Stellar Spectroscopy during Exoplanet Transits: Dissecting fine structure across stellar surfaces

TL;DR

This paper discusses how differential spectroscopy during exoplanet transits can be used to analyze small stellar surface regions, testing 3D stellar atmosphere models and improving understanding of stellar properties.

Contribution

It introduces the potential of using high-quality transit spectra to reconstruct stellar surface line profiles, enabling detailed tests of stellar atmosphere models beyond the Sun.

Findings

Reconstruction of line profiles in bright transit hosts like HD209458 is feasible.

Center-to-limb variations in line shapes can test 3D stellar atmosphere models.

Current data quality allows detailed spectral analysis of some exoplanet host stars.

Abstract

Differential spectroscopy during exoplanet transits permits to reconstruct spectra of small stellar surface portions that successively become hidden behind the planet. The center-to-limb behavior of stellar line shapes, asymmetries and wavelength shifts will enable detailed tests of 3-dimensional hydrodynamic models of stellar atmospheres, such that are required for any precise determination of abundances or seismic properties. Such models can now be computed for widely different stars but have been feasible to test in detail only for the Sun with its resolved surface structure. Although very high quality spectra are required, already current data permit reconstructions of line profiles in the brightest transit host stars such as HD209458 (G0 V).