Jan Hendrik Oort (1900{1992)vdkruit/jea3/homepage/JHOIAU.pdf · variationswith azenith telescope. I...

Jan Hendrik Oort (1900–1992)Observational astronomer

Pieter C. van der KruitJacobus C. Kapteyn Professor of AstronomyKapteyn Astronomical Institute, Groningen

www.astro.rug.nl/∼vdkruit

IAU General Assembly, Vienna, August 2018

Piet van der Kruit Master of the Galactic System

Background


I Based on my biography of Oort.

I To appear in 2019.

I Springer Astrophysics & SpaceScience Library.

I ‘Sequel’ to Kapteyn; similarset-up, etc.

I Also about 700 pages.


I Oort grew up in Oegstgeest nearLeiden.

I His father was a psychiatrist, but hisancestors were all clergymen.

I Oort went to study physics orastronomy in Groningen because ofthe fame of Jacobus Kapteyn.

I Willem de Sitter had reorganizedLeiden Observatory, but could not getAntoon Pannekoek hired for theAstrometric Department.

I So he offered Oort a job in Leiden, butfelt he needed observational(astrometric) experience first.


I Oort about Kapteyn:Two things were always prominent:first the direct and continuous relationto observations, and secondly toalways aspire to, as he said, lookthrough things and not be distractedfrom this clear starting point by vagueconsiderations.


Yale Observatory


I De Sitter got Frank Schlesingerto offer Oort a fellowship atYale Observatory.

I Oort worked at Yale from1922-1924.

I The research was on latitudevariations with a zenithtelescope.

I Use of star trails near zenith ofstars of known declination;switch direction halfway thenight.


I Oort observed for two years(except for a few months ofmilitary service).

I After that Oort moved toLeiden Observatory.

I Here he worked on astrometricproblems but mainly on histhesis work concerning stars ofhigh velocity.

I Yale data eventually proveduseless, because of platemovements in plate holder.


I Already as a student thehigh-velocity starsintrigued him.

I They seemed to comefrom only one hemisphereof the celestial globe.

I Now known to be halopopulation.


I In 1927 Oort obtained his PhD in Groningen with Pieter vanRhijn as supervisor.


I Thesis did not solve the problemof high-velocity stars.

I Also in 1927 Oort married hiswife Mieke.


I Oort worked on GalacticStructure:

I Galactic differentialrotation.

I Vertical force Kz.I Galactic structure

including absorption.

I Used stellar dynamics,founded by ArthurEddington amd JamesJeams.


Perkins Observatory


I Oort became interested in photometry of extragalactic nebulae.

I Oort had two important job offers:I Harvard 1928.

Too much teaching, no formalrelation with the Observatory andobserving facilities.

I Columbia 1930.No commitment for a telescope(60-70 inch reflector in the south).


Harlan Stetson, director of Perkins.

I IAU General Assembly inCambridge, Mass. (1932).

I Oort went to PerkinsObservatory afterwardsfor a few months.

I New 69-inch telescope inDelaware, Ohio.

I Largest telescope in USA,except for Mount Wilson100-inch.


I Aim was to obtain platesof galaxies for surfacephotometry.

I Poor weather (no surprisein Ohio).

I Did get some materialthough.


I Mieke Oort ‘assisted’ him.

I In the end plates provedunsuitable.

I Reason shift of mirrorwith hour angle.

I Pieter Oosterhoff, fellowat Mount Wilson, tooksome plates on 60-inchTelescope.


I Staff Leiden Observatory in 1931 (insert Oosterhoff).

I First row: Coert Hins, Oort, Ejnar Hertzsprung, de Sitter, Jan

Woltjer.


Mount Wilson Observatory


I In 1939 Oort tried again.

I Occasion wasinauguration McDonaldObservatory in Texas.

I Oort was a prominentspeaker at thesymposium.

I Here Oort presented hisfamous 1940-paper onvertex deviation andgalaxy dynamics.


0

I Presented photometry oftwo systems fromOosterhoff’s plates.

I Outlined deprojectionanalysis and dynamicalstudies of externalgalaxies.

I Applied to NGC 3115with spectral data byMilton Humason.

I Inconsistent due toincorrect velocities.


I Afterwards Oort went toMount Wilson, where heobserved with the 60-inchand 100-inch telescopes.

I He took 60 plates of 17galaxies (withOosterhoff’s plates thisgave a sample of 20).

I Calibration was throughsensitometer spots andout-of-focus exposures inKapteyn Selected Areas.


McDonald Observatory


I Calibration ambiguous betweenspots and SA’s.

I In 1947 Oort spent a few monthsat Yerkes.

I He obtained observing time atMcDonald 82-inch with WilliamHiltner to try photoelectricphotometry.

I Oort also visited Pasadena and Palomar Mountain; was one ofthe first to look through the 200-inch.


I Obtained photoelectricphotometery of 7 galaxies.

I Data reduced by Kees vanHouten; published in1954.

I Proved out-of-focus SAstars as correctcalibration.

I This opened the way to reduction of plate material.


Kees van Houten, Gart Westerhout,

King Kwee, Maarten Schmidt 1953.

I In 1960 van Houtenpresented a PhD thesiswith surface photometryof the twenty galaxies.

I Some of the very firsttwo-dimensional surfacebrightness maps of asubstantial sample ofgalaxies.


Conclusions


I Oort was more an observational astronomer rather than atheoretician.

I Extensively trained by Schlesinger.

I American job offers declined mostly because of lack of accessto telescopes.

I Oort’s work on stellar dynamics was built on fundamentaltheory by Eddington and Jeans and theoretial work of Lindblad.

I Between 1930 and 1950 he observed extensively to dophotographic surface photometry of galaxies.


Jan Hendrik Oort (1900{1992)vdkruit/jea3/homepage/JHOIAU.pdf · variationswith azenith telescope. I...

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