measurements with aerodynamic shock tubes, a piston compressor, and a high-temperature graphite furnace. LASER optical-pumping experiments were also developed at that time. The laboratory had a stimulating atmosphere, especially during visits by W.R.S. Garton from Imperial College and other well-known scientists.
When Leo Goldberg, who had first identified CO vibration-rotation bands in the infrared solar spectrum in 1951, was made aware of absorptions around wavelengths of 180 nm in solar spectra obtained by the Naval Research Laboratory with a rocket-borne spectrograph, he suspected that they could stem from the strong fourth positive system of CO. Bill and Ed Reeves then reproduced this VUV part of the spectrum of CO by heating argon gas with a small admixture of CO to solar atmosphere temperatures (ca. 5000 K) in a shock tube. This work confirmed CO as an important source of opacity in the solar atmosphere at VUV wavelengths.
Another important astrophysical problem that Bill and colleagues, in particular Martin Huber, worked on in the mid-1960’s was the solar iron abundance. At the time, there was a discrepancy of about a factor of 10 between the abundance determined using spectroscopic observations and that from measurements of iron in meteorites. Spectroscopic data from NBS (later NIST) that were used to analyze the former were found to be seriously in error.
For the measurements at HCO, an apparatus to use the so-called ‘hook method’ was added to the spectroscopic equipment in the Shock Tube Lab: a Mach-Zehnder interferometer was combined with a stigmatic spectrograph so that the anomalous dispersion in the vicinity of spectral lines could be photographed through a shock-heated plasma. Thus, one avoided the problem of saturation that occurs in measuring the absorption of strong spectral lines. A spectrum photographed simultaneously in absorption and by the hook method thereby extended the range of measurable line-strengths to a factor of 106.
Bill was also heavily involved with the Solar Satellite Project, which was led by his friend and long-time colleague Ed Reeves. They were together at UWO, in neighboring labs at Imperial College, and had been hired by Goldberg at the same time; when at HCO, they shared an office with their desks facing one another. At Imperial College, Ed had worked with W.R.S. Garton, and the three of them had productive collaborations for many years thereafter at the HCO.
Bill contributed to the development of instruments for three of the Orbiting Solar Observatory (OSO) series of satellites, and for the S-055 extreme ultraviolet spectroheliometer on Skylab. S-055 was the only spectroscopic instrument on Skylab with photoelectric detection, and thus obtained real-time data; all the other big instruments on Skylab used film to collect data which delayed analysis until the film could be returned to the ground. This sequence of space instruments laid much of the early groundwork for our current understanding of the outer solar atmosphere. For example, the OSO observations first revealed coronal “holes” in plain sight on the disk; we now know these are the seat of the fast solar wind.
Parkinson and Reeves developed a sounding rocket instrument for suborbital measurements of the absolute spectral radiance of the quiet Sun in the 130 to 180 nm wavelength range with high spectral resolution and low spatial resolution so that the observations were averaged over the chromospheric network. At the time, there were large discrepancies in the absolute spectral radiance observations of the quiet Sun in this wavelength range. The instrument consisted of a 93-cm focal length, off-axis parabola, telescope mirror feeding a scanning Ebert spectrometer with a photomultiplier detector. Three flights of this instrument, the latter led by John Kohl, gave results for absolute spectral radiance that are consistent with all later observations.
Bill would sometimes bring one of his young sons to the rocket launches. Once when they were at a favorite Mexican restaurant called La Posta in Mesilla, New Mexico, Bill’s son Richard walked up to the cage of a talking Myna bird, and the bird said: “Hi Rich;” well Richard’s astonishment that the bird seemed to know his name was memorable. Launch delays due to wind conditions were common, and on one such occasion, Bill’s younger son Dougald was treated to a weekend trip to the Grand Canyon; Dougald, Bill and John Kohl had a good time throwing snowballs into the canyon and estimating their fall distance from the amount of time it took to hear them hit the ground.
A consortium of scientists from the HCO, Imperial College and Culham Laboratory in the U.K., and York University in Canada made the first VUV observations of the extended solar corona with a rocket-borne, objective-grating spectrograph that was flown into the path of totality of the March 1970 solar eclipse. The observations revealed H I Lyman-α (Ly-α 121 nm) emission extending outward to beyond 1.5 solar radii from Sun-center. Parkinson and Reeves were the HCO lead scientists for this project. Giancarlo Noci from Arcetri Observatory recognized that such measurements could be used to determine coronal outflow velocities with the Doppler dimming technique. That led Parkinson along with Reeves and Robert Noyes to contact Kohl and ask him if he would be interested in developing a rocket instrument to make such measurements in the absence of a natural eclipse. Following Kohl’s design, Bill arranged to convert the Ebert spectrometer rocket program into a program to develop what was then called a Lyman-α coronagraph-spectrometer. This led to three “proof of concept” rocket flights, and ultimately to Kohl’s Spartan 201 Ultraviolet Coronagraph Spectrometer and his UVCS instrument on the SOHO satellite.
Performing spectroscopic laboratory astrophysics in a project group that included engineers and technicians, who designed, built, tested, and calibrated space instruments, had the advantage that technical experts could support the building of instruments for laboratory experiments as well. Moreover, combining space observations with laboratory experiments provided insurance for scientists involved in preparing instruments for space research in case of launch delays. If there was a transient lack of data from space observations, the scientists involved were not empty-handed, they could nevertheless publish results, namely those of their laboratory-astrophysics work.
