Relations between global seismic parameters and activity cycles of the Sun

AbstractWavelength positions of photospheric absorption lines may be affected by surface convection (stellar granulation). Asymmetries and wavelength shifts originate from correlated velocity and brightness patterns: rising (blueshifted) elements are hot (bright), and convective blueshifts result from a larger contribution of such blueshifted photons than of redshifted ones from the sinking and cooler (darker) gas. For the Sun, the effect is around 300 m s−1, expected to increase in F-type stars, and in giants. Magnetic fields affect convection and induce lineshift variations over stellar activity cycles. A sufficient measuring precision reveals also the temporal variability of line wavelengths (due to the evolution of granules on the stellar surface). A major future development to come from adaptive optics and optical interferometry will be the study of wavelength variations across spatially resolved stars, together with their spatially resolved time variability. Thus, precise radial velocities should soon open up new vistas in stellar atmospheric physics.

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Synoptic solar observations of the Solar Flare Telescope focusing on space weather

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2020044 ◽

2020 ◽

Vol 10 ◽

pp. 41 ◽

Cited By ~ 1

Author(s):

Yoichiro Hanaoka ◽

Takashi Sakurai ◽

Ken’ichi Otsuji ◽

Isao Suzuki ◽

Satoshi Morita

Keyword(s):

Magnetic Field ◽

Solar Flare ◽

Space Weather ◽

Solar Observation ◽

The Sun ◽

Solar Observations ◽

Solar Filaments ◽

Field Information ◽

Activity Cycles ◽

Synoptic Observations

The solar group at the National Astronomical Observatory of Japan is conducting synoptic solar observation with the Solar Flare Telescope. While it is a part of a long-term solar monitoring, contributing to the study of solar dynamo governing solar activity cycles, it is also an attempt at contributing to space weather research. The observations include imaging with filters for Hα, Ca K, G-band, and continuum, and spectropolarimetry at the wavelength bands including the He I 1083.0 nm/Si I 1082.7 nm and the Fe I 1564.8 nm lines. Data for the brightness, Doppler signal, and magnetic field information of the photosphere and the chromosphere are obtained. In addition to monitoring dynamic phenomena like flares and filament eruptions, we can track the evolution of the magnetic fields that drive them on the basis of these data. Furthermore, the magnetic field in solar filaments, which develops into a part of the interplanetary magnetic cloud after their eruption and occasionally hits the Earth, can be inferred in its pre-eruption configuration. Such observations beyond mere classical monitoring of the Sun will hereafter become crucially important from the viewpoint of the prediction of space weather phenomena. The current synoptic observations with the Solar Flare Telescope is considered to be a pioneering one for future synoptic observations of the Sun with advanced instruments.

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Sun-like Stars: magnetic fields, cycles and exoplanets

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316003288 ◽

2015 ◽

Vol 11 (A29A) ◽

pp. 360-364

Author(s):

Rim Fares

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Large Scale ◽

Observational Constraints ◽

The Sun ◽

Field Generation ◽

Large Scale Magnetic Field ◽

Planetary Orbits ◽

Activity Cycles ◽

Magnetic Cycles

AbstractIn Sun-like stars, magnetic fields are generated in the outer convective layers. They shape the stellar environment, from the photosphere to planetary orbits. Studying the large-scale magnetic field of those stars enlightens our understanding of the field properties and gives us observational constraints for field generation dynamo models. It also sheds light on how “normal” the Sun is among Sun-like stars. In this contribution, I will review the field properties of Sun-like stars, focusing on solar twins and planet hosting stars. I will discuss the observed large-scale magnetic cycles, compare them to stellar activity cycles, and link that to what we know about the Sun. I will also discuss the effect of large-scale stellar fields on exoplanets, exoplanetary emissions (e.g. radio), and habitability.

