Surface effects on the red giant branch

Research output: Contribution to journalArticlepeer-review

Authors

Colleges, School and Institutes

External organisations

  • Aarhus Universitet
  • Max-Planck-Institut für Sonnensystemforschung
  • Georg August Universitaet

Abstract

Individual mode frequencies have been detected in thousands of individual solar-like oscillators on the red giant branch (RGB). Fitting stellar models to these mode frequencies, however, is more difficult than in main-sequence stars. This is partly because of the uncertain magnitude of the surface effect: the systematic difference between observed and modelled frequencies caused by poor modelling of the near-surface layers. We aim to study the magnitude of the surface effect in RGB stars. Surface effect corrections used for main-sequence targets are potentially large enough to put the non-radial mixed modes in RGB stars out of order, which is unphysical. Unless this can be circumvented, model fitting of evolved RGB stars is restricted to the radial modes, which reduces the number of available modes. Here, we present a method to suppress gravity modes (g-modes) in the cores of our stellarmodels, so that they have only pure pressure modes (p-modes).We showthat themethod gives unbiased results and apply it to three RGB solar-like oscillators in double-lined eclipsing binaries: KIC 8410637, KIC 9540226, and KIC 5640750. In all three stars, the surface effect decreases the model frequencies consistently by about 0.1-0.3 μHz at the frequency of maximum oscillation power vmax, which agrees with existing predictions from three-dimensional radiation hydrodynamics simulations. Though our method in essence discards information about the stellar cores, it provides a useful step forward in understanding the surface effect in RGB stars.

Details

Original languageEnglish
Pages (from-to)4697-4709
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume478
Issue number4
Early online date3 May 2018
Publication statusPublished - 21 Aug 2018

Keywords

  • Binaries: eclipsing, KIC 8410637, KIC 9540226, Stars: evolution, Stars: individual: KIC 5640750, Stars: interiors, Stars: oscillations