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    题名: 豺狼座分子雲中的年輕星球;Young Stellar Population in the Lupus Molecular Clouds
    作者: 張雅婷;Ya-ting Jhang
    贡献者: 天文研究所
    关键词: 年輕星球;豺狼座;Lupus;young stellar population;molecular clouds
    日期: 2009-05-26
    上传时间: 2009-09-22 10:13:37 (UTC+8)
    出版者: 國立中央大學圖書館
    摘要: 豺狼座分子雲為鄰近的南天恆星形成區,由許多濃密程度不同的分子雲氣集 結而成,其中第一號到第四號分子雲具有明顯恆星形成活動,尤其以豺狼座第三 號雲的分子濃度最高且年輕恆星數量最多。豺狼座第五號至第九號分子雲則之前 沒發現恆星形成活動的證據。本論文主要針對豺狼座第三號及第五號雲搜尋具備 Hα 發射線和紅外超量特性的年輕恆星。我們利用UKST 的Hα 巡天影像和 2MASS 近紅外的資料庫,尋找典型金牛座T 型星。在豺狼座第三號暗雲中,在 一平方度天區內,利用我們的方法,除了在最濃密的區域中找出,所有已知的典 型金牛座T 型星以外,我們另外發現四顆未知的Hα 發射星,其中兩顆位於暗雲 北邊且有紅外超量的特性,其中之一根據光譜確認為典型金牛座T 型星,這意味 著這區域的年輕恆星分佈並非侷限在暗雲濃密處,因此可能需要重新考量該區域 的恆星形成歷史;其他三顆Hα發射星根據光譜確認為具有活躍色球層活動的M 型矮(dMe) 星。利用同樣方法分析,在第五號分子雲區找到一顆未知的Hα發射 星,但它不具有紅外超量,所以可能只是dMe 而非年輕恆星,我們因此確認這 區域無恆星活動。 The Lupus molecular cloud complex is a nearby star-forming region in the southern sky. The Lupus 1-4 molecular clouds are associated with obvious ongoing star-forming activities, among which Lupus 3 clouds has the highest molecular column density and hosts the largest number of T Tauri stars, signifying recent, active star formation. The Lupus 5-9 clouds show no star formation activities. We used archival UK Schmidt Telescope H-alpha Sky Survey and 2MASS point-source catalog to identify in Lupus 3 (known to have atctive star formation) and Lupus 5 (known to have no star formation) candidate low-mass pre-main sequence stars, namely the classical T Tauri stars (CTTSs), which are characterized by H-alpha emission and near-infrared excess. Some of the bright candidates were observed by optical spectroscopy. In Lupus 3, almost all known CTTSs were found in our study. In addition, we identified 4 candidates H-alpha stars not previously catalogued. Two of them show a very strong H-alpha line in emission and prominent near-infrared excess, yet are located away (0.4 deg) from the densest parts of the molecular clouds so have been overlooked by earlier surveys. This suggests that the young stellar sample, thus the star formation history, in the region may be largely incomplete. The other two H-alpha stars were spectroscopically confirmed to be active chromospheric M dwarfs (dMe stars). Extending our analysis to Lupus 5, we found only one candidate whose spectrum indeed shows the H-alpha line, but without notable near-infrared excess. This H-alpha star therefore is likely a dMe, rather than a young star. Our study thereby confirms that the Lupus 5 cloud is quiescent in star formation.
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