第三纪麦哲伦云的自行I：HST/WFC3数据和轨道意义
Third-Epoch Magellanic Cloud Proper Motions I: HST/WFC3 data and Orbit Implications
摘要：
本文利用三个时期的\textit{Hubble Space Telescope}观测资料，以具有背景类星体的场为中心，以$\sim 7$年为基线，给出了大、小麦哲伦云（LMC & SMC）的自行。前两个时期，过去分析的主题，获得了ACS/HRC，并已重新分析这里。WFC 3/UVIS新的第三个时期增加了时间基线，并提供了更好的系统控制。三个历元的数据产生的自行随机误差只有1-2%，每个字段。对于LMC，这足以约束内部自行动力学，这将在另一篇论文中讨论。本文着重讨论了质心自行的隐含值：mu_W（LMC）= -1.910 +/- 0.020 mas/yr，mu_N（LMC）= 0.229 +/- 0.047 mas/yr，mu_W（SMC）= -0.772 +/- 0.063 mas/yr，mu_N（SMC）= -1.117 +/- 0.061 mas/yr。我们结合对银河系中太阳运动的修正理解得出银心速度：v_{tot,LMC} = 321 +/- 24 km/s和v_{tot,SMC} = 217 +/- 26 km/s。我们的自行不确定性现在主要是由于我们对云的内部运动学和几何学的理解有限，我们的速度不确定性主要是由距离误差决定的。对银河系周围的云的轨道计算允许一系列的轨道周期，这取决于银河系和LMC的不确定质量。周期$\lesssim 4$陀螺被排除，这对传统的麦哲伦流模型提出了挑战。如果要求LMC和SMC必须是至少几个Gyr的束缚对，则首选第一次坠落轨道（其他论点也支持这一点）。
英文摘要：
We present proper motions for the Large & Small Magellanic Clouds (LMC & SMC) based on three epochs of \textit{Hubble Space Telescope} data, spanning a $\sim 7$ yr baseline, and centered on fields with background QSOs. The first two epochs, the subject of past analyses, were obtained with ACS/HRC, and have been reanalyzed here. The new third epoch with WFC3/UVIS increases the time baseline and provides better control of systematics. The three-epoch data yield proper motion random errors of only 1-2% per field. For the LMC this is sufficient to constrain the internal proper motion dynamics, as will be discussed in a separate paper. Here we focus on the implied center-of-mass proper motions: mu_W(LMC) = -1.910 +/- 0.020 mas/yr, mu_N(LMC) = 0.229 +/- 0.047 mas/yr, and mu_W(SMC) = -0.772 +/- 0.063 mas/yr, mu_N(SMC) = -1.117 +/- 0.061 mas/yr. We combine the results with a revised understanding of the solar motion in the Milky Way to derive Galactocentric velocities: v_{tot,LMC} = 321 +/- 24 km/s and v_{tot,SMC} = 217 +/- 26 km/s. Our proper motion uncertainties are now dominated by limitations in our understanding of the internal kinematics and geometry of the Clouds, and our velocity uncertainties are dominated by distance errors. Orbit calculations for the Clouds around the Milky Way allow a range of orbital periods, depending on the uncertain masses of the Milky Way and LMC. Periods $\lesssim 4$ Gyr are ruled out, which poses a challenge for traditional Magellanic Stream models. First-infall orbits are preferred (as supported by other arguments as well) if one imposes the requirement that the LMC and SMC must have been a bound pair for at least several Gyr.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
