New and improved orbits of some historical comets: 6TH and 7TH centuries

Five comets from the 6th century and three from the 7th century are studied. In some cases, new orbital elements are provided, or existing ones are refined to better fit the observations. In addition, comments are presented on specific questions raised by other authors about these historical comets, such as their periodicity, association with meteor showers, or even their mere existence. We consider in particular the cases of C/539 W1 and 1P/607H1 (Halley), both particularly interesting from a historical point of view and for the questions they raise in this regard. Finally, we also examine the proposed membership of some 6th-century comets to the Kreutz Sungrazer group.