We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. We combine these with prior studies to build a list of 525 known L, T, and Y dwarfs within 20 pc of the Sun, 38 of which are presented here for the first time. Using published photometry and spectroscopy as well as our own follow-up, we present an array of color–magnitude and color–color diagrams to further characterize census members, and we provide polynomial fits to the bulk trends. Using these characterizations, we assign each object a T _eff value and judge sample completeness over bins of T _eff and spectral type. Except for types ≥T8 and T _eff < 600 K, our census is statistically complete to the 20 pc limit. We compare our measured space densities to simulated density distributions and find that the best fit is a power law () with α = 0.6 0.1. We find that the evolutionary models of Saumon & Marley correctly predict the observed magnitude of the space density spike seen at 1200 K < T _eff < 1350 K, believed to be caused by an increase in the cooling timescale across the L/T transition. Defining the low-mass terminus using this sample requires a more statistically robust and complete sample of dwarfs ≥Y0.5 and with T _eff < 400 K. We conclude that such frigid objects must exist in substantial numbers, despite the fact that few have so far been identified, and we discuss possible reasons why they have largely eluded detection.

我们展示了 361 个 L、T 和 Y 矮人的最终斯皮策三角视差。我们将这些与之前的研究结合起来，建立了一个包含 525 个已知的 L、T 和 Y 矮星的列表，其中 20 颗太阳位于 20 pc 以内，其中 38 个是首次在此展示。使用已发表的光度测量和光谱以及我们自己的后续行动，我们展示了一系列颜色-幅度和颜色-颜色图，以进一步表征人口普查成员，并提供多项式拟合大宗趋势。使用这些特征，我们为每个对象分配一个T _eff值，并在T _eff和光谱类型的bin 上判断样本完整性。≥T8 和T _eff型除外< 600 K，我们的人口普查统计完成到 20 pc 的限制。我们将测量的空间密度与模拟的密度分布进行比较，发现最佳拟合是幂律 ( )，α = 0.6 0.1。我们发现 Saumon & Marley 的进化模型正确预测了在 1200 K < T _eff < 1350 K 时观察到的空间密度尖峰的幅度，据信这是由 L/T 过渡期间冷却时间尺度的增加引起的。使用这个样本定义低质量终点需要一个统计上更稳健和完整的矮星样本 ≥Y0.5 和T _eff < 400 K。我们得出结论，尽管迄今为止很少有被发现的事实，但这种寒冷的物体必须大量存在，并且我们讨论了它们在很大程度上躲避检测的可能原因。