通向Z和型爆发的途径：V426射手座事件（HBHA 1704-05）
The path to Z And-type outbursts: The case of V426 Sagittae (HBHA 1704-05)
摘要：
恒星V426 Sge（HBHA~1704-05）最初被归类为发射线天体和半规则变星，在2018年8月初变亮，显示出共生恒星爆发的特征。我们的目标是确认V426 Sge作为经典共生星的性质，确定光极小的光度星历，并建议从1968年共生新星爆发到2018年Z和型爆发的路径。我们重建了大约1900年V426 Sge的历史光变曲线（LC），并使用原始的低分辨率和高分辨率光谱，辅以Swift-XRT和UVOT，光学UBVRcIc和近红外JHKL测光，在2018年爆发和随后的平静期间获得。历史LC显示从1900年到1967年没有共生样活动。1968年，V426 Sge经历了一次共生新星爆发，并在1990年左右停止。大约从1972年开始，LC中出现了周期为$493.4\pm 0.7$天的波状轨道相关变化。这被2018年8月初至2019年2月中旬的Z And型爆发所打断。在2018年爆发的最大值，燃烧的白矮星（WD）将其温度提高到$>2\times 10^5$ K，产生$\sim 7\times 10^{37}(d/3.3kpc)^2$ erg/s的光度，并以$\sim 3\times 10^{-6}$ M $_{\odot}$ /年的速度吹出风。供体是一颗正常的M4-5 III巨星，而吸积体是一颗低质量的$\sim$ 0.5 M $_{\odot}$ WD。在从共生新星爆发到静止相的过渡过程中，大多数共生新星的LC沿轨道出现明显的正弦变化。当WD的吸积暂时超过稳定燃烧的上限时，随后的最终爆发是Z和型的。在这一点上，系统成为一个经典的共生星。
英文摘要：
The star V426 Sge (HBHA~1704-05), originally classified as an emission-line object and a semi-regular variable, brightened at the beginning of August 2018, showing signatures of a symbiotic star outburst. We aim to confirm the nature of V426 Sge as a classical symbiotic star, determine the photometric ephemeris of the light minima, and suggest the path from its 1968 symbiotic nova outburst to the following 2018 Z And-type outburst. We re-constructed an historical light curve (LC) of V426 Sge from approximately the year 1900, and used original low- and high-resolution spectroscopy complemented with Swift-XRT and UVOT, optical UBVRcIc and near-infrared JHKL photometry obtained during the 2018 outburst and the following quiescence. The historical LC reveals no symbiotic-like activity from 1900 to 1967. In 1968, V426 Sge experienced a symbiotic nova outburst that ceased around 1990. From approximately 1972, a wave-like orbitally related variation with a period of $493.4\pm 0.7$ days developed in the LC. This was interrupted by a Z And-type outburst from the beginning of August 2018 to the middle of February 2019. At the maximum of the 2018 outburst, the burning white dwarf (WD) increased its temperature to $>2\times 10^5$ K, generated a luminosity of $\sim 7\times 10^{37}(d/3.3kpc)^2$ erg/s, and blew a wind at the rate of $\sim 3\times 10^{-6}$ M$_{\odot}$/yr. The donor is a normal M4-5 III giant and the accretor is a low-mass $\sim$0.5 M$_{\odot}$ WD. During the transition from the symbiotic nova outburst to the quiescent phase, a pronounced sinusoidal variation along the orbit develops in the LC of most symbiotic novae. The following eventual outburst is of Z And-type, when the accretion by the WD temporarily exceeds the upper limit of the stable burning. At this point the system becomes a classical symbiotic star.
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