Title: Identification and characterization of nascent planetary nebulae with OH and H$_2$O masers Show Chinese title

Title: 具有OH和H$_2$O脉泽的新生行星状星云的识别与特征分析

Abstract: Stars like the Sun expel their outer layers and form planetary nebulae (PNe) as they evolve into white dwarfs. PNe exhibit diverse morphologies, the origins of which are not fully understood. PNe with OH (OHPNe) and H$_{2}$O (H$_{2}$OPNe) masers are thought to be nascent PNe. However, the number of known OHPNe and H$_{2}$OPNe remains small, and only in eight cases the position of the maser emission has been found to coincide with the PN, using the high astrometric accuracy of interferometric observations. In order to identify more OHPNe and H$_{2}$OPNe, we used public databases and our own ATCA/VLA observations to match the positions of OH and H$_{2}$O masers with known PNe and radio continuum emitters, considering radio continuum emission as a possible tracer of the photoionized gas that characterizes PNe. Here we report the confirmation of positional coincidence of maser emission with one more PN, and 12 PN candidates. Moreover, we have confirmed three evolved stars as `water fountains' (WFs) hosting H$_2$O masers. These WFs are associated with radio continuum emission, but their possible nature as PNe has not yet been confirmed. Although a final characterization of maser-emitting PNe as a group still requires confirmation of more objects, their distribution in the infrared color-color diagrams suggests that they are a heterogeneous group of PNe. In particular, the new OHPN IRAS 07027$-$7934 has been reported to contain a late [WC]-type central star, while the maser emission implies an O-rich envelope. This property is found in only one other known maser-emitting PN, although we found evidence that other confirmed and candidate OHPNe may also have mixed chemistry, since they show emission from polycyclic aromatic hydrocarbons. The new WF IRAS 18443$-$0231 shows radio continuum that is dominated by strong and variable non-thermal emission, as in magnetized outflows. Show Chinese abstract

Abstract: 像太阳这样的恒星在演化成白矮星的过程中会抛出外层，形成行星状星云（PNe）。 PNe表现出多样的形态，其起源尚未完全明了。 具有OH（OHPNe）和H$_{2}$O（H$_{2}$OPNe）脉泽的PNe被认为是年轻的PNe。 然而，已知的OHPNe和H$_{2}$OPNe数量仍然很少，只有在八个案例中，通过干涉测量观测的高天体测量精度，发现脉泽辐射的位置与PNe相吻合。 为了识别更多的OHPNe和H$_{2}$OPNe，我们使用了公共数据库和我们自己的ATCA/VLA观测数据，将OH和H$_{2}$O脉泽的位置与已知的PNe和射电连续谱发射体进行匹配，考虑射电连续谱发射作为表征PNe的光致电离气体的可能示踪物。 在此，我们报告了脉泽辐射与另一个PNe的位置吻合的确认，以及12个PNe候选体。 此外，我们已经确认了三颗演化的恒星作为“水喷泉”（WFs），它们拥有H$_2$O脉泽。 这些WFs与射电连续谱发射有关，但它们作为PNe的可能性尚未得到确认。 尽管作为一组的脉泽发射PNe的最终特征仍需要更多物体的确认，但它们在红外颜色-颜色图中的分布表明，它们是PNe的一个异质群体。 特别是，新发现的OHPN IRAS 07027$-$7934被报道包含一个晚期[WC]型中心星，而脉泽辐射暗示了一个富氧包层。 这种特性仅在另一个已知的脉泽发射PNe中发现，尽管我们发现证据表明其他已确认和候选的OHPNe也可能具有混合化学成分，因为它们显示出多环芳烃的发射。 新的 WF IRAS 18443$-$0231 显示出由强且变化的非热辐射主导的射电连续谱，如同磁化喷流一样。