Year: 2024
Type: article
Abstract: Context. The A-type metallic-line (Am) stars are typically considered to be non-magnetic or to possess very weak sub-G magnetic fields. This view has been repeatedly challenged in the literature; most commonly for the bright hot Am star o Peg. Several studies claim to have detected 1–2 kG field of unknown topology in this object, possibly indicating a new process of magnetic-field generation in intermediate-mass stars. Aims. In this study, we revisit the evidence of a strong magnetic field in o Peg using new high-resolution spectropolarimetric observations and advanced spectral fitting techniques. Methods. We estimated the mean magnetic field strength in o Peg from the high-precision CRyogenic InfraRed Echelle Spectrograph (CRIRES+) measurement of near-infrared (NIR) sulphur lines. We modelled this observation with a polarised radiative transfer code, including treatment of the departures from local thermodynamic equilibrium. In addition, we used the least-squares deconvolution multi-line technique to derive longitudinal field measurements from archival optical spectropolarimetric observations of this star. Results. Our analysis of the NIR S I lines reveals no evidence of Zeeman broadening, ruling out magnetic field with a strength exceeding 260 G. This null result is compatible with the relative intensification of Fe II lines in the optical spectrum, taking into account blending and uncertain atomic parameters of the relevant diagnostic transitions. Longitudinal field measurements on three different nights also yield null results with a precision of 2 G. Conclusions. This study refutes the claims of kG-strength dipolar or tangled magnetic field in o Peg. This star therefore appears to be non-magnetic, with surface magnetic field characteristics no different from those of other Am stars.
Authors: O. Kochukhov, A. M. Amarsi, A. Lavail, H. L. Ruh, A. Hahlin, A. Hatzes, E. Nagel, N. Piskunov, K. Pouilly, A. Reiners, M. Rengel, U. Seemann, D. Shulyak
Institutions: Uppsala University, Centre National de la Recherche Scientifique, Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, University of Göttingen, Thüringer Landessternwarte Tautenburg, 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, Royal Swedish Academy of Sciences, Swedish National Space Agency, Bundesministerium für Bildung und Forschung, Vetenskapsrådet, Ministerio de Ciencia e Innovación, Uppsala Universitet, Agencia Estatal de Investigación
Awards: G121809054, G1753065040, G2262748287, G2627485041, G2660406951, G3179668627, Accurate compositions of Sun-like stars, G3487714248, Verbundprojekt CRIRES+: A High Efficiency, Cross-dispersed High Resolution Infrared Spectrograph for the VLT. Teilprojekt 2, 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, G5421974903, G5519479261, G7084143925, Verbundprojekt 05A2017 - VLT-CRIRES: CRIRES+ - Ein hocheffizienter, spektral höchstauflösender kreuzdispergierter Infrarotspektrograph für das VLT der Europäischen Südsternwarte. Teilprojekt 2, 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: W6921961312
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