We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the dayside of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2 m Subaru telescope. The telluric and stellar lines are removed using a detrending algorithm, SysRem. The residuals are then cross-correlated with OH and H₂O planetary spectrum templates produced using several different line lists. We check and confirm the accuracy of OH line lists by cross-correlating with the spectrum of GJ 436. As a result, we detect the emission signature of OH at K _p of km s⁻¹ and v _sys of −0.3 km s⁻¹ with a signal-to-noise ratio (S/N) of 5.4 and a significance of 5.5σ. Additionally, we marginally detect H₂O emission in the H-band with an S/N of 4.0 and a significance of 5.2σ using the POKAZATEL line list. However, no significant signal is detected using the HITEMP 2010, which might be due to differences in line positions and strengths, as well as the incompleteness of the line lists. Nonetheless, this marginal detection is consistent with the prediction that H₂O is mostly thermally dissociated in the upper atmosphere of the ultra-hot Jupiters. Therefore, along with CO, OH is expected to be one of the most abundant O-bearing molecules in the dayside atmosphere of ultra-hot Jupiters and should be considered when studying their atmospheres.

我们报告了在太阳系外行星大气中首次检测到羟基自由基 (OH) 发射特征，在这种情况下，在 WASP-33b 的白天。我们分析了使用 8.2 m 斯巴鲁望远镜上的红外多普勒光谱仪拍摄的 WASP-33b 的高分辨率近红外发射光谱。使用去趋势算法SysRem去除大地和恒星线。然后将残差与使用几个不同行列表生成的OH 和 H ₂ O 行星光谱模板进行互相关。我们检查并确认OH行列出的与GJ 436的频谱结果互相关的准确性，我们检测OH的排放签名在ķ _p的公里S ^-1和v _sys of -0.3 km s ^-1具有 5.4 的信噪比 (S/N) 和 5.5 σ的显着性。此外，我们检测轻微ħ ₂ Ó在发射ħ波段具有4.0的S / N和5.2的显着性σ使用POKAZATEL线列表。然而，使用 HITEMP 2010 没有检测到显着信​​号，这可能是由于线路位置和强度的差异，以及线路列表的不完整。尽管如此，这种边缘检测与 H ₂O 主要在超热木星的高层大气中热解离。因此，与 CO 一起，OH 有望成为超热木星日侧大气中最丰富的含 O 分子之一，在研究它们的大气时应予以考虑。