# A Transmission Spectrum Of HD 189733b From Multiple Broadband Filter Observations

## TL;DR

This study presents a multi-band photometric transmission spectrum of HD 189733b, revealing variations in apparent planetary radius across wavelengths, and demonstrates ground-based observatory capabilities for exoplanet atmospheric characterization.

## Contribution

First multi-band broadband transit observations of HD 189733b using a 2.3-m ground telescope, creating an ultra-low resolution transmission spectrum with MCMC and Gaussian processes.

## Key findings

- Apparent planet radius increases from z'-band to u'-band.
- Results are consistent with previous studies of HD 189733b.
- Observations demonstrate ground-based capability to measure exoplanet atmospheres.

## Abstract

We present new multi-broadband transit photometry of HD 189733b obtained at the Wyoming Infrared Observatory. Using an ensemble of five-band Sloan filter observations across multiple transits we have created an "ultra-low" resolution transmission spectrum to discern the nature of the exoplanet atmosphere. The observations were taken over three transit events and total 108 u', 120 g', 120 r', 110 i', and 116 z' images with an average exposure cadence of seven minutes for an entire series. The analysis was performed with a Markov-Chain Monte-Carlo method assisted by a Gaussian processes regression model. We find the apparent planet radius to increase from 0.154 +0.000920-0.00096 R* at z'-band to 0.157 +0.00074-0.00078 R* at u'-band. Whether this apparent radius implies an enhanced Rayleigh scattering or clear or grey planet atmosphere is highly dependent on stellar spot modeling assumptions, but our results are consistent with the literature for HD 189733b. This set of observations demonstrates the ability of our 2.3-m ground-based observatory to measure atmospheres of large exoplanets.