Do I need a new Title?

I was recently given responsibility to lead of team in a project managment capacity, the members of which have previously been superior to me and will continue to be with respect to other aspects of my job.I have working on this project for some time, but getting no cooperation from these people because I carry no authority. The solution has been to put me officially in charge of meetings and hold people accountalbe for specific tasks.

My question is: Do I need a title ( like Team Leader or Team Manager or something you may suggest) in order to really make it clear that, with respect to this project I am the leader, and the memberso of the team are answrable to me?

I appreciate any insight.