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THE PLEIADES an Astrometric and Photometric Study of an Open Cluster

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THE PLEIADES an Astrometric and Photometric Study of an Open Cluster iNis-mf—9022 r THE PLEIADES an astrometric and photometric study of an open cluster «•••—I 1—24° FLOOR VAN LEEUWEN THE PLEIADES an astrometric and photometric study of an open cluster THE PLEIADES an astrometric and photometric study of an open cluster proefschrift ter verkrijging van de graad van Doktor in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit te Leiden, op gezag van de Rector Magnificus Dr. A.A.H. Kassenaar, hoogleraar in de Faculteit der Geneeskunde, volgens het besluit van het College van Dekanen te verdedigen op donderdag 26 mei 1983 te klokke 15.15 uur door Floor van Leeuwen geboren te Amsterdam in 1952 Sterrewacht Leiden Royal Greenwich Observatory, U.K. 1983 Beugelsdijk Leiden B.V. De beoordelingscommissie bestond uit de volgende leden: Professor Dr. A. Blaauw, promotor Dr. J. Lub, referent Professor Dr. J.H, van der Waals voorzitter van de Subfaculteit Sterrenkunde en Natuurkunde Professor Dr. H.C, van de Hulst Professor Dr. W.B. Burton Professor Dr. C, Zwaan Errata page tU Reference 3 read '18UU' instead of '1W 16 Reference 23 read '19«6' instead of '19U51 70 2nd par., 5th line read 'surface gravity' instead of 'temperature' 80 Tabled add: 1531. m=1?.5B, obs: 1931. per .a!' ."^hr, flares: ? 112 Equ.16 read 'n(n»nCi)' instead of 'n(l)1 116 Equ.32 read ' (x(0.i)a+ yC'l.if )' instead of • (x(o,i)+y(n,i))' STELLINGEN behorende bij het proefschrift De PLEIADEN, An Astrometrie and Photometric Study of an Open Cluster 1. De onzekerheid in de ruimtelijke snelheden zoals die door O.J.Eggen in 1963 (Astronomical Journal Vol 68, p 697) zijn bepaald voor heldere A type sterren bedraagt ten minste ^7 km/sec. 2. De details welke Eggen(1963) in de verdeling van ruimtelijke snelheden onderscheidt zijn significant kleiner dan 7 km/sec en daardoor statistisch niet te rechtvaardigen. 3. Het bestaan van een "Pleiades Moving Group" is door Eggen(1963) geenszins aangetoond, H, Discrepanties tussen cluster leeftijden zoals afgeleid van pre en post hoofdreeks ster evolutie modellen duiden niet noodzakelijk enkel op een spreiding in leeftijden voor cluster leden maar kunnen ook deels het gevolg zijn van onvolledigheid in de beschrijving van het sterevolutie proces. (R.Stauffer, 1979: Astron.Journal Vol 85, p 1341) 5. De klassieke astronomische waarneem technieken, zoals astrometrie en fotometrie, bieden nog volop mogelijkheden tot het verkrijgen van nieuwe gezichtspunten in de sterrenkunde. 6. Het onderzoek naar variabele sterren dient gestimuleerd te worden. 7. In het kader van de Brits-Nederlandse samenwerking met betrekking tot de sterrenwacht op La Palma dient een eenvoudige vergelijk fotometer ontwikkeld te worden. 8. De variabele sterren welke geklassificeerd worden als BY Dra, RS CVn, CC Eri, FK Com en de K sterren in de Pleiaden zijn allen in eerste instantie variabel door een interactie tussen de hoge hoeksnelheden en de convectie zones die al deze sterren gemeen hebben. (sectie 3.3 van dit proefschrift) 9. Door bezuinigingen op posities wordt veel wetenschappelijk werk sterk vertraagd in afronding en publikatie. 10. Het classificeren van nog niet verklaarde visuele en radar waarnemingen als UFO onttrekt mogelijk interessante waarnemingen aan wetenschappelijk onderzoek. 11. Het verdient aanbeveling de onderverdeling van het genus Aloe te herzien en daarbij, in navolging van het onderscheid met Haworthia's en Gasteria's, de nadruk te leggen op de verschillende bloeiwijzen eerder dan de verschillen in groeivorm. (G.W.Reynolds, The Aloes of South Africa, 1976, A.A.Balkema, Rotterdam) 12. De plantengroei en zijn aanpassing aan het heersende klimaat kan veel informatie verschaffen over de langere termijn betrouwbaarheid van de klimaats omstandigheden rond een astronomisch waarneem station. aan Gtoèka en Magda Contents Historical development leading to the present work 8 1.1 The Pleiades as observed from 1829 to 1950 8 1.3 Outline of the present work 13 Notes to the presentation 13 References 14 The astrometric measurements and their reduction 17 2.0 Summary 17 2.1 Introduction 18 2.2 The astrometric measurements 21 2.2.1 The ASTROSGAN as astrometric measuring device 21 2.2.2 The photometric and positional parameters 21 2.2.3 The interpretation of the photometric parameters 26 2.2.1 The positional accuracies 30 2.3 Construction of the reference frame of positions 31 2.3.1 The preparatory catalogue of star positions 31 2.3.2 The ideal picture 33 2.3.3 The transformations 35 2.3.3.1 Transformations between linear pictures for different plate centres 35 2.3.3.2 Transformations between linear and ideal pictures 36 2.3.4 The influence of the earth atmosphere 36 2.3.5 Aberrations 