| Item type |
学位論文 / Thesis or Dissertation(1) |
| 公開日 |
2010-02-22 |
| タイトル |
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タイトル |
Kinematic Structure and Ionization of Optical Jets Associated with Young Stellar Objects |
| タイトル |
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タイトル |
Kinematic Structure and Ionization of Optical Jets Associated with Young Stellar Objects |
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言語 |
en |
| 言語 |
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言語 |
eng |
| 資源タイプ |
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資源タイプ識別子 |
http://purl.org/coar/resource_type/c_46ec |
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資源タイプ |
thesis |
| 著者名 |
西川, 貴行
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| フリガナ |
ニシカワ, タカユキ
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| 著者 |
NISHIKAWA, Takayuki
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| 学位授与機関 |
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学位授与機関名 |
総合研究大学院大学 |
| 学位名 |
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学位名 |
博士（理学） |
| 学位記番号 |
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内容記述タイプ |
Other |
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内容記述 |
総研大甲第1035号 |
| 研究科 |
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値 |
物理科学研究科 |
| 専攻 |
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値 |
09 天文科学専攻 |
| 学位授与年月日 |
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学位授与年月日 |
2007-03-23 |
| 学位授与年度 |
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値 |
2006 |
| 要旨 |
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内容記述タイプ |
Other |
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内容記述 |
Optical jets and molecular bipolar outflows are two major manifestations<br />of outflowing activities associated with young stellar objects （YSOs）．It is<br />not clear how these two outflow activities are related with each other．One of<br />the major scenarios is that a collimated jet seen in the optical－IR wavelength<br />entrains its ambient molecular material，a1lowing the molecular outflow to<br />occur. In order for us to tackle this issue，it is crucial to understand how jets<br />interact with ambient material．<br /> In addition to the kinematics，the mass loss rate and mass momentum<br />transfer rate of are key parameters to investigate how the jet interacts<br />with the ambient material. However，the mass momentum is poorly known<br />because the hydrogen density is not easily derived， as is different from the<br />electron density that is measured from forbidden line emissions． If we assume<br />that a jet is fully ionized, i.e. the electron density is nearly equal to the<br />hydrogen density，the mass momentum of the jet derived from its optical<br />emission lines is not sufficient to drive the molecular outflow associated with<br />it. In contrast，recent studies have suggested that jets are almost neutral，<br />indicating that a jet may have momentum sufficient to drive a molecular outflow．<br /> In order to study the issues described above，we made slit-scan observa-<br />tions of Hα and [NII] 6583 Å emission lines toward two bright jets，HH46/47<br />and the HL Tau jet，with Subaru Telescope. The large diameter of the tele-<br />scope，together with the high spectral resolution of the spectrograph（High<br />Dispersion Spectrograph，R =3.6×10<sup>40</sup> or Δv＝8km s<sup>-1</sup>）allowed us to<br />study the kinematics of these jets in unprecedented detail．Furthermore，the<br />slit-scan technique with a long slit provided us with kinematic information<br />of the entire jets．<br /> We found that，in both jets，the Hα emission traces both the main jet<br />component（<i>V</i><small>LSR</small>＝－160～－180km s<sup>-1</sup>）and distinct lower velocity com-<br />ponent （|<i>V</i><small>LSR</small>| ≤ 120km s<sup>-1</sup>）. The [NII] emission, on the other hand，is<br />primarily associated with the main jet component and is much faint or ab－<br />sent in the lower velocity component. In the HH 46/47 jet，the velocities<br />of Hαand [NII] emission lines match well in their main jet components．<br />The lower velocity components are associated with one-sided bow shocks<br />and with one of the Hα filaments that was previous identified with the<br /><i>Hubble Space Telescope.</i> In the HL Tau jet，the lower velocity component<br />is associated with indivisual knots, which is explained by the lower velocity<br />emmituion arising in the laterals of bow shocks. While the main jet component<br />is associated with the ejecta, the lower velocity component is produced as a<br />result of the interaction between the ejecta and the surrounding gas.