We present an optical to near-infrared transmission spectrum of the inflated hot Jupiter WASP-52b using three transit observations from the Space Telescope Imaging Spectrograph ( STIS ) mounted on the Hubble Space Telescope , combined with Spitzer /Infrared Array Camera ( IRAC ) photometry at 3.6 \mu m and 4.5 \mu m. Since WASP-52 is a moderately active ( log ( L _ { x } / L _ { bol } ) = - 4.7 ) star , we correct the transit light curves for the effect of stellar activity using ground-based photometric monitoring data from the All-Sky Automated Survey for Supernovae ( ASAS-SN ) and Tennessee State University ’ s Automatic Imaging Telescope ( AIT ) .
We bin the data in 38 spectrophotometric light curves from 0.29 to 4.5 \mu m and measure the transit depths to a median precision of 90 ppm .
We compare the transmission spectrum to a grid of forward atmospheric models and find that our results are consistent with a cloudy spectrum and evidence of sodium at 2.3 \sigma confidence , but no observable evidence of potassium absorption even in the narrowest spectroscopic channel .
We find that the optical transmission spectrum of WASP-52b is similar to that of the well-studied inflated hot Jupiter HAT-P-1b , which has comparable surface gravity , equilibrium temperature , mass , radius , and stellar irradiation levels .
At longer wavelengths , however , the best fitting models for WASP-52b and HAT-P-1b predict quite dissimilar properties , which could be confirmed with observations at wavelengths longer than \sim 1 \mu m. The identification of planets with common atmospheric properties and similar system parameters will be insightful for comparative atmospheric studies with the James Webb Space Telescope .