The Bipolar HR Carinae Nebula: Dynamics and Chemical Abundances

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Abstract
We present the results of a new set of medium resolution spectroscopic observations and high-resolution coronographic images of the nebula around the Galactic luminous blue variable (LBV) HR Carinae. The observations were carried out at the ESO/NTT (La Silla) in 1995 May and 1996 January. The nebular morphology and kinematics confirm that the nebula around HR Carinae is truly bipolar and very reminiscent of the η Carinae nebula. The previously identified "filaments" outline the edges of two symmetrical expanding bubbles, originating from the star and located, respectively, in the NW and SE quadrants. The small compact inner nebula, a few arcsec in size, previously detected, represents the "waist" of the bipolar distribution. The orientation in the images and the kinematical study have allowed us to define the true orientation of the bubbles, whose major axis lies at an angle of 50° with the plane of the sky, at an inclination of approximately 30° on the line of sight. The maximum projected expansion velocity is of the order of 100 km s-1. In the light of these new kinematical data, we revise the dynamical timescale to a younger age of 5000 yr. The nebula around HR Carinae is relatively young and fast, at variance with other well known LBV nebulae such as AG Carinae's. Spectroscopically, the nebula is of low excitation with [O III] absent, and [N II] fairly strong. [Ni II] λ6667 is detected, but only in the inner regions (≤5''). We find that the electron density increases from 400 cm-3 in the outer regions to more than 104 cm-3 in the innermost regions. An analysis of the chemical abundances in different regions of the nebula finds that N is overabundant, indicating that the nebula is composed of CNO processed stellar material. We find that the filamentary H II region, seen to the NW of HR Carinae, is at the same distance and is composed of material with typical H II region abundances, and has a morphology that suggests it has been shaped by the wind of HR Carinae.

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