臺灣博碩士論文加值系統

在變星的研究當中,週期是其中相當重要的一個特質。目前的 文獻中有許多尋找變星週期的方法供我們使用,例如:Lomb- Scargle periodogram, Phase Dispersion Minimization, SigSpec等。我們使用OGLE-III所發表的變星資料庫來比較以上三種方法尋找週期的準確度及效率,發現SigSpec對於不同種類的脈動變星的表現最佳。因此在本篇論文中,我們依據觀測到的變星資料配合SigSpec來尋找其週期。除此之外,我們透過前人所發表的經驗 法則得知:脈動變星在其可見光波段和紅外波段的星等變化有著一個大約為常數的比值,Amp(I)/Amp(V) ≃ 0.61。我們利用這個 前人對於脈動變星的經驗法則,研發了一種能將脈動變星的不同波段觀測資料合併的方法,藉由合併的光變曲線,我們將能增加觀測變星的時間覆蓋率。我們也將不同種類的脈動變星的星等變化做了進一步的分析 (使用 Fourier decomposition technique 以得到光變曲線的振幅),並將其結果應用在實際合併的觀測資料上。最後,根據我們所做的數據模擬,使用我們的方法所合併得到的光變曲線,在使用SigSpec尋找週期方面的確能夠得到更高的準確率。至於對於那些僅有非常少數觀測資料的變星而言,我們的合併方法也能夠有效的增進其週期結果。

Period is one of the most important quantities in variable star research. Various methods exist in the literature to search for period for a given variable star, such as Lomb-Scargle periodogram, Phase Dispersion Minimization, SigSpec and etc. We compared three period search methods by using various pulsating stars with known periods given in the OGLE-III database, and found that SigSpec gave the highest success rate. Therefore, we have applied SigSpec to the light curves of variables in this thesis. In addition, we have developed a method to combine the V band and I band measurements into a single light curve to improve the time coverage of a classical pulsating star. The fundamental idea of our method is to use an empirical relation between the IV band amplitudes for a classical pulsating star, Amp(I)/Amp(V) ≃ 0.61 when combining the IV band light curves. In order to verify this empirical relation, we use Fourier decomposition technique to measure the amplitude ratios for classical pulsating stars found in the OGLE-III database. According to our numerical simulations, the combined light curves can improve the accuracy of period search when using SigSpec. For the pulsating variable stars having only a small number of measurements in IV bands, our method can improve their period searching results.

1 Introduction 1
1.1 Variable Stars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Period Search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Data Description 6
2.1 The Optical Gravitational Lensing Experiment-III . . . . . . . . . . . 6
2.1.1 OGLE-III Catalogue of Variable Stars . . . . . . . . . . . . . 7
2.2 Tenagra – NGC 7039 . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3 Single-Band Period Search 11
3.1 Test Results using OGLE-III data . . . . . . . . . . . . . . . . . . . . 11
3.1.1 Outliers of Comparison Results . . . . . . . . . . . . . . . . . 13
3.2 NGC 7039 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4 Two-Band Period Search 18
4.1 Combining V I Band Light Curves . . . . . . . . . . . . . . . . . . . . 18
4.2 Relations between IV band Amplitudes Ratio for Pulsating Stars . . 19
4.3 Physical Reason Behind the Amplitude Ratio . . . . . . . . . . . . . 24
5 Simulation 26
5.1 Procedure of The Simulations . . . . . . . . . . . . . . . . . . . . . . 26
5.2 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6 Summary 37
Bibliography 39

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