THIRD-EPOCH MAGELLANIC CLOUD PROPER MOTIONS. I. HUBBLE SPACE TELESCOPE/WFC3 DATA AND ORBIT IMPLICATIONS
THIRD-EPOCH MAGELLANIC CLOUD PROPER MOTIONS. I. HUBBLE SPACE TELESCOPE/WFC3 DATA AND ORBIT IMPLICATIONS
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DOI：
10.1088/0004-637x/764/2/161
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发表时间：
2013-01
期刊：
影响因子：
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通讯作者：
N. Kallivayalil;R. P. van der Marel;G. Besla;Jay Anderson;C. Alcock
中科院分区：
文献类型：
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作者：
N. Kallivayalil;R. P. van der Marel;G. Besla;Jay Anderson;C. Alcock
我们提出了自行的大，小麦哲伦云（LMC和SMC）的基础上的三个时代的哈勃太空望远镜的数据，跨越107年的基线，并集中在领域与背景类星体。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。三历元数据产生的自行随机误差只有1%-2%的每场。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。这里我们集中讨论隐含的质心自行：μW，LMC = −1.910 ± 0.020 mas yr−1，μN，LMC = 0.229 ± 0.047 mas yr−1，和μW，SMC = −0.772 ± 0.063 mas yr−1，μN，SMC = −1.117 ± 0.061 mas yr−1。我们将结果与对银河系中太阳运动的修正理解相结合，得出银河系的银心速度：vtot，LMC = 321 ± 24 km s−1和vtot，SMC = 217 ± 26 km s−1。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，而我们的速度不确定性则主要是由于距离误差。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104 Gyr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）。
We present proper motions for the Large and Small Magellanic Clouds (LMC and SMC) based on three epochs of Hubble Space Telescope data, spanning a ∼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: μW, LMC = −1.910 ± 0.020 mas yr−1, μN, LMC = 0.229 ± 0.047 mas yr−1, and μW, SMC = −0.772 ± 0.063 mas yr−1, μN, SMC = −1.117 ± 0.061 mas yr−1. We combine the results with a revised understanding of the solar motion in the Milky Way to derive Galactocentric velocities: vtot, LMC = 321 ± 24 km s−1 and vtot, SMC = 217 ± 26 km s−1. 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 ≲ 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.