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Aperture Photometry at the Unisa Observatory

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Aperture Photometry at the Unisa Observatory APERTURE PHOTOMETRY AT THE UNISA OBSERVATORY: SYSTEM EVALUATION VIA LIGHT CURVES OF ECLIPSING BINARIES by VANESSA PIETERS submitted in fulfilment of the requirements for the degree of MASTER OF SCIENCE in the subject ASTRONOMY at the UNIVERSITY OF SOUTH AFRICA SUPERVISOR: PROFESSOR W F WARGAU JOINT SUPERVISOR: MR J GOCHERMANN NOVEMBER 1993 SUMMARY The University of South Africa has built a small observatory for teaching and research. The 35cm Schmidt-Cassegrain reflector and the SSP-5A photometer with Johnson UBV filters were used to evaluate the local possibilities for aperture photometry. Extinction and transformation coefficients and zero points were determined with the RPHOT software package from standard star photometry. To determine the system limits, UBV light curves were obtained for four eclipsing binaries, ranging between magnitudes 7 and 13. In B the limit is 12,5, in U it is 12,0 and in V only 11,0 with large scatter even for bright objects. The rapidly varying sky background in an urban site may be a major cause. A related problem is the large, fixed photometer diaphragm, aggravating the bright sky situation. Possible solutions to this and other problems were suggested. The system can be used fruitfully, especially for single filter photometry of periodic and nonperiodic variables. iii TABLE OF CONTENTS Page FIGURES viii TABLES ix CHAPTER 1 INTRODUCTION 1 1.1 Aperture photometry with small telescopes 1 1.2 Aperture photometry at disadvantaged sites 2 1.3 Variable star observation in the southern hemisphere 3 1.4 The Unisa Observatory (UNIOBS) 3 1.5 Outline of the study 4 CHAPTER 2 THE TELESCOPE 6 2.1 General information 6 2.2 Optics 6 2.3 Suitability of the C14’s optics for aperture photometry 11 2.3.1 Telescope type 11 2.3.2 F-ratio 14 2.3.3 Scale in the focal plane 14 2.3.4 Size of objective 15 2.3.5 The mount 16 2.3.6 Tracking 16 2.3.7 Setting 18 Summary 18 CHAPTER 3 THE PHOTOMETER 20 3.1 Types of photoelectric photometers 20 3.1.1 The sequential photometer 20 3.1.2 The simultaneous photometer 24 3.1.3 The multi-star photometer 25 3.2 The photomultiplier tube 25 3.2.1 Theoretical base 25 iv 3.2.2 : Types of photomultipliers 27 3.2.3 : Structure of a PMT 28 3.2.4 : Measurement of anode current 31 3.2.5 : Evaluating PMT function 32 3.2.5.1 : Sensitivity, drift and amplification 32 3.2.5.2 : Dark current 32 , 3.2.5.3 : Dead time 32 3.3 : The model SSP-5A photometer 33 3.3.1 : The photometer system 33 3.3.2 : Detailed structure and function of the photometer 33 3.3.2.1 : The flip mirror and viewing eyepiece 34 3.3.2.2 : The aperture stop or diaphragm 35 3.3.2.3 : The Fabry lens 35 3.3.2.4 : Filter slide 35 3.3.2.5 : The photomultiplier tube 36 3.3.2.6 : Preamplifier 38 3.3.2.7 : Main circuit board 38 3.3.3 : The performance of the SSP-5A 40 Summary 41 CHAPTER 4 : THE PHOTOMETRIC SYSTEM: FILTERS 43 4.1 : Fundamental characteristics of photometer filters 43 4.2 : Types of filters 46 4.2.1 : Glass filters 46 4.2.2 : Other types of filters 48 4.3 : The Johnson UBV filters 48 4.4 : The U, B, V and C filters for the SSP-5A 51 4.5 : Mounting and control of the SSP-5A filter system 53 Summary 54 CHAPTER 5 : THE STANDARD REDUCTION PROCEDURE 55 5.1 : Working definition of data reduction 55 5.2 : Steps in data reduction 55 5.3 : Preliminary steps 57 V 5.3.1 Dead-time correction 57 5.3.2 Achieving gain scale uniformity 58 5.3.3 Subtracting sky background 59 5.4 Calculating instrumental magnitudes and colours 59 5.5 Correcting for extinction 62 5.5.1 Calculating the air mass 62 5.5.2 Calculating first order extinction coefficients 64 5.5.3 Correcting for second order extinction 65 5.6 Determining zero-points 66 5.7 Determining transformation coefficients 70 5.8 The Moffat-Vogt correction 71 Summary 74 CHAPTER 6 DATA ACQUISITION AND REDUCTION BY MEANS OF THE RPHOT SOFTWARE PACKAGE 75 6.1 General information 75 6.2 Setting the system parameters 75 6.3 The catalogues 77 6.3.1 AST AR. CAT 78 6.3.2 FOE.CAT 79 6.3.3 SOE.CAT 79 6.3.4 COMP.CAT 79 6.3.5 VAR.CAT 80 6.4 The observing list prompt 80 6.5 The data acquisition programme 81 6.6 The initial reduction programme 85 6.7 Extinction/transformation coefficients programme 86 6.7.1 Full extinction/transformation calculation 87 6.7.2 First order extinction calculation only 88 6.7.3 Second order extinction and first order extinction calculation only 89 6.8 Final reduction programme 90 6.9 The plotting programme 91 6.9.1 Slowmode plots (light curves) 92 6.9.2 : Fastmode plots (occultations) 92 Linear regression plots 93 .