On the excitation mechanism in roAp stars

Balmforth, N. J.; Cunha, M. S.; Dolez, N.; Gough, D. O.; Vauclair, S.

doi:10.1046/j.1365-8711.2001.04182.x

Cited by 172 publications

(241 citation statements)

References 36 publications

(42 reference statements)

Supporting

Mentioning

231

Contrasting

Order By: Relevance

“…It is clear that all the radial modes in the roAp frequency regime (1 mHz < v < 3 mHz) are damped. The results are similar to those found by Balmforth et al (2001) in their equatorial model. We also see an increased damping near the acoustic cut-off frequency.…”

Section: The Damping Ratessupporting

confidence: 91%

“…In particular, Balmforth et al (2001) demonstrated that the interplay between magnetism and convection in roAp stars can lead to excitation of some modes through driving in the polar regions. However, we expect that the atmospheric behaviour found in the present calculations will nonetheless be representative of more realistic models.…”

Section: Discussionmentioning

confidence: 99%

“…Balmforth et al (2001) showed that magnetic fields at the magnetic poles can suppress convection sufficiently to allow high-overtone pulsations to be excited…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Applications of Non-Adiabatic Radial Pulsation Equations to roAp Stars

Medupe¹,

Christensen‐Dalsgaard

Kurtz³

2002

International Astronomical Union Colloquium

View full text Add to dashboard Cite

Abstract. We apply a code that solves grey radial non-adiabatic pulsation equations with consistent treatment of radiative transfer to the roAp frequency regime. We find evidence for the existence of chromospheric modes at frequencies 2.5 mHz, 3.7 mHz, 4.6 mHz and 5.7 mHz in the equilibrium model we used. We also find that, since the oscillations are not adiabatic at the surfaces of roAp stars, better surface boundary conditions need to be considered in future studies.

show abstract

Section: The Damping Ratessupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Applications of Non-Adiabatic Radial Pulsation Equations to roAp Stars

Medupe¹,

Christensen‐Dalsgaard

Kurtz³

2002

International Astronomical Union Colloquium

View full text Add to dashboard Cite

show abstract

“…Since their discovery by Kurtz (1982), only 61 of these objects have been identified (see Smalley et al 2015 for a catalogue). The pulsations are high-overtone pressure modes (p modes) thought to be driven by the κ-mechanism acting in the H i ionisation zone (Balmforth et al 2001). However, Cunha et al (2013) ⋆ Based on service observations made with the WHT operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.…”

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.

View full text Add to dashboard Cite

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.

show abstract

“…The reason may be due to the presence of a magnetic field in this case. Extension of this kind of studies have been discussed for roAp stars by Balmforth et al 2001.…”

Section: The Stellar Casementioning

confidence: 99%

Thermohaline Convection in Main Sequence Stars

Vauclair

2008

Proc. IAU

Self Cite

View full text Add to dashboard Cite

Abstract. Thermohaline convection is a well known subject in oceanography, which has long been put aside in stellar physics. In the ocean, it occurs when warm salted layers sit on top of cool and less salted ones. Then the salted water rapidly diffuses downwards even in the presence of stabilizing temperature gradients, due to double diffusion between the falling blobs and their surroundings. A similar process may occur in stars in case of inverse µ-gradients in a thermally stabilized medium. Here we describe this process and some of its stellar applications.Keywords. stars:evolution, convection, stars: abundances What is thermohaline convection?Thermohaline convection is a wellknown process in oceanography : warm salted layers on the top of cool unsalted ones rapidly diffuse downwards even in the presence of stabilizing temperature gradients, due to the different diffusivities of heat and salt. When a warm salted blob falls down in cool fresh water, the heat diffuses out more quickly than the salt. The blob goes on falling due to its weight until it mixes with the surroundings. This leads to the so-called salt fingers (Figure 1). Thermohaline convection is a double diffusive convection. When the gradients are reversed, another kind of double diffusive convection occurs, which is generally referred to as semi convection.The condition for the salt fingers to develop is related to the density variations induced by temperature and salinity perturbations. Two important characteristic numbers are defined :• the density anomaly ratio∂ S ) T ,P while ∇T and ∇S are the average temperature and salinity gradients in the considered zone• the so-called "Lewis number"where κ S and κ T are the saline and thermal diffusivities while τ S and τ T are the saline and thermal diffusion time scales. The density gradient is unstable and overturns into dynamical convection for R ρ < 1 while the salt fingers grow for R ρ 1. On the other hand they cannot form if R ρ is larger than the ratio of the thermal to saline diffusivities τ −1 as in this case the salinity difference between the blobs and the surroundings is not large enough to overcome buoyancy.Salt fingers can grow if the following condition is satisfied :1 R ρ τ −1 (1.3)In the ocean, τ is typically 0.01. 97https://www.cambridge.org/core/terms. https://doi

show abstract

On the excitation mechanism in roAp stars

Cited by 172 publications

References 36 publications

Applications of Non-Adiabatic Radial Pulsation Equations to roAp Stars

Applications of Non-Adiabatic Radial Pulsation Equations to roAp Stars

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

Thermohaline Convection in Main Sequence Stars

Contact Info

Product

Resources

About