The Sculptor dwarf spheroidal galaxy is a Milky Way satellite with predominantly old stellar population, and therefore the ideal target to study early chemical evolution. The chemical abundances of photospheres of stars reveal the composition of their birth environment; studying stars of different ages, therefore, provides insight into the chemical enrichment history of the galaxy in which they dwell. High-resolution spectra of 100 stars were used to further explore the chemical enrichment history of the Sculptor dwarf spheroidal galaxy. For the first time, the elements S and Zn were measured in large sample of stars, in a stellar system other than the Milky Way. These elements are of special interest, since they are volatile and not depleted onto dust in interstellar gas. Therefore, S and Zn abundances can be used for direct comparison with abundances in absorption systems observed at high redshifts. During the analysis of these data, the first (CEMP-no) star in Sculptor was discovered, but these kinds of stars are believed to show the chemical abundance pattern the very first stellar generation left behind. This exciting discovery, led to the theoretical investigation of the frequency and origin of CEMP stars in the Milky Way dwarf satellites

Skúladóttir, Ása

English

NARCIS 

Sulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxy

University of Groningen

   University of GroningenSulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxySkúladóttir, ÁsaIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2016Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Skúladóttir, Á. (2016). Sulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxy. [Groningen]:Rijksuniversiteit Groningen.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019AcknowledgementsFuture-me will probably not claim that the few years I spent in Groningen were mybest, due to various health issues. But when it came to science, I was lucky. With veryinteresting (and sometimes unexpected!) results, I enjoyed my work tremendously.Even more important, was my luck to have supervisors that were not only great sci-entists, but also great people, which does not always go together. The words “I havethe best supervisors ever!” have probably never been said as often by a Ph.D. student.Eline, Stefania & Vanessa, thanks for being inspiring and for moulding me (and mysometimes stubborn mind) into a better scientist.Special thanks to Else, for joining me in Chile for an observing run, and to myoffice mates for being nice people. Thanks to Sietske for being a good student, andhelping me with the Dutch summary; to Yuan for being a good friend, and for creatingthe thesis design, without you I would have been stuck with MS Paint and a wholelot of panic. Also, thanks to Hwang Chansung for inspiring me to try to be a betterperson and for making me happy. General thanks to everyone else who supported meand helped in any way, or simply joined me in an interesting conversation.I am perfectly aware of the fact that I would not be here if not for the privilegeswith which I have been provided, so mom, dad, thanks for everything. Especially forgiving me three younger siblings: Sigga, Sóla & Jón Daði, you are awesome. Last butnot least, thanks to Stella, my best friend, my family, for being there for the good andthe bad, and for listening to me ramble on about technical details of my work whenmost of it probably never made any sense.Ása

University of Groningen Research Database

  
 University of Groningen
Sulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxy
Skúladóttir, Ása
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from
it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date:
2016
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Skúladóttir, Á. (2016). Sulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxy [Groningen]:
Rijksuniversiteit Groningen
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the
author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
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Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the
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Download date: 11-02-2018


