BLAAUW’S PREDECESSORS IN GRONINGEN: J.C. KAPTEYNkhan/blaauw100/presentations/01-vdKruit.pdf ·...

Jacobus Cornelius KapteynKapteyn’s works

Kapteyn’s LegacyConclusions

BLAAUW’S PREDECESSORS IN GRONINGEN:J.C. KAPTEYN

Pieter C. van der KruitJacobus C. Kapteyn Professor of Astronomy

Kapteyn Astronomical Institutewww.astro.rug.nl/∼vdkruit

Groningen – April 7, 2014

Piet van der Kruit, Blaauw-100 Blaauw’s predecessors in Groningen: J.C. Kapteyn



Jacobus Cornelius KapteynEarly yearsUtrecht and LeidenAccidental astronomer?Groningen

Kapteyn’s worksCape Photographic DurchmusterungParallaxesStar StreamsPlan of Selected AreasKapteyn Universe

Kapteyn’s Legacy

Conclusions




I I will talk only about Kapteyn,leaving P.J. van Rhijn and therest to David Baneke.

I What I will be presenting isbased on a biography that I amwriting.

I Expected to be published sometime this fall.




Early yearsUtrecht and LeidenAccidental astronomer?Groningen

Jacobus Cornelius Kapteyn(1851–1921)





Early years

I We know most about his youngeryears from the biography by HenriettaHertzsprung-Kapteyn (1928).





I Kapteyn was born on January19, 1851 in the municipality ofBarneveld.

I His parents were Gerrit JacobusKapteyn (1812–1879) andElisabeth Cornelia Koomans(1814–1896).

I They ran a boarding school forboys.





I He was the tenth child of fifteen.

I This is a family reunion around 1877.





I Kapteyn was educated at theboarding school of his parents.

I He lster complained of lack ofattention by his parents.





I He must have had an interest in astronomy from an early age.

I As a teenager he produced a starmap.





I Apparently the boarding school had a small ‘observatory’.

I He enrolled at the University of Utrecht in 1868 to studymathematics and physics.





Utrecht and Leiden

I He studied with C.H.D. BuysBallot (1831–1899) and C.H.C.Grinwis (1818–1890).

I And obtained his PhD in 1875under Grinwis.

I The title was ‘A study ofvibrating, flat membranes’.





I After his studies he wasappointed ‘observator’ at LeidenObservatory.

I He worked there under thedirector Hendricus G. van deSande Bakhuyzen.

I His work was mainly astrometry.





Accidental astronomer?

I Adriaan van Maanen1 in his obituary:

I ‘... his doctoral thesis was in physics: “Onderzoek der TrillendePlatte Vliezen”.Just at this time, however, the position of observer at theLeiden Observatory was vacant, and Kapteyn applied for andobtained the position.By this accidental circumstance astronomy secured the privilegeof counting Kapteyn as one of its workers and before long asone of its foremost leaders.’

I James Jeans2:I ‘It would appear that during his student days Kapteyn was

not particularly attracted to astronomy, ...’

1Astrophysical Journal 56, 145-153 (1922).2Monthly Notices Royal Astronomical Society 83, 250 (1923).





I I discovered a letter of van de Sande Bakhuyzen to the Ministerdefending his choice for Kapteyn as ‘observator’.

I Kapteyn did as much astronomy as possible in Utrecht, butcould not do a PhD thesis there at that time.

I Kapteyn tried to move to Leiden to do a thesis, but wasprohibited by finances.

I Van de Sande Bakhuyzen thought of Kapteyn, when Valentinerleft.

I He actually had Kapteyn on trial in Leiden for a few months.

I Kapteyn certainly did not enter astronomy ‘by accident’.





Groningen

I He was appointedProfessor of astronomyand theoreticalmechanics in 1877 atthe University ofGroningen and he tookup his chair in 1878.

I He married Catharina Elisabeth (Elise) Kalshoven (1855–1945)on July 16, 1879.





I In spite of many efforts he failed to obtain his own observatory.

I Some of this is due to obstruction by Leiden and Utrecht.




Cape Photographic DurchmusterungParallaxesStar StreamsPlan of Selected AreasKapteyn Universe

Kapteyn’s works





Cape PhotographicDurchmusterung

I David Gill (1843–1914) at theRoyal Observatory at Cape ofGood Hope wanted to producea photographic durchmusterung.

