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The Metallicities and Kinematics of Rr Lyrae Variables from Asas

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The Metallicities and Kinematics of Rr Lyrae Variables from Asas THE METALLICITIES AND KINEMATICS OF RR LYRAE VARIABLES FROM ASAS Xiao Chen 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 2015 Committee: Andrew C. Layden, Advisor John B. Laird Dale W. Smith ii ABSTRACT Andrew C. Layden, Advisor Studying RR Lyrae stars (RRLs) is a useful way to understand the formation and struc- ture of our Galaxy. We obtained spectra of 89 RRLs of Bailey type ab. After processing these spectra, we obtained the radial velocity for each star. We also derived the pseudoequivalent widths (EWs) of CaIIK, Hδ,Hγ and Hβ from their absorption lines. Then we transformed our EWs to the same system used in Layden [14], and calculated the metal abundances. To investigate the kinematics and metallicities of our RRLs, we derived rotation veloci- ties and velocity dispersions from stars' radial velocities. After combining our radial velocities and the literature proper motions, we derived space motions for 85 of our RRLs. We plotted rotation velocities against metallicities, and found an abrupt change at [F e=H] ≈ −1:0. iii ACKNOWLEDGMENTS My sincere gratitude goes to my advisor, Dr. Andrew C. Layden, for his great patience and helpful guidance. This research project would not be accomplished without him. I would also like to thank my committe members, Dr. John B. Laird and Dr. Dale W. Smith. Their assistance and instructions have been of great help to this thesis. Finally, I would like to thank my parents. Their support and love have encouraged me to get this far. iv TABLE OF CONTENTS Page CHAPTER 1. INTRODUCTION ::::::::::::::::::::::::::::: 1 CHAPTER 2. SPECTROSCOPIC DATA :::::::::::::::::::::::: 6 2.1 Observing . 6 2.2 Image Processing . 7 2.3 Spectral Processing . 8 CHAPTER 3. DATA FROM THE LITERATURE ::::::::::::::::::: 15 3.1 Photometry . 15 3.2 Galactic Dust Reddening and Extinction . 23 CHAPTER 4. RADIAL VELOCITIES :::::::::::::::::::::::::: 25 4.1 Radial Velocity Method . 25 4.2 Radial Velocity Checks . 28 4.3 Radial Velocities . 31 CHAPTER 5. METALLICITIES ::::::::::::::::::::::::::::: 35 5.1 Equivalent Widths . 35 5.1.1 Measurements . 35 5.1.2 Calibrating EWs . 39 5.2 Metallicities . 41 5.2.1 Rough [Fe/H] . 45 5.2.2 Interstellar CaK . 46 5.2.3 Hβ .................................. 46 5.2.4 Final [Fe/H] . 47 5.2.5 Rising Branch . 48 CHAPTER 6. KINEMATICS ::::::::::::::::::::::::::::::: 50 6.1 Rotation Velocities . 50 v 6.1.1 Net Rotations . 50 6.1.2 Plots and Analysis . 52 6.1.3 Combining . 56 6.2 Woolley Solutions . 56 6.3 Space Motions . 59 6.4 Discussion . 62 CHAPTER 7. CONCLUSION ::::::::::::::::::::::::::::::: 65 REFERENCES ::::::::::::::::::::::::::::::::::::::: 67 vi LIST OF FIGURES Figure Page 1.1 Galactic Components . 1 1.2 Two Galactic Formation Models . 4 2.1 Trim the Spectra . 8 2.2 Fix Bad Pixels . 9 2.3 2D to 1D . 9 2.4 Intensity vs. x-pixel . 10 2.5 Typical Final Spectrum . 12 2.6 High S/N Final Spectrum . 13 2.7 Low S/N Final Spectrum . 14 3.1 Good Phase Sample . 20 3.2 Bad Phase Sample . 21 3.3 Hammer Projection . 22 3.4 Galactic Dust . 23 4.1 Typical Peak and Object/Template Pair . 26 4.2 Poor Peak . 26 4.3 Narrow & Wide Peak . 27 4.4 HD 693 . 29 4.5 Templates . 30 4.6 RV vs. Phase for ASAS 004025 . 33 4.7 RV vs. Phase for ASAS 232246 . 