scholarly journals Asteroseismic signatures of magnetic activity variations in solar-type stars

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.

scholarly journals Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude

Solar Physics ◽  
2020 ◽  
Vol 295 (12) ◽  
Author(s):  
Scott W. McIntosh ◽  
Sandra Chapman ◽  
Robert J. Leamon ◽  
Ricky Egeland ◽  
Nicholas W. Watkins
Keyword(s):  
Solar Cycle ◽  
Sunspot Number ◽  
Sunspot Cycle ◽  
Periodic Variation ◽  
Magnetic Activity ◽  
The Sun ◽  
Magnetic Cycle ◽  
Hilbert Transforms ◽  
Observational Astronomy ◽  
Activity Cycles

AbstractThe Sun exhibits a well-observed modulation in the number of spots on its disk over a period of about 11 years. From the dawn of modern observational astronomy, sunspots have presented a challenge to understanding—their quasi-periodic variation in number, first noted 175 years ago, has stimulated community-wide interest to this day. A large number of techniques are able to explain the temporal landmarks, (geometric) shape, and amplitude of sunspot “cycles,” however, forecasting these features accurately in advance remains elusive. Recent observationally-motivated studies have illustrated a relationship between the Sun’s 22-year (Hale) magnetic cycle and the production of the sunspot cycle landmarks and patterns, but not the amplitude of the sunspot cycle. Using (discrete) Hilbert transforms on more than 270 years of (monthly) sunspot numbers we robustly identify the so-called “termination” events that mark the end of the previous 11-yr sunspot cycle, the enhancement/acceleration of the present cycle, and the end of 22-yr magnetic activity cycles. Using these we extract a relationship between the temporal spacing of terminators and the magnitude of sunspot cycles. Given this relationship and our prediction of a terminator event in 2020, we deduce that sunspot Solar Cycle 25 could have a magnitude that rivals the top few since records began. This outcome would be in stark contrast to the community consensus estimate of sunspot Solar Cycle 25 magnitude.

scholarly journals Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry

2019 ◽  
Vol 626 ◽  
pp. A38 ◽  
Author(s):  
A. F. Lanza ◽  
Y. Netto ◽  
A. S. Bonomo ◽  
H. Parviainen ◽  
A. Valio ◽  
...  
Keyword(s):  
Maximum Entropy ◽  
Differential Rotation ◽  
Activity Cycle ◽  
Magnetic Activity ◽  
Model Parameters ◽  
The Sun ◽  
Level Of Activity ◽  
Spot Model ◽  
Rotational Evolution ◽  
Solar Type

Context. The study of young Sun-like stars is fundamental to understanding the magnetic activity and rotational evolution of the Sun. Space-borne photometry by the Kepler telescope provides unprecedented datasets to investigate these phenomena in Sun-like stars. Aims. We present a new analysis of the entire Kepler photometric time series of the moderately young Sun-like star Kepler-17 accompanied by a transiting hot Jupiter. Methods. We applied a maximum-entropy spot model to the long-cadence out-of-transit photometry of the target to derive maps of the starspot filling factor versus the longitude and the time. These maps are compared to the spots occulted during transits to validate our reconstruction and derive information on the latitudes of the starspots. Results. We find two main active longitudes on the photosphere of Kepler-17, one of which has a lifetime of at least ∼1400 days although with a varying level of activity. The latitudinal differential rotation is of solar type, that is, with the equator rotating faster than the poles. We estimate a minimum relative amplitude ΔΩ/Ω between ∼0.08 ± 0.05 and 0.14 ± 0.05, our determination being affected by the finite lifetime of individual starspots and depending on the adopted spot model parameters. We find marginal evidence of a short-term intermittent activity cycle of ∼48 days and an indication of a longer cycle of 400−600 days characterized by an equatorward migration of the mean latitude of the spots as in the Sun. The rotation of Kepler-17 is likely to be significantly affected by the tides raised by its massive close-by planet. Conclusion. We confirm the reliability of maximum-entropy spot models to map starspots in young active stars and characterize the activity and differential rotation of this young Sun-like planetary host.

