克普勒任務觀測G型星超級閃焰的資料分析

Data Analysis of Superflares on G-type Stars Observed by Kepler Mission

吳季儒(Chi-ju Wu)

指導教授 ： 葉永烜

國立中央大學/地球科學學院/太空科學研究所/碩士(2014年)

摘要

此篇論文中，我分析由克普勒任務所觀察的77個G型恆星的光度變化，且扣除假事件後找到4944個確定的超級閃焰事件。藉由計算其時間以及利用史蒂芬-波茲曼定理來估計閃焰能量，這些超級閃焰的能量介於5×1034 - 1036 爾格，且似乎有一個能量上限2×1037 爾格。 此外，持續較長的閃焰有較小的振幅，在光度的時間序列中也表現較多的小突起，表示有多個閃焰。而持續時間短的閃焰的衰退期較平滑。每顆星的閃焰頻率符合冪次定理，但冪次指數變化由0.68±0.24 至 2.91±0.29，若只考慮閃焰發生頻率高於10%的星，冪次指數變化由1.2至2.18。且趨勢顯示，自轉周期較短的恆星容易有較大的冪次指數。另外，兩個恆星活躍程度的指標表示大部分的恆星一年會發生3至20個超級閃焰，且大部分時間有0.5 – 5% 恆星表面積的恆星黑子。最小的產生超級閃焰的恆星黑子約為0.5% 恆星表面積，為太陽紀錄上最大的太陽黑子。大部分介於能量1034-1035 爾格的超級閃焰有8-25% 恆星表面積的恆星黑子。由恆星自轉相位和閃焰發生時間點的關係顯示只有7.3% 的超級閃焰發生於相對較大的黑子面對觀測者，而有9.5%的閃焰發生於相對較小黑子時。

關鍵字

太陽 ； 恆星 ； 閃焰 ； 頻率 ； 超級閃焰

並列摘要

In this thesis, I analyze the light curves of 77 G type stars observed by Kepler Mission based on flaring events and well-defined periodicity, and find 4944 confirmed superflares excluding the false events. By estimating the flares duration and flare energy with Stefan-Boltzmann law, I find the superflares have energy on average of 5×1034 - 1036 ergs and saturation with 2×1037 ergs. Furthermore, the long duration flares tend to have smaller flare amplitudes with several bumps in the decay phase, while short duration flares have higher amplitudes with smooth decay. Additionally, the power-law index γ values vary widely from 0.68±0.24 to 2.91±0.29, suggesting that the stars are at random phases, and have different chromospheric activities. If we only consider the stars with flare percentage larger than 10%, the γ values have range 1.2-2.18. Additionally, a trend is shown that the stars with shorter rotation periods tend to have larger power-law indices. Moreover, two indicators of the stellar activity show that most of the stars have 3-20 superflares a year; and that the stars generally have spot coverage 0.5 - 5% of surface. The lowest limit of spot size to produce superflares need to be larger than 0.5% of stellar surface, which is the size of the biggest sun spot in 1947. And most of superflares with 1034-1035 ergs have 8-25% spot coverage. Besides, the relation between stellar phase and flare timing shows that there are 7.3% of superflares occur at the dimmer part of light curve, and 9.5% at the brightest part of light curves.

並列關鍵字

solar ； G-type stars ； flare ； frequency ； superflares

參考文獻

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