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Identification and Characterization of Long Period Variable Stars in the Globular Cluster M69

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Identification and Characterization of Long Period Variable Stars in the Globular Cluster M69 IDENTIFICATION AND CHARACTERIZATION OF LONG PERIOD VARIABLE STARS IN THE GLOBULAR CLUSTER M69 Paul W. Husband Jr. 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 2017 Committee: Andrew C. Layden, Advisor John B. Laird Dale W. Smith ii ABSTRACT Andrew Layden, Advisor Observations of the globular cluster M69 were taken from August 2009 to September 2014 using the 0.4-m PROMPT #4 telescope in Chile. This telescope took observations in V and I bandpass filters, approximately once per week, for ten months of each year. Using the image subtraction software suite ISIS, the cluster was examined for variable stars with an emphasis on long period variable stars. As a part of the overall project the long period variable stars were examined for multiple period relationships, including long secondary periods. The long period variables stars were also plotted in a color magnitude diagram, along with the rest of the stars in the images, to help evaluate the location of the long period variable stars on the diagram. Plots of period vs. I magnitude, period vs. I magnitude range, and I magnitude range vs I magnitude were also plotted to assess whether measurements of one or two characteristics would provide insight into other characteristics of the long period variable stars. The light curves, period examination, and tools to conduct them, are presented in the body of this paper. Having 400+ images in V and I filters over a 5-year time frame is an improvement over the previous work on M69, which was either photographic or photoelectric. Based on these observations magnitudes, periods, and classification of seven previously known long period variable stars were reconfirmed or improved, eight new long period variable stars were classified as semi-regular, and three stars were marked for further investigation. iii To my wife, Tamara Without whom, this project would still be “in progress” Love you iv ACKNOWLEDGMENTS First, I have to acknowledge the guidance and support provided by Dr. Andrew C. Layden. His availability, knowledge, and patience were limitless and I cannot adequately express my appreciation for his help during this project. Dr. John B. Laird and Dr. Dale W. Smith, the remaining members of the supervisory committee, were also very helpful through this process in ways too numerous to list. I also have to mention Dr. Farida Selim. Her tireless efforts supporting my research as an undergraduate student took me places, and in directions, I doubt I would have found on my own. My parents, Paul and Dawnnene, made this possible. Without their love and support, even when I squandered opportunities as a child, never wavered. The child they raised to be able to achieve what I have so far, with so much left before me, is a testament to their resilience and patience. My brother, Eric, helped prepared me for many adversities and I look forward to seeing what he achieves. Then there is Tamara, who made this happen. Without her, I would not have travelled across the country to pursue a chance at happiness. Without her, I would not have enrolled in school full time. Without her, I may not have made it to this far, and definitely not as quickly as I have. “Thank you” seems too small a response, but it is a good down payment before the next adventure begins. v TABLE OF CONTENTS Page CHAPTER 1 INTRODUCTION ........................................................................................... 1 CHAPTER 2 OBSERVATIONS ........................................................................................... 6 2.1 Telescope ............................................................................................................. 6 2.2 CCD ..................................................................................................................... 6 2.3 Filters ................................................................................................................... 7 2.4 Observing Seasons ............................................................................................... 8 2.5 Observation Statistics ........................................................................................... 9 CHAPTER 3 IMAGE ANALYSIS ....................................................................................... 13 3.1 Image Preparation ................................................................................................ 13 3.2 Interpolation......................................................................................................... 14 3.3 Subtraction ........................................................................................................... 14 3.3 Detection .............................................................................................................. 16 3.4 Light Curves, Flux Correction, and Apparent Magnitude ................................... 18 CHAPTER 4 RESULTS ........................................................................................................ 20 4.1 Variable Star V5 ................................................................................................. 22 4.2 Variable Star V4 ................................................................................................. 29 4.3 Variable Star V1 ................................................................................................. 32 4.4 Variable Star V3 ................................................................................................. 34 4.5 Variable Star V6 ................................................................................................. 36 4.6 Variable Star V7 ................................................................................................. 38 4.7 Variable Star V8 ................................................................................................. 40 vi 4.8 Variable Star NV12 ............................................................................................. 42 4.9 Variable Star NV19 ............................................................................................. 44 4.10 Variable Star NV101 .......................................................................................... 45 4.11 Variable Star NV103 .......................................................................................... 47 4.12 Variable Star NV104 .......................................................................................... 48 4.13 Variable Star NV105 .......................................................................................... 50 4.14 Variable Star NVa .............................................................................................. 51 4.15 Variable Star NVb .............................................................................................. 53 4.16 Variable Star NVc .............................................................................................. 54 4.17 Variable Star NVd .............................................................................................. 56 4.18 Variable Star NVe .............................................................................................. 57 CHAPTER 5 CONCLUSION ................................................................................................ 59 REFERENCES ...................................................................................................................... 67 vii LIST OF FIGURES Figure Page 1 Air Mass vs. Heliocentric Julian Date. ...................................................................... 9 2 V Filter FWHM Values. ............................................................................................ 11 3 I_long filter FWHM Values. ...................................................................................... 12 4 I_short filter FWHM values. ...................................................................................... 12 5 Reference images (“ref.fits”) from ISIS. ................................................................... 15 6 Subtracted V filter image from 2010 Sep 18 ............................................................. 16 7 Variable star locations. ............................................................................................... 17 8 V filter light curve with single period of 196 days. ................................................... 25 9 V filter light curve with the 196 & 98 day model. ..................................................... 26 10 V filter light curve with 196, 98, and 423 day periods. ............................................. 27 11 I_long light curve with 196-day model. ..................................................................... 28 12 I_long light curve with model created with 196, 96, and 454-day periods. .............. 28 13 Graph demonstrating the similarity between I_long and I_short. .............................. 29 14 I_long light curve for V5 with model of 196.5, 97.1, and 440.4 days. ...................... 29 15 V Filter Light Curve for V4. ...................................................................................... 31 16 I filter light curve for V4. ........................................................................................... 32 17 V Filter light curve for V1. ........................................................................................ 34 18 I filter light curve for V1. ..........................................................................................
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