= Stellar activity
<Stellar activity> is variable magnetic behaviour in a <star>'s outer layers, including <starspots>, atmospheric heating and eruptive phenomena. Rotation carries regions of different brightness and line shape across the visible disc. Their changing contribution alters both the stellar <light curve> and the apparent <Doppler shift>, even when the <star>'s centre of <mass> has no corresponding orbital motion.
This makes <stellar activity> both a subject of study and a source of <stellar noise> in <exoplanet> searches. A changing <stellar spectral-line bisector> tests whether a line is deforming rather than simply translating in <wavelength>. Simultaneous brightness measurements supply another diagnostic. Actual observing times matter because an <activity-period alias in radial-velocity sampling> can place an activity-related signal at a misleading period.
Back to article page
