We present transmission spectroscopy of the warm Saturn-mass exoplanet WASP-39b made with the Very Large Telescope FOcal Reducer and Spectrograph (FORS2) across the wavelength range 411–810 nm. The transit depth is measured with a typical precision of 240 parts per million (ppm) in wavelength bins of 10 nm on a V = 12.1 mag star. We detect the sodium absorption feature (3.2 σ ) and find evidence of potassium. The ground-based transmission spectrum is consistent with Hubble Space Telescope ( HST ) optical spectroscopy, supporting the interpretation that WASP-39b has a largely clear atmosphere. Our results demonstrate the great potential of the recently upgraded FORS2 spectrograph for optical transmission spectroscopy, with which we obtained HST -quality light curves from the ground.
CITATION STYLE
Nikolov, N., Sing, D. K., Gibson, N. P., Fortney, J. J., Evans, T. M., Barstow, J. K., … Wilson, P. A. (2016). VLT FORS2 COMPARATIVE TRANSMISSION SPECTROSCOPY: DETECTION OF Na IN THE ATMOSPHERE OF WASP-39b FROM THE GROUND. The Astrophysical Journal, 832(2), 191. https://doi.org/10.3847/0004-637x/832/2/191
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