Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001a%26a...374..265w&link_type=abstract
Astronomy and Astrophysics, v.374, p.265-279 (2001)
Astronomy and Astrophysics
Astrophysics
53
Line: Profiles, Polarisation, Stars: Magnetic Fields, Stars: Atmospheres
Scientific paper
With the aim of establishing a benchmark for the detailed calculation of the polarised line profiles of magnetic stars, we describe an intercomparison of LTE Stokes profiles calculated using three independent, state-of-the-art magnetic spectrum synthesis codes: Cossam, Invers10 and Zeeman2. We find, upon establishing a homogeneous basis for the calculations (identical definitions of the Stokes parameters and the magnetic and stellar reference frames, identical input model stellar atmosphere, identical input atomic data, and identical chemical element abundances and magnetic field distributions), that local and disc-integrated Stokes IQUV profiles of Fe II lambda 4923.9 calculated using the three codes agree very well. For the illustrative case of disc-integrated profiles calculated for abundance log nFe/ntot=-4.60, dipole magnetic field intensity Bd=5 kG, and projected rotational velocity v_esin i=20 km s-1, Stokes I profiles (depth ~ 40% of the continuum flux Ic) agree to within about 0.05% rms of Ic, Stokes V profiles (full amplitude ~ 10%) to within about 0.02% rms of Ic, and Stokes Q and U profiles (full amplitudes ~ 2%) at the sub-0.01% rms level. These differences are sufficiently small so as to allow for congruent interpretation of the best spectropolarimetric data available, as well as for any data likely to become available during the near future. This indicates that uncertainties in modeling Stokes profiles result overwhelmingly from uncertainties in input atomic and physical data, especially the state and structure of model stellar atmospheres.
Bagnulo Stefano
Kochukhov Oleg
Landstreet John Darlington
Piskunov Nicolai
Stift Martin J.
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