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Studies of Subdwarf B Stars Michael David Reed Iowa State University

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Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 2001 Studies of subdwarf B stars Michael David Reed Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Astrophysics and Astronomy Commons Recommended Citation Reed, Michael David, "Studies of subdwarf B stars " (2001). Retrospective Theses and Dissertations. 665. https://lib.dr.iastate.edu/rtd/665 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. ProQuest Information and Learning 300 North Zeeb Road, Ann Arbor, Ml 48106-1346 USA 800-521-0600 Studies of Subdwarf B Stars by Michael David Reed A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Astrophysics Program of Study Committee: Steven D. Kawaler, Major Professor Scot J. Kleinman Russell J. Lavery Curt Struck Hal Stem Paul Can field Iowa State University Ames, Iowa 2001 Copyright © Michael David Reed, 2001. All rights reserved. UMI Number: 3034212 UMI ® UMI Microform 3034212 Copyright 2002 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 ii Graduate College Iowa State University This is to certify that the doctoral dissertation of Michael David Reed has met the dissertation requirements of Iowa State University Signature was redacted for privacy. Major Professor Signature was redacted for privacy. For the Major Program iii TABLE OF CONTENTS ABSTRACT xvii CHAPTER 1. INTRODUCTION 1 1.1 Evolution of Solar-Type Stars 2 1.2 Subdwarf B Stars 3 1.2.1 Outside Appearances 5 1.2.2 Binarity 6 1.2.3 Speculation About the Origins of Subdwarf B Stars 9 1.3 Pulsating Subdwarf B Stars 10 1.3.1 Overview of Pulsation Properties 11 1.3.2 Pulsating Subdwarf B Stars as Probes of Stellar Evolution and Stellar Systems 11 1.4 The Goals of this Work 12 CHAPTER 2. ASTEROSEISMOLOGY METHODS AND TOOLS 15 2.1 Obtaining and Reducing Time-Series Photometry 16 2.1.1 Photoelectric Photometry 16 2.1.2 Data Reduction 17 2.1.3 The Temporal Spectrum 18 2.1.4 Beating Down Aliases with Multi Site Data 19 2.2 Pulsation Theory 22 2.2.1 Classes of Pulsation Modes 23 2.2.2 Asymptotic Properties of Nonradial Modes 25 2.2.3 Effects of Rotation on Pulsation Frequencies 27 IV 2.2.4 Mode Trapping 28 2.2.5 Changes in the Pulsation Period 28 2.3 Detailed Stellar Models 29 2.3.1 Evolutionary Models 29 2.3.2 Pulsation Period Calculation 31 2.4 Practical Implications of Pulsation Theory 32 2.4.1 Observable i Values 32 2.4.2 Pattern Matching 32 2.4.3 Abundance of Pulsations 33 2.4.4 Measuring Evolutionary Changes 34 2.5 Successful Applications of Asteroseismology 35 2.5.1 A Single, Rich Pulsater 35 2.5.2 A Single Star, Viewed Over Several Seasons 36 2.5.3 Using an Ensemble of Pulsators to Identify Pulsation Modes 36 2.5.4 O-C 38 2.6 Conclusions 40 CHAPTER 3. SUBDWARF B STARS AS BINARIES 41 3.1 Observed Subdwarf B Stars in Binaries 41 3.1.1 Methods of Detecting Binary Stars 41 3.1.2 Binary Frequency of Subdwarf B Stars 42 3.1.3 Theoretical Considerations 44 3.2 Effects on Pulsation Due to Binarity 45 3.2.1 Time Delay and Doppler Shift 45 3.2.2 O-C 48 3.2.3 Complicated Light Curves 48 3.2.4 Temporal Spectra of Simulated Data 51 3.2.5 Reducing Data with Orbital Aliasing 55 3.2.6 Correcting the Lightcurve for Binarity 60 V 3.3 Other Possible Manifestations of Binarity 63 3.4 Conclusions 63 CHAPTER 4. BACKGROUND AND OBSERVATIONS OF INDIVID­ UAL STARS 65 4.1 PB 8783 65 4.2 PG 1605+072 68 4.3 Feige 48 73 4.4 PG 1336-018 78 4.4.1 Xcov 17 Observations 80 4.4.2 Xcov 21 Observations 81 4.5 