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تسجيل مستخدم جديدThe pecular magnetic field morphology of the white dwarf WD 1953-011: evidence for a large-scale magnetic flux tube?
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We present and interpret new spectropolarimetric observations of the magnetic white dwarf WD 1953-011. Circular polarization and intensity spectra of the H$alpha$ spectral line demonstrate the presence of two-component magnetic field in the photosphere of this star. The geometry consists of a weak, large scale component, and a strong, localized component. Analyzing the rotationally modulated low-field component, we establish a rotation period $P_{rot} = 1.4480 pm 0.0001$ days. Modeling the measured magnetic observables, we find that the low-field component can be described by the superposition of a dipole and quadrupole. According to the best-fit model, the inclination of the stellar rotation axis with respect to the line of sight is $i approx 20^circ$, and the angle between the rotation axis and the dipolar axis is $beta approx 10^circ$. The dipole strength at the pole is about 180 kG, and the quadrupolar strength is about 230 kG. These data suggest a fossil origin of the low-field component. In contrast, the strong-field component exhibits a peculiar, localized structure (``magnetic spot) that confirms the conclusions of Maxted and co-workers. The mean field modulus of the spot ($|B_{spot}| = 520 pm 7$ kG) together with its variable longitudinal magnetic field having a maximum of about +400 kG make it difficult to describe it naturally as a high-order component of the stars global poloidal field. Instead, we suggest that the observed strong-field region has a geometry similar to a magnetic flux tube.
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