A Dynamo Interpretation of Stellar Activity Cycles

1996 ◽  
Vol 460 ◽  
pp. 848 ◽  
Author(s):  
S. L. Baliunas ◽  
E. Nesme-Ribes ◽  
D. Sokoloff ◽  
W. H. Soon
Keyword(s):  
Stellar Activity ◽  
Activity Cycles

scholarly journals Solar and stellar activity cycles

2008 ◽  
Vol 118 ◽  
pp. 012032 ◽  
Author(s):  
Matthias Rempel
Keyword(s):  
Stellar Activity ◽  
Activity Cycles

Modulation of solar and stellar activity cycles

2008 ◽  
pp. 25-47 ◽  
Author(s):  
N. O. Weiss ◽  
S. M. Tobias
Keyword(s):  
Stellar Activity ◽  
Activity Cycles

scholarly journals Evolution of Co-existing Long and Short Period Stellar Activity Cycles

2017 ◽  
Vol 845 (1) ◽  
pp. 79 ◽  
Author(s):  
Axel Brandenburg ◽  
Savita Mathur ◽  
Travis S. Metcalfe
Keyword(s):  
Stellar Activity ◽  
Short Period ◽  
Activity Cycles

scholarly journals STELLAR ACTIVITY CYCLES: WHY DO WE NEED IN THE LONG-TERM MEASUREMENTS OF THE MAGNETIC FIELD?

2017 ◽  
Vol 30 (0) ◽  
pp. 124-125
Author(s):  
S. I. Plachinda ◽  
V. V. Butkovskaya
Keyword(s):  
Magnetic Field ◽  
Stellar Activity ◽  
Activity Cycles ◽  
The Magnetic Field

scholarly journals Solar and stellar activity cycles

1995 ◽  
Vol 32 (06) ◽  
pp. 32-3294-32-3294
Keyword(s):  
Stellar Activity ◽  
Activity Cycles

scholarly journals The Mount Wilson Program for Stellar Activity Cycles

1983 ◽  
Vol 102 ◽  
pp. 113-132
Author(s):  
Arthur H. Vaughan
Keyword(s):  
Stellar Mass ◽  
Present Review ◽  
Current Evidence ◽  
Stellar Activity ◽  
Activity Cycles

The present review will focus upon the incidence, form, and characteristic timescale of long-term chromospheric variations that, from the work of O.C. Wilson and his successors, can be descerned in records of CaII H and K emission now extending over 16 years, and the relation, if any, between properties of activity cycles and stellar mass, age, and rate of rotation, in the light of current evidence.

scholarly journals Transition from spot to faculae domination

2018 ◽  
Vol 621 ◽  
pp. A21 ◽  
Author(s):  
Timo Reinhold ◽  
Keaton J. Bell ◽  
James Kuszlewicz ◽  
Saskia Hekker ◽  
Alexander I. Shapiro
Keyword(s):  
Time Series ◽  
Phase Difference ◽  
Process Model ◽  
Activity Cycle ◽  
Magnetic Activity ◽  
Cycle Period ◽  
Stellar Activity ◽  
Rotation Periods ◽  
Active Stars ◽  
Activity Cycles

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.

Stellar activity cycles

2008 ◽  
pp. 1-18
Author(s):  
Sallie L. Baliunas
Keyword(s):  
Stellar Activity ◽  
Activity Cycles

scholarly journals HD 38858: a solar-type star with an activity cycle of ∼10.8 yr

2018 ◽  
Vol 620 ◽  
pp. A34 ◽  
Author(s):  
M. Flores ◽  
J. F. González ◽  
M. Jaque Arancibia ◽  
C. Saffe ◽  
A. Buccino ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Activity Cycle ◽  
Earth Planet ◽  
Stellar Activity ◽  
Balmer Lines ◽  
Solar Type ◽  
Activity Cycles ◽  
Novel Strategy ◽  
Solar Type Star

Context. The detection of chromospheric activity cycles in solar-analogue and twin stars can be used to place the solar cycle in a wider context. However, relatively few of these stars with activity cycles have been detected. It is well known that the cores of the Ca II H&K lines are modulated by stellar activity. The behaviour of the Balmer and other optical lines with stellar activity is not yet completely understood. Aims. We search for variations in the Ca II H&K, Balmer, and Fe II lines modulated by stellar activity. In particular, we apply a novel strategy to detect possible shape variations in the Hα line. Methods. We analysed activity signatures in HD 38858 using HARPS and CASLEO spectra obtained between 2003 and 2017. We calculated the Mount Wilson index (SMW), log(R′HK), and the statistical moments of the Ca II H&K, Balmer, and other optical lines. We searched for periodicities using the generalized Lomb-Scargle periodogram. Results. We detect a long-term activity cycle of 10.8 yr in Ca II H&K and Hα in the solar-analogue star HD 38858. In contrast, this cycle is marginally detected in the Fe II lines. We also detect a noticeable variation in radial velocity that seems to be produced by stellar activity. Conclusions. HD 38858 is the second solar-analogue star where we find a clear activity cycle that is replicated in the Balmer lines. Spectral indexes based on the shape of Hα line seem to be more reliable than the fluxes in the same line for detecting activity variations. The cyclic modulation we detected gives place to a variation in radial velocity that previously has been associated with a super-Earth planet. Finally, due to the similarity of HD 38858 with the Sun, we recommend to continue monitoring this star.

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