The CoRoT target HD 49933 II. Comparison of theoretical mode amplitudes with observations

R. Samadi, H. G. Ludwig, K. Belkacem, M. J. Goupil, Othman Benomar, B. Mosser, M. A. Dupret, F. Baudin, T. Appourchaux, E. Michel

Research output: Contribution to journalArticle

Abstract

Context: The seismic data obtained by CoRoT for the star HD 49933 enable us for the first time to measure directly the amplitudes and linewidths of solar-like oscillations for a star other than the Sun. From those measurements it is possible, as was done for the Sun, to constrain models of the excitation of acoustic modes by turbulent convection. Aims: We compare a stochastic excitation model described in Paper I with the asteroseismology data for HD 49933, a star that is rather metal poor and significantly hotter than the Sun. Methods: Using the seismic determinations of the mode linewidths detected by CoRoT for HD 49933 and the theoretical mode excitation rates computed in Paper I for the specific case of HD 49933, 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. Results: Except at rather high frequency, our amplitude calculations are within 1-σ error bars of the mode surface velocity spectrum derived with the HARPS spectrograph. The same is found with respect to the mode amplitudes in intensity derived for HD 49933 from the CoRoT data. On the other hand, at high frequency (? ≳ 1.9 mHz), our calculations depart significantly 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, we present calculations which assume the "new" solar chemical mixture to be in better agreement with the seismic data than those that assumed the "old" solar chemical mixture. Conclusions. These results validate in the case of a star significantly hotter than the Sun and α 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.We also show that it is important to take the surface metal abundance of the solar-like pulsators into account.

Original languageEnglish (US)
Article numberA15
JournalAstronomy and Astrophysics
Volume509
Issue number1
DOIs
StatePublished - Jan 1 2010

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seismic data
sun
metal
stars
acoustics
excitation
metals
solar oscillations
asteroseismology
hot stars
comparison
convection
oscillation
metal surfaces
spectrographs
modeling
calculation
approximation
chemical
rate

Keywords

  • Convection - Turbulence - Stars
  • HD 49933
  • Helioseismology - Stars
  • Individual
  • Oscillations - Sun

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Samadi, R., Ludwig, H. G., Belkacem, K., Goupil, M. J., Benomar, O., Mosser, B., ... Michel, E. (2010). The CoRoT target HD 49933 II. Comparison of theoretical mode amplitudes with observations. Astronomy and Astrophysics, 509(1), [A15]. https://doi.org/10.1051/0004-6361/200911868

The CoRoT target HD 49933 II. Comparison of theoretical mode amplitudes with observations. / Samadi, R.; Ludwig, H. G.; Belkacem, K.; Goupil, M. J.; Benomar, Othman; Mosser, B.; Dupret, M. A.; Baudin, F.; Appourchaux, T.; Michel, E.

In: Astronomy and Astrophysics, Vol. 509, No. 1, A15, 01.01.2010.

Research output: Contribution to journalArticle

Samadi, R, Ludwig, HG, Belkacem, K, Goupil, MJ, Benomar, O, Mosser, B, Dupret, MA, Baudin, F, Appourchaux, T & Michel, E 2010, 'The CoRoT target HD 49933 II. Comparison of theoretical mode amplitudes with observations', Astronomy and Astrophysics, vol. 509, no. 1, A15. https://doi.org/10.1051/0004-6361/200911868
Samadi, R. ; Ludwig, H. G. ; Belkacem, K. ; Goupil, M. J. ; Benomar, Othman ; Mosser, B. ; Dupret, M. A. ; Baudin, F. ; Appourchaux, T. ; Michel, E. / The CoRoT target HD 49933 II. Comparison of theoretical mode amplitudes with observations. In: Astronomy and Astrophysics. 2010 ; Vol. 509, No. 1.
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abstract = "Context: The seismic data obtained by CoRoT for the star HD 49933 enable us for the first time to measure directly the amplitudes and linewidths of solar-like oscillations for a star other than the Sun. From those measurements it is possible, as was done for the Sun, to constrain models of the excitation of acoustic modes by turbulent convection. Aims: We compare a stochastic excitation model described in Paper I with the asteroseismology data for HD 49933, a star that is rather metal poor and significantly hotter than the Sun. Methods: Using the seismic determinations of the mode linewidths detected by CoRoT for HD 49933 and the theoretical mode excitation rates computed in Paper I for the specific case of HD 49933, 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. Results: Except at rather high frequency, our amplitude calculations are within 1-σ error bars of the mode surface velocity spectrum derived with the HARPS spectrograph. The same is found with respect to the mode amplitudes in intensity derived for HD 49933 from the CoRoT data. On the other hand, at high frequency (? ≳ 1.9 mHz), our calculations depart significantly 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, we present calculations which assume the {"}new{"} solar chemical mixture to be in better agreement with the seismic data than those that assumed the {"}old{"} solar chemical mixture. Conclusions. These results validate in the case of a star significantly hotter than the Sun and α 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.We also show that it is important to take the surface metal abundance of the solar-like pulsators into account.",
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AU - Benomar, Othman

AU - Mosser, B.

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AB - Context: The seismic data obtained by CoRoT for the star HD 49933 enable us for the first time to measure directly the amplitudes and linewidths of solar-like oscillations for a star other than the Sun. From those measurements it is possible, as was done for the Sun, to constrain models of the excitation