Conclusion 84 CHAPTER 5. PATTERN ANALYSIS 92 5.1 PB8783 93 5.1.1 Complications Due to Binarity 94 5.2 PG1605 97 5.3 Feige 48 98 5.4 PG1336 100 5.4.1 Xcov 17 101 5.4.2 Xcov 21 101 5.5 Conclusion 102 CHAPTER 6. STABILITY AND EVOLUTION OF PULSATIONS 105 6.1 PB8783 106 6.2 PG1605 109 6.3 Feige 48 114 6.4 PG1336 117 6.5 Conclusions 118 CHAPTER 7. STUDIES OF THE ENTIRE GROUP 120 7.1 The Pulsation Dependence Across the HR Diagram 120 vi 7.2 Scaling with Surface Gravity and Radius 121 7.3 Conclusions 125 CHAPTER 8. NEW TOOLS FOR ASTEROSEISMOLOGY 126 8.1 Using Eclipses to Identify Pulsation Modes 126 8.1.1 Eclipse modeling 126 8.1.2 Eclipse Data 128 8.2 Tipped pulsation axis 132 8.2.1 Determining the Mode Structure in Xcov Data- Simulations 133 8.2.2 Xcov 21 Data 139 8.3 Tipped eclipses 140 8.4 Results 141 CHAPTER 9. CONCLUSIONS 145 9.1 Results from this Work 145 9.1.1 Observations 145 9.1.2 Applying the Tools of Asteroseismology 146 9.1.3 Developing New Tools 150 9.2 Ramifications of this Work 152 9.3 Where to go for answers 154 9.4 Conclusion 155 APPENDIX A. SEARCHING FOR COMPANIONS TO SUBDWARF B STARS USING INFRARED COLORS 156 BIBLIOGRAPHY 168 vii LIST OF TABLES Table 3.1 Orbital parameters for simulated light curves 53 Table 3.2 Grouping of data used in simulations 53 Table 3.3 Effects of binarity on pulsation for binaries of various lengths 62 Table 4.1 Properties of the four sdBV stars selected for study in this work; in order of increase log g 66 Table 4.2 The 11 modes detected during the multi-site campaign. (From O'Donoghue et al., 1998) for PB 8783 68 Table 4.3 The 10 largest amplitude modes of PG 1605 detected during the multi- site campaign. (From Kilkenny et al. 1999) 73 Table 4.4 Observations of PG 1605 74 Table 4.5 Observations of Feige 48 76 Table 4.6 Subgroups used in pulsation analysis for Feige 48 77 Table 4.7 Comparison of frequencies (in /^Hz) detected in various runs for Feige 48. Formal LSQ errors are provided in parentheses 78 Table 4.8 Best solution using all the data for Feige 48. Formal LSQ errors in parenthesis 78 Table 4.9 Period list for PG 1336 from Xcov 17 (Formal LSQ errors are in paren­ theses) 87 Table 4.10 Observations of PG 1336 from Xcov 21 88 Table 4.11 Period List for PG 1336 from Xcov 21. Formal LSQ errors in parenthesis.(/ denote modes also detected in Xcov 17 data, g denotes modes observed only in Xcov 21.) 90 viii Table 5.1 Separations of the 11 modes in Table 4.2 for PB 8783 94 Table 5.2 Comparison between Model and Observed modes in PG 1605. (From Kawaler, 1999) 97 Table 5.3 Comparison of observed pulsation periods with best-fit evolutionary model of appropriate Teff and log g for Feige 48 99 Table 5.4 Comparison of observed stellar parameters with models for Feige 48. 100 Table 5.5 Comparison of Model to Observations in PG 1336 101 Table 5.6 Observed periods (from Xcov21) of PG 1336 split by an integer number of rotation frequencies 102 Table 6.1 Groupings used for phase calculations of PG 1605. Note that the mul- tisite data contains subgroups used in Figure 6.4 113 Table 6.2 Least squares determined frequencies, in fj.Hz, near 2742/iHz by year for PG 1605. Amplitudes (in mma) are in parenthesis 113 Table 8.1 Pulsation modes detected in simulations 127 Table 8.2 Period List for PG 1336 from Xcov 21 for primary eclipse data. (Formal LSQ errors in parenthesis.) 131 Table 8.3 Phases and FT signatures for individual pulsation modes in the case of a tipped pulsation axis 136 Table 8.4 Phases for pulsations in simulated 'A' and 'B' data sets.
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