Astrid Peth, portrayed by Kylie Minogue, was the Doctor’s companion during the 2007 Christmas special “Voyage of the Damned”.
She is from the planet Sto. Astrid is a waitress on the starship Titanic. Astrid helps the Doctor, but is killed while she saves him. After saving the Titanic, the Doctor realises that Astrid was still wearing a teleporter bracelet when she died. He tries to bring her back to life, but it does not work fully: Astrid now is a ghost-like energy being. In the end, the Doctor sends Astrid away to fly through the universe.