Unstable standard candles. Periodic light-curve modulation in fundamental mode classical Cepheids

Smolec, R.

doi:10.1093/mnras/stx679

Cited by 16 publications

(12 citation statements)

References 37 publications

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“…Interestingly, in the majority of stars, a peak at the modulation frequency is also observed. Very similar frequency spectrum patterns were detected in fundamental mode classical Cepheids by Smolec (2017).…”

Section: Modulation Of Pulsation In Type II Cepheidssupporting

confidence: 70%

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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Section: Modulation Of Pulsation In Type II Cepheidssupporting

confidence: 70%

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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“…Such variations are found across the HR diagram, in giant stars, such as Cepheids (e.g. Derekas et al 2017;Smolec 2017), RR Lyrae (e.g. Benkő et al 2019), and Mira-like stars (e.g.…”

Section: Introductionmentioning

confidence: 94%

Modelling stochastic signatures in classical pulsators

Avelino

Cunha

Chaplin

2020

Monthly Notices of the Royal Astronomical Society

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We consider the impact of stochastic perturbations on otherwise coherent oscillations of classical pulsators. The resulting dynamics are modelled by a driven damped harmonic oscillator subject to either an external or an internal forcing and white noise velocity fluctuations. We characterize the phase and relative amplitude variations using analytical and numerical tools. When the forcing is internal the phase variation displays a random walk behaviour and a red noise power spectrum with a ragged erratic appearance. We determine the dependence of the root mean square phase and relative amplitude variations (σ ∆ϕ and σ ∆A/A , respectively) on the amplitude of the stochastic perturbations, the damping constant η, and the total observation time t obs for this case, under the assumption that the relative amplitude variations remain small, showing that σ ∆ϕ increases with t 1/2 obs becoming much larger than σ ∆A/A for t obs η −1 . In the case of an external forcing the phase and relative amplitude variations remain of the same order, independent of the observing time. In the case of an internal forcing, we find that σ ∆ϕ does not depend on η. Hence, the damping time cannot be inferred from fitting the power of the signal, as done for solar-like pulsators, but the amplitude of the stochastic perturbations may be constrained from the observations. Our results imply that, given sufficient time, the variation of the phase associated to the stochastic perturbations in internally driven classical pulsators will become sufficiently large to be probed observationally.

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“…F-mode Cepheids appear more stable, but lowamplitude periodic modulation was reported in the only Fmode Cepheid in the Kepler field, V1154 Cyg (Derekas et al 2012;Kanev et al 2015;Derekas et al 2017). Finally, Smolec (2017) reported low-amplitude periodic modulation of pulsation in 51 F-mode Cepheids in the Magellanic Clouds, showing that for pulsation periods around 10 days the phenomenon may be quite common. Cycle-to-cycle variation of the radial velocities hinting at modulation were also reported (eg., Anderson 2014;Anderson 2016Anderson , 2018.…”

Section: Introductionmentioning

confidence: 95%

Frequency analysis of OGLE-IV photometry for classical Cepheids in Galactic fields: non-radial modes and modulations

Rathour

Smolec

Netzel

2021

Monthly Notices of the Royal Astronomical Society

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We analyse photometry of ∼2000 Galactic Cepheids available in the OGLE Collection of Variable Stars. We analyse both Galactic disk and Galactic bulge fields; stars classified both as single- and multi-periodic. Our goal was to search for additional low-amplitude variability. We extend the sample of multi-mode radial pulsators by identifying ten new candidates for double-mode and six new candidates for triple-mode pulsation. In the first overtone OGLE sample, we found twelve Cepheids with additional periodicity having period ratio Px/P1O ∈ (0.60, 0.65). These periodicities do not correspond to any other radial mode. While such variables are abundant in the Magellanic Clouds, only one Cepheid of this class was known in the Galaxy before our analysis. Comparing our sample with the Magellanic Cloud Cepheids we note a systematic shift towards longer pulsation periods for more metal rich Galactic stars. Moreover in eleven stars we find one more type of additional variability, with characteristic frequencies close to half of that reported in the group with (0.60, 0.65) period ratios. Two out of the above inventory show simultaneous presence of both signals. Most likely, origin of these signals is connected to excitation of non-radial pulsation modes. We report three Cepheids with low-amplitude periodic modulation of pulsation: two stars are single-mode fundamental and first overtone Cepheids and one is a double-mode Cepheid pulsating simultaneously in fundamental and in first overtone modes. Only the former mode is modulated. It is a first detection of periodic modulation of pulsation in this type of double-mode Cepheids.

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Unstable standard candles. Periodic light-curve modulation in fundamental mode classical Cepheids

Cited by 16 publications

References 37 publications

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

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

Modelling stochastic signatures in classical pulsators

Frequency analysis of OGLE-IV photometry for classical Cepheids in Galactic fields: non-radial modes and modulations

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