"Die neue Opel Astra" or "Der neue Opel Astra"
As I know the articles, der, die and das are definited regarding to the noun (the last, the main noun,...).
So I woud expect, that the article "die" belongs to Astra: "die Astra" and then also "die neue Opel Astra", but I've found "Der neue Opel Astra" - even in the material for learning German. Opel can means more than Astra, but not in grammar. I've even found record "der neune Astra".
In fact I can't find die Astra in german dictionary, but just die Aster - femal gender.