The Starfish Twins: Two Young Planetary Nebulae with Extreme Multipolar Morphology
The Starfish Twins: Two Young Planetary Nebulae with Extreme Multipolar Morphology
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海星双胞胎：两个具有极端多极形态的年轻行星状星云
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发表时间：
2000
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影响因子：
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通讯作者：
R. Sahai
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作者：
R. Sahai
我们呈现了两个天体He 2-47和M1-37的Hα图像，这两个天体是在哈勃太空望远镜对年轻行星状星云（PN）进行成像调查期间获得的，这些年轻行星状星云是根据它们的低激发特性选择的。这两个天体呈现出高度非球面的形态，其特征是围绕中心星星分布着多个叶瓣。这样的形态在任何天体物理学背景下都从未见过。短轴附近的明亮结构表明存在致密的赤道环面（在M1-37中看到边缘，在He 2-47中看到部分椭圆环）。在这两个星云中，中心星星被发现偏离腰部区域的几何对称中心。He 2-47和M1-37的多瓣是最近（几百年前）才产生的，这是基于对它们膨胀年龄的粗略估计。这些PN的极端多极形态支持最近的假设Sahai & Trauger，塑造PN的主要代理商是高速准直流出，在晚期渐近巨分支（AGB）和/或早期后AGB进化阶段，这些流出改变其方向episodically，和/或多个准直流出不同的轴操作（准）同时。为了充分理解He 2-47和M1-37的显著形态特征，需要对现有理论进行重大修改或提出全新的想法。
We present Hα images of two objects, He 2-47 and M1-37, obtained during a Hubble Space Telescope imaging survey of young planetary nebulae (PNs) selected on the basis of their low-excitation characteristics. The two objects show a highly aspherical morphology, characterized by multiple lobes distributed around the central star. Such a morphology has never been seen before in any astrophysical setting. Bright structures near the minor axes indicate the presence of dense equatorial tori (seen edge-on in M1-37 and as partial elliptical rings in He 2-47). In both nebulae, the central star is found to be offset from the geometrical center of symmetry of the waist region. The multiple lobes of He 2-47 and M1-37 have been produced fairly recently (a few hundred years ago), based on rough estimates of their expansion ages. The extreme multipolar morphology of these PNs supports the recent hypothesis of Sahai & Trauger that the primary agents for shaping PNs are high-speed collimated outflows that operate during the late asymptotic giant branch (AGB) and/or early post-AGB evolutionary phase; these outflows change their direction episodically, and/or multiple collimated outflows with different axes operate (quasi)simultaneously. Drastic modifications of existing theories or completely new ideas are needed in order to obtain a full understanding of the salient morphological features of He 2-47 and M1-37.