Detection of sodium absorption in WASP-17b with Magellan

Abstract: We present the detection of sodium absorption in the atmosphere of the extrasolar planet WASP-17b, an inflated 'hot-Jupiter' in a tight orbit around an F6 dwarf. In-transit observations of WASP-17 made with the MIKE spectrograph on the 6.5-m Magellan Telescope were analysed for excess planetary atmospheric absorption in the sodium I 'D' doublet spectral region. Using the interstellar sodium absorption lines as reference, we detect an excess 0.58 \pm 0.13 per cent transit signal, with 4.5{\sigma} confidence, at 1.5 {\AA} bandwidth around the stellar sodium absorption feature. This result is consistent with the previous VLT detection of sodium in WASP-17b, confirming that the planet has a highly inflated atmosphere.