FU Orionis objects (FUors) are rapidly-accreting, pre-main sequence objects that are known to exhibit large outbursts at optical and near-infrared wavelengths, with post-eruption, small-scale photometric variability superimposed on longer-term trends. In contrast, little is known about the variability of FUors at longer wavelengths. To explore this further, we observed six FUor objects using the NOrthern Extended Millimeter Array (NOEMA) and for a subset of three objects we obtained coordinated observations with NOEMA and the Lowell Discovery Telescope (LDT). In combination with previously published NOEMA observations from 2014, our 2017 observations of V1735 Cyg provide the first detection of variability in an FUor object at 2.7 mm. In the absence of significant optical variability, we discount the possibility that the mm flux density changed as a result of irradiation from the central disk. In addition, a change in the dust mass due to infall is highly unlikely. A plausible explanation for the change in 2.7 mm flux density is variability in free-free emission due to changes in the object's jet/wind. Thus, it may be that free-free emission in some FUor objects is significant at $\sim$3 mm and must be considered when deriving disk masses in order to help constrain the mechanism responsible for triggering FUor outbursts.

中文翻译：

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对 FU 或物体的毫米变异性研究

猎户座 FU 天体 (FUors) 是快速吸积的主序前天体，已知它们在光学和近红外波长下表现出大爆发，喷发后的小尺度光度变化叠加在长期趋势上。相比之下，人们对较长波长下 FUors 的可变性知之甚少。为了进一步探索这一点，我们使用 NOrthern 扩展毫米阵列 (NOEMA) 观测了六个 FUor 天体，对于三个天体的子集，我们使用 NOEMA 和洛厄尔发现望远镜 (LDT) 进行了协调观测。结合之前发布的 2014 年 NOEMA 观测结果，我们 2017 年对 V1735 Cyg 的观测首次提供了对 2.7 毫米 FU 或物体变异性的检测。在没有显着的光学可变性的情况下，我们忽略了 mm 通量密度因中心圆盘的辐射而发生变化的可能性。此外，由于落入而引起的灰尘质量变化的可能性很小。对 2.7 mm 通量密度变化的合理解释是由于物体的喷射/风的变化而导致的自由发射的变化。因此，在一些 FUor 物体中的自由发射可能在 $\sim$3 mm 处很重要，并且在推导盘质量时必须考虑，以帮助约束触发 FUor 爆发的机制。