GHRS Instrument Science Report 078

"Multi-Orbit CVZ GHRS Observations and the Temperature of the Pre-Amp"

A.B. Schultz and J. Bacinski

Oct 14, 1996

Abstract

Multi-orbit observations in the CVZ (more than about 15 hours) are
affected by a temperature rise in the GHRS Pre-Amp, resulting in
anomalous "absorptions" (so-called flaky diodes). This problem was
first noticed during a Side 2 Cycle 5 program, 6086 (14 orbits), and
repeated during Side 2 program 6072 (25 orbits). During long periods of
CVZ observing, the GHRS Pre-Amp temperature will slowly rise to the
high temperature limit. As the Pre-Amp temperature rises, the integrity
of the Pre-Amp is compromised resulting in nonlinear amplification of
input charge from diodes. This effectively results in the appearance of
flaky diodes in spectra, as if a change in the threshold voltage had
changed the sensitivity of diodes.