From solar to stellar brightness variations

Witzke, V.; Шапиро, А. И.; Solanki, S. K.; Krivova, N. A.; Schmutz, W.

doi:10.1051/0004-6361/201833936

Cited by 39 publications

(49 citation statements)

References 50 publications

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“…It was shown earlier that metallicity has a significant effect on facular contrasts, and thus on stellar variability in solar-like stars (Karoff et al 2018;Witzke et al 2018). In this work, our aim is to understand the effect of metallicity on the detectability of the rotation periods in solar-like stars.…”

Section: Introductionmentioning

confidence: 94%

Effect of metallicity on the detectability of rotational periods in solar-like stars

Witzke

Reinhold

Шапиро

et al. 2020

A&A

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Accurate determination of stellar rotation periods is important for estimating stellar ages as well as for understanding stellar activity and evolution. While for about thirty thousand stars in the Kepler field rotation periods can be determined, there are over hundred thousand stars, especially with low photometric variability and irregular pattern of variations, for which rotational periods are unknown. Here, we investigate the effect of metallicity on the detectability of rotation periods. This is done by synthesising light curves of hypothetical stars, which are identical to our Sun, with the exception of the metallicity. These light curves are then used as an input to the period determination algorithms. We find that the success rate for recovering the rotation signal has a minimum close to the solar metallicity value. This can be explained by the compensation effect of facular and spot contributions. In addition, selecting solar-like stars with near-solar effective temperature, near solar photometric variability, and with metallicity between M/H = -0.35 and M/H = 0.35 from the Kepler sample, we analyse the fraction of stars for which rotational periods have been detected as a function of metallicity. In agreement with our theoretical estimate we found a local minimum for the detection fraction close to the solar metallicity. We further report rotation periods of 87 solar-like Kepler stars for the first time.

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Section: Introductionmentioning

confidence: 94%

Effect of metallicity on the detectability of rotational periods in solar-like stars

Witzke

Reinhold

Шапиро

et al. 2020

A&A

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“…At the same time, metallicity can affect other aspects of magnetic activity that we have not taken into account. For example, Witzke et al (2018) showed that, for a fixed activity level, metallicity affects the brightness contrasts between faculae and the photosphere, leading to differences in the optical variability and detectability of rotation. Karoff et al (2018) studied a solar analog with the same age but twice the metallicity of the Sun ([Fe/H]=+0.3).…”

Section: Implications For Activity-age Relationshipmentioning

confidence: 99%

The Impact of Metallicity on the Evolution of the Rotation and Magnetic Activity of Sun-like Stars

Amard

2020

ApJ

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The rotation rates and magnetic activity of Sun-like and low-mass ( 1.4M ) main-sequence stars are known to decline with time, and there now exist several models for the evolution of rotation and activity. However, the role that chemical composition plays during stellar spin-down has not yet been explored. In this work, we use a structural evolution code to compute the rotational evolution of stars with three different masses (0.7, 1.0, and 1.3 M ) and six different metallicities, ranging from [Fe/H] = −1.0 to [Fe/H] = +0.5. We also implement three different wind-braking formulations from the literature (two modern and one classical) and compare their predictions for rotational evolution. The effect that metallicity has on stellar structural properties, and in particular the convective turnover timescale, leads the two modern wind-braking formulations to predict a strong dependence of the torque on metallicity. Consequently, they predict that metal rich stars spin-down more effectively at late ages ( 1 Gyr) than metal poor stars, and the effect is large enough to be detectable with current observing facilities. For example, the formulations predict that a Sun-like (solar-mass and solar-aged) star with [Fe/H] = −0.3 will have a rotation period of less than 20 days. Even though old, metal poor stars are predicted to rotate more rapidly at a given age, they have larger Rossby numbers and are thus expected to have lower magnetic activity levels. Finally, the different wind-braking formulations predict quantitative differences in the metallicity-dependence of stellar rotation, which may be used to test them.

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“…The total photometric amplitude of 0.37 mmag for the solar cycle has been computed by Shapiro et al (2016). Such a small value was explained in Witzke et al (2018) by the incident combination of solar fundamental parameters and the spectral location of the Strömgren b and y pass bands. Furthermore, from Table B.1, it can be seen that 8 of the 27 stars with measured cycle periods exhibit a chromospheric activity cycle classified as excellent (flag chrom = 3).…”

Section: Activity Cycle Phase Differencementioning

confidence: 99%

Transition from spot to faculae domination

Reinhold

Bell

Kuszlewicz

et al. 2018

A&A

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Context. The study of stellar activity cycles is crucial to understand the underlying dynamo and how it causes magnetic activity signatures such as dark spots and bright faculae. Having knowledge about the dominant source of surface activity might allow us to draw conclusions about the stellar age and magnetic field topology, and to put the solar cycle in context. Aims. We investigate the underlying process that causes magnetic activity by studying the appearance of activity signatures in contemporaneous photometric and chromospheric time series. Methods. Lomb-Scargle periodograms are used to search for cycle periods present in the photometric and chromospheric time series. To emphasize the signature of the activity cycle we account for rotation-induced scatter in both data sets by fitting a quasi-periodic Gaussian process model to each observing season. After subtracting the rotational variability, cycle amplitudes and the phase difference between the two time series are obtained by fitting both time series simultaneously using the same cycle period. Results. We find cycle periods in 27 of the 30 stars in our sample. The phase difference between the two time series reveals that the variability in fast-rotating active stars is usually in anti-phase, while the variability of slowly rotating inactive stars is in phase. The photometric cycle amplitudes are on average six times larger for the active stars. The phase and amplitude information demonstrates that active stars are dominated by dark spots, whereas less-active stars are dominated by bright faculae. We find the transition from spot to faculae domination to be at the Vaughan–Preston gap, and around a Rossby number equal to one. Conclusions. We conclude that faculae are the dominant ingredient of stellar activity cycles at ages ≳2.55 Gyr. The data further suggest that the Vaughan–Preston gap cannot explain the previously detected dearth of Kepler rotation periods between 15 and 25 days. Nevertheless, our results led us to propose an explanation for the lack of rotation periods to be due to the non-detection of periodicity caused by the cancelation of dark spots and bright faculae at ∼800 Myr.

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From solar to stellar brightness variations

Cited by 39 publications

References 50 publications

Effect of metallicity on the detectability of rotational periods in solar-like stars

Effect of metallicity on the detectability of rotational periods in solar-like stars

The Impact of Metallicity on the Evolution of the Rotation and Magnetic Activity of Sun-like Stars

Transition from spot to faculae domination

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