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Chemical and Kinematic Properties of Bright Metal Poor

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Chemical and Kinematic Properties of Bright Metal Poor Chemical and Kinematic Properties of Bright Metal Poor Stars ARCHNEM MASSACHUSETTS INSTITUTE OFTECHNOLOLGy by Weishuang Linda Xu AUG 10 2015 Submitted to the Department of Physics LIBRARIES in partial fulfillment of the requirements for the degree of Bachelor of Science in Physics at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2015 Massachusetts Institute of Technology 2015. All rights reserved. Signature redacted A uthor .................................. .-...-. .. ... Department of Physics May 9, 2015 Signature redacted C ertified by .......................... ............... .............. Anna Frebel Assistant Professor of Physics Thesis Supervisor Signature redacted / - A ccepted by ........................... - - Nergis Mavalvala Physics Senior Thesis Coordinator 2 Chemical and Kinematic Properties of Bright Metal Poor Stars by Weishuang Linda Xu Submitted to the Department of Physics on May 9, 2015 , in partial fulfillment of the requirements for the degree of Bachelor of Science in Physics Abstract In this work, I analyze the high-resolution spectra of 20 stars, chosen for their low metallicity rFe/HI < -2.5 and proximity to the sun. Using these spectra I model the atmospheres of these stars by determing stellar parameters {Teff, log(g), p, [Fe/H]} and obtain also their chemical abundances for 17 elements including Fe, C, Sr, and Ba. Three of these stars are found to possess an overabundance of Carbon relative to Iron. Combining these chemical abundances with those from previously analyzed spectra from the same bright metal-poor star sample, I perform orbit determination and integration on a total of 59 metal-poor stars and extract their kinematic parame- ters. I also explore how these results depend on the assumed mass of the Milky Way. These chemical and kinematic results are then combined and compared with com- paratively metal-rich (-2.5 < [Fe/H] < 0) samples; a conal distribution of velocity components with respect to metallicity is observed, as well as two distinct populations in eccentricity. The 59 bright metal-poor stars were identified as residing in the inner halo of the Milky Way. Thesis Supervisor: Anna Frebel Title: Assistant Professor of Physics 3 4 Acknowledgments I am infinitely grateful to my wonderful supervisors and mentors Anna Frebel and Heather Jacobson. They provided more support, advice, direction, help, and timely prodding than I can quantify and made this entire project a very fun process in the end. I most definitely would not have a thesis without either of them, and at this point I owe them a whole of physics and astronomy and life advice. Not to mention that they bore not a little amount of undergraduate flakiness and confusion with incredible patience. I am thankful as well to the 6th floor of Kavli and all its inhabitants in general, particularly those who stopped by my annexed hallway desk in the middle of their busy grad student lives to chat. They made my work a lot more pleasant and I always felt welcome there. Thank you especially to Alex Ji who tolerated my biweekly usage of him as post-choir keycard access. Thank you to my lovely family and friends whose smiles, company, and conversa- tion carried me through college and the brilliant and brutal process that was MIT. I look to seeing most all of you back in sunny California. I extend my thanks finally to Fr, Qg, Sl, Al, Rz and all the others for all their love, support, patience, solidarity, and warmth that has been unequivocally critical to my happiness for the past years, in ways academic or otherwise. I genuinely wouldn't be myself without them. And of course thank you 0 for apples and bump functions and everything in between; there is very little I can justify with words here. 5 6 This doctoral thesis has been examined by a Committee of the Department of Physics as follows: Professor Nergis Mavalvala.................................. Senior Thesis Coordinator Professor of Physics Signature redacted Professor Anna Frebel................ Thesis Supervisor Assistant Professor of Physics 8 Contents 1 Introduction 17 2 Analysis of Spectral Data 19 2.1 Initial Processing: Normalization and Doppler Correction .... 19 2.2 Measuring Equivalent Widths of Spectral Features ... .... 21 2.3 Modeling Stellar Parameters from Equivalent Widths . ... 25 2.3.1 From Equivalent Widths to Abundances .... .. .. 26 2.3.2 Stellar Parameter Fitting ............. ... 27 2.3.3 Stellar Parameters of 20 Metal-Poor Stars . .. .... 29 2.4 Abundances of Non-Iron Elements ............ ... 29 2.4.1 Abundances of General non-Iron Metals .... .. 31 2.4.2 Synthetic fitting of Sr, Ba, and C Lines ..... ... 32 2.4.3 Chemical Abundances of 20 Metal Poor Stars . .. 38 3 Analysis of Kinematic Data 41 3.1 Parameters for Galactic Orbit Integration ....... 41 3.1.1 Astrometric Data: RA, Dec, and Proper Motions 42 3.1.2 Heliocentric Velocities .............. 42 3.1.3 Heliocentric Distances .............. 