DODO巡天II：双子座直接成像搜索赤道附近和北半球白矮星周围的亚恒星和行星质量伴星
The DODO Survey II: A Gemini Direct Imaging Search for Substellar and Planetary Mass Companions around Nearby Equatorial and Northern Hemisphere White Dwarfs
摘要：
简并天体周围的简并天体巡天（DODO）的目的是通过直接成像在白矮星周围的宽轨道上寻找质量很低的棕矮星和太阳系外行星。直接探测到这样的伴星将允许光谱研究温度比目前观测到的最冷的褐矮星低得多（< 500 K）的物体。这些超低质量的亚恒星天体的光谱型可能大于T8.5，因此可能属于Y矮星光谱序列。探测到白矮星周围的行星将证明这种物体可以在恒星演化的最后阶段幸存下来，并限制其祖先周围的行星系的频率（质量在1.5 - 8个太阳质量之间，即，早B到中F）。本文介绍了对23颗赤道附近和北半球白矮星进行的多历元J波段共同自行巡天观测结果。我们排除了任何常见的自行同伴的存在，从每次观察的完整性极限确定的限制质量，18个白矮星。对于剩下的五个目标，白矮星的运动与每个视场中不运动的背景物体没有充分分离。这些目标需要额外的观测，以最终排除任何共同的自行同伴的存在。从我们的完整性限制，我们初步建议，< 5% of white dwarfs have substellar companions with effective temperatures >500 K之间的预计物理分离60 - 200 AU。
英文摘要：
The aim of the Degenerate Objects around Degenerate Objects (DODO) survey is to search for very low mass brown dwarfs and extrasolar planets in wide orbits around white dwarfs via direct imaging. The direct detection of such companions would allow the spectroscopic investigation of objects with temperatures much lower (< 500 K) than the coolest brown dwarfs currently observed. These ultra-low mass substellar objects would have spectral types > T8.5 and so could belong to the proposed Y dwarf spectral sequence. The detection of a planet around a white dwarf would prove that such objects can survive the final stages of stellar evolution and place constraints on the frequency of planetary systems around their progenitors (with masses between 1.5 - 8 solar masses, i.e., early B to mid F). This paper presents the results of a multi-epoch J band common proper motion survey of 23 nearby equatorial and northern hemisphere white dwarfs. We rule out the presence of any common proper motion companions, with limiting masses determined from the completeness limit of each observation, to 18 white dwarfs. For the remaining five targets, the motion of the white dwarf is not sufficiently separated from the non-moving background objects in each field. These targets require additional observations to conclusively rule out the presence of any common proper motion companions. From our completeness limits, we tentatively suggest that < 5% of white dwarfs have substellar companions with effective temperatures > 500 K between projected physical separations of 60 - 200 AU.
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