Doppler-Zeeman mapping of the rapidly rotating magnetic CP star HD 37776

We present the results of our analysis of magnetic-field configuration and abundance anomalies on the surface of the rapidly rotating, chemically pecu liar helium-strong variable B2 V star HD 37776 with unresolved Zeeman compo nents of spectral lines. Simultaneous inversion of the observed Stokes I an d V profiles, which realizes the method of Doppler-Zeeman mapping [1], has been applied for the first time. Spectroscopic observations were carried ou t with the Main stellar spectrograph of the 6-m Special Astrophysical Obser vatory telescope equipped with a Zeeman analyzer and CCD array, which allow ed spectra in right- and left-hand circularly polarized light to be taken s imultaneously at a signal-to-noise ratio S/N greater than or equal to 200 [ 2]. The profile width of winged spectral lines (reaching 5 Angstrom) is det ermined by Zeeman line splitting; however, the observed Zeeman components a re blurred and unresolved because of the rapid stellar rotation. When solvi ng the inverse problem, we sought for the magnetic-field configuration in t he form of a combination of arbitrarily oriented dipole, quadrupole, and oc tupole placed at the stellar center. The observed Stokes I and V profiles f or eight spectral lines of He, O II, Al III, Si III, and Fe III averaged ov er the visible stellar surface were used as input data. We constructed a mo del of the magnetic field from the condition of coincidence of magnetic map s obtained from different lines of different chemical elements and from the condition of a minimum profile residual. This model is a combination of ce ntered coaxial dipole and quadrupole with the dominant quadrupole component at 30 degrees < i < 50 degrees, beta = 40 degrees, and a maximum surface f ield strength H-s = 60 kG. A comparison of our abundance maps with the held configuration shows that the He concentration is at a maximum in the regio ns of maximum radial field, while the maximum concentrations of O, Al, Si, and Fe coincide with the regions of maximum tangential field. (C) 2000 MAIK "Nauka/Interperiodica".