0 Assigned ID: 673 ----- Attempting Submission 1 (Fri Apr 11 18:47:16 GMT 2014) ----- HST Phase I Proposal 673 (proximity_proposal.apt) successfully submitted. ----- Attempting Submission 2 (Fri Apr 11 20:30:27 GMT 2014) ----- The Cosmic Origins Spectrograph (COS) has gathered science grade HeII Lyman-alpha forest spectra towards 22 quasars. The vast majority of these show an enhancement in the ionization of helium at the redshift of the background quasar (the line-of-sight proximity zone) and most also show additional enhancements along the line-of-sight owing to adjacent quasars (transverse proximity zones). These zones can be used to constrain the lifetimes of a statistically representative set of quasars on the extremely interesting timescale of 1-100 Myr and, at the higher redshifts probed by HST/COS, also the reionization of the second electron of helium. However, to extract this information requires radiative transfer calculations. We outline a regimen of such calculations that should lay the groundwork to be able to interpret HST/COS HeII Lyman-alpha forest observations. QUASAR ABSORPTION LINES AND IGM Default Medium false true false false true SUPPORTED