<br /> Observed Hα line profiles suggest that the shock velocities at the bow<br />shocks and the Hα filament with respect to the ambient gas are 60－80km s<sup>-1</sup><br />and 120－130 km s<sup>-1</sup> for HH46/47 and HL Tau，respectively. These are<br />markedly smaller than the three dimensional（3－D）velocities of the jets（～300<br />km s<sup>-1</sup>）． The discrepancy between the shock velocity and 3－D velocity is<br />explained if the ambient gas moves outward by～200km s<sup>-1.</sup>. The velocity<br />of the ambient gas measured in the HH46/47 jet is similar to those of HH<br />47A and 47D，giant bow shocks ahead of the observed region.<br /> Through detailed analysis，we concluded that the outward motion of the<br /> ambient gas is a result of prompt entrainment，i．e. a jet sweeps up ambient<br />material at its head by a large bow shock，but not of turbulent entrainment，<br />the other entrainment mechanism proposed to date．Indeed，our high spec-<br />tral resolution slit-scan observations of Hαshow that the main jet component<br />has a uniform radial velocity of <i>V</i><small>LSR</small>＝－160km s<sup>-1</sup>（Δv＝10km s<sup>-1</sup>）and<br />did not show the presence of slow Hα components（ |<i>V</i><small>LSR</small> | ≤ 120km s-<sup>1</sup>）<br />along the edges of the jets．Such slow Hα emission was reported in previous<br />observations and was proposed to arise from turbulent boundary layers be-<br />tween the main flow and the ambient gas. Our results indicate that Hα and<br />[NII] originate from the main jet component（i．e. the ejecta），and also from<br />bow shocks and Hα filaments，but not from turbulent mixing layers.<br /> We also investigated the ionization fraction in the jets using the [NII] / Hα<br />flux ratio. In the case of HH46/47，the ratio is 0.2-0.5 in the main jet<br />component and even higher in some other regions．Shock model calculations<br />show that the ratio is sensitive to the ionization fraction of preshock gas if<br />the shock velocity is less than l00 km s<sup>-1</sup>． The observed high ratio for HH<br />46/47 is expected if its main jet component is considerably ionized，although<br />previous observations proposed a much lower ionization fraction of≤0.2．<br />The [NII] / Hαflux ratio is significantly smaller than 0.2 in the one-side bow<br />shocks and Hα filaments, indicating that the gas surrounding the ejecta is<br />rather neutral．<br /> For the HL Tau jet，the observed [NII] / Hα flux ratio markedly vary from<br />one region to another: 0.1-0.7 at the base of the jet，less than 0.1 in knot<br />A，～0.2 in knot B，～0.4 in knot C，and ～0.7 in knot D．Because the shock<br/>velocities of the HL Tau jet exceed 100 km s<sup>-1</sup> in some regions，the ratio<br />does not directly reflect the ionization fraction of preshock gas. At the knots<br />A－D，the [NII] / Hαflux ratio increases from ＜0.1 to 0.7 with distance from<br />the source. This suggests that the preshock density decreases with distance<br />from the source．The ratio at the lateral of the bow shocks is less than<br />～0.1，suggesting that the ambient medium is almost neutral．At the base<br />of the jet，the observed [NII] / Hα flux ratio decreases from 0.7 to 0.1 as the<br />distance from the source increase. This suggests that the ionization fraction<br />decreases with distance as a result of radiative recombination．<br /> We compared the [NII] / Hα ratio in the main jet components of the HH<br />46/47 jet and HL Tau jet. The ratio for the HH 46/47 jet is higher（0.2－0.5）<br />than that for the HL Tau（≤ 0.2），indicating high ionization fraction．Such<br />a difference suggests that the radiation from a nearby O star irradiates the<br />ambient gas of the HH 46/47 system，which is located near the HII region<br />Gum nebula，causing the high ionization fraction in the main jet component．<br />Another possible interpretation is that radiative cooling by recombination is<br />not efficient in the HH 46/47 jet because of its low density，thus allowing the<br />high ionization fraction in the jet significantly away from the driving source． |
| 所蔵 |
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値 |
有 |
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内容記述タイプ |
Other |
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内容記述 |
application/pdf |
要旨・審査要旨 (382.0 kB)
