The Interstellar Extinction Curve: A Puzzling Problem of Wave-optics

Abstract: The spectrum of a star can be deeply modified when the star is observed through an interstellar cloud. Understanding the nature of these modifications is an issue for several fields of astrophysics, from interstellar chemistry to cosmology or star distance estimates. I will show that besides a classical linear extinction (similar to extinction by aerosols in the atmosphere) over the whole visible-UV wavelength range, the modifications of a reddened star’s spectrum arise from a substantial contribution of light forward-scattered by hydrogen within the cloud on the line of sight. The importance of the scattering is such that if a star could be observed behind a cloud of pure hydrogen (no dust) it will appear many times brighter in the UV than without the cloud on the line of sight. This talk concerns astrophysicists but also physicists interested by a remarkable and counterintuitive application of coherent scattering and diffraction theory that remains to be formalized.
 

Please note that this talk was originally scheduled for April 29, but has been rescheduled for TUESDAY, APRIL 30, at 12:05pm.