Rapidly Oscillating Ap Stars

Kurtz, D. W.

doi:10.1146/annurev.astro.28.1.607

Cited by 69 publications

(102 citation statements)

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“…In many cases low degree means = 1 (e.g. Kurtz 1990). However, this interpretation is not unique as underlined by previous authors (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…Asteroseismological observations of roAp stars over the last twenty years (Kurtz 1990) have raised the question of the understanding of the oscillations in a star when a global and permanent magnetic field is present. Non-radial oscillations of roAp stars have periods between 4 and 16 min.…”

Section: Introductionmentioning

confidence: 99%

“…The observed photometric variations indicate that they are likely high-order, low-degree p-modes, perturbed by some physical process related to the presence of a permanent magnetic field, which is known to be mainly dipolar at the surface of these stars. One of the arguments in favor of this interpretation is that the oscillations can be interpreted with the so-called "oblique rotator" model of Kurtz (1990) which considers the oscillations as essentially = 1 modes aligned with the dipolar magnetic field of the star. Recently, Bigot & Dziembowski (2002) noticed that this alignment need not be strict and that the pulsation axis lies somewhere between the rotation and magnetic axis.…”

Section: Introductionmentioning

confidence: 99%

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Oscillations of magnetic stars: I. Axisymmetric shear Alfvén modes of a spherical shell in a dipolar magnetic field

Rincon

Rieutord

2003

A&A

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Abstract.We carry out an investigation of axisymmetric shear Alfvén waves in a spherical layer of an incompressible resistive fluid when a strong dipolar magnetic field is applied. A decomposition on the spherical harmonics base is used to compute the eigenmodes of the system. Numerical results show that the least-damped Alfvénic modes naturally concentrate near the magnetic polar axis. These modes also show internal shear/magnetic layers associated with resonant field lines. This model is useful when modelling planetary cores sustaining a dynamo, magnetic neutron stars or to the magnetic layer of roAp stars. In this latter case, it shows that shear Alfvén waves provide a good instance of non-perturbative effects due to the strong magnetic field of such stars.

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“…In many cases low degree means = 1 (e.g. Kurtz 1990). However, this interpretation is not unique as underlined by previous authors (e.g.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Oscillations of magnetic stars: I. Axisymmetric shear Alfvén modes of a spherical shell in a dipolar magnetic field

Rincon

Rieutord

2003

A&A

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“…Some Ap stars also exhibit photometric variability in the period range of ∼5−20 min (high-overtone, low-degree, and non-radial pulsation modes). These stars are known as rapidly A&A 581, A138 (2015) oscillating Ap (roAp) stars (Kurtz 1990) and are not the subject of the present paper.…”

Section: Introductionmentioning

confidence: 99%

A search for photometric variability in magnetic chemically peculiar stars using ASAS-3 data

Bernhard

Hümmerich

Otero

et al. 2015

A&A

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Context. The (magnetic) chemically peculiar (CP) stars of the upper main sequence are well-suited laboratories for investigating the influence of magnetic fields on the stellar surface because they produce abundance inhomogeneities (spots), which results in photometric variability that is explained in terms of the oblique rotator model. CP stars exhibiting this phenomenon are normally classified as α 2 Canum Venaticorum (ACV) variables. It is important to increase the sample of known rotational periods among CP stars by discovering new ACV variables. An increased sample size will contribute to the understanding of the CP stars' evolution in time. Aims. We aim at discovering new ACV variables in the public data of the third phase of the All Sky Automated Survey (ASAS-3). Furthermore, by analysis of the available photometric data, we intend to derive rotational periods of the stars. Methods. The ASAS-3 data were cross-correlated with the Catalogue of Ap, HgMn, and Am stars in order to analyse the light curves of bona fide CP and related stars. The light curves were downloaded and cleaned of outliers and data points with a flag indicating bad quality. Promising candidates showing a larger scatter than observed for constant stars in the corresponding magnitude range were searched for periodic signals using a standard Fourier technique. Objects exhibiting periodic signals well above the noise level were considered and visually inspected, whereas borderline cases were rejected. Results. In total, we found 323 variables, from which 246 are reported here for the first time, and 77 were probably wrongly classified before. The observed variability pattern of most stars is in accordance with an ACV classification. For some cases, it is difficult to distinguish between the light curves of double-waved ACVs and the variability induced by orbital motion (ellipsoidal variables/eclipsing variables), especially for objects exhibiting very small amplitudes and/or significant scatter in their light curves. Thus, some eclipsing or rotating ellipsoidal variables might be present. However, we are confident that the given periods are the correct ones. There seems to be a possible weak correlation between the rotational period and colour, in the sense that cooler magnetic CP stars rotate more slowly. However, this correlation seems to disappear when correcting for the interstellar reddening. Conclusions. The next steps have to include a compilation of all available rotational periods from the literature and a detailed investigation of the astrophysical parameters of these stars. This includes a determination of the individual masses, luminosities, ages, and inclination angles. However, this information cannot be straightforwardly determined from photometric data alone.

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“…The Ap stars are hydrogen-burning stars with strong magnetic fields. Rapid oscillations (relative to the spin frequency) have been observed in the subclass of stars known as RoAp stars (Kurtz 1990). These oscillations have been identified as high-overtone p-modes.…”

Section: Introductionmentioning

confidence: 99%

Normal Modes of Rotating Magnetic Stars

Morsink

Rezania

2002

ApJ

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We investigate the effect of a magnetic field on the global oscillation modes of a rotating fluid star in the magnetohydrodynamic approximation. We present general equations for the modification of any type of fluid mode due to a general magnetic field that is not aligned with the star's spin axis. In the case of any internal dipole magnetic field, we derive the equations for the frequency corrections to the r-modes. We solve for the frequency correction explicitly for the case when the internal dipole field is force-free, including the uniform density case. In the weak-field limit, the spatial form of the r-mode velocity perturbation is unchanged, but the magnitude of the frequency in the rotating frame increases.

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Rapidly Oscillating Ap Stars

Cited by 69 publications

References 0 publications

Oscillations of magnetic stars: I. Axisymmetric shear Alfvén modes of a spherical shell in a dipolar magnetic field

Oscillations of magnetic stars: I. Axisymmetric shear Alfvén modes of a spherical shell in a dipolar magnetic field

A search for photometric variability in magnetic chemically peculiar stars using ASAS-3 data

Normal Modes of Rotating Magnetic Stars

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