It has been reported that the extinction law for Type Ia supernovae (SNe Ia) may be different from the one in the Milky Way, but the intrinsic color of SNe Ia and the dust extinction are observationally mixed. In this study, we examine photometric properties of SNe Ia in the nearby universe (z ≲ 0.04) to investigate the SN Ia intrinsic color and the dust extinction. We focus on the Branch spectroscopic classification of 34 SNe Ia and morphological types of host galaxies. We carefully study the distribution of their peak colors on the B − V, V − R color–color diagram, as well as the color excess and absolute magnitude deviation from the stretch-color relation of the bluest SNe Ia. We find that SNe Ia which show the reddest color occur in early-type spirals and the trend holds when divided into Branch sub-types. The dust extinction becomes close to the Milky Way like extinction if we exclude some peculiar red Broad Line (BL) sub-type SNe Ia. Furthermore, two of these red BLs occur in elliptical galaxies, a less-dusty environment, suggesting intrinsic color diversity in BL sub-type SNe Ia.

中文翻译：

---

附近 Ia 型超新星的内在颜色多样性

据报道，Ia 型超新星（SNe Ia）的消光规律可能与银河系中的不同，但 SNe Ia 的固有颜色和尘埃消光在观测上是混合的。在这项研究中，我们检查了附近宇宙 (z ≲ 0.04) 中 SNe Ia 的光度特性，以研究 SN Ia 固有颜色和尘埃消光。我们专注于 34 SNe Ia 的分支光谱分类和宿主星系的形态类型。我们仔细研究了它们在 B-V、V-R 颜色-颜色图上的峰值颜色分布，以及与最蓝 SNe Ia 的拉伸颜色关系的颜色过量和绝对量级偏差。我们发现显示最红颜色的 SNe Ia 出现在早期类型的螺旋中，并且在划分为分支子类型时趋势保持不变。如果我们排除一些特殊的红色宽线（BL）亚型SNe Ia，尘埃灭绝变得接近银河系。此外，其中两个红色 BL 出现在椭圆星系中，这是一个尘埃较少的环境，表明 BL 亚型 SNe Ia 具有内在的颜色多样性。