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Discoveries and Achievements of HST Concerning Eta Car

 

  1. 1991--1996: The first high-resolution images of the bipolar Homunculus ejecta-nebula* [,,,,]
  2. 1991--1995: The first spectrogram ever obtained of the primary star []
  3. 1991--1997: The Weigelt knots are slow-moving ejecta with exotic spectra, not companion stars [,,]
  4. 1997: The bizarre "UV laser" phenomenon* [,,]
  5. 1991--1999: Accurate measurements of the Homunculus' age based on expansion rate [,,].
  6. 1999--2001: Bizarre emission lines of Strontium in the Homunculus []
  7. 1999--2006: The star's rapid brightening since the mid-1990's [,,]
  8. 2001: Spectroscopic proof of the Homunculus' equatorial skirt, the best attainable estimate of the bipolar inclination angle, and the best available assessment of Eta Car's distance from us (limited by geometrical ambiguities, not by data quality) []
  9. 1999--2003: A younger "Little Homunculus" exists inside the Homunculus nebula []
  10. 2003: The star's wind is probably bipolar (or at least it was in 2001) []
  11. 2003: First detailed spectroscopy of the star during a "periastron event" [,]
  12. 2010: Assessment of the secondary star's luminosity and temperature []
  13. 2003--2010: A "sea change" or change of state in the star's spectrum since 1998 [,]
  14. 2014: The 2014.6 periastron event was quite different from its predecessors, confirming a major change in the mass outflow [,]
* Historically, item 1 is less clear than the others. The Homunculus was called "bipolar" before HST [,], and one special image made in 1985 strikingly resembles the later HST images -- but unfortunately it wasn't published until 1995 []. Arguably the most significant discovery in the HST images was not the pair of lobes, but rather their small-scale granulation and also the equatorial skirt. Concerning item 5, the Homunculus' expansion age was estimated as early as 1958, but ground-based photos didn't have good enough spatial resolution for definite conclusions. After 2000, adaptive-optics IR images became good enough for these purposes [].