־6.9.3 Summary 94 CHAPTER 7 DETERMINATION OF EXTINCTION AND TRANSFORMATION COEFFICIENTS FOR THE UNISA SYSTEM 95 7.1 Aim 95 7.2 Procedure 95 7.3 Results 97 7.3.1 Raw data from DTAK 97 7.3.2 Initial reduced data file from IREX 98 7.3.3 Extinction and transformation coefficients 100 7.3.3.1 Second order extinction coefficients 100 7.3.3.2 First order extinction coefficients 102 7.3.3.3 Transformation coefficients and zero points 104 7.4 The contents of COEFF.DAT versus that of RPARMS.DAT 104 Summary 107 CHAPTER 8 ECLIPSING BINARIES 108 8.1 Definition 108 8.2 Close binary systems 110 8.2.1 The Roche model 110 8.2.2 Detached systems 111 8.2.3 Semi-detached systems 111 8.2.4 Contact systems 112 8.3 Classification on the basis of light curve shape 113 8.3.1 General considerations 113 8.3.2 Algols 113 8.3.3 p Lyrae systems 115 8.3.4 W UMa' systems 115 Summary 116 CHAPTER 9 LIGHT CURVES OF ECLIPSING BINARIES OBTAINED AT THE UNISA OBSERVATORY 118 vii 9.1 : Choosing the programme objects 118 9.2 : The observing sequence 119 The light curves 120 ־. 9.3 9.3.1 : V759 Cen 120 9.3.1.1 : Background 120 Observations and results 121 .־ 9.3.1.2 9.3.1.3 : Discussion 124 9.3.2 : RR TrA 126 9.3.2.1 : Background 126 9.3.2.2 : Observations and results 126 9.3.2.3 : Discussion 130 9.3.3 : RW PsA 132 9.3.3.1 : Background 132 9.3.3.2 : Observations and results 133 9.3.3.3 : Discussion 136 9.3.4 : BF Pav 137 9.3.4.1 : Background 137 9.3.4.2 : Observations and results 137 9.3.4.3 : Discussion 140 Summary 140 CHAPTER 10 : CONCLUSION 141 10.1 : Limiting magnitudes for the Unisa aperture photometry system 141 10.2 : Problems and possible solutions 142 10.3 : Possibilities of the system 144 BIBLIOGRAPHY ............................................................................................... 146 1PPENDIX 1 ..................................................................................................... 149 2 ...................................................................................................... 150 3 ...................................................................................................... 152 4 ...................................................................................................... 159 5 ...................................................................................................... 160 6 ...................................................................................................... 179 7 ...................................................................................................... 218 8 ...................................................................................................... 238 ACKNOWLEDGEMENTS .................................................................................. 248 viii FIGURES Page Figure 2.1 ............................................................................................................ 9 2.2 10 2.3 ............................................................................................................ 13 2.4 ....................... ............................ ....................................................... 17 3.1 .................................................... i............. ;....................................... 21 3.2 ............................................................................................................ 22 3.3 ............................................................................................................ 28 3.4 ............................................................................................................ 33 3.5 ............................................................................................................ 34 3.6 ............................................................................................................ 36 3.7 ............................................................................................................ 39 3.8 ............................................................................................................ 40 3.9 ............................................................................................................ 41 4.1 ............................................................................................................ 47 - 4.2 ............................................................................................................ 49 4.3 ............................................................................................................ 50 4.4 ............................................................................................................ 52 4.5 ........................................................................................................... 52 4.6 ............................................................................................................ 53 5.1 ........................................................................................................... 68 6.1 ..........................................................................................................
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