In search of C₂ and C₆₀ and improved line-profile fitting techniques

Hodgkinson, Gerald James (2000). In search of C₂ and C₆₀ and improved line-profile fitting techniques. PhD thesis The Open University.



High resolution spectra (λ/Ʌλ-90,000) of interstellar Na I (5889 Å) toward 18 stars spread over one half of the Galactic plane, including six stars in the direction of the SgrOBl Association, revealed several velocity components. A radial velocity of ~7km s-1 relative to the Local Standard of Rest was found in most sight lines and interpreted to arise in nearby diffuse clouds. Two velocity components were detected toward Sgr OB 1. Each of the associated clouds extends about 5 degrees in diameter in the sky. A third feature in that direction was identified with the Reigel-Crutcher cloud, part of an extensive cloud system spanning some 80 by 25 degrees in the sky.
High resolution observations were made in the region of the C2 Phillips (2-0) band towards 8 stars and the carbon star TX Psc, allowing upper limits of log N(C2) to be determined towards these stars and a comparison of C2 and CN spectra, respectively.
Medium resolution observations towards 31 stars were made covering the wavelength range 3820 Å to 3895 Å in a circumstellar search for a feature attributed to C60. The sight lines represent a wide range of circumstellar environments where C60 could be formed, including Wolf-Rayet, OB stars, A to M-type stars, the Red Rectangle, ß Pictoris, and ƞ Carinae. No conclusive evidence was found for C60. The results of the analysis are presented here for the first time. The Wolf-Rayet spectra fell into three distinct groups:
a). showing weak O VI and He I absorption,
b). An unidentified P-Cygni like profile near 3875 Å, and
c). An emission feature near 3830 A that was interpreted as arising from O VI.
The spectrum of ƞ Carinae revealed differences in minor features when compared with published spectra made in 1953 and 1961. The spectral range includes the position of optical lines of interstellar CH and CN, and upper limits to their column density were estimated. Suggestions are made for other optical observations at a higher resolution.
A computer program to analyse the observed interstellar atomic absorption lines was developed on a home PC. This was compared STARLINK program DIPSO, and used in addition to standard software to analyse the Na and Ca observations. It can estimate the values, with their standard errors, of the velocities, velocity dispersions and column densities of single or multiple components through a choice of two different search algorithms. The program works automatically after a few initial parameters are entered. Different weighting functions for the sum-of-squares can be applied. The capabilities of the home-PC and significance of this for research in astronomy and astrophysics is discussed.

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