Cyclotron spectroscopy of HU Aquarii

Abstract

Abstract. We present the results of a combined analysis of low-resolution spectroscopy and high-speed optical photometry of the bright eclipsing polar HU Aqr, obtained in its high accretion state. Cyclotron harmonic emission in a field of B 34 MG became evident and could be traced through the whole optical bright phase. The cyclotron harmonics display an asymmetric motion as a function of phase which requires a certain forward tilt of the magnetic field lines in the emission region. The optical bright phase is more extended than the bright phase in soft X-rays suggesting a more extended emission region. Also, ingress into and egress from the optical eclipse last much longer in the optical than at X-ray wavelengths. These observations require the existence of an accretion arc with total extent of about 20• . The soft X-ray accretion spot is located at the far end of the arc, where the bulk of matter is accreted. The arc is likely to be more extended than the foot-line of field lines connecting to the ballistic accretion stream in a dipolar geometry. This together with the required tilt of the accreting field lines suggest a more complex magnetic geometry than a simple dipole.

XMM-Newtonand optical observations of the eclipsing polar CSS081231:071126+440405

“…This is opposite to what is observed in other polars where the highest redshift was observed when the accretion spot was approaching the limb of the WD (see e.g. Schwope et al 2003;Burwitz et al 1996, for the cases of HU Aqr and RX J0453.4−4213), and it is contrary to what is expected for plasma emission from a point-like, isothermal accretion region. As a result, this observation could be evidence of an extended cyclotron-emitting region with successively self-eclipsing parts belonging to regions of slightly different field strengths.…”

“…10) using the models in a series of papers (see e.g. Campbell et al 2008;Schwope et al 2003, and references therein).…”

Doppler tomography of the asynchronous polar BY Camelopardalis

“…been slow. Early follow-up observations after the identification with the HEAO1 scanning modulation collimator experiment (Remillard et al 1986) revealed properties common to the class of AM Herculis binaries: variations at optical and X-ray wavelengths with a tentative spin period of 200 min, strong circular polarisation (mostly of positive sign), optical low states down to V ≥ 17 m as measured from Harvard plates and the detection of cyclotron humps consistent with a magnetic field strength of 40.8 MG (Cropper et al 1989) or 28 MG (Schwope 1991).…”

“…Data of highest resolution and sufficient signal-to-noise can resolve the Roche lobe in Doppler coordinates (Schwarz et al 2002) and reveal asymmetric illumination of the secondary (Schwope et al 1997;Watson et al 2003). (b) Emission from the stream leaving the secondary star through the L 1 -point, seen as a cometary tail parallel to the v x axis.…”

“…(b) Emission from the stream leaving the secondary star through the L 1 -point, seen as a cometary tail parallel to the v x axis. Good examples where this horizontal stream is the dominant emitting source are the maps of the eclipsing polars HU Aqr (high state, Schwope et al 1997) and V1309 Ori (Staude et al 2001). The exact location in the tomogram should follow that of a ballistic trajectory (Lubow & Shu 1975) and is determined by the systems mass ratio only.…”