Infrared Spectroscopy of the Secondary Star in ST Leonis Minoris: Implications for Evolution and High‐/Low‐State Behavior in Cataclysmic Variables

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Abstract
We present time-resolved K-band spectra of the polar ST LMi obtained during a time of zero mass transfer. Analysis of these first ever phase-resolved observations of an uncontaminated cataclysmic variable (CV) secondary star show no evidence for ellipsoidal variations, affects due to gravity darkening, or irradiation of the L1 point. The data indicate instead that the secondary star has a phase-dependent temperature including the existence of a localized cooler region centered near orbital phase 0.8. We examine a few possible explanations for such phenomena and conclude that the most likely cause is due to starspot activity. The location of the critical Roche surface calculated with respect to the physical stellar surface of the secondary star is shown to change during the lifetime of a cataclysmic variable and thereby effect its evolution. Previous suggestions of low-state behavior being caused by a starspot placed at L1 are shown not to work. However, an active chromosphere on the secondary star is both consistent with the current observations and may naturally explain high-/low-state behavior in CVs.

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