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Fig. 4

image

Top panel: α factor versus Teff for sample A exhibits consistency across a broad temperature range. The black line corresponds to the linear fit to values with an uncertainty within 2-σ of the mean of the distribution as shown by coloured squares (grey squares lie outside the 2-σ of the distribution). The histograms to the right side of the panel display the distribution of α values for two effective temperature regimes, using Teff = 5500 K as a threshold. Bottom panel: α factor versus Prot from McQuillan et al. (2014) for sample B shows a slight decrease in α with rotation period. The coloured segments indicate the mean of α for the different Prot ranges as indicated in Table 3. The histograms to the right of the panel indicate the distribution of α values for two rotation period regimens, using 21 d as a threshold. For both panels, the error bars represent 2-σ uncertainties of the α values over all Kepler quarters available for each star. The grey squares lie outside of a 2-σ of the distribution. The dashed red and green horizontal lines represent the α factor values in the extreme cases with all variability being due to spots (α = 0.21) and all due to faculae (α = 0.14), respectively1.

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