Stellar magnetism: empirical trends with age and rotation

Vidotto, A. A.; Gregory, S. G.; Jardine, M.; Donati, J.‐F.; Petit, P.; Morin, J.; Folsom, C. P.; Bouvier, J.; Cameron, A. Collier; Hussain, G. A. J.; Marsden, S. C.; Waite, I. A.; Farès, R.; Jeffers, S. V.; Nascimento, J. D. do

doi:10.1093/mnras/stu728

Cited by 404 publications

(546 citation statements)

References 127 publications

(127 reference statements)

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“…Recently, efforts are underway to calibrate asteroseismology ages by comparing them to gyrochronology measurements do Nascimento et al 2014;Lebreton & Goupil 2014;Angus et al 2015). Furthermore, Vidotto et al (2014) found a correlation between the average large-scale magnetic field strength and the stellar age according to |B V | ∝ t −0.655 similar to Skumanich's law, calling this method magnetochronology. A review article on various age dating methods was provided by Soderblom (2010).…”

Section: Succeeding Measurements At the Mount Wilson Observatorymentioning

confidence: 99%

Rotation, differential rotation, and gyrochronology of activeKeplerstars

Reinhold

Gizon

2015

A&A

180

170

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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%

Rotation, differential rotation, and gyrochronology of activeKeplerstars

Reinhold

Gizon

2015

A&A

180

170

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“…This has obvious consequences on stellar evolution (Charbonnel et al 2013), the depletion of light elements such as Lithium (Bouvier 2008;Eggenberger et al 2012a), and the type of magnetic dynamos that may be instrumental in young solartype stars (Vidotto et al 2014a). We return to these aspects in the next section.…”

Section: Differential Rotationmentioning

confidence: 99%

Improved angular momentum evolution model for solar-like stars

Gallet

Bouvier

2015

A&A

Self Cite

229

290

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Context. Understanding the physical processes that dictate the angular momentum evolution of solar-type stars from birth to maturity remains a challenge for stellar physics. Aims. We aim to account for the observed rotational evolution of low-mass stars over the age range from 1 Myr to 10 Gyr. Methods. We developed angular momentum evolution models for 0.5 and 0.8 M stars. The parametric models include a new wind braking law based on recent numerical simulations of magnetised stellar winds, specific dynamo and mass-loss rate prescriptions, as well as core-envelope decoupling. We compare model predictions to the distributions of rotational periods measured for low-mass stars belonging to star-forming regions and young open clusters. Furthermore, we explore the mass dependence of model parameters by comparing these new models to the solar-mass models we developed earlier.Results. Rotational evolution models are computed for slow, median, and fast rotators at each stellar mass. The models reproduce reasonably well the rotational behaviour of low-mass stars between 1 Myr and 8−10 Gyr, including pre-main sequence to zero-age main sequence spin up, prompt zero-age main sequence spin down, and early-main sequence convergence of the surface rotation rates. Fast rotators are found to have systematically shorter disk lifetimes than moderate and slow rotators, thus enabling dramatic pre-main sequence spin up. They also have shorter core-envelope coupling timescales, i.e., more uniform internal rotation. As for the mass dependence, lower mass stars require significantly longer core-envelope coupling timescales than solar-type stars, which results in strong differential rotation developing in the stellar interior on the early main sequence. Lower mass stars also require a weaker braking torque to account for their longer spin-down timescale on the early main sequence, while they ultimately converge towards lower rotational velocities than solar-type stars in the longer term because of their reduced moment of inertia. We also find evidence that the mass dependence of the wind braking efficiency may be related to a change in the magnetic topology in lower mass stars. Conclusions. We have included in parametric models the main physical processes that dictate the angular momentum evolution of low-mass stars. The models suggest that these processes are quite sensitive to both mass and instantaneous rotation rate. We have worked out and reported here the main trends of these mass and rotation dependencies, whose origin still have to be addressed through a detailed modelling of magnetised stellar winds, internal angular momentum transport processes, and protoplanetary disk dissipation mechanisms.

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“…Stars with relatively rapidly rotating convective cores (small Rossby numbers Ro; see Section 3.1) would generate strong core fields, while stars with slowly rotating cores might not produce strong and/or stable internal magnetic fields. Indeed, several recent studies of dynamo action in young solar-type stars (Vidotto et al 2014;See et al 2015;Folsom et al 2016) have shown that their dynamos produce field strengths that saturate for  Ro 0.1, and which scale as µ ---…”

Section: Incidence Rate Of Strong Magnetic Fields In Red Giant Starsmentioning

confidence: 99%

Asteroseismic Signatures of Evolving Internal Stellar Magnetic Fields

Cantiello

Fuller

Bildsten

2016

ApJ

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Recent asteroseismic analyses indicate the presence of strong (B  10 5 G) magnetic fields in the cores of many red giant stars. Here, we examine the implications of these results for the evolution of stellar magnetic fields, and we make predictions for future observations. Those stars with suppressed dipole modes indicative of strong core fields should exhibit moderate but detectable quadrupole mode suppression. The long magnetic diffusion times within stellar cores ensure that dynamo-generated fields are confined to mass coordinates within the main-sequence (MS) convective core, and the observed sharp increase in dipole mode suppression rates above 1.5 M e is likely explained by the larger convective core masses and faster rotation of these more massive stars. In clump stars, core fields of ∼10 5 G can suppress dipole modes, whose visibility should be equal to or less than the visibility of suppressed modes in ascending red giants. High dipole mode suppression rates in low-mass (M  2 M e ) clump stars would indicate that magnetic fields generated during the MS can withstand subsequent convective phases and survive into the compact remnant phase. Finally, we discuss implications for observed magnetic fields in white dwarfs and neutron stars, as well as the effects of magnetic fields in various types of pulsating stars.

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Stellar magnetism: empirical trends with age and rotation

Cited by 404 publications

References 127 publications

Rotation, differential rotation, and gyrochronology of activeKeplerstars

Rotation, differential rotation, and gyrochronology of activeKeplerstars

Improved angular momentum evolution model for solar-like stars

Asteroseismic Signatures of Evolving Internal Stellar Magnetic Fields

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