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T. R. Gull (NASA/GSFC), K. E. Nielsen (CUA & NASA/GSFC), G. Vieira (SSAI & NASA.GSFC), F. Bruhweiler, E. Verner (CUA & NASA/GSFC), Eta Car HST Treasury Team
Eta Carinae is intimately surrounded by ejecta from the great event of the 1840's (the Homunculus), an event of the 1890's (the Little Homunculus) and an ongoing, complex wind modulated by a 5.53-year periodicity. Over the several month long minimum, major changes occur in the star and the complex ejecta. During the 2003.5 minimum, we were fortunate to monitor these changes with HST/STIS in CCD long slit mode (52"x0.1" aperture, ~40 km/s velocity resolution) and in MAMA echelle modes (0.3"x0.2" aperture; 3 and 10 km/s velocity resolution). Both high spatial and high spectral resolution are key to separating stellar from nebular changes.
The stellar UV dropped during the minimum due to foreground gas, not dust, absorption. However, many stellar NUV P-Cygni Fe II lines around 3000A actually brightened.
Structures in the vicinity to Eta Carinae dropped in excitation and ionization. One bead of an apparent string encircling Eta Carinae actually became brighter than the star in P-Cygni Fe II lines. Lyman-alpha-pumped Fe II lines faded in the Weigelt blobs and the Little Homunculus. Broad, spatially-extended absorptions of Fe II lines appeared briefly close to the star. Toward Weigelt B and D, a broad nebular absorption developed extending from -140 km/s to -40 km/s. The Si III] and Fe III nebular emissions near 1900A disappeared. In line of sight, the -146 km/s absorption component, associated with the Little Homunculus, dropped in ionization and excitation. The -513 km/s absorption component, associated with the Homunculus and therefore much more distant, showed little change. Many Fe II narrow absorption components between -50 and -380 km/s appeared briefly. The multiplicity of these components and their nearly periodic spacing suggest they are related to the 5.53-year cycle.
These observations were done through the STScI under STIS GTO and HST GO funding.
The author(s) of this abstract have provided an email address for comments about the abstract: Theodore.R.Gull@NASA.GOV
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Bulletin of the American Astronomical Society, 36 #2
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