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Paper: Astrophysical and Technical Aspects of Astrometric Methods on Hubble
Volume: 338, Astrometry in the Age of the Next Generation of Large Telescopes
Page: 298
Authors: Currie, D.G.
Abstract: The astrometric analysis of eta Carinae, the associated homunculus, the surrounding ejected debris field and the inner core region with its more recent ejecta has provided both a wide variety of astrophysical results and a study on the use, methods and accuracy of astrometric procedures, both for the "plane of the sky" and for radial velocity or 3D astrometry, on extended or diffuse objects. From an astrophysical point of view, it has revealed the origin, history and 3D structure of the homunculus that was ejected in the Great Eruption of 1842. Additional information on the structure of the homunculus has been provided by the use of the Fabry-Perot with ADONIS on the European Southern Observatory's 3.6 meter telescope at La Silla, Chile. The analysis of the surrounding ejected debris has yielded information on the history of previous eruptions and may yield information as to the physical nature of these earlier eruptions. The interaction of the debris from various eruptions addresses the current state of the circumstellar media. Finally, recent analysis of the inner core region, using both the UVES spectrograph on the ESO's VLT at Paranal, Chile and the WFPC and the HRC/ACS on HST has yielded a definitive determination of the date of the origin of the Weigelt blobs. It should also yield definitive information on the motion of the inner disk. In general, it has yielded a large body of new information and, in addition, it has also greatly constrained theories and conjectures as to the history, structure, origin and evolution of eta Carinae and its ejecta.

On the other hand, eta CAR has also been a very interesting object for the technical development of astrometric methods for use on diffuse objects. It is bright enough to allow multiple observations to understand the reproducibility of the results without a large penalty for telescope time. It is also bright enough to provide sufficient photons in an acceptable exposure time to obtain a very good signal-to-noise ratio so that other error sources may be quantitatively studied. Finally, the nature of the illumination and scattering of the homunculus is such that there is relatively little change in the apparent structure between the visible (for the WFPC and ACS of Hubble) and the infrared observations by groundbased adaptive optics systems. This allows an on-going quantitative evaluation of the performance of the AO systems and their associated image reconstruction programs.

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