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We investigate photometric variations due to stellar activity which inducesystematic radial-velocity errors (so-called "jitter") for the four targets inthe Hyades open cluster observed by the K2 mission (EPIC 210721261, EPIC210923016, EPIC 247122957, and EPIC 247783757). Applying Gaussian processregressions to the K2 light curves and the near-infrared (NIR) light curvesobserved with the IRSF 1.4-m telescope, we derive the wavelength dependences ofthe photometric signals due to stellar activity. To estimate the temporalvariations in the photometric variability amplitudes between the twoobservation periods of K2 and IRSF, separated by more than 2 years, we analyzea number of K2 targets in Hyades that have also been observed in Campaigns 4and 13 and find a representative variation rate over 2 years of 38%pm71%.Taking this temporal variation into account, we constrain projected sizes andtemperature contrast properties of the starspots in the stellar photosphere tobe approximately 10% and 0.95, respectively. These starspot properties caninduce relatively large differences in the variability amplitude over differentobservational passbands, and we find that radial-velocity jitter may be moresuppressed in the NIR than previously expected. Our result supports profits ofon-going exoplanet search projects that are attempting to detect or confirmyoung planets in open clusters via radial-velocity measurements in the NIR.

Wavelength Dependence of Activity-Induced Photometric Variations for Young Cool Stars in Hyades