In order to detect exoplanet transmission spectrum in high spectral resolution, it is necessary to  model the stellar line profile change during transit. The stellar line profile change is mostly due to two effects: Rossiter-McLaughlin (RM) effect and the Centre-to-Limb Variation (CLV) effect. The RM effect is due to the stellar rotation while the CLV effect is due to the differential limb darkening.

I have developed a model to simulate the RM+CLV effect simultaneously for different stellar lines. This model has been applied to different planetary systems.

Hα line in KELT-9

For Hα line during the the transit of KELT-9b, the RM effect is very strong because the star is rotating very fast.

The above figure shows stellar line profile change during transit. X-axis is wavelength expressed as the RV values relative to the Hα line centre. Y-axis is the planetary orbital phase. The bright region around line centre is due to the RM effect and the green line indicates the RV of the rotating stellar surface which is obscured by the planet. The CLV effect causes the line shape to shallower during mid-transit (phase =0) and deeper during limb-transit (phase ~ ±0.05).

Publication: Yan & Henning, 2018, Nature Astronomy

Na D lines in HD 189733

Publication: Yan et al. 2017, A&A, 603, A73.

Na D lines in WASP-69

Publication: Casasayas-Barris et al. 2017, A&A, 608, A135

Na D lines and Hα line in KELT-20

Publication: Casasayas-Barris et al. 2018 A&A


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