Open Access
Table 1
Qualitative comparison of the R-TLSE formalism and ECLIPSE-Xλ.
| Conceptual element | R-TLSE | ECLIPSE-Xλ |
|---|---|---|
| Model formulation | Disk-averaged, 1D correction factor ϵλ applied to the intrinsic transit depth. | Pixel-resolved 2D stellar disk; transit depth obtained from explicit occultation of a limb-darkened star with embedded active regions. |
| Limb darkening | No explicit limb darkening; the stellar disk is treated as uniformly bright. | Includes wavelength-dependent limb darkening via a four-parameter law. |
| Transit geometry | Absent from the R-TLSE contamination factor; the same ϵλ is used for any impact parameter. | Full transit geometry (impact parameter) is treated self-consistently in the pixel-based light-curve calculation. |
| Location of active regions on the stellar disk | Only the total filling factor matters; the spatial distribution of spots and faculae across the disk is not resolved. | Active regions are placed at specific latitudes and longitudes; their projected position on the disk, together with limb darkening and foreshortening effects, modulates the amplitude and wavelength dependence of the contamination signal. |
| Spotless configuration | In the absence of active regions the contamination factor is unity and the transmission spectrum is strictly flat. | Even for a spotless star the transmission spectrum can show a mild positive or negative slope in Rp/R⋆(λ), driven solely by limb darkening and transit geometry. |
| Starspots | Unocculted cool spots always imprint a net increase in transit depth toward shorter wavelengths, i.e., a positive optical slope. | Cool spots tend to drive a positive slope, but the net trend can be weakened, canceled, or even reversed depending on the impact parameter. |
| Faculae | Unocculted faculae always reduce the transit depth toward shorter wavelengths, producing a negative optical slope. | Faculae tend to generate a negative slope, but the final wavelength dependence results from the competition between facular contrast and the geometry–induced trend, and can be substantially weaker or of opposite sign. |
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