scholarly journals The Solar-Stellar Connection and Disconnection

2004 ◽  
Vol 219 ◽  
pp. 11-28 ◽  
Author(s):  
Klaus G. Strassmeier
Keyword(s):  
Magnetic Field ◽  
Meridional Circulation ◽  
Magnetic Activity ◽  
Driving Mechanism ◽  
The Sun ◽  
Dynamo Action ◽  
Convective Envelope ◽  
Surface Rotation ◽  
Single Process ◽  
Solar Type

The study of stellar activity is now an almost classical astronomical topic. The first Ca ii-H&K observations were made a hundred years ago by Eberhard & Schwarzschild1 and many thousand papers were published after its rediscovery some three decades ago by O. C. Wilson. The complexity of the atmospheric and interior magnetic activity as observed on the Sun is hard, if not impossible, to extrapolate to solar-type stars. So far there is no solar twin found, despite that it appears that just a single process acts as the driving mechanism for activity in all atmospheric layers and partially even in the convective envelope: the dynamodriven magnetic field. In this paper, I will try to give examples where the solar analogy holds and where it is clearly not appropriate, putting some emphases on differential surface rotation and meridional circulation. I stress the importance of mapping stellar surfaces as fingerprints of the underlying dynamo action and directly measure surface magnetic fields.

Solar Rotation, Irradiance Changes and Climate

1994 ◽  
Vol 143 ◽  
pp. 244-251
Author(s):  
Elizabeth Nesme-Ribes ◽  
Dmitry Sokoloff ◽  
Robert Sadourny
Keyword(s):  
Magnetic Fields ◽  
Internal Rotation ◽  
Solar Rotation ◽  
Total Solar Irradiance ◽  
Magnetic Activity ◽  
Convective Envelope ◽  
Surface Rotation ◽  
Solar Type ◽  
Activity Cycles ◽  
The Impact

Magnetic activity cycles for solar-type stars are believed to originate from non-uniform internal rotation. To determine this depthwise angular velocity distribution, helioseismology is a valuable source of information. Surface rotation, as traced by sunspot motion, is a well-observed parameter with data going back to the beginning of the telescopic era. This long sunspot series can be used in understanding the behaviour of the Sun’s surface rotation, the connection with its internal rotation, and thereby its magnetic activity. Apparent solar diameter is another important parameter. This is related to the structure of the convective envelope and how it reacts to the presence of magnetic fields. Both these parameters are related to the solar output, and can provide a surrogate for total solar irradiance, by way of a theoretical modeling of the response of the convective zone to the emergence of periodic magnetic fields. The impact of solar variability on the terrestrial climate is also addressed.

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

Astrophysics ◽  
2016 ◽  
Vol 59 (1) ◽  
pp. 101-113 ◽  
Author(s):  
E. A. Bruevich ◽  
V. V. Bruevich ◽  
E. V. Shimanovskaya
Keyword(s):  
Comparative Analysis ◽  
The Sun ◽  
Solar Type ◽  
Activity Cycles

scholarly journals The Sun in time: age, rotation, and magnetic activity of the Sun and solar-type stars and effects on hosted planets

2008 ◽  
Vol 4 (S258) ◽  
pp. 395-408 ◽  
Author(s):  
Edward F. Guinan ◽  
Scott G. Engle
Keyword(s):  
Main Sequence ◽  
High Energy ◽  
Magnetic Activity ◽  
The Sun ◽  
X Ray ◽  
Multi Wavelength ◽  
Solar Type ◽  
Rotation Age ◽  
Energy Emissions ◽  
Solar Analogs

