arXiv 2302.027232023-02-06astro-ph.SRastro-ph.GA

高质量年轻天体G24 .33 $+$ 0.14}中6.7~GHz脉泽耀斑期间脉泽谱线的多频VLBI观测

Multi-frequency VLBI observations of maser lines during the 6.7~GHz maser flare in the high-mass young stellar object G24.33$+$0.14}

A. Kobak, A. Bartkiewicz, M. Szymczak, M. Olech, M. Durjasz, P. Wolak, J. O. Chibueze, T. Hirota, J. Eislöffel, B. Stecklum, A. Sobolev, O. Bayandina, G. Orosz,… 展开作者

A. Kobak, A. Bartkiewicz, M. Szymczak, M. Olech, M. Durjasz, P. Wolak, J. O. Chibueze, T. Hirota, J. Eislöffel, B. Stecklum, A. Sobolev, O. Bayandina, G. Orosz, R. A. Burns, Kee-Tae Kim, S. P. van den Heever

备注：: Accepted by A\&A
发表信息：: A&A 671, A135 (2023)
DOI：: 10.1051/0004-6361/202244772

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摘要：

最近的研究表明，6.7千兆赫甲醇脉泽耀斑可以是一个强有力的工具，用于验证脉泽产生的机制，甚至在高质量恒星形成的早期阶段吸积率变化的具体签名。我们描述的空间结构和演变的甲醇和水脉泽在耀斑的甲醇脉泽发射在6.7 GHz的HMYSO G24.33 $+$ 0.14。利用VLBA对6.7和12.2GHz甲醇脉泽和22.2GHz水汽脉泽进行了三个历元的成像，并利用托伦32米望远镜对甲醇谱线进行了监测。利用EVN和LBA获得了耀斑期间的6.7GHz脉泽图。WISE数据被用来寻找6.7 GHz脉泽和IR通量之间的相关性。6.7 GHz甲醇脉泽云团分布在$\sim$ 3500 Au上，虽然在两个月的时间尺度上其亮度随总通量密度的变化而变化，但大多数云团的形态是稳定的。12.2 GHz的甲醇脉泽云覆盖面积的数量级小于6.7 GHz的发射，和两个过渡出现从相同的脉泽气体。22.2 GHz脉泽云团位于中心区域，在VLBI观测的两个月期间，显示出亮度的系统性增加和大小和方向的适度变化，以及最强云团的速度漂移。时间滞后估计意味着传播的物质条件的变化的区域与亚光速（$\sim$ 0.3 c）。发现IR（4.6 $μ$ m）和6.7 GHz通量密度的紧密相关性，支持辐射泵浦模型。与230 GHz的ALMA数据的比较表明，甲醇脉泽分布在旋转盘的内部，而22.2 GHz的发射痕迹的双极流出或喷流结构的紧凑的内部组件。

英文摘要：

Recent studies have shown that 6.7 GHz methanol maser flares can be a powerful tool for verifying the mechanisms of maser production and even the specific signatures of accretion rate changes in the early stages of high-mass star formation. We characterize the spatial structure and evolution of methanol and water masers during a flare of methanol maser emission at 6.7 GHz in the HMYSO G24.33$+$0.14. VLBA was used to image the 6.7 and 12.2 GHz methanol and 22.2 GHz water vapor masers at three epochs guided by monitoring the methanol line with the Torun 32m telescope. The 6.7 GHz maser maps were also obtained with the EVN and LBA during the flare. WISE data were used to find correlations between the 6.7 GHz maser and IR fluxes. The 6.7 GHz methanol maser cloudlets are distributed over $\sim$3500 au, and the morphology of most of them is stable although their brightness varies following the course of the total flux density on a timescale of two months. The 12.2 GHz methanol maser cloudlets cover an area an order of magnitude smaller than that of 6.7 GHz emission, and both transitions emerge from the same masing gas. The 22.2 GHz maser cloudlets lie in the central region and show a systematic increase in brightness and moderate changes in size and orientation, together with the velocity drift of the strongest cloudlet during two months of the VLBI observing period. Time lag estimates imply the propagation of changes in the physical conditions of the masing region with a subluminal speed ($\sim$0.3c). A tight correlation of IR (4.6$μ$m) and 6.7 GHz flux densities is found, supporting the radiative pumping model. Comparison with the 230 GHz ALMA data indicates that the methanol masers are distributed in the inner part of the rotating disk, whereas the 22.2 GHz emission traces the compact inner component of the bipolar outflow or a jet structure.

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