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Kinematic Structure and Ionization of Optical Jets Associated with Young Stellar Objects Kinematic Structure and Ionization of Optical Jets Associated with Young Stellar Objects 西川, 貴行ニシカワ, タカユキ NISHIKAWA, Takayuki Optical jets and molecular bipolar outflows are two major manifestations of outflowing activities associated with young stellar objects （YSOs）．It is not clear how these two outflow activities are related with each other．One of the major scenarios is that a collimated jet seen in the optical－IR wavelength entrains its ambient molecular material，a1lowing the molecular outflow to occur. In order for us to tackle this issue，it is crucial to understand how jets interact with ambient material． 　In addition to the kinematics，the mass loss rate and mass momentum transfer rate of are key parameters to investigate how the jet interacts with the ambient material.　However，the mass momentum is poorly known because the hydrogen density is not easily derived， as is different from the electron density that is measured from forbidden line emissions． If we assume that a jet is fully ionized, i.e. the electron density is nearly equal to the hydrogen density，the mass momentum of the jet derived from its optical emission lines is not sufficient to drive the molecular outflow associated with it. In contrast，recent studies have suggested that jets are almost neutral， indicating that a jet may have momentum sufficient to drive a molecular outflow． 　　In order to study the issues described above，we made slit-scan observa- tions of Hα and [NII] 6583 Å emission lines toward two bright jets，HH46/47 and the HL Tau jet，with Subaru Telescope. The large diameter of the tele- scope，together with the high spectral resolution of the spectrograph（High Dispersion Spectrograph，R =3.6×1040 or Δv＝8km s-1）allowed us to study the kinematics of these jets in unprecedented detail．Furthermore，the slit-scan technique with a long slit provided us with kinematic information of the entire jets． 　　We found that，in both jets，the Hα emission traces both the main jet component（VLSR＝－160～－180km s-1）and distinct lower velocity com- ponent （|VLSR| ≤ 120km s-1）.　The [NII] emission, on the other hand，is primarily associated with the main jet component and is much faint or ab－ sent in the lower velocity component. 　In the HH 46/47 jet，the velocities of Hαand [NII] emission lines match well in their main jet components． The lower velocity components are associated with one-sided bow shocks and with one of the Hα filaments that was previous identified with the Hubble Space Telescope.　In　the　HL　Tau　jet，the　lower　velocity　component is associated with indivisual knots, which is explained by the lower velocity emmituion arising in the laterals of bow shocks. While the main jet component is associated with the ejecta, the lower velocity component is produced as a result of the interaction between the ejecta and the surrounding gas. 　　Observed Hα line profiles suggest that the shock velocities at the bow shocks and the Hα filament with respect to the ambient gas are 60－80km s-1 and 120－130 km s-1 for HH46/47 and HL Tau，respectively.　These are markedly smaller than the three dimensional（3－D）velocities of the jets（～300 km s-1）．　　The discrepancy between the shock velocity and 3－D velocity is explained if the ambient gas moves outward by～200km s-1..　The velocity of the ambient gas measured in the HH46/47 jet is similar to those of HH 47A and 47D，giant bow shocks ahead of the observed region. 　　Through detailed analysis，we concluded that the outward motion of the ambient gas is a result of prompt entrainment，i．e. a jet sweeps up ambient material at its head by a large bow shock，but not of turbulent entrainment， the other entrainment mechanism proposed to date．Indeed，our high spec- tral resolution slit-scan observations of Hαshow that the main jet component has a uniform radial velocity of VLSR＝－160km s-1（Δv＝10km s-1）and did not show the presence of slow Hα components（ |VLSR | ≤ 120km s-1） along the edges of the jets．Such slow Hα emission was reported in previous observations and was proposed to arise from turbulent boundary layers be- tween the main flow and the ambient gas.　Our results indicate that Hα and [NII] originate from the main jet component（i．e. the ejecta），and also from bow shocks and Hα filaments，but not from turbulent mixing layers. 　　 We also investigated the ionization fraction in the jets using the [NII] / Hα flux ratio.　In the　case　of　HH46/47，the ratio is 0.2-0.5 in the main jet component and even higher in some other regions．Shock model calculations show that the ratio is sensitive to the ionization fraction of preshock gas if the shock velocity is less than l00 km s-1．　The　observed　high　ratio　for HH 46/47 is expected if its main jet component is considerably ionized，although previous observations proposed a much lower ionization fraction of≤0.2． The [NII] / Hαflux ratio is significantly smaller than 0.2 in the one-side bow shocks and Hα filaments, indicating that the gas surrounding the ejecta is rather neutral． 　　For the HL Tau jet，the observed [NII] / Hα flux ratio markedly vary from one region to another: 0.1-0.7 at the base of the jet，less than 0.1 in knot A，～0.2 in knot B，～0.4 in knot C，and ～0.7 in knot D．Because the shock velocities of the HL Tau jet exceed 100 km s-1 in some regions，the ratio does not directly reflect the ionization fraction of preshock gas. At the knots A－D，the [NII] / Hαflux ratio increases from ＜0.1 to 0.7 with distance from the source. This suggests that the preshock density decreases with distance from the source．The ratio at the lateral of the bow shocks is less than ～0.1，suggesting that the ambient medium is almost neutral．At the base of the jet，the observed [NII] / Hα flux ratio decreases from 0.7 to 0.1 as the distance from the source increase. This suggests that the ionization fraction decreases with distance as a result of radiative recombination． 　　We compared the [NII] / Hα ratio in the main jet components of the HH 46/47 jet and HL Tau jet. The ratio for the HH 46/47 jet is higher（0.2－0.5） than that for the HL Tau（≤ 0.2），indicating high ionization fraction．Such a difference suggests that the radiation from a nearby O star irradiates the ambient gas of the HH 46/47 system，which is located near the HII region Gum nebula，causing the high ionization fraction in the main jet component． Another possible interpretation is that radiative cooling by recombination is not efficient in the HH 46/47 jet because of its low density，thus allowing the high ionization fraction in the jet significantly away from the driving source． application/pdf 総研大甲第1035号 eng thesis https://ir.soken.ac.jp/records/431 博士（理学） 2007-03-23 総合研究大学院大学 https://ir.soken.ac.jp/record/431/files/甲1035_要旨.pdf application/pdf 382.0 kB 2016-02-17 https://ir.soken.ac.jp/record/431/files/甲1035_本文.pdf application/pdf 24.5 MB 2016-02-17