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Investigating the Break in the Cepheid Period-Luminosity Relation and Its Implications

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Investigating the Break in the Cepheid Period-Luminosity Relation and Its Implications University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations 1896 - February 2014 1-1-2005 Investigating the break in the Cepheid period-luminosity relation and its implications. Chow-Choong, Ngeow University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_1 Recommended Citation Ngeow, Chow-Choong,, "Investigating the break in the Cepheid period-luminosity relation and its implications." (2005). Doctoral Dissertations 1896 - February 2014. 2004. https://scholarworks.umass.edu/dissertations_1/2004 This Open Access Dissertation is brought to you for free and open access by ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations 1896 - February 2014 by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. INVESTIGATING THE BREAK IN THE CEPHEID PERIOD-LUMINOSITY RELATION AND ITS IMPLICATIONS A Dissertation Presented by CHOW-CHOONG NGEOW Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY May 2005 Department of Astronomy © Copyright by Chow-Choong Ngeow All Rights Reserved INVESTIGATING THE BREAK IN THE CEPHEID PERIOD-LUMINOSITY RELATION AND ITS IMPLICATIONS A Dissertation Presented by CHOW-CHOONG NGEOW Approved as to style and content by: Shashi Kanbur, Chair Ron Snell, Department Chair Department of Astronomy / dedicate this Thesis Dissertation to my parents, Yin-Ngee Ngeow & Chiew-Hong Lim, and to my girl friend, Judy Chen. ACKNOWLEDGMENTS I would like to ax^knowledge my advisor, Prof. Shashi Kanbur, for the teaching, guidance, assis- tance, support and encouragement through out my work in this Thesis Dissertation for the past 5 years. This work would not be possible to accomplish without the supervision from my advisor. I would also like to acknowledge the discussions, assistance and arguments with my collaborators, Dr. Douglas Leonard, Dr. Sergei Nikolaev, Prof. Nail Tanvir and Prof. Robert Buchler, for providing me the opportunities to work and learn from them. The thoughtful discussions with Prof. Gustav Tammann is acknowledged either. The travel grants I received from various sources are appreciated, which include the //5T research grants of AR-8752 (PI: S. Kanbur) k GO-9155 (PI: D. Leonard), the International TVavel Grant from the American Astronomical Society, the accommodation grant from the Gaia Symposium and the travel grants from the Graduate School of the University of Massachusetts. Without these grants, I cannot attend the meetings to present some results from this Thesis Dissertation. The assistantships (both teaching and research assistantship) from the Department of Astronomy, University of Massachusetts, and from the HST research grants of AR-8752 & GO-9155 are greatly appreciated. It is impossible for me to study and work on my Thesis Dissertation in this department without these assistantships. I would to acknowledge the peoples in the Department of Astronomy, University of Massachusetts. I thank those professors who taught and educated me when I took their classes. Many thanks to the professors, post-docs and graduate students in the department for the interactions both within and outside the academic works. Thanks a lot to the T.A.s that we worked together for the AST-103. I also would like to thank the secretaries in the department for handling the administrative tasks, and the graduate program director. Prof. John Kwan, for the academic advising through out my study in this department. Finally, I would like to thank for my parents, my family and my girl-friend for the constant support and encouragement throughout my life. V ABSTRACT INVESTIGATING THE BREAK IN THE CEPHEID PERIOD-LUMINOSITY RELATION AND ITS IMPLICATIONS MAY 2005 CHOW-CHOONG NGEOW B.Sc, OHIO STATE UNIVERSITY COLUMBUS M.Sc, UNIVERSITY OF MASSACHUSETTS AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Shashi Kanbur The Cepheid period-luminosity (PL) relation is a major component in the distance scale lad- der. This relation has been considered to be linear (within period ranges of ~ 2 to ~ 100 days) universal and (i.e., metallicity independent) for a long time. However, recent work has strongly suggested that the PL relation for the Large Magellanic Cloud (LMC) Cepheids is non-linear with a discontinuity at 10 days. In addition, the LMC period-color (PC) relation is also shown to be non-linear. Besides this, the Cepheid PL relation could also be non-universal. The aim of this Thesis Dissertation is to investigate these two problems of the Cepheid PL relation, in particular to examine the non-linearity of the LMC PL relation and its implications in the distance scale studies, as well as for the stellar structure, pulsation and evolution. The works for this Thesis Dissertation involve both the empirical and statistical analysis of the existing