B.E. Turner

Cyanoacetylene in dense interstellar clouds

Statistical equilibrium calculations were performed and matched to the observations of several sources. These calculations indicate the following: homogeneous cloud models are inadequate for at least one source, Sgr B2, for which a two-component (core-halo) model is presented; the observed lines of HC/sub 3/N are usually, if not always, optically thin; fairly high densities (> or =10/sup 4/ cm/sup -3/) are generally required to account for the observed lines; the J=1..-->..0 transition of HC/sub 3/N in Sgr B2 probably a weak maser. Several sources are discussed individually. (AIP)

Observation of the 6/sub 16/: 5/sub 15/ transitions of acetaldehyde in Sagittarius B2

The 6/sub 16/: 5/sub 15/ transitions of acetaldehyde have been observed in the Sgr B2 molecular cloud. The large line width suggests that both the the A and E symmetry states are present with essentially equal intensity. This is the first observation of acetaldehyde at millimeter wavelengths, and the intensity indicates that many other millimeter wave lines of acetaldehyde should be detectable. (AIP)

CRL 2688: A post-carbon-star object and probable planetary nebula progenitor

Millimeter-wavelength emission is observed toward CRL 2688 from H/sup 12/CN, H/sup 13/CN, CS, and HC/sub 3/N. The similarity of this emission and that from the molecular envelope of the carbon star IRC+10216 establishes, beyond a reasonable doubt, that CRL 2688 is a post--carbon-star object. It appears probable that both of these objects will evolve into planetary nebulae. An evolutionary sequence leading from carbon stars to planetary nebulae is outlined. (AIP)

EXPANDING MOLECULAR ENVELOPES AROUND EVOLVED STARS

We surveyed a total of 73 late-type giant stars, IRC and CRL infrared sources, and planetary nebulae in the J=1..-->..0 rotational transition of carbon monoxide. Broad CO emission lines were detected in seven (and probably eight) carbon-rich stars (C/O>1) and in two (and probably three) oxygen-rich stars (O/C>1). Two of the carbon-rich stars also showed HCN emission.

MOLECULAR ENVELOPES AROUND EVOLVED STARS AND ORIGIN OF PLANETARY-NEBULAE

We surveyed a total of 37 late-type giant stars and IRC and CRL infrared sources in the J=1..mu..0 rotational transition of carbon monoxide. Broad CO emission lines were detected toward six stars. Combination of these results with other CO observations of similar objects suggests that a majority of the red-giant stars with the largest mass-loss rates are carbon-rich (C/O>1) or S-type (C/Oapprox.1).Infrared surveys tend to support this assertion. We suggest that these stars will evolve into planetary nebulae of the classical type, i.e., those having a few tenths of a solar mass and radius 0.1-0.7 pc. Most of these should, there fore, show carbon richness in the nebular matter. Planetaries originating from somwhat lower-mass stars (M approx.1.1 M/sub sun/), such as those found in globular clusters, in the galactic halo, or near the galactic center, have much smaller ionized masses and radii and may be oxygen-rich (O/C>1)

Cyanoacetylene: new lines and sources in the galaxy

Microwave emission from the J = 8 → 7 through the J = 11 → 10 rotational transitions of HC3N has been detected in the directions of Sgr(NH3A), Sgr B2, and Orion A. A map of the J = 8 → 7 emission around Sgr B2 shows that the emitting region extends at least 2′ in galactic longitude and 3′ in galactic latitude. Column densities may be comparable to those of HCN in some sources. This molecule is thus more abundant in the interstellar medium than would be expected from its complexity, and may provide clues to formation processes where it is found.