We have performed a detailed spectral analysis of the helium-rich hot subdwarf EC 20187-4939 using data obtained in the SALT survey of helium-rich hot subdwarfs. We have measured its effective temperature, surface gravity and chemical abundances from the spectrum. Its radius has also been determined by fitting the spectral energy distribution using photometric data, from which a mass of 0.44 Msun has been inferred using the measurement of surface gravity. This star is particularly abundant in helium and nitrogen, whilst being both carbon and oxygen-weak. The surface abundances and mass have been found to be consistent with a helium white dwarf merger product. The abundance effects of alpha captures on nitrogen during the merger process and possible connections between EC 20187-4939 and other carbon-weak related objects are discussed.
The SALT survey of helium-rich hot subdwarfs: final sample and classification
Armagh Observatory and Planetarium（阿马赫天文台和天文馆）；Institut für Physik und Astronomie, Universität Potsdam（波茨坦大学物理与天文学研究所）；School of Mathematics and Physics, Queen’s University Belfast（贝尔法斯特女王大学数学与物理学院）；Astrophysics Research Cluster, School of Mathematical and Physical Sciences, University of Sheffield（谢菲尔德大学数理科学学院天体物理学研究集群）；Department of Astronomy, University of Cape Town（开普敦大学天文学系）；South African Astronomical Observatory（南非天文台）；Australian Astronomical Optics, Faculty of Science and Engineering, Macquarie University（麦考瑞大学科学与工程学部澳大利亚天文光学）
Ammonium salt formation and abundance in protoplanetary disks
Université Bordeaux, CNRS, Bordeaux INP, ISM, UMR 5255（波尔多大学）；Carl Sagan Center, SETI Institute（卡尔·萨根中心，SETI研究所）；NASA Ames Research Center（NASA艾姆斯研究中心）
