On the first δ Sct–roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars
Article
Article Title | On the first δ Sct–roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars |
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ERA Journal ID | 1074 |
Article Category | Article |
Authors | Murphy, Simon J. (Author), Saio, Hideyuki (Author), Takada-Hidai, Masahide (Author), Kurtz, Donald W. (Author), Shibahashi, Hiromoto (Author), Takata, Masao (Author) and Hey, Daniel R. (Author) |
Journal Title | Monthly Notices of the Royal Astronomical Society |
Journal Citation | 498 (3), pp. 4272-4286 |
Number of Pages | 15 |
Year | 2020 |
Publisher | Oxford University Press |
Place of Publication | United Kingdom |
ISSN | 0035-8711 |
1365-2966 | |
Digital Object Identifier (DOI) | https://doi.org/10.1093/mnras/staa2667 |
Web Address (URL) | https://academic.oup.com/mnras/article/498/3/4272/5901445 |
Abstract | Strong magnetic fields in chemically peculiar A-type (Ap) stars typically suppress low-overtone pressure modes (p modes) but allow high-overtone p modes to be driven. KIC 11296437 is the first star to show both. We obtained and analysed a Subaru spectrum, from which we show that KIC 11296437 has abundances similar to other magnetic Ap stars, and we estimate a mean magnetic field modulus of 2.8±0.5 kG. The same spectrum rules out a double-lined spectroscopic binary, and we use other techniques to rule out binarity over a wide parameter space, so the two pulsation types originate in one δ Sct--roAp hybrid pulsator. We construct stellar models depleted in helium and demonstrate that helium settling is second to magnetic damping in suppressing low-overtone p modes in Ap stars. We compute the magnetic damping effect for selected p and g modes, and find that modes with frequencies similar to the fundamental mode are driven for polar field strengths ≲4 kG, while other low-overtone p modes are driven for polar field strengths up to ∼1.5 kG. We find that the high-order g modes commonly observed in γ Dor stars are heavily damped by polar fields stronger than 1--4 kG, with the damping being stronger for higher radial orders. We therefore explain the observation that no magnetic Ap stars have been observed as γ Dor stars. We use our helium-depleted models to calculate the δ Sct instability strip for metallic-lined A (Am) stars, and find that driving from a Rosseland mean opacity bump at ∼5×104 K caused by the discontinuous H-ionization edge in bound-free opacity explains the observation of δ Sct pulsations in Am stars. |
Keywords | asteroseismology; stars: chemically peculiar; stars: interiors; stars: magnetic field; stars: oscillations; stars: variables: δ scuti; Astrophysics - Solar and Stellar Astrophysics |
ANZSRC Field of Research 2020 | 510109. Stellar astronomy and planetary systems |
Public Notes | This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. |
Byline Affiliations | University of Sydney |
Tohoku University, Japan | |
Tokai University, Japan | |
University of Central Lancashire, United Kingdom | |
University of Tokyo, Japan | |
Institution of Origin | University of Southern Queensland |
https://research.usq.edu.au/item/q73v1/on-the-first-sct-roap-hybrid-pulsator-and-the-stability-of-p-and-g-modes-in-chemically-peculiar-a-f-stars
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