`Pure' Supernovae and Accelerated Expansion of the Universe
  A special class of type Ia supernovae that is not subject to ordinary and additional intragalactic gray absorption and chemical evolution has been identified. Analysis of the Hubble diagrams constructed for these supernovae confirms the accelerated expansion of the Universe irrespective of the chemical evolution and possible gray absorption in galaxies. 
M. V. Pruzhinskaya, E. S. Gorbovskoy, V. M. Lipunov
astro-ph.CO