@phdthesis{Helbert2003,
author = {Helbert, Jörn},
year = {2003},
title = {Studying the longterm evolution of gas activity in the coma of Comet C/1995 O1
(Hale-Bopp), with a special focus on the chemistry of carbon bearing molecules},
type = {Dissertation},
url = "http://dx.doi.org/10.17169/refubium-11390",
}