Circumstellar Dust in Planetary Nebulae and Proto-Planetary Nebulae

摘要

Over the last decade, we have come to realize that mass loss on the asymptotic giant branch (AGB) has major effects on the formation of planetary nebulae (PN), and many observable characteristics (e.g. haloes, molecular envelopes) of PN can be traced back to the circumstellar envelopes of their AGB progenitors (Kwok 1982). The large infrared excesses observed in PN are certainly due to the remnant of the AGB envelopes which have cooled as the result of expansion (Kwok 1990, Zhang Kwok 1991). The detections of the 9.7 pm silicate and the 11.3 /cm SiC features, both commonly observed in AGB stars, provide confirmations to this link between AGB and PN (Aitken & Roche 1982, Zhang & Kwok 1990).