The near-UV transit of HD 189733b with the XMM–Newton optical monitor

George W King,Panayotis Lavvas,David Ehrenreich,Tom Louden,Maria E Steinrueck,Peter J Wheatley,Lía Corrales,Vincent Bourrier,Alain Lecavelier Des Etangs

doi:10.1093/mnras/stab1863

Abstract

ABSTRACT We present analysis of XMM–Newton optical monitor observations in the near-ultraviolet of HD 189733, covering 20 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 RJ at 4950 Å) in the UVW2 and UVM2 bandpasses, respectively. We also find no statistically significant variation in the transit depth across the 8 yr baseline of the observations. We rule out extended broad-band 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.

Highlights

One of the key aspects in characterising discovered exoplanets is investigating their atmospheric composition
The Hubble Space Telescope (HST) is capable of observing in the NUV with its COS, STIS, and WFC3/UVIS instruments (Fossati et al 2010; Haswell et al 2012; Vidal-Madjar et al 2013; Sing et al 2019; Wakeford et al 2020; Cubillos et al 2020), though the majority of transmission spectroscopy experiments performed with HST have focused on the optical, near-infrared, and some FUV (e.g. Kreidberg et al 2014; Ehrenreich et al 2015; Sing et al 2016)
One thing to note is that detailed simulations of aerosol formation in hot Jupiter atmospheres predict that transmission spectrum will eventually flatten at shorter wavelengths (Powell et al 2019)

Summary

Introduction

One of the key aspects in characterising discovered exoplanets is investigating their atmospheric composition. Transiting planets are good targets for this as the apparent transit depth varies as a function of wavelength This variation is driven by the bulk elemental composition, molecular, and particulate species present in any atmosphere maintained by the planet. The Hubble Space Telescope (HST) is capable of observing in the NUV with its COS, STIS, and WFC3/UVIS instruments (Fossati et al 2010; Haswell et al 2012; Vidal-Madjar et al 2013; Sing et al 2019; Wakeford et al 2020; Cubillos et al 2020), though the majority of transmission spectroscopy experiments performed with HST have focused on the optical, near-infrared, and some FUV (e.g. Kreidberg et al 2014; Ehrenreich et al 2015; Sing et al 2016)

Results

Discussion

Conclusion