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The origin of the excess transit absorption in the HD 189733 system: planet or star?

Barnes, J. R.; Haswell, C. A.; Staab, D. and Anglada-Escudé, G. (2016). The origin of the excess transit absorption in the HD 189733 system: planet or star? Monthly Notices of the Royal Astronomical Society, 462(1) pp. 1012–1028.

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We have detected excess absorption in the emission cores of Ca II H&K during transits of HD 189733b for the first time. Using observations of three transits, we investigate the origin of the absorption, which is also seen in Hα and the Na I D lines. Applying differential spectrophotometry methods to the Ca II H and Ca II K lines combined, using respective passband widths of Δλ = 0.4 and 0.6 Å yields excess absorption of td = 0.0074 ± 0.0044 (1.7σ; Transit 1) and 0.0214 ± 0.0022 (9.8σ; Transit 2). Similarly, we detect excess Hα absorption in a passband of width Δλ = 0.7 Å, with td = 0.0084 ± 0.0016 (5.2σ) and 0.0121 ± 0.0012 (9.9σ). For both lines, Transit 2 is thus significantly deeper. Combining all three transits for the Na I D lines yields excess absorption of td = 0.0041 ± 0.0006 (6.5σ). By considering the time series observations of each line, we find that the excess apparent absorption is best recovered in the stellar reference frame. These findings lead us to postulate that the main contribution to the excess transit absorption in the differential light curves arises because the normalizing continuum bands form in the photosphere, whereas the line cores contain a chromospheric component. We cannot rule out that part of the excess absorption signature arises from the planetary atmosphere, but we present evidence which casts doubt on recent claims to have detected wind motions in the planet's atmosphere in these data.

Item Type: Journal Item
Copyright Holders: 2016 The Authors
ISSN: 1365-2966
Keywords: techniques: spectroscopic; planets and satellites: atmospheres; stars: activity; stars: atmospheres; stars: chromospheres
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Research Group: Health and Wellbeing PRA (Priority Research Area)
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Item ID: 48857
Depositing User: John Barnes
Date Deposited: 07 Mar 2017 14:42
Last Modified: 31 May 2019 22:58
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