A SEARCH FOR VARIATIONS IN THE MAGNETIC-FIELD OF THE WHITE-DWARF PG-1658+441

Zeeman polarimetric observations of the magnetic white dwarf PG 1658+4 41 are presented. The mean longitudinal magnetic field is 668 +/- 16 k G, The parameters of the geometric magnetic-dipole model are constrain ed. The angle between the line of sight and the magnetic axis is 44 de grees +/- 9 degrees. The possibilities for sin unambiguous determinati on of all dipole parameters by measuring the transverse component of t he magnetic held using the pi and sigma components of spectral Lines a re explored; the results of the first such observations are reported. The observations of 1991 have revealed significant variability of the longitudinal magnetic field on a time scale of about half an hour and a 2.5-hr period of field variations. More recent observations show no magnetic variability. This behavior is discussed in terms of the prese nce of several magnetic spots at various latitudes on the surface of t his white dwarf.