Rotation and differential rotation of active<i>Kepler</i>stars

Reinhold, Timo; Reiners, A.; Basri, Gibor

doi:10.1051/0004-6361/201321970

Cited by 353 publications

(454 citation statements)

References 67 publications

(102 reference statements)

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“…High-precision instruments like the CoRoT and Kepler telescopes provide the opportunity to observe multiple rotation periods associated with latitudinal differential rotation (DR), which was observed for many active stars (Reinhold et al 2013). Moreover, spot rotation periods heavily rely on their evolutionary timescales, which becomes more important for less active stars.…”

Section: Succeeding Measurements At the Mount Wilson Observatorymentioning

confidence: 99%

“…To detect periodic signals in the data we use the LombScargle periodogram in a prewhitening approach as described in Reinhold et al (2013). Each quarter is analyzed individually and in the same way.…”

Section: Analysis Of Individual Quartersmentioning

confidence: 99%

“…As mentioned earlier long-term instrumental effects are sometimes difficult to distinguish from slow rotation, especially in an automated period search of a large sample of objects. Furthermore, for this particular sample rotation periods of less than 45 days were measured in Reinhold et al (2013). Measurements of alias periods Notes.…”

Section: Analysis Of the Full Time Seriesmentioning

confidence: 99%

“…Encouraged by high-precision photometry of the CoRoT and Kepler satellites, measurements of stellar rotation periods have become numerous in recent years, unprecedented in their number and accuracy (Meibom et al 2011a;Affer et al 2012;McQuillan et al 2013aMcQuillan et al ,b, 2014Nielsen et al 2013;Walkowicz & Basri 2013;Reinhold et al 2013). Owing to magnetic braking, the rotation period of a star is linked to its age.…”

Section: Introductionmentioning

confidence: 99%

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Rotation, differential rotation, and gyrochronology of activeKeplerstars

Reinhold

Gizon

2015

A&A

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Context. In addition to the discovery of hundreds of exoplanets, the high-precision photometry from the CoRoT and Kepler satellites has led to measurements of surface rotation periods for tens of thousands of stars, which can potentially be used to infer stellar ages via gyrochronology. Aims. Our main goal is to derive ages of thousands of field stars using consistent rotation period measurements derived by different methods. Multiple rotation periods are interpreted as surface differential rotation (DR). We study the dependence of DR with rotation period and effective temperature. Methods. We reanalyze a previously studied sample of 24 124 Kepler stars using different approaches based on the Lomb-Scargle periodogram. Each quarter (Q1-Q14) is treated individually using a prewhitening approach. Additionally, the full time series and their different segments are analyzed. Results. For more than 18 500 stars our results are consistent with the rotation periods from McQuillan et al. (2014, ApJS, 211, 24). Of these, more than 12 300 stars show multiple significant peaks, which we interpret as DR. Dependencies of the DR with rotation period and effective temperature could be confirmed, e.g., the relative DR increases with rotation period. Gyrochronology ages between 100 Myr and 10 Gyr were derived for more than 17 000 stars using different gyrochronology relations, most of them with uncertainties dominated by period variations. We find a bimodal age distribution for T eff between 3200-4700 K. The derived ages reveal an empirical activity-age relation using photometric variability as stellar activity proxy. Additionally, we found 1079 stars with extremely stable (mostly short) periods. Half of these periods may be associated with rotation stabilized by non-eclipsing companions, the other half might be due to pulsations. Conclusions. The derived gyrochronology ages are well constrained since more than ∼93.0% of the stars seem to be younger than the Sun where calibration is most reliable. Explaining the bimodality in the age distribution is challenging, and limits accurate stellar age predictions. The relation between activity and age is interesting, and requires further investigation. The existence of cool stars with almost constant rotation period over more than three years of observation might be explained by synchronization with stellar companions, or a dynamo mechanism keeping the spot configurations extremely stable.

