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We present the detection of neutral helium at 10833A in the atmosphere ofWASP-52b and tentative evidence of helium in the atmosphere of the grazingWASP-177b, using high-resolution observations acquired with the NIRSPECinstrument on the Keck II telescope. We detect excess absorption by helium inWASP-52b's atmosphere of $3.44 \pm 0.31$% ($11\sigma$), or equivalently $66 \pm5$ atmospheric scale heights. This absorption is centered on the planet's restframe ($\Delta v = 0.00 \pm 1.19$km s$^{-1}$). We model the planet's escapeusing a 1D Parker wind model and calculate its mass-loss rate to be $\sim 1.4\times 10^{11}$g s$^{-1}$, or equivalently 0.5% of its mass per Gyr. ForWASP-177b, we see evidence for red-shifted ($\Delta v = 6.02 +/- 1.88$kms$^{-1}$) helium-like absorption of $1.28 \pm 0.29$% (equal to $23 \pm 5$atmospheric scale heights). However, due to residual systematics in thetransmission spectrum of similar amplitude, we do not interpret this assignificant evidence for He absorption in the planet's atmosphere. Using a 1DParker wind model, we set a $3\sigma$ upper limit on WASP-177b's escape rate of$7.9 \times 10^{10}$ g s$^{-1}$. Our results, taken together with recentliterature detections, suggest the tentative relation between XUV irradiationand He I absorption amplitude may be shallower than previously suggested. Ourresults highlight how metastable helium can advance our understanding ofatmospheric loss and its role in shaping the exoplanet population.

Keck/NIRSPEC studies of He I in the atmospheres of two inflated hot gas giants orbiting K dwarfs: WASP-52b and WASP-177b