Comet Hale–Bopp: Velocity Field Of Ions From Fabry-Pérot Imaging

Fabry-Perot interferograms of comet Hale-Bopp were obtained on several nights in March and April 1997. For this purpose we utilized the 2-channel focal reducer of the Max-Planck-Institute for Aeronomy at the 2-m telescope of the Pik Terskol Observatory. Solid Fabry-Perot etalons of resolving power 30000 were used in both channels of the focal reducer. The main aim of this study is to measure the velocities and abundances of OH+ and H2O+, both ions closely related to the same parent molecule, H2O. In the blue channel interferograms we identified several individual OH+ rotational lines of the A3Πi - X3Σ− (0-0) transition and measured their Doppler shifts. The target emissions in the red channel were the H2O+ lines of the A2A1 − X2B1 (10-0) band. We found that the line of sight velocities, obtained from the Doppler shifted wavelengths of emissions in the comet are higher in sunward direction than in the plasma tail and do not exceed 20 km s–1. The corresponding values, deprojected in antisolar direction, are consistent with predictions by magnetohydrodynamical models of the solar-wind-comet interaction, when one accounts for the extremely high gas production rate of comet Hale-Bopp.