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Paper: Protoplanetary Nebula AFGL 2688 in the Light of New Spectral Data: Structure and Kinematic
Volume: 518, Physics of Magnetic Stars
Page: 203
Authors: Yushkin, M. V.; Klochkova, V. G.; Panchuk, V. E.
Abstract: The new observational data of the protoplanetary nebula AFGL 2688 with high spectral resolution (R=60,000) were obtained with the spectrograph NES of the 6-meter telescope BTA. The absorption photospheric lines are clearly identified in the spectra of both northern and southern reflection lobes of the nebula. The redshift of photospheric lines relative to the systemic velocity is explained as the effect of radiation scattering in the expanding circumstellar envelope. Precise measurements of the radial velocities of various spectral features allow to define the object geometry. For the first time the kinematic characteristics of a separate dust and gas components of the reflection lobes were measured. Analysis of the complex NaI D line profiles revealed a significantly higher velocity of the dust component of the nebula than that of the gaseous component. Perhaps we observe the effect of radiation driven wind (acceleration of dust grains by radiation pressure). A comparison of the chemical abundances of the central star and the circumstellar envelope allows us to suggest that the inner altered by CN-cycle layers of the star was uncovered due to post-AGB mass loss process. It is perhaps that the AFGL 2688 progenitor was massive J-type carbon star.
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