DISCOVERY OF TWO NEW, CARBON-RICH PROTO--PLANETARY NEBULAE: IRAS Z02229 + 6208 AND IRAS 07430+1115

摘要

We report the discovery of two new carbon-rich proto--planetary nebulae (PPNs), IRAS Z02229 + 6208 and 07430+ 11l5. Optical spectroscopy of these sources and another previously discovered PPN, IRAS 0543l +0852, reveals the presence of C-2, and C-3, in absorption. All three objects have the spectra of G--K supergiants, consistent with the expectations of their being PPNs. New ground-based optical and infra- red photometry, combined with the IRAS measurements, show double-peak spectral energy distributions for each, this suggests that the asymptotic giant branch (AGB) mass loss has ended and these objects are in the post-AGB phase of evolution. The remnant of the molecular envelope is detected in CO emission for the first time in all three objects, using the CO (3--2) line. The 3.3 and 11.3 um emission features commonly attributed to the polycyclic aromatic hydrocarbon molecules have been detected in IRAS 07430+ l l l5. Strikingly absent in IRAS 07430+ 1l l5, however, is the 21 pm emission feature, found in the other two and in all but one of the other PPNs known to show C, in absorption.