**DIPS 3/2007**[tex source, PostScript, PDF file, dvi]-
**Title:**On Ricci flat metrics possessing non-trivial Conformal Killing Algebras.**Author:**Rossella PiscopoWe prove that a non-trivial conformal Killing algebra with bidimensional orbits of a 4-dimensional pseudo-Riemannian manifold is isomorphic to the Rotondaro algebra either of dimension 3, or of 4. We also give an exact description of Ricci flat 4-metrics that admit a non-trivial Conformal Killing algebra with bidimensional orbits.

14 pages, LaTeX-2e.

To compile source files (**.tex**) one needs the title page style files titlatex.tex.