The nature of p-modes and granulation in HD 49933 observed by CoRoT

TL;DR

This study analyzes CoRoT observations of HD 49933 to identify pulsation modes and compare them with stellar models, revealing a preference for solar metallicity and nonadiabatic modeling for better frequency matches.

Contribution

It introduces a Bayesian approach for fitting stellar oscillation spectra and provides the first detailed comparison of observed p-modes with models for HD 49933.

Findings

26 pulsation frequencies identified as radial and dipolar modes

Best-fitting models have solar composition and match the star's position in the H-R diagram

Nonadiabatic models better reproduce observed frequencies than adiabatic ones

Abstract

Context: Recent observations of HD49933 by the space-photometric mission CoRoT provide photometric evidence of solar type oscillations in a star other than our Sun. The first published reduction, analysis, and interpretation of the CoRoT data yielded a spectrum of p-modes with l = 0, 1, and 2. Aims: We present our own analysis of the CoRoT data in an attempt to compare the detected pulsation modes with eigenfrequencies of models that are consistent with the observed luminosity and surface temperature. Methods: We used the Gruberbauer et al. frequency set derived based on a more conservative Bayesian analysis with ignorance priors and fit models from a dense grid of model spectra. We also introduce a Bayesian approach to searching and quantifying the best model fits to the observed oscillation spectra. Results: We identify 26 frequencies as radial and dipolar modes. Our best fitting model has solar composition and coincides within the error box with the spectroscopically determined position of HD49933 in the H-R diagram. We also show that lower-than-solar Z models have a lower probability of matching the observations than the solar metallicity models. To quantify the effect of the deficiencies in modeling the stellar surface layers in our analysis, we compare adiabatic and nonadiabatic model fits and find that the latter reproduces the observed frequencies better.