Cover: Ines Sigel
Printed by: Ipskamp Drukkers, Enschede
ISBN: 978-90-367-8736-6 (printed version)
ISBN: 978-90-367-8736-9 (electronic version)
Contents
1 Introduction 1
1.1 The Local Group . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Sculptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Stellar archaeology . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Carbon-enhanced metal-poor (CEMP) stars . . . . . . . . . . . . 9
1.4 This thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2 Technical background 13
2.1 Stellar spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.1 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2 Stellar atmosphere models . . . . . . . . . . . . . . . . . . . . . . 16
2.2.1 Effective temperature, Teff . . . . . . . . . . . . . . . . . . 16
2.2.2 Surface gravity, log g . . . . . . . . . . . . . . . . . . . . . 17
2.2.3 Microturbulence velocity, vt . . . . . . . . . . . . . . . . . 18
2.2.4 Metallicity, [Fe/H] . . . . . . . . . . . . . . . . . . . . . . 18
2.3 Abundance determination . . . . . . . . . . . . . . . . . . . . . . 18
2.3.1 EW vs synthetic spectra method . . . . . . . . . . . . . . 18
2.3.2 Line list . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3.3 Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3 Sulphur abundances in theSculptor dwarf spheroidal galaxy 21
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . 23
3.2.1 Observations . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2.2 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3 Stellar parameters and model atmospheres . . . . . . . . . . . . . 25
3.4 Abundance measurements . . . . . . . . . . . . . . . . . . . . . . 25
3.4.1 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.5 NLTE corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.6 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . 32
iv CONTENTS
3.6.1 Possible outliers . . . . . . . . . . . . . . . . . . . . . . . . 32
3.6.2 The trend of [S/Fe] with [Fe/H] . . . . . . . . . . . . . . . 35
3.6.3 Comparison of [S/Fe] and [S/Mg] . . . . . . . . . . . . . . 36
3.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.8 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4 Zinc abundances in theSculptor dwarf spheroidal galaxy 47
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . 50
4.3 Velocity measurements . . . . . . . . . . . . . . . . . . . . . . . . 51
4.4 Abundance analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.4.1 Stellar parameters . . . . . . . . . . . . . . . . . . . . . . 54
4.4.2 New targets . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.4.3 Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.4.4 Neodymium . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.4.5 Zinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.4.6 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.5 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . 64
4.5.1 Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.5.2 Neodymium . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.5.3 Zinc in Sculptor . . . . . . . . . . . . . . . . . . . . . . . . 66
4.5.4 Zinc in the Local Group and beyond . . . . . . . . . . . . 70
4.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.7 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5 The first carbon-enhanced metal-poor star in Sculptor 79
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . 82
5.2.1 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2.2 Continuum normalization . . . . . . . . . . . . . . . . . . 83
5.3 Stellar parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.4 Abundance measurements . . . . . . . . . . . . . . . . . . . . . . 85
5.4.1 Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.4.2 Oxygen, carbon, and nitrogen . . . . . . . . . . . . . . . . 89
5.4.3 Indicators of mixing, 12C/13C ratio and Li . . . . . . . . . 90
5.4.4 Alpha elements . . . . . . . . . . . . . . . . . . . . . . . . 92
5.4.5 Odd-Z elements . . . . . . . . . . . . . . . . . . . . . . . . 93
5.4.6 Iron-peak elements . . . . . . . . . . . . . . . . . . . . . . 93
5.4.7 Heavy elements . . . . . . . . . . . . . . . . . . . . . . . . 93
5.5 Error analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
5.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5.6.1 Carbon in Sculptor . . . . . . . . . . . . . . . . . . . . . . 96
5.6.2 The general abundance pattern . . . . . . . . . . . . . . . 98
CONTENTS v
5.7 Origin of the abundance pattern . . . . . . . . . . . . . . . . . . . 100
5.7.1 Alpha and iron-peak elements . . . . . . . . . . . . . . . . 100
5.7.2 Carbon-enhancement . . . . . . . . . . . . . . . . . . . . . 100
5.7.3 The lighter n-capture elements . . . . . . . . . . . . . . . . 103
5.8 Possible formation scenario . . . . . . . . . . . . . . . . . . . . . . 105
5.9 The CEMP-no fraction in Sculptor . . . . . . . . . . . . . . . . . 107
5.10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
5.11 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
6 Carbon-enhanced metal-poor starsin dwarf galaxies 117
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
6.2 Observations of carbon-rich stars . . . . . . . . . . . . . . . . . . 120
6.3 Cosmological merger-tree model . . . . . . . . . . . . . . . . . . . 123
6.4 Results: the global picture . . . . . . . . . . . . . . . . . . . . . . 127
6.4.1 Star formation histories . . . . . . . . . . . . . . . . . . . 131
6.5 Data comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
6.5.1 Carbon-enhanced stars in Sculptor . . . . . . . . . . . . . 133
6.5.2 Carbon-enhanced stars in ultra-faint dwarfs . . . . . . . . 135
6.6 The low-[Fe/H] tail of Sculptor . . . . . . . . . . . . . . . . . . . 137
6.7 Summary and discussion . . . . . . . . . . . . . . . . . . . . . . . 138
Bibliography 143
English summary 157
Nederlandse Samenvatting 165
Íslensk samantekt 173
Acknowledgements 181



