Year: 2025
Type: article
Abstract: Context. Magnetic field investigations of Sun-like stars, using Zeeman splitting of non-polarised spectra, in the optical and H-band have found significantly different magnetic field strengths for the same stars, the cause of which is currently unknown. Aims. We aim to further investigate this issue by systematically analysing the magnetic field of ξ Boo A, a magnetically active G7 dwarf, using spectral lines at different wavelengths. Methods. We used polarised radiative transfer accounting for the departures from local thermodynamic equilibrium to generate synthetic spectra. To find the magnetic field strengths in the optical, H-band, and K-band, we employed MCMC sampling analysis of high-resolution spectra observed with the spectrographs CRIRES+, ESPaDOnS, NARVAL, and UVES. We also determine the formation depth of different lines by calculating the contribution functions for each line employed in the analysis. Results. We find that the magnetic field strength discrepancy between lines in the optical and H-band persists even when treating the different wavelength regions consistently. In addition, the magnetic measurements derived from the K-band appear to more closely align with the optical. The H-band appears to yield magnetic field strengths ∼0.4 kG with a statistically significant variation while the optical and K-band is stable at ∼0.6 kG for observations spanning about two decades. The contribution functions reveal that the optical lines form at a significantly higher altitude in the photosphere compared to those in the H- and K-band. Conclusions. While we find that the discrepancy remains, the variation of formation depths could indicate that the disagreement between magnetic field measurements obtained at different wavelengths is linked to the variation of the magnetic field along the line of sight and between different structures, such as star spots and faculae, in the stellar photosphere.
Authors: A. Hahlin, O. Kochukhov, P. Chaturvedi, E. Guenther, A. Hatzes, U. Heiter, A. Lavail, E. Nagel, N. Piskunov, K. Pouilly, A. D. Rains, A. Reiners, M. Rengel, U. Seeman, D. Shulyak
Institutions: Uppsala University, Tata Institute of Fundamental Research, Thüringer Landessternwarte Tautenburg, Centre National de la Recherche Scientifique, Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, University of Göttingen, University of Geneva, Max Planck Institute for Solar System Research, European Southern Observatory, Instituto de Astrofísica de Andalucía
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, Deutsche Forschungsgemeinschaft, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Bundesministerium für Bildung und Forschung, Knut och Alice Wallenbergs Stiftelse, Vetenskapsrådet, Uppsala Universitet, Agencia Estatal de Investigación
Awards: G1747646805, G1791431613, G3480869486, G3487714248, G4408153509, Verbundprojekt CRIRES+: A High Efficiency, Cross-dispersed High Resolution Infrared Spectrograph for the VLT. Teilprojekt 2, G4526231891, G463062595, Stellar accretion and magnetism in young binaries, Magnetic fields of red dwarf stars and their impact on terrestrial exoplanets, Stellar magnetic activity: a key factor for evolution, atmospheres and habitability of terrestrial exoplanets, G5519479261, G5894067328, G7084143925, Verbundprojekt 05A2017 - VLT-CRIRES: CRIRES+ - Ein hocheffizienter, spektral höchstauflösender kreuzdispergierter Infrarotspektrograph für das VLT der Europäischen Südsternwarte. Teilprojekt 2, G7434936867, Verbundprojekt CRIRES: Super-CRIRES: A High Efficiency, Cross-dispersed High Resolution Infrared Spectrograph for the VLT of the European Southern Observatory. Teilprojekt 2
OpenAlex ID: W6884519664
FWCI:
Cites:
Cited by:
Related to: