This is my sentence, and I was hoping to make it sound more academic:
The aim is to ascertain whether or not the actors from the two films analysed can be considered to be heroes
Is there a better, more academic way of saying 'whether or not'?
It OK to want to use language that's appropriate for your audience, but when one wants to "sound academic" one runs the risk of sounding artificial as well. It's best to write in as natural a style as possible, while remaining clear, and then to root out anything that's plainly inappropriate. There's nothing about whether or not that's unsuitable for an academic audience, though you could lose the or not without disadvantage. You could also replace whether [or not] with if.
I like determine better here because ascertain is usually related to establishing facts, while here you are concerned with coming to a subjective judgment.
Now that I think about it, I'd also omit to be before heroes. Say out loud
and see if it isn't more pleasing than the alternative
You could say "to ascertain the extent to which the actors can be considered...."
Or just say "whether", and drop the "or not".