Water masers accompanying OH and methanol masers in star formation regions
Water masers accompanying OH and methanol masers in star formation regions
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DOI：
10.1111/j.1365-2966.2010.16791.x
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发表时间：
2010-04
影响因子：
4.8
通讯作者：
S. Breen;J. Caswell;S. Ellingsen;C. Phillips
中科院分区：
文献类型：
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作者：
S. Breen;J. Caswell;S. Ellingsen;C. Phillips
澳大利亚紧凑型望远镜阵列已用于在 22 GHz 水跃迁时以弧秒精度测量 379 个微波激射器的位置。主要观测目标是与南银河平面恒星形成区 (SFR) 相关的 202 个 OH 脉泽。在第二个时期，大多数目标再次被观测到，并添加了新的甲醇脉泽目标。这里报道的许多水脉泽都是新发现的，还有一些是多年前帕克斯望远镜单天线观测所报道的，其位置不确定性超过 10 角秒。微波激射器的变化往往很剧烈，很少有与二十年前发现的特征直接对应的特征。在我们目前的观测中，相隔不到一年，光谱通常是不同的，但即使在测量稍有不同的特征时，后期的位置也大多对应于先前测量的检测到的脉泽站点，在整个站点的典型范围内，几角秒。精确的水位置显示，大约 79%（202 个中的 160 个）OH 脉泽站点显示出一致的水脉泽发射，这是该统计数据迄今为止获得的最佳估计；然而，在许多情况下，存在额外的水位点偏离 OH 目标，因此只有不到一半的水脉泽与 1665 MHz 基态 OH 脉泽对应物重合。我们不太均匀的甲醇目标样本不适合对其与水脉泽的关联进行全面调查，但我们能够探索这三种物质的峰值发射速度之间的差异，并量化水脉泽峰值与系统速度之间通常较大的偏差。人们发现，由两个或三个不同但邻近的位点组成的簇是很常见的，每个位点都显示一个或几个主要的分子转变。我们还报告了在某些位点检测到的超紧凑 HII 区域。结合对来自斯皮策银河遗产红外中面巡天非凡（GLIMPSE）目录中的红外源的相关性的调查，这些比较研究使得利用脉塞特性将恒星形成的相对演化阶段分配给各个地点方面取得了进一步的进展。
The Australia Telescope Compact Array has been used to measure positions with arcsecond accuracy for 379 masers at the 22-GHz transition of water. The principal observation targets were 202 OH masers of the variety associated with star formation regions (SFRs) in the Southern Galactic plane. At a second epoch, most of these targets were observed again, and new targets of methanol masers were added. Many of the water masers reported here are new discoveries and others had been reported, with position uncertainties exceeding 10 arcsec, from Parkes telescope single-dish observations many years ago. Variability in the masers is often acute, with very few features directly corresponding to those discovered two decades ago. Within our current observations, less than a year apart, spectra are often dissimilar, but positions at the later epoch, even when measured for slightly different features, mostly correspond to the detected maser site measured earlier, to within the typical extent of the whole site, of a few arcseconds. The precise water positions show that approximately 79 per cent (160 of 202) of the OH maser sites show coincident water maser emission, the best estimate yet obtained for this statistic; however, there are many instances where additional water sites are present offset from the OH target, and consequently less than half of the water masers coincide with a 1665-MHz ground-state OH maser counterpart. Our less uniform sample of methanol targets is not suitable for a full investigation of their association with water masers, but we are able to explore differences between the velocities of peak emission from the three species and quantify the typically larger deviations shown by water maser peaks from systemic velocities. Clusters of two or three distinct but nearby sites, each showing one or several of the principal molecular masing transitions, are found to be common. We also report the detection of ultracompact HII regions towards some of the sites. In combination with an investigation of correlations with IR sources from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) catalogue, these comparative studies allow further progress in the use of the maser properties to assign relative evolutionary stages in star formation to individual sites.