Pulsations in the atmosphere of the roAp star HD 24712 - II. Theoretical models

Saio, Hideyuki; Ryabchikova, T. A.; Sachkov, Mikhail

doi:10.1111/j.1365-2966.2009.16235.x

Cited by 31 publications

(43 citation statements)

References 38 publications

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“…To put this result into context, the value found for the large frequency separation is very similar to that of the well-studied roAp star HD 24712 (see, e.g., Saio et al 2010). Moreover, the frequency region of pulsation is also approximately the same.…”

Section: The Pulsation Of Hd 134214 -A Twin Of Hd 24712?mentioning

confidence: 55%

“…Secondly, current models suggest that for a star like HD 24712, the amplitude of the radiative flux variation due to pulsation has its maximum at the magnetic poles, regardless of the dominant value of l (see Fig. 12 in Saio et al 2010). Therefore, the observed amplitudes should not have a large dependency on l, assuming comparable intrinsic amplitudes.…”

Section: The Pulsation Of Hd 134214 -A Twin Of Hd 24712?mentioning

confidence: 99%

“…comm. ) using the method outlined in Saio et al (2010). The model parameters are M = 1.65 M , log R = 0.2694, log T eff = 3.8584, log L = 0.9250, X = 0.70, Z = 0.02 and B p = 4.1 kG.…”

Section: The Pulsation Of Hd 134214 -A Twin Of Hd 24712?mentioning

confidence: 99%

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MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214

Gruberbauer

Huber²,

Kuschnig³

et al. 2011

A&A

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We report on the analysis of high-precision space-based photometry of the roAp (rapidly oscillating Ap) stars HD 9289, HD 99563, and HD 134214. All three stars were observed by the MOST satellite for more than 25 days, allowing unprecedented views of their pulsation. We find previously unknown candidate frequencies in all three stars. We establish the rotation period of HD 9289 (8.5 d) for the first time and show that the star is pulsating in two modes that show different mode geometries. We present a detailed analysis of HD 99563's mode multiplet and find a new candidate frequency that appears to be independent of the previously known mode. Finally, we report on 11 detected pulsation frequencies in HD 134214, nine of which have never before been detected in photometry, and three of which are completely new detections. Thanks to the unprecedentedly small frequency uncertainties, the p-mode spectrum of HD 134214 can be seen to have a well-defined large frequency spacing similar to the well-studied roAp star HD 24712 (HR 1217).

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Section: The Pulsation Of Hd 134214 -A Twin Of Hd 24712?mentioning

confidence: 55%

Section: The Pulsation Of Hd 134214 -A Twin Of Hd 24712?mentioning

confidence: 99%

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MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214

Gruberbauer

Huber²,

Kuschnig³

et al. 2011

A&A

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“…Obviously, some of the well studied roAp stars are far from the instability region, and their oscillation frequencies seem to be above the acoustic cutoff frequency. In fact, pulsation phase variations in the atmosphere of some of these stars indicate the presence of running waves (e.g., HR 1217, Saio et al 2010;HD 134214, Saio et al 2012). We still do not fully understand the excitation of high-order p modes in roAp stars.…”

Section: Excitation Of High-order P Modes In Roap Starsmentioning

confidence: 99%

Pulsation of magnetic stars

Saio

2013

Proc. IAU

Self Cite

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Abstract. Some Ap stars with strong magnetic fields pulsate in high-order p modes; they are called roAp (rapidly oscillating Ap) stars. The p-mode frequencies are modified by the magnetic fields. Although the large frequency separation is hardly affected, small separations are modified considerably. The magnetic field also affects the latitudinal amplitude distribution on the surface. We discuss the property of axisymmetric p-mode oscillations in roAp stars.Keywords. stars: magnetic fields, stars: oscillations Observational properties of roAp starsThe group of rapidly oscillating Ap (roAp) stars was discovered by Kurtz (1982) more than thirty years ago (it consisted of five members then). Since then, the number of known roAp stars has increased to around 40-50 (still increasing); a recent list is given by Kurtz et al. (2006). They are chemically-peculiar main-sequence stars having masses ranging from ∼ 1.5 to ∼ 2 M ⊙ , and effective temperatures from ∼ 6400 to ∼ 8400 K. On the H-R diagram (Fig 1, left panel), they lie in and around the δ Sct instability strip. However, the oscillation frequencies are much higher than those of δ Sct variables as seen in the right panel of Fig. 1, which plots dominant frequencies of roAp and δ Sct stars with respect to the effective temperature. The roAp stars pulsate in high-order p modes whose frequencies range from ∼ 1 to ∼ 3 mHz (periods; ∼ 6 − 21 min), while δ Sct stars

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“…HD 24712 is thus one of twelve roAp stars discovered so far that oscillate above about 2 mHz and, as such, constitutes a good test case for the pulsation excitation models. Even if the observed frequencies can be fitted relatively well with theoretical frequencies for model stars whose positions on the Hertzsprung-Russell (HR) diagram are close to the position of HD 24712 (Cunha 2001;Cunha et al 2003;Saio et al 2010), no excited oscillation modes with frequencies appropriate for HD 24712 can be found. All the modes are damped, and the κ-mechanism in the hydrogen ionization area that is generally invoked to explain the excitation of pulsation modes in roAp stars (Balmforth et al 2001;Cunha 2002) seems to be too weak to be able to excite supercritical high-order p modes.…”

Section: Introductionmentioning

confidence: 99%

The fundamental parameters of the roAp star HD 24712

Perraut

Brandão

Cunha

et al. 2016

A&A

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Context. There is still a debate about the nature of the mechanism that causes the pulsation excitation of the rapidly oscillating Ap stars that oscillate above the highest theoretically acoustic frequency. HD 24712 is a good test case for such a study because it is bright, its parallax accurately determined, and its frequency spectrum is well known. Aims. Visible long-baseline interferometry is a unique technique for measuring accurate angular diameters of targets as small as the brightest roAp stars, and thus estimating accurate radii by a method as independent as possible of atmosphere models. Methods. We used the visible spectrograph VEGA at the CHARA long-baseline optical array to observe HD 24712, and we derived its limb-darkened diameter. We also estimated its bolometric flux from spectroscopic data in the literature and determined its radius, luminosity, and effective temperature. Results. We determined a limb-darkened angular diameter of 0.335 ± 0.009 mas for HD 24712 and derived a radius of R = 1.772 ± 0.057 R , a luminosity of L = 7.2 ± 1.8 L , and an effective temperature of T eff = 7235 ± 280 K, which is in very close agreement with the values provided by the self-consistent stratified model developed for this star. We used these fundamental parameters to set HD 24712 in the Hertzsprung-Russell diagram. Its position is marginally consistent with the region where high radial order modes are predicted to be excited by the κ-mechanism. Conclusions. We conclude that oscillations in this star are most likely not driven by the κ-mechanism.

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Pulsations in the atmosphere of the roAp star HD 24712 - II. Theoretical models

Cited by 31 publications

References 38 publications

MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214

MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214

Pulsation of magnetic stars

The fundamental parameters of the roAp star HD 24712

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