[论文解读] Major Outburst and Splitting of Long-Period Comet C/2015 ER61 (Pan-STARRS)

Z. Sekanina|arXiv (Cornell University)|Dec 8, 2017

Astro and Planetary Science被引用 3

一句话总结

本文研究了长周期彗星 C/2015 ER61（Pan-STARRS）的重大爆发及其后续分裂，提出2017年4月5日的核碎片化事件同时触发了爆发和形成了一颗微弱的伴核。该伴核以小于1 m s⁻¹的速度分离，表现出极端的亮度变化，并在数周内解体，非引力减速表明其尺寸小于100米，为彗星碎片化动力学提供了新见解。

ABSTRACT

In early April 2017, five weeks before passing through perihelion, the dust-poor comet C/2015 ER61 was observed to undergo a major outburst, during which its intrinsic brightness increased briefly by about 2 mag. Evidence is presented in this paper to suggest that the flare-up was in all likelihood a product of an event of nuclear fragmentation that gave birth to a companion nucleus, which was first detected more than nine weeks later, on June 11, and remained under observation for 19 days. The companion is found to have separated from the parent nucleus with a velocity of less than 1 m/s; subsequently it was subjected to a nongravitational deceleration of 14 units of 10^{-5} the Sun's gravitational acceleration. The companion's overall dimensions can from this value be estimated al less than one hundred meters across. Unlike the primary nucleus, the companion displayed considerable fluctuations in brightness on time scales spanning at least three orders of magnitude, from a fraction of one hour to weeks. The long temporal gap between the companion's birth and first detection appears to be a corollary of the brightness variability. Evidence from the light curve suggests that the companion became detectable only because of large amounts of debris that it started shedding as well as increased activity from area newly exposed by progressive fragmentation, the same process that also resulted in the companion's impending disintegration by the end of June of in early July.

研究动机与目标

• 确定2017年4月C/2015 ER61的爆发是否由核碎片化引起。
• 估算新形成的伴核从主核分离的时间、速度和方向。
• 利用天体测量数据建模伴核的轨道运动，并通过非引力减速评估其物理特性。
• 研究碎屑抛射与渐进式碎片化的角色，以解释伴核在9周延迟后被探测到的原因。
• 将C/2015 ER61的爆发与碎片化行为与其他已知分裂彗星进行比较，以完善爆发与碎片耐受性模型。

提出的方法

• 利用五名日本观测者提供的CCD星等，构建了高时间密度的光 light curve，通过系统性光度校正确保数据一致性。
• 采用适用于分裂彗星的多参数模型（Sekanina 1978, 1982），拟合主核与伴核之间的42个天体测量偏移。
• 应用三参数碎片化模型，估算分离速度（0.9 m s⁻¹）与非引力减速（14.3 × 10⁻⁵ g☉）。
• 结合碎片耐受性与非引力减速之间的关系（Sekanina 1982），约束伴核的尺寸与寿命。
• 分析伴核在分钟至周时间尺度上的亮度变化，推断其可观测窗口与解体时间线。
• 将爆发开始时间（4月5.2 UT）与伴核分离时间（4月21日至5月13日）交叉比对，以检验因果关联。

实验结果

研究问题

• RQ1 2017年4月C/2015 ER61的爆发是否由核碎片化引起？
• RQ2 伴核从主核分离的速度与方向为何？
• RQ3 非引力力如何影响伴核的运动？这对其尺寸有何含义？
• RQ4 为何伴核在形成九周后才被探测到？
• RQ5 何种物理过程使伴核得以被探测，并导致其迅速解体？

主要发现

• C/2015 ER61的爆发始于4月5.2 UT，上升时间为2.6 ± 1天，与典型彗星爆发一致。
• 伴核以0.9 m s⁻¹的速度从主核分离，方向与轨道运动相反，且位于轨道平面以下。
• 非引力减速为14.3 × 10⁻⁵倍太阳引力加速度，表明伴核整体尺寸小于100米。
• 伴核直到6月11日才被探测到，即形成九周后，原因在于其极端的亮度变化与初始光度极低。
• 伴核的可探测性得益于碎屑抛射以及新暴露的挥发性表面活动增强，这些过程也导致其在6月下旬或7月上旬迅速解体。
• 伴核的运动与物理行为最合理的解释是渐进式碎片化，与爆发是核破裂的直接结果一致。