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Isolated T Tauri Stars Toward the Taurus-Auriga Star Forming Region
https://ir.soken.ac.jp/records/2471
https://ir.soken.ac.jp/records/24719d5e1fa2-0cbf-4e99-800b-0ab9cf5145c8
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本文 (18.3 MB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||
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| 公開日 | 2011-12-26 | |||||
| タイトル | ||||||
| タイトル | Isolated T Tauri Stars Toward the Taurus-Auriga Star Forming Region | |||||
| タイトル | ||||||
| タイトル | Isolated T Tauri Stars Toward the Taurus-Auriga Star Forming Region | |||||
| 言語 | en | |||||
| 言語 | ||||||
| 言語 | eng | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||
| 資源タイプ | thesis | |||||
| 著者名 |
瀧田 , 怜
× 瀧田 , 怜 |
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| フリガナ |
タキタ , サトシ
× タキタ , サトシ |
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| 著者 |
TAKITA, Satoshi
× TAKITA, Satoshi |
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| 学位授与機関 | ||||||
| 学位授与機関名 | 総合研究大学院大学 | |||||
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| 学位名 | 博士（理学） | |||||
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| 内容記述タイプ | Other | |||||
| 内容記述 | 総研大甲第1415号 | |||||
| 研究科 | ||||||
| 値 | 物理科学研究科 | |||||
| 専攻 | ||||||
| 値 | 11 宇宙科学専攻 | |||||
| 学位授与年月日 | ||||||
| 学位授与年月日 | 2011-03-24 | |||||
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| 値 | 2010 | |||||
| 要旨 | ||||||
| 内容記述タイプ | Other | |||||
| 内容記述 | It is fundamental to investigate the origin of low-mass stars and planets in order toanswer how the Sun and the Earth were formed. Many surveys of young stellar objects (YSOs) have been performed toward molecular clouds in wide wavelengths range from optical to radio wavelengths. On the other hand, substantial amount of weak-line T Tauri stars (WTTSs) have been found far away from active molecular clouds by the Xray observations. This indicates that many isolated T Tauri stars (TTSs) are thought to be still unexplored. Therefore, unbiased survey of YSOs are required in order to understand star formation process. For this purpose, we have carried out a survey of TTSs with the all-sky survey data by the Japanese infrared astronomical satellite, AKARI. The first step of our observational study is the survey of isolated TTSs at mid infrared(MIR) wavelengths with the AKARI All-Sky Survey. Since TTSs exhibit infrared excess emission from circumstellar disks, we first studied previously known TTSs to perceive what colours do TTSs show. Among 516 previously known TTS slaying in a 1800-square-degree region around the Taurus star forming region, we detected132 TTSs in the MIR. To construct more complete data sets, we also used other all-sky surveys such as 2MASS (the Two-Micron All-Sky Survey; near-infrared (NIR)wavelengths) and UCAC3 (the third US Naval Observatory (USNO) CCD Astrograph Catalogue; optical wavelengths). It is indispensable to distinguish TTSs from possible contamination of other types of objects such as Asymptotic Giant Branch (AGB) stars(carbon and OH/IR stars), post-AGB stars, planetary nebulae (PNe), as well as galaxies, that also show infrared excess emission. Using the MIR colour, we discarded most of AGB stars from the sample. We also separated most of galaxies from TTSs using the colour-magnitude diagram of optical–NIR wavelengths data. Finally, we extracted TTS candidate sources with IR excess emission, avoiding contamination from normal(main-sequence) stars, which do not present excess emission. About 40% and 5% of AKARI detected known Classical T Tauri stars (CTTSs) and Weak-line T Tauri stars(WTTSs) satisfy these criteria, respectively. On the basis of our criteria, we selected 176 out of 14 725 AKARI sources toward the Taurus region. There are 150 previously known sources, and 117 of them (about 80%) are YSOs including other star forming regions near the Taurus. The remaining 26 sources are newly found TTS candidates. We performed follow-up optical spectroscopic observations for these sources to determine their youth from Lii absorption line. We confirmed that 23 out of 27 (including1 possible binary) sources have sufficient Li absorption to be classified as TTSs. This validate the usefulness of our criteria. From the line width of H_ emission, we classified23 new TTSs into 15 CTTSs and 8 WTTSs. We obtained 9 new isolated CTTSs and6 new isolated WTTSs. There are only 8 isolated CTTSs previously, and we increased the number of them to 17. We found that the origin of most of isolated TTSs is most probably small clouds around the Taurus molecular cloud, from their proper motions determined by UCAC3.For the 23 new TTSs, at least 5 sources seem not to be related to known star forming regions, considering their spatial distributions and directions of proper motions. Furthermore, the dispersion of known/new TTSs’ proper motions is _15 km s1. This value far exceeds the typical value of _1 km s1, for the case that sources were originated from a cloud with size of _1 pc. This fact suggests that not all TTSs were born in the molecular cloud cores which were gravitationally bound to the Taurus molecular cloud. If TTSs were formed in not only the Taurus molecular cloud but also small clouds which do not relate to the Taurus, the large velocity dispersion is thought to come from the inter-cloud velocity dispersion. We investigated the Hi clouds in the region, and found that the dispersion in radial velocity of the clouds is _12 km s1,comparable to the dispersion of the TTS proper motion. Considering that the molecular clouds are formed from Hi clouds, inter-cloud velocity dispersion of molecular clouds is expected to be similar, and stars originated from these clouds are also expected to show large velocity dispersion. We also verify whether there are any differences between TTSs associated to active clouds and those isolated from clouds. The CTTS/WTTS ratios of AKARI detected TTSs are 81/31 and 12/16 for inside and outside the clouds, respectively. If we consider the typical age of a CTTS (_1 Myr) and WTTS (_10 Myr), TTSs associated to the clouds seem to be relatively young. We determined disk masses using the AKARI far-infrared data, and found no remarkable difference. We further classified AKARI detected TTSs with their slopes of the SED in the NIR–MIR wavelengths into three kinds of sources; those with envelopes, with disks, and without surrounding materials. For TTSs in our sample and associated to clouds, about a quarter of them have envelopesand a few % of them are naked. On the other hand, for isolated TTSs, a few %of them have envelopes and about one third of them are naked. This also supports the idea that TTSs associated to the clouds are relatively younger than those isolated from the clouds. We conclude that most of isolated TTSs toward the Taurus were born in isolated small clouds. Considering the fraction of known TTSs, about 30% of TTSs toward the Taurus were born as isolated. This implies that the star formation in small isolated clouds occupies significant fraction in the low-mass star formation activity. We find that circumstellar disks of isolated TTSs are more evolved than those of associated TTSs. |
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| 値 | 有 | |||||
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| 内容記述タイプ | Other | |||||
| 内容記述 | application/pdf | |||||
