The puzzle of the formation of T8 dwarf Ross 458c
The puzzle of the formation of T8 dwarf Ross 458c
复制标题
T8矮人罗斯458c的形成之谜
DOI：
10.1093/mnras/stad753
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发表时间：
2023
影响因子：
4.8
通讯作者：
Freedman, Richard
中科院分区：
文献类型：
--
作者：
Gaarn, Josefine;Burningham, Ben;Faherty, Jacqueline K.;Visscher, Channon;Marley, Mark S.;Gonzales, Eileen C.;Calamari, Emily;Bardalez Gagliuffi, Daniella;Lupu, Roxana;Freedman, Richard
在最低质量，棕矮星和巨大系外行星之间的区别往往是模糊的，文献分类很少反映氘燃烧边界。大气特征可以揭示行星形成途径对极低质量褐矮星种群的贡献程度，通过揭示它们的丰度分布是否与当地种群的丰度分布不同，或者在伴星的情况下，是否与它们的主恒星不同。T8矮星Ross 458c可能是一对M矮星的行星质量伴侣，之前的研究表明它是多云的。本文介绍了利用1.0-2.4µm范围内的存档光谱数据对Ross 458c进行检索分析的结果。我们测试了无云模型以及各种多云模型，发现Ross 458c的大气最好用多云模型来描述（强烈推荐）。CH4/H2O比预期的高。从平衡化学和合理的碳氧比（C/O）的角度来看，这个值很难理解。与热化学网格模型的比较表明，如果ch4和H2O在2000 K淬火，需要剧烈混合，则C/O为≈1.35。我们发现[C/H]比值为+0.18，这与主系统的金属丰度相符，表明大气中缺少氧气。即使在极端混合的情况下，隐含的碳氧比也远远超出了典型的恒星状态，这表明要么是一种非恒星的形成途径，要么是通过迄今未建模的化学或冷凝过程封存了大量的氧气。
At the lowest masses, the distinction between brown dwarfs and giant exoplanets is often blurred and literature classifications rarely reflect the deuterium burning boundary. Atmospheric characterization may reveal the extent to which planetary formation pathways contribute to the population of very low mass brown dwarfs, by revealing whether their abundance distributions differ from those of the local field population or, in the case of companions, their primary stars. The T8 dwarf Ross 458c is a possible planetary-mass companion to a pair of M dwarfs, and previous work suggests that it is cloudy. We here present the results of the retrieval analysis of Ross 458c, using archival spectroscopic data in the 1.0–2.4 µm range. We test a cloud-free model as well as a variety of cloudy models and find that the atmosphere of Ross 458c is best described by a cloudy model (strongly preferred). The CH4/H2O is higher than expected at. This value is challenging to understand in terms of equilibrium chemistry and plausible carbon-to-oxygen (C/O) ratios. Comparisons to thermochemical grid models suggest a C/O of ≈1.35, if CH4and H2O are quenched at 2000 K, requiring vigorous mixing. We find a [C/H] ratio of +0.18, which matches the metallicity of the primary system, suggesting that oxygen is missing from the atmosphere. Even with extreme mixing, the implied C/O is well beyond the typical stellar regime, suggesting either a non-stellar formation pathway or the sequestration of substantial quantities of oxygen via hitherto unmodelled chemistry or condensation processes.
褐矮星的形成：理论
DOI：
10.1007/978-3-319-30648-3_95-1
发表时间：
2018
期刊：
arXiv: Astrophysics of Galaxies
影响因子：
--
作者：
A. Whitworth
通讯作者：
A. Whitworth