Kavli Affiliate: Robert Cameron
| First 5 Authors: Veronika Witzke, Alexander I. Shapiro, Nadiia M. Kostogryz, Robert Cameron, Benjamin V. Rackham
| Summary:
The reliable characterization of planetary atmospheres with transmission
spectroscopy requires realistic modeling of stellar magnetic features, since
features that are attributable to an exoplanet atmosphere could instead stem
from the host star’s magnetic activity. Current retrieval algorithms for
analysing transmission spectra rely on intensity contrasts of magnetic features
from 1D radiative-convective models. However, magnetic features, especially
faculae, are not fully captured by such simplified models. Here we investigate
how well such 1D models can reproduce 3D facular contrasts, taking a G2V star
as an example. We employ the well established radiative magnetohydrodynamic
code MURaM to obtain three-dimensional simulations of the magneto-convection
and photosphere harboring a local small-scale-dynamo. Simulations without
additional vertical magnetic fields are taken to describe the quiet solar
regions, while simulations with initially 100 G, 200 G and 300 G vertical
magnetic fields are used to represent different magnetic activity levels.
Subsequently, the spectra emergent from the MURaM cubes are calculated with the
MPS-ATLAS radiative transfer code. We find that the wavelength dependence of
facular contrast from 1D radiative-convective models cannot reproduce facular
contrasts obtained from 3D modeling. This has far reaching consequences for
exoplanet characterization using transmission spectroscopy, where accurate
knowledge of the host star is essential for unbiased inferences of the
planetary atmospheric properties.
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