LONG PERIOD VARIABLE STARS IN THE GLOBULAR CLUSTER M5 (NGC 5904) Kyle Pellegrin A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 2020 Committee: Andrew C. Layden, Advisor John B. Laird Dale W. Smith c 2020 � Kyle Pellegrin All Rights Reserved iii ABSTRACT Andrew C. Layden, Advisor Long Period Variable (LPV) stars have been poorly studied in globular clusters due to having long pulsation periods ranging from 30-1000 days. Previous cluster studies have focused mainly on RR Lyrae variables, which only require a few days of observations in order to well quantify their light curves, making these studies of little use to understand LPV behavior. M5 is a prime target for studying LPV stars, and its characteristics have been well studied (such as metallicity, distance, etc.), but little work has been done previously on the LPV populations. Images of M5 were collected by the PROMPT telescopes at Cerro Tololo Inter-American Observatory (CTIO) over 8 months, spanning most of 2011, with additional data provided by the BGSU observatory in 2007, 2009, 2010. This wide time span allows for a thorough char- acterization of LPVs that has not previously been possible. Initial light curve results have been very promising, with successful characterization of W Virginis and RV Tauri type variables. The variability of known LPVs, V50 and V171-V180, were also successfully characterized with un- precedented detail. Updated periods were determined for the eleven known LPVs, four new LPVs were discov- ered, and four additional stars were found to be suspected variable stars. The creation of a Color Magnitude Diagram (CMD) supports the hypothesis that LPV pulsations become more regular, and amplitudes increase, as a star moves up the RGB. Finally, all of the evidence from the PROMPT data set was compiled and each star variability type was determined based upon the observed light curves and the star’s location on the CMD. Suggestions for future observations was also provided to assist in future work improving the characterization of each LPV. iv To my wife Anna and my family who always believed in me v ACKNOWLEDGMENTS This work would not have been possible without the direction and support from Dr. Andrew Layden. Dr. Layden provided a welcoming and nurturing environment to do research in and his endless support, knowledge, and patience are appreciated beyond words. I would also like to thank the members of the thesis committee Dr. John Laird and Dr. Dale Smith, who both provided great feedback that have helped improve this paper to what is seen today. I’d also like to thank my parents, Steve and Cheryl, who always encouraged me to follow my dreams. I cannot thank them enough for their love and support along the way. Finally, I owe a big thanks to my wife Anna who has supported me in this endeavor through thick and thin. This wouldn’t have been possible with out her love, support, and patience. vi TABLE OF CONTENTS Page CHAPTER 1. INTRODUCTION .............................. 1 CHAPTER 2. OBSERVATIONS .............................. 5 2.1 Location . 5 2.2 Equipment . 5 2.2.1 Telescope and Camera . 5 2.2.2 Filters . 5 2.3 Observing Procedure . 6 2.3.1 Exposure Times . 6 2.3.2 Requesting Observations . 6 CHAPTER 3. PRELIMINARY IMAGE ANALYSIS .................... 8 3.1 Initial Review of Images . 8 3.1.1 Observing Cadence . 9 3.1.2 Reference Star Selection . 10 3.2 Statistics from Digital Images . 11 3.2.1 CCD Cameras and Poisson Statistics . 11 3.2.2 Sky Background . 13 3.2.3 Full Width at Half Maximum . 13 3.2.4 Ellipticity . 15 CHAPTER 4. ISIS IMAGE SUBTRACTION ........................ 16 4.1 Introduction . 16 4.2 Image Preparations before Using the ISIS Process . 17 4.2.1 Image Scaling . 17 4.2.2 Image Alignment . 18 4.2.3 Image Trimming . 