7. Radial velocity
Fig. 15 shows mean radial velocities of absorption and emission components of Fe II lines. Solid squares indicate radial velocities of the absorption components measured on the high dispersion spectra and open squares indicate those of the emission components (Table 3). The observational error is smaller than the symbols. The mean radial velocities of absorption components measured on the medium dispersion spectra (Table 2) are given by triangles with error bar.
When the emission components were strong in the early stage, the absorption components on the medium dispersion spectra had systematically larger negative radial velocities with respect to those of the high dispersion spectra. Because of the lower spectral resolution, the red side of the absorptions may have been filled by the emission components. The values measured on the medium dispersion spectra in the early stage, therefore, may not have represented the real velocity of absorptions. The radial velocity of the absorption components in the earliest stage may have been roughly -220 km s-1, which was estimated by an extrapolation from the results measured on the high dispersion spectra. The emission components were nearly stable at -57.7 km s-1. The blue-shift of the absorption components with respect to the emission components may have been about -160 km s-1 in the earliest stage. The same quantity was -126 km s-1 in September and -96 km s-1 in December. Such low velocities are fairly unusual among classical novae. For example, even in the slowest classical nova HR Del, the absorption components of H I and metallic lines were blue-shifted by about km s-1 in the early stage and about -200 km s-1 at the end of pre-maximum stage (Hutchings 1971). Only RR Pic had a still lower blue-shift (-72 km s-1) of absorption components in the pre-maximum stage (Lunt 1926; Table 10.2 of Payne-Gaposchkin 1957).
The blue-shift of the absorption components decreased with time during the pre-maximum stage (Fig. 15) like as other novae. On the light maximum, however, the blue-shift slightly increased. Probably a new high velocity absorption system emerged on the light maximum.
© European Southern Observatory (ESO) 1998
Online publication: September 17, 1998