The CoRoT target HD 49933: 2- Comparison of theoretical mode amplitudes with observations

Abstract

From the seismic data obtained by CoRoT for the star HD 49933 it is possible, as for the Sun, to constrain models of the excitation of acoustic modes by turbulent convection. We compare a stochastic excitation model described in Paper I (arXiv:0910.4027) with the asteroseismology data for HD 49933, a star that is rather metal poor and significantly hotter than the Sun. Using the mode linewidths measured by CoRoT for HD 49933 and the theoretical mode excitation rates computed in Paper I, we derive the expected surface velocity amplitudes of the acoustic modes detected in HD 49933. Using a calibrated quasi-adiabatic approximation relating the mode amplitudes in intensity to those in velocity, we derive the expected values of the mode amplitude in intensity. Our amplitude calculations are within 1-sigma error bars of the mode surface velocity spectrum derived with the HARPS spectrograph. The same is found with the mode amplitudes in intensity derived for HD 49933 from the CoRoT data. On the other hand, at high frequency, our calculations significantly depart from the CoRoT and HARPS measurements. We show that assuming a solar metal abundance rather than the actual metal abundance of the star would result in a larger discrepancy with the seismic data. Furthermore, calculations that assume the ``new'' solar chemical mixture are in better agreement with the seismic data than those that assume the ``old'' solar chemical mixture. These results validate, in the case of a star significantly hotter than the Sun and Alpha Cen A, the main assumptions in the model of stochastic excitation. However, the discrepancies seen at high frequency highlight some deficiencies of the modelling, whose origin remains to be understood.

8 pages, 3 figures (B-W and color), accepted for publication in Astronomy & Astrophysics. Corrected typo in Eq. (4). Updated references. Language improvements

References in corpus (1)

• The amplitude of solar oscillations using stellar techniques

Cited by in corpus (16)

• Asteroseismology of red giants from the first four months of Kepler data: Global oscillation parameters for 800 stars
• Accurate p-mode measurements of the G0V metal-rich CoRoT target HD 52265
• A Bayesian approach to scaling relations for amplitudes of solar-like oscillations in Kepler stars
• The solar-like CoRoT target HD 170987: spectroscopic and seismic observations
• Granulation properties of giants, dwarfs, and white dwarfs from the CIFIST 3D model atmosphere grid
• How accurate are stellar ages based on stellar models ? I. The impact of stellar models uncertainties
• Stellar granulation as seen in disk-integrated intensity. II. Theoretical scaling relations compared with observations
• Amplitude and lifetime of radial modes in red giant star spectra observed by Kepler
• Pulsation spectrum of Delta Sct stars: the binary HD 50870 as seen with CoRoT and HARPS
• Planetary transit candidates in the CoRoT LRa01 field
• Stellar oscillations. II The non-adiabatic case
• Amplitudes of solar-like oscillations in red-giant stars: Evidences for non-adiabatic effects using CoRoT observations
• Turbulent eddy-time-correlation in the solar convective zone
• A Distant Mirror: Solar Oscillations Observed on Neptune by the Kepler K2 Mission
• Stochastic excitation of acoustic modes in stars
• The efficiency of mixed modes for angular momentum transport