LINE BROADENING IN THE PRESENCE OF STRONG MAGNETIC-FIELDS

In strong magnetic fields the degeneracy among atomic energy levels of the same principle quantum number in hydrogen is removed by Zeeman sp litting. We investigated the line broadening of such isolated transiti ons by means of stationary (i.e. d lambda/dB = 0) Balmer transitions. At the stationary points an absorption edge occurs in the flux spectru m. Two such absorption edges were observed with high spectral resoluti on in the spectrum of the magnetic white dwarf Grw+70 degrees 8247. Th e local line profiles are estimated by means of the flux gradient in t he edge and the actual position of the edge. (Local means at that area on the stellar sphere where the corresponding transition becomes stat ionary.) The line absorption starts 5-6 Angstrom beyond the correspond ing turn around points and altogether the local line widths are approx imately 20 Angstrom. Since in non-magnetic white dwarfs above 10000K, Stark effect is the dominating line broadening mechanism, we performed quantum mechanical calculations referring to hydrogen including both, (strong) magnetic fields and electric fields. According to the corres ponding electron density, the randomly fluctuating electric field, whi ch is caused by neighbouring free electron and ions, is typical 10(7) Vm(-1) in non-magnetic white dwarfs. Within some restrictions (e.g. on ly electric fields parallel to the magnetic field are yet investigated ) both, the commencement of line absorption 5-6 Angstrom beyond the st ationary wavelength and the overall width of approximately 20 Angstrom of the local line profile, cannot be explained by such randomly fluct uating electric fields, as far as the physical conditions (e.g. electr on density) of non-magnetic white dwarfs are applied. This, and the in fluence of other line broadening mechanisms, is discussed in some deta il.