# A precise optical transmission spectrum of the inflated exoplanet WASP-52b

## TL;DR

This study presents a high-precision optical transmission spectrum of the inflated hot Jupiter WASP-52b, revealing a mostly flat spectrum with a potential unknown absorber at longer wavelengths, challenging existing atmospheric models.

## Contribution

First precise optical transmission spectrum of WASP-52b using Gaussian process noise modeling, highlighting limitations of current atmospheric models in explaining observed features.

## Key findings

- Spectrum is flat across 4000-7750 Å, consistent with a grey cloud layer.
- Deeper transit observed at wavelengths > 7750 Å, indicating an unknown absorber.
- Standard models do not fully explain the spectral features.

## Abstract

We have measured a precise optical transmission spectrum for WASP-52b, a highly inflated hot Jupiter with an equilibrium temperature of 1300 K. Two transits of the planet were observed spectroscopically at low resolution with the auxiliary-port camera (ACAM) on the William Herschel Telescope (WHT), covering a wide range of 4000-8750 \AA. We use a Gaussian process approach to model the correlated noise in the multi-wavelength light curves, resulting in a high precision relative transmission spectrum with errors on the order of a pressure scale height. We attempted to fit a variety of different representative model atmospheres to the transmission spectrum, but did not find a satisfactory match to the entire spectral range. For the majority of the covered wavelength range (4000-7750 \AA) the spectrum is flat, and can be explained by an optically thick and grey cloud layer at 0.1 mbar, but this is inconsistent with a slightly deeper transit at wavelengths $> 7750$ \AA. We were not able to find an obvious systematic source for this feature, so this opacity may be the result of an additional unknown absorber.