Erika Böhm-Vitense, a pioneering researcher in convection and other processes in stellar atmospheres, died in Seattle, Washington, on 21 January 2017. Erika was born on 3 June 1923 to Wilma and Hans Vitense in Kurau, Germany, and was raised in Lübeck, the middle of three sisters. Both of her parents were teachers. Erika started at Tübingen University in 1943, but transferred to Kiel University in 1945 because of the strong physics and astronomy department there. She received her undergraduate Diploma in 1948 and a Ph.D. in 1951 under the supervision of Professor Albrecht Unsöld. Her Ph.D. thesis encompassed two topics: Continuous absorption coefficients as a function of pressure and temperature in the sun and a grid of stellar atmosphere models. She was awarded the prize for the best Ph.D. thesis at Kiel in 1951.
Erika stayed on as a Research Assistant. In 1953 she married fellow Kiel astrophysicist Karl-Heinz Böhm and afterwards was known as Erika Böhm-Vitense. After Karl-Heinz received his Ph.D. in 1954, the couple made a one-year visit to Lick Observatory and the University of California Berkeley. During this visit she had the opportunity to collaborate with Otto Struve and other astronomers who were using observations with large telescopes to unravel the complexities of stellar evolution.
When Erika and Karl-Heinz returned to Kiel, he was on a tenure-track appointment and she became a Privatdozentin, which meant that she was associated with the university but not in a permanent paid position. The same title applied to her when they moved to the University of Heidelberg in 1964. Occasional funding was available to support her work in Germany and on visits to Berkeley, but, as was usual in those times, she was affected by rules prohibiting academic couples from both being hired in the same department. During these years the couple produced four wonderful children: Hans, Manfred, Helga and Eva.
Erika and Karl-Heinz both said that a major factor that attracted them to the fledgling Astronomy Department at the University of Washington (UW) in January 1968 was the presence of a mainframe computer. At Heidelberg they had to ship their IBM cards to Stuttgart University to run their programs and wait days for the results. They also said that Seattle reminded them of Kiel, where they first started their careers. A final non-trivial factor was that one of us (GW) was able to hire Erika as a Senior Research Associate. At last a stable salary! Erika was appointed as a full professor at UW in 1971. Her appointment came right before the end of anti-nepotism rules that prevented many female members of academic couples from obtaining tenure-track university appointments. The department chair had to assure the UW President that Erika worked independently of her husband on research (she did entirely) in order for an exception to be made for her professorial appointment.
Erika's research began on the theoretical side of stellar astrophysics. Her Ph.D. thesis on the relationships between stellar parameters such as temperature and gravity to spectral types and colors was a fundamental contribution. An early interest, as well as a theme that she returned to throughout her career, was the scale-height of convection in stellar interiors. She made important contributions to the “mixing-length” theory that to this day remains a puzzle. Her 1953 paper, in which she applied the mixing length approximation to stellar atmospheres and interiors, has been referenced 279 times from 1955 to 2017. The rotation of stars and turbulence in stellar photospheres were also subjects of her theoretical and observational work for decades. Erika liked to work on real stars: single, binary, and in clusters. In the 1960s and 1970s she combined theory and observations in optical studies of a dazzling variety of objects: helium stars, peculiar A stars, Cepheid variables, supergiants, old giant stars and open clusters, to name a few.
The launch of the International Ultraviolet Explorer (IUE) satellite in 1978 provided Erika with whole new set of observational and theoretical problems to explore. She realized that characteristics of stellar chromospheres are best explored in the ultraviolet and took advantage of IUE's capabilities to study the relationships between stellar temperatures, chromospheric activity, rotation, and convection. Stars with enhanced barium abundances also attracted her attention, and she was able to show that the “barium stars” have white dwarf companions which have influenced the abundances measured in the brighter star in the binary system. Her research continued to blend observations and theory. She and her students delved into the relationships between chromospheres, convective layers and the elusive “mixing-length” (a scale-height measure for convection) in stars of spectral types A and F.
Between 1989 and 1992 Erika produced a three-volume set of textbooks entitled Introduction to Stellar Astrophysics. Volume 1 covers basic stellar parameters, Volume 2 discusses stellar atmospheres, and Volume 3 takes on stellar interiors. Many astrophysics graduate students have dog-eared copies of these books. The many graduate students who took her courses at UW and the students who worked on theses or other research projects with Erika valued both her knowledge and the kindness and respect she showed in all of their interactions with her.
Erika received considerable recognition for her research. In 1966 she received the Annie Jump Cannon Prize from the American Astronomical Society. She was elected a Fellow of the American Association for the Advancement of Science in the 1980s. In 2003 the Deutsche Astronomische Gesellschaft awarded her the Karl Schwarzschild Medal, its top prize for outstanding scientific contributions.
We both knew Erika for many decades and will miss her friendship, kindness, and wisdom. We would like to thank Hans, Manfred, Helga, and Eva Boehm for their help. A valuable reference on Erika's contributions to astrophysics is a review by George Herbig in the volume Stellar and Circumstellar Astrophysics, a 70th birthday celebration for K. H. Böhm and E. Böhm-Vitense. (Ed., G. Wallerstein and A. Noriega-Crespo. San Francisco: Astronomical Society of the Pacific Conference Proceedings, 57 (1994): 3-10).