过渡能隙瞬态AT 2018 hso：对发光红新星现象的新见解
The transitional gap transient AT 2018hso: new insights on the luminous red nova phenomenon
摘要：
目的：AT 2018 hso是一个新的瞬变，表现出LRNe和类似SN 2008 S的中等亮度红色瞬变（ILRT）之间的过渡性质。通过对观测参数的详细分析，我们的研究支持它实际上属于LRN类，并且很可能是由两颗大质量恒星合并产生的。研究方法：我们获得了10个月的光学和近红外光度监测，和11个时代的低分辨率光谱的AT~ 2018 hso。我们比较了它的观察到的性质与其他ILRT和LRNe。我们还检查了大约15年前获得的哈勃太空望远镜（HST）档案图像，以限制祖星的属性。结果如下：AT 2018 hso的光变曲线显示出第一个尖锐的峰（Mr = -13.93 mag），随后是更宽和更浅的第二个峰，类似于光学带中的平台。光谱随时间发生显著变化。早期的时间谱显示出突出的巴耳末发射线和弱的Ca II]双峰，这通常在ILRT中观察到。然而，在连续温度的主要下降，窄金属吸收线的外观，在H $α$强度和配置文件的主要变化，和分子带的出现支持LRN分类。在HST存档图像中，在AT 2018 hso位置可能检测到I ~ -8等源，这与合并前大质量双星的预期一致，类似于M101中2015 LRN的前身。结论：我们为AT~ 2018 hso的LRN分类提供了合理的论据。这项研究揭示了LRNe的可观测性比过去认为的越来越多的异质性，使得LRNe和ILRT之间的区分有时很棘手。这表明需要监测间隙瞬变的整个演变，以避免错误分类。
英文摘要：
Aims: AT 2018hso is a new transient showing transitional properties between those of LRNe and the class of intermediate luminosity red transients (ILRTs) similar to SN 2008S. Through the detailed analysis of the observed parameters, our study support that it actually belongs to the LRN class, and was likely produced by the coalescence of two massive stars. Methods: We obtained ten months of optical and near-infrared photometric monitoring, and eleven epochs of low-resolution optical spectroscopy of AT~2018hso. We compared its observed properties with those of other ILRTs and LRNe. We also inspected the archival Hubble Space Telescope (HST) images obtained about 15 years ago to constrain the progenitor's properties. Results: The light curves of AT 2018hso show a first sharp peak (Mr = -13.93 mag), followed by a broader and shallower second peak, that resembles a plateau in the optical bands. The spectra dramatically change with time. Early time spectra show prominent Balmer emission lines and a weak Ca II] doublet, which is usually observed in ILRTs. However, the major decrease in the continuum temperature, the appearance of narrow metal absorption lines, the major change in the H$α$ strength and profile, and the emergence of molecular bands support a LRN classification. The possible detection of an I ~ -8 mag source at the position of AT 2018hso in HST archive images is consistent with expectations for a pre-merger massive binary, similar to the precursor of the 2015 LRN in M101. Conclusions: We provide reasonable arguments to support a LRN classification for AT~2018hso. This study reveals growing heterogeneity in the observables of LRNe than thought in the past, making sometimes tricky the discrimination between LRNe and ILRTs. This suggests the need of monitoring the entire evolution of gap transients to avoid misclassifications.
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