ARTS repository - University of Groningen

   University of GroningenSulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxySkúladóttir, ÁsaIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2016Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Skúladóttir, Á. (2016). Sulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxy. [Thesis fullyinternal (DIV), University of Groningen]. Rijksuniversiteit Groningen.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 09-09-2023Cover: Ines SigelPrinted by: Ipskamp Drukkers, EnschedeISBN: 978-90-367-8736-6 (printed version)ISBN: 978-90-367-8736-9 (electronic version)Contents1 Introduction 11.1 The Local Group . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 Sculptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Stellar archaeology . . . . . . . . . . . . . . . . . . . . . . . . . . 51.3 Carbon-enhanced metal-poor (CEMP) stars . . . . . . . . . . . . 91.4 This thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Technical background 132.1 Stellar spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 132.1.1 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . 142.2 Stellar atmosphere models . . . . . . . . . . . . . . . . . . . . . . 162.2.1 E!ective temperature, Te! . . . . . . . . . . . . . . . . . . 162.2.2 Surface gravity, log g . . . . . . . . . . . . . . . . . . . . . 172.2.3 Microturbulence velocity, vt . . . . . . . . . . . . . . . . . 182.2.4 Metallicity, [Fe/H] . . . . . . . . . . . . . . . . . . . . . . 182.3 Abundance determination . . . . . . . . . . . . . . . . . . . . . . 182.3.1 EW vs synthetic spectra method . . . . . . . . . . . . . . 182.3.2 Line list . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.3.3 Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Sulphur abundances in theSculptor dwarf spheroidal galaxy 213.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . 233.2.1 Observations . . . . . . . . . . . . . . . . . . . . . . . . . 233.2.2 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . 243.3 Stellar parameters and model atmospheres . . . . . . . . . . . . . 253.4 Abundance measurements . . . . . . . . . . . . . . . . . . . . . . 253.4.1 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.5 NLTE corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.6 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . 32iv CONTENTS3.6.1 Possible outliers . . . . . . . . . . . . . . . . . . . . . . . . 323.6.2 The trend of [S/Fe] with [Fe/H] . . . . . . . . . . . . . . . 353.6.3 Comparison of [S/Fe] and [S/Mg] . . . . . . . . . . . . . . 363.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.8 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394 Zinc abundances in theSculptor dwarf spheroidal galaxy 474.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . 504.3 Velocity measurements . . . . . . . . . . . . . . . . . . . . . . . . 514.4 Abundance analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 534.4.1 Stellar parameters . . . . . . . . . . . . . . . . . . . . . . 544.4.2 New targets . . . . . . . . . . . . . . . . . . . . . . . . . . 564.4.3 Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . 594.4.4 Neodymium . . . . . . . . . . . . . . . . . . . . . . . . . . 594.4.5 Zinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604.4.6 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634.5 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . 644.5.1 Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . 644.5.2 Neodymium . . . . . . . . . . . . . . . . . . . . . . . . . . 664.5.3 Zinc in Sculptor . . . . . . . . . . . . . . . . . . . . . . . . 664.5.4 Zinc in the Local Group and beyond . . . . . . . . . . . . 704.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724.7 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 The first carbon-enhanced metal-poor star in Sculptor 795.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . 825.2.1 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . 835.2.2 Continuum normalization . . . . . . . . . . . . . . . . . . 835.3 Stellar parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 845.4 Abundance measurements . . . . . . . . . . . . . . . . . . . . . . 855.4.1 Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875.4.2 Oxygen, carbon, and nitrogen . . . . . . . . . . . . . . . . 895.4.3 Indicators of mixing, 12C/13C ratio and Li . . . . . . . . . 905.4.4 Alpha elements . . . . . . . . . . . . . . . . . . . . . . . . 925.4.5 Odd-Z elements . . . . . . . . . . . . . . . . . . . . . . . . 935.4.6 Iron-peak elements . . . . . . . . . . . . . . . . . . . . . . 935.4.7 Heavy elements . . . . . . . . . . . . . . . . . . . . . . . . 935.5 Error analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965.6.1 Carbon in Sculptor . . . . . . . . . . . . . . . . . . . . . . 965.6.2 The general abundance pattern . . . . . . . . . . . . . . . 98CONTENTS v5.7 Origin of the abundance pattern . . . . . . . . . . . . . . . . . . . 1005.7.1 Alpha and iron-peak elements . . . . . . . . . . . . . . . . 1005.7.2 Carbon-enhancement . . . . . . . . . . . . . . . . . . . . . 1005.7.3 The lighter n-capture elements . . . . . . . . . . . . . . . . 1035.8 Possible formation scenario . . . . . . . . . . . . . . . . . . . . . . 1055.9 The CEMP-no fraction in Sculptor . . . . . . . . . . . . . . . . . 1075.10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1085.11 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096 Carbon-enhanced metal-poor starsin dwarf galaxies 1176.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186.2 Observations of carbon-rich stars . . . . . . . . . . . . . . . . . . 1206.3 Cosmological merger-tree model . . . . . . . . . . . . . . . . . . . 1236.4 Results: the global picture . . . . . . . . . . . . . . . . . . . . . . 1276.4.1 Star formation histories . . . . . . . . . . . . . . . . . . . 1316.5 Data comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . 1326.5.1 Carbon-enhanced stars in Sculptor . . . . . . . . . . . . . 1336.5.2 Carbon-enhanced stars in ultra-faint dwarfs . . . . . . . . 1356.6 The low-[Fe/H] tail of Sculptor . . . . . . . . . . . . . . . . . . . 1376.7 Summary and discussion . . . . . . . . . . . . . . . . . . . . . . . 138Bibliography 143English summary 157Nederlandse Samenvatting 165Íslensk samantekt 173Acknowledgements 181

