类型IIn超新星1998S的非球形证据

我们在1998年3月7日UT于Keck-II 10米望远镜上获得的光学光谱极化数据，以及从超新星发现（1998年3月2日UT）起的前494天的总光谱数据。发现该超新星表现出较高的线性极化，暗示其连续光谱散射环境具有显著的非球形。除去星际极化后，极化光谱以p约为2%的平坦连续光谱为特征，并伴随明显的极化变化，这些变化与总光谱中看到的宽线（FWZI >= 20,000 km/s）和窄线（未分辨，FWHM < 300 km/s）相关。When analyzed in terms of a polarized continuum with unpolarized broad-line recombination emission, an intrinsic continuum polarization of p ~ 3% results (the highest yet found for a SN), suggesting a global asphericity of >= 45% from the oblate, electron-scattering dominated models of Hoflich (1991). The smooth, blue continuum evident at early times is shown to be inconsistent with a reddened, single-temperature blackbody, instead having a color temperature that increases with decreasing wavelength. Broad emission-line profiles with distinct blue and red peaks are seen in the total flux spectra at later times, perhaps suggesting a disk-like or ring-like morphology for the dense (n_e ~ 10^7 cm^{-3}) circumstellar medium. Implications of the circumstellar scattering environment for the spectropolarimetry are discussed, as are the effects of uncertain removal of interstellar polarization.