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 in the Hα 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 the inner Lagrangian point, L1. Furthermore, we report a new "extreme low state" of the system at V ~ 18.5 mag. 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 Hα component seen in the low state. The second is an additional redshifted 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 6275 Å, which has been previously identified as a Zeeman σ^- absorption component of Hα. This feature appears at just those phases when the accretion pole region is most directly visible and most nearly face-on to the observer.

Key words: binaries: close; stars: activity; stars: general; stars: individual (ST Leonis Minoris); stars: magnetic fields

^* Based on observations from the WIYN Observatory, which is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatory.
^** Based on observations obtained with the Mayall 4 m telescope at Kitt Peak National Observatory, a division of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.

Print publication: Issue 4 (2007 April)
Received 2006 November 6, accepted for publication 2006 December 9
Published 2007 March 12