Stellar and Solar Magnetic Activity Cycles

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The investigators will provide a better understanding of activity in cool stars on three essential timescales: activity-cycle (of order years), rotational (months), and short-term (days). The main effort is to continue the Solar-Stellar Spectrograph (SSS) project currently underway at Lowell Observatory. The SSS spectrograph is well suited for this task. It covers several important chromospheric diagnostic lines, including Ca II H and K and H alpha, as well as most of the optical spectrum from wavelengths 5000 to 9000 angstroms. It is a dedicated instrument, associated with Lowell Observatory's 1.1-meter John Hall telescope, which receives starlight from the telescope focal plane via a fiber-optic feed, but is also equipped with a solar "telescope" -- a raw fiber that sees the Sun as an unresolved disk. Sunlight and starlight are therefore recorded via the same optics and detectors -- a unique advantage. The spectra thus recorded can be studied in several ways. Time series observations of the emergent flux in spectral lines responsive to solar and stellar activity reveals the phase, amplitude, and morphology of activity cycles present. The SSS target list includes all stars brighter than visual magnitude 7.1 lying near the Sun's location on the main sequence (roughly spectral types F5 through K7, with emphasis between F8 and G8), as well as the Sun itself. Examination of seasonal variability reveals the degree of rotational modulation -- the change in emission level arising not from the activity cycle, but from the passage of active regions across the visible hemispheres. This provides insights regarding the degree of chromospheric activity that accompanies cycles of various amplitudes and morphologies. The spectrum-to-spectrum variability examined across a broad ensemble of related spectral lines, reveals changes in solar and stellar activity on both short and long timescales. This is a new method of interpreting solar and stellar activity, developed for this project that will be fully exploited in the proposed grant cycle.