Optical spectrum of the bipolar nebula AFGL 2688

Based on echelle spectra obtained at the prime focus of the 6-m telescope, we have determined for the first time the detailed chemical composition of one of the components of the bipolar nebula identified with the intense infrared source AFGL 2688 by the model-atmosphere method. The iron abundance [Fe/H] = -0.59 dex derived for AFGL 2688 suggests that the object probably belongs to an intermediate population of the Galaxy. The stellar atmosphere exhibits high carbon and nitrogen abundances, [C/Fe] = +0.73 and [N/Fe] = +2.00, and C/O > 1, confirming that the object is at the post-AGE stage. However. the detected overabundance of s-process elements (yttrium and barium) relative to iron is modest: [X/Fe] = +0.55. The lanthanides are even less enhanced: for La, Ce, Pr, and Nd, the mean abundance relative to iron is [la/Fe] = +0.26. This behavior of the heavy metals is consistent with the low intensity of the 21-mu m band in the infrared spectrum of AFGL 2688; the intensity of this emission band is great in the spectra of all the studied PPN with large overabundances of s-process elements. An analysis of the radial velocities measured from spectral features originating in the atmosphere and in the circumstellar shell has revealed a high-velocity (similar to 60 km s(-1)) component of the stellar wind from AFGL 2688. (C) 2000 MAIK "Nauka/Interperiodica".