论文标题
在球状群集47图卡纳的四个矮人Nova候选者的接近脉冲检测
Near-ultraviolet detections of four dwarf nova candidates in the globular cluster 47 Tucanae
论文作者
论文摘要
我们研究了银河球状簇（GC）47图卡纳（47 TUC）的近粉状物（NUV）变异性。这项工作是在瞬态紫外线对象项目的GC子项目中进行的，该程序旨在查找和研究瞬态和强烈可变的紫外线源。球状簇是瞬态搜索的理想目标，因为它们的恒星密度很高和可变系统的大量人群。使用所有使用UVM2滤波器在Neil Gehrels Swift天文台上使用UV/光学望远镜（UVOT）获得的47 TUC的档案观测值，我们使用使用差异图像分析的专业管道搜索了UV变异性。我们发现了四个明确的瞬态，以下是SW1-4，其位置与已知的灾难变量（CVS）或先前使用Hubble Space望远镜观测值确定的CV候选者相一致。所有四个来源均表现出重大爆发。基于推断的爆发特性和与已知CV的关联，我们暂定将UV瞬变识别为CV-WARF NOVAE（DNE）。以前在47 TUC：V2中观察到了两个DNE，该位置与SW4的位置一致。和Ako 9，在任何UVOT观察期间都没有爆发。因此，我们将已知的47 TUC中的DNE数量增加到5，并且在所有银河GC中的DNE总数合计从14增加到17。我们在GCS中明显稀缺的背景下讨论了我们的结果。我们建议可能的原因是观察性偏见，例如由于GC中未解决的恒星的高背景以及所使用的望远镜的角度分辨率有限，灵敏度有限。我们还检测到47 TUC中的一个强大可变源，可以将其确定为已知的RR Lyrae Star HV 810。我们发现其周期相对于从1988年获取的数据所测量的时期显着增加。
We investigate near-ultraviolet (NUV) variability in the Galactic globular cluster (GC) 47 Tucanae (47 Tuc). This work was undertaken within the GC sub-project of the Transient UV Objects project, a programme which aims to find and study transient and strongly variable UV sources. Globular clusters are ideal targets for transient searches because of their high stellar densities and large populations of variable systems. Using all archival observations of 47 Tuc obtained with the UV/optical telescope (UVOT) aboard the Neil Gehrels Swift observatory with the uvm2 filter, we searched for UV variability using a specialised pipeline which utilises difference image analysis. We found four clear transients, hereafter SW1-4, with positions consistent with those of known cataclysmic variables (CVs) or CV candidates identified previously using Hubble Space Telescope observations. All four sources exhibit significant outbursts. Based on the inferred outburst properties and the association with known CVs, we tentatively identify the UV transients as CV-dwarf novae (DNe). Two DNe have been previously observed in 47 Tuc: V2, which has a position consistent with that of SW4; and AKO 9, which was not in outburst during any of the UVOT observations. We thus increase the known number of DNe in 47 Tuc to 5 and the total number of detected DNe in all Galactic GCs combined from 14 to 17. We discuss our results in the context of the apparent scarcity of DNe in GCs. We suggest that the likely cause is observational biases, such as limited sensitivity due to the high background from unresolved stars in the GC and limited angular resolution of the telescopes used. We additionally detected one strongly variable source in 47 Tuc, which could be identified as the known RR Lyrae star HV 810. We found its period to have significantly increased with respect to that measured from data taken in 1988.
