[Paper Review] Rotation and magnetism of Kepler pulsating solar-like stars. Towards asteroseismically calibrated age-rotation relations

R. A. García, T. Ceillier+17 more|Americanae (AECID Library)|Mar 27, 2014

Stellar, planetary, and galactic studiesPhysics and Astronomy116 references118 citations

TL;DR

This study analyzes rotation and magnetic activity in 540 Kepler solar-like stars using asteroseismic ages to calibrate age-rotation relations. By combining two light-curve analysis methods (GWPS and ACF) across two data reduction pipelines (PDC-MAP and KADACS), it identifies distinct rotation-age relationships across hot dwarfs, cool dwarfs, and subgiants, with 61.5% of cool dwarfs showing solar-like magnetic activity levels, highlighting the need to account for stellar population effects in gyrochronology.

ABSTRACT

Kepler ultra-high precision photometry of long and continuous observations provides a unique dataset in which surface rotation and variability can be studied for thousands of stars. Because many of these old field stars also have independently measured asteroseismic ages, measurements of rotation and activity are particularly interesting in the context of age-rotation-activity relations. In particular, age-rotation relations generally lack good calibrators at old ages, a problem that this Kepler sample of old-field stars is uniquely suited to address. We study the surface rotation and photometric magnetic activity of a subset of 540 solar-like stars on the main- sequence and the subgiant branch for which stellar pulsations have been measured. The rotation period was determined by comparing the results from two different analysis methods: i) the projection onto the frequency domain of the time-period analysis, and ii) the autocorrelation function (ACF) of the light curves. Reliable surface rotation rates were then extracted by comparing the results from two different sets of calibrated data and from the two complementary analyses. We report rotation periods for 310 out of 540 targets (excluding known binaries and candidate planet-host stars); our measurements span a range of 1 to 100 days. The photometric magnetic activity levels of these stars were computed, and for 61.5% of the dwarfs, this level is similar to the range, from minimum to maximum, of the solar magnetic activity. We demonstrate that hot dwarfs, cool dwarfs, and subgiants have very different rotation-age relationships, highlighting the importance of separating out distinct populations when interpreting stellar rotation periods. Our sample of cool dwarf stars with age and metallicity data of the highest quality is consistent with gyrochronology relations reported in the literature.

Motivation & Objective

• To calibrate age-rotation-activity relations in old-field stars using asteroseismic ages from Kepler photometry.
• To measure surface rotation periods and photometric magnetic activity levels in a homogeneous sample of 540 main-sequence and subgiant stars.
• To assess the reliability of gyrochronology by separating stellar populations based on temperature, gravity, and evolutionary stage.
• To evaluate whether photometric activity indices can serve as proxies for long-term magnetic activity, particularly for solar-analog stars.
• To identify limitations in current activity-rotation and age-activity relations due to incomplete sampling of magnetic cycles.

Proposed method

• Applied two independent detection methods—Gaussian Process Power Spectral (GWPS) analysis and Autocorrelation Function (ACF) analysis—to extract rotation periods from Kepler light curves.
• Used two calibrated light-curve products—PDC-MAP and KADACS—across the analysis to ensure robustness and reduce systematic errors.
• Computed a photometric activity index ⟨Sph,k=5⟩ that accounts for rotation period to quantify magnetic activity levels across the sample.
• Classified stars into three groups: hot dwarfs (Teff > 6250 K), cool main-sequence dwarfs (Teff ≤ 6250 K, log g > 4.0), and subgiants (Teff ≤ 6250 K, log g ≤ 4.0) for population-specific analysis.
• Cross-verified results by excluding known binaries and planet-host candidates to ensure rotational periods reflect intrinsic stellar rotation.
• Compared results from high-precision asteroseismic age estimates with rotation periods to assess consistency with existing gyrochronology relations.

Experimental results

Research questions

• RQ1 How do rotation periods and magnetic activity levels vary across distinct stellar populations (hot dwarfs, cool dwarfs, subgiants) in the Kepler field?
• RQ2 To what extent do asteroseismically derived ages improve the calibration of age-rotation relations compared to traditional methods?
• RQ3 Are photometric activity indices reliable indicators of long-term magnetic activity for solar-like stars, especially when observing time spans are limited?
• RQ4 Why do rotation-age relationships differ significantly between hot dwarfs, cool dwarfs, and subgiants, and how can this be modeled?
• RQ5 Can the observed activity levels in 61.5% of cool dwarfs be interpreted as solar-like variability, and what does this imply for stellar magnetic cycles?

Key findings

• Rotation periods were reliably measured for 310 out of 540 stars, spanning 1 to 100 days, using a combination of GWPS and ACF methods across two data reduction pipelines.
• Hot dwarfs exhibit faster rotation than cool dwarfs due to weaker magnetic braking, consistent with their thinner convective envelopes.
• Subgiants show longer rotation periods (10–100 days), dependent on their main-sequence progenitor temperature and expansion degree on the subgiant branch.
• 61.5% of cool main-sequence dwarfs have photometric magnetic activity levels comparable to the Sun’s minimum to maximum cycle variation.
• The rotation-age relationship differs significantly across stellar populations, indicating that population-specific calibration is essential for accurate gyrochronology.
• A subset of stars with high-precision asteroseismic ages and spectroscopic constraints shows a rotation-age slope consistent with literature gyrochronology relations, validating the method for future application.