34 5.1 Absorption Lines . 36 5.2 Hβ Line . 37 5.3 CaIIK Line for A Cool Star . 38 5.4 CaIIK Line for A Hot Star . 39 vii 5.5 Hδ For Calibrating EWs . 40 5.6 H2 vs. Phase . 43 5.7 The Relation of Phase and EWs . 44 5.8 WK vs. H2 . 45 5.9 FeH vs. Phase . 49 6.1 Angle Relations . 51 6.2 Rotational Velocities . 53 6.3 Vs vs. cos Ψ . 54 6.4 Combined Rotational Velocities . 57 6.5 Combined Vs vs. cos Ψ . 58 6.6 Space Motions . 61 viii LIST OF TABLES Table Page 2.1 Comparison Format Sample . 7 3.1 ASAS Data Sample . 16 3.2 Photometry Data Sample from ASAS . 18 3.3 Final Data from PDM . 19 4.1 FXCOR Data . 28 4.2 Data of Template Stars . 31 4.3 Fitted RVs . 33 5.1 EW Regions . 38 5.2 Coefficients of the Fitted Lines . 40 5.3 Calibrated EWs . 42 5.4 Final Metallicities . 48 5.5 Calibrating Rising Branch . 49 6.1 Values of Rotational Velocities . 55 6.2 Values of Combined Rotational Velocities . 56 6.3 Woolley Solutions . 59 6.4 Woolley Solutions from Combined Data . 59 6.5 Space Motions . 60 6.6 MWTD . 60 6.7 Kinematics of the Halo and Disk Stars . 62 6.8 Test1 . 63 6.9 Test2 . 64 1 CHAPTER 1. INTRODUCTION The major components of the Milky Way are the disk, the halo and the nucleus or central bulge. Figure 1.1 shows the structure of our Galaxy. The left picture is the top view of the Galaxy, while the right picture is the side view of it. In order to understand these components, the metallicity must be mentioned first. When a massive star is in its last stage, it starts to fuse iron. Then the iron is ejected to space by a supernova detonation. In this case, new stars have higher metal abundances than the old stars. They are metal-rich stars. Thus, the ratio of iron-to-hydrogen, called metallicity, can indicate the age of a star. Its expression is NF e − NF e [F e=H] = log10( ) log10( )⊙ (1.1) NH NH where NF e and NH are the iron and hydrogen atom numbers per unit of volume respectively. ⊙ means the Sun. Obviously, our Sun has a metallicity of 0.0. Metal-rich stars have large values, around 0.0; and metal-poor stars have small values, some old stars have metallicity as low as −4:5 [7]. The disk contains most of the dust, gas and stars of our galaxy. The dust and gas Figure 1.1: Components of the Milky Way. This picture is from JCCC [11]. 2 between stars are called the interstellar medium, which has an influence on the stars' distance measurements. Our Sun is a disk star. Instead of residing near the center of the disk, the Sun lies about one-third away from the center. Its distance from the center of the Galaxy is 8.0 0.5 kpc. Thin disk and thick disk are the main components of the disk. Thin disk is about 50 pc in height, while the thick disk has a height of about 1.4 kpc. However, the stellar number density of the thick disk is about 2% of the density of the thin disk. [7] The stars in the thin disk are younger than the stars in the thick disk. The metallicities of thin disk stars have a range of −0:5 < [F e=H] < 0:3, while most thick disk stars have −0:6 < [F e=H] < −0:4, though some thick disk stars may have very low metallicities, as low as −1:6 [10]. The disk stars rotate around the center of our galaxy with uniform velocities. The halo contains plenty of globular clusters and field stars (stars that are not in globular clusters). They are very old stars. Astronomers estimate that there are 230 globular clusters in the halo, and more than half of the clusters have been.
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