Atomic and Molecular Aspects of Astronomical Spectra

Abstract

In the first section of this thesis, we present the atomic part of our investigation.A C 2+ atomic target was prepared and used to generate theoretical data required in the investigation of recombination lines that arise from collisions between electrons and ions in thin plasma found in planetary nebulae and other astrophysical objects. The R-matrix method of electron scattering theory was used to describe the C 2+ plus electron system. Theoretical data concerning bound and autoionizing states were generated in the intermediate-coupling approximation by R-matrix and Autostructure codes and compared to experimental data. The comparison revealed very good agreement. These theoretical data were then used to generate dielectronic recombination data for C + which include transition lines, oscillator strengths, radiative transition probabilities, as well as emissivity and dielectronic recombination coefficients. The data were cast in the form of a line list, called SS1, containing 6187 optically-allowed transitions which include many C ii lines observed in astronomical spectra. The data were validated by comparison to C + recombination data obtained from a number of sources in the literature. This line list was used to analyze the spectra from a number of astronomical objects, mainly planetary nebulae, and identify their electron temperature where the observational data were obtained from the literature. The electron temperature investigation was also extended to include free electron energy analysis which uses observational and theoretical data of FF and FB transitions to investigate the long-standing problem of discrepancy between the results of recombination and forbidden lines analysis and its possible connection to the electron distribution (Maxwellian or non-Maxwellian).

The Present and Future of Planetary Nebula Research. A White Paper by the IAU Planetary Nebula Working Group

“…Central star binaries with intermediate periods must exist. While at separations of a few solar radii to a few AU there will be no binary central stars because the AGB progenitor would have swept the companion into a common envelope and dramatically reduced the orbital separation, from a few AU to ∼100 AU we do expect companions to exist and to have interacted with the AGB star, affecting the mass-loss geometry and possibly the mass-loss rate as well (Soker 1997). Such binaries would have no light variability and only slight radial velocity variability.…”

“…Currently, we expect that the fraction of PN that have experienced a binary interaction of their central star to be a consequence of the fraction of close binaries in the 1-8M ⊙ main sequence population, which is roughly 20-30% (Raghavan et al 2010). However, the high incidence of non spherical PNe (∼80%; , alongside the lack of a quantitative single-star theory that explains these non-spherical shapes (Soker 2006;Nordhaus et al 2007), has prompted questions of whether the PN phenomenon is associated preferentially with binarity. If this were so, by necessity, there would be some AGB stars that never develop a PN because they do not suffer an interaction (Soker & Subag 2005;De Marco & Soker 2011).…”

“…However, the magnetic fields in those hydrodynamic simulations are artificially constant because gas movement does not feed back to the field strength and direction. Recently, Soker (2006) and Nordhaus & Blackman (2006) have demonstrated how such feedback would quench the field in approximately a century, eliminating the source of global mass-loss shaping that is needed to obtain non spherical PNe.…”

“…More extensive calculations for this ion should be carried out in intermediate coupling and cover a broad range of temperatures and densities. Sochi (2012) presents new intermediate coupling calculations of C ii, but only includes the dielectronic recombination.…”