WISE Y DWARFS AS PROBES OF THE BROWN DWARF–EXOPLANET CONNECTION
WISE Y DWARFS AS PROBES OF THE BROWN DWARF–EXOPLANET CONNECTION
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智慧矮星作为褐矮星与系外行星连接的探测器
DOI：
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发表时间：
2014
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通讯作者：
E. Wright
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文献类型：
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作者：
C. Beichman;C. Gelino;J. Kirkpatrick;M. Cushing;S. Dodson;M. Marley;C. Morley;E. Wright
我们已经确定了15个WISE发现的晚型棕矮星（6个T8-9和9个Y矮星）的天体测量位置，使用Spitzer-II望远镜，哈勃太空望远镜。结合8至20个历元的数据，我们得出这些物体的视差和自行，这使得大多数在15 pc内。对于年龄大于几个Gyr，建议从运动学的考虑，我们发现质量为10-30兆焦耳的基础上的标准模型的演变低质量的物体与一系列的质量估计个别对象，这取决于模型的问题。其中三个最冷的天体的有效温度为350 K，推断质量为10-15 MJup。我们的视差距离证实了早期的测光估计和直接测量，并表明质量低于15兆焦耳的天体数量相对于质量更高的天体来说必须是平坦的或下降的。最冷的Y矮星的质量可能与最近成像的附近年轻恒星的行星质量同伴的质量相似。在这个质量范围内的物体在星际和原行星环境中似乎都很少见，它们可能都是通过引力碎裂形成的--星际云中的褐矮星和原行星盘中的伴星。然而，在这两种情况下，这个质量范围内的物体相对较少，这一事实表明，这种机制在两种环境中都是无效的。
We have determined astrometric positions for 15 WISE-discovered late-type brown dwarfs (six T8-9 and nine Y dwarfs) using the Keck-II telescope, the Spitzer Space Telescope, and the Hubble Space Telescope. Combining data from 8 to 20 epochs we derive parallactic and proper motions for these objects, which puts the majority within 15 pc. For ages greater than a few Gyr, as suggested from kinematic considerations, we find masses of 10–30 MJup based on standard models for the evolution of low-mass objects with a range of mass estimates for individual objects, depending on the model in question. Three of the coolest objects have effective temperatures ∼350 K and inferred masses of 10–15 MJup. Our parallactic distances confirm earlier photometric estimates and direct measurements and suggest that the number of objects with masses below about 15 MJup must be flat or declining, relative to higher mass objects. The masses of the coldest Y dwarfs may be similar to those inferred for recently imaged planet-mass companions to nearby young stars. Objects in this mass range, which appear to be rare in both the interstellar and protoplanetary environments, may both have formed via gravitational fragmentation—the brown dwarfs in interstellar clouds and companion objects in a protoplanetary disk. In both cases, however, the fact that objects in this mass range are relatively infrequent suggests that this mechanism must be inefficient in both environments.