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Multi-Color Photometry of Supergiants and Cepheids

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Multi-Color Photometry of Supergiants and Cepheids X-641-71-184 $" 'PREPRINT MULTI-COLOR PHOTOMETRY OF SUPERGIANTS AND CEPHEIDS THOMAS KELSALL MAY 1971 S~z5-p ----- GODARDd SPACE-48,wFLIGHT -CENTER GREENBELT, MARYLAND -30- (NASA CKUKOTMX OR AD NUMBER) (CATEGORY) LLTGOY MULTI-COLOR PHOTOMETRY OF SUPERGIATS AND CEPHEIDS by Thomas Kelsall Dissertation submitted to the Faculty of the Graduate School of the University of Maryland in partial fulfillment of the requirements for the degree of Doctor of Philosophy 1971 ABSTRACT Title of Thesis: Multi-color Photometry of Supergiants and Cepheids Thomas Kelsall, Doctor of Philosophy, 1971 Thesis directed by: Roger A. Bell, Associate Professor of Astronomy The results of photometry of supergiants and cepheids in a seven filter system are presented. A color index is used in combination with other colors to produce four indices freed from the effects of inter­ stellar reddening. These four indices give measures of the Balmer discontinuity, effects of the metallic line absorption in the violet region of the spectra, break in the spectrum across the G-band, and the strength of the cyanogen band head at 4216. The separation of supergiants from stars of other luminosity classes is possible. This is performed by a non-linear mapping of the colors onto an M ,logT H-R diagram. Population discrimination for cepheids appears impossible from a study of the colors. However, it is shown that the values of various color-color loop areas can be used to distinguish cepheids of Pop. I and Pop. II. This procedure is superior as it is independent of interstellar reddening. The Balmer discontinuity index for supergiants and cepheids is insensitive to the effects of line blanketing. We speculate that this will allow for a precise calibration in terms of gravity. The strengths of the metallic line absorption and CN absorption are strongly corre­ lated. No obvious correlation is found between galactic position and and chemical composition, as indicated from the strength of the metallic line index. DEDICATION I dedicate this thesis to two gentlemen who gave me much for which I am thankfnl -­ my father Mr. Bernard Kelsall my teacher and friend Dr. Uco Van Wijk ii ACkNOWLEDGEMENTS I offer sincere thanks to Dr. Roger A. Bell, my advisor, for the giving of his critical insights, time, and patience. I am grateful to Dr. Nicholas U. Mayall, Director of Kitt Peak National Observatory, for the opportunity to use the facilitids of his observatory. I also thank the observatory staff for their assistance and friendliness, and in particular, Dr. David L. Crawford, Mrs' Jeannette Barnes, and Mr. J. C. Golson. For the reading of the manuscript and helpful advice I thank the Drs. Donat Wentzel and Michael A'Hearn. Acknowledgement is made to Dr. Richard J. Drachman and Dr. Bengt Strimgren for their many useful discussions. Mr. Andrew Butz and Mr. Charles Mahaffey gave aid in the reading of the charts, proof reading of the punched data, and numerous othe assistances for which I am thankful. To my wife Ann I offer appreciation for the aid given, both direct and indirect. "Opereted by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. iii TABLE OF CONTENTS Chapter Page DEDICATION . ii ACKNOWLEDGEMENTS ................................................ iii I INTRODUCTION .1 1-1. Preamble .......................................... 1 1-2. Theoretical Work and Its Motivational Basis ....... 1 1-3. Basic Cepheid Parameters from Observations ....... 16 1-4. Intrinsic Colors .................................. 35 1-5. Aims of the Investigation ......................... 37 II. THE OBSERVATIONS.......................................... 49 2-1. The Filters....................................... 49 2-2. Equipment and Data Gathering...................... 50 III. TIE STANDARD SYSTEM....................................... 58 3-1. Photometric Quantities............................ 58 3-2. Basic Processing Procedure ...................... 59 3-3. Construction of the Observational System's Standards......................................... 61 5-4. Final Comments................................... 65 IV. ORDINARY,STAR RESULTS..................................... 76 4-1. Reduction and Results............................. 76 4-2. Mode of Analysis.................................. 76 4-3. Color Excess Ratios............................... 79 4-4. Bracketed Colors Versus Spectral Type............. 82 4-5. Intrinsic Values for (b-y) and G .................. 83 4-6. Physical Meaning of [G] and [N] ................... 84 iv Chapter Page V. LUMINOSITY CLASSIFICATION.................................. 107 5-1. Objective and Procedure ............................ 107 5-2. Source of the Data .................................. 