Sodium Absorption From the Exoplanetary Atmosphere of HD189733b Detected in the Optical Transmission Spectrum

TL;DR

This paper reports the first ground-based detection of sodium absorption in the atmosphere of exoplanet HD189733b using high-resolution spectroscopy during transits, revealing a stronger sodium signal than in similar hot Jupiters.

Contribution

First ground-based detection of sodium in an exoplanet atmosphere using high-resolution optical transmission spectroscopy.

Findings

Sodium absorption detected at >3-sigma significance

Absorption depth is approximately three times larger than that of HD209458b

Indicates different atmospheric properties between the two hot Jupiters

Abstract

We present the first ground-based detection of sodium absorption in the transmission spectrum of an extrasolar planet. Absorption due to the atmosphere of the extrasolar planet HD189733b is detected in both lines of the NaI doublet. High spectral resolution observations were taken of eleven transits with the High Resolution Spectrograph (HRS) on the 9.2 meter Hobby-Eberly Telescope (HET). The NaI absorption in the transmission spectrum due to HD189733b is (-67.2 +/- 20.7) x 10^-5 deeper in the ``narrow'' spectral band that encompasses both lines relative to adjacent bands. The 1-sigma error includes both random and systematic errors, and the detection is >3-sigma. This amount of relative absorption in NaI for HD189733b is ~3x larger than detected for HD209458b by Charbonneau et al. (2002), and indicates these two hot-Jupiters may have significantly different atmospheric properties.