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Characterising the surface magnetic fields of T Tauri stars with high-resolution near-infrared spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy. European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.ORCID iD: 0000-0003-3061-4591
European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany.
2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A99Article in journal (Refereed) Published
Abstract [en]

Aims: In this paper, we aim to characterise the surface magnetic fields of a sample of eight T Tauri stars from high-resolution near-infrared spectroscopy. Some stars in our sample are known to be magnetic from previous spectroscopic or spectropolarimetric studies. Our goals are firstly to apply Zeeman broadening modelling to T Tauri stars with high-resolution data, secondly to expand the sample of stars with measured surface magnetic field strengths, thirdly to investigate possible rotational or long-term magnetic variability by comparing spectral time series of given targets, and fourthly to compare the magnetic field modulus < B > tracing small-scale magnetic fields to those of large-scale magnetic fields derived by Stokes V Zeeman Doppler Imaging (ZDI) studies.

Methods: We modelled the Zeeman broadening of magnetically sensitive spectral lines in the near-infrared K-band from high-resolution spectra by using magnetic spectrum synthesis based on realistic model atmospheres and by using different descriptions of the surface magnetic field. We developped a Bayesian framework that selects the complexity of the magnetic field prescription based on the information contained in the data.

Results: We obtain individual magnetic field measurements for each star in our sample using four different models. We find that the Bayesian Model 4 performs best in the range of magnetic fields measured on the sample (from 1.5 kG to 4.4 kG). We do not detect a strong rotational variation of < B > with a mean peak-to-peak variation of 0.3 kG. Our confidence intervals are of the same order of magnitude, which suggests that the Zeeman broadening is produced by a small-scale magnetic field homogeneously distributed over stellar surfaces. A comparison of our results with mean large-scale magnetic field measurements from Stokes V ZDI show different fractions of mean field strength being recovered, from 25-42% for relatively simple poloidal axisymmetric field topologies to 2-11% for more complex fields.

Place, publisher, year, edition, pages
EDP SCIENCES S A , 2019. Vol. 630, article id A99
Keywords [en]
stars: pre-main sequence, stars: magnetic field, line: profiles
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-395836DOI: 10.1051/0004-6361/201935695ISI: 000487978300006OAI: oai:DiVA.org:uu-395836DiVA, id: diva2:1365598
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council, 621-2014-5720Swedish National Space Board, 185/14Swedish National Space Board, 137/17Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved

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Lavail, AlexisKochukhov, Oleg

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