Granulation signatures as seen by Kepler short-cadence data. I. A decoupling between granulation and oscillation timescales for dwarfs

Abstract

Granulation is the observable signature of convection in envelopes of low-mass stars, forming the background in stellar power spectra. While well-studied in evolved giants, granulation on the MS has received less attention. We here study and characterise granulation signatures of MS and SGB stars, extending previous studies of giants to provide a continuous physical picture across evolutionary stages. We analyse 753 Kepler short-cadence stars using a Bayesian nested-sampling framework to evaluate three background descriptions and compare model preferences. This yields full posterior distributions for all parameters, enabling robust comparisons across a diverse stellar sample. No universal preference between background models is found. Assuming a Gaussian oscillation envelope, ${\nu }_{\max }$ estimates are sensitive to model misspecification, with the resulting systematics exceeding the formal uncertainties. The envelope width scales with ${\nu }_{\max }$ across models and shows a dependence on effective temperature. Total granulation amplitudes in dwarfs broadly follow giant-based scalings, however a decoupling appears between the timescale of the primary granulation and the oscillations for MS stars cooler than the Sun. The prolonged granulation timescale is reproduced by 3D simulations of a K-dwarf, driven by reduced convective velocities due to more efficient convective energy transport in denser envelopes. The prolonged granulation timescale increases the frequency separation to the oscillation excess, potentially aiding seismic detectability, while the reduced convective velocities may influence the excitation of stellar oscillations and relate to the low amplitudes observed in cool dwarfs. Finally, we contribute a dataset linking granulation, oscillations, and stellar parameters, providing a foundation for future investigations into their interdependence across the HR diagram.

14 pages, 9 figures, accepted for publication in A&A, abstract abridged

References in corpus (45)

• The chemical composition of the Sun
• Gaia Data Release 3: Summary of the content and survey properties
• dynesty: A Dynamic Nested Sampling Package for Estimating Bayesian Posteriors and Evidences
• Ages and fundamental properties of Kepler exoplanet host stars from asteroseismology
• Testing Scaling Relations for Solar-Like Oscillations from the Main Sequence to Red Giants using Kepler Data
• The connection between stellar granulation and oscillation as seen by the Kepler mission
• The Stagger-grid: A Grid of 3D Stellar Atmosphere Models - I. Methods and General Properties
• Standing on the shoulders of Dwarfs: the $Kepler$ asteroseismic LEGACY sample I - oscillation mode parameters
• Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo
• Asteroseismology of 16000 Kepler Red Giants: Global Oscillation Parameters, Masses, and Radii
• Characterization of the power excess of solar-like oscillations in red giants with Kepler
• The relation between $\Delta \nu$ and ${\nu }_{max}$ for solar-like oscillations
• Gaia Data Release 3: Astrophysical parameters inference system (Apsis) I -- methods and content overview
• An ancient extrasolar system with five sub-Earth-size planets
• Granulation in Red Giants: observations by the Kepler mission and 3D convection simulations
• Radius determination of solar-type stars using asteroseismology: What to expect from the Kepler mission
• Solar Oscillations and Convection: II. Excitation of Radial Oscillations
• Characteristics of solar-like oscillations in red giants observed in the CoRoT exoplanet field
• A Grid of 3D Stellar Atmosphere Models of Solar Metallicity: I. General Properties, Granulation and Atmospheric Expansion
• Predicting the detectability of oscillations in solar-type stars observed by Kepler
• Amplitudes of solar-like oscillations: a new scaling relation
• The First APOKASC Catalog of Kepler Dwarf and Subgiant Stars
• DIAMONDS: a new Bayesian Nested Sampling tool. Application to Peak Bagging of solar-like oscillations
• Bayesian peak-bagging of solar-like oscillators using MCMC: A comprehensive guide
• Automated preparation of Kepler time series of planet hosts for asteroseismic analysis
• NGC 6819: testing the asteroseismic mass scale, mass loss, and evidence for products of non-standard evolution
• Intrinsic photometric characterisation of stellar oscillations and granulation. Solar reference values and CoRoT response functions
• K2P${}^2$ $-$ A photometry pipeline for the K2 mission
• Visibilities and bolometric corrections for stellar oscillation modes observed by Kepler
• Metallicity effect on stellar granulation detected from oscillating red giants in open clusters
• Hydrodynamical simulations of convection-related stellar micro-variability. I. Statistical relations for photometric and photocentric variability
• Observations of intensity fluctuations attributed to granulation and faculae on Sun-like stars from the Kepler mission
• Stellar granulation as seen in disk-integrated intensity. II. Theoretical scaling relations compared with observations
• PBjam: A Python package for automating asteroseismology of solar-like oscillators
• The PLATO Solar-like Light-curve Simulator: A tool to generate realistic stellar light-curves with instrumental effects representative of the PLATO mission
• On the safe use of prior densities for Bayesian model selection
• Expanding the frontiers of cool-dwarf asteroseismology with ESPRESSO. Detection of solar-like oscillations in the K5 dwarf $\epsilon$ Indi
• The relationship between photometric and spectroscopic oscillation amplitudes from 3D stellar atmosphere simulations
• Kepler main-sequence solar-like stars: surface rotation and magnetic-activity evolution
• Luminaries in the Sky: The TESS Legacy Sample of Bright Stars. I. Asteroseismic detections in naked-eye main-sequence and sub-giant solar-like oscillators
• A simple method to measure numax for asteroseismology: application to 16,000 oscillating Kepler red giants
• A Homogeneous Catalog of Oscillating Solar-Type Stars Observed by the Kepler Mission and a New Amplitude Scaling Relation Including Chromospheric Activity
• The signature of granulation in a solar power spectrum as seen with CO${}^5$BOLD
• Asteroseismology with PBjam 2.0: measuring dipole mode frequencies in coupling regimes from main sequence to low-luminosity red giant stars
• Granulation signatures in 3D hydrodynamical simulations: evaluating background model performance using a Bayesian nested sampling framework