   University of GroningenSulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxySkúladóttir, ÁsaIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2016Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Skúladóttir, Á. (2016). Sulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxy. [Thesis fullyinternal (DIV), University of Groningen]. Rijksuniversiteit Groningen.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 30-10-2023Cover: Ines SigelPrinted by: Ipskamp Drukkers, EnschedeISBN: 978-90-367-8736-6 (printed version)ISBN: 978-90-367-8736-9 (electronic version)Contents1 Introduction 11.1 The Local Group . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 Sculptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Stellar archaeology . . . . . . . . . . . . . . . . . . . . . . . . . . 51.3 Carbon-enhanced metal-poor (CEMP) stars . . . . . . . . . . . . 91.4 This thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Technical background 132.1 Stellar spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 132.1.1 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . 142.2 Stellar atmosphere models . . . . . . . . . . . . . . . . . . . . . . 162.2.1 E!ective temperature, Te! . . . . . . . . . . . . . . . . . . 162.2.2 Surface gravity, log g . . . . . . . . . . . . . . . . . . . . . 172.2.3 Microturbulence velocity, vt . . . . . . . . . . . . . . . . . 182.2.4 Metallicity, [Fe/H] . . . . . . . . . . . . . . . . . . . . . . 182.3 Abundance determination . . . . . . . . . . . . . . . . . . . . . . 182.3.1 EW vs synthetic spectra method . . . . . . . . . . . . . . 182.3.2 Line list . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.3.3 Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Sulphur abundances in theSculptor dwarf spheroidal galaxy 213.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . 233.2.1 Observations . . . . . . . . . . . . . . . . . . . . . . . . . 233.2.2 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . 243.3 Stellar parameters and model atmospheres . . . . . . . . . . . . . 253.4 Abundance measurements . . . . . . . . . . . . . . . . . . . . . . 253.4.1 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.5 NLTE corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.6 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . 32iv CONTENTS3.6.1 Possible outliers . . . . . . . . . . . . . . . . . . . . . . . . 323.6.2 The trend of [S/Fe] with [Fe/H] . . . . . . . . . . . . . . . 353.6.3 Comparison of [S/Fe] and [S/Mg] . . . . . . . . . . . . . . 363.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.8 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394 Zinc abundances in theSculptor dwarf spheroidal galaxy 474.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . 504.3 Velocity measurements . . . . . . . . . . . . . . . . . . . . . . . . 514.4 Abundance analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 534.4.1 Stellar parameters . . . . . . . . . . . . . . . . . . . . . . 544.4.2 New targets . . . . . . . . . . . . . . . . . . . . . . . . . . 564.4.3 Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . 594.4.4 Neodymium . . . . . . . . . . . . . . . . . . . . . . . . . . 