Polars Changing State: Multiwavelength Long‐Term Photometry and Spectroscopy of QS Telescopii, V834 Centauri, and BL Hydri

Abstract

ABSTRACTLong‐term optical and near‐infrared photometric and blue spectroscopic observations were obtained for QS Telescopii, V834 Centauri, and BL Hydri. The optical light curves of all three polars displayed large magnitude changes during our observations. These same high‐state and low‐state transitions were also apparent in near‐infrared JHK photometry, although with decreased amplitude. The color of the polar with respect to its state was examined and found not to be a good indicator of the instantaneous state. During transitions from low to high state, a nearly constant magnitude difference was observed in all three polars. This Δm value was found to be consistent with the level expected to occur if accretion onto the white dwarf reached the Eddington luminosity during the high state. The high‐state Balmer decrement was measured for each star and used to estimate that the temperature of the emission‐line–forming region was ∼12,000 K, with NH near 12.8 dex. No relationship between the Balmer emission‐line strength and the white dwarf magnetic field strength was seen, in contrast to a good correlation between these two parameters observed for UV emission lines.