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Starspots, plages, and activity cycles cause radial velocity variations thatcan either mimic planets or hide their existence. To verify the authenticity ofnewly discovered planets, observers may search for periodicity in spectroscopicactivity indices such as Ca H & K and H$\alpha$, then mask out any Dopplersignals that match the activity period or its harmonics. However, not everyspectrograph includes Ca H & K, and redder activity indicators are needed forplanet searches around low-mass stars. Here we show how new activity indicatorscan be identified by correlating spectral line depths with a well-knownactivity index. We apply our correlation methods to archival HARPS spectra of$\epsilon$ Eri and $\alpha$ Cen B and use the results from both stars togenerate a master list of activity-sensitive lines whose core fluxes areperiodic at the star's rotation period. Our newly discovered activityindicators can in turn be used as benchmarks to extend the list of knownactivity-sensitive lines toward the infrared or UV. With recent improvements inspectrograph illumination stabilization, wavelength calibration, and telluriccorrection, stellar activity is now the biggest noise source in planetsearches. Our suite of $> 40$ activity-sensitive lines is a first step towardallowing planet hunters to access all the information about spots, plages, andactivity cycles contained in each spectrum.

the astronomical journal

New Methods for Finding Activity-Sensitive Spectral Lines: Combined  Visual Identification and an Automated Pipeline Find a Set of 40 Activity  Indicators