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Section: Succeeding Measurements At the Mount Wilson Observatorymentioning

confidence: 99%

Section: Analysis Of Individual Quartersmentioning

confidence: 99%

Section: Analysis Of the Full Time Seriesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Rotation, differential rotation, and gyrochronology of activeKeplerstars

Reinhold

Gizon

2015

A&A

Self Cite

182

170

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“…For space-based observations, we are confident that even if a spot configuration is less favorable than CoRoT-2a, a unique interpretation is possible from the clean window function and the high photometric precision (e.g., Reinhold et al 2013). Furthermore, inversion of a time series using a spot-modeling approach also allows the extraction of spot longitudes and fractional spot coverage (e.g., Strassmeier & Bopp 1992;Lanza et al 2009;Savanov & Dmitrienko 2012;Roettenbacher et al 2013).…”

Section: Introductionmentioning

confidence: 96%

Stellar rotation, binarity, and lithium in the open cluster IC 4756

Strassmeier

Weingrill

Granzer

et al. 2015

A&A

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Context. An important aspect in the evolutionary scenario of cool stars is their rotation and the rotationally induced magnetic activity and interior mixing. Stars in open clusters are particularly useful tracers for these aspects because of their known ages. Aims. We aim to characterize the open cluster IC 4756 and measure stellar rotation periods and surface differential rotation for a sample of its member stars. Methods. Thirty-seven cluster stars were observed continuously with the CoRoT satellite for 78 days in 2010. Follow-up highresolution spectroscopy of the CoRoT targets and deep Strömgren uvbyβ and Hα photometry of the entire cluster were obtained with our robotic STELLA facility and its echelle spectrograph and wide-field imager, respectively. Results. We determined high-precision photometric periods for 27 of the 37 CoRoT targets and found values between 0.155 and 11.4 days. Twenty of these are rotation periods. Twelve targets are spectroscopic binaries of which 11 were previously unknown; orbits are given for six of them. Six targets were found that show evidence of differential rotation with ΔΩ/Ω in the range 0.04−0.15. Five stars are non-radially pulsating stars with fundamental periods of below 1 d, two stars are semi-contact binaries, and one target is a micro-flaring star that also shows rotational modulation. Nine stars in total were not considered members because of much redder color(s) and deviant radial velocities with respect to the cluster mean. Hα photometry indicates that the cluster ensemble does not contain magnetically over-active stars. The cluster average metallicity is -0.08 ± 0.06 (rms) and its logarithmic lithium abundance for 12 G-dwarf stars is 2.39 ± 0.17 (rms). Conclusions. The cluster is 890 ± 70 Myrs old with an average turn-off mass of 1.8 M and a solar or slightly subsolar metallicity. The distance modulus is 8. m 02 and the average reddening E(b − y) = 0. m 16. The cluster is masked by a very inhomogeneous foreground and background dust distribution and our survey covered 38% of the cluster. The average lithium abundance and the rotation periods in the range 1.7 to 11.4 d are consistent with the cluster age.

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Time‐series analysis of long‐term photometry of BM Canum Venaticorum

et al. 2017

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† The analyzed photometry and numerical results of the analysis are both published electronically at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/yyy/ Axxx.Long-term photometry is commonly used to monitor chromospheric activity of late-type stars. We study standard Johnson differential V photometry of the RS CVn binary BM Canum Venaticorum (BM CVn) spanning over a quarter of a century. Our main aims are to determine the activity cycles, the rate of surface differential rotation, and the rotation period of the active longitudes of BM CVn. The continuous period search (CPS) algorithm is applied to the photometry. The changes of the mean and amplitude of the light curves are used to search for activity cycles. The rotation period changes give an estimate of the rate of surface differential rotation. The Kuiper method is applied to the epochs of the primary and secondary minima to search for active longitudes. The photometry reveals the presence of a stable mean light curve (MLC) connected to the orbital period P orb = 20. d 6252 of this binary. We remove this MLC from the original V magnitudes, which gives us the corrected V ′ magnitudes. These two samples of V and V ′ data are analyzed separately with CPS. The fraction of unreliable CPS models decreases when the MLC is removed. The same significant activity cycle of approximately 12.5 years is detected in both V and V ′ samples. The estimate for the surface differential rotation coefficient, k ≥ 0.10, is the same for both samples, but the number of unrealistic period estimates decreases after removing the MLC. The same active longitude period of P al = 20. d 511 ± 0. d 005 is detected in the V and V ′ magnitudes. This long-term regularity in the epochs of primary and secondary minima of the light curves is not caused by the MLC. On the contrary, the MLC hampers the detection of active longitudes.

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Rotation and differential rotation of activeKeplerstars

Cited by 353 publications

References 67 publications

Rotation, differential rotation, and gyrochronology of activeKeplerstars

Rotation, differential rotation, and gyrochronology of activeKeplerstars

Stellar rotation, binarity, and lithium in the open cluster IC 4756

Time‐series analysis of long‐term photometry of BM Canum Venaticorum

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