Y-type dwarfs are not in Celestia. They should considered a type of brown dwarf. If you try to create an entry for Y-type dwarfs in the celestia.cfg file, the star you choose as Y will have its spectral class set to "?" which generates a white star. Anyone know how to fix, or how to make extra star classes in Celestia anyway?
Also - Q-type stars are *not explicitly* Neutron stars, but rather novae. Annie Jump Cannon used the Q class for miscellaneous. Also see: https://en.wikipedia.org/wiki/Q_star