Wide Field Imaging and the Velocity Structure in the Coma of Hale–Bopp

• Published in: Earth, moon, and planets moon, and planets, 2002-06, Vol.90 (1-4), p.45-56
• Main Authors: Harris, Walter M, Morgenthaler, Jeffrey P, Scherb, Frank, Anderson, Christopher, Oliversen, Ronald J
• Format: Article
• Language: English
• Subjects: Comet heads; Comets; Emission lines; Photochemicals; Velocity; Velocity gradient
• ISSN: 0167-9295; 1573-0794
• DOI: 10.1023/A:1021556132765

The comae of very active comets have a substantiallymore complex coma than their weaker cousins.The primary cause of this is photolytic heating and collisionsthat occur over an ever-larger volume of the coma asQH2O increases. Collisionswith the photochemical daughters ofwater in this regionmodify the radial distributions and outflowvelocity of each species, excite and quench metastableemissions, and introduce velocity gradients from photolyticheating. Comet Hale–Bopp was the first comet forwhich the collisional coma was both spatially resolvableand comparable in extent to the scale lengths ofmajor coma species. In the case of this object,the classical assumptions that make it possible toinvert radial emission line profiles, brightnesses, andlineshapes to production rate and velocity eitherdo not hold or require adjustment to work.Here we describe how a large collision zone modifies thecoma, how it affects the classical methods for obtainingproduction rate and velocity, and discuss how wide fieldimaging may be combined with modified versions ofsimple models to address the complications and extract somestructural information.