1RXS J174320.1-042953: another polar with a red-shifted absorption component in emission line wings

Abstract

We present the results of a spectroscopic and multi-band photometric study of the magnetic cataclysmic variable 1RXS J174320.1-042953. Multi-band photometry confirms a periodic modulation with an orbital period of $P_{\rm orb}=0.0864 \pm 0.0001$ days. Using the estimated secondary mass of $\sim0.15\,\mathrm{M_\odot}$ and, the X-ray-based white dwarf mass of $\sim0.75\,\mathrm{M_\odot}$, we obtain values of $q\sim0.2$ and a system inclination of $47^\circ\pm10^\circ$. The optical spectra of 1RXS J174320.1-042953 are dominated by strong, complex, asymmetric, and highly variable single-peaked emission lines of the Balmer series, \ion{He}{i}, and \ion{He}{ii}, which are characteristic of polar-type magnetic cataclysmic variables. Doppler tomography reveals no evidence of a Keplerian accretion disc, supporting the classification of the system as a polar. The H$β$ and \ion{He}{ii} emission lines can be decomposed into at least two distinct components. The low-velocity components have semi-amplitudes of approximately 170 km s$^{-1}$ (H$β$) and 147 km s$^{-1}$ (\ion{He}{ii}), while the high-velocity components reach about 317 km s$^{-1}$ and 460 km s$^{-1}$, respectively. The low-velocity component is likely associated with the irradiated side of the secondary star facing the white dwarf and/or the vicinity of the L$_1$ point, whereas the high-velocity component is related to the accretion-stream structure. A redshifted absorption component in the emission-line wings is detected at orbital phases near $ϕ\approx 0.0$, reaching velocities up to $\sim1400$ km s$^{-1}$ and likely produced by accretion-stream material crossing the line of sight.