In 1968, Bill was appointed Senior Research Associate at the HCO, and, when the Center for Astrophysics was created in 1973, he was appointed Associate Director for Atomic & Molecular Physics, a position he held for 15 years. His laboratory work continued, with a focus on atomic and molecular data needed to solve problems in astrophysics.
Together with Pino Tondello of Padua University, and supported by Frank Tomkins of the Argonne National Lab, Bill introduced the method of ‘flash pyrolysis’ into the Observatory’s spectroscopy lab. Here, one inserted atoms of astrophysical interest into a quartz tube — either in finely divided form or as a thin film — and evaporated, dissociated and excited them by igniting a flash tube that was wrapped around the quartz tube. By use of a bright continuum background source, one thus obtained clean absorption spectra of Cu I, Ba I, and even Ba II; notably, the spectrum of neutral Sulphur (S I) revealed transitions from excited states that lead to self-ionization.
Kohl, Larry Gardner, and Bill, together with a series of Harvard Ph.D. students, measured ion-electron impact excitation and dielectric recombination cross sections needed to verify theoretical values being used to analyze spectra of the solar transition region. The experiments used a beam of multiply charged ions that were extracted from an oscillatory discharge ion source and focused through differential vacuum pumping apertures into an ultrahigh vacuum chamber where the ion beam was crossed with an electron beam. With Peter Smith and others, Bill measured atomic intersystem (spin-changing) line lifetimes used in line-ratio diagnostics of the solar corona. And, Bill arranged for Kouichi Yoshino and Daryl Freeman to move from the Air Force Cambridge Research Laboratory to CfA in 1976 along with their 6.65-m spectrograph and its even bigger vacuum tank and 20-ton, steel and concrete, optical bench that floated on air jacks. The three of them and Smith measured spectra and cross sections of molecules found in diffuse interstellar clouds and planetary atmospheres.
Projects to study the spectrum of the Sun from space continued also. Bill was especially proud that the Solar & Terrestrial Atmospheres Spectrometer instrument was in the first group of experiments chosen for study of potential instrumentation for observations from the Space Shuttle. That whole program was cancelled by NASA, but the productive suborbital rocket spectrometer continued.
Kohl and Bill carried out three more suborbital flights of the Ebert spectrometer in 1973 and 1974 that studied the spectral ranges 117 to 185 nm and 225 to 320 nm. These three flights provided data for a paper on the components of the Balmer-α spectral line of He II in the solar spectrum, a pair of papers on the observations and theoretical analysis of the Mg II h & k lines, and data for the atlas: “Center and Limb Solar Spectrum in High Spectral Resolution: 225.2 to 319.6 nm” by Kohl, Bob Kurucz, and Parkinson. The atlas provided plots of the high-resolution observations along with line identifications from Kurucz’s simulated solar spectrum. This rocket flight also provided the observational data for determining the first positive evidence for the presence of the element boron in the Sun and a value for the solar boron abundance. The latter was used for many years in studies of the formation of the light nuclides in the solar system.
At the Observatory, Bill was a strong supporter of the Library and chaired the Library Committee for many years. As Lecturer in the Department of Astronomy at Harvard, he supervised many graduate and post-doctoral students who were starting their careers — a wonderful mentor to many who remember him fondly.
Many of Bill’s colleagues and students came from other laboratories and countries; this led to collaborations with Wellesley College; Argonne National Laboratory; Imperial College London; the Space Science Department of ESA at ESTEC; the Observatoire de Paris, Meudon; ETH-Zürich; Lund University; University of Padua; National Research Council of Canada; and KEK in Japan. His contributions were recognized by his colleagues worldwide when he was elected President of Commission 14 (Atomic & Molecular Data) of the International Astronomical Union (IAU).
Bill was thus a groundwork figure in getting recognition of the astronomy sub-discipline ‘Laboratory Astrophysics’ by the IAU, as was demonstrated by the creation of today's Laboratory Astrophysics Commission (B5) that addresses the multi-disciplinary atomic, molecular, and surface-property data requirements of modern astronomy and planetary science.
Bill was an enthusiast. He was licensed to raise peacocks and rare pheasants on his 13-acre farm in the town of Harvard, Massachusetts. For a time, he raised Christmas trees; one year, Christmas tree profits were used to buy his sons a pool table. A portion of the land was used as an apple orchard for many years. He and Phyllis travelled the world attending pheasant meetings and acquiring books for Peacock Books, Phyllis’s company that specialized in rare books about birds. Bill loved good food, good wine, vintage port, and very ripe Stilton cheese. In the late ‘60s, he bought a 1936 Bentley drop head coupé (viz., a 2-door, 4-seat convertible — see photo). His colleagues remember many wonderful picnics and dinners hosted by Bill and Phyllis, and when Garton was visiting, it was a treat to see the right-hand-drive Bentley arriving at the Observatory with Parkinson at the wheel and Garton in his bowler hat alongside.
The authors thank Maria McEachern at the John G. Wolbach Library at the Harvard-Smithsonian Center for Astrophysics for her assistance.