Searching for Be Stars in Open Clusters by using PTF Observations

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/74065

Title:	Searching for Be Stars in Open Clusters by using PTF Observations
Authors:	游昌憲;Yu, Chang-Hsien
Contributors:	天文研究所
Keywords:	B型發射線星;疏散星團;帕洛瑪瞬變工廠;氫原子發射光譜譜線;Be stars;Open clusters;Palomar Transient Factory;H alpha emission line
Date:	2017-08-24
Issue Date:	2017-10-27 13:07:11 (UTC+8)
Publisher:	國立中央大學
Abstract:	我們通稱在光譜中出現巴耳末發射線的B型恆星為Be星，這樣的特性是由於Be星的環星盤結構所形成，不過Be星的形成與演化至今都還不是很明白，因此，透過在不同年齡的疏散星團中尋找Be星的巡天方式可以很有效的了解其形成與演化。我們使用帕洛瑪瞬變工廠(Palomar Transient Factory)的H$\alpha$資料尋找在104個疏散星團中的Be星，分析步驟如下：(一)利用帕洛瑪瞬變工廠的HA656及HA663測光資料篩選出H alpha發射線星~(二)結合徑向恆星分布密度圖、近紅外波段色等圖及恆星的自行運動的分析方式確認疏散星團內的星是否為成員星~(三)使用J-H和H-Ks的雙色圖來決定Be星的候選星。在這104個疏散星團中，我們在其中的32個星團找到了96個Be星候選星，透過分析後得到這些候選星的特性結果如下：(一)在大多數擁有Be星的疏散星團中，他們所擁有Be星的比例皆小於10%。~(二)年齡落在$10^{7.5}$-$10^{8.5}$年的疏散星團有很高的機率找到Be星。~(三)在我們的Be 候選星並沒有看到有隨著年紀變動向星團中心集中的現象。~(四)在我們的Be候選星中，多數候選星擁有與已知Be星相同的中紅外顏色增量的現象。~(五)所有候選星中有一個Be星的候選星擁有長周期的光變現象，它在2000天的時間內亮度變化了0.3個星等。;A Be star is "a non-supergiant B star that has, or had at some time, one or more Balmer lines in emission". The Balmer emission lines are thought to originate from curcumstellar disks, but the formation and evolution of Be stars are still unclear. Therefore, the comprehensive survey of Be stars in star clusters of different ages is crucial to understand the formation and evolution of Be stars. We used H-alpha photometry of the Palomar Transient Factory (PTF) to search for Be stars in 104 open clusters. The procedure is as follow: Firstly, H-alpha emitters are selected by using the PTF on-line (HA656) and off-line (HA663) photometry. Secondly, the radial density profile, the near-infrared color-magnitude diagram, and the proper motions (PMs) are adopted to identify their memberships. Thirdly, the J-H and H-Ks colors are used further to ascertain Be membership. In total, we identified 96 Be candidates in 32 of 104 open clusters. Our results are: (1) The Be fraction of most clusters with Be stars is below 10%; (2) The clusters with age between $10^{7.5}$ - $10^{8.5}$ years have high probability to form Be stars; (3) There is no star concentration toward the cluster center of Be stars regardless of ages; (4) Most Be candidates have mid-infrared color excess, which is similar to known Be stars. (5) Of these 96 Be candidates, there is one Be candidate showing long-term variability with 0.3 magnitude in about 2000 days.
Appears in Collections:	[Graduate Institute of Astronomy] Electronic Thesis & Dissertation

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