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Astronomy.Ohio-State.Edu/˜Jaj/ Nucleo/) Trans-iron Elements in Evolved Stars Dissertation der Mathematisch-Naturwissenschaftlichen Fakult¨at der Eberhard Karls Universit¨atT¨ubingen zur Erlangung des Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) vorgelegt von Lisa Lobling¨ aus Herrenberg T¨ubingen 2020 Gedruckt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakult¨at der Eberhard Karls Universit¨atT¨ubingen. Tag der m¨undlichen Qualifikation: 25.05.2020 Dekan: Prof. Dr. Wolfgang Rosenstiel 1. Berichterstatter: Prof. Dr. Klaus Werner 2. Berichterstatter: Prof. Dr. Dr. Stephan Geier Contents List of Abbreviations iii Zusammenfassung v Summary vii Preface 1 1 Introduction 5 1.1 Final stages in the evolution of stars with low and intermediate mass . .5 1.2 Hydrogen-deficient post-AGB stars . .6 1.3 Mass transfer . .8 1.4 Abell 35-like objects and barium CSPNe . 11 1.5 Stellar atmosphere modeling . 11 1.5.1 Theory of radiation transfer and atmosphere modeling . 12 1.5.2 Numerical implementation in the ATLAS code . 15 1.5.3 Numerical implementation in the TMAP code . 15 1.6 Trans-iron elements . 16 1.6.1 Handling of trans-iron elements in the TMAP code . 17 2 Work in context 19 2.1 Spectral analysis of the barium central star of the planetary nebula Hen 2−39......................... 19 2.2 Spectral analysis of the hybrid PG 1159-type central stars of the planetary nebulae Abell 43 and NGC 7094 . 20 2.3 First discovery of trans-iron elements in a DAO-type white dwarf . 20 3 Publications 23 3.1 Refereed journals . 23 3.2 Unrefereed journals . 24 ii Contents 4 Results 91 4.1 Spectral analysis of the barium central star of the planetary nebula Hen 2−39......................... 91 4.2 Spectral analysis of the hybrid PG 1159-type central stars of the planetary nebulae Abell 43 and NGC 7094 . 92 4.3 First discovery of trans-iron elements in a DAO-type white dwarf . 95 5 Outlook 97 Bibliography 108 List of Abbreviations (V)LTP (very) late thermal pulse, comprises LTP and VLTP AFTP AGB final thermal pulse AGB asymptotic giant branch AGB asymptotischer Riesenast CE common-envelope CS central star CSPN central star of the planetary nebula DA-type WD WD with H-dominated atmosphere DAO-type WD WD with H-dominated atmosphere showing prominent lines of H i and He ii DB-type WD WD with He-dominated atmosphere showing prominent lines of He i DO-type WD WD with He-dominated atmosphere showing prominent lines of He ii EHB extended horizontal branch FTP final thermal pulse HRD Hertzsprung-Russell diagram IGE iron-group element, i.e. calcium to nickel (atomic number 20 ≤ Z ≤ 28) LTE local thermodynamic equilibrium LTP late thermal pulse MLT mixing length theory iv List of Abbreviations NLTE non-local thermodynamic equilibrium ODF opacity-distribution function OS opacity-sampling PhD Doctor of Philosophy PN planetary nebula r-process rapid neutron-capture process RLOF Roche-lobe overflow s-process slow neutron-capture process S/N signal-to-noise ratio sdB subluminous B-type stars sdO subluminous O-type stars TDU third dredge-up TE thermodynamic equilibrium TEE Transeisenelement, see TIE TIE trans-iron element, i.e. copper and beyond (atomic number Z > 28) TMAP T¨ubingenModel-Atmosphere Package (https://uni-tuebingen.de/de/41621) TOSS T¨ubingenOscillator Strength Service (http://dc.g-vo.org/TOSS) TP thermal pulse UV ultraviolet UVES Ultraviolet and Visual Echelle Spectrograph VLT Very Large Telescope VLTP very late thermal pulse WD white dwarf ZSPN Zentralstern des planetarischen Nebels Zusammenfassung In dieser Arbeit werden Spektralanalysen verschiedener Sterntypen vorgestellt, deren Fokus auf den H¨aufigkeiten von Transeisenelementen (TEE) liegt. Das ubergeordnete¨ Ziel ist es, die Nukleosynthese schwerer Elemente durch Neutroneneinfang auf dem asymptotischen Riesenast (AGB) zu untersuchen. Diese Analysen k¨onnen helfen, ein besseres Verst¨andnis von Prozessen wie Konvektion, Diffusion, Sternwind und Massenverlust zu erlangen, die fur¨ die Entstehung des beobachteten H¨aufigkeitsmusters verantwortlich sind. Die erste Arbeit (L¨obling et al. 2019a) pr¨asentiert die Analyse des Barium-Zentralsterns des planetarischen Nebels (ZSPN) Hen 2−39. Im Zentrum des Nebels befindet sich ein Doppelsternsystem, bestehend aus ei- nem Unterriesen vom Spektraltyp K und dem heißen, ionisierenden post-AGB-Stern. Wir best¨atigten die Kohlenstoff- und Barium-Anreicherung des Unterriesen und bestimmten die H¨aufigkeiten beziehungsweise Obergrenzen fur¨ die H¨aufigkeiten von insgesamt 39 Elemen- ten. Aus dem Vergleich des beobachteten H¨aufigkeitsmusters im Begleiter mit theoretischen Berechnungen fur¨ die Nukleosynthese schließen wir, dass Massentransfer mit einem hohen Akkretionsbruchteil von ca. 15 % der vom Prim¨arstern verlorenen Masse erforderlich ist, weshalb Wind-Roche-Lobe-Overflow