I Kapteyn offered to measureGill’s plates and produce thestar positions and magnitudes.

I The Cape PhotographicDurchmusterung (454,875 stars)was published in three volumesin 1896, 1897 and 1900.





I Henriette Hertzsprung-Kapteyn:I ‘During the Christmas holidays of 1885 he read in Leiden in an

astronomical journal an article by David Gill, Her Majesty’sastronomer at Cape of Good Hope, about a major project hewanted to undertake. He was planning to produce a catalog ofthe stars in the southern hemisphere down to magnitude 10 andusing photographic methods.’

I ‘Instantly, the thought occurred to Kapteyn: ‘Here is mychance!’. He immediately wrote to Gill and offered tocollaborate with him.’

But that is not the way it happend!





I Declinations were very inaccurate.

I Due to unknown amounts of flexure in the telescope andrefraction (‘bending’) of light in the atmosphere.

I He published a Copernicus paper in 1883:





I Kapteyn devised a method tomeasure absolute declinatons,using only azimuths, differencesin comparable zenith distances ifyou already know the pole’saltitude.

I Then he devised a method tomeasure that using also onlythese and timing of passage ofthe prime vertical.

I He tested it in Leiden with theuniversal instrument.

I He contacted Gill, who startedan observational program ...

I ... and Gill lured Kapteyn into offering his services for the CPD.





I He devised theparallactic methodand measured thepositions andmagnitudes of454,875 stars.

I The method means that you ‘observe’ the plate with a smalltelescope at the same distance as that of the focus in thetelescope.





I He was given two smallrooms in the laboratory ofG. Heymans (1857–1930),professor of psychologyand philosophy.

I The Cape PhotographicDurchmusterung waspublished in threevolumes, between 1896and 1900.





Stellar parallaxes

I Kapteyn felt that progressrequired the measurement ofparallaxes on a grand scale.

I Even before the CPD, he triedto measure annual parallaxes bydifferential meridian timingmeasurements.

I If parallax is 0.1 arcsec and itsdeclination 50◦, then parallaxcorresponds to time differenceof 0.02 seconds of time.

I So you need extremely accuratetimings.





I Only possible with manyrepeated measurements.

I Kapteyn used on theLeiden meridian circlewith a ‘Registrir-Apparat’or strip recorder (spring1885, Christmas 1885 and1886, and in spring 1887).

I He selected 15 stars with high proper motion that may be nottoo distant.

I Results published in Astronomische Nachtichten (preliminary)in 1889 and in Annalen van de Sterrewacht te Leiden in 1891.





Star pKapteyn HD pmodern Remarksmilli-arcsec milli-arcsec

BB VII 81 (pr.) 74± 27 79210 172.06± 6.31 Flare star; binary79211 156.45± 8.58 Flare star; binary

θ Ursa. Maj. 52± 26 82328 74.19± 0.16 Spectroscopic binaryBB VII 85 64± 22 84031 54.89± 0.92 Variable star20 Leon. Min. 62± 29 86728 66.46± 0.32 High proper-motion starBB VII 89 176± 24 88230 205.21± 0.34 Flare starBB VII 94 101± 26 90508 43.65± 0.43 High proper-motion starBB VII 95 38± 27 91347 26.48± 0.59 High proper-motion starLal. 20670 −6± 28 92855 26.84± 0.50 Star in double systemBB VII 104 428± 30 95735 392.64± 0.67 Flare starBB VII 105 168± 27 – 206.27± 1.00 High proper-motion starBB VII 110 30± 27 101177 43.01± 0.73 Spectroscopic binaryBB VII 111 16± 32 102158 20.29± 0.70 Star in double systemBB VII 112 139± 26 103095 109.99± 0.41 High proper-motion starBB VII 114 −28± 42 104556 17.5 ± 0.51 High proper-motion starBB VII 119 56± 34 105631 40.77± 0.66 High proper-motion star

This really is very, very good!!





I He proposed to measureparalaxes from multipleexposures.

I Not adopted for the Cartedu Ciel.

I Kapteyn realised thatparallaxes are too small tomeasure except for thenearest stars.

I Solution is to usestatistical methods usingproper motions for‘secular’ parallaxes.





I Anders Donner (1854–1938)from Helsingfors provided himwith many plates for bothproper motions and parallaxdeterminations.

