An Expanding Toroidal Envelope Around the PPN IRAS 07134+1005

[[abstract]]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 ?rst in the form of a long-period, slow and isotropic wind (i.e. AGB wind), and then ends its ejection with a ?nal ?erce 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-?t 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 ?m feature could be the reason for this long jet-lag. However, the jet-lag of another 21 ?m 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 ?m feature.