Solar-like oscillations in red giants observed with Kepler: influence of increased timespan on global oscillation parameters

Author(s)

S. Hekker, Y. Elsworth, B. Mosser, T. Kallinger, W. J. Chaplin, J. De Ridder, R. A. García, D. Stello, B. D. Clarke, J. R. Hall, K. A. Ibrahim

Abstract

Context. The length of the asteroseismic timeseries obtained from the

Kepler satellite analysed here span 19 months. Kepler provides the

longest continuous timeseries currently available, which calls for a

study of the influence of the increased timespan on the accuracy and

precision of the obtained results. Aims: We aim to investigate

how the increased timespan influences the detectability of the

oscillation modes, and the absolute values and uncertainties of the

global oscillation parameters, i.e., frequency of maximum oscillation

power, νmax, and large frequency separation between modes

of the same degree and consecutive orders, ⟨ Δν ⟩ .

Methods: We use published methods to derive νmax

and ⟨ Δν ⟩ for timeseries ranging from 50 to 600 days

and compare these results as a function of method, timespan and ⟨

Δν ⟩ . Results: We find that in general a minimum

of the order of 400 day long timeseries are necessary to obtain reliable

results for the global oscillation parameters in more than 95% of the

stars, but this does depend on ⟨ Δν ⟩ . In a

statistical sense the quoted uncertainties seem to provide a reasonable

indication of the precision of the obtained results in short (50-day)

runs, they do however seem to be overestimated for results of longer

runs. Furthermore, the different definitions of the global parameters

used in the different methods have non-negligible effects on the

obtained values. Additionally, we show that there is a correlation

between νmax and the flux variance. Conclusions: We

conclude that longer timeseries improve the likelihood to detect

oscillations with automated codes (from ~60% in 50 day runs to >95%

in 400 day runs with a slight method dependence) and the precision of

the obtained global oscillation parameters. The trends suggest that the

improvement will continue for even longer timeseries than the 600 days

considered here, with a reduction in the median absolute deviation of

more than a factor of 10 for an increase in timespan from 50 to 2000

days (the currently foreseen length of the mission). This work shows

that global parameters determined with high precision - thus from long

datasets - using different definitions can be used to identify the

evolutionary state of the stars.

 

Values of the global oscillation parameters can be obtained from the

authors upon request.

Organisation(s)

Department of Astrophysics

External organisation(s)

University of Amsterdam (UvA), University of Birmingham, Université de recherche Paris Sciences et Lettres, Katholieke Universiteit Leuven, Université Paris VII - Paris-Diderot, The University of Sydney, National Aeronautics & Space Administration (NASA)

Journal

Astronomy & Astrophysics

Volume

544

ISSN

0004-6361

DOI

https://doi.org/10.1051/0004-6361/201219328

Publication date

08-2012

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics

Keywords

Portal url

https://ucrisportal.univie.ac.at/en/publications/dce8e29e-6bea-46d3-9521-12616b051269