Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the “Planetary” Mass Regime
Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the “Planetary” Mass Regime
复制标题
DOI：
10.3847/1538-4365/aaf6af
复制
发表时间：
2018-12
期刊：
影响因子：
--
通讯作者：
J. Kirkpatrick;E. Martin;R. Smart;Alfred J. Cayago;C. Beichman;F. Marocco;C. Gelino;J. Faherty-
中科院分区：
文献类型：
--
作者：
J. Kirkpatrick;E. Martin;R. Smart;Alfred J. Cayago;C. Beichman;F. Marocco;C. Gelino;J. Faherty-
我们利用斯皮策望远镜（143）、美国海军天文台（18）、新技术望远镜（14）和英国红外望远镜（9）的观测结果，对184颗晚T型和Y型矮星进行了初步的三角测量。为了完成对≥T6矮星的20 pc普查，我们联合收割机将这些测量与先前公布的另外44个天体的三角测量和另外7个天体的分光光度距离估计相结合。对于这235个对象，我们估计温度，筛选到五个150 K宽Teff箱覆盖范围300-1050 K，确定每个的完整性限制，并计算空间密度。为了锚定褐矮星质谱的高质量端，我们编制了一份20秒差距内的早期至中期L矮星列表。我们运行模拟使用各种功能形式的质量函数通过两套不同的进化代码来计算Teff的预测分布。这些预测与我们的L、T和Y观测结果的最佳拟合是一个简单的幂律模型，α = 0.6（其中），这意味着场亚恒星质量函数的斜率与附近恒星形成区和年轻星团中的褐矮星的斜率大致一致。此外，我们发现，已发表的对数正态形式的版本并不能预测空间密度从1050到350 K的稳定上升。我们还发现，如果存在的话，低质量的形成截止值低于1005 MJup，这证实了附近年轻移动群体的发现，并意味着极低质量的物体在银河系的一生中一直在形成。
We present preliminary trigonometric parallaxes of 184 late-T and Y dwarfs using observations from Spitzer (143), the U.S. Naval Observatory (18), the New Technology Telescope (14), and the United Kingdom Infrared Telescope (9). To complete the 20 pc census of ≥T6 dwarfs, we combine these measurements with previously published trigonometric parallaxes for an additional 44 objects and spectrophotometric distance estimates for another 7. For these 235 objects, we estimate temperatures, sift into five 150 K wide Teff bins covering the range 300–1050 K, determine the completeness limit for each, and compute space densities. To anchor the high-mass end of the brown dwarf mass spectrum, we compile a list of early- to mid-L dwarfs within 20 pc. We run simulations using various functional forms of the mass function passed through two different sets of evolutionary code to compute predicted distributions in Teff. The best fit of these predictions to our L, T, and Y observations is a simple power-law model with α ≈ 0.6 (where ), meaning that the slope of the field substellar mass function is in rough agreement with that found for brown dwarfs in nearby star-forming regions and young clusters. Furthermore, we find that published versions of the log-normal form do not predict the steady rise seen in the space densities from 1050 to 350 K. We also find that the low-mass cutoff to formation, if one exists, is lower than ∼5 MJup, which corroborates findings in young, nearby moving groups and implies that extremely low-mass objects have been forming over the lifetime of the Milky Way.