We re-examine the well-known discrepancy between ionic abundances determined via the analysis of recombination lines (RLs) and collisionally excited lines (CELs). We show that abundance variations can be mimicked in a {\it chemically homogeneous} medium by the presence of dense X-ray irradiated regions which present different ionisation and temperature structures from those of the more diffuse medium they are embedded in, which is predominantly ionised by extreme-ultraviolet radiation. The presence of X-ray ionised dense clumps or filaments also naturally explains the lower temperatures often measured from O {\sc ii} recombination lines and from the Balmer jump when compared to temperatures determined by CELs. We discuss the implications for abundances determined via the analysis of CELs and RLs and provide a simple analytical procedure to obtain upwards corrections for CEL-determined abundance. While we show that the abundance discrepancy factor (ADF) and the Balmer Jump temperature determined from observations of the Orion Nebula can simultaneously be reproduced by this model (implying upward corrections for CELs by a factor of 1.15), we find that the required X-ray fluxes exceed the known Orion's stellar and diffuse X-ray budget, if we assume that the clumps are located at the edge of the blister. We propose, however, that spatially resolved observations may be used to empirically test the model, and we outline how the framework developed in this letter may be applied in the future to objects with better constrained geometries (e.g. planetary nebulae).
Close binary central stars and the abundance discrepancy - new extreme objects
最近的工作（Corradi et al. 2015，Jones et al. 2016）表明，极端丰度差异的现象，即复合线丰度超过碰撞激发线丰度的10倍或更多，似乎与具有近距离双星的行星状星云密切相关。为了进一步研究，我们已经获得了一个样本的星云与已知的近距离双星的光谱，使用FORS 2的VLT，我们已经发现了几个新的极端丰度差异对象。我们没有发现任何非极端的差异，这表明很大一部分星云的近距离双星中心恒星也有一个极端的丰度差异。
Current Unsolved Problems in Planetary Nebulae Research
University of British Columbia（不列颠哥伦比亚大学）；Laboratory for Space Research, University of Hong Kong（香港大学太空研究所）；University of Washington（华盛顿大学）；National Sun Yat Sen University（国立中山大学）；Valpariso University（瓦尔帕莱索大学）；Instituto de Astronomía, Universidad Nacional Autónoma de México（墨西哥国立自治大学天文学研究所）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Jodrell Bank Centre for Astrophysics, Department of Physics & Astronomy, University of Manchester（曼彻斯特大学物理与天文学院乔德雷尔银行天体物理学中心）
Extragalactic Planetary Nebulae (xPNe). Determining Distances out to 100 Mpc and the Renaissance of the PN Luminosity Function Method
ESO（欧洲南方天文台）；MPE（马克斯·普朗克地外物理研究所）；AIP（阿基米德研究所）；CAR, Univ. Hertfordshire（赫特福德大学计算与应用研究中心）；FINCA（图尔库天体物理学中心）；LMU（慕尼黑大学）；NSFʼs NOIRLab（美国国家科学基金会NOIR天文实验室）；Department of Astronomy & Astrophysics, The Pennsylvania State University（宾夕法尼亚州立大学天文与天体物理系）
The Kinematics of the Permitted C II $λ$ 6578 Line in a Large Sample of Planetary Nebulae
本文介绍了76个行星状星云中83条视线的C II $λ$ 6578允许谱线的高光谱分辨率光谱观测结果，其中大部分是用位于Sierra San Pedro Mártir的国家天文台的2.1m望远镜上的Manchester Echelle摄谱仪获得的。我们研究了C Ⅱ $λ$ 6578允许谱线相对于其它允许谱线和碰撞激发谱线的运动学。统计上，我们发现，运动学的C II $λ$ 6578线是不是那些预期的，如果这条线产生的重组的C $^{2+}$离子或荧光的C $^+$离子在电离平衡中的化学均匀的星云等离子体，但相反，它的运动学是那些适合的体积比预期的更内部。这个样本中的行星状星云具有明确的形态，并且与银河系凸起中的对应物相比，H $α$线宽限制在有限的范围内（没有大的值），这两者都可以解释为年轻星云壳的结果，星云模型也支持这一推论。关于长期存在的化学丰度之间的差异推断允许和碰撞激发的发射线在光电离星云，我们的研究结果意味着，多个等离子体成分通常发生在行星状星云。
SDSS-V LVM: A spatially resolved study of the physical conditions and the chemical abundance discrepancy in the Lagoon Nebula (M 8)
Universidad de Chile（智利大学）；Carnegie Institution for Science（卡内基科学研究所）；Space Telescope Science Institute（太空望远镜科学研究所）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；European Southern Observatory（欧洲南方天文台）；Universität Heidelberg（海德堡大学）
Investigating the electron temperature of [Ar IV] in planetary nebulae using the DESIRED database
Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉帕尔马大学）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）；Instituto de Astronomía, Universidad Nacional Autónoma de México（墨西哥国立自治大学天文研究所）；Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理科学研究所）；Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE SECIHTI)（国家天体物理学、光学和电子学研究所）
DREAMS. JWST Spectroscopy of a $z=8.3$ Galaxy with an ALMA Dust Continuum Detection: Early Dust, Very High $T_{\rm dust}$, and a Multi-wavelength [OIII] Ratio Discrepancy
Institute for Cosmic Ray Research, The University of Tokyo（宇宙射线研究所，东京大学）；Department of Physics, Graduate School of Science, The University of Tokyo（理学研究科物理学系，东京大学）；National Astronomical Observatory of Japan（日本国立天文台）；Astronomical Science Program, Graduate Institute for Advanced Studies, SOKENDAI（综合研究大学院大学天文学研究科，SOKENDAI）；Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), The University of Tokyo（宇宙线起源研究宇宙前沿中心（Kavli IPMU），东京大学）；Institute of Liberal Arts and Science, Kanazawa University（金泽大学教养部）
Kinematics and physical structure of Ou 5: A bipolar planetary nebula with extreme abundance discrepancy and an eclipsing binary core
Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México（墨西哥国立自治大学射电天文学与天体物理研究所）；Instituto de Astronomía, Universidad Nacional Autónoma de México, Sede Ensenada（墨西哥国立自治大学天文研究所恩塞纳达校区）；Constructor University（建筑大学）；Heidelberg Institute for Theoretical Studies（海德堡理论研究所）
A Morpho-kinematic Study of Galactic High-ADF PNe Based on the VLT/UVES Deep Spectroscopy
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Science（中国科学院大学）；Xinjiang Astronomical Observatory, Chinese Academy of Sciences（中国科学院新疆天文台）；The University of Hong Kong（香港大学）；Beijing Normal University（北京师范大学）；New Cornerstone Science Laboratory, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台新Cornerstone科学实验室）；Yunnan University（云南大学）
Intermediate- and high-resolution optical spectroscopy on the nascent planetary nebula Vy 2-2: Evidence of binary-star evolution
Instituto de Astrofísica de Andalucía (IAA), CSIC（安达卢西亚天体物理研究所 (IAA)，西班牙高等科学研究委员会）；Departamento de Astronomía, Universidad de Guanajuato（瓜纳华托大学天文学系）；ISDEFE
