Free Access
Volume 581, September 2015
Article Number A43
Number of page(s) 16
Section Stellar atmospheres
Published online 31 August 2015

Online material

Appendix A: Additional figures

thumbnail Fig. A.1

Same as Fig. 7 but for the F3V and the M0V star.

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thumbnail Fig. A.2

Same as Fig. 13, but for the F3V, K0V, K5V and M0V simulations.

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thumbnail Fig. A.3

Same as Fig. A.2, but for the Ti i line at 2223 nm and for the K- and M-star simulations.

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In Fig. 7 in Sect. 3.2, the magnetic limb brightening is given in the Johnson passbands UX, B, V, R, and I for the G2V star. Figure A.1 shows the limb brightening for the F3V and M0V simulations. The magnetic limb brightening is largest for the F3V star and becomes smaller towards lower effective temperatures as the faculae become less bright and less frequent (cf. Fig. 4).

In Fig. 13 in Sect. 4.3, disc-integrated profiles of the Fe i line at 617.3 nm are given for the G2V simulations without magnetic field (grey curves) and with B0 = 500 G (blue and red curves) where the magnetic field has been ignored for the spectral line synthesis for the red curves in order to disentangle the effect of the modified atmospheric structure from that of the Zeeman effect. Here, we give analogous plots for further simulations for the same spectral line (Fig. A.2) and for the Ti i line at 2223 nm (Fig. A.3).

As Fig. A.2 illustrates, the Fe i line is significantly affected by line weakening in the F3V star. Similar to the G2V-star case, the line is shifted to the red (in particular its wings) by the modified convective flows. The Zeeman effect has

a relatively small impact on the spectral line profile. In the K stars, the thermodynamic modifications seem less important than the Zeeman effect without rotation (left panels). In the rotating case (right panel), both effects are of similar magnitude. As they are of opposite sign, the apparent broadening of the line by the Zeeman effect is reduced by the modifications in the atmosphere structure. In the M stars (here, only the M0V is shown), the impact of the modified thermodynamics and flows is very small. For these stars, systematic errors in Stokes-I measurements of the magnetic field caused by differences in atmospheric structure between magnetised and unmagnetised regions will probably be the small.

Figure A.3 shows the same plots as Fig. A.2 but for the Ti i line and only for the K- and M-type stars. Although the line weakening is stronger for this line in the K-type stars (cf. Fig. 8), possibly leading to an underestimation of the unsigned average field from Stokes-I measurements, the general detection of magnetic field is probably more feasible in this line as the broadening due to the Zeeman effect is larger and leads to extended line wings. The line profiles from the M-star simulations are almost unaffected by the modifications of the thermodynamical atmosphere structure.

© ESO, 2015

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