Defocused transmission spectroscopy: a potential detection of sodium in the atmosphere of WASP-12b

J. R. Burton, C. A. Watson, P. Rodríguez-Gil, I. Skillen, S. P. Littlefair, S. Dhillon, D. Pollacco

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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.
Original languageUndefined/Unknown
Pages (from-to)1071-1082
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date16 Nov 2014
Publication statusPublished - Jan 2015

Bibliographical note

14 pages, 12 figures, 2 tables - MNRAS accepted


  • astro-ph.EP
  • astro-ph.SR

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