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研究生： 陳怡頻
Yi-Ping Chen
論文名稱： 利用二微米巡天觀測(2MASS)資料以恆星計數方法分析銀盤結構
The Galactic disk structure by 2MASS star counts
指導教授： 陳文屏
Wen-Ping Chen
口試委員:
學位類別： 碩士
Master
系所名稱： 理學院 - 物理學系
Department of Physics
畢業學年度： 93
語文別： 中文
論文頁數： 73
中文關鍵詞： 恆星計數 、薄盤 、厚盤 、二微巡天觀測(2MASS) 、銀盤
外文關鍵詞： star counts, thick disk, Galactic disk, 2MASS, thin disk
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    • 摘要
    我們利用恆星計數的方式，分析二微米巡天觀測(2MASS) 資料，以得知我們銀河盤面的結構。分析銀盤結構的模型主要由兩的參數所構成 — 一個為薄盤另一個為厚盤，這兩種盤上的恆星分佈，以銀河中心為點，在徑向和垂直方向上,都呈現指數衰減的情況。因此我們企圖利用2MASS 資料，並把它分成K = 5–9 mag (主要為巨星組成的薄盤) 和 K = 11–14 mag (主要為矮星組成的薄盤)兩個光度範圍。並朝l = 180° (亦即反銀心方) 的方向去挑選星場，且計算從銀盤面到南北兩極的每個星場密度。假使厚盤密度的只有薄盤的百分之二，那我們的資料對於估計厚盤參數並不敏感。在K = 5–9 mag (巨星) 的亮星星場，因為星數太少，所以無法估計由巨星組成的薄盤，至於由矮星 (K = 11–14 mag)所組成的薄盤，在銀盤之北及之南的分布相當，且厚度135 ± 80 pc，徑向尺度為700 ± 500 pc。

    Abstract
    We apply star counting technique on the Two Micron All Sky Survey (2MASS) point-source catalog in an attempt to diagnose the disk structure of the Milky Way Galaxy. The analytical disk model includes two stellar components, a thin and a thick disk, both with doubly exponential distributions in radial and height directions. We present how the projected stellar densities for 2MASS sources from K = 5 to 9 mag (dominated by thin disk giants) and from K = 11 to 14 mag (dominated by thin disk dwarfs), vary from the Galactic Equator to the North Galactic Pole and to the South Galactic pole in Galactic longitude l = 180 degrees. Assuming a nominal 2% contribution from the thick disk relative to the thin disk, our data are not sensitive to the thick disk. Because of the low surface density in the K = 5 to 9 mag sample, we counted not set a firm constraint to the distribution of the thin disk giants. For thin disk dwarfs, our analysis yields a scale height of 135 ± 80 pc and with a radial scale length of 700 ± 500 pc.

    Contents List of Figures Ⅴ List of Tables Ⅵ 1 Introduction 1 1.1 The Galactic Model …………………………………………………………2 1.2 Motivation of Our Study ………………………………………………….4 2 Star Counts Data 5 2.1 The 2MASS Data Base …………………………………………………..5 2.2 Selection of Random Fields ………………………………………………5 2.2.1 Two-Point Correlation Function ……………………………………6 2.2.2 Two-Point Correlation Function on Multiple Angular Scales ……….7 2.3 Adopted 2MASS Star Fields ……………………………………………….9 2.4 The Final 2MASS Field Selected in This Study …………………………14 3 Comparison with The Data 17 4 Conclusions 23 References 24 Appendix A1 Two-point correlation function on multiple angular scales of uniform random field 25 Appendix A2 The uniform random fields for l =180 deg, b = 2 to 88 deg 58 Appendix A3 The uniform random fields for l =180 deg, b = - 2 to - 88 deg 62

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