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Arne Slettebak

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Arne Slettebak
Born(1925-08-08)August 8, 1925
Freistadt Danzig
(nowGdansk,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 anaturalizedAmericanastronomerwho served as chair of the astronomy department at theOhio State Universityfrom 1962 to 1987 and director of thePerkins Observatoryfrom 1959 to 1978.

Slettebak was born in theFree City of Danzigbefore emigrating to the United States at a young age. He obtained a degree in physics in 1945 and adoctoratein astronomy from theUniversity of Chicagoin 1949, the latter under the supervision ofWilliam Wilson Morganwith a thesis onO-typeandB-typestars.

Slettebak joined theOhio State Universityshortly after and was instrumental in re-establishing a separate astronomy department; he retired in 1994. His principal research interests were instellar rotationandBe stars,and he published over 90 papers, abstracts and articles throughout his career. The main-belt asteroid9001 Slettebak,discovered in 1981, was named in his honour.

Early life and education

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Arne Edwin[1]Slettebak was born in theFree City of Danzig(in modern dayGdansk,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 theUniversity of Chicago,graduating with aBSdegree in physics in 1945 and obtaining aPhDin astronomy in 1949.[2]His doctoral dissertation, which he completed under the guidance ofWilliam Wilson Morgan,was concerned with the rotational velocities ofO-typeandB-typestars.[3]As a graduate student, he worked as a research assistant at theYerkes Observatoryconductingastronomical spectroscopyinvestigations.[4]He also contributed to parts of what became theMorgan-Keenan systemtogether with Morgan's other doctoral studentsNancy Grace RomanandWilliam P. Bidelman.[5]

Career

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

After receiving his PhD, Slettebak joined theOhio State Universityas an instructor the same year.[2]He became assistant professor in 1950 and held aFulbright fellowshipat theHamburg Observatoryfor the 1955–56 academic year, where he conducted research on the structures of galaxies.[4]

He was promoted to associate professor in 1958 and then full professor in 1959 when he assumed the role of director of thePerkins Observatoryfrom Geoffrey Keller;[6][7]he would hold this position until 1978.[2]Also in 1959, he took over directorship of theMcMillin ObservatoryfromJ. Allen Hynek.[6][8]

Slettebak was a major force in the re-establishment of a separate astronomy department, which was approved in November 1962.[9]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][8][10]

He also helped forge an agreement between the Ohio State University,Ohio Wesleyan UniversityandLowell Observatoryto move the Perkins Observatory's 69-inchreflecting telescopeto Lowell inFlagstaff, Arizona.[2]A 16-inchSchmidt telescopeand a 32-inch reflector were donated to Perkins and replaced the 69-inch telescope.[11]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][13]It continued serving as the primary research instrument for Ohio State's astronomy department until 1998.[c][2]

Slettebak held anotherFulbright fellowshipsfor the 1974–75 academic year, this time atVienna University.[16]During his career, he also undertook visiting professorships in Vienna andStrasbourg.[2]He was a councilor of theAmerican Astronomical Societyfrom 1964 to 1967 and served in several commissions of theInternational Astronomical Union,including as president of Commission 45 (Stellar Classification) from 1979 to 1982.[2][17]

From 1961 to 1978, Slettebak represented Ohio State on the board of directors of theAssociation of Universities for Research in Astronomy,and was chair of its scientific committee between 1970 and 1973.[2][18]He retired from the astronomy department in 1994, becoming professor emeritus.[2]In 2015, the Ohio State Universityplanetariumwas renamed the Arne Slettebak Planetarium in honour of his legacy.[10]

Research

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

Slettebak's main research interests werestellar rotation,spectroscopy and the study ofBe 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 afterOtto Struveand his collaborators provided conclusive observational evidence for axial rotation in single stars.[19][20]However, afterPol Swingsdetermined that the axial rotation ofbinary starsclose 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.[21]

AfterWorld 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.[22][23]He made extensive measurements of the rotational velocities of stars, initially making use of Struve andGrigory Shajn's graphical model during the 1950s and 60s,[22]and subsequently on with numerical models.[2][24]One of his research projects was conducted jointly withCase Institute of Technologyand sponsored by theOffice of Naval Research.[4]

Slettebak measured Be stars with axial rotational velocities of over 400-500 km/s, which averaged 150 km/s more thanB-type starsas a class.[25][26]He discovered groups of stars that had very low rotational velocities,[27]and also found both that starsat a later stage of their lifewere slower thandwarf starsand thatmetallic-line starshad much smaller rotational velocities than average dwarf stars.[28]Slettebak's data was used byAllan Sandageto show that the lower rotational velocities above the main sequence were consistent with theories of stellar evolution.[29]

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 themain sequenceincreases from low values inF-type starsto a maximum in B-type stars.[26]

In 1955 and 1958, he conducted research in astronomical spectroscopy at theMount WilsonandPalomarobservatories inCalifornia.[4]Slettebak remained active in research even after retirement, publishing the last of his more than 90 papers, abstracts and articles in 1998.[2][10]

Personal life and death

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Slettebak married Constance Lorraine Pixler, a music graduate from theCollege of Wooster,on August 28, 1949;[1]the couple had a daughter and a son.[30]He died on May 20, 1999 at the age of 73 inWorthington, Ohioafter a brief illness.[2][30]Pixler died in 2006 at the age of 82.[31]

Notes

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  1. ^Instruction and research at theMcMillin Observatoryhad already diminished significantly, mainly because its 12.5-inchrefracting telescopewas too small and had, by 1931, been dwarfed by 69-inch telescope present at thePerkins Observatory.[8]
  2. ^Perkins Observatory was already owned byOhio Wesleyan Universityand jointly operated with theOhio State Universityprior to the transfer.[12]
  3. ^In 1998, Ohio State ended its partnership with Ohio Wesleyan andLowell Observatory,and the 72-inch mirror was sold to Lowell.[14][15]

References

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

Sources

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