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Comparative Analysis of the Activity Cycles of the Atmospheres of the Sun and of Stars of the Solar-Type

Astrophysics ◽

10.1007/s10511-016-9420-2 ◽

2016 ◽

Vol 59 (1) ◽

pp. 101-113 ◽

Cited By ~ 1

Author(s):

E. A. Bruevich ◽

V. V. Bruevich ◽

E. V. Shimanovskaya

Keyword(s):

Comparative Analysis ◽

The Sun ◽

Solar Type ◽

Activity Cycles

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Starspot rotation rates versus activity cycle phase: Butterfly diagrams of Kepler stars are unlike that of the Sun

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834373 ◽

2019 ◽

Vol 622 ◽

pp. A85 ◽

Cited By ~ 5

Author(s):

M. B. Nielsen ◽

L. Gizon ◽

R. H. Cameron ◽

M. Miesch

Keyword(s):

Effective Temperature ◽

Rotation Rate ◽

Activity Cycle ◽

Magnetic Activity ◽

Activity Level ◽

The Sun ◽

Rotation Rates ◽

Rotation Periods ◽

Activity Cycles ◽

The Mean

Context. During the solar magnetic activity cycle the emergence latitudes of sunspots change, leading to the well-known butterfly diagram. This phenomenon is poorly understood for other stars since starspot latitudes are generally unknown. The related changes in starspot rotation rates caused by latitudinal differential rotation can, however, be measured. Aims. Using the set of 3093 Kepler stars with measured activity cycles, we aim to study the temporal change in starspot rotation rates over magnetic activity cycles, and how this relates to the activity level, the mean rotation rate of the star, and its effective temperature. Methods. We measured the photometric variability as a proxy for the magnetic activity and the spot rotation rate in each quarter over the duration of the Kepler mission. We phase-folded these measurements with the cycle period. To reduce random errors, we performed averages over stars with comparable mean rotation rates and effective temperature at fixed activity-cycle phases. Results. We detect a clear correlation between the variation of activity level and the variation of the starspot rotation rate. The sign and amplitude of this correlation depends on the mean stellar rotation and – to a lesser extent – on the effective temperature. For slowly rotating stars (rotation periods between 15 − 28 days), the starspot rotation rates are clearly anti-correlated with the level of activity during the activity cycles. A transition is observed around rotation periods of 10 − 15 days, where stars with an effective temperature above 4200 K instead show positive correlation. Conclusions. Our measurements can be interpreted in terms of a stellar “butterfly diagram”, but these appear different from that of the Sun since the starspot rotation rates are either in phase or anti-phase with the activity level. Alternatively, the activity cycle periods observed by Kepler are short (around 2.5 years) and may therefore be secondary cycles, perhaps analogous to the solar quasi-biennial oscillations.

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POLAR ACTIVITY OF THE SUN AND CONTINUOUS ACTIVITY CYCLES IN THE PERIOD 15–24 ACTIVITY CYCLES

Proceedings of the 22nd All-Russia Conference on Solar and Solar-Terrestrial Physics ◽

10.31725/0552-5829-2018-365-368 ◽

2018 ◽

Author(s):

A.G. Tlatov ◽

◽

K.A. Tlatova ◽

◽

Keyword(s):

The Sun ◽

Continuous Activity ◽

Activity Cycles

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Asteroseismic signatures of magnetic activity variations in solar-type stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313014348 ◽

2013 ◽

Vol 9 (S301) ◽

pp. 213-216

Author(s):

Travis S. Metcalfe

Keyword(s):

Sunspot Cycle ◽

Magnetic Activity ◽

The Sun ◽

Historical Overview ◽

Solar Type ◽

Activity Cycles ◽

Internal Properties

AbstractObservations of magnetic activity cycles in other stars provide a broader context for our understanding of the 11-year sunspot cycle. The discovery of short activity cycles in a few stars, and the recognition of analogous variability in the Sun, suggest that there may be two distinct dynamos operating in different regions of the interior. Consequently, there is a natural link between studies of magnetic activity and asteroseismology, which can characterize some of the internal properties that are relevant to dynamos. I provide a brief historical overview of the connection between these two fields (including prescient work by Wojtek Dziembowski in 2007), and I highlight some exciting results that are beginning to emerge from the Kepler mission.

