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Astron. Astrophys. 320, 568-574 (1997)

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6. Summary and remarks

Using imaging data and high-dispersion spectroscopic data, we have analyzed the nebula around the LBV HR Car and confirmed its bipolar structure. The two lobes have angular sizes of approximately [FORMULA] and [FORMULA] and their expansion velocities amount to [FORMULA] km s-1. Bipolar nebulae are actually not very common among the known LBVNs (Nota et al. 1995). The HR Car nebula will be the second bipolar LBVN ever reported, with the Homunculus Nebula of [FORMULA] Car being the first. The formation of the bipolar nebula around HR Car is probably similar to that of the Homunculus nebula. The Homunculus was ejected in the last century with an expansion velocity of [FORMULA] km s-1 (e.g. , Gaviola 1950; Meaburn et al. 1987; Meaburn et al. 1993; Damineli Neto et al. 1993). The LBV nebulae around HR Car and [FORMULA] Car provide an opportunity to probe the evolution of LBVNs. In such a scenario the formation of a LBVN starts with a nebula that looks more like the Homunculus (150 yr old) and then evolves into a structure similar to the bipolar nebula of HR Car ([FORMULA] yr old). The formation and evolution of a LBVN may depend on the strength of the eruption, initial expansion velocity, and the mass and density in the shell as well as in the surrounding medium. Since so many parameters are unknown, it is necessary to identify and use as many LBVNs as possible to complete our understanding of LBVN formation and evolution.

Both LBVNs of HR Car and [FORMULA] Car show bipolar morphology pinched by an equatorial plane. This morphology may be supportive of the recent theory of wind compressed disks (Bjorkman and Cassinelli 1993; Mac Low et al. 1996). In these models, the disk of higher density in the equatorial plan, formed by the wind and rotation of the star during the main sequence phase, is responsible for the mass ejection in preferred polar directions, which lead to the formation of bipolar shaped LBVNs. To verify this formation mechanism, a better understanding of the kinematic structure of LBVN is needed.

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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