Empirically revealed properties of Rieger-type cycles of stellar activity

Arkhypov, O. V.; Khodachenko, M. L.

doi:10.1051/0004-6361/202140629

Cited by 4 publications

(3 citation statements)

References 29 publications

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“…The RTCs become more pronounced during the solar activity maximum. There is a potential connection between RTCs and the modulation of the solar magnetic dynamo process, as discussed in Arkhypov & Khodachenko (2021) and references therein. Possible reasons encompass the role of inertial g-and r-waves, also known as Rossby waves, as modulators of the emergence of magnetic flux in the Sun.…”

Section: Introductionmentioning

confidence: 99%

“…Possible reasons encompass the role of inertial g-and r-waves, also known as Rossby waves, as modulators of the emergence of magnetic flux in the Sun. Arkhypov & Khodachenko (2021) analyze photometric data from 1726 main sequence stars with varying effective temperatures and rotation periods to study RTCs in other stars. Two types of RTCs are identified among the surveyed stars.…”

Section: Introductionmentioning

confidence: 99%

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Prediction of Short Stellar Activity Cycles using Derived and Established Empirical Relations between Activity and Rotation Periods

Althukair,

Tsiklauri

2023

Res. Astron. Astrophys.

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In our previous work, we investigated the occurrence rate of super-flares on various types of stars and their statistical properties, with a particular focus on G-type dwarfs, using entire Kepler data. The said study also considered how the statistics change with stellar rotation period, which in turn, had to be determined. Using such new data, as a by-product, we found 138 Kepler IDs of F- and G-type main sequence stars with rotation periods less than a day (P rot < 1 day). On one hand, previous studies have revealed short activity cycles in F-type and G-type stars and the question investigated was whether or not short-term activity cycles are a common phenomenon in these stars. On the other hand, extensive studies exist which establish an empirical connection between a star’s activity cycle and rotation periods. In this study, we compile all available Kepler data with P rot < 1 day, and rely on an established empirical relation between P cyc and P rot with the aim to provide predictions for very short 5.09 ≤ P cyc ≤ 38.46 day cases in a tabular form. We propose an observation to measure P cyc using a monitoring program of stellar activity (e.g., activity-related chromospheric emission S-index) or a similar means for the Kepler IDs found in this study in order put the derived empirical relations between P cyc and P rot derived here to the test. We also propose an alternative method for measuring very short P cyc, using flare-detection algorithms applied to future space mission data.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Prediction of Short Stellar Activity Cycles using Derived and Established Empirical Relations between Activity and Rotation Periods

Althukair,

Tsiklauri

2023

Res. Astron. Astrophys.

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“…Recently, Lanza et al (2019) re-analysed the light curves of the same star for all Kepler quarters and found an additional cycle of 400-500 days. Arkhypov & Khodachenko (2021) studied 1726 Kepler stars and found two types of Rieger cycles: one independent of the stellar P rot (for the stars with T eff 5500 K) and the other proportional to P rot (for the stars with T eff 6300 K). Therefore, it is becoming increasingly clear that space mission data may reveal Rieger cycles in the activity of other solar-like stars.…”

