EAST觀測網之星震數據分析:GN And與BI CMi之光度曲線

Preliminary Data Reduction of Asteroseismic Data from EAST Network and Light Curves of GN And and BI CMi

張靖歆(Chin-Shin Chang)

指導教授 ： 周定一

國立清華大學/理學院/天文研究所/碩士(2006年)

https://doi.org/10.6843/NTHU.2006.00535

摘要

星震學(Asteroseismology)的研究主要在於，藉由觀測星球的光度變化，可以解析出該星的震波模式，進而推知星球的化學組成與內部結構。臺灣地暉星震觀測網(Taiwan Earthshine and AsteroSeismology Telescopes)的其中一個研究目的就是星震學。由於星震學的研究需要長時間不間斷的觀測，因此，臺灣地暉星震觀測網的目標是在全球建立可以接力觀測的站台。目前已開始運作的站台在西班牙加納利群島的Tenerife島上；此外，在新竹清華大學物理館頂樓也有一個測試用的觀測站。觀測網的站台都可以自動觀測，或是透過網路遠距遙控觀測。

目前，我們用西班牙與台灣的站台觀測了兩顆δ scuti變星，GN And與BI CMi。我們的觀測結果顯示，GN And 是五等變星，並有0.07天的震盪週期與0.05等的振幅；BI CMi是九等變星，有0.11天的週期與0.07等的振幅。此外，測試結果顯示，我們的系統可以測量九等變星１％的振幅。在此，點徑測光法(Aperture Photometry)與PSF(Point-Spread-Function)測光法被用來分析數據。結果顯示，在星場疏散的情形下，兩種方法得到的光度曲線差異不大。此外，我們用星圖空間上的擾動來估計誤差，結果顯示，用此方法估計的誤差非常小。

關鍵字

星震 ； 地暉星震觀測網

並列摘要

Taiwan Earthshine and AsteroSeismology Telescopes(EAST) is a global network used to study earthshine and asteroseismology. The ultimate goal of EAST is to construct fully automatic observatories around the globe and obtain data uninterruptly. At present, two stations are constructed. The prototype system is at the campus of National Tsing Hua University, Hsinchu, Taiwan. Besides, the first system has been installed at Teide Observatory, Tenerife, Spain. EAST stations can be operated automatically or controlled remotely through the Internet.

In this thesis, preliminary result on asteroseismology with Taiwan EAST Network is presented. We observed two delta scuti variable stars, GN And and BI CMi, with EAST at Hsinchu and Tenerife. Light curves of GN And, a 5-magnitude star, show a regular oscillating period of 0.07 days, amplitude of 0.05 magnitudes, and the estimated error is less than 2%. Light curve of BI CMi, a 9-magnitude star, has a regular oscillating period of 0.11 days, amplitude of 0.07 magnitude, and the estimated error is down to 1%. This result indicates EAST can measure 9-magnitude variable stars down to 1% variations.

Two photometry methods, aperture photometry and PSF photometry, are used to analyze data. We assume a symmetric Gaussian distribution on a star profile for PSF photometry. Light curves obtained from both methods have little difference, which means that, for a disperse star distribution, the difference is not obvious. The error of measured magnitude is estimated based on the spatial fluctuation of the clean images. We assume the spatial fluctuation relative to the smooth point spread function(PSF) of the target star is due to errors. The error estimated by this assumption is quite small.

There are several interesting scientific topics that can be studied with EAST data, such as searching for new variable stars and occultation events.

並列關鍵字

Asteroseismology ； EAST Network

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