I He had met Donner at themeeting of the Carte du Ciel inParis in 1887.





Star Streams

I Kapteyn devoted his carreer tothe problem of the Structure ofthe Sidereal System.

I He used proper motions forstatistical distances andassumed that

I Luminosity curve everywherethe same.

I Stellar motions in space haveno prefered direction.

I No insterstellar absorption.





I Kapteyn build amathematical structure tofind the space distributionof stars from counts andproper motions.

I However, then he discovered the Two Star Streams, showingtwo opposite, preferred directions.





I He first presented that at aCongress during the 1904Louisiana Purchase Exposition.

I This was organized by SimonNewcomb (1835-1909) of NavalObservatories, who had visitedKapteyn in Groningen.

I This introduced him toAmerican astronomy,particularly Hale at MountWilson and Pickering atHarvard.





I The concept of Star Streamswas quickly confirmed, a.o. byArthur Eddington (1882–1944).

I However, Karl Schwarzschild(1873–1916) proposed ananisotropic velocity ellipsoid.

I Kapteyn and for a long timeEddington did not accept this,as the properties of stars in bothstreams were differrent.

I Kapteyn had to find a new way to determine the distribution ofstars in space.





Plan of Selected Areas

I He devised the Plan of SelectedAreas, which he discussed withmany colleagues, starting in St.Louis and later in Capetown.

I Eventually it became 120 areasacross the sky (+46).

I All measurable properties ofstars should be determined.





I In St. Louis he met George E.Hale, who adopted the ‘Plan’ asprime program for his new60-inch telescope.

I Kapteyn was appointed staffassociate for three months/year.

I He went to Mt. Wilson eachyear from 1908 to 1914.





I Kapteyn took very much acoordinating role in the SelectedAreas project.

I Plates were measured in hisAstronomical Laboratory; an‘observatory without atelescope’.

I It did come along reasonablywell, certainly as far as starcounts were concerned withplates taken at Harvard andMount Wilson.





I The problem Kapteyn worriedabout very much was that ofextinction by interstellar dust.

I He assumed Thompsonscattering and predictedselective absorption.

I He found about 0.3 mag kpc−1.

I With appreciable absorption wewould be in a special positionnear the highest star density.

I Shapley found very littlereddening towards globularclusters.

I This led him to provisionally analyse star counts for the case ofa transparent space.





Kapteyn Universe

I In the end he produced the KapteynUniverse with the Sun away from thecenter.

I He did derive a correct verticaldistribution.

I Using velocities he laid the foundationsfor studies of galactic dynamics.

I First determination of local massdensity (Oort limit).




Kapteyn’s Legacy




I Kapteyn introduced the concept of the astronomical laboratory.

I It remained small (professor + assistant).




Assistants:Veenstrade SitterWeersmaZernikevan RhijnKreiken(unpaid)

I Pieter van Rhijn (1886–1960) had done a PhD thesis in 1915.

I Change of colour with distance and apparent magnitude and ofmean parallax with magnitude and proper motion

I Was appointed Kapteyn’s successor in 1921.




I Leiden Observatory presentedmore opportunitites.

I Kapteyn took part in thereorganisation in 1918.

I De Sitter (professor since 1908became director and led thetheoretical department.

I Hertzsprung started theastrophysics department.

I Kapteyn became part-timeadjuct-director and led theastrometry department.

I Pannekoek rejected butappointed in Amsterdam.




I The Kapteyns first stayed with their daughter in Amsterdam,bit bought a house in Hilversum to live the rest of their lives.




I Kapteyn never did live there.

I After a prolonged illness (Kahler’s disease?) he died on June18, 1922 in Amsterdam.




Conclusions




Some points to take away from all of this.

I Kapteyn was not an ‘accidental’ astronomer, but already at ayoung age wanted to become one.

I Kapteyn did not offer Gill his CPD assistance out of the blue;they were already collaborating and Gill had carefully nursedhim into offering this.

I Although Kapteyn induced that absorption would givereddening and subsequently found a reasonable value for it,Shapley’s absence of absorption towards globular clusters atleast contributed to his neglect of it.

I Kapteyn left a strong Dutch school of astronomy with deSitter, Hertzsprung (and Oort) in Leiden, van Rhijn inGroningen and Pannekoek in Amsterdam.

I (Not covered). All his students testify that Kapteyn was a veryinspiring teacher.


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