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Arne Slettebak

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Arne Slettebak
Born(1925-08-08)August 8, 1925
Freistadt Danzig
(now Gdansk, Poland)
DiedMay 20, 1999(1999-05-20) (aged 73)
Worthington, Ohio, United States
CitizenshipUnited States (1932–1999)
Alma materUniversity of Chicago (BS, PhD)
Spouse
Constance Pixler
​
(m. 1949)​
Children2
Scientific career
FieldsAstronomy
Institutions
ThesisOn the Axial Rotation of the Brighter O and B Stars (1949)
Doctoral advisorWilliam Wilson Morgan

Arne Edwin Slettebak (August 8, 1925 – May 20, 1999) was a naturalized American astronomer who served as chair of the astronomy department at the Ohio State University from 1962 to 1987 and director of the Perkins Observatory from 1959 to 1978.

Slettebak was born in the Free City of Danzig before emigrating to the United States at a young age. He obtained a degree in physics in 1945 and a doctorate in astronomy from the University of Chicago in 1949, the latter under the supervision of William Wilson Morgan with a thesis on O-type and B-type stars.

Slettebak joined the Ohio State University shortly after and was instrumental in re-establishing a separate astronomy department; he retired in 1994. His principal research interests were in stellar rotation and Be stars, and he published over 90 papers, abstracts and articles throughout his career. The main-belt asteroid 9001 Slettebak, discovered in 1981, was named in his honour.

Early life and education

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Arne Edwin[1] Slettebak was born in the Free City of Danzig (in modern day Gdansk, Poland) on August 8, 1925 to Norwegian parents. His family emigrated to the United States in 1927, and he gained citizenship in 1932.[2] He studied at the University of Chicago, graduating with a BS degree in physics in 1945 and obtaining a PhD in astronomy in 1949.[2] His doctoral dissertation, which he completed under the guidance of William Wilson Morgan, was concerned with the rotational velocities of O-type and B-type stars.[3][4] As a graduate student, he worked as a research assistant at the Yerkes Observatory conducting astronomical spectroscopy investigations.[5] He also contributed to parts of what became the Morgan-Keenan system together with Morgan's other doctoral students Nancy Grace Roman and William P. Bidelman.[6]

Career

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A photo of the building housing the McMillin observatory taken in 1971.
Site of the McMillin Observatory pictured in 1971
A photo of the main facade of the Perkins Observatory with two trees in front of it.
Main facade of the Perkins Observatory

After receiving his PhD, Slettebak joined the Ohio State University as an instructor the same year.[2] He became assistant professor in 1950 and held a Fulbright fellowship at the Hamburg Observatory for the 1955–56 academic year, where he conducted research on the structures of galaxies.[5]

He was promoted to associate professor in 1958 and then full professor in 1959 when he assumed the role of director of the Perkins Observatory from Geoffrey Keller;[7][8] he would hold this position until 1978.[2] Also in 1959, he took over directorship of the McMillin Observatory from J. Allen Hynek.[7][9]

Slettebak was a major force in the re-establishment of a separate astronomy department, which was approved in November 1962.[10] He became chair of the newly-independent entity and remained in this position until 1987.[2] From 1964 to 1968, he supervised the department's move from the McMillin Observatory, whose building had been deemed too small and unsafe, and Orton Hall to its current location at the Smith Physics Laboratory.[a][9][12]

He also helped forge an agreement between the Ohio State University, Ohio Wesleyan University and Lowell Observatory to move the Perkins Observatory's 69-inch reflecting telescope to Lowell in Flagstaff, Arizona.[2] A 16-inch Schmidt telescope and a 32-inch reflector were donated to Perkins and replaced the 69-inch telescope.[13] After its transfer, the telescope's optics were upgraded to a 72-inch mirror and it was used jointly by the two universities and the observatory.[b][2][15] It continued serving as the primary research instrument for Ohio State's astronomy department until 1998.[c][2]

Slettebak held another Fulbright fellowship for the 1974–75 academic year, this time at the University of Vienna.[18] During his career, he also undertook visiting professorships in Vienna and Strasbourg.[2] He was a councilor of the American Astronomical Society from 1964 to 1967 and served on several commissions of the International Astronomical Union, including as president of Commission 45 (Stellar Classification) from 1979 to 1982.[2][19]

From 1961 to 1978, Slettebak represented Ohio State on the board of directors of the Association of Universities for Research in Astronomy, and was chair of its scientific committee between 1970 and 1973.[2][20] He retired from the astronomy department in 1994, becoming professor emeritus.[2] In 2015, the Ohio State University planetarium was renamed the Arne Slettebak Planetarium in honour of his legacy.[12]

Research

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Slettebak found that the rotational velocities of stars along the main sequence (visible here as a prominent diagonal band from upper left to lower right) increase from low values in F-type stars to a maximum in B-type stars.

Slettebak's main research interests were stellar rotation, spectroscopy and the study of Be stars; for the latter subject, he organised multiple colloquia at the International Astronomical Union.[2]

The topic of stellar rotation been in a 'golden age' during the 1930s after Otto Struve and his collaborators provided conclusive observational evidence for axial rotation in single stars.[21][22] However, after Pol Swings determined that the axial rotation of binary stars close to each other and with short periods tends to be approximately or perfectly synchronized with orbital motion, the field was abandoned for around 15 years.[23]

After World War II, interest in measurements of stellar axial rotation was renewed by Slettebak, who published a series of papers on the topic starting in 1949.[24][25] He made extensive measurements of the rotational velocities of stars, initially making use of Struve and Grigory Shajn's graphical model during the 1950s and 60s,[24] and subsequently on with numerical models.[2][26] One of his research projects was conducted jointly with Case Institute of Technology and sponsored by the Office of Naval Research.[5]