Section: Introductionmentioning

confidence: 99%

Rieger-type cycles on the solar-like star KIC 2852336

Gurgenashvili

Zaqarashvili

Kukhianidze

et al. 2022

A&A

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Context. A Rieger-type periodicity of 150–180 days (six to seven times the solar rotation period) has been observed in the Sun’s magnetic activity and is probably connected with the internal dynamo layer. Observations of Rieger cycles in other solar-like stars may give us information about the dynamo action throughout stellar evolution. Aims. We aim to use the Sun as a star analogue to find Rieger cycles on other solar-like stars using Kepler data. Methods. We analyse the light curve of the Sun-like star KIC 2852336 (with a rotation period of 9.5 days) using wavelet and generalised Lomb-Scargle methods to find periodicities over rotation and Rieger timescales. Results. Besides the rotation period of 9.5 days, the power spectrum shows a pronounced peak at a period of 61 days (about six times the stellar rotation period) and a less pronounced peak at 40–44 days. These two periods may correspond to Rieger-type cycles and can be explained by the harmonics of magneto-Rossby waves in the stellar dynamo layer. The observed periods and theoretical properties of magneto-Rossby waves lead to the estimation of the dynamo magnetic field strength of 40 kG inside the star. Conclusions. Rieger-type cycles can be used to probe the dynamo magnetic field in solar-type stars at different phases of evolution. Comparing the rotation period and estimated dynamo field strength of the star KIC 2852336 with the corresponding solar values, we conclude that the ratio Ω/BD, where Ω is the angular velocity and BD is the dynamo magnetic field, is the same for the star and the Sun. Therefore, the ratio can be conserved during stellar evolution, which is consistent with earlier observations that younger stars are more active.

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Tachocline Alfvén waves manifested in stellar activity

Arkhypov¹,

Khodachenko²

2023

A&A

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Context. The short-time (< 700 days) periodicities of both the stellar and solar activity that controls space weather are usually are discussed as manifestations of Rossby modes in tachoclines. Various interpretations of this phenomenon that have been proposed, in particular for the Sun, can be verified by considering the broad population of nonsolar-type stars. Aims. We look for surface stellar activity features, drifting in longitude, and compare their drift rates with those predicted for different low-frequency waves in stellar photospheres and tachoclines. Methods. Analogously to the Hovmöller diagrams in meteorology, we constructed a dynamic diagram of stellar activity pattern (DDSAP) to visualize the rotational variability of the stellar radiation flux as a function of rotation phase and time. We used the high-precision light curves of the fast-rotating main sequence stars, with rotation periods of 0.5 to 4 days, from the Kepler mission database. Results. We found quasi-periodic drifting lanes (DLs) of various durations and intensities in the DDSAPs for 108 stars. In the course of analysis, we carried out a correction of the stellar rotation periods by nullifying the drifts of the longest-lasing DLs that are presumably related to the long-lived starspot complexes co-rotating with the star. We discovered a clear elongated cluster of the absolute values of the DLs’ drift rates versus the stellar effective temperatures. This cluster cannot be attributed to any accidental contaminations of the light curves or manifestation of waves in the stellar photospheres, because of their extremely short timescales. An approximate equality of the absolute values of positive and negative drift rates of the considered DLs makes it impossible to interpret them in terms of Kelvin and/or magneto-Rossby waves in the stellar tachoclines. It is only global kink-type Alfvénic oscillations of the tachocline as a whole that allow us to interpret the estimated drift rates forming the above-mentioned cluster, as well as the related activity periodicities and turnover times in the convective zones. The corresponding magnetic field strength appears to be about 50 kG, which is approximately in the middle of the range of assumptions discussed in the literature. Conclusions. Alfvén waves are an important, albeit commonly ignored factor in stellar interiors. Apparently, the global tachocline’s Alfvén waves ought to play a role in triggering emergence of the magnetic flux tubes. Their manifestation in stellar activity opens up a unique way of probing the magnetic field strength in tachoclines of individual stars. Since the investigations of the tachocline waves performed thus far have been based on the shallow-fluid approximation, and also assuming a rigid fixed bottom of the tachocline layer, the global kink-type Alvénic disturbances of the whole tachocline layer have not been considered. The reported observational detection of signatures of such waves, manifested in specific longitude drifts of the stelar surface activity pattern, calls for a more detailed theoretical study.

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Empirically revealed properties of Rieger-type cycles of stellar activity

Cited by 4 publications

References 29 publications

Prediction of Short Stellar Activity Cycles using Derived and Established Empirical Relations between Activity and Rotation Periods

Prediction of Short Stellar Activity Cycles using Derived and Established Empirical Relations between Activity and Rotation Periods

Rieger-type cycles on the solar-like star KIC 2852336

Tachocline Alfvén waves manifested in stellar activity

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