Schedule Feb 09, 2006
Using Optical and UV Spectra of Young Supernova Remnants to Study the Physics of Collisionless Shocks
Parviz Ghavamian (JHU)

Our understanding of astrophysical collisionless shocks is limited because they occur in conditions too extreme to model in terrestrial laboratories.The plasma processes responsible for heating and isotropizing the electron and ion distributions at the shock front are poorly understood. In cases where the collisionless shock is non-radiative (adiabatic) and propagates into partially neutralgas, the excitation of cold hydrogen and charge exchange with hot ions close to the shock frontproduces both narrow and broad lines in the optical (Balmer emission) and UV (Lyman emission). The excitation of heavy ions (He, C, N and O) alsoproduces broad emission lines in the optical and UV range. I will show how spectroscopy of non-radiative supernova remnants provides valuable diagnostics of the plasma heating processes in highMach number interstellar shocks. The observations can be compared with predictions from numerical shock models to (1) infer the degree of electron-ion and ion-ion temperatureequilibration in collisionless shocks from the emission line widths and flux ratios, and (2) gain clues to the collisionless heating mechanism(s) from the shapes of the broad hydrogen line profiles.

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