CRL 2688and CRL 618: Proto-Planetary Nebulae,

摘要

2.6 mm CO J = 1 to 0 emission has been detected from the peculiar infrared objects CRL 2688 (the Egg Nebula) and CRL 618. The observed parabolic line-shape can be interpreted as optically thick emission from a uniformly expanding molecular envelope with a size smaller than the telescope beam. The line-width indicates an expansion velocity on the order of 20 km/s. Other molecular lines similar to those observed in the envelope of the carbon star IRC+10216 are also observed in CRL 2688, even though the central star in CRL 2688 has a relatively early spectral type (F5Ia). In CRL 618, the existence of an expanding molecular envelope around a central star with spectral type B0 implies that the central star has evolved within a very short time (<10,000 years) from a cool, perhaps carbon rich star. The presence of mass-loss and the rapid evolution of the central stars suggest that CRL 2688 and CRL 618 may be proto-planetary nebulae.