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Contamination from a nearby star cannot explain the anomalous transmission spectrum of the ultra-short period giant planet WASP-103b

Southworth, John; Evans, Daniel F.

Contamination from a nearby star cannot explain the anomalous transmission spectrum of the ultra-short period giant planet WASP-103b Thumbnail


Authors

Daniel F. Evans



Abstract

The planet in the WASP-103 system is an excellent candidate for transmission spectroscopy because of its large radius and high temperature. Application of this technique found a variation of radius with wavelength which was far too strong to be explained by scattering processes in the planetary atmosphere. A faint nearby star was subsequently detected, whose contamination of the transit light curves might explain this anomaly. We present a reanalysis of published data in order to characterise the faint star and assess its effect on the measured transmission spectrum. The faint star has a mass of 0.72 +/- 0.08 Msun and is almost certainly gravitationally bound to the planetary system. We find that its effect on the measured physical properties of the planet and host star is small, amounting to a planetary radius larger by 0.6 sigma and planetary density smaller by 0.8 sigma. Its influence on the measured transmission spectrum is much greater: the spectrum now has a minimum around 760 nm and opacity rises to both bluer and redder wavelengths. It is a poor match to theoretical spectra and the spectral slope remains too strong for Rayleigh scattering. The existence of the faint nearby star cannot therefore explain the measured spectral properties of this hot and inflated planet. We advocate further observations of the system, both with high spatial resolution in order to improve the measured properties of the faint star, and with higher spectral resolution to confirm the anomalous transmission spectrum of the planet.

Journal Article Type Article
Acceptance Date Aug 2, 2016
Online Publication Date Aug 4, 2016
Publication Date Nov 21, 2016
Publicly Available Date May 26, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 463
Issue 1
Pages 37-44
DOI https://doi.org/10.1093/mnras/stw1943
Keywords astronomy, physics, planetary systems stars, fundamental parameters stars, WASP-103
Publisher URL http://dx.doi.org/10.1093/mnras/stw1943

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