New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?

Eiff, M. Ammler‐von; Reiners, A.

doi:10.1051/0004-6361/201118724

Cited by 92 publications

(53 citation statements)

References 29 publications

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“…These authors predicted a very strong temperature dependence (dΩ ∝ T 8.9 eff ), which is not supported by our measurements. Light blue diamonds show measurements 7 from Ammler-von Eiff & Reiners (2012) that are in good agreement with our findings. Theoretical predictions from Küker & Rüdiger (2011) are shown as dash-dotted red and dashed orange curve.…”

Section: Differential Rotationsupporting

confidence: 88%

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: Differential Rotationsupporting

confidence: 88%

Rotation, differential rotation, and gyrochronology of activeKeplerstars

Reinhold

Gizon

2015

A&A

180

170

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“…Using the Fourier transform method Reiners & Schmitt (2003) also found that α increases with rotation period for F-G stars. This result was confirmed by Ammler-von Eiff & Reiners (2012) who compiled previous results and new measurements for A-F stars. Barnes et al (2005) found that ΔΩ only weakly correlates with rotation rate according ΔΩ ≈ Ω 0.15 .…”

Section: Fig 16 Comparison Of Periods Fromsupporting

confidence: 74%

Rotation and differential rotation of activeKeplerstars

Reinhold

Reiners

Basri

2013

A&A

350

397

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Context. The Kepler space telescope monitors more than 160 000 stars with an unprecedented precision providing the opportunity to study the rotation of thousands of stars. Aims. We present rotation periods for thousands of active stars in the Kepler field derived from Q3 data. In most cases a second period close to the rotation period was detected that we interpreted as surface differential rotation (DR). We show how the absolute and relative shear (ΔΩ and α = ΔΩ/Ω, respectively) correlate with rotation period and effective temperature. Methods. Active stars were selected from the whole sample using the range of the variability amplitude. To detect different periods in the light curves we used the Lomb-Scargle periodogram in a pre-whitening approach to achieve parameters for a global sine fit. The most dominant periods from the fit were associated to different surface rotation periods. Our purely mathematical approach is capable of detecting different periods but cannot distinguish between the physical origins of periodicity. We ascribe the existence of different periods to DR, but spot evolution could also play a role. Because of the large number of stars the period errors are estimated statistically. We thus cannot exclude the existence of false positives among our periods.Results. In our sample of 40 661 active stars we found 24 124 rotation periods P 1 between 0.5 and 45 days, with a mean of P 1 = 16.3 days. The distribution of stars with 0.5 < B − V < 1.0 and ages derived from angular momentum evolution that are younger than 300 Myr is consistent with a constant star-formation rate; the detection among older stars is incomplete probably because of our active sample selection. A second period P 2 within ±30% of the rotation period P 1 was found in 18 616 stars (77.2%). Attributing these two periods to DR we found that for active stars other than the Sun the relative shear α increases with rotation period, and slightly decreases with effective temperature. The absolute shear ΔΩ slightly increases from ΔΩ = 0.079 rad d −1 at T eff = 3500 K to ΔΩ = 0.096 rad d −1 at T eff = 6000 K. Above 6000 K, ΔΩ shows much larger scatter. The dependence of ΔΩ on rotation period is weak over a large period range. Conclusions. Latitudinal differential rotation measured for the first time in more than 18 000 stars provides a comprehensive picture of stellar surface shear. This picture is consistent with major predictions from mean-field theory, and seems to support these models. To what extent our observations are prone to false positives and selection bias has not been fully explored, and needs to be addressed using other data, including the full Kepler time coverage.

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“…Reiners & Schmitt 2002Ammler-von Eiff & Reiners 2012, and references therein). For HD 105382 and HD 131120, Briquet et al (2004) obtained v sin i = 70 ± 5 and 60 ± 5 km s −1 , respectively, from modelling of He and Si surface spots by assuming constant surface rotation.…”

Section: Rotational Velocities From Spot Modelling or Asteroseismologymentioning

confidence: 99%

On the use of the Fourier transform to determine the projected rotational velocity of line-profile variable B stars

Aerts

Simón‐Díaz

Groot

et al. 2014

A&A

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Context. The Fourier transform method is a popular tool for deriving the rotational velocities of stars from their spectral line profiles. However, its domain of validity does not include line-profile variables with time-dependent profiles. Aims. We investigate the performance of the method for such cases, by interpreting the line-profile variations of spotted B stars and of pulsating B stars, as if their spectral lines were caused by uniform surface rotation along with macroturbulence. Methods. We perform time-series analysis and harmonic least-squares fitting of various line diagnostics and of the outcome of several implementations of the Fourier transform method. Results. We find that the projected rotational velocities derived from the Fourier transform vary appreciably during the pulsation cycle whenever the pulsational and rotational velocity fields have similar magnitudes. The macroturbulent velocities derived while ignoring the pulsations can vary by tens of km s −1 during the pulsation cycle. The temporal behaviour of the deduced rotational and macroturbulent velocities are in antiphase with each other. The rotational velocity is in phase with the second moment of the line profiles. Conclusions. The application of the Fourier method to stars with considerable pulsational line broadening may lead to an appreciable spread in the values of the rotation velocity, and, by implication, of the deduced value of the macroturbulence. These two quantities should therefore not be derived from single snapshot spectra if the aim is to use them as a solid diagnostic evaluating stellar evolution models of slow-to-moderate rotators.

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New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?

Cited by 92 publications

References 29 publications

Rotation, differential rotation, and gyrochronology of activeKeplerstars

Rotation, differential rotation, and gyrochronology of activeKeplerstars

Rotation and differential rotation of activeKeplerstars

On the use of the Fourier transform to determine the projected rotational velocity of line-profile variable B stars

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