Other
Scientific paper
Jul 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997dps....29.3712h&link_type=abstract
American Astronomical Society, DPS meeting #29, #37.12; Bulletin of the American Astronomical Society, Vol. 29, p.1048
Other
Scientific paper
Observations of the C2 Swan Bands in comet Hale-Bopp and a simple spectral model were used to study the spatial evolution of C2 excitation temperatures. The data set provides better spectral resolution than in studies of other comets. The analysis presented here is a first-order look at C2 temperatures near perihelion in this bright comet. Comet Hale-Bopp provided an opportunity to obtain observations of the C2 Swan bands from the 0.6 m telescope at Sommers-Bausch Observatory in Boulder, Colorado. We used a grating spectrograph with an 832 x 832 CCD detector to take data within a month of perihelion at moderate spectral resolution ( ~ 1.2 Angstroms FWHM). Spatial resolution was limited due to poor seeing at the site (5-10 arcsec). Four nights of usable spectra were obtained overall. The C2 Swan bands have been shown to exhibit non-equilibrium vibrational and rotational populations near cometary nuclei due to the long time ( ~ 3000 sec) required to reach fluorescence equilibrium (Rousselot et al., Icarus, 341, 1995; Rousselot et al., A & A, 645, 1994). We used Boltzmann distributions for the upper electronic state (d (3}Pi_ {g) ) to create model spectra and to estimate relative emission rates. Using fits to the observed spectra and band intensity ratios, we present effective rotational and vibrational excitation temperatures as a function of cometocentric distance. Because the spectrograph slit was aligned at various position angles relative to the Sun-comet axis, we investigate the possibility of excitation temperature variations due to spatial features. With our spectral resolution, individual rotational lines are partially resolved. A number of C2 lines can be identified, possibly allowing the removal of contaminating lines due to NH2 fluorescence. Thus, C2 excitation temperatures may be established to better accuracy than in previous works. Improved understanding of the C2 emissions allows better determinations of C2 formation/destruction processes and of carbon isotope ratios.
Brain Dave
Burger Matthew Howard
Hill Steven M.
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