Echelle Spectroscopy of the Central Stars of Planetary Nebulae

Citation

McCarthy, James K. (1988) Echelle Spectroscopy of the Central Stars of Planetary Nebulae. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/jzsq-vr40. https://resolver.caltech.edu/CaltechETD:etd-09172008-093354

Abstract

Presented in this work are the results of a spectroscopic study of the central stars of planetary nebulae (CSPN) conducted at high resolution. From detailed comparisons of their photospheric absorption line profiles observed at high signal-to-noise with the NLTE model atmosphere line profiles of Kudritzki, et al., in Munich, West Germany, the photospheric effective temperatures (T_eff), surface gravities (g), and helium abundances (y) were derived. Placement of the CSPN in the distance-independent log(g) - log(T_eff) diagram allowed central star masses and evolutionary ages to be deduced via comparisons with published evolutionary model calculations. Spectroscopic distances to the CSPN were estimated from the best fit model fluxes, leading to dynamical expansion ages for the surrounding nebulae which were typically much greater than the corresponding CSPN evolutionary ages. Two possible reasons for this timescale disagreement were quantitatively investigated: (1) the nebulae could have experienced a phase of rapid photo-ionization of material ejected while the stars were still on the AGB, or (2) the AGB - CSPN evolutionary transition times could have been increased by small additional amounts of residual envelope material remaining after the superwind mass loss phase.

An important preliminary phase of this project was the design and construction of a CCD echelle spectrograph for the Palomar 1.5 m telescope. The spectrograph was designed to cover the wavelength range 3200 Å to 7000 Å, utilizing 57 diffracted orders from the echelle grating. Fused quartz prism cross-dispersing elements and an all-transmitting camera lens system contribute to the extremely high throughput of the instrument; the combined telescope and echelle spectrograph efficiency is approximately 20% from above the atmosphere. Details of the echelle spectrograph optical and mechanical designs are presented.

The scientific objectives of the CSPN study with this new instrument required a thorough investigation into the data reduction process for CCD echelle spectra, and a set of Fortran subroutines were written for this purpose as part of the FIGARO data reduction package. The philosophy and algorithms employed in these routines are discussed, and a detailed description of each of the commands is provided in an Appendix for future reference.

Thesis Files