Please use this identifier to cite or link to this item: http://rportal.lib.ntnu.edu.tw:80/handle/20.500.12235/102720
Title: 原行星狀星雲 IRAS 07134+1005 中環星包層形狀與動力學之研究
An Expanding Toroidal Envelope Around the PPN IRAS 07134+1005
Authors: 李沃龍
李景輝
Lee, Wo-lung
Lee, Chin-Fei
楊淳惠
Yang, Chun-Hui
Keywords: 原行星狀星雲
PPN
IRAS 07134+1005
Issue Date: 2010
Abstract: 這篇論文中,我報告了利用Submillimeter Array (SMA) 觀測原行星狀星雲 [Pre-planetary Nebula (PPN)] IRAS 07134+1005 中的環星包層裡,CO J=3-2 輻射線的觀測結果。PPN是中低質量恆星 (主序帶質量為 0.5 ∼ 8 個太陽質量) 演化過程中,漸進分支巨星 [Asymptotic Giant Branch (AGB) star] 演化到行星狀星雲 [Planetary Nebula (PN)] 的短暫過渡態天體。我們相信在漸進分支巨星階段,恆星會長期,穩定,緩慢且均向的噴出自身物質 (也就是 AGB 風)。最後,以猛烈的快風 (superwind) 大量的噴出自身物質而結束漸進分支巨星階段。當恆星噴出的物質形成與恆星分離的環星包層時,我們稱此環星包層與中心恆星組成的系統為原行星狀星雲。IRAS 07134+1005 的近紅外線與中紅外線影像顯示出它的環星包層具有橢圓殼狀且赤道部份密度較強的結構 (甜甜圈形狀)。這些紅外線影像也顯示出這個赤道密度增強不是均勻的,而是東邊比西邊強。然而,SMA CO J=3-2 和 BIMA CO J=1-0 的觀測結果都沒有顯示 IRAS 07134+1005 在赤道增強的部份有如此明顯的東西邊輻射線強度的差別。這個結果指出,CO 在這個環星包層裡可能是光學厚 (optically thick) 的分子。為了研究這個環星包層的物理特性,我用一個短軸部份密度增強的膨脹橢球殼來模擬它。我在模型中加入了輻射轉移 (radiative transfer)。我的擬合最好的模型顯示出,IRAS 07134+1005的快風層的質量損失率 (mass-loss rate) 大約是 3 × 10−5 M⊙ yr−1 ,這個結果非常接近 Meinxer et al. 在2004年提出來的質量損失率 (3 × 10−5 M⊙ yr−1)。這個 PPN 大約在2000年前結束了物質的噴發,而快風層大約噴發了 1100 年。如果這個PPN未來會有噴流形成,那麼它的噴流延遲 (jet-lag,噴流形成晚於甜甜圈結構的時間) 至少有 2000 年。這個值比 Huggins 在2007提出的平均噴流延遲 (300年)長很多。Nakashima et al. 在 2009 年提出 IRAS 07134+1005 的 21微米譜線特徵或許是長噴流延遲的原因。然而,另外一個具有 21 微米譜線特徵的 PPN IRAS04296+5435 的噴流延遲小於 Huggins 提出的平均值。因此,長的噴流延遲或許跟21微米譜線特徵並無關連。
This thesis presents the Submillimeter Array (SMA) observation results of the circumstellar envelope of the pre-planetary nebula (PPN) IRAS 07134+1005 in CO J=3-2 emission. PPN is an object in a transient phase between the asymptotic giant branch (AGB) phase and planetary nebula (PN) phase in the stellar evolution of a low to intermediate-mass star (initial main-sequence mass of 0.5 M⊙ ∼ 8M⊙ ). An AGB star is believed to eject its material first in the form of a long-period, slow and isotropic wind (i.e. AGB wind), and then ends its ejection with a final fierce eruption, the so-called superwind. When the ejecta forms a detached envelope around the central post-AGB star, we called this system a PPN. Previous near-IR (Ueta et al. 2005) and mid-IR images (Kwok et al. 2002) of IRAS 01734+1005 showed that it has an elliptical shell-like envelope with an equatorial density enhancement (i.e. torus). The CO observation also shows a similar elliptical shell-like envelope. In order to derive the physical properties of this envelope, I modeled it with an expanding ellipsoidal shell with an equatorial density enhancement. The radiative transfer is included in my model. My best-fit model suggests that the mass-loss rate in the superwind region of this envelope is ∼ 3 × 10−5 M⊙ yr−1 , the same as that estimated by Meixner et al. (2004). This source ended its ejection ∼ 2000 years ago with a superwind that has a duration of ∼ 1100 years. If this source happens to have jets in the future, its jet-lag, after the cessation of the torus, would be at least 2000 years. This jet-lag is much longer than the mean value of 300 years obtained by Huggins (2007). Nakashima et al. (2009) proposed that the 21 µm feature could be the reason for this long jet-lag. However, the jet-lag of another 21 µm PPN IRAS 04296+5435 is less than the mean value. Therefore, the long jet-lag of this source could have no relationship with the 21 µm feature.
URI: http://etds.lib.ntnu.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=%22http://etds.lib.ntnu.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=id=%22GN0697410107%22.&%22.id.&
http://rportal.lib.ntnu.edu.tw:80/handle/20.500.12235/102720
Other Identifiers: GN0697410107
Appears in Collections:學位論文

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