40 2.3.6 The central 3 by 3 degrees field 41 2.3.7 Construction of the catalogue of 1978 positions 43 2.4 Determination of the proper motions 48 2.4.1 Reducing old epoch plates to new epoch reference positions 48 2.4.2 Definition of the proper motion system in the central region 48 2.4.3 The proper motions in the outlying regions 50 Appendix 1 Definition of the proper motions 51 Appendix 2 Updating mechanism for proper motions 51 References 52 The photometric observations, differential reddening and the variable K-stars in the Pleiades 53 3.0 Summary 53 3.1 VBLUW photometry of the Pleiades and a determination of its distance 54 3.1.0 Summary 54 3.1.1 Introduction 55 3.1.2 Selection of stars 56 3.1.3 The measurements 57 3.1.4 Identification of members 58 3.1.5 The distance to the Pleiades 59 3.2 Differential reddening in the Pleiades 67 3.2.0 Summary 67 3.2.1 Introduction 67 3.2.2 Empirical reddening corrections 68 3.2.3 Theoretical grid reddening corrections 69 3,3 Variable K-type stars in the Pleiades 73 3.3.0 Summary 73 3.3.1 Introduction 73 3.3.2 The photometric measurements 75 3.3.2.1 1980 measurements 75 3.3.2.2 1981 measurements 78 3.3.3 The photometric data and their interpretation 79 3.3.3.1 The Hghtourves and periods 83 3.3.3.2 The colour indices 79 3.3.H Spectroscopie observations 86 3.3.5 Rotational modulation 86 3.3.6 The angular momentum 89 3.3.7 Future prospects 90 References 91 4. On the distribution of masses and motions in the Pleiades 95 4,0 Summary 95 1 Introduction 96 4.2 The density distributions 98 4.2.1 The counts 98 4.2.2 Surface and space density distributions 100 4.2.3 The noise level of the density distribution 104 4.3 The occurrence of hard binaries 105 4.4 The luminosity and mass functions 109 4.4.1 The observed luminosity function 109 4.4.2 The fainter extension 111 4.5 The internal motions 113 4.5.1 The influence of plate reductions on proper motions 113 4.5.2 The influences of the motion of the Sun relative to the cluster 115 4.5.2.1 The relative radial velocity 115 4.5.2.2 The relative secular parallax 117 4.5.2.3 On the detection of real rotation and expansion 119 4.5.3 The internal velocities 119 4.6 The potential energy distribution and the total mass of the Pleiades 121 4.7 The Galactic tidal force and mass segregation 125 4.8 Conclusions 127 References 129 Nederlandse samenvatting 132 Studie overzicht 137 Dankwoord 138 1. Historical development leading to the present work 1.1 The Pleiades as observed from 1829 to 1950 The Pleiades are among the oldest observed objects In the sky. Refer- ences to them date back more than 4500 years. Also positional research on the cluster is relatively old. It started with the mapping of the cluster by Galilei (1); in 1653 the first map based on his telescope observations was published. The first reasonably accurate relative positions of stars in the Pleiades were provided In 1755 by Le Monnter (2). All positional work those days was performed using meridian telescopes and had as Its main purpose the provision of a reference frame for the determination of the positions of the Moon and Planets and for navigation. The positions of the Pleiades were especially used to determine the parallax and angular diameter of the moon, as they could provide many reference points In a small area, (at the occasion of occultation). In 1829, Bessel (3) started observing the Pleiades at the Observatory of Ktfnigsberg with the Heliometer built by Fraunhofer. This Instrument, of which the basic Idea was developed by 01e Romer in 1675, is a refractor of which the objective has been cut in two equal halves. By shifting one half with respect to the other, two shifted images are observed of the same object. Distances between stars can be measured accurately using a Helio- meter, by first aligning the shifting direction with the two stars and then shifting one half of the objective till one of the images of one star co- incides with one of the other star. The angular distance of the stars is then determined by the shift of the objectives and the focal distance of the telescope» In the report of his observations and those performed later by Plantamour and Schluter, Bessel added a new purpose to positional astronomy, with which he Initiated astrophysical research on the Pleiades. Beasel wrote: Endlich habe Ich einer mSglichst slcheren Bestlmmung der relativen Orter dieser Sterne elnen for sich selbst bestehenden Werth beigelegt, indem ich glaube, dass eine Zeit kommen wird, fur welche die Frage nach den Inneren Bewegungen dieses merkwurdigen Sternhaufens ein Interesse gewinnen wird, welches, bei aussersten Kleinheit dieser Bewegungen, nur durch friihere Beobachtungen befriedigt werden kann, wenn sle durch die Anwendung der dazu geeignetsten Mittel erlangt worden sind und daher die grösste erreichbare Genauigkeit besltzen.
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