Poster abstract details

In this poster, we report the preliminary results of a CARMA observation of the 21~$\mu$m source IRAS 22272+5435 in the CO $J=2$--1 line. The target is a proto-typical 21~$\mu$m source: i.e., a carbon-rich proto-planetary nebula with strong emission at 21 $\mu$m. The 21~$\mu$m sources are a fascinating sample to investigate the metamorphosis of intermediate-mass evolved stars, because they are lying within a particular narrow evolutionary range (i.e., early post-AGB). A recent SMA CO observation of IRAS 07134+1005, another typical 21~$\mu$m source, revealed an expanding torus corresponding to the emission region of the 21~$\mu$m feature, but did not find a jet, which is often detected together with a torus. We have suggested that this phenomenon might be a common characteristic of 21 $\mu$m sources, but of course we need to investigate more 21~$\mu$m sources to compare the morpho-kinematic properties. However, since the angular size of the circumstellar envelopes of 21~$\mu$m sources is generally too small, only the biggest object IRAS 07134+1005 has been able to be resolved by conventional interferometers until the advent of CARMA. In this project, we have obtained high-resolution CO map of IRAS 22272+5435, which has a second biggest size of the circumstellar envelope among known 21~$\mu$m sources. In the preliminary results, we found that the CO properties of IRAS 22272+5435 is clearly different from that of IRAS 07134+1005. For example, elongations seen the mid-infrared and CO images are extended in mutually perpendicular directions, although in the case of IRAS 07134+1005 the CO map matches up with the mid-infrared image.