Do you have any other information? For instance, when and where was your mother born? Who were her parents?
When was Causmus von Bornemann born? When and where did he marry?
Do you have any particular Bornemann family in Ireland that you've been researching?
I will check and see what I can find, but records in Indonesia aren't usually available online. You can sometimes find them at a Family History Center on microfilm. Am I correct that Djokjarkarta is the city now known as Yogyakarta in Java?