Frequency splitting in AP stars

Dziembowski, W. A.; Goode, P. R.

doi:10.1086/184542

Cited by 86 publications

(71 citation statements)

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“…The pulsation axis of these stars is inclined to the rotation axis, and closely aligned with the magnetic one, leading to the oblique pulsator model (Kurtz 1982;Shibahashi & Saio 1985b,a;Dziembowski & Goode 1985;Shibahashi & Takata 1993;Takata & Shibahashi 1994, 1995Bigot & Dziembowski 2002;Bigot & Kurtz 2011). Oblique pulsation allows the pulsation modes to be viewed from varying aspects over the rotation cycle of the star, giving constraints on the pulsation geometry that are not available for any other type of pulsating star (other than the Sun, which is uniquely resolved).…”

Section: Introductionmentioning

confidence: 99%

HD 24355 observed by theKepler K2mission: a rapidly oscillating Ap star pulsating in a distorted quadrupole mode

Holdsworth

Kurtz

Smalley

et al. 2016

Mon. Not. R. Astron. Soc.

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We present an analysis of the first Kepler K2 mission observations of a rapidly oscillating Ap (roAp) star, HD 24355 (V = 9.65). The star was discovered in SuperWASP broadband photometry with a frequency of 224.31 d −1 (2596.18 µHz; P = 6.4 min) and an amplitude of 1.51 mmag, with later spectroscopic analysis of low-resolution spectra showing HD 24355 to be an A5 Vp SrEu star. The high precision K2 data allow us to identify 13 rotationally split sidelobes to the main pulsation frequency of HD 24355. This number of sidelobes combined with an unusual rotational phase variation show this star to be the most distorted quadrupole roAp pulsator yet observed. In modelling this star, we are able to reproduce well the amplitude modulation of the pulsation, and find a close match to the unusual phase variations. We show this star to have a pulsation frequency higher than the critical cut-off frequency. This is currently the only roAp star observed with the Kepler spacecraft in Short Cadence mode that has a photometric amplitude detectable from the ground, thus allowing comparison between the mmag amplitude ground-based targets and the µmag spaced-based discoveries. No further pulsation modes are identified in the K2 data, showing this star to be a single-mode pulsator.

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Section: Introductionmentioning

confidence: 99%

HD 24355 observed by theKepler K2mission: a rapidly oscillating Ap star pulsating in a distorted quadrupole mode

Holdsworth

Kurtz

Smalley

et al. 2016

Mon. Not. R. Astron. Soc.

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“…The preferential excitation of this mode might be provided by some selective properties of the excitation mechanism itself (Dolez & Gough 1982, Shibahashi 1983, Dziembowski 1984, Dziembowski & Goode 1985, Dolez et al 1988). An alternative explanation related with the magnetically-induced lateral inhomogeneity of the acoustic cutoff frequency, was considered by Shibahashi (1991).…”

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confidence: 99%

“…It was first demonstrated by Roberts & Soward (1983) and Campbell & Papaloizou (1986), that wave transformation in the magnetic atmosphere can provide a significant dissipation of the acoustic mode energy. For acoustic waves which propagate almost vertically near the surface, the generation of Alfvenic waves requires the magnetic field to have both a horizontal and vertical component.…”

mentioning

confidence: 99%

“…These simple qualitative arguments suggest that I = 1, m = 0 mode with maximum amplitudes in polar regions might suffer smaller energy losses than t = 1, m = 1 mode. Our quantitative estimates are based on the perturbation analysis developed by Roberts & Soward (1983). Their result for the relative loss of the acoustic energy flux in the polytropic atmosphere of index n can be written as…”

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confidence: 99%

“…Note that the perturbation analysis of Roberts & Soward (1983) breaks down when B , < B " i.e., near the magnetic equator. The correct analysis remains to be developed; it is reasonable to expect, however, that a more accurate description of R(6) in the equator region will not change the qualitative conclusions.…”

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confidence: 99%

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