http://arxiv.org/abs/1807.00577
In-depth studies of exoplanetary atmospheres are becoming reality. To unveil in detail their properties, together with higher S/N spectra we need more sophisticated analysis methods. With high-resolution spectrographs, we can not only detect the sodium feature in the atmosphere of exoplanets, but also characterize it studying its line-profile. After finding a clearly w-shaped sodium line-profile in the transmission spectrum of HD189733b, we investigated possible sources of contamination, trying to find solutions for a correction from these spurious deformations. Analyzing the single transmission spectra of HD189733b in the wavelength space, we show that the main sodium signal that causes the absorption in the transmission spectrum is centered in the stellar rest frame. We concentrate on two stellar effects that contaminate the transmission spectrum: center-to-limb variations and stellar rotation. We show how the line-profile is influenced by both these effects. While for CLV we correct using simulated theoretical stellar spectra, we provide a new method, based directly on observational data, to correct for the RM contribution to the line-profile of the retrieved transmission spectrum. We apply the corrections to the spectra of HD189733b. Our analysis brings to line-profiles of the Na D lines in the transmission spectrum which are narrower than previously reported. The correction of the D2 line, deeper than the D1, is probably still incomplete as the planetary radius is more enlarged at this wavelength. Careful detrending from spurious stellar effects followed by an inspection in the velocity space is mandatory when studying the line-profile of atmospheric features in the high-resolution transmission spectrum of exoplanets. Higher S/N data coupled with improved atmospheric models will in future allow us to adapt the magnitude of the corrections of stellar effects in an iterative way.
F. Borsa and A. Zannoni
Tue, 3 Jul 18
63/95
Comments: 8 pages, 11 figures. Accepted for publication in A&A
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