A new look at dynamo cycle amplitudes

Saar, S. H.; Brandenburg, Axel

doi:10.1002/1521-3994(200208)323:3/4<357::aid-asna357>3.0.co;2-i

Cited by 33 publications

(68 citation statements)

References 9 publications

(16 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, we found a small anti-correlation between the contrast C and the Rossby number (see Fig. 9); this result does not agree with the results of Saar & Brandenburg (2002) who did not find any clear correlation between the cycle amplitude and Ro.…”

Section: Rossby Numbercontrasting

confidence: 99%

“…At first sight no clear correlation appears, but if we look at the stars that show evidence of long-lived features (red triangles), a slight correlation seems to be present. Saar & Brandenburg (2002) observed the opposite, that there was an anti-correlation, but we note that their result concerns stars where they observed magnetic cycles while our subsample only shows long-lived features.…”

Section: Magnetic Index and Other Parameterscontrasting

confidence: 61%

“…They showed that chromospheric activity directly depends on the Rossby number Ro = P rot /τ c , where τ c is the convective turnover time. Saar & Brandenburg (2002) showed that the magnetic activity cycle period and the rotation rate were also linked through this quantity. We computed the Rossby numbers for our sample of stars.…”

Section: Magnetic Index and Other Parametersmentioning

confidence: 95%

“…A relation between the S -index and the rotation period has been established by Saar & Brandenburg (2002). In Fig.…”

Section: Magnetic Index and Other Parametersmentioning

confidence: 99%

See 3 more Smart Citations

Magnetic activity of F stars observed byKepler

Mathur

García

Ballot

et al. 2014

A&A

161

195

View full text Add to dashboard Cite

Context. The study of stellar activity is important because it can provide new constraints for dynamo models when combined with surface rotation rates and the depth of the convection zone. We know that the dynamo mechanism, which is believed to be the main process that rules the magnetic cycle of solar-like stars, results from the interaction between (differential) rotation, convection, and magnetic field. The Kepler mission has already been collecting data for a large number of stars during four years allowing us to investigate magnetic stellar cycles. Aims. We investigated the Kepler light curves to look for magnetic activity or even hints of magnetic activity cycles. Based on the photometric data we also looked for new magnetic indexes to characterise the magnetic activity of the stars. Methods. We selected a sample of 22 solar-like F stars that have a rotation period shorter than 12 days. We performed a timefrequency analysis using the Morlet wavelet yielding a magnetic proxy for our sample of stars. We computed the magnetic index S ph as the standard deviation of the whole time series and the index S ph , which is the mean of standard deviations measured in subseries of length five times the rotation period of the star. We defined new indicators, such as the contrast between high and low activity, to take into account the fact that complete magnetic cycles are not observed for all the stars. We also inferred the Rossby number of the stars and studied their stellar background. Results. This analysis shows different types of behaviour in the 22 F stars. Two stars show behaviour very similar to magnetic activity cycles. Five stars show long-lived spots or active regions suggesting the existence of active longitudes. Two stars in our sample seem to have a decreasing or increasing trend in the temporal variation of the magnetic proxies. Finally, the last group of stars shows magnetic activity (with the presence of spots) but no sign of cycle.

show abstract

Section: Rossby Numbercontrasting

confidence: 99%

Section: Magnetic Index and Other Parameterscontrasting

confidence: 61%

Section: Magnetic Index and Other Parametersmentioning

confidence: 95%

“…A relation between the S -index and the rotation period has been established by Saar & Brandenburg (2002). In Fig.…”

Section: Magnetic Index and Other Parametersmentioning

confidence: 99%

See 2 more Smart Citations

Magnetic activity of F stars observed byKepler

Mathur

García

Ballot

et al. 2014

A&A

161

195

View full text Add to dashboard Cite

show abstract

“…This illustrates that the use of fractional amplitudes obscures the fact that the more active, faster rotators in general have a much larger variability than the Sun, which indicates a much more efficient dynamo. Indeed, Saar & Brandenburg (2002) studied cycle amplitudes for a stellar ensemble and found that ∆R HK / R HK ∝ R HK −0.23 , fractional amplitude decreases with increased activity. In an upcoming work we will use the longer timeseries available today to reexamine cycle properties such as amplitude and period for an ensemble of solar analogs.…”

Section: Linearity Of S With Kmentioning

confidence: 99%

The Mount Wilson Observatory S-Index of the Sun

Egeland

Soon

Baliunas³

et al. 2017

ApJ

104

118

View full text Add to dashboard Cite

The most commonly used index of stellar magnetic activity is the instrumental flux scale of singlyionized calcium H & K line core emission, S, developed by the Mount Wilson Observatory (MWO) HK Project, or the derivative index R HK . Accurately placing the Sun on the S scale is important for comparing solar activity to that of the Sun-like stars. We present previously unpublished measurements of the reflected sunlight from the Moon using the second-generation MWO HK photometer during solar cycle 23 and determine cycle minimum S 23,min = 0.1634 ± 0.0008, amplitude ∆S 23 = 0.0143 ± 0.0012, and mean S 23 = 0.1701 ± 0.0005. By establishing a proxy relationship with the closely related National Solar Observatory Sacramento Peak calcium K emission index, itself well-correlated with the Kodaikanal Observatory plage index, we extend the MWO S time series to cover cycles 15-24 and find on average S min = 0.1621 ± 0.0008, ∆S cyc = 0.0145 ± 0.0012, S cyc = 0.1694 ± 0.0005. Our measurements represent an improvement over previous estimates which relied on stellar measurements or solar proxies with non-overlapping time series. We find good agreement from these results with measurements by the Solar-Stellar Spectrograph at Lowell Observatory, an independently calibrated instrument, which gives us additional confidence that we have accurately placed the Sun on the S-index flux scale.

show abstract

AsteroFLAG: First results from hare‐and‐hounds Exercise #1

Chaplin¹,

Appourchaux

Arentoft

et al. 2008

Astron Nachr

View full text Add to dashboard Cite

We report on initial results from the first phase of Exercise #1 of the asteroFLAG hare and hounds. The asteroFLAG group is helping to prepare for the asteroseismology component of NASA's Kepler mission, and the first phase of Exercise #1 is concerned with testing extraction of estimates of the large and small frequency spacings of the low-degree p modes from Kepler-like artificial data. These seismic frequency spacings will provide key input for complementing the exoplanet search data.

show abstract

A new look at dynamo cycle amplitudes

Cited by 33 publications

References 9 publications

Magnetic activity of F stars observed byKepler

Magnetic activity of F stars observed byKepler

The Mount Wilson Observatory S-Index of the Sun

AsteroFLAG: First results from hare‐and‐hounds Exercise #1

Contact Info

Product

Resources

About