| Issue |
A&A
Volume 689, September 2024
|
|
|---|---|---|
| Article Number | A36 | |
| Number of page(s) | 11 | |
| Section | Stellar structure and evolution | |
| DOI | https://doi.org/10.1051/0004-6361/202450543 | |
| Published online | 30 August 2024 | |
A conclusive non-detection of magnetic field in the Am star o Peg with high-precision near-infrared spectroscopy⋆
1
Department of Physics and Astronomy, Uppsala University, Box 516 75120 Uppsala, Sweden
2
Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, IRAP/UMR 5277, 14 Avenue Edouard Belin, 31400 Toulouse, France
3
Institut für Astrophysik und Geophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
4
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
5
Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
6
Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
7
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
8
Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
Received:
29
April
2024
Accepted:
21
May
2024
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.
Key words: stars: chemically peculiar / stars: early-type / stars: magnetic field / stars: individual: o Peg
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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