Ancient eruptions of η Carinae: a tale written in proper motions
Ancient eruptions of η Carinae: a tale written in proper motions
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DOI：
10.1093/mnras/stw2019
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发表时间：
2016-09
影响因子：
4.8
通讯作者：
M. M. Kiminki-M.;M. Reiter;N. Smith
中科院分区：
文献类型：
--
作者：
M. M. Kiminki-M.;M. Reiter;N. Smith
我们分析了哈勃太空望远镜对船底座外喷出物的H$\α$+[N II]成像的八个时期。近800节的自行运动表明，探测到的喷射物分为三个明显的年龄段，可以追溯到公元1250年左右，公元1550年左右，以及19世纪40年代大喷发期间或之前不久。来自这些群体的喷射物分布在不同的地点，并为埃塔汽车在19世纪之前经历了多次大喷发提供了强有力的限制。1250和1550事件并不具有与Homunculus相同的轴对称性；1250事件尤其不对称，甚至是单边的。此外，S山脊中与大喷发有关的喷射物似乎比古人喷发早了几十年。我们基本上探测到了跨越多个时代的弹道扩张。我们没有发现可以通过撞击周围物质来为软X射线壳层提供动力的观测到的结的大规模减速的证据，这表明观测到的X射线是由19世纪40年代快速、稀薄的喷射物超越较老的致密结而产生的。早期的减速和随后的滑行不能解释较老的外部喷射物的起源-需要19世纪之前的重大间歇性质量损失。过去喷发的时间尺度和几何形状为驱动Eta Car行为的任何理论物理机制提供了重要的约束。不重复的机制，如近双星在三元系中的合并，将需要额外的复杂性来解释观察结果。
We analyze eight epochs of Hubble Space Telescope H$\alpha$+[N II] imaging of Eta Carinae's outer ejecta. Proper motions of nearly 800 knots reveal that the detected ejecta are divided into three apparent age groups, dating to around 1250 A.D., to around 1550 A.D., and to during or shortly before the Great Eruption of the 1840s. Ejecta from these groups reside in different locations and provide a firm constraint that Eta Car experienced multiple major eruptions prior to the 19th century. The 1250 and 1550 events did not share the same axisymmetry as the Homunculus; the 1250 event was particularly asymmetric, even one-sided. In addition, the ejecta in the S ridge, which have been associated with the Great Eruption, appear to predate the ejection of the Homunculus by several decades. We detect essentially ballistic expansion across multiple epochs. We find no evidence for large-scale deceleration of the observed knots that could power the soft X-ray shell by plowing into surrounding material, suggesting that the observed X-rays arise instead from fast, rarefied ejecta from the 1840s overtaking the older dense knots. Early deceleration and subsequent coasting cannot explain the origin of the older outer ejecta---significant episodic mass loss prior to the 19th century is required. The timescale and geometry of the past eruptions provide important constraints for any theoretical physical mechanisms driving Eta Car's behavior. Non-repeating mechanisms such as the merger of a close binary in a triple system would require additional complexities to explain the observations.