$Gaia$ white dwarfs within 40 pc II: the volume-limited northern hemisphere sample
Jack McCleery, Pier-Emmanuel Tremblay, Nicola Pietro Gentile Fusillo, Mark A. Hollands, Boris T. Gänsicke, Paula Izquierdo, Silvia Toonen, Tim Cunningham, Alberto Rebassa-Mansergas
本文概述了从$Gaia$数据发布2（DR 2）中探测到的距太阳40 pc以内的北半球白矮星样本。我们发现521个来源是光谱证实的简并恒星，其中111个首先被确定为白矮星候选人从$Gaia$ DR 2和后续最近与威廉赫歇尔望远镜和加那利大望远镜。另外三个白矮星候选者仍然没有被光谱观测到，六个尚未解决的双星已知包括一个白矮星，但不是我们最初在$Gaia$ DR 2赫兹斯普朗-罗素图（HRD）中选择的白矮星。大气参数计算从$Gaia$和泛星测光的样本中的所有对象，确认大多数的趋势，以前观察到的小得多的20 pc样本。本地的白矮星与银河系盘运动学非常一致，只有四个晕候选者。我们发现DAZ白矮星的质量明显小于整个DA种群（$\overline{M}_\mathrm{DAZ} = 0.59\,\mathrm{M}_\odot$，$\overline{M}_\mathrm{DA} = 0.66\,\mathrm{M}_\odot$）。这可能表明，行星形成的效率较低，在更高质量的恒星，产生更多的大质量白矮星。我们检测到一个序列的结晶白矮星的质量范围从$0.6\ \lesssim M/\mathrm{M}_\odot \lesssim\ 1.0\,$，并发现，绝大多数的对象的序列具有标准的运动学特性，对应于平均的样品，这表明它们的性质可以单独的结晶解释。我们还探测到56颗宽双星，包括一颗白矮星和26颗双简并双星。
英文摘要：
We present an overview of the sample of northern hemisphere white dwarfs within 40 pc of the Sun detected from $Gaia$ Data Release 2 (DR2). We find that 521 sources are spectroscopically confirmed degenerate stars, 111 of which were first identified as white dwarf candidates from $Gaia$ DR2 and followed-up recently with the William Herschel Telescope and Gran Telescopio Canarias. Three additional white dwarf candidates remain spectroscopically unobserved and six unresolved binaries are known to include a white dwarf but were not in our initial selection of white dwarfs in the $Gaia$ DR2 Hertzsprung-Russell diagram (HRD). Atmospheric parameters are calculated from $Gaia$ and Pan-STARRS photometry for all objects in the sample, confirming most of the trends previously observed in the much smaller 20 pc sample. Local white dwarfs are overwhelmingly consistent with Galactic disc kinematics, with only four halo candidates. We find that DAZ white dwarfs are significantly less massive than the overall DA population ($\overline{M}_\mathrm{DAZ} = 0.59\,\mathrm{M}_\odot$, $\overline{M}_\mathrm{DA} = 0.66\,\mathrm{M}_\odot$). It may suggest that planet formation is less efficient at higher mass stars, producing more massive white dwarfs. We detect a sequence of crystallised white dwarfs in the mass range from $0.6\ \lesssim M/\mathrm{M}_\odot \lesssim\ 1.0\,$ and find that the vast majority of objects on the sequence have standard kinematic properties that correspond to the average of the sample, suggesting that their nature can be explained by crystallisation alone. We also detect 56 wide binaries including a white dwarf and 26 double degenerates.
Solar meridional circulation from twenty-one years of SOHO/MDI and SDO/HMI observations: Helioseismic travel times and forward modeling in the ray approximation
The DODO Survey II: A Gemini Direct Imaging Search for Substellar and Planetary Mass Companions around Nearby Equatorial and Northern Hemisphere White Dwarfs
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。
Science Enabled by a 30-Meter-Class Telescope in the Northern Hemisphere: Massive Stars at Low Metallicity
Centro de Astrobiología, CSIC-INTA（天体生物学中心，西班牙高等科学研究委员会-国家航空航天技术研究所）；Departamento de Astrofísica, Universidad de La Laguna（拉古纳大学天体物理学系）；Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Departamento de Física, Universidad de Alicante（阿利坎特大学物理系）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所）；Instituto de Astrofísica de Andalucía, CSIC（安达卢西亚天体物理研究所，西班牙高等科学研究委员会）
Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake. How do Planetary Systems Form?
Centro de Astrobiología (CAB), CSIC-INTA（天文生物学中心）；Instituto de Astrofísica de Canarias（加那利天体物理学研究所）；Universidad de La Laguna（拉古纳大学）；Max-Planck Institute for Astronomy (MPIA)（马克斯·普朗克天文学研究所）；LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎天文台LESIA实验室）；Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多大学天体物理学实验室）；Institut universitaire de France (IUF)（法国高等研究院）
Apache Point Observatory follow-up of ACcelerating Candidate ExopLanet host Stars (APO ACCELS): Ages for 166 Accelerating Stars in the Northern Hemisphere
