WASP-52b is a low density hot Jupiter orbiting a moderately active K2V star .
Previous low-resolution studies have revealed a cloudy atmosphere and found atomic Na above the cloud deck .
Here we report the detection of excess absorption at the Na doublet , the H \alpha line , and the K D _ { 1 } line .
We derived a high-resolution transmission spectrum based on three transits of WASP-52b , observed with the ultra stable , high-resolution spectrograph ESPRESSO at the VLT .
We measure a line contrast of 1.09 \pm 0.16 % for Na D _ { 1 } , 1.31 \pm 0.13 % for Na D _ { 2 } , 0.86 \pm 0.13 % for H \alpha , and 0.46 \pm 0.13 % for K D _ { 1 } , with a line FWHM range of 11–22 km s ^ { -1 } .
We also find that the velocity shift of these detected lines during the transit is consistent with the planet orbital motion , thus confirming their planetary origin .
We do not observe any significant net blueshift or redshift that can be attributed to planetary winds .
We use activity indicator lines as control but find no excess absorption .
However , we do notice signatures arising from the Center-to-Limb variation ( CLV ) and the Rossiter-McLaughlin ( RM ) effect at these control lines .
This highlights the importance of the CLV+RM correction in correctly deriving the transmission spectrum , which , if not corrected , could resemble or cancel out planetary absorption in certain cases .
WASP-52b is the second non-ultra-hot Jupiter to show excess H \alpha absorption , after HD 189733b .
Future observations targeting non-ultra-hot Jupiters that show H \alpha could help reveal the relation between stellar activity and the heating processes in the planetary upper atmosphere .