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PROPERTIES OF BRIGHT VARIABLE STARS IN UNUSUAL METAL RICH CLUSTER NGC 6388 Gustavo A. Cardona V. AThesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 2011 Committee: Andrew C. Layden, Advisor John B. Laird Dale W. Smith ii ABSTRACT Andrew C. Layden, Advisor We have searched for Long Period Variable (LPV) stars in the metal-rich cluster NGC 6388 using time series photometry in the V and I bandpasses. A CMD was created, which displays the tilted red HB at V = 17.5 mag. and the unusual prominent blue HB at V = 17 to 18 mag. Time-series photometry and periods have been presented for 63 variable stars, of which 30 are newly discovered variables. Of the known variables nine are LPVs. We are the first to present light curves for these stars and to classify their variability types. We find 3 LPVs as Mira, 6 as Semi-regulars (SR) and 1 as Irregular (Irr.), 18 are RR Lyrae, of which we present complementary time series and period for 14 of these stars, and 7 are Population II Cepheids, of which we present complementary time series and period for 4 of them. The newly discovered variables are all suspected LPV stars and we classified them, using time series photometry and periods, as Mira for 1 star, SR for 15 stars, Irr for 7 stars, Suspected Variables for 7 stars, out of which there are 3 very bright stars that could have overexposed the CCD, with no definite borderline between the SR and Irr stars. Once classified we used probable distance for the cluster center and location on the CMD to establish possible membership, which left us with 63 possible cluster members, but the crowdedness of the cluster and the fact that the cluster is located near the bulge of the Milky Way prevents us from establishing a better certainty for its membership. iii Dedicado a mis padres Humberto Cardona y Magaly Velasquez, por haberme introducido el “Cosmos” y por ensa˜narme que nunca hay l`ımite para lo que queremos lograr mientras uno no deje de so˜nar iv ACKNOWLEDGMENTS First and foremost, my utmost gratitude to my advisor, Dr. Andrew Layden, for his patience, enthusiasm, encouragement and countless amount of hours he spent imparting knowledge while guiding me through this project. I would also like to thank the faculty and staffat the Physics and Astronomy department in BGSU for their support for the past two years. Special gratitude to my classmates,and expcially to Moe Abbas, my partner in crime, whose help while we raked through innumerable journals, books and across many obstacles to understand the material so we could apply it to our thesis, will never be forgotten. Words fail to express my appreciation to my parents, Humberto and Magaly, and my two best friends, my wife, Soo Choi, and my brother, Juan David Cardona, for their unwavering support and faith in what I was doing, and because each day they reminded me of the fact that following your dreams is never the wrong path to undertake. Finally to my friends and family, because they were all uniquely important in the suc- cessful realization of my thesis. v TABLE OF CONTENTS Page CHAPTER 1. INTRODUCTION ............................. 1 CHAPTER 2. PROCESSING ............................... 8 2.1 Observations . 8 2.2 Calibrations . 9 2.3 Combining................................... 14 CHAPTER 3. PHOTOMETRY .............................. 17 3.1 ISIS . 18 3.1.1 Setting up for ISIS . 18 3.1.2 Running ISIS . 19 3.2 DAOPHOT .................................. 25 3.2.1 SettingupforDAOPHOT . 25 3.2.2 RunningDAOPHOT ........................ 26 CHAPTER 4. CALIBRATION .............................. 37 4.1 Standard Stars . 37 4.2 Variable Stars . 47 CHAPTER 5. COLOR MAGNITUDE DIAGRAM ................... 51 5.1 Isochrones . 56 CHAPTER 6. VARIABLE STARS ............................ 59 6.1 Variability Detection . 59 6.1.1 Variability detection with ISIS . 59 6.1.2 VariabilitydetectionwithDAOPHOT . 59 6.2 Magnitude vs. time Detection . 63 6.3 Variable Properties . 69 6.4 Known Variables . 70 vi 6.4.1 Comparison with LEM . 72 6.4.2 Comparison with PSCS . 83 6.4.3 Comparison With Corwin et al................... 106 6.5 NewFoundVariables ............................. 113 CHAPTER 7. CLUSTER MEMBERSHIP ........................ 142 7.1 Projected distance from the center . 142 7.2 Location on the CMD diagram . 143 CHAPTER 8. CONCLUSIONS .............................. 150 8.1 Summary . 150 8.2 Future Research . 154 REFERENCES ....................................... 158 vii LIST OF FIGURES Figure Page 2.1 Dark current across the CCD . 11 2.2 Comparison of frame after calibration . 15 2.3 Comparison between good and bad frame stacking . 