A Photometric and Spectroscopic Study of the Cataclysmic Variable ST LMi during 2005-2006

Abstract

We present orbit-resolved spectroscopic and photometric observations of the polar ST LMi during its recent low and high states. In the low state spectra, we report the presence of blue and red satellites to the H-alpha emission line; the velocities and visibility of the satellites vary with phase. This behavior is similar to emission line profile variations recently reported in the low state of AM Her, which were interpreted as being due to magnetically-confined gas motions in large loops near the secondary. Our low-state spectroscopy of ST LMi is discussed in terms of extreme chromospheric activity on the secondary star. Concurrent photometry indicates that occasional low-level accretion may be present, as well as cool regions on the secondary near L1. Furthermore, we report a new ``extreme low-state'' of the system at V~18.5mag. Our orbital high-state spectroscopy reveals changes in the emission line profiles with orbital phases that are similar to those reported by earlier high-state studies. The complicated emission line profiles generally consist of two main components. The first has radial velocity variations identical to that of the major emission H-alpha component seen in the low state. The second is an additional red-shifted component appearing at the phases of maximum visibility of the accreting column of the white dwarf; it is interpreted as being due to infall velocities on the accreting magnetic pole of the white dwarf. At the opposite phases, an extended blue emission wing appears on the emission line profiles. We confirm the presence of a broad absorption feature near 6275Ang which has been previously identified as Zeeman sigma(-) absorption component to H-alpha. This feature appears at just those phases when the accretion pole region is mostly directly visible and most nearly face-on to the observer.