42 3.2 Orbits of Metal-Poor Stars ................ 44 3.2.1 Uncertainty of Orbits ............... 45 3.3 Orbital Potentials with Various Milky Way Masses . 45 9 4 Interpretation of Results 51 4.1 The Bidelman-McConnell Sample ...... .............. 51 4.2 Correlations between Metallicity and Orbital Kinematics . ...... 52 4.3 Identification of Halo Stars ........... ............ 53 4.4 Carbon Abundances . ........ ........ ......... 55 5 Conclusions and Future Work - 59 A Tables 61 10 List of Figures 2-1 Full spectrum of HE 2208-1239 after normalization and Doppler cor- rection ............ ....................... 20 2-2 Signal-to-Noise ratio as a function of wavelength for the spectrum of HE 2201-4043 ........ .............................. 20 2-3 Normalization of the 3600-1670 aperture of the spectra of HE 2208-1239 with a 4th-order spline function and 30A knot spacing. ........ 21 2-4 The spectra of HE 2208-1239 (in black), before [left] and after [right] corrections for Doppler shifting to match the template spectra of HD140283 (show n in blue) .............................. 22 2-5 Gaussian fits to various spectral features for HE 2235 -5058. The equivalent width of each fit is calculated automatically by SMH. 23 2-6 The approximate curve of growth for a Sun-like star. Image taken from [5 1 .......... ....................... .... 2 7 2-7 The Ha and Ho features of HE 2201-4043 compared with those of well known metal-poor stars. The reference stars used here are HD122563 (blue), HE 1523-0901 (red), CS22892-52 (green), HD140283 (ma- genta), G64-12 (cyan). One can infer that Teff of this star is roughly ~ 4700K . ....... ........ ........ ....... ... 28 2-8 Before temperature correction parameters for HE 2201-4043. The blue regression lines are not meaningful and can be ignored. ..... 31 2-9 After temperature correction parameters for HE 2201 -4043. The blue regression lines are not meaningful and can be ignored. ........ 32 11 2-10 20 metal-poor stars plotted on an isochrone (left). The log(g) - A plot (right) confirms that the input microturbulence factor is within expectation. ...... ........... ............ ... 33 2-11 59 stars from the bright metal-poor sample plotted on an isochrone. 33 2-12 Determination of Ti II abundance for HE 1317-0407. The red points indicate lines that were discarded due to excess noise or blending. .. 34 2-13 Determination of Mg I abundance for HE 1317-0407. There are sig- nificantly fewer lines than Ti or Fe. ................... 34 2-14 Fitting to Sr lines of HE 1311-0131 with synthetic spectra; the upper panels show the residuals of the fits in the lower panels. ..... ... 36 2-15 Fitting to Ba lines of HE 1311-0131 with synthetic spectra; the upper panels show the residuals of the fits in the lower panels. ........ 37 2-16 Fitting to CH forests of HE 1311-0131 with synthetic spectra; the upper panels show the residuals of the fits in the lower panels. .... 39 2-17 Chemical Abundances of 20 stars against previous literature ..... 40 3-1 Reading of Mv values from an isochrone plot with [Fe/H]z=-3.0. The Teff and log(g) parameters determine the star's position on the isochrone. 43 3-2 Plot of energy loss over time for HE 0201-3142. The energy error grows with time but is still very small (AE/E < 10-7). ........... 44 3-3 Integrated galactic orbits for a few stars in X--Y (left), R-Z (middle), and R - VR (right) spaces. .... ........... ........ 46 3-4 Integrated orbit of HE 1216-1554 under error perturbations of pmRA, pm Dec, and distance. .. ............ ........... 47 3-5 Changes in eccentricity, orbital apsis, and maximum orbital height (both in kpc) with varying assumptions on Milky Way mass. The abscissa shows the stars indexed 1-59. ..... ............. 49 4-1 Plots of Iron abundance [Fe/H] against eccentricity and U, V, W veloc- ities. ............. ....................... 5 2 12 4-2 Plots of Iron abundance [Fe/H] and U, V, W velocities for both this project and the B+Mc sample .................. .... 54 4-3 Plots of Iron abundance IFe/HI against eccentricity for both this project and the B+Mc sample. ................. ......... 55 4-4 Plot of orbital energies (tangential against radial velocity) for both these and the B+Mc stars. The dotted arcs are equipotential and the metal-rich disk is confined inside the 100 km/s arc. .......... 56 4-5 Plot of Carbon abundance as [C/Fe against [Fe/HJ, eccentricity, sur- face gravity, maximum height, and orbital apsis. A star is Carbon- enhanced at [C/Fe]>1. ... ........ ........ ....... 56 4-6 Plots of Carbon abundance as [C/Fe] containing both the stars in this work and the Bidelman-McConnell stars. ...... .......... 57 13 14 List of Tables 2.1 Stellar Parameters before and after temperature correction ...... 30 2.2 Chemical Abundances for 20 metal-poor stars ............. 40 A .1 A strom etry .. ......................... ..... 62 A.2 Astrometry (cont) ......... .................... 63 A.3 Heliocentric Distances .......................... 64 A.4 Heliocentric Distances (cont) ... .................... 65 A.5 Stellar Parameters .......
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