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Transmission spectra probe exoplanetary atmospheres, but they can also bestrongly affected by heterogeneities in host star photospheres through thetransit light source effect. Here we build upon our recent study of the effectsof unocculted spots and faculae on M-dwarf transmission spectra, extending theanalysis to FGK dwarfs. Using a suite of rotating model photospheres, weexplore spot and facula covering fractions for varying activity levels and theassociated stellar contamination spectra. Relative to M dwarfs, we find thatthe typical variabilities of FGK dwarfs imply lower spot covering fractions,though they generally increase with later spectral types, from $\sim 0.1\%$ forF dwarfs to 2-4$\%$ for late-K dwarfs. While the stellar contamination spectraare considerably weaker than those for typical M dwarfs, we find that typicallyactive G and K dwarfs produce visual slopes that are detectable inhigh-precision transmission spectra. We examine line offsets at H$\alpha$ andthe Na and K doublets and find that unocculted faculae in K dwarfs canappreciably alter transit depths around the Na D doublet. We find thatband-averaged transit depth offsets at molecular bands for CH$_{4}$, CO,CO$_{2}$, H$_{2}$O, N$_{2}$O, O$_{2}$, and O$_{3}$ are not detectable fortypically active FGK dwarfs, though stellar TiO/VO features are potentiallydetectable for typically active late-K dwarfs. Generally, this analysis showsthat inactive FGK dwarfs do not produce detectable stellar contaminationfeatures in transmission spectra, though active FGK host stars can produce suchfeatures and care is warranted in interpreting transmission spectra from thesesystems.

The Transit Light Source Effect II: The Impact of Stellar Heterogeneity on Transmission Spectra of Planets Orbiting Broadly Sun-like Stars