16 3.1 Comparison between original and trimmed image . 19 3.2 Convolution of two square pulses . 22 3.3 Comparison of two star profiles . 24 3.4 PHOT task values . 28 3.5 Subtracted image . 32 3.6 Montage Image . 35 4.1 Carreta et al. CMD with studied stars . 40 4.2 Comparison between Carreta et al. and Stetson standard stars . 41 4.3 Dependence of calibrated data . 48 4.4 V4locatedintheCMD .............................. 49 5.1 Color Magnitude Diagram for the whole field . 52 5.2 Tidal radius in the master frame . 54 5.3 SelectiveCMDforNGC6388........................... 55 5.4 Isochrones plotted over CMD . 58 6.1 ISIS var.fits image . 60 6.2 Variability index for Season 3 . 62 6.3 Zoomed-in variability index . 62 6.4 θ vs. Period graph . 64 6.5 Folded curve using θ close to 1 . 65 6.6 Folded curve using θ close to 1 . 65 6.7 Sample light curve . 67 viii 6.8 chi2 vs trial periods for template fitting method . 67 6.9 Foldedcurveusingtemplatefittingmethod . 68 6.10 CandidatevariablestarsfoundusingISIS . 71 6.11 CandidatevariablestarsfoundusingDAOPHOT . 71 6.12 VariableV2lightcurve .............................. 74 6.13 VariableV3lightcurve .............................. 75 6.14 VariableV4lightcurve .............................. 76 6.15 VariableV5lightcurve .............................. 77 6.16 VariableV6lightcurve .............................. 78 6.17 VariableV7lightcurve .............................. 79 6.18 VariableV8lightcurve .............................. 80 6.19 VariableV9lightcurve .............................. 81 6.20 VariableV12lightcurve.............................. 82 6.21 VariablestarscomparedwithPSCS . 84 6.22 Light curve vs. Folded curve for RRLyrae . 85 6.23 Difference in periods for sample RRL . 85 6.24 Variable17lightcurve............................... 86 6.25 Variable18lightcurve............................... 87 6.26 Variable21lightcurve............................... 88 6.27 Variable22lightcurve............................... 89 6.28 Variable23lightcurve............................... 90 6.29 Variable26lightcurve............................... 91 6.30 Variable26lightcurvewithPSCSperiod . 91 6.31 Variable27lightcurve............................... 92 6.32 Variable28lightcurve............................... 93 6.33 Variable29lightcurve............................... 94 ix 6.34 Variable30lightcurve............................... 95 6.35 Variable31lightcurve............................... 96 6.36 Variable35lightcurve............................... 97 6.37 Variable36lightcurve............................... 98 6.38 Variable36foldedlightcurve . 99 6.39 Variable36lightcurve. 100 6.40 Variable49lightcurve. 101 6.41 Variable50lightcurve. 102 6.42 Variable51lightcurve. 103 6.43 Variable53lightcurve. 104 6.44 Variable53foldedlightcurve . 104 6.45 Variable55lightcurve. 105 6.46 SuspectedVariableSV2lightcurve. 107 6.47 SuspectedVariableSV5lightcurve. 108 6.48 VariableV59lightcurve. 109 6.49 VariableV67lightcurve. 110 6.50 VariableV68lightcurve. 111 6.51 VariableV69lightcurve. 112 6.52 VariableNV30lightcurve. 113 6.53 VariableNV7lightcurve ............................. 114 6.54 VariableNV14lightcurve. 115 6.55 VariableNV1lightcurve ............................. 116 6.56 VariableNV15lightcurve. 117 6.57 VariableNV10lightcurve. 118 6.58 VariableNV9lightcurve ............................. 119 6.59 VariableNV12lightcurve. 120 x 6.60 VariableNV22lightcurve. 121 6.61 VariableNV5lightcurve ............................. 122 6.62 VariableNV21lightcurve. 123 6.63 VariableNV18lightcurve. 124 6.64 VariableNV26lightcurve. 125 6.65 VariableNV28lightcurve. 126 6.66 VariableNV27lightcurve. 127 6.67 VariableNV4lightcurve ............................. 128 6.68 VariableNV16lightcurve. 129 6.69 VariableNV3lightcurve ............................. 130 6.70 VariableNV23lightcurve. 131 6.71 VariableNV25lightcurve. 132 6.72 VariableNV24lightcurve. 133 6.73 VariableNV2lightcurve ............................. 134 6.74 VariableNV17lightcurve. 135 6.75 VariableNV17lightcurve. 136 6.76 VariableNV20lightcurve. 137 6.77 VariableNV8lightcurve ............................. 138 6.78 VariableNV6lightcurve ............................. 139 6.79 VariableNV19lightcurve. 140 6.80 VariableNV11lightcurve. 141 7.1 Location of Rcore,Rhalf mass and Rtidal in our field ov view . 144 − 7.2 Isochrones over plotted CMD . 146 7.3 Isochrone over plotted CMD with LPV candidates . 148 8.1 Variable stars . 152 8.2 LPV stars compared using Isochrone . 153 xi 8.3 Classified variables in the CMD . 155 xii LIST OF TABLES Table Page 3.1 ALSfileoutput................................... 30 4.1 Standars stars in comparison datasets . ..
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