- I'm a big fan of Rhianna.
- I'm a big fan of Rhianna's.
I find both acceptable, but think I think I would prefer (1)? For pronouns, though, I think they must be possessive pronouns.
- *I'm a big fan of you.
- I'm a big fan of yours.
- *I'm a big fan of her.
- I'm a big fan of hers.
But I think it's strictly animacy based, since for inanimates I think the possessive form is ruled out, or is at least worse.
- I'm a big fan of coffee.
- *I'm a big fan of coffee's.
- I'm a big fan of Star Trek.
- *I'm a big fan of Star Trek's.
- I'm a big fan of it.
- *I'm a big fan of its.
I don't think the acceptability of (1) is related to a sort of corporate entity reading of "Rhianna." Both of the following seem fine to me:
- I'm a friend of Joel.
- I'm a friend of Joel's.
Thoughts?