Astron. Astrophys. 326, 218-220 (1997)

1. Introduction

KPD 0253+5052 was detected during a survey for galactic-plane ultraviolet excess objects with an (U-B) color of about -1.0 by Downes & Margon (1983 ). They presented a medium resolution (15Å) optical spectrum, which shows distinct Zeeman split absorption lines of the Balmer series. The magnetic fieldstrength was determined to be MG . Later Achilleos & Wickramasinghe (1989 ) used this spectrum for their model spectrum calculations. They concluded that the optical spectrum of KPD 0253+5052 is well explained by a model with a magnetic dipole, which is offset in z-direction by 0.1-0.2 white dwarf radii, a dipole field strength of (12-14) MG , and a viewing angle of . Our phaseresolved spectropolarimetric data also point to a magnetic field geometry, which deviates from a centered dipole. Preliminary investigations favor an offset dipole with offsets not only along the dipole axis but also perpendicular to it. A detailed discussion of the determination of the field geometry by means of model spectra calculated with semiempirical and radiative transfer methods will be published in a forthcoming paper (Friedrich et al. 1997 ).

An effective temperature of K (Liebert et al. 1985 ) and 15000 K (Achilleos & Wickramasinghe 1989 ) was estimated from colors and model flux distributions, respectively.

KPD 0253+5052 was also investigated by means of white light polarimetry in the spectral range of 3200Å to 8600Å by Schmidt & Norsworthy (1991 ). Although the polarimetric variability could be confirmed by this observation, the poor sampling pattern led to several aliases in the power spectrum. Therefore only a relatively crude rotation period of h , derived from one night's data, was given.

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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