594.4.5 Zinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604.4.6 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634.5 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . 644.5.1 Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . 644.5.2 Neodymium . . . . . . . . . . . . . . . . . . . . . . . . . . 664.5.3 Zinc in Sculptor . . . . . . . . . . . . . . . . . . . . . . . . 664.5.4 Zinc in the Local Group and beyond . . . . . . . . . . . . 704.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724.7 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 The first carbon-enhanced metal-poor star in Sculptor 795.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805.2 Observations and data reduction . . . . . . . . . . . . . . . . . . . 825.2.1 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . 835.2.2 Continuum normalization . . . . . . . . . . . . . . . . . . 835.3 Stellar parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 845.4 Abundance measurements . . . . . . . . . . . . . . . . . . . . . . 855.4.1 Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875.4.2 Oxygen, carbon, and nitrogen . . . . . . . . . . . . . . . . 895.4.3 Indicators of mixing, 12C/13C ratio and Li . . . . . . . . . 905.4.4 Alpha elements . . . . . . . . . . . . . . . . . . . . . . . . 925.4.5 Odd-Z elements . . . . . . . . . . . . . . . . . . . . . . . . 935.4.6 Iron-peak elements . . . . . . . . . . . . . . . . . . . . . . 935.4.7 Heavy elements . . . . . . . . . . . . . . . . . . . . . . . . 935.5 Error analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965.6.1 Carbon in Sculptor . . . . . . . . . . . . . . . . . . . . . . 965.6.2 The general abundance pattern . . . . . . . . . . . . . . . 98CONTENTS v5.7 Origin of the abundance pattern . . . . . . . . . . . . . . . . . . . 1005.7.1 Alpha and iron-peak elements . . . . . . . . . . . . . . . . 1005.7.2 Carbon-enhancement . . . . . . . . . . . . . . . . . . . . . 1005.7.3 The lighter n-capture elements . . . . . . . . . . . . . . . . 1035.8 Possible formation scenario . . . . . . . . . . . . . . . . . . . . . . 1055.9 The CEMP-no fraction in Sculptor . . . . . . . . . . . . . . . . . 1075.10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1085.11 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096 Carbon-enhanced metal-poor starsin dwarf galaxies 1176.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186.2 Observations of carbon-rich stars . . . . . . . . . . . . . . . . . . 1206.3 Cosmological merger-tree model . . . . . . . . . . . . . . . . . . . 1236.4 Results: the global picture . . . . . . . . . . . . . . . . . . . . . . 1276.4.1 Star formation histories . . . . . . . . . . . . . . . . . . . 1316.5 Data comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . 1326.5.1 Carbon-enhanced stars in Sculptor . . . . . . . . . . . . . 1336.5.2 Carbon-enhanced stars in ultra-faint dwarfs . . . . . . . . 1356.6 The low-[Fe/H] tail of Sculptor . . . . . . . . . . . . . . . . . . . 1376.7 Summary and discussion . . . . . . . . . . . . . . . . . . . . . . . 138Bibliography 143English summary 157Nederlandse Samenvatting 165Íslensk samantekt 173Acknowledgements 181

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Sulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxy

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