On the first δSct-roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars
| Autor: | Masao Takata, D. W. Kurtz, Daniel R. Hey, Hiromoto Shibahashi, Masahide Takada-Hidai, Hideyuki Saio, Simon J. Murphy |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
oscillations [stars]
variables: δscuti [stars] Opacity Field (physics) FOS: Physical sciences F500 Astrophysics asteroseismology 01 natural sciences Asteroseismology chemically peculiar [stars] 0103 physical sciences Astrophysics::Solar and Stellar Astrophysics 010303 astronomy & astrophysics Solar and Stellar Astrophysics (astro-ph.SR) Astrophysics::Galaxy Astrophysics Physics interiors [stars] 010308 nuclear & particles physics Astronomy and Astrophysics Magnetic field Stars Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science magnetic field [stars] Magnetic damping Polar Astrophysics::Earth and Planetary Astrophysics Instability strip |
| Zdroj: | Murphy, S J, Saio, H, Takada-Hidai, M, Kurtz, D W, Shibahashi, H, Takata, M & Hey, D R 2020, ' On the first δSct-roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars ', Monthly Notices of the Royal Astronomical Society, vol. 498, no. 3, pp. 4272-4286 . https://doi.org/10.1093/mnras/staa2667 |
| ISSN: | 1129-6437 0035-8711 |
| Popis: | 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 $2.8\pm0.5$ 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 $\delta$ 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 $\lesssim4$ kG, while other low-overtone p modes are driven for polar field strengths up to $\sim$1.5 kG. We find that the high-order g modes commonly observed in $\gamma$ 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 $\gamma$ Dor stars. We use our helium-depleted models to calculate the $\delta$ Sct instability strip for metallic-lined A (Am) stars, and find that driving from a Rosseland mean opacity bump at $\sim$$5\times10^4$ K caused by the discontinuous H-ionization edge in bound-free opacity explains the observation of $\delta$ Sct pulsations in Am stars. Comment: Accepted for publication in MNRAS |
| Databáze: | OpenAIRE |
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