Non-Detection of Polarized, Scattered Light from the HD 189733b Hot Jupiter

TL;DR

This study used the POLISH instrument to search for polarized scattered light from HD 189733b but found no significant variability, challenging previous claims of strong polarization signals from the exoplanet's atmosphere.

Contribution

The paper provides a high-confidence non-detection of polarized light from HD 189733b, contradicting earlier reports and setting tighter upper limits on polarimetric variability.

Findings

No significant polarimetric variability detected

Upper limit to variability is Delta_P < 7.9 x 10^(-5)

Previous claims of large polarization signals are not supported

Abstract

Using the POLISH instrument, I am unable to reproduce the large-amplitude polarimetric observations of Berdyugina et al. (2008) to the >99.99% confidence level. I observe no significant polarimetric variability in the HD 189733 system, and the upper limit to variability from the exoplanet is Delta_P < 7.9 x 10^(-5) with 99% confidence in the 400 nm to 675 nm wavelength range. Berdyugina et al. (2008) report polarized, scattered light from the atmosphere of the HD 189733b hot Jupiter with an amplitude of two parts in 10^4. Such a large amplitude is over an order of magnitude larger than expected given a geometric albedo similar to other hot Jupiters. However, my non-detection of polarimetric variability phase-locked to the orbital period of the exoplanet, and the lack of any significant variability, shows that the polarimetric modulation reported by Berdyugina et al. (2008) cannot be due to the exoplanet.