Logo (Main page)

New data on the cpmplex field structure of chemically peculiar stars

Russian version  

    As a result of BTA observations of 23 chemically peculiar stars with strong magnetic fields, it was found that in 22 of them the longitudinal magnetic field, measured from the hydrogen line cores are considerably lower (by about 1/3) than the value measured from metal lines in the same spectra. (See Figures 1 and 2 - a star with a strong field 53 Cam is taken as an example).
    According to the theory of stellar atmospheres, the hydrogen line cores are formed in higher layers of the atmosphere than the metal lines. Therefore, the following interpretation appears the most natural: magnetic field decreases very steeply with height in the atmosphere with a gradient of two orders of magnitude larger than ought to be in the framework of the generally accepted dipole field model of these objects.
    We show that neither the methodical effects, nor the known features of CP stars (e.g., the spots of chemical elements on the surface) can fully create a false observed effect. The presence of a strong radial gradient of the magnetic field, averaged over the entire visible hemisphere of the star produces serious difficulties in the theoretical description - the star can not be stable in such fields. However, the observations show that the atmospheres of peculiar stars are very stable and constant. During the all the studies (for decades now), no spot migrations, flares, outflows of matter or other manifestations of instability were detected.
    Nevertheless, it is obvious that the dramatic overall field decrease in the lines, formed in higher atmospheric layers, discovered in the observations on the BTA, indicates a more complex structure of magnetic fields of chemically peculiar stars than considered up to date. New approaches need to be developed in order to interpret the data.
D.O.Kudryavtsev and I.I.Romanuyk (SAO)

Contact - I.I.Romanuyk

Fig.1. The figure shows the curves of the variability of the longitudinal field component Be with the rotational period phase for the star 53 Cam. It is evident that the field strength, measured from hydrogen lines core (red dots) and the amplitude of its variability is much lower than that measured from metal lines (blue dots).

Fig.2. The Zeeman spectrum of a star with a strong magnetic field, 53 Cam. Red shows the right circularly polarized spectrum, blue - the left circularly polarized one. At the top of the figure the behavior of the V-Stokes parameter with wavelength is demonstrated. It is clearly seen that the polarization signal in the hydrogen line core is much smaller than that obtained from the metal lines, the longitudinal magnetic field Be, measured along the metal lines is +3620±110 gauss, from the hydrogen line it amounts to +1570±550 gauss.