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Diagnostic of stellar magnetic fields with cumulative circular polarisation profiles
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
2015 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 580, A39Article in journal (Refereed) Published
Abstract [en]

Information about stellar magnetic field topologies is obtained primarily from hi.gh-resolution circular polarisation (Stokes V) observations. Because of their generally complex morphologies, the stellar Stokes V profiles are usually interpreted with elaborate inversion techniques such as Zeeman Doppler imaging (ZDI). Here we further develop a new method for interpreting circular polarisation signatures in spectral lines using cumulative Stokes V profiles (anti-derivative of Stokes V. This method is complimentary to ZDI and can be applied to validate the inversion results or when the available observational data are insufficient for an inversion. Based on the rigorous treatment of polarised line formation in the weak-field regime, we show that, for rapidly rotating stars, the cumulative Stokes V profiles contain information about the spatially resolved longitudinal magnetic field density. Rotational modulation of these profiles can be employed for a simple, qualitative characterisation of the stellar magnetic field topologies. We apply this diagnostic method to the archival observations of the weak-line T Tauri star V410 Tau and Bp He-strong star HD 37776. We show that the magnetic field in V410 Tau is dominated by an azimuthal component, in agreement with the ZDI map that we recover from the same data set. For HD 37776 the cumulative Stokes V profile variation indicates the presence of multiple regions of positive and negative field polarity. This behaviour agrees with the ZDI results, but contradicts the popular hypothesis that the magnetic field of this star is dominated by an axisymmetric quadrupolar component.

Place, publisher, year, edition, pages
2015. Vol. 580, A39
Keyword [en]
magnetic fields, stars: activity, stars: magnetic field, stars: individual: V410 Tau, stars: individual: HD 37776
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:uu:diva-263460DOI: 10.1051/0004-6361/201526318ISI: 000360020200039OAI: oai:DiVA.org:uu-263460DiVA: diva2:860965
Knut and Alice Wallenberg FoundationSwedish Research CouncilSwedish National Space Board
Available from: 2015-10-14 Created: 2015-09-30 Last updated: 2015-10-14Bibliographically approved

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Kochukhov, Oleg
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