Issue |
A&A
Volume 453, Number 2, July II 2006
|
|
---|---|---|
Page(s) | 699 - 715 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361:20054353 | |
Published online | 16 June 2006 |
The diagnosis of the mean quadratic magnetic field of Ap stars
European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: gmathys@eso.org
Received:
13
October
2005
Accepted:
12
January
2006
Aims.We assess the validity of the method of determination of the mean quadratic field modulus and we explore its limits.
Methods.We analyse high spectral resolution, high signal-to-noise spectra of a few Ap stars, and of a superficially normal main-sequence A star, recorded over a broad wavelength range with EMMI at the NTT.
Results.We introduce a revised form of the regression equation
describing the dependence of the second-order moment of the line
profiles about their centre, in natural light, on various
parameters of the corresponding transitions. We show that
interpretation of the observed dependences allows one to determine the
mean quadratic magnetic field modulus of the studied stars, and their
v . We explain why the contributions to the
quadratic field of the mean square magnetic field modulus and of the
mean square longitudinal field cannot in general be disentangled.
For those stars of the sample that have resolved magnetically
split lines, we show that the derived values of the quadratic
field are mostly consistent with the values of the mean
longitudinal magnetic field and of the mean magnetic field modulus at
the observed phase. However there are some hints that they may
occasionally slightly underestimate the actual field. This suggests
that the method is unlikely to yield spurious field detections.
In addition, we illustrate the importance for this type of analyses
of using, as far as possible, samples of lines of a single ion,
and to specify in the presentation of the results which ion was used.
Conclusions.The results presented in this paper lend strong support to the validity of the quadratic field diagnostic method to obtain a realistic quantitative characterisation of the magnetic fields Ap and related stars.
Key words: stars: chemically peculiar / stars: magnetic fields / methods: data analysis / line: profiles
© ESO, 2006
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