Slettebak measured Be stars with axial rotational velocities of over 400-500 km/s, which averaged 150 km/s more than B-type stars as a class.[27][28] He discovered groups of stars that had very low rotational velocities,[29] and also found both that stars at a later stage of their life were slower than dwarf stars and that metallic-line stars had much smaller rotational velocities than average dwarf stars.[30] Slettebak's data was used by Allan Sandage to show that the lower rotational velocities above the main sequence were consistent with theories of stellar evolution.[31]

Later in his career, Slettebak compiled the main results of statistical studies on stellar rotation conducted between 1930 and 1970, determining that the distribution of rotational velocities for stars along the main sequence increases from low values in F-type stars to a maximum in B-type stars.[28]

In 1955 and 1958, he conducted research in astronomical spectroscopy at the Mount Wilson and Palomar observatories in California.[5] Slettebak remained active in research even after retirement, publishing the last of his more than 90 papers, abstracts and articles in 1998.[2][12]

Personal life and death

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Slettebak married Constance Lorraine Pixler, a music graduate from the College of Wooster, on August 28, 1949;[1] the couple had a daughter and a son.[32] He died on May 20, 1999 at the age of 73 in Worthington, Ohio after a brief illness.[2][32] Pixler died in 2006 at the age of 82.[33]

Notes

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  1. ^ Instruction and research at the McMillin Observatory had already diminished significantly, mainly because its 12.5-inch refracting telescope was too small and had, by 1931, been dwarfed by 69-inch telescope present at the Perkins Observatory.[11]
  2. ^ Perkins Observatory was already owned by Ohio Wesleyan University and jointly operated with the Ohio State University prior to the transfer.[14]
  3. ^ In 1998, Ohio State ended its partnership with Ohio Wesleyan and Lowell Observatory, and the 72-inch mirror was sold to Lowell.[16][17]

References

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  1. ^ a b "Daughter of Former Athol Pastor Will Become Bride Sunday". Athol Daily News. August 18, 1949. p. 3. Retrieved July 2, 2024 – via Newspapers.com.
  2. ^ a b c d e f g h i j k l m n o p Pogge & Newsom 2000, pp. 1686–1687.
  3. ^ "Alumni: Arne E. Slettebak, 1949". University of Chicago. Archived from the original on December 14, 2023. Retrieved December 14, 2023.
  4. ^ Slettebak 1949.
  5. ^ a b c d "Astronomical Lectures Set At University". The Columbia Record. March 20, 1961. p. 12. Retrieved July 24, 2024 – via Newspapers.com.
  6. ^ Osterbrock 1997, p. 305.
  7. ^ a b Jossem 1969, pp. 70, 102.
  8. ^ "OSU Board Upholds Oath". The Daily Sentinel-Tribune. December 12, 1959. p. 2. Retrieved July 24, 2024 – via Newspapers.com.
  9. ^ a b Wenning 2020, p. 18.
  10. ^ Jossem 1969, pp. 69.
  11. ^ Wenning 2020, p. 16.
  12. ^ a b c "OSU Planetarium to be named for Professor Arne Slettebak". The Ohio State University. April 15, 2015. Archived from the original on June 4, 2024. Retrieved December 15, 2023.
  13. ^ "Giant Scope Readied for Arizona Trip". The Plain Dealer. March 4, 1961. p. 4. Retrieved July 24, 2024 – via Newspapers.com.
  14. ^ "New Observatory To Be Built At Perkins South of Delaware". The Marion Star. March 18, 1960. p. 12. Retrieved July 24, 2024 – via Newspapers.com.
  15. ^ Hoyt, William (January 7, 1960). "5th Largest Reflector To Locate Here". Arizona Daily Sun. p. 1. Retrieved July 24, 2024 – via Newspapers.com.
  16. ^ Eicher, David J. (May 18, 2023). "America's observatory enters a new age". Astronomy.com. Archived from the original on February 21, 2024. Retrieved July 24, 2024.
  17. ^ "About OSU Astronomy". The Ohio State University. Archived from the original on July 3, 2024. Retrieved July 24, 2024.
  18. ^ "Arne Slettebak". Fulbright Program. Archived from the original on July 23, 2024. Retrieved July 24, 2024.
  19. ^ "Arne Slettebak". International Astronomical Union. Archived from the original on May 22, 2024. Retrieved July 25, 2024.
  20. ^ "Arne Slettebak" (PDF). Department of Astronomy Magazine. The Ohio State University. 2004. p. 31. Archived (PDF) from the original on March 30, 2024. Retrieved July 31, 2024.
  21. ^ Hearnshaw 1990, p. 199.
  22. ^ Tassoul 2000, p. 3.
  23. ^ Tassoul 2000, pp. 3–4.
  24. ^ a b Tassoul 2000, p. 4.
  25. ^ Hearnshaw 1990, pp. 199–200.
  26. ^ Diaz et al. 2011, p. 1.
  27. ^ Hearnshaw 1990, pp. 199, 332.
  28. ^ a b Tassoul 2000, p. 12.
  29. ^ Hearnshaw 1990, p. 200.
  30. ^ Hearnshaw 1990, pp. 200, 349.
  31. ^ Hearnshaw 1990, p. 349.
  32. ^ a b "Deaths: 1940s and 1950s". Class Notes. The University of Chicago Magazine. Vol. 92, no. 4. University of Chicago. April 2000. Archived from the original on June 20, 2010. Retrieved July 2, 2024.
  33. ^ "Constance Slettebak Obituary". The Columbus Dispatch. December 10, 2006. Archived from the original on July 24, 2024. Retrieved July 24, 2024 – via Legacy.com.

Sources

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