16176

Eta Car comma the only giant eruption survivor that can be studied well comma has been unsteady in recovering from the 1830-1870 explosion. About 20 years ago its spectroscopic and photometric trends dramatically accelerated -- signaling a rapid decrease in the primary mass loss rate. This is a novel clue to the stellar interior.s thermal and rotational disequilibrium following the eruption. Meanwhile comma d_commaspectroscopic eventsd_comma occur at 5.54-year intervals marking the companion star.s periastron. HST showed that the basic nature of these events changed between 2003 and 2014 --but we do not know whether this change was temporary comma or permanent comma or the precursor to something more extreme. Hence the next spectroscopic event comma in early 2020 comma is crucial. For reasons noted in the proposal comma ground-based instruments have inadequate spatial resolution for this purpose comma and can.t observe the UV. 2020 will be our last opportunity for HST spectroscopy comma and the star will be irreversibly changed when suitable instruments become available sometime in the future. Therefore we propose an adequate set of STIS-CCD and STIS-MAMA observations. They will be valuable for a wide range of topics including stellar instabilities comma colliding-wind physics comma and abnormal emission-line processes as well as eta Car.s recovery from a giant eruption.