Recent changes in the near-ultraviolet and optical structure of eta Carinae

Multiepoch HST/WFPC2 images of eta Carinae are used to investigate the rela tionship between the photometric variability of the circumstellar nebula an d the variability of the central star. In the past few years, the central s tar has brightened considerably, and the response of the reflection nebula to this brightening has been surprisingly complex. While the central star h as brightened by a factor of 2 at near-ultraviolet and optical wavelengths, bright dust condensations in the bipolar lobes have increased by only a fa ctor of similar to 1.3, and dark lanes between these dust condensations hav e brightened by factors of 1.5-2 Certain regions of the nebula have brighte ned much more than the star itself (as much as a factor of 8), and others h ave actually faded, despite the brightening of the star. Some of the anomal ous fading can be attributed to contributions of intrinsic CS mi and [N II] line emission. The variations of the equivalent width of [S III] lambda 63 12 and [N II] lambda 6583 as measured in the WFPC2 F631N and F658N filters follow the same trend of other high-excitation lines observed in ground-bas ed spectra during eta Car's 5.5 yr spectroscopic cycle, and the amplitude o f the change accounts for the total change measured in ground-based spectra for these same lines. The WFPC2 images indicate, however, that these high- excitation lines are emitted by circumstellar gas at distances of a few hun dred to a few thousand AU from the star, probably located in the equatorial plane. Thus, periodic ionization of gas at large distances from the centra l star appears to dominate the spectroscopic changes that define the 5.5 yr cycle. The fact that the variable high-excitation emission is extended pla ces important constraints on models for eta Car's 5.5 yr spectroscopic vari ability.