Spectroastrometry: Eta Carinae as an Example

摘要

The use of a long-slit imaging spectrograph to scan a stellar disk and its neigh-boring media can bring a voluminous amount of data that can not easily be obtained via 2-D imaging. As for a proof of concept, the Hubble Space Tele-scope/Space Telescope Imaging Spectrograph (HST/STIS) has been utilized to scan through the ejecta of the super-massive star Eta Carinae. This "mapping" of η Carinae has resulted in a 3-dimensional data cube with the spatial resolution of 0.1" and velocity resolution of 32 km~(-1) near Hβ emission. Figures 1 and 2 demonstrate the robustness of this spectroastrometric method. First, Figure 1 shows the [Fe II] emission velocity map of the central region of 77 Carinae. Extended intrinsic emission structures are mostly composed of Little Homunculus and the equatorial ejecta (Ishibashi et al. 2003). Second, Figure 2 zooms into the central region of i Carinae shown in Figure 1. The two panels show blue (left) and red-shifted (right) emission features. In these velocity maps, there appears a faint "ring" like structure with =0.5" radius that surrounds ri Carinae. Its apparent ellipticity indicates that the "ring" may be tilted by degs, which is consistent to the inclination of the bipolar Homunculus Neb-ula. The existence of such a ring-like structure has been suspected (Smith et al. 2000 and references therein), but the study of its dynamical structure had never been possible before this spectroastrometric work.