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The Incidence of Chemically Peculiar Stars in Open Clusters”

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DISSERTATION Titel der Dissertation “The incidence of chemically peculiar stars in open clusters” Verfasser Mag. Martin Netopil angestrebter akademischer Grad Doktor der Naturwissenschaften (Dr.rer.nat) Wien, im April 2013 Studienkennzahl lt. Studienblatt: A 091 413 Dissertationsgebiet lt. Studienblatt: Astronomie Betreuer: Ao.Prof.Dr.HansMichaelMaitzen Contents Zusammenfassung V Abstract VII 1 Introduction & Objectives 1 2 Propertiesofchemicallypeculiarstars 5 2.1 Rotation................................... 6 2.2 Magneticfield................................ 15 2.3 ThetemperaturescaleofCPstars. 20 3 Detectionofchemicallypeculiarstars 29 3.1 Classificationspectroscopy . .. 36 4 Why studying open clusters? 41 4.1 Datacompilation .............................. 43 5 The open cluster sample 45 5.1 Photoelectric ∆a survey .......................... 45 5.1.1 Collinder121 ............................ 45 5.1.2 Collinder132 ............................ 45 5.1.3 Collinder140 ............................ 46 5.1.4 IC2391 ............................... 46 5.1.5 IC2602 ............................... 47 5.1.6 IC4665 ............................... 47 5.1.7 IC4725 ............................... 47 5.1.8 Melotte 20 (α Persei)........................ 48 5.1.9 Melotte22(Pleiades). 48 5.1.10 Melotte111(ComaBerenices) . 48 5.1.11 NGC1039.............................. 49 5.1.12 NGC1662.............................. 50 5.1.13 NGC1901.............................. 50 5.1.14 NGC2169.............................. 50 5.1.15 NGC2232.............................. 50 5.1.16 NGC2287.............................. 51 5.1.17 NGC2343.............................. 51 I II Contents 5.1.18 NGC2362.............................. 51 5.1.19 NGC2422.............................. 51 5.1.20 NGC2423.............................. 52 5.1.21 NGC2447.............................. 52 5.1.22 NGC2451A/B........................... 52 5.1.23 NGC2516.............................. 53 5.1.24 NGC2546.............................. 53 5.1.25 NGC2632(Praesepe) . 53 5.1.26 NGC3114.............................. 54 5.1.27 NGC3228.............................. 54 5.1.28 NGC3532.............................. 55 5.1.29 NGC5460.............................. 55 5.1.30 NGC5662.............................. 56 5.1.31 NGC6087.............................. 56 5.1.32 NGC6281.............................. 56 5.1.33 NGC6405.............................. 57 5.1.34 NGC6475.............................. 57 5.1.35 NGC7092.............................. 57 5.1.36 NGC7243.............................. 57 5.1.37 Trumpler10............................. 58 5.2 CCD∆a survey-PartI .......................... 58 5.2.1 Collinder272 ............................ 58 5.2.2 Lyng˚a14............................... 58 5.2.3 Melotte105 ............................. 58 5.2.4 NGC2099.............................. 59 5.2.5 NGC2169.............................. 59 5.2.6 NGC2439.............................. 59 5.2.7 NGC2489.............................. 60 5.2.8 NGC2567.............................. 60 5.2.9 NGC2658.............................. 60 5.2.10 NGC3114.............................. 60 5.2.11 NGC3960.............................. 61 5.2.12 NGC5281.............................. 61 5.2.13 NGC6134.............................. 61 5.2.14 NGC6192.............................. 61 5.2.15 NGC6204.............................. 62 5.2.16 NGC6208.............................. 62 5.2.17 NGC6250.............................. 62 5.2.18 NGC6396.............................. 63 5.2.19 NGC6451.............................. 63 5.2.20 NGC6611.............................. 63 5.2.21 NGC6705.............................. 63 5.2.22 NGC6756.............................. 64 5.2.23 Pismis20 .............................. 64 5.3 CCD∆a survey-PartII.......................... 64 Contents III 5.3.1 Berkeley11 ............................. 64 5.3.2 Berkeley94 ............................. 65 5.3.3 Haffner15.............................. 65 5.3.4 King21 ............................... 65 5.3.5 Lyng˚a1 ............................... 66 5.3.6 NGC1502.............................. 66 5.3.7 NGC3105.............................. 66 5.3.8 NGC3293.............................. 66 5.3.9 NGC5999.............................. 67 5.3.10 NGC6031.............................. 67 5.3.11 NGC6268.............................. 67 5.3.12 NGC6405.............................. 68 5.3.13 NGC6802.............................. 68 5.3.14 NGC6830.............................. 68 5.3.15 NGC6834.............................. 68 5.3.16 NGC7235.............................. 69 5.3.17 NGC7296.............................. 69 5.3.18 NGC7510.............................. 69 5.3.19 Ruprecht44............................. 