# First Light of Engineered Diffusers at the Nordic Optical Telescope Reveal Time Variability in the Optical Eclipse Depth of WASP-12b

## TL;DR

This study demonstrates the use of engineered diffusers on the Nordic Optical Telescope for high-precision photometry, revealing time variability in the optical eclipse depth of exoplanet WASP-12b and providing new transmission spectrum data.

## Contribution

It introduces the application of engineered diffusers for reliable, high-precision ground-based photometry and reports novel findings on the variability of WASP-12b's eclipse depth.

## Key findings

- Photometric precision within sub-millimagnitude level achieved.
- New blue-band transit depth measurement for CoRoT-1b disfavoring Rayleigh slope.
- Detected significant variability in WASP-12b's eclipse depth, deviating from HST data.

## Abstract

We present the characterization of two engineered diffusers mounted on the 2.5 meter Nordic Optical Telescope, located at Roque de Los Muchachos, Spain. To assess the reliability and the efficiency of the diffusers, we carried out several test observations of two photometric standard stars, along with observations of one primary transit observation of TrES-3b in the red (R-band), one of CoRoT-1b in the blue (B-band), and three secondary eclipses of WASP-12b in V-band. The achieved photometric precision is in all cases within the sub-millimagnitude level for exposures between 25 and 180 seconds. Along a detailed analysis of the functionality of the diffusers, we add a new transit depth measurement in the blue (B-band) to the already observed transmission spectrum of CoRoT-1b, disfavouring a Rayleigh slope. We also report variability of the eclipse depth of WASP-12b in the V-band. For the WASP-12b secondary eclipses, we observe a secondary-depth deviation of about 5-sigma, and a difference of 6-sigma and 2.5-sigma when compared to the values reported by other authors in similar wavelength range determined from Hubble Space Telescope data. We further speculate about the potential physical processes or causes responsible for this observed variability