This old presentation to a meeting was made upon an idea of PhD advisor F. Boulanger. It was also a draft for a paper submitted to A&A which was fortunately refused. I understood very soon after that all was wrong in this paper, the idea (that grain extinction properties vary with location), the model (the Desert, Boulanger, Puget interstellar dust model), the shock calculations (made to fit what we wanted to show), the conclusion (variations of dust composition in the vicinity of Spica). I therefore, despite the insistance of F. Boulanger, definitely dropped the paper and its ideas, and believe it should not be used for scientific purpose.
Author comment submitted on 11 March, 2011 by Frederic Zagury ( firstname.lastname@example.org )