Physics
Scientific paper
Nov 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt..........b&link_type=abstract
PhDT. Utrecht Rijksuniversiteit Doctor de Wiskunde en Natuurwetenschappen Thesis
Physics
11
Post-Agb, Circumstellar Matter, Spectroscopy
Scientific paper
A study has been made of a sample of post-Asymptotic Giant Branch stars. Diatomic carbon (C2) and CN absorption in the optical spectrum of a dozen stars have been studied using high-resolution optical spectroscopy. These lines were identified as being formed in the circumstellar shell (AGB ejecta) surrounding the carbon-rich post-AGB stars. Expansion velocity, rotational temperature, kinetic temperature, column density, and local density of the line forming region were determined. It was shown that these lines could be used to study the physical and chemical conditions of the circumstellar environment of these stars. CH+ absorption and emission was studied in two post-AGB stars and we suggest the circumbinary disk to be the line-formation region. Three post-AGB stars have been studied in detail: HD101584, HR4049, and HD56126. For HD101584 it was found that this is an interacting binary system with an photometric (an likely orbital) period of 218 days. Due to binary interaction the star has a very high-mass loss rate. Wind material obscures the star by means of a so-called "iron curtain". Several different spectral lines are identified which probe different regions of the binary system. The complete optical spectrum of HR4049 has been studied. Not a single metal line was detected. Variability of H alpha and NaID is discussed in terms of it binary nature. Short-term variability of HD56126 has been studied by means of the Hα profile. Pulsation is likely the origin for the variability which is of the order of a month.
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