Nonradial oscillations in classical Cepheids: the problem revisited

Mulet-Marquis, C.; Glatzel, W.; Baraffe, I.; Winisdoerffer, Christophe

doi:10.1051/0004-6361:20066757

Cited by 19 publications

(21 citation statements)

References 9 publications

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“…However, linear pulsation calculations predict that in classical Cepheids all modes of < 4 should be heavily damped (Osaki 1977). This conclusion has recently been confirmed by new calculations of Mulet-Marquis et al (2007), who have found that all non-radial modes of < 5 should be damped. We note that this is a very different situation from that encountered in the RR Lyr models, where many modes of = 1, 2 are linearly excited (Dziembowski & Cassisi 1999).…”

Section: O N C L U S I O N Smentioning

confidence: 80%

Frequency analysis of Cepheids in the Large Magellanic Cloud: new types of classical Cepheid pulsators

Moskalik

Kołaczkowski

2009

Monthly Notices of the Royal Astronomical Society

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We have performed a detailed systematic search for multiperiodicity in the Population I Cepheids of the Large Magellanic Cloud. In this process, we have identified for the first time several new types of Cepheid pulsational behaviour. We have found two triple‐mode Cepheids pulsating simultaneously in the first three radial overtones. In 9 per cent of the first overtone (FO) Cepheids, we have detected weak but well‐resolved secondary periodicities. They appear either very close to the primary pulsation frequency or at a much higher frequency with a characteristic period ratio of 0.60–0.64. In either case, the secondary periodicities must correspond to non‐radial modes of oscillation. This result presents a major challenge to the theory of stellar pulsations, which predicts that such modes should not be excited in Cepheid variables. Non‐radial modes have also been found in three of the fundamental first overtone (FU/FO) double‐mode Cepheids, but no such oscillations have been detected in single‐mode Cepheids pulsating in the FU mode. In 19 per cent of double‐mode Cepheids pulsating in the first two radial overtones (FO/SO type), we have detected a Blazhko‐type periodic modulation of amplitudes and phases. Both modes are modulated with a common period, which is always longer than 700 d. Variations of the two amplitudes are anticorrelated, and maximum of one amplitude always coincides with minimum of the other. We have compared observations of modulated FO/SO Cepheids with predictions of theoretical models of the Blazhko effect, showing that the currently most popular models cannot account for properties of these stars. We propose that the Blazhko effect in FO/SO Cepheids can be explained by a non‐stationary resonant interaction of one of the radial modes with another, perhaps non‐radial, mode of oscillations.

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Section: O N C L U S I O N Smentioning

confidence: 80%

Frequency analysis of Cepheids in the Large Magellanic Cloud: new types of classical Cepheid pulsators

Moskalik

Kołaczkowski

2009

Monthly Notices of the Royal Astronomical Society

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“…To avoid the propagation of non-radial modes (Mulet-Marquis et al 2007) as much as possible, we chose a "small" box with an aspect ratio L x /L z = 1. If we refer to classical hydrodynamic instabilities, the critical horizontal wavelength λ crit from which instability develops is, in general, a bit larger than the vertical extent L z of the domain.…”

Section: Resultsmentioning

confidence: 99%

Direct numerical simulations of the $\mathsf{\kappa}$-mechanism

Gastine¹,

Dintrans²

2008

A&A

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Context. We present a purely-radiative hydrodynamical model of the κ-mechanism that sustains radial oscillations in Cepheid variables. Aims. We determine the physical conditions favourable for the κ-mechanism to occur inside a layer, with a configurable conductivityhollow. We complete nonlinear direct numerical simulations (DNS) that initiate from these most favourable conditions. Methods. We compare the results of a linear-stability analysis, applied to radial modes using a spectral solver, and a DNS, which is developed from a high-order finite difference code. Results. We find that by changing the location and shape of the hollow, we can generate well-defined instability strips. For a given position in the layer, the amplitude and width of the hollow appear to be key parameters to vary to attain unstable modes driven by the κ-mechanism. The DNS, starting from the favourable conditions, confirm both the growth rates and the structures of linearly-unstable modes. Nonlinear saturation is produced by intricate couplings between excited fundamental mode and higher damped overtones.

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“…Their growth rates are at least an order of magnitude lower than for radial modes (Van Hoolst, Dziembowski & Kawaler 1998). Calculations for classical Cepheids (which are more massive) indicate that non-radial low degree modes are not excited (Mulet-Marquis et al 2007).…”

Section: Rv Tau Stars With Modulation Periods Closementioning

confidence: 88%

Diversity of dynamical phenomena in type II Cepheids of the OGLE collection

Smolec

Moskalik

Plachy

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We have analysed the photometry of 924 type II Cepheids from the Galactic bulge observed by the Optical Gravitational Lensing Experiment. Our goal was to detect and analyse various dynamical phenomena, including, e.g. multi-mode pulsation, perioddoubled pulsation, period-k pulsation, or quasi-periodic modulation of pulsation. First examples of double-mode BL Her-type stars, pulsating simultaneously in the fundamental and first overtone modes are reported. Two double-mode pulsators are not isolated cases however, but form an extension of recently identified class of long-period RRd stars. Period doubling effect was detected in three BL Her-type stars: two were identified previously and one is a new discovery. Through identification of numerous period-doubled W Vir stars we show that the appearance of the period doubling effect, and hence the transition towards RV Tau class, is a smooth process that starts at pulsation periods slightly above 15 d. Interchange of the deep and shallow pulsation cycles is identified in tens of RV Tau variables. One RV Tau star is a strong candidate for period-4 pulsation. Quasi-periodic modulation of pulsation in all sub-classes of type II Cepheids is reported for the first time. Modulation was detected in 16 BL Her, 9 W Vir and in 7 RV Tau stars. In the last case, modulation is the most likely scenario, but two other scenarios, excitation of non-radial modes, or period-4 pulsation, can also account for the observed pulsation pattern. Irregular changes of pulsation amplitude and period on various time-scales are common in all subgroups of type II Cepheids.

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Nonradial oscillations in classical Cepheids: the problem revisited

Cited by 19 publications

References 9 publications

Frequency analysis of Cepheids in the Large Magellanic Cloud: new types of classical Cepheid pulsators

Frequency analysis of Cepheids in the Large Magellanic Cloud: new types of classical Cepheid pulsators

Direct numerical simulations of the $\mathsf{\kappa}$-mechanism

Diversity of dynamical phenomena in type II Cepheids of the OGLE collection

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