JWST对贫金属T矮星WISEA J155349.96+693355.2的观测：首颗与Gaia-Enceladus银河系子结构相关联的褐矮星
JWST Observations of the Metal-poor T Dwarf WISEA J155349.96+693355.2: The First Brown Dwarf Associated with the Gaia-Enceladus Milky Way Substructure
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中文总结 AI 辅助
本研究通过JWST光谱观测确认WISEA J155349.96+693355.2为贫金属T矮星，其运动学和化学特征与Gaia-Enceladus子结构恒星一致，成为首颗与该银河系子结构关联的褐矮星。
中文摘要 AI 辅助
我们展示了JWST NIRSpec和MIRI对贫金属T矮星WISEA J155349.96+693355.2的观测。NIRSpec/prism加上MIRI/LRS的联合光谱（R ~ 100）提供了0.6-12微米的光谱覆盖，揭示了H2O、CH4和NH3吸收特征的存在，增强的碰撞诱导H2吸收，以及微弱或缺失的CO和CO2吸收，这些都是贫金属低温大气层的指标。将光谱数据与一系列大气模型进行比较，得出有效温度Teff = 960+28-32 K和太阳比例金属丰度[M/H] = -1.16+0.28-0.25 dex。我们发现不确定的三角视差（可能受到Lutz-Kelker偏差影响）可能被高估的迹象。采用光度距离得出热光度log10Lbol/Lsun = -5.29 ± 0.10，由此推断Teff = 974 ± 56 K，与通过我们的大气模型拟合得出的温度一致。从中等分辨率（R ~ 3,000）的NIRSpec/G395H光谱中，我们测量了径向速度为-163 ± 5 km/s，结合该源的实测自行和估计距离，表明其具有高偏心（e ≥ 0.9）的银河系轨道，与吸积晕天体一致。WISEA J155349.96+693355.2的UVW运动学、整体金属丰度以及适度的α元素增强（[α/Fe] = +0.15+0.04-0.06 dex）均与Gaia-Enceladus银河系子结构中识别的恒星相当，使其成为首个具有运动学和化学关联证据的褐矮星。
英文摘要
We present JWST NIRSpec and MIRI observations of the metal-poor T dwarf WISEA J155349.96+693355.2. The combined NIRSpec/prism plus MIRI/LRS spectrum (R ~ 100) provides 0.6-12 $μ$m spectroscopic coverage that reveals the presence of H$_2$O, CH$_4$, and NH$_3$ absorption features, enhanced collision-induced H$_2$ absorption, and weak or absent CO and CO$_2$ absorption, all indicators of a metal-poor low-temperature atmosphere. Comparison of the spectral data to a suite of atmosphere models yields an effective temperature $T_{\rm eff}$ = 960$^{+28}_{-32}$ K and a solar-scaled metallicity of [M/H] = -1.16$^{+0.28}_{-0.25}$ dex. We find indications that the uncertain trigonometric parallax, likely subject to Lutz-Kelker bias, may be overestimated. Adopting the photometric distance yields a bolometric luminosity log$_{10}L_{bol}/L_{\odot}$ = -5.29 $\pm$ 0.10, from which we infer $T_{\rm eff}$ = 974 $\pm$ 56 K, consistent with the temperature derived via our atmospheric model fits. From the moderate-resolution (R ~ 3,000) NIRSpec/G395H spectrum, we measure a radial velocity of -163 $\pm$ 5 km/s, which combined with the source's measured proper motion and estimated distance indicates a highly eccentric (e $\geq$ 0.9) Galactic orbit consistent with an accreted halo object. The UVW kinematics of WISEA J155349.96+693355.2, its bulk metallicity, and its modest alpha enrichment ([$α$/Fe] = +0.15$^{+0.04}_{-0.06}$ dex) are all equivalent to stars identified in the Gaia-Enceladus Milky Way substructure, making it the first brown dwarf with kinematic and chemical evidence of association.
发表机构
- NSF National Optical-Infrared Astronomy Research Laboratory（美国国家光学红外天文研究实验室）
- Radcliffe Institute for Advanced Study at Harvard University（哈佛大学拉德克利夫高等研究院）
- Department of Astronomy & Astrophysics, UC San Diego（加州大学圣地亚哥分校天文与天体物理系）
- Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University（西北大学跨学科天体物理学探索与研究中心）
- Department of Astrophysics, American Museum of Natural History（美国自然历史博物馆天体物理系）
- Department of Physics, Graduate Center, City University of New York（纽约市立大学研究生中心物理系）
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