An astrometric analysis of eta Carinae's eruptive history using HST WFPC2 and ACS observations
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eta Carinae is one of the most massive and engimatic stars in our galaxy. The star, estimated to be well over a hundred times more massive and millions of times brighter than our sun, is shrouded in an expanding cloud of gas and debris that was ejected around 1843 during it's so-called "Great Eruption" and surrounded by what appear to be fields of debris from previous eruptions. The fundamental nature of the star is not well understood. Quite basic questions remain, such as: is the star a binary? Various questions and disagreements are also present in the literature regarding the various debris features, their physical characteristics, and what they tell us about the star's history. In this dissertation, Hubble Space Telescope (HST) observations spanning nearly a decade and utilizing both the Wide Field/Planetary Camera 2 (WFPC2) and the Advanced Camera for Surveys (ACS) instruments---the most accurate visible imaging data yet taken of eta Carinae---are used to address many of these fundamental issues. In the first section, HST/ACS data taken during 2003--2005 is used to address the question of binarity. Based on an astrometric analysis of the data, binary reflex motion is detected in the primary and, by combining these results with those of other authors, allows us to derive the physical parameters of the resultant system. In the second section, 1995 WFPC2 and 2003 ACS data are used to make the most precise measurements yet of the debris around the central star. A date of origin is derived for the Homunculus, and a new, much shorter interval for the duration of the Great Eruption. Certain equatorial features, previously associated with an 1890 eruptive event are instead shown to be coeval with the Homunculus features and are thus associated with the Great Eruption. New debris associations outside the Homunculus are identified and their dates of origin are determined, implying eruptive events that preceeded the Great Eruption. These results add both significant new insight into our understanding of eta Carinae and its history and introduce important new constraints for any theoretician who seeks to model the star, the Great Eruption, or earlier events.