利用VLT/CRIRES+对HIP 67522 b的大气表征：VLT/CRIRES+提示行星更重并暗示氘分馏
Atmospheric characterization of HIP 67522 b with VLT/CRIRES+. VLT/CRIRES+ suggests a heavier planet and hints at deuterium fractionation
AI总结：
利用VLT/CRIRES+的高分辨率光谱，通过探测H₂O和CO并反演质量、C/O比及氘富集，发现HIP 67522 b比JWST估计更重，并首次暗示系外行星大气中的氘分馏。
摘要：
年轻的凌星系外行星为探测行星在关键早期演化阶段的大气提供了独特机会。HIP 67522 b是一颗17 Myr的热木星，具有极低的体密度，是高分辨率透射光谱的理想目标。我们旨在利用地基高分辨率近红外光谱表征HIP 67522 b的大气成分、热结构和动力学。我们在2025年1月30日的一次凌星期间，使用VLT/CRIRES+在K2166波段获得了高分辨率光谱。我们应用交叉相关技术和贝叶斯嵌套采样反演来约束分子丰度、温度结构和大气动力学。我们以20σ检测到H₂O，以5σ检测到CO，证实了这颗低质量巨行星的极端延展大气。-2.9 ± 0.2 km s⁻¹的速度偏移表明存在昼夜风。自转速度被约束为<1.8 km s⁻¹（3σ），与潮汐锁定一致。反演分析表明行星质量为29.8 ± 3地球质量，大气垂直等温。该质量是JWST大气观测估计质量的两倍，且在3σ上不一致，因此对行星的实际密度留下疑问。利用CRIRES+数据推导的质量，我们得到C/O比为0.83 ± 0.09，约为太阳值的1.5倍，以及亚太阳金属丰度[C+O/H] = -0.8 ± 0.4，如果大气有云，该值可以增加，这是我们数据单独无法解决的一个简并。我们报告了HDO的暂定2σ检测，其相对于原太阳D/H比的富集因子约为1000。如果得到确认，这将是系外行星大气中氘的首次检测，并且需要强烈的逃逸率来解释。
英文摘要：
Young transiting exoplanets provide unique opportunities to probe planetary atmospheres during the critical early phases of evolution. HIP 67522 b, a 17 Myr old hot Jupiter with an extraordinarily low bulk density, represents an ideal target for high-resolution transmission spectroscopy. We aim to characterize the atmospheric composition, thermal structure, and dynamics of HIP 67522 b using ground-based high-resolution near-infrared spectroscopy. We obtained high-resolution spectra with VLT/CRIRES+ in the K2166 band during a transit on 30 January 2025. We applied cross-correlation techniques and Bayesian nested sampling retrievals to constrain molecular abundances, temperature structure, and atmospheric dynamics. We detect H$_2$O at 20$σ$ and CO at 5$σ$, confirming the extremely extended atmosphere of this low-mass giant. A velocity offset of $-2.9 \pm 0.2$ km s$^{-1}$ indicates day-to-night winds. The rotation velocity is constrained to <1.8 km s$^{-1}$ at 3$σ$, consistent with tidal locking. Retrieval analysis suggests a planetary mass of 29.8 $\pm$ 3 Earth masses and a vertically isothermal atmosphere. This mass is two times larger than the mass estimated from JWST atmospheric observations and inconsistent at 3$σ$ hence leaving a doubt on the actual planetary density of the planet. Using the mass derived from the CRIRES+ data, we derive a C/O ratio of $0.83 \pm 0.09$, about 1.5 times solar, and a subsolar metallicity [C+O/H] $= -0.8 \pm 0.4$ which can be increased if the atmosphere is cloudy, a degeneracy our data alone cannot resolve. We report a tentative 2$σ$ detection of HDO with an extreme enrichment factor of $\sim$1000 relative to the protosolar D/H ratio. If confirmed, this would be the first detection of deuterium in an exoplanet atmosphere and would require intense escape rate to be explained.
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