Aperture synthesis observations of low-mass protostars in the Taurus Molecular Cloud:  Formation Processes of Protoplanetary Disks  in Protostellar Envelopes

横川, 創造; ヨコガワ, ソウゾウ; YOKOGAWA, Sozo

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Aperture synthesis observations of low-mass protostars in the Taurus Molecular Cloud: Formation Processes of Protoplanetary Disks in Protostellar Envelopes

https://ir.soken.ac.jp/records/417

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要旨・審査要旨 / Abstract, Screening Result (408.9 kB)
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Item type

学位論文 / Thesis or Dissertation(1)

公開日

2010-02-22

タイトル

Aperture synthesis observations of low-mass protostars in the Taurus Molecular Cloud: Formation Processes of Protoplanetary Disks in Protostellar Envelopes

タイトル

Aperture synthesis observations of low-mass protostars in the Taurus Molecular Cloud: Formation Processes of Protoplanetary Disks in Protostellar Envelopes

言語

jpn

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

横川, 創造

フリガナ

ヨコガワ, ソウゾウ

著者

YOKOGAWA, Sozo

学位授与機関

学位授与機関名

総合研究大学院大学

学位名

博士（理学）

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総研大甲第719号

研究科

値

数物科学研究科

専攻

値

09 天文科学専攻

学位授与年月日

2003-09-30

学位授与年度

値

2003

要旨

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Formation process of a protoplanetary disk around a low-mass YSO is one of the most interesting issues in modern astronomy, which is deeply related to the origin of the solar system. Although previous survey observations of low-mass YSOs have revealed evolution from protostar phase to T Tauri star phase, such as dissipations of envelope gases, dust concentrations from envelopes to circumstellar disks, and expansion of accretion disks. However, the formation process of a protoplanetary disk, how and when the protoplanetary disk has formed, is not still understood.
In this thesis, I examine the structure and evolution of circumstellar envelopes and disks around protostars to reveal the formation process of a protoplanetary disk in a protostellar envelope through aperture synthesis observations of low-mass YSOs in the Taurus Molecular Cloud (TMC).
In the chapter I, since protoplanetary disks have large diversity of disk masses, radii and angular momenta, we tried to reveal one of the causes of the diversity: the outflow-triggered star formation in low-mass star-forming regions. We performed CS J=2-1 and J=3-2 observations of the class 0 protostar L1551 NE to investigate the interaction feature between L1551 NE and the outflow of the nearby protostar L1551 IRS 5, since L1551 NE is deeply embedded in the outflow of L1551 IRS 5. Significant CS emission around L1551 NE was detected at the eastern tip of the swept-up shell of the outflow of L1551 IRS 5, and the following new structures were successfully revealed: a compact disklike component with a size of 1000 AU just at L1551 NE, an arc-shaped structure around L1551 NE, open toward L1551 NE, with a size of 5000 AU, i.e., a bow shock, and a distinct velocity gradient of the dense gas, i.e., deceleration along the outflow axis of L1551 IRS 5. Since the age of L1551 NE is comparable to the timescale of the interaction, it is plausible that the formation of L1551 NE was induced by the outflow impact. This is a first case of the outflow-triggered star formation in low-mass star forming regions.
In the following chapters II and III, we presented the results of aperture synthesis observations of 13CO (J=1-0) and (J=2-1) line emissions toward the binary protostar L1551 IRS 5 and the single protostar HL Tau. 13CO (J=1-0) observations of L1551 IRS 5 have revealed the centrally condensed envelope. The envelope shows infall and rotation motion toward the central sources. The infall velocity of the envelope is consistent to the free-fall velocity around a central mass of 0.5 M_\odot, whereas the rotational velocity has a radial dependence of r^-1, suggesting the specific angular momentum of the gases has conversed during the contraction of the envelope. Furthermore, the 13CO (J=2-1) observations of L1551 IRS 5 show a disklike structure in the central part of the envelope. A distinct velocity gradient is detected along the major axis of the structure, whereas no prominent gradient is detected along the minor axis, suggesting a purely rotating disk. The disk radius estimated to be 500 AU. This radius is significantly larger than the centrifugal radius derived from the local specific angular momentum of the envelope of L1551 IRS 5, although a Keplerian disk is theoretically thought to form with the centrifugal radius in the envelope. Neither the gravitational interaction between the disk and the binary sources nor the turbulent viscosity in the disk seems a plausible mechanism to make such a large rotating disk. 13CO (J=1-0) observations of HL Tau have revealed the extended infalling envelope. A velocity gradient of the emission clearly aligns the minor axis of the envelope, whereas no prominent gradient is detected along the major axis of the envelope, suggesting that the envelope around HL Tau is almost infalling. Even in 13CO (J=2-1) imaging, a rotational disklike component could not be found, suggesting that a Keplerian rotating disk around HL Tau seems to be as small as 100 AU and is likely to be comparable to the typical centrifugal radius of the low mass YSOs in the TMC.
In the chapter IV, we presented the 13CO(J=1-0) observations of the protostar Haro 6-5B. Although Haro 6-5B is considered as a protostar, only a compact disklike structure which exhibits rotation motion is detected with a tiny extended envelope, suggesting that most of the envelope has already dissipated. Since the rotation radius of Haro 6-5B is about 400 AU which is comparable to that of L1551 IRS 5, Haro 6-5B might be a binary protostars.
In the chapter V, we examine the physical properties of low-mass YSOs, both our samples and the data of previous studies to reveal a formation mechanism of a protoplanetary disk. In the case studies of a binary protostar L1551 IRS 5 and a single protostar HL Tau as describe in the chapter II and III, the rotation disk around L1551 IRS 5 is clearly revealed, whereas that around HL Tau is not detected. Furthermore, the envelope around L1551 IRS 5 shows rotation motion with infall motion, whereas that around HL Tau shows almost only rotating, suggesting that the large amount of local specific angular momenta of envelopes might form a binary system and a large rotating disk. A comparison of the local specific angular momenta between single stars and binary systems, however, shows no obvious difference. These results suggest that differences between binary system and single star formations are quite subtle distinctions of physical properties of protostellar cores and envelopes.

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Aperture synthesis observations of low-mass protostars in the Taurus Molecular Cloud: Formation Processes of Protoplanetary Disks in Protostellar Envelopes

× 横川, 創造

× ヨコガワ, ソウゾウ

× YOKOGAWA, Sozo

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