Physical Structures of the Type Ia Supernova Remnant N103B

N103B is a Type Ia supernova remnant (SNR) projected in the outskirts of the superbubble around the rich cluster NGC 1850 in the Large Magellanic Cloud (LMC). We have obtained Hα and continuum images of N103B with the Hubble Space Telescope (HST) and high-dispersion spectra with the 4 m and 1.5 m telescopes at Cerro Tololo Inter-American Observatory. The HST Hα image exhibits a complex system of nebular knots inside an incomplete filamentary elliptical shell that opens to the east, where X-ray and radio emission extends farther out. Electron densities of the nebular knots, determined from the [S ii] doublet, reach 5300 cm^-3, indicating an origin of circumstellar medium, rather than interstellar medium. The high-dispersion spectra reveal three kinematic components in N103B: (1) a narrow component with [N ii] λ6583/Hα ∼ 0.14 from the ionized interstellar gas associated with the superbubble of NGC 1850 in the background, (2) a broader Hα component with no [N ii] counterpart from the SNR's collisionless shocks into a mostly neutral ambient medium, and (3) a broad component, ΔV ∼ 500 km s^-1, in both Hα and [N ii] lines from shocked material in the nebular knots. The Balmer-dominated filaments can be fitted by an ellipse, and we adopt its center as the site of SN explosion. We find that the star closest to this explosion center has colors and luminosity consistent with a 1M_⊙ surviving subgiant companion as modeled by Podsiadlowski. Follow-up spectroscopic observations are needed to confirm this star as the SN's surviving companion.