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标题：CS Cha B: A disc-obscured M-type star mimicking a polarised planetary companion ⋆
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作者：S. Y. Haffert ; R. G. van Holstein ; C. Ginski 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2020
卷号：640
页码：1-8
DOI：10.1051/0004-6361/202038706
语种：English
出版社：EDP Sciences
摘要：Context.Direct imaging provides a steady flow of newly discovered giant planets and brown dwarf companions. These multi-object systems can provide information about the formation of low-mass companions in wide orbits and/or help us to speculate about possible migration scenarios. Accurate classification of companions is crucial for testing formation pathways.Aims.In this work we further characterise the recently discovered candidate for a planetary-mass companion CS Cha b and determine if it is still accreting.Methods.MUSE is a four-laser-adaptive-optics-assisted medium-resolution integral-field spectrograph in the optical part of the spectrum. We observed the CS Cha system to obtain the first spectrum of CS Cha b. The companion is characterised by modelling both the spectrum from 6300 Å to 9300 Å and the photometry using archival data from the visible to the near-infrared (NIR).Results.We find evidence of accretion and outflow signatures in Hαand OI emission. The atmospheric models with the highest likelihood indicate an effective temperature of 3450 ± 50 K with a loggof 3.6 ± 0.5 dex. Based on evolutionary models, we find that the majority of the object is obscured. We determine the mass of the faint companion with several methods to be between 0.07M⊙and 0.71M⊙with an accretion rate ofṀ= 4 × 10−11±0.4M⊙yr−1.Conclusions.Our results show that CS Cha B is most likely a mid-M-type star that is obscured by a highly inclined disc, which has led to its previous classification using broadband NIR photometry as a planetary-mass companion. This shows that it is important and necessary to observe over a broad spectral range to constrain the nature of faint companions.
关键词：enplanets and satellites: individual: CS Cha Bstars: low-massaccretionaccretion disksstars: windsoutflowstechniques: imaging spectroscopy