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

Rathour, Rajeev Singh; Smolec, R.; Netzel, H.

doi:10.1093/mnras/stab1603

Cited by 12 publications

(4 citation statements)

References 40 publications

(68 reference statements)

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“…It is possible that in these stars we see the nonradial mode directly. Such stars are already known among RR Lyrae stars (Netzel & Smolec 2019;Benkő et al 2021) and classical Cepheids (Rathour et al 2021).…”

Section: Other Additional Signals In Rrc Starsmentioning

confidence: 96%

Frequency analysis of the first-overtone RR Lyrae stars based on Extended Aperture Photometry from K2 data

Netzel¹,

Molnar²,

Plachy³

et al. 2023

A&A

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Context. Additional low-amplitude signals have been observed in many RR Lyrae stars separate from pulsations in radial modes. The most common of these are short-period signals forming a period ratio of around 0.60–0.65 with the first overtone and long-period signals forming a period ratio of around 0.68. The RR Lyrae stars may also exhibit quasi-periodic modulation in their light curves, the so-called Blazhko effect. Aims. We used the extensive sample of the first-overtone RR Lyrae stars observed by the Kepler telescope during the K2 mission to search for and characterize additional low-amplitude signals. The K2 data provides space-based photometry for a statistically significant sample. Hence, this data is excellent for studying the pulsation properties of RR Lyrae stars in detail. Methods. We used K2 space-based photometry for RR Lyrae candidates from Campaigns 0–19. We selected RR Lyrae stars pulsating in the first overtone and performed a frequency analysis for each star to characterize their frequency contents. Results. We classified 452 stars as first-overtone RR Lyrae. From that sample, we selected 281 RR0.61 stars, 67 RR0.68 stars, and 68 Blazhko stars. We found particularly interesting stars that show all of the above phenomena simultaneously. We detected signals in RR0.61 stars that form period ratios lower than those observed for the majority of stars of this type. These signals likely form a new sequence in the Petersen diagram, around a period ratio of 0.60. In 32 stars, we detected additional signals that form a period ratio close to that expected in RRd stars, but the classification of these stars as RRd is uncertain. We also report a discovery of additional signals in eight stars that form a new group in the Petersen diagram around the period ratio of 0.465–0.490. The nature of this periodicity remains unknown.

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Section: Other Additional Signals In Rrc Starsmentioning

confidence: 96%

Frequency analysis of the first-overtone RR Lyrae stars based on Extended Aperture Photometry from K2 data

Netzel¹,

Molnar²,

Plachy³

et al. 2023

A&A

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“…In pulsating stars, such as Cepheids (Rathour et al 2021), RR Lyrae stars (Kurtz et al 2016), δ Scuti stars (Breger & Montgomery 2014), HADSs (Niu et al 2017), SX Phoenicis stars (Xue & Niu 2020), γ Dor stars (Kurtz et al 2015), pulsating white dwarfs (Wu 2001), β Cep stars (Degroote et al 2009), and slowly pulsating B stars (Pápics et al 2017), harmonics of independent pulsation modes are quite common. These harmonics arise from L8, page 3 of 13 Niu, J.-S. and Xue, H.-F.: A&A, 682, L8 ( 2024) the non-sinusoidal nature of light curves and indicate the nonlinearity of the star's pulsation.…”

Section: Harmonics and Combinationsmentioning

confidence: 99%

Unveiling the intricate symphony of nonlinear pulsation mode interactions in high-amplitude δ Scuti stars

Niu,

Xue

2024

A&A

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Information on the interiors of stars can be gleaned from their pulsations. Pulsation modes, which are determined by the internal state and structure of a star, are typically considered stable over short timescales. These independent pulsation modes have been used in asteroseismology to determine the interior structures of stars. Here, we report the discovery of peculiar pulsation mode interactions in the high-amplitude delta Scuti star KIC 6382916 (J19480292+4146558) that challenge the reliability of independent pulsation modes as indicators of a star's internal structure. Through analysis of archival data, we find distinct variations in the amplitudes and frequencies of three independent pulsation modes and their harmonics and combinations over approximately 20 days. These variations can reach amplitudes of about 140<!PCT!> and frequency variations of about 12<!PCT!>. Correlation analysis of amplitude and frequency variations reveal additional pulsation mode interaction details and patterns. Notably, our findings regarding the phenomena related to the harmonics of independent pulsation modes challenge the traditional understanding in this area. These discoveries serve as cornerstones for future research and advance nonlinear asteroseismology.

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“…Harmonics are usually accompanied by the independent pulsation modes amongst pulsating stars, such as Cepheids (Rathour et al 2021), RR Lyrae stars (Kurtz et al 2016), δ Scuti stars (Breger & Montgomery 2014), high-amplitude δ Scuti stars (Niu et al 2017), SX Phoenicis stars (Xue & Niu 2020), γ Dor stars (Kurtz et al 2015), pulsating white dwarfs (Wu 2001), β Cep stars (Degroote et al 2009), and SPB stars (Pápics et al 2017). It is generally believed that the harmonics come from the non-sinusoidal of light curves, which indicates the non-linearity of the star's pulsation.…”

Section: Introductionmentioning

confidence: 99%

Uncorrelated Amplitude and Frequency Variations of the Harmonics in SX Phoenicis Star XX Cygni

Niu¹,

Xue²

2023

Preprint

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Harmonics are quite common in pulsating stars, and they are always considered to mimic the behaviors of their independent parent pulsation modes and not taken as the key information for asteroseismology. Here, we report an SX Phoenicis star XX Cygni, whose periodogram is dominated by the fundamental frequency f 0 = 7.41481 ± 0.00004 c d −1 and its 19 harmonics. According to the analysis of the archival data from TESS , we find that both the amplitudes and frequencies of the fundamental mode and the harmonics vary within TESS Sectors 14-17 and 54-57, which might be caused by the contamination by neighbouring stars. What is more interesting is that, the harmonics show significantly uncorrelated amplitude and frequency variations over time. Some possible origins and interesting issues are proposed to scheme the further research of this hidden corner in current asteroseismology.

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

Cited by 12 publications

References 40 publications

Frequency analysis of the first-overtone RR Lyrae stars based on Extended Aperture Photometry from K2 data

Frequency analysis of the first-overtone RR Lyrae stars based on Extended Aperture Photometry from K2 data

Unveiling the intricate symphony of nonlinear pulsation mode interactions in high-amplitude δ Scuti stars

Uncorrelated Amplitude and Frequency Variations of the Harmonics in SX Phoenicis Star XX Cygni

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