Aperture after upgrade to Yosemite

After migrating to Yosemite the Aperature 3.5 app no longer works. It is grayed out with a cross hash in the avatar in my applications. Can I delete this non functional app by dragging it to the trash?

Secondly, what happened to the old Aperture library and it pictures that migrated to photos? Is it remained and linked to Photos or is the old Aperture 3.5 Library, which was huge, just buried somewhere? If the ole library is not needed and sitting around, I would prefer to free up the HD space.

I am dismayed I lost all my organization albums. All photos are now organized by Month, day, Year. Apple really did not think about its user with this change. I am now exclusively using LR, but many of my old pictures are still stuck in Photo.