RR LYRAE STARS IN LARGE MAGELLANIC CLOUD GLOBULAR CLUSTERS By Charles A. Kuehn III A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Astrophysics and Astronomy 2011 ABSTRACT RR LYRAE STARS IN LARGE MAGELLANIC CLOUD GLOBULAR CLUSTERS By Charles A. Kuehn III The Oosterhoff phenomenon presents a challenge to the accretion model for the buildup of at least part of the Milky Way halo. The existence of the Oosterhoff gap among the globular clusters in the halo of the Milky Way, while globular clusters in satellite galaxies tend to fall in this gap, seems to contradict the idea that the halo was formed through the accretion of objects similar to these current satellite galaxies. This dissertation seeks to better understand the Oosterhoff phenomenon through a systematic study of RR Lyrae stars in globular clusters in the Large Magellanic Cloud (LMC). Similar studies have been carried out on a set of Milky Way globular clusters which fall in the Oosterhoff-I (Oo-I) and Oosterhoff-II (Oo-II) classes but few studies with the requisite level of detail have been carried out on extragalactic objects. This dissertation set out to study the differences between RR Lyrae stars in Oo- I/II clusters and those in Oo-int clusters. Answers for three specific questions were sought. 1.) How do the properties of double-mode RR Lyrae stars in Oo-int clusters compare to those in Oo-I/II clusters? 2.) How do the positions of RR Lyrae stars on the Bailey diagram differ between stars in Oo-int clusters and those in Oo-I/II clusters. 3.) How do the physical properties of RR Lyrae stars, obtained through the Fourier decomposition of their light curves, change when going from Oo-I/II clusters to Oo-int clusters? The implications that this study has on the nature of the Oosterhoff dichotomy are also discussed. Copyright by CHARLES A. KUEHN III 2011 To Mom, Dad, Nana, Grandpa, and the rest of my family. To my grandmother and Papa who wished that they had been able to see me receive my PhD. iv ACKNOWLEDGMENTS There are many people who I wish to thank for their role in making this dissertation possible. First off I want to thank my adviser Horace Smith, whose guidance over the years not only made this dissertation possible, but allowed me to even get to this point in my career. M´arcio Catelan for his guidance over the years and his valuable comments on not only this thesis but other projects that we have collaborated on. Karen Kinemuchi for her proofreading of this dissertation and her advice on how to survive the dissertation writing and defense process. Nathan De Lee for his assis- tance on computer related matters when I was first starting out. The undergraduate students; Lisa Taylor, Randall McClellan, Kristina Looper, and Kyra Dame for their assistance with parts of this project. I wish to thank Catherine Kennedy for her support and friendship which were important in helping me get to this point. Thanks to Christopher Waters for the LATEX class used to format this thesis. v TABLE OF CONTENTS List of Tables....................................... ................. viii List of Figures...................................... ................. x List of Symbols...................................... ................ xiii 1 Introduction...................................... ................ 1 2 Milky Way Formation................................. ........... 4 2.1 StructureoftheMilkyWay .................... 4 2.2 FormationoftheMilkyWayHalo ................ 6 3 RR Lyrae Variables.................................. ............ 10 3.1 Magnitudes............................. 10 3.2 RR Lyrae Properties and Pulsation Mechanism . 12 3.3 RRLyraeClasses ......................... 16 3.4 OosterhoffGroups ......................... 18 3.5 OtherTypesofVariableStars. .. .. 20 4 Observations, Data Reduction, and Physical Property Determina- tion............................................... ............... 23 4.1 Observations and Image Processing . 23 4.2 Photometry and Variable Identification . 24 4.3 Determination of RR Lyrae Physical Properties . 26 4.3.1 FourierDecomposition. 26 4.3.2 RRabVariables......................... 27 4.3.3 RRcVariables ......................... 29 5 NGC 1466........................................... ............. 31 5.1 DataReductionforNGC1466 .................. 32 5.2 VariableStars ........................... 34 5.2.1 RRLyraeStars......................... 43 5.2.2 Comments on Individual RR Lyrae Stars . 44 5.2.3 RRdStars............................ 45 5.2.4 OtherVariables......................... 46 5.3 PhysicalPropertiesoftheRRLyraeStars . 50 5.4 DistanceModulus ......................... 53 5.5 OosterhoffClassification...................... 54 vi 6 Reticulum......................................... ............... 