A search for kilogauss magnetic fields in white dwarfs and hot subdwarf stars

We present new results of a survey for weak magnetic fields among DA white dwarfs, including some brighter hot subdwarf stars. We have detected variable circular polarization in the H alpha line of the hot subdwarf star Feige 34 (spectroscopic type: sdO). From these data, we estimate that the longitudinal magnetic field of this star varies from -1.1 +/- 3.2 to + 9.6 +/- 2.6 kG, with a mean of about + 5 kG and a period longer than 2 hr. In this study, we also confirm the magnetic nature of white dwarf WD 1105-048, found earlier in a study by Aznar Cuadrado and coworkers, and present upper limits of kilogauss longitudinal magnetic fields of the five brightest DA white dwarfs. Our data support the finding of Aznar Cuadrado and coworkers that similar to 25% of white dwarfs have kilogauss magnetic fields. This frequency also confirms results of early estimates obtained using the magnetic field function of white dwarfs (Fabrika & Valyavin).