AI 中文总结
本研究利用JWST等数据构建统一色-星等图序列，揭示凌日行星与亚恒星天体的大气化学差异，发现重力而非辐照主导甲烷特征，为检验大气模型提供了统一图谱。
AI 中文摘要
色-星等图（CMDs）在天体物理学中具有基础性作用，应用范围涵盖星系、恒星、褐矮星等，而詹姆斯·韦布空间望远镜（JWST）如今将其拓展至温度重叠的凌日系外行星与自发光亚恒星天体。我们汇编了13颗凌日巨行星、57颗自发光天体以及受辐照褐矮星ZTF J0038+2030 B的JWST昼侧发射光谱，覆盖温度约350-2600 K、表面重力log g=2.5-5.5，以及约2150颗SPHEREx极冷矮星，将其转换为2MASS J/Ks波段及5个NIRCam中波段的合成测光，这些中波段可分离H₂O、CH₄、CO₂和CO特征。低重力与膨胀半径使凌日行星类似年轻亚恒星天体，高海拔云团提升光球层，导致光谱特征更浅、颜色更红。凌日行星在J对J-K色-星等图上遵循L矮星序列，WASP-80 b（平衡温度T_eq~800 K）未呈现T矮星特有的蓝移转向，表明受辐照、低重力大气中L/T转变延迟或受抑制。甲烷出现从亚恒星大气延迟至凌日行星大气，多云的辐射-对流模型显示，低重力与云的回热作用使大气向以CO为主的化学状态转变，从而抑制光球层CH₄。受辐照但年老、高重力的褐矮星ZTF J0038+2030 B（昼侧温度T_day=1049 K，log g=5.4）呈现出与场T矮星类似的深昼侧甲烷带，说明重力而非辐照是主导控制因素。CO₂/CO诊断显示，凌日行星与直接成像行星质量伴星的CO₂相对吸收强于场褐矮星，与星子吸积导致的金属丰度增强一致。这些色-星等图序列为自发光与受辐照大气提供了统一的、可用于模型检验的图谱。
英文摘要
Color-magnitude diagrams (CMDs) have been foundational across astrophysics, from galaxies and stars to brown dwarfs, and JWST now extends them to transiting exoplanets and self-luminous substellar objects at overlapping temperatures. We compile JWST dayside emission spectra for 13 transiting giant planets, 57 self-luminous objects, and the irradiated brown dwarf ZTF J0038+2030 B, spanning ~350-2600 K and log g = 2.5-5.5, plus ~2150 SPHEREx ultracool dwarfs, converted to synthetic photometry in 2MASS J/Ks and five NIRCam medium bands isolating H2O, CH4, CO2, and CO. Low gravity and inflated radii make transiting planets resemble young substellar objects, with shallower features and redder colors from high-altitude clouds that raise the photosphere. Transiting planets follow the L-dwarf sequence on the J versus J-K CMD, with WASP-80 b (T_eq~800 K) showing no T-dwarf-like blueward turn, suggesting a delayed or suppressed L/T transition in irradiated, low-gravity atmospheres. Methane onset is delayed from substellar to transiting-planet atmospheres, and cloudy radiative-convective models indicate that lower gravity and cloud back-warming shift atmospheres toward CO-dominated chemistry, suppressing photospheric CH4. The irradiated but old, high-gravity brown dwarf ZTF J0038+2030 B (T_day = 1049 K, log g = 5.4) shows a deep, field-T-dwarf-like dayside methane band, implicating gravity rather than irradiation as the dominant control. CO2-to-CO diagnostics place transiting and directly imaged planetary-mass companions at stronger relative CO2 absorption than field brown dwarfs, consistent with metallicity enhancement from planetesimal accretion. These CMD sequences provide a unified, model-testable map for self-luminous and irradiated atmospheres.
CommentsAccepted for publication in AJ. Code and data to reproduce all figures: https://doi.org/10.5281/zenodo.22101390 . Interactive spectra and color-magnitude browser: https://spectra.guangweifu.com
