White dwarfs with emission lines from gaseous debris discs are among the rarest examples of planetary remnant hosts, but at the same time they are key objects for studying the final evolutionary stage of planetary systems. Making use of the large number of white dwarfs identified in Gaia Data Release 2 (DR2), we are conducting a survey of planetary remnants and here we present the first results of our search: six white dwarfs with gaseous debris discs. This first publication focuses on the main observational properties of these objects and highlights their most unique features. Three systems in particular stand out: WD J084602.47+570328.64 displays an exceptionally strong infrared excess that defies the standard model of a geometrically thin, optically thick dusty debris disc; WD J213350.72+242805.93 is the hottest gaseous debris disc host known with $\mbox{$T_{\mathrm{eff}}$}=29\,282$ K; and WD J052914.32–340108.11 in which we identify a record number of 51 emission lines from five elements. These discoveries shed light on the underlying diversity in gaseous debris disc systems and bring the total number of these objects to 21. With these numbers we can now start looking at the properties of these systems as a class of objects rather than on a case-by-case basis.

中文翻译：

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盖亚时代带有行星残骸的白矮星——一、六种发射线系统

带有气体碎片盘发射线的白矮星是行星残骸宿主中最罕见的例子，但同时它们也是研究行星系统最终演化阶段的关键对象。利用 Gaia Data Release 2 (DR2) 中确定的大量白矮星，我们正在对行星残骸进行调查，在这里我们展示了我们搜索的第一个结果：六颗带有气态碎片盘的白矮星。第一份出版物重点介绍了这些天体的主要观测特性，并强调了它们最独特的特征。三个系统特别突出： WD J084602.47+570328.64 显示出异常强烈的红外过量，这与几何上薄、光学厚的尘埃碎片盘的标准模型相悖；西部数据 J213350.72+242805。93 是已知的最热气态碎片盘宿主，$\mbox{$T_{\mathrm{eff}}$}=29\,282$ K；和 WD J052914.32–340108.11，其中我们从五个元素中确定了创纪录的 51 条发射线。这些发现揭示了气体碎片盘系统的潜在多样性，并使这些天体的总数达到 21 个。有了这些数字，我们现在可以开始将这些系统的属性视为一类天体，而不是个案- 案例基础。