how did Ulic Qel-Droma disappear when he died?

Ulic Qel-Droma was a jedi, who turned Sith and then was stripped of the Force and lived in exile on Yavin 4. but then the guy that had brought him to Yavin 4, Hoggon, shot him after realizing he had transported a criminal/foe to the jedi order, of which Hoggon respected deeply. as Ulic lay dying in Vima Sunrider's arms he disappeared like Obi-Wan and Yoda did.

ALSO: at the end of ROTJ, when obi wan, yoda and anakin are lined up as spirits, how did Anakin get there? his body didnt disappear when he died in Luke's arms, so did he somehow master that technique when he returned to the light side and the mix of his extreme midi-chlorian count? and what is with that sebastian guy who played the old anakin as a ghost? he looks nothing like David Prowse.

Welcome to the boards. Your question is not saga-related. I'm not knowledgable about the EU, but it seems for appropriate for one of the EU forums