Eta Carina Research

Publications and Simulations

• Abstract: Nebulae around luminous blue variable (LBV) stars are often characterized by a bipolar, prolate form. In the standard interpretation of the generalized interacting stellar winds model, this bipolar form is attributed to an asymmetry in the density structure of the ambient medium. However, there is limited observational evidence to suggest that such an asymmetric medium is present in most LBV nebulae. In this work we use scaling relations derived from the theory of radiatively driven winds to model the outflows from LBV stars, taking account of stellar rotation and the associated latitudinal variation of the stellar flux due to gravity darkening. We show that, for a star rotating close to its critical speed, the decrease in effective gravity near the equator and the associated decrease in the equatorial wind speed results naturally in a bipolar, prolate interaction front, even for a spherically symmetric ambient medium. Moreover, when gravity darkening is included, the resulting density of the outburst is also strongest over the prolate poles. We discuss the implications of these results for the formation of windblown nebulae in general.

• Abstract: We have constructed an interacting winds scenario to account for the geometric and kinematic properties of the Homunculus in eta Carinae as seen in recent Hubble Space Telescope observations. Winds from a giant eruption in 1840-1860 sweep into a small (10^14 cm), dense (~10^14 cm^-3), 2 M_&sun;, near-nuclear toroidal ring. The external medium is uniform at ~2000 particles cm^-3. The ring is all but destroyed by the winds in the eruption. Even so, it manages to provide a good deal of collimation to the mass ejected in the first 20 years. Subsequent weaker outflows ram into the outburst gas and initiate surface instabilities and wrinkles. Unlike earlier models, ours is in accordance with the observation that no large, extended disklike distribution is seen around the nebula that could have collimated the bipolar lobes. Models with cooling form essentially ballistic flows (that is, a pair of cones each with a spherical base) whose lateral edges become wrinkled by shear instabilities. A new aspect of the radiative models is the fragmentation of the dense ring, which may help to explain the thin, radial filamentary structure that is seen in the equatorial region of the Homunculus. Adiabatic models become very hot quickly and explode through the nascent cones into the confining gas before the dense collar is destroyed. A pair of spherical lobes form. After 150 years the lobe walls are corrugated by shearing instabilities. These lobes morph into a large, single balloon after about another 300 years.
• Simulations: Movies of simulations described in this paper (still under construction)

Other Links and Sources of Information

• More images of Eta Carina are available from the Chandra Web Site