Dear Jan,
Ancestry.com has a family website "Emanuelson/Ellickson" where you should be able to find more information about Tonnas Emanuelson. My grand-aunt, Anna Mari Ellickson Emanuelson, was Tonnas' wife, and mother of his nine children.
I suspect that as a Tjader you know Bette Tjader, who I have been in correspondence with. I sent her my version of the family history. It's called "Norsk Children."