利用星團中已知造父變星在顏色-星等圖上的位置尋找新的造父變星;Finding New Cepheids in the Open Clusters with Their Location in the Color-Magnitude Diagram–Tests with Existing Data and Known Cepheids

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题名:	利用星團中已知造父變星在顏色-星等圖上的位置尋找新的造父變星;Finding New Cepheids in the Open Clusters with Their Location in the Color-Magnitude Diagram–Tests with Existing Data and Known Cepheids
作者:	駱世昌;Luo, Shih-Chang
贡献者:	天文研究所
关键词:	造父變星;疏散星團;顏色-星等圖;Cepheid;Open Cluster;Color-Magnitude Diagram
日期:	2019-08-15
上传时间:	2019-09-03 14:27:49 (UTC+8)
出版者:	國立中央大學
摘要:	造父變星若是疏散星團成員的話，可以利用其週期-光度的關係來確定疏散星團的距離。我們依據初始質量函數可以得知星團中包含由質量由小至大的恆星，而其中4到20個太陽質量的恆星演化中會在顏色-星等圖上會經歷不穩定帶而轉換成造父變星。然而目前已知只有24個造父變星存在於疏散星團中，相較於銀河系超過3000個疏散星團佔不到1%。本篇論文是以WEBDA及2MASS數據庫中的已知造父變星去確定造父變星在顏色-星等圖中不穩定帶範圍，再利用篩選條件的不穩定帶、空間機率、逕向速度機率、顏色指數機率、年齡搜尋2MASS數據庫裡不穩定帶範圍含有候選造父變星的疏散星團。以國立中央大學天文所鹿林天文台的SLT對找出擁有12個候選造父變星的6個疏散星團做可見光B、V、R、I四個波段的光度觀測6至7個月，將候選造父變星觀測的資料以差異測光、Lomb-Scargle periodogram、平均星等-星等標準差圖進行分析，以上述三種分析方式顯示12個候選造父變星皆不是造父變星。我們利用後來有在疏散星團內找到的造父變星Be 51 #162與Be 55 #107檢驗篩選條件，檢驗結果顯示不穩定帶、空間機率、逕向速度機率、年齡依舊適合當作是篩選條件，而顏色指數機率並不適合當作是篩選條件。;Cepheids in open clusters can use its period-luminosity relation to determine distance of the open clusters. According to an initial mass function, we expect member stars in open clusters include both low and high mass stars. Based on stellar evolution, 4~20 solar mass stars will eventually enter the instability strip in their lifetime and become Cepheids. However, only 24 Cepheids were found in open clusters. In comparison there are more than 3000 open clusters in our Galaxy, it is not more than 1%. In this thesis, receiving the Cepheids of open clusters′ data from WEBDA and 2MASS database to make the locus of the instability strip in the Color-Magnitude Diagram. We use the instability strip, spatial membership probability, proper motion membership probability, photometric membership probability and age to look for the open clusters that have candidate Cepheids in 2MASS database. Then observed 6 open clusters that have 12 candidate Cepheids in B, V, R, I bands by SLT in Lulin Observatory in 6~7 months. Final, we analyzed these candidate Cepheids by Differential Photometry, LS Periodogram and Mean Magnitude-Standard Deviation of Magnitude Diagram, and we determined that 12 candidate Cepheids are not Cepheids. We used 2 new Cepheids of open clusters to examine the filter condition. It showed the instability strip, spatial membership probability, proper motion membership probability and age that can used, but photometric membership probability is not.
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