The effect of the stellar absorption line centre-to-limb variation on exoplanet transmission spectrum observations

Abstract

Transit spectroscopy is one of the most commonly used techniques for exoplanet atmosphere characterisation. This technique has been used to detect ionized and neutral species in exoplanet atmospheres by comparing the observed stellar lines in and out of transit. The centre-to-limb variation (CLV) of the stellar lines across the stellar disk is an important effect for transmission spectroscopy, since it results in a change of stellar line depth when the planet transits different parts of the stellar disk. We reanalyse the transit data of HD 189733b taken with the HARPS spectrograph to study the CLV effect during transit. The transmission light curve of the Na i D line so obtained shows a clear imprint of the CLV effect. We use a one-dimensional non-LTE stellar spectral model to simulate the CLV effect. After applying the correction, the measurement of the Na i absorption in the atmosphere of HD 189733b becomes better determined. We compare the CLV effect of HD 189733b to that of HD 209458b. The CLV effects are different for these two benchmark planetary systems and this is attributed to their different stellar effective temperatures and transit impact parameters. We then explore the general CLV effect that occurs during exoplanet transits. Normally, a star with a lower effective temperature exhibits a stronger CLV effect and its CLV feature extends over a relatively broad wavelength range. The transit impact parameter (b) describes the transit trajectory on the stellar disk and thus determines the actual manifestation of the CLV effect. We introduce a b-diagram which describes the behavior of the CLV effect as the function of different impact parameters. With improving observational precision, a careful modeling and correction of the CLV effect is necessary for exoplanet atmosphere characterisation using transit spectroscopy.

Accepted for publishing on A&A

References in corpus (15)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• Temperate Earth-sized planets transiting a nearby ultracool dwarf star
• Improved parameters for extrasolar transiting planets
• Sodium Absorption From the Exoplanetary Atmosphere of HD189733b Detected in the Optical Transmission Spectrum
• Spectroscopy Made Easy: Evolution
• Spectrally resolved detection of sodium in the atmosphere of HD189733b with the HARPS spectrograph
• Ground-based detection of sodium in the transmission spectrum of exoplanet HD209458b
• Using Stellar Limb-Darkening to Refine the Properties of HD 209458b
• HST/STIS Optical Transit Transmission Spectra of the hot-Jupiter HD209458b
• Non-LTE line formation for heavy elements in four very metal-poor stars
• Center-to-Limb Variation of Solar 3-D Hydrodynamical Simulations
• The origin of the excess transit absorption in the HD 189733 system: planet or star?
• Exoplanetary atmospheric sodium revealed by the orbital motion. Narrow-band transmission spectroscopy of HD 189733b with UVES
• The centre-to-limb variations of solar Fraunhofer lines imprinted upon lunar eclipse spectra - Implications for exoplanet transit observations

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