New results in RR Lyrae modeling: Convective cycles, additional modes and more

Molnár, L.; Kollath, Zoltán; Szabo, Robert M.; Plachy, E.

doi:10.1002/asna.201211807

Cited by 9 publications

(6 citation statements)

References 27 publications

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“…The reason of its absence could be that it is in fact a non-radial mode close to the frequency of the second overtone. It can also be hypothesized that the excited mode exists in a parameter space that 1D models have avoided so far, similar to the discovery of period doubling and the low-amplitude first overtone in some RRab models (Molnár et al 2012). We note, however, that the mode was not detected during the extensive survey of those models.…”

Section: Additional Modes In Rrab Starssupporting

confidence: 70%

An RR Lyrae family portrait: 33 stars observed in Pisces with K2-E2

Molnár¹,

Szabo²,

Moskalik³

et al. 2015

Mon. Not. R. Astron. Soc.

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A detailed analysis is presented of 33 RR Lyrae stars in Pisces observed with the Kepler space telescope over the 8.9-day long K2 Two-Wheel Concept Engineering Test. The sample includes not only fundamental-mode and first overtone (RRab and RRc) stars but the first two double-mode (RRd) stars that Kepler detected and the only modulated first-overtone star ever observed from space so far. The precision of the extracted K2 light curves made it possible to detect low-amplitude additional modes in all subtypes. All RRd and non-modulated RRc stars show the additional mode at P X /P 1 ∼ 0.61 that was detected in previous space-based photometric measurements. A periodicity longer than the fundamental mode was tentatively identified in one RRab star that might belong to a gravity mode. We determined the photometric [Fe/H] values for all fundamental-mode stars and provide the preliminary results of our efforts to fit the double-mode stars with non-linear hydrodynamic pulsation models. The results from this short test run indicate that the K2 mission will be, and has started to be, an ideal tool to expand our knowledge about RR Lyrae stars. As a by-product of the target search and analysis, we identified 165 bona-fide double-mode RR Lyrae stars from the Catalina Sky Survey observations throughout the sky, 130 of which are new discoveries.

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Section: Additional Modes In Rrab Starssupporting

confidence: 70%

An RR Lyrae family portrait: 33 stars observed in Pisces with K2-E2

Molnár¹,

Szabo²,

Moskalik³

et al. 2015

Mon. Not. R. Astron. Soc.

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“…Finally, non-linear hydrodynamic modelling of secondovertone Cepheids will be vitally important to determine whether mode resonances occur in these stars. Recent advancements in 1D pulsation codes revealed that both RR Lyrae and BL Herculis (short period Type II Cepheid) models may exhibit multimode pulsation, mode resonances, chaos, and small-amplitude modulation (Kolláth et al 2011;Molnár et al 2012;Plachy, Kolláth & Molnár 2013;Smolec & Moskalik 2012. If mode interactions can be identified in second-overtone Cepheid models, they will undoubtedly support the case of the mode resonance model, and will point towards a unified model for the Blazhko effect in Cepheid and RR Lyrae stars.…”

Section: Discussionmentioning

confidence: 94%

V473 Lyrae, a unique second-overtone Cepheid with two modulation cycles

Molnár¹,

Szabados²

2014

Monthly Notices of the Royal Astronomical Society

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V473 Lyrae is the only Galactic Cepheid with confirmed periodic amplitude and phase variations similar to the Blazhko effect observed in RR Lyrae stars. We collected all available photometric data and some radial velocity measurements to investigate the nature of the modulation. The comparison of the photometric and radial velocity amplitudes confirmed that the star pulsates in the second overtone. The extensive data set, spanning more than 40 years, allowed us to detect a secondary modulation cycle with a period of approximately 5300 days or 14.5 years. The secondary variations can be detected in the period of the primary modulation, as well.Phenomenologically, the light variations are analogous to the Blazhko effect. To find a physical link, we calculated linear hydrodynamic models to search for potential mode resonances that could drive the modulation and found two viable half-integer (n:2) and three n:4 resonances between the second overtone and other modes. If any of these resonances will be confirmed by non-linear models, it may confirm the mode resonance model, a common mechanism that can drive modulations both in RR Lyrae and Cepheid stars.

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“…However, beside the period-doubled ones, chaotic hydrodynamic models were also found (Plachy, Molnár & Kolláth 2013). Further analysis showed that in these models the first overtone is also present and it is a crucial component in the occurrence of chaos (Molnár et al 2012a). Molnár et al (2012b) also argued that these three radial modes are present in the star RR Lyr.…”

Section: Introductionmentioning

confidence: 91%

Low-dimensional chaos in RR Lyrae models

Plachy

Kollath

Molnár

2013

Monthly Notices of the Royal Astronomical Society

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The recent precise photometric observations and successes of the modelling efforts transformed our picture of the pulsation of RR Lyrae stars. The discovery of additional frequencies and the period doubling phenomenon revealed that a significant interaction may occur between pulsational modes. The signs of irregularities were detected both in observed light curves and hydrodynamic calculations.In this paper we present the analysis of four peculiar hydrodynamic model solutions. All four solutions were found to be chaotic. The fractal (Lyapunov) dimensions of their attractors were calculated to be ∼2.2. We also investigated possible resonances between the fundamental mode and the first overtone in the dynamical neighbourhood of these models. The most important is the 6:8 resonance that was also detected in the Kepler observations of RR Lyrae itself. These results reveal that the investigation of chaotic models is important in discovering and understanding resonances in RR Lyrae stars.

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New results in RR Lyrae modeling: Convective cycles, additional modes and more

Cited by 9 publications

References 27 publications

An RR Lyrae family portrait: 33 stars observed in Pisces with K2-E2

An RR Lyrae family portrait: 33 stars observed in Pisces with K2-E2

V473 Lyrae, a unique second-overtone Cepheid with two modulation cycles

Low-dimensional chaos in RR Lyrae models

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