Nonradial Pulsations in Classical Cepheids of The Magellanic Clouds

Moskalik, P.; Kołaczkowski, Z.; Mizerski, Tomasz

doi:10.1017/s0252921100011210

Cited by 13 publications

(30 citation statements)

References 3 publications

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“…5 we do not expect instability for l = 3 and 4. We can thus conclude that if low-degree p-modes with l ≤ 2 were necessary to explain the observations of Moskalik et al (2004), they cannot be attributed to a linear instability of these modes. Rather, other effects, such as, e.g., nonlinear mode coupling, have to be invoked for an explanation of their excitation.…”

Section: Discussionmentioning

confidence: 82%

“…The stellar model whose parameters are thought to match the properties of the Cepheid observed by Moskalik et al (2004) is found to be unstable both with respect to radial and nonradial perturbations. Following modes up to l = 500, we find the following unstable modes: the fundamental p-mode for l = 0 and between 9 ≤ l ≤ 368, the first overtone for l = 0 and between 6 ≤ l ≤ 13, and the second overtone for l = 0, 5, and 6.…”

Section: Discussionmentioning

confidence: 90%

“…2 and 3 for a specific Cepheid model. Since our work is motivated by the observations of Moskalik et al (2004), we selected a model that could describe the properties of one of the observed LMC targets where secondary periodicities were detected. The observed Cepheid, LMC-SC2-208897, is a first overtone pulsator with a period of P 1 = 2.42 days and absolute magnitude M V ∼ −3.2.…”

Section: Comparing the Two Methodsmentioning

confidence: 99%

“…More recently, Moskalik et al (2004) found low-amplitude secondary periodicities in a few first overtone Cepheids of the Large Magellanic Cloud, with frequencies close to the unstable, radial, first overtone. These newly discovered periodicities were interpreted as nonradial modes.…”

Section: Introductionmentioning

confidence: 97%

“…But unfortunately, these observations have not been confirmed yet. The observations of Moskalik et al (2004) are based on photometrical data, implying that if nonradial modes are indeed detected, they must be low-degree modes. According to Osaki (1977), however, these modes should be stable.…”

Section: Introductionmentioning

confidence: 99%

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Nonradial oscillations in classical Cepheids: the problem revisited

Mulet-Marquis

Glatzel²,

Baraffe

et al. 2007

A&A

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Context. We analyse the presence of nonradial oscillations in Cepheids, a problem that has not been theoretically revised since the work of Dziembowski (1977, Acta Astron., 27, 95) and Osaki (1977, PASJ, 29, 235). Our analysis is motivated by a work of Moskalik et al. (2004, ASPC, 310, 498), which reports the detection of low-amplitude periodicities in a few Cepheids of the large Magellanic cloud. These newly discovered periodicities were interpreted as nonradial modes. Aims. Based on linear nonadiabatic stability analysis, our goal is to reanalyse the presence and stability of nonradial modes, taking into account improvement in the main input physics required for the modelling of Cepheids. Methods. We compare the results obtained from two different numerical methods used to solve the set of differential equations: a matrix method and the Ricatti method. Results. We show the limitation of the matrix method for finding low-order p-modes (l < 6), because of their dual character in evolved stars such as Cepheids. For higher order p-modes, we find excellent agreement between the two methods. Conclusions. No nonradial instability is found below l = 5, whereas many unstable nonradial modes exist for higher orders. We also find that nonradial modes remain unstable, even at hotter effective temperatures than the blue edge of the Cepheid instability strip, where no radial pulsations are expected.

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Section: Discussionmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 90%

Section: Comparing the Two Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Nonradial oscillations in classical Cepheids: the problem revisited

Mulet-Marquis

Glatzel²,

Baraffe

et al. 2007

A&A

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Multi-periodic Oscillations in Cepheids and RR Lyrae-Type Stars

Moskalik¹

2012

Astrophysics and Space Science Proceedings

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Classical Cepheids and RR Lyrae-type stars are usually considered to be textbook examples of purely radial, strictly periodic pulsators. Not all the variables, however, conform to this simple picture. In this review I discuss different forms of multi-periodicity observed in Cepheids and RR Lyrae stars, including Blazhko effect and various types of radial and nonradial multi-mode oscillations. Blazhko effectBlazhko effect is a slow, nearly periodic modulation of the pulsation amplitude and phase. It is observed in many RR Lyrae stars, both of RRab (fundamental mode) and of RRc type (overtone pulsators). The modulation period can range from a few days to over 2500 days [44]. The phenomenon was discovered over a century ago ([4, 40]) and was the first identified departure from the "strictly periodic" paradigm.Blazhko effect has been detected in various stellar systems, including Magellanic Clouds [48,49], galactic bulge [44] and several globular clusters (e.g [30]). By no mean it is a rare phenomenon. Modulation occurs in ∼ 50% of the field RRab stars ([18, 2]). The incidence rates reported in other RR Lyrae populations are up to 4 times lower, perhaps because of lower quality of the available data. In most stellar systems the incidence rate of Blazhko modulation is higher in RRab stars than in RRc stars. The opposite is true only in the globular cluster Omega Centauri, where unusually high fraction (38%) of modulated RRc stars has been found [30].Blazhko effect is usually associated with the RR Lyrae variables, but it can also occur (albeit rarely) in classical Cepheids. A modulation with a period of ∼ 1200 days is observed in a single-mode overtone Cepheid V473 Lyr [7]. The amplitude and phase modulation has also been recently discovered in a number of LMC double-mode Cepheids [28]. These latter variables will be discussed in Sec. 2.2.

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