Abstract X-rays and extreme ultraviolet (EUV) emissions from solar flares rapidly change the physical composition of Earth’s thermosphere ionosphere, thereby causing space weather phenomena such as communication failures. Numerous empirical models have been developed to estimate effects flare on upper atmosphere. We verified reproduction emission spectra using a one-dimensional hydrodynamic cal...

Accurate measurements of the D/H ratio in our Galaxy provide critical tests of Galactic chemical evolution and constrain the primor-dial value of D/H. Very high quality ultraviolet spectra from the GHRS and STIS instruments on HST have been analyzed for lines of sight toward both early and late-type stars and hot white dwarfs. We will summarize the results that are being obtained for D/H along ...