AbstractMulti-wavelength studies of solar analogs (G0–5 V stars) with ages from ~50 Myr to 9 Gyr have been carried out as part of the “Sun in Time” program for nearly 20 yrs. From these studies it is inferred that the young (ZAMS) Sun was rotating more than 10× faster than today. As a consequence, young solar-type stars and the early Sun have vigorous magnetohydrodynamic (MHD) dynamos and correspondingly strong coronal X-ray and transition region/chromospheric FUV–UV emissions (up to several hundred times stronger than the present Sun). Also, rotational modulated, low amplitude light variations of young solar analogs indicate the presence of large starspot regions covering ~5–30% of their surfaces. To ensure continuity and homogeneity for this program, we use a restricted sample of G0–5 V stars with masses, radii, Teff, and internal structure (i.e. outer convective zones) closely matching those of the Sun. From these analogs we have determined reliable rotation-age-activity relations and X-ray–UV (XUV) spectral irradiances for the Sun (or any solar-type star) over time. These XUV irradiance measures serve as input data for investigating the photo-ionization and photo-chemical effects of the young, active Sun on the paleo-planetary atmospheres and environments of solar system planets. These measures are also important to study the effects of these high energy emissions on the numerous exoplanets hosted by solar-type stars of different ages. Recently we have extended the study to include lower mass, main-sequence (dwarf) dK and dM stars to determine relationships among their rotation spin-down rates and coronal and chromospheric emissions as a function of mass and age. From rotation-age-activity relations we can determine reliable ages for main-sequence G, K, M field stars and, subsequently, their hosted planets. Also inferred are the present and the past XUV irradiance and plasma flux exposures that these planets have endured and the suitability of the hosted planets to develop and sustain life.

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

2019 ◽  
Vol 622 ◽  
pp. A85 ◽  
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.

From the Sun to solar-type stars: radial velocity, photometry, astrometry and logR′HK time series for late-F to early-K old stars

2019 ◽  
Vol 15 (S354) ◽  
pp. 286-294
Author(s):  
Nadège Meunier ◽  
Anne-Marie Lagrange
Keyword(s):  
Radial Velocity ◽  
Large Range ◽  
Magnetic Activity ◽  
Activity Levels ◽  
The Sun ◽  
Lower Mass ◽  
Solar Type ◽  
Low Mass ◽  
Average Activity ◽  
The Impact

AbstractSolar simulations and observations showed that the detection of Earth twins around Sun-like stars is difficult in radial velocities with current methods techniques. The Sun has proved to be very useful to test processes, models, and analysis methods. The convective blueshift effect, dominating for the Sun, decreases towards lower mass stars, providing more suitable conditions to detect low mass planets. We describe the basic processes at work and how we extended a realistic solar model of radial velocity, photometry, astrometry and LogR′HK variability, using a coherent grid of stellar parameters covering a large range in mass and average activity levels. We present selected results concerning the impact of magnetic activity on Earth-mass planet detectability as a function of stellar type. We show how such realistic simulations can help characterizing the effect of stellar activity on RV and astrometric exoplanet detection.

V1005 Her: a solar-type shallow-contact binary in a triply fossil system

2019 ◽  
Vol 489 (2) ◽  
pp. 2677-2684 ◽  
Author(s):  
L-Y Zhu ◽  
Z H Wang ◽  
X M Tian ◽  
L J Li ◽  
X Gao
Keyword(s):  
Magnetic Activity ◽  
Light Curves ◽  
Cyclic Variation ◽  
Third Body ◽  
Light Curve Analysis ◽  
Short Period ◽  
Contact Binary ◽  
Solar Type ◽  
Activity Cycles ◽  
Minimal Mass

ABSTRACTFour sets of complete multicolour light curves of the short-period solar-type eclipsing binary V1005 Her are presented. It is found that the depth of the primary minima in the light curves went deeper from 2013 to 2018, and then became shallower again in 2019, while those of the secondary minima were unchanged. The total-eclipse characteristics in the light curves enable us to determine reliable photometric solutions of this system. Our results from the detailed light-curve analysis show that V1005 Her is a W-type shallow-contact binary with spot activities. We have monitored this system for 7 yr and 22 new times of light minimum have been determined. Together with those collected from the literature, we investigate its Observed-Calculated O–C curve and detect a cyclic variation. Because of the insufficient energy, this cyclic change cannot be explained by magnetic activity cycles of the components even if it has high spots activities. The detected cyclic variation is more plausible as the results of the light-time effect due to the existence of a third body orbiting around the central binary. The minimal mass of the additional stellar companion is determined around 0.45 M⊙ in both circular orbit and eccentric orbit cases when a total mass of 1.2 M⊙ for the binary is adopted. This mass is larger than that of the less massive component of the central binary. It implies that the secondary body was not replaced by the third body during early stellar interactions, suggesting that it is a fossil system and keeps original dynamical information.

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