Stellar granulation as seen in disk-integrated intensity. II. Theoretical scaling relations compared with observations

Author(s)

R. Samadi, K. Belkacem, H.-G. Ludwig, E. Caffau, T. L. Campante, G. R. Davies, T. Kallinger, M. N. Lund, A. Baglin, S. Mathur, R. A. Garcia

Abstract

Context. A large set of stars observed by CoRoT and Kepler shows clear

evidence for the presence of a stellar background, which is interpreted

to arise from surface convection, i.e., granulation. These observations

show that the characteristic time-scale (τeff) and the

root-mean-square (rms) brightness fluctuations (σ) associated with

the granulation scale as a function of the peak frequency

(νmax) of the solar-like oscillations. Aims: We aim

at providing a theoretical background to the observed scaling relations

based on a model developed in Paper I. Methods: We computed for

each 3D model the theoretical power density spectrum (PDS) associated

with the granulation as seen in disk-integrated intensity on the basis

of the theoretical model published in Paper I. For each PDS we derived

the associated characteristic time (τeff) and the rms

brightness fluctuations (σ) and compared these theoretical values

with the theoretical scaling relations derived from the theoretical

model and the measurements made on a large set of Kepler targets.

Results: We derive theoretical scaling relations for τeff

and σ, which show the same dependence on νmax as the

observed scaling relations. In addition, we show that these quantities

also scale as a function of the turbulent Mach number

(ℳa) estimated at the photosphere. The theoretical

scaling relations for τeff and σ match the

observations well on a global scale. Quantitatively, the remaining

discrepancies with the observations are found to be much smaller than

previous theoretical calculations made for red giants.

Conclusions: Our modelling provides additional theoretical support for

the observed variations of σ and τeff with

νmax. It also highlights the important role of

ℳa in controlling the properties of the stellar

granulation. However, the observations made with Kepler on a wide

variety of stars cannot confirm the dependence of our scaling relations

on ℳa. Measurements of the granulation background and

detections of solar-like oscillations in a statistically sufficient

number of cool dwarf stars will be required for confirming the

dependence of the theoretical scaling relations with

ℳa.

 

Appendices are available in electronic form at www.aanda.org

Organisation(s)

Department of Astrophysics

External organisation(s)

Landessternwarte Königstuhl (LSW), Université de recherche Paris Sciences et Lettres, University of Birmingham, Aarhus University, National Center for Atmospheric Research (NCAR), Space Science Institute, Université Paris VII - Paris-Diderot

Journal

Astronomy & Astrophysics

Volume

559

No. of pages

12

ISSN

0004-6361

DOI

https://doi.org/10.1051/0004-6361/201220817

Publication date

11-2013

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics, 103003 Astronomy

Keywords

Portal url

https://ucrisportal.univie.ac.at/en/publications/8551d576-7593-4f4f-aa69-a1086f3a24bb