3 research outputs found

    Nightside condensation of iron in an ultra-hot giant exoplanet

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    Ultra-hot giant exoplanets receive thousands of times Earth's insolation. Their high-temperature atmospheres (>2,000 K) are ideal laboratories for studying extreme planetary climates and chemistry. Daysides are predicted to be cloud-free, dominated by atomic species and substantially hotter than nightsides. Atoms are expected to recombine into molecules over the nightside, resulting in different day-night chemistry. While metallic elements and a large temperature contrast have been observed, no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night ("evening") and night-to-day ("morning") terminators could, however, be revealed as an asymmetric absorption signature during transit. Here, we report the detection of an asymmetric atmospheric signature in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this signature thanks to the combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. Iron must thus condense during its journey across the nightside.Comment: Published in Nature (Accepted on 24 January 2020.) 33 pages, 11 figures, 3 table

    FORS1 is getting Blue: New Blue Optimised Detectors and High Throughput Filters

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    Ground-based observations in the ultraviolet part of the electromagnetic spectrum are notoriously difficult owing to absorption of the atmosphere, of optical elements and the poorer efficiency of detectors. Now that CCD detectors with excellent UV response and cosmetic quality have become available, it was time to optimise FORS1 for imaging, low-resolution spectroscopic and polarimetric observations in the blue-UV. As a bonus, a new set of broadband filters with very high trans-mission and carefully defined filter bands were installed
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