Infrared observations of metastable 2$^3$S helium absorption with ground- and space-based spectroscopy are rapidly maturing, as this species is a unique probe of exoplanet atmospheres. Specifically, the transit depth in the triplet feature (with vacuum wavelengths near 1083.3 nm) can be used to constrain the temperature and mass loss rate of an exoplanet's upper atmosphere. Here, we present a new photometric technique to measure metastable 2$^3$S helium absorption using an ultra-narrowband filter (full-width at half-maximum of 0.635 nm) coupled to a beam-shaping diffuser installed in the Wide-field Infrared Camera (WIRC) on the 200-inch Hale Telescope at Palomar Observatory. We use telluric OH lines and a helium arc lamp to characterize refractive effects through the filter and to confirm our understanding of the filter transmission profile. We benchmark our new technique by observing a transit of WASP-69b and detect an excess absorption of $0.498\pm0.045$% (11.1$\sigma$), consistent with previous measurements after considering our bandpass. Then, we use this method to study the inflated gas giant WASP-52b and place a 95th-percentile upper limit on excess absorption in our helium bandpass of 0.47%. Using an atmospheric escape model, we constrain the mass loss rate for WASP-69b to be $5.25^{+0.65}_{-0.46}\times10^{-4}~M_\mathrm{J}/\mathrm{Gyr}$ ($3.32^{+0.67}_{-0.56}\times10^{-3}~M_\mathrm{J}/\mathrm{Gyr}$) at 7,000 K (12,000 K). Additionally, we set an upper limit on the mass loss rate of WASP-52b at these temperatures of $2.1\times10^{-4}~M_\mathrm{J}/\mathrm{Gyr}$ ($2.1\times10^{-3}~M_\mathrm{J}/\mathrm{Gyr}$). These results show that ultra-narrowband photometry can reliably quantify absorption in the metastable helium feature.

中文翻译：

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用超窄带光度法对 WASP-69b 和 WASP-52b 大气中亚稳态氦的约束

使用地面和空间光谱对亚稳态 2$^3$S 氦吸收的红外观测正在迅速成熟，因为该物种是系外行星大气的独特探测器。具体来说，三重态特征（真空波长接近 1083.3 nm）中的传输深度可用于限制系外行星高层大气的温度和质量损失率。在这里，我们提出了一种新的光度测量技术，使用与安装在宽场中的光束整形扩散器耦合的超窄带滤波器（半高全宽为 0.635 nm）来测量亚稳态的 2$^3$S 氦吸收。帕洛玛天文台 200 英寸黑尔望远镜上的红外相机 (WIRC)。我们使用大地 OH 线和氦弧灯来表征通过滤光片的折射效应，并确认我们对滤光片透射曲线的理解。我们通过观察 WASP-69b 的过境来对我们的新技术进行基准测试，并检测到 0.498\pm0.045$%（11.1$\sigma$）的过度吸收，这与考虑我们的带通后的先前测量结果一致。然后，我们使用这种方法来研究膨胀的气体巨行星 WASP-52b，并将我们的氦带通中的 0.47% 的过量吸收设置为 95% 的上限。使用大气逃逸模型，我们将 WASP-69b 的质量损失率限制为 $5.25^{+0.65}_{-0.46}\times10^{-4}~M_\mathrm{J}/\mathrm{Gyr}$ ($3.32^{+0.67}_{-0.56}\times10^{-3}~M_\mathrm{J}/\mathrm{Gyr}$) 在 7,000 K (12,000 K)。此外，我们为 WASP-52b 在这些温度下的质量损失率设置了上限 $2.1\times10^{-4}~M_\mathrm{J}/\mathrm{Gyr}$ ($2.1\times10^{-3 }~M_\mathrm{J}/\mathrm{Gyr}$)。