Defocussed Transmission Spectroscopy: A potential detection of sodium in the atmosphere of WASP-12b

TL;DR

This paper introduces defocussed transmission spectroscopy, a ground-based technique that reduces systematic errors and tentatively detects sodium in the atmosphere of exoplanet WASP-12b, demonstrating its potential for exoplanet atmospheric studies.

Contribution

The paper presents a novel defocussed transmission spectroscopy method and demonstrates its application to detect sodium in an exoplanet atmosphere, improving ground-based observational accuracy.

Findings

Tentative detection of sodium in WASP-12b's atmosphere.

Reduction of systematic errors in ground-based spectroscopy.

Method outlines for future improvements.

Abstract

We report on a pilot study of a novel observing technique, defocussed transmission spectroscopy, and its application to the study of exoplanet atmospheres using ground-based platforms. Similar to defocussed photometry, defocussed transmission spectroscopy has an added advantage over normal spectroscopy in that it reduces systematic errors due to flat-fielding, PSF variations, slit-jaw imperfections and other effects associated with ground-based observations. For one of the planetary systems studied, WASP-12b, we report a tentative detection of additional Na absorption of 0.12+/-0.03[+0.03]% during transit using a 2A wavelength mask. After consideration of a systematic that occurs mid-transit, it is likely that the true depth is actually closer to 0.15%. This is a similar level of absorption reported in the atmosphere of HD209458b (0.135+/-0.017%, Snellen et al. 2008). Finally, we outline methods that will improve the technique during future observations, based on our findings from this pilot study.