arXiv 2001.117472020-01-31astro-ph.SR

模棱两可的瞬态ASASSN-17 hx。一个可能的新星冒充者

The ambiguous transient ASASSN-17hx. A possible nova-impostor

Elena Mason, Steven N. Shore, Paul Kuin, Terry Bohlsen

备注：: accepted for publication on A&A
发表信息：: A&A 635, A115 (2020)
DOI：: 10.1051/0004-6361/201937025

摘要：

一些瞬变，虽然根据其最大和早期下降光谱被归类为新星，但对其真实性质以及是否可能存在新星冒充者产生了怀疑。我们通过光谱学（3000-10000 μ m，500<R<100000），辅以Swift UV和AAVSO光度测定法，监测到一颗候选新星，它在最大值和早期衰减时显示出明显不寻常的光变曲线。我们使用的谱线系列来表征喷出物的动力学，结构和质量。我们发现，喷出物是在自由弹道膨胀和典型的经典新星的结构。然而，它们的导出质量至少比经典新星的典型喷出物质量大一个数量级。具体来说，我们发现M $_{ej}\simeq$ 9 $\times$ 10 $^{-3}$ M $_\odot$独立于填充因子$\varepsilon$ =1的距离。通过将距离限制在0.08-0.10的范围内，我们推导出$\varepsilon$，得到质量为7 $\times$ 10 $^{-4}\lesssim$ M $_{ej}\lesssim$ 9 $\times$ 10 $^{-4}$ M $_\odot$。星云光谱的特征是异常强的日冕发射线，将电离源能量限制在20-250 eV的范围内，可能在75-100或75-150 eV的范围内达到峰值。我们将这个来源与其他表现出类似行为的慢新星联系起来，并建议它们可能形成一个独特的物理子群。它们可能是发生在质量非常低的白矮星上的经典新星爆炸的结果，也可能是一种完全不同类型的瞬变的冒充者。

英文摘要：

Some transients, although classified as novae based on their maximum and early decline optical spectra, cast doubts on their true nature and whether nova impostors might exist. We monitored a candidate nova which displayed a distinctly unusual light curve at maximum and early decline through optical spectroscopy (3000-10000 Å, 500<R<100000) complemented with Swift UV and AAVSO optical photometry. We use the spectral line series to characterize the ejecta dynamics, structure, and mass. We found that the ejecta are in free ballistic expansion and structured as typical of classical novae. However, their derived mass is at least an order of magnitude larger than the typical ejecta masses obtained for classical novae. Specifically, we found M$_{ej}\simeq$9$\times$10$^{-3}$ M$_\odot$ independent of the distance for a filling factor $\varepsilon$=1. By constraining the distance we derived $\varepsilon$ in the range 0.08-0.10, giving a mass 7$\times$10$^{-4}\lesssim$ M$_{ej}\lesssim$9$\times$10$^{-4}$ M$_\odot$. The nebular spectrum, characterized by unusually strong coronal emission lines, confines the ionizing source energy to the range 20-250 eV, possibly peaking in the range 75-100 or 75-150 eV. We link this source to other slow novae which showed similar behavior and suggest that they might form a distinct physical sub-group. They may result from a classical nova explosion occurring on a very low mass white dwarf or be impostors for an entirely different type of transient.

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