69 5.3.20 Ruprecht115 ............................ 70 5.3.21 Ruprecht120 ............................ 70 5.3.22 Ruprecht130 ............................ 71 5.3.23 Stock16............................... 71 6 Open cluster parameters 73 6.1 Metallicity.................................. 73 6.1.1 A homogeneous approach to determine metallicity . .... 76 6.2 Thefinalopenclusterparameters . 102 7 Membership analysis 111 8 Results 123 8.1 Thefinaldataset .............................. 123 8.2 MassesandfractionalagesofCPstars. 127 8.3 Evolutionwithage ............................. 130 8.3.1 Formerinvestigations. 130 8.3.2 Results based on the ∆a survey .................. 132 8.4 Dependenciesbesideage . 142 8.5 The early stage of chemically peculiar stars . ...... 146 9 Outlook 151 A The data 153 References 161 IV Contents List of Abbreviations 171 List of Figures 173 List of Tables 181 Acknowledgements 183 Curriculum vitae 185 Zusammenfassung Die Entstehung und Entwicklung von chemisch pekuliaren (CP) Sternen ist nach wie vor nicht restlos gekl¨art, und das obwohl die ersten Vertreter dieser Sterngruppe bereits vor mehr als 110 Jahren entdeckt wurden. Aus astrophysikalischer Sicht sind diese Ob- jekte von großem Interesse, da sie zahlreiche besondere Eigenschaften in sich vereinen. Diese Dissertation widmet sich der Untersuchung einer Untergruppe der CP Sterne, die neben Uberh¨ ¨aufigkeiten von Elementen der Eisengruppe (zB. Chrom) und seltenen Erden wie Europium, auch starke Magnetfelder und eine langsame Rotation aufweisen. Basierend auf einer Auswahl von gut untersuchten nahen Feldsternen wird der m¨ogliche Zusammenhang zwischen diesen Eigenschaften betrachtet. Das Hauptaugenmerk galt jedoch der Untersuchung einer m¨oglichen Abh¨angigkeit zwischen der Anzahl von CP Sternen und deren Alter. Fur¨ diesen Zweck wurden die Ergebnisse von mehreren ∆a Studien in Sternhaufen herangezogen. Dieses fotometrische Filtersystem erm¨oglicht ei- ne effiziente und zeitsparende Detektion der magnetischen CP Sterne auf Grund einer charakteristischen Flussdepression bei 520nm. Im Vergleich zu Feldsternen bieten of- fene Sternhaufen den großen Vorteil, dass zum Beispiel das Alter und die Entfernung statistisch gesehen genauer bestimmt werden k¨onnen. Der Grund dafur¨ liegt in der mehr oder weniger gleichzeitigen Entstehung aller Mitglieder aus einer einzigen Mo- lekulwolke.¨ Nach der Analyse der Mitgliedswahrscheinlichkeit aller mittels ∆a untersuchten Objekte und der Bestimmung der jeweiligen Sternhaufenparameter konnte gezeigt wer- den, dass eine Abh¨angigkeit zwischen der Anzahl von CP Sternen und deren Alter besteht. Allerdings konnte dies durch die allgemeine Sternentwicklung erkl¨art werden. Das wurde¨ unter anderem bedeuten, dass CP Sterne sp¨atestens beim Erreichen der Hauptreihe bereits ihre typischen Eigenschaften zeigen. Des Weiteren konnte zumin- dest ein Vertreter dieser Gruppe gefunden werden, der sich vermutlich noch auf der Vorhauptreihe befindet. V VI Zusammenfassung Abstract The formation and evolution of chemically peculiar (CP) stars is still a matter of debate, although the first representatives were detected already more than 110 years ago. From the astrophysical point of view, these objects are of particular interest, since they combine a wide variety of specific properties. This work deals with a subgroup of CP stars, showing beside overabundances of some iron-peak (e.g. Chromium) and rare earth elements like Europium, also strong ordered magnetic fields as well as a slow rotation. Based on a selection of well inves- tigated close field stars, the possible connections of these properties were examined. However, the main research focus was the analysis of a relationship between the num- ber of CP stars and their age. For this purpose, the results of the extensive ∆a survey in open clusters were used. This photometric filter system allows an efficient and eco- nomic detection of magnetic CP stars due to a characteristic flux depression at 520nm. Compared to field stars, open clusters offer the big advantage that for example the age and the distance can be determined more accurately on a statistical basis, since all member stars of an open cluster originate more or less at the same time from a single molecular cloud. After the membership analysis of all in ∆a investigated objects and the determi- nation of the cluster parameters, it was shown that the occurrence of CP stars depend on age, but can be explained by the general evolution of stars. This entails amongst others that CP stars show their typical characteristics already as soon as they have arrived the main-sequence, or even before. Furthermore, we were able to detect at least one representative, probably still in its pre-main-sequence phase. VII VIII Abstract Chapter 1 Introduction & Objectives For the first time, the
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