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N–S asymmetry in the differential rotation of the sun and its variation with the solar activity cycles

New Astronomy ◽

10.1016/s1384-1076(03)00046-0 ◽

2003 ◽

Vol 8 (6) ◽

pp. 529-536 ◽

Cited By ~ 20

Author(s):

M.Sh Gigolashvili ◽

T.G Mdzinarishvili ◽

D.R Japaridze ◽

B.B Chargeishvili

Keyword(s):

Solar Activity ◽

Differential Rotation ◽

The Sun ◽

Activity Cycles ◽

Solar Activity Cycles

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Shapes of stellar activity cycles

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037666 ◽

2020 ◽

Vol 638 ◽

pp. A69

Author(s):

T. Willamo ◽

T. Hackman ◽

J. J. Lehtinen ◽

M. J. Käpylä ◽

N. Olspert ◽

...

Keyword(s):

Solar Cycle ◽

Large Scale ◽

Magnetic Activity ◽

The Sun ◽

Data Set ◽

Cycle Asymmetry ◽

Asymmetric Shape ◽

Activity Cycles ◽

Magnetohydrodynamic Simulations ◽

Fast Rise

Context. Magnetic activity cycles are an important phenomenon both in the Sun and other stars. The shape of the solar cycle is commonly characterised by a fast rise and a slower decline, but not much attention has been paid to the shape of cycles in other stars. Aims. Our aim is to study whether the asymmetric shape of the solar cycle is common in other stars as well, and compare the cycle asymmetry to other stellar parameters. We also study the differences in the shape of the solar cycle, depending on the activity indicator that is used. The observations are also compared to simulated activity cycles. Methods. We used the chromospheric Ca II H&K data from the Mount Wilson Observatory HK Project. In this data set, we identified 47 individual cycles from 18 stars. We used the statistical skewness of a cycle as a measure of its asymmetry, and compared this to other stellar parameters. A similar analysis has been performed for magnetic cycles extracted from direct numerical magnetohydrodynamic simulations of solar-type convection zones. Results. The shape of the solar cycle (fast rise and slower decline) is common in other stars as well, although the Sun seems to have particularly asymmetric cycles. Cycle-to-cycle variations are large, but the average shape of a cycle is still fairly well represented by a sinusoid, although this does not take its asymmetry into account. We find only slight correlations between the cycle asymmetry and other stellar parameters. There are large differences in the shape of the solar cycle, depending on the activity indicator that is used. The simulated cycles differ in the symmetry of global simulations that cover the full longitudinal range and are therefore capable of exciting non-axisymmetric large-scale dynamo modes, and wedge simulations that cover a partial extent in longitude, where only axisymmetric large-scale modes are possible. The former preferentially produce positive and the latter negative skewness.

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About long term modulation of cosmic rays in the 23-24 solar activity cycles

NMDB@Home 2020 - Cosmic ray studies with neutron detectors ◽

10.38072/2748-3150/p3 ◽

2021 ◽

pp. 23-29

Author(s):

Anatoly V. Belov ◽

Raisa T. Gushchina ◽

Victor Yanke

Keyword(s):

Magnetic Field ◽

Solar Activity ◽

Cosmic Rays ◽

Solar Magnetic Field ◽

The Sun ◽

Model Calculations ◽

Activity Cycles ◽

The Magnetic Field ◽

Solar Activity Cycles

Recently, there has been a significant trend in magnetic fields on the Sun. The total magnetic field of the Sun from the end of the 22nd cycle of solar activity (SA) has more than halved and this decrease continues. Chan- ges in the magnetic field are the key to all the active phenomena occurring on the Sun and in the heliosphere and, accordingly, to processes in cosmic rays. In long-term CR variations in 23-24 cycles of SA the attenuation of the solar magnetic field is displayed and these variations turned out to be the smallest for the entire time of CR observations. Model calculations of CR modulation for 21-22 and 23-24 cycles of SA showed: with a slight difference in the regression characteristics obtained, the distribution of contributions to the generated CR modulation from the effects of various SA indices is strongly varies in the analyzed periods. Possible reasons for the features of the last two CA cycles are discussed.

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