The near-UV transit of HD 189733b with the XMM-Newton Optical Monitor

TL;DR

This study analyzes near-ultraviolet transits of HD 189733b using XMM-Newton data, confirming transit depths consistent with optical measurements and finding no significant variation over 8 years.

Contribution

First detailed near-UV transit analysis of HD 189733b with XMM-Newton, showing consistent transit depths and constraining extended absorption.

Findings

Transit depths match optical measurements

No significant variation over 8 years

Extended broadband absorption ruled out

Abstract

We present analysis of XMM-Newton Optical Monitor observations in the near-ultraviolet of HD 189733, covering twenty primary transits of its hot Jupiter planet. The transit is clearly detected with both the UVW2 and UVM2 filters, and our fits to the data reveal transit depths in agreement with that observed optically. The measured depths correspond to radii of $1.059^{+0.046}_{-0.050}$ and $0.94^{+0.15}_{-0.17}$ times the optically-measured radius (1.187 R$_{\rm J}$ at 4950 \r{A}) in the UVW2 and UVM2 bandpasses, respectively. We also find no statistically significant variation in the transit depth across the 8 year baseline of the observations. We rule out extended broadband absorption towards or beyond the Roche lobe at the wavelengths investigated, although observations with higher spectral resolution are required to determine if absorption out to those distances from the planet is present in individual near-UV lines.