107 5-5. Color-Spectral Type Relationships .................. 109 5-4- Supergiant Discriminants ........................... 111 VI. BASIC CEPHEID RESULTS....................................... 129 6-1. Photometry and Data ................................ 129 6-2. The Periods .............................. .... .... 129 6-3. Color-Phase Results ................................ 132 6-4. Comparison with the Supergiants.................... 132 6-5. A Population II Discriminant....................... 133 6-6. (b-y) Color Excesses ............................... 134 6-7. (b-y)0 and the Effective Temperature............... 136 VII. COMBINED CEPEEID-SUPERGIANT RESULTS........................ 169 7-1. The 'Supercolor' Method ............................ 169 7-2. Comparison of the Cepheid and Supergiant Mean Colors ......................................... 172 7-3. Metal Content and Galactic Structure ............... 175 7-. Comments on Williams' Work ......................... 173 7-5. Conclusions ........................................ 175 APPENDIX A. STAR IDENTIFICATIONS ................................. 195 APPENDIX B. DATA FROM WILLIAMS AND STROMOREN ..................... 205 APPENDIX C. COEFFICIENTS OF THE SUPEECOLORS ...................... 216 LITERATURE CITED .................................................. 218 LIST OF TABLES Table Page 1.1. Slope of the P-L relation for SMC cepheids ................ 42 1.2. Physical properties of classical cepheids ................. 43 2.1. Transmission characteristics of the filters used in this investigation ........................................ 53 2.2. Comparison of the transmission characteristics of uvby filter sets No. 1 and.No. 2 ............................... 54 2.3. Summary of the observational runs at Kitt Peak National Observatory ............................................... 55 3.1. The color-extinction coefficients ........................ 65 3.2. Observations of the standard stars........................ 66 3.3. Standard star probable errors ........................... 70 4.1. Observations of the ordinary stars....................... 86 4.2. Effective wavelengths .................................... 98 4.3. Color excess ratios from external sources................ 98 4.4. Color excess ratios determined from cepheids at maximum light..................................................... 99 4.5. Color excess ratios determined from free parameter fitting ................................................... 99 4.6. Final adopted color excess ratios ......................... 99 5.1. The mean reddening-free colors for all luminosity classes ................................................... 114 5.2. RDMS dispersions in the mean colors at any spectral type ... 18 6.1. Observations of the cepheids .............................. 138 6.2. Cepheid periods ........................................... 149 6.3. Cepheid color excesses determined from using the relation - G0 = 0.543*(b-y)0 -,0.1l0 ...................... 151 7-1. Deviations of the FO to KO supergiants about the mean color lines defined with [G] as independent coordinate.... 178 vi vii Table Page 7.2. Average deviations of the Pop. I cepheids about the mean color lines defined with [G] as independent coordinate ................................................ 182 7.3. Reanalysis of Williams' long period cepheid data ......-.... 184 A.1. Catalog of identificatioa data for the program stars ...... 196 BA1. Comparison of Williams' original and transformed reddening-free colors to those of Kelsall's ................ 206 B.2. Comparison of Stromgren's original and transformed reddening-free colors to those of Kelsall's ................ 210 0.1. The Mv.upercolor coefficients for the various [G] regions .................................................... 217 LIST OF FIGURES Figure Page 1.1. Magnitude differences versus relative surface displacements at points of equal color for 6 Cep ......... 44 1.2. Comparison of the observed and computed light curves for 8 Cep .............. .......................... 44 1.3. Observed and computed line profiles for weak Fe I lines in p Aql .......................................... 45 1.4. Contribution of various regions in a star to the maintenance of pulsation ................................. 45 1.5. Variation with temperature of the V and B magnitudes for black-bodies. The observed dependence of the mean V and B magnitudes with period ................................. 46 1.6. Location of the F, G and K supergiants and the cepheid S Sge in a six-color (V-B),(R-I) diagram ................. 47 1.7. Determination of the (B-V) color excess through the use of r photometry ...................................... 48 2.1. Transmission scans for the filters used in this investigation ...........................................
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