19 4.2.4 Step 1: Reference Image Creation . 21 vii 4.2.5 Step 2: Image Subtraction . 21 4.2.6 Step 3: Creating a Composite Image . 23 4.3 Identification of Known Variable Stars . 25 4.3.1 World Coordinate System . 25 4.3.2 Marking Known Variables . 27 CHAPTER 5. PERIOD DETERMINATION ........................ 30 5.1 Flux Difference Photometry with ISIS . 30 5.2 Period Determination . 30 5.2.1 Period Aliases and Harmonics . 32 5.2.2 Determining Period Uncertainty . 32 5.3 Two Test Cases with Known Variables . 33 5.3.1 Light Curve Analysis of V42 . 33 5.3.2 Light Curve Analysis of V84 . 35 5.4 Known Long Period Variables . 38 5.4.1 Light Curve Analysis of V50 . 38 5.4.2 Light Curve Analysis of V171 . 42 5.4.3 Light Curve Analysis of V172 . 44 5.4.4 Light Curve Analysis of V173 . 48 5.4.5 Light Curve Analysis of V174 . 50 5.4.6 Light Curve Analysis of V175 . 52 5.4.7 Light Curve Analysis of V176 . 54 5.4.8 Light Curve Analysis of V177 . 58 5.4.9 Light Curve Analysis of V178 . 60 5.4.10 Light Curve Analysis of V179 . 62 5.4.11 Light Curve Analysis of V180 . 65 5.5 Newly Discovered Variable Stars . 68 5.5.1 Light Curve Analysis of V309 . 68 viii 5.5.2 Light Curve Analysis of V312 . 70 5.5.3 Light Curve Analysis of V313 . 72 5.5.4 Light Curve Analysis of V403 . 74 5.6 Summary of Results: New Variable Stars . 76 5.7 New Suspected Variable Stars . 77 5.7.1 Light Curve Analysis of V300 . 77 5.7.2 Light Curve Analysis of V307 . 80 5.7.3 Light Curve Analysis of V315 . 82 5.7.4 Light Curve Analysis of V318 . 84 5.8 Summary of Results: Suspected Variable Stars . 86 CHAPTER 6. CREATION OF A COLOR MAGNITUDE DIAGRAM ........... 88 6.0.1 Photutils for PSF Photometry . 88 6.0.2 Transformation of Instrumental Magnitudes to Standard Magnitudes . 89 CHAPTER 7. DISCUSSION OF RESULTS ........................ 93 7.1 Variable Star Type Designations . 93 7.2 Known LPVs . 93 7.2.1 Summary of Results for V50 . 95 7.2.2 Summary of Results for V171 . 96 7.2.3 Summary of Results for V172 . 97 7.2.4 Summary of Results for V173 . 98 7.2.5 Summary of Results for V174 . 98 7.2.6 Summary of Results for V175 . 99 7.2.7 Summary of Results for V176 . 100 7.2.8 Summary of Results for V177 . 100 7.2.9 Summary of Results for V178 . 101 7.2.10 Summary of Results for V179 . 102 7.2.11 Summary of Results for V180 . 103 ix 7.3 Newly Discovered Variable Stars . 104 7.3.1 Summary of Results for V309 . 104 7.3.2 Summary of Results for V312 . 105 7.3.3 Summary of Results for V313 . 105 7.3.4 Summary of Results for V403 . 105 7.4 Summary of Suspected Variable Stars . 106 7.4.1 Summary of Results for V300 . 106 7.4.2 Summary of Results for V307 . 107 7.4.3 Summary of Results for V315 . 107 7.4.4 Summary of Results for V318 . 108 CHAPTER 8. CONCLUSION ................................ 109 8.1 Comparison of Variability along the RGB . 109 8.2 Suggested Cadence for Future Observations . 111 8.3 Long Secondary Periods in LPVs . 113 8.4 Comparison of LPVs to M13 . 114 8.5 Final Summary of Results . 117 BIBLIOGRAPHY.. 109 x LIST OF FIGURES Figure Page 3.1 Examples of unusable images . 8 3.2 Observing cadence of PROMPT dataset . 9 3.3 Airmass vs. Julian Date . 10 3.4 The star inside the orange circle is the reference star for the globular cluster. 11 3.5 Examples of various color mapping schemes . 12 3.6 Distribution of sky background counts from PROMPT data set . 13 3.7 Comparison of FWHM values across each image in the data set . 14 3.8 Measured ellipticity values across the PROMPT dataset. 15 4.1 Step 1: Reference image creation . 16 4.2 Step 2: Creating subtracted images . 17 4.3 Step 3: Creating the composite image . 17 4.4 Position of the cluster center across entire data set . 19 4.5 Trimmed area of image . 20 4.6 Reference image . 22 4.7 Examples of subtracted.