GALEX and Optical Light Curves of WX LMi, SDSSJ103100.5+202832.2 and SDSSJ121209.31+013627.7

TL;DR

This study analyzes UV light curves of three low accretion rate polars, revealing phase-aligned UV variations linked to magnetic poles and suggesting hot spots with temperatures around 10,000-14,000K, with complex geometries.

Contribution

First detailed UV light curve analysis of low accretion rate polars showing phase-aligned UV variations and hot spot modeling.

Findings

UV variations match magnetic pole locations in optical

Hot spots have temperatures of 10,000-14,000K

Spot sizes differ between FUV and NUV wavelengths

Abstract

{\it GALEX} near ultraviolet (NUV) and far-ultraviolet (FUV) light curves of three extremely low accretion rate polars show distinct modulations in their UV light curves. While these three systems have a range of magnetic fields from 13 to 70 MG, and of late type secondaries (including a likely brown dwarf in SDSSJ121209.31+013627.7), the accretion rates are similar, and the UV observations imply some mechanism is operating to create enhanced emission zones on the white dwarf. The UV variations match in phase to the two magnetic poles viewed in the optical in WX LMi and to the single poles evident in the optical in SDSSJ1212109.31+013627.7 and SDSSJ103100.55+202832.2. Simple spot models of the UV light curves show that if hot spots are responsible for the UV variations, the temperatures are on the order of 10,000-14,000K. For the single pole systems, the size of the FUV spot must be smaller than the NUV and in all cases, the geometry is likely more complicated than a simple circular spot.