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Radio emission from the massive stars in the galactic super star cluster Westerlund 1

机译：银河超级恒星团Westerlund 1中大质量恒星的无线电发射

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Aims. Current mass-loss rate estimates imply that mainsequence line-driven winds are not sufficient to strip away the H-richenvelope to yield Wolf-Rayet (WR) stars. The rich transitionalpopulation of the young massive cluster Westerlund1 (Wd1)provides an ideal laboratory to observe and constrain mass-lossprocesses throughout the transitional phase of stellar evolution. Methods. We present an analysis of deep radio continuumobservations of Wd1 obtained with the Australia Telescope CompactArray at four frequency bands that permit investigation of theintrinsic characteristics of the radio emission. Results. We detect 18 cluster members, a sample dominated by thecool hypergiants, with additional detections amongst the hotterOBsupergiants and WRstars. The radio properties of thesample are diverse, with thermal, non-thermal and compositethermalon-thermal sources present. Mass-loss rates determined forstars with partially optically thick stellar winds are 10-5yr-1across all spectral types, insufficient to enable the formation of WRsduring a massive star lifetime, and the stars must undergo a period ofgreatly enhanced mass loss. The sgB[e] starW9, the brightestradio source in Wd1, may provide an example, with a currentmass-loss rate an order of magnitude higher than the other clustermembers, and an extended nebula interpreted as a wind from an earlierepoch with a density the current wind. Such an envelope structure inW9 is reminiscentof luminous blue variables, and one that shows evidence of two eras ofhigh, possibly eruptive mass loss. Surprisingly, three of the OBsupergiants are detected, implying unusually dense winds, though theyare embedded in more extended emission regions that may influence thederived parameters. They also may have composite spectra, suggestingbinarity, which can lead to a higher flux than expected from a stellarwind. Spatially resolved nebulae are associated with three of the fourRSGs and three of the six YHGs in the cluster, which are due toquiescent mass loss rather than outbursts. The extended nebulae of W20and W26 have a cometary morphology, implying significant interactionwith either the intracluster medium or cluster wind. For some of thecool star winds, the ionizing source may be a companion star though thecluster radiation density is sufficiently high to provide the necessaryionizing radiation. Five WRstars are detected with compositespectra, interpreted as arising in colliding-wind binaries. Key words: stars: evolution - H II regions - open clusters and associations: individual: Westerlund 1
机译：目的当前的质量损失率估计表明，主序线驱动的风不足以剥离H富集层以产生Wolf-Rayet（WR）星。年轻的大规模星团Westerlund1（Wd1）的丰富的过渡种群为观察和限制整个恒星演化过渡阶段的质量损失过程提供了理想的实验室。方法。我们目前对澳大利亚望远镜CompactArray在四个频段上进行的Wd1的深层无线电连续观测进行了分析，从而可以研究无线电发射的本征特性。结果。我们检测到18个集群成员，这些样本由超酷的超巨人控制，另外还有更热的超巨星和WRstars之间的检测。样品的辐射特性是多种多样的，存在热，非热和复合热/非热源。在所有光谱类型中，具有部分光学上厚的恒星风的恒星的质量损失率在10-5yr-1之间，不足以在巨大的恒星寿命期间形成WR，并且恒星必须经历一段大大增强的质量损失时期。 sgB [e] starW9是Wd1中最亮的放射源，可以提供一个例子，其当前的质量损失率比其他星团成员高一个数量级，而扩展的星云则被解释为来自较早时期的风，其密度为电流风。 W9中的这种包络结构使人联想到发光的蓝色变量，并且它显示了两个时代，即可能发生喷发性高质量损失的证据。出乎意料的是，检测到三个超霸王巨星，这暗示着异常的密集风，尽管它们嵌入了可能影响派生参数的更扩展的发射区域。它们还可能具有复合光谱，表明存在二元性，这可能导致比星风预期的通量更高。空间分辨星云与星团中四个RSG和三个YHG中的三个相关，这是由于静态质量损失而不是爆发。 W20和W26的扩展星云具有彗星形态，这意味着与星团内部介质或星团风有明显的相互作用。对于某些凉爽的恒星风，电离源可能是伴星，尽管集群辐射密度足够高，可以提供必要的电离辐射。用复合光谱检测到五颗WRstar，解释为在碰撞风二进制中产生。关键词：恒星：演化-H II区-疏散星团和协会：个人：Westerlund 1

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