als wahrscheinlichster Massentransfermechanismus in diesem System anzusehen ist. Die beiden anderen Arbeiten pr¨asentieren Spektralanalysen von heißen post-AGB-Sternen mittels NLTE-Sternenatmosph¨arenmodellen. In L¨obling et al. (2019c) wurden die spektro- skopischen Zwillinge, die ZSPN von Abell 43 und NGC 7094, analysiert. Neben der Effektiv- temperatur und der Oberfl¨achenschwerebeschleunigung wurden genaue H¨aufigkeiten fur¨ eine Vielzahl von Elementen, darunter TEE, bestimmt. Außer fur¨ Sauerstoff, sind die beobachteten H¨aufigkeiten in Ubereinstimmung¨ mit theoretischen Werten aus Sternentwicklungsrechnun- gen fur¨ ein Szenario mit einem finalen thermischen Puls beim Verlassen des AGB, der das Wasserstoffdefizit verursacht hat. Die oberen Grenzwerte fur¨ die TEE-H¨aufigkeiten sind geringer als die extrem hohen Werte, die in Atmosph¨aren von heißen wasserstoffarmen Weißen Zwergen gemessen werden und best¨atigen daher, dass die Diffusion der fur¨ die Anreicherung verantwortliche Prozess ist. Fur¨ die beiden ZSPN wird dies durch einen starken Sternwind verhindert. Um die Hypothese zu uberpr¨ ufen,¨ dass fur¨ die TEE-Anreicherung der Atmosph¨aren von wasserstoffarmen post-AGB-Sternen eine Entwicklung mit einem finalen thermischen Puls und der resultierenden Durchmischung von Hulle¨ und Zwischenschalenmaterial n¨otig ist, analysierten wir den heißen ZSPN Abell 35 (L¨obling et al. 2019b). In diesem Fall waren wir erfolgreich und fanden eine starke Anreicherung, die nicht erwartet wurde. Der Stern ist vi Zusammenfassung wasserstoffreich und von geringer Masse, was eine großfl¨achige Vermischung uber¨ einen finalen thermischen Puls ebenso wie durch einen sogenannten third dredge-up“ ausschließt. Der ” wissenschaftliche Fortschritt, der sich aus diesem Ergebnis ergibt, besteht darin, dass wir in Frage stellen mussen,¨ ob eine Durchmischung von Hulle¨ und Zwischenschalenregion fur¨ die eigentumlichen¨ Elementh¨aufigkeiten und die starke TEE-Anreicherung in wasserstoffarmen Weißen Zwergen notwendig ist oder ob lediglich Diffusion die ursprunglich¨ vorhandenen TEE anreichert. Summary In this work, we performed spectral analyses of different types of stars focusing on the abundances of trans-iron elements (TIEs). The overarching aim is to constrain neutron- capture nucleosynthesis via the slow (s) process on the asymptotic giant branch (AGB) as well as processes like mixing, diffusion, stellar wind, and mass loss that are responsible for the formation of the observed abundance pattern. The first paper (L¨oblinget al. 2019a) presents our analysis of the barium (Ba) central star of the planetary nebula (CSPN) Hen 2−39. The nucleus consists of a binary containing a K-type subgiant and the hot ionizing post-AGB star. We confirmed the carbon (C) and Ba enrichment of the subgiant companion and determined abundances and abundance limits for 39 elements in total. From the comparison of the observed abundance pattern in the secondary with theoretical predictions for nucleosynthesis calculations, we find that mass transfer with a high fraction of accretion of ≈ 15 % of the mass that was ejected by the primary is required. Hence, wind-Roche-lobe overflow (RLOF) is considered the most likely mass transfer mechanism in this system. The other two works present spectral analyses of hot post-AGB stars by means of non-local thermodynamic equilibrium (NLTE) stellar atmosphere models. In L¨oblinget al. (2019c), we aimed to revise the effective temperature and surface gravity as well as to determine abundances for a multitude of elements including TIEs in the spectroscopic twins, the CSPNe Abell 43 and NGC 7094. The observed abundances, besides of oxygen (O), are in agreement with theoretical calculations for an AGB final thermal pulse (AFTP) evolution that causes the hydrogen (H)-deficiency. The upper abundance limits for TIEs lie below the strong enrichment found in hot H-deficient white dwarfs (WDs) and confirms that diffusion is the process responsible for the enrichment. For the two CSPNe, this is prevented by a strong stellar wind. To test the hypothesis of s-process enrichment of the surfaces of H-deficient stars through final-flash mixing, we analyzed the hot H-rich CSPN Abell 35 (L¨oblinget al. 2019b). In this case, we were successful and found a strong enrichment to an amount that was unexpected. The star is H-rich and of extremely low mass which rules out large-scale mixing via a final thermal pulse (FTP) or third dredge-up (TDU). The scientific progress drawn from this result is, that we need to question the explanation that final flash mixing is really necessary for this peculiar surface abundance pattern or whether it is just diffusion starting from initial material. Preface A multitude of chemical elements is of central importance for life in the way we know
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