Cepheid data in different metallicity environments (Galactic, LMC and SMC) to characterize the break of the PL and PC relations, and the construction of stellar pulsation models using existing pulsation codes in attempt to understand the physics behind the break in the LMC PL and PC relations. The universality of the Cepheid PL relation is also studied with similar approaches. These works include: (a) developing the Fourier techniques to improve the Cepheid light curve fitting method; (b) testing the non-universality of the PL relation by comparing the Cepheid distances to HST observed galaxies with the Galactic and LMC PL relations and the statistical test of the vi consistency of Galactic and LMC PL relation; (c) analyzing empirically and statistically for the non-linear PL, PC and AC (amplitude-color) relations for the Galactic, LMC and SMC Cepheid at maximum, mean and minimum light; (d) investigating the effect of non-linear PL relation in distance scale studies; and (e) constructing the Galax:tic and LMC models with the stellar pulsation codes in attempt to account for the non-linear and/or non-universal Cepheid PC and PL relations. vii . TABLE OF CONTENTS Page ACKNOWLEDGMENTS . V ABSTRACT vi LIST OF TABLES LIST OF FIGURES XV CHAPTER 1. INTRODUCTION ^ 1.1 The Cepheid Variables j 1.1.1 Cepheids as Astrophysical Tools 5 1.2 The Cepheid Period-Luminosity Relation 7 1.2.1 The Non-Linearity of the Cepheid PL Relation 8 1.3 Structure of this Thesis Dissertation 12 2. CEPHEID LIGHT CURVES RECONSTRUCTION WITH FOURIER EXPANSION AND INTERRELATIONS 15 2.1 The Cepheid Light Curve I5 2.1.1 The Problems in Reconstructing the Light Curve 16 2.2 Fourier Expansion with Simulated Annealing Techniques 18 2.2.1 Results and Problems of the Fits 22 2.3 The Fourier Interrelations 23 2.4 Error Analysis for Light Curve Reconstruction when Applied to HST Cepheids 27 2.5 Conclusion and Discussion for this Chapter 30 3. THE EXTRA-GALACTIC CEPHEID DISTANCE SCALE FROM LMC AND GALACTIC PL RELATIONS 36 3.1 Cepheids and the Extra-Galactic Distance Scale 37 3.2 General Methodology for Deriving the Cepheid Distance 38 3.2.1 A Note on the Random Errors for //q 41 viii 3.3 HST Data and Analysis .... 42 3.3.1 The Adopted PL Relations 45 3.4 Results for the Calibrated Cepheid Distances 3.4.1 Comparisons with Published Results 49 3.4.2 Distance Moduli from Various PL Relations 53t:o 3.4.3 The Effect of the Metallicity 55 3.5 Conclusion and Discussion for this Chapter gg PL RELATIONS FOR GALACTIC CEPHEID VARIABLES WITH INDEPENDENT DISTANCE MEASUREMENTS: COMPARISON TO THE LMC PL RELATIONS ... Dl 4.1 The Need of the Galactic PL Relation gj 4.2 Galactic Cepheids with Independent Distance Measurements 62 4.2.1 The Adopted Distances to the Galactic Cepheids 65 4.3 The Galactic PL Relation g-, 4.3.1 The Effect of FO Cepheids gg 4.3.2 The effect of open cluster distances from Turner & Burke 2002 69 4.4 Comparison to Published Results 70 4.4.1 Comparison with other Galactic PL relations 70 4.4.2 Comparison with the LMC PL Relation 71 4.5 Conclusion and Discussion for this Chapter 73 THE NON-LINEAR PL RELATIONS FOR THE LMC CEPHEIDS FROM OPTICAL TO NEAR INFRARED 74 5.1 Recent Studies of the Non-Linear PL Relation 74 5.2 LMC Data and the Extinction Corrections 75 5.3 Analysis and Results 78 5.3.1 Statistical Tests for the Data 79 5.4 Conclusion and Discussion for this Chapter 84 PERIOD-COLOR AND AMPLITUDE-COLOR RELATIONS IN THE CLASSICAL CEPHEID VARIABLES I: THE EMPIRICAL RESULTS 87 6.1 Purposes for Studying the Period-Color and Amplitude-Color Relations at Maximum, Mean and Minimum Light 87 6.2 The Galactic, LMC and SMC Data 89 6.3 Analysis and the Results from the Statistical Test 93 6.4 The Period-Color and Amplitude-Color Relations 97 6.4.1 Results of the Period-Color Relations 97 6.4.2 Results of the Amplitude-Color Relations 99 6.4.3 Combining the PC and AC Relations 99 ix 6.5 The LMC PL Relations at Maximum, Mean and Minimum Light 100 6.6 Conclusion and Discussion for this Chapter 101 7. THE LINEARITY OF THE WESENHEIT FUNCTION: IMPLICATION OF THE NON-LINEAR LMC PL RELATION IN DISTANCE APPLICATION SCALE^Ai^r. 105 7.1 Non-Linearity of the PL Relation and the Distance Scale Application in^ 7.2 The Wesenheit Function 108 7.2.1 Testing the Linearity of the Wesenheit Function 109 7.3 Wesenheit Function and the Distance Scale Application 113 7.4 Conclusion and Discussion for this Chapter [ \ \ [ [ Hg 8. PERIOD-COLOR AND AMPLITUDE-COLOR RELATIONS IN THE CLASSICAL CEPHEID VARIABLES II: THE GALACTIC MODELS 118 8.1 Cepheid PC & AC Relations, the HIF-Photosphere Interaction and the PL Relations 8.2 Methods, Models and Code Description 12o 8.3 Results for the Galactic Models 124 8.3.1 The Relations PC I25 8.3.2 The AC Relations 130 8.3.3 The Interaction of the HIF and Photosphere 131 8.3.4 Cepheids with log(P) < 0.8 135 8.4 Light Curve Structure of the Models 136 8.5 Conclusion and Discussion for this Chapter I37 9.
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