Kinematics and Ultraviolet to Infrared Morphology of the Inner Homunculus of η Carinae

Abstract

We present the first ultraviolet and optical images of η Car and its circumstellar Homunculus nebula, obtained with the Advanced Camera for Surveys/High Resolution Camera (ACS/HRC) on board the Hubble Space Telescope (HST). Compared to those at visual wavelengths, UV images reveal excess emission 0.1"-0.6" from the central source along the minor axis that may emanate from the outer parts of η Car's nonspherical stellar wind, which dominates the UV flux from η Car. The UV emission fills the cavity inside a dust torus measured from infrared (IR) data; within 0.2" of the star the UV emission projects a morphology reminiscent of the IR torus, but it is a factor of 10 smaller. This ``little torus'' seen in the UV may be related to the ``Little Homunculus'' discovered recently, signifying recurrent mass ejections with the same geometry. Finally, we reexamine the kinematics of nebular condensations near the star (Weigelt objects C and D) in HST images and spectra obtained over the past decade. We measure heliocentric velocities slower than previous estimates, and from proper motions we derive an ejection date of 1908+/-12 yr, assuming linear motion. However, because of radiative acceleration, these objects may have been ejected earlier-perhaps during the 1890 outburst of η Car. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.