59 6.1 VariableStars ........................... 61 6.2 PhysicalPropertiesoftheRRLyraeStars . 69 6.3 DistanceModulus ......................... 72 6.4 OosterhoffClassification...................... 73 7 NGC 1786........................................... ............. 75 7.1 VariableStars ........................... 76 7.1.1 RRLyraeStars......................... 83 7.2 PhysicalPropertiesoftheRRLyraeStars . 87 7.3 DistanceModulus ......................... 91 7.4 OosterhoffClassification...................... 92 8 NGC 2210........................................... ............. 96 8.1 RRLyraeStars........................... 97 8.2 PhysicalPropertiesoftheRRLyraeStars . 99 8.3 DistanceModulus ......................... 101 8.4 OosterhoffClassification. .. .. 101 9 Exploring Oosterhoff Intermediate Systems . ..........104 9.1 StructureoftheInstabilityStrip . 104 9.2 IndicatorsofOosterhoffStatus . 106 9.3 Bailey Diagrams for Oosterhoff Intermediate Objects . ... 110 9.3.1 NGC1466vsDraco ...................... 113 9.3.2 NGC1466vsNGC2210.................... 115 9.3.3 NGC2210vsNGC2257.................... 116 9.3.4 NGC 1466 andNGC 2210 vs Oosterhoff I/IISystems . 118 9.3.5 OosterhoffIntermediateLocus? . 120 10 Trends in Physical Properties ....................... ............. 122 11 Conclusions...................................... ................ 136 A NGC 1466 Light Curves................................ ..........141 B Reticulum Light Curves.............................. ............178 C NGC 1786 Light Curves................................ ..........198 References ......................................... .............. 235 vii LIST OF TABLES 3.1 Filters and Their Wavelengths . .. 12 3.2 PropertiesofRRLyraestars. 12 3.3 OosterhoffGroupProperties. 18 4.1 InstrumentProperties. 23 5.1 NGC 1466 Variables: Identification and Coordinates . ....... 38 5.2 NGC 1466 Variables: Photometric Properties . ..... 40 5.3 NGC1466Variables: Photometry . 43 5.4 NGC1466RRd’s: PhotometricParameters . .. 45 5.5 NGC1466RRabFourierCoefficients . 50 5.6 NGC1466RRcFourierCoefficients . 51 5.7 NGC1466RRabPhysicalProperties . 51 5.8 NGC1466RRcPhysicalProperties . 52 6.1 Reticulum Variables: Identification and Coordinates . .......... 65 6.2 Reticulum Variables: Photometric Properties . ....... 66 6.3 Reticulum RRd’s: Photometric Parameters . ..... 67 6.4 Reticulum RRab Fourier Coefficients . .. 70 6.5 Reticulum RRc Fourier Coefficients . .. 70 6.6 Reticulum RRab Physical Properties . ... 71 6.7 Reticulum RRc Physical Properties . ... 72 7.1 NGC 1786 Variables: Identification and Coordinates . ....... 77 viii 7.2 NGC 1786 Variables: Photometric Properties . ..... 80 7.3 NGC1786RRd’s: PhotometricParameters . .. 83 7.4 NGC1786RRabFourierCoefficients . 89 7.5 NGC1786RRcFourierCoefficients . 89 7.6 NGC1786RRabPhysicalProperties . 90 7.7 NGC1786RRcPhysicalProperties . 90 8.1 NGC 2210 Variables: Photometric Properties . ..... 97 8.2 NGC2210RRabFourierCoefficients . 99 8.3 NGC2210RRcFourierCoefficients . 99 8.4 NGC2210RRabPhysicalProperties . 100 8.5 NGC2210RRcPhysicalProperties . 100 9.1 PropertiesforStellarSystems . ... 112 10.1 RRab Physical Properties for Previously Studied Clusters ........ 122 10.2 RRc Physical Properties for Previously Studied Clusters ......... 123 10.3 RRab Physical Properties for LMC Clusters . ..... 130 10.4 RRc Physical Properties for LMC Clusters . ..... 130 ix LIST OF FIGURES 3.1 HRDiagramforRRLyraeStars . 14 3.2 RRLyraeBaileyClasses ........................... 17 3.3 Average period vs metallicity for Globular Clusters . ......... 19 3.4 Milky Way Halo Period-Amplitude Diagram . ... 21 4.1 ExampleofaFourierSeriesFit . 27 5.1 NGC1466CMD ............................... 32 5.2 NGC1466CMD:HorizontalBranch . 33 5.3 NGC1466:RRabLightCurves . 35 5.4 NGC1466:RRcLightCurves . .. .. 36 5.5 NGC1466:RRdLightCurves. 37 5.6 NGC1466PetersenDiagram . .. .. 47 5.7 NGC1466:ACLightCurve ......................... 48 5.8 NGC 1466: B vs V Amplitudes ....................... 49 5.9 NGC 1466: V -bandBaileyDiagram. 55 5.10 NGC 1466: B-bandBaileyDiagram. 56 5.11 NGC 1466: RRLyrae RawPeriod Distribution . ... 57 5.12 NGC 1466: RR Lyrae Fundamentalized Period Distribution ....... 58 6.1 ReticulumCMD ............................... 60 6.2 ReticulumCMD:HorizontalBranch . 61 6.3 Reticulum: RRabLightCurves . 62 x 6.4 Reticulum:RRcLightCurves . 63 6.5 Reticulum:RRdLightCurves . 64 6.6 ReticulumPetersenDiagram. 69 6.7 Reticulum: V -bandBaileyDiagram. 73 6.8 Reticulum: B-bandBaileyDiagram. 74 7.1 NGC1786CMD ............................... 84 7.2 NGC1786CMD:HorizontalBranch . 85 7.3 NGC1786:RRabLightCurves . 86 7.4 NGC1786:RRcLightCurves . .. .. 87 7.5 NGC1786:RRdLightCurves. 88 7.6 NGC 1786: V -bandBaileyDiagram. 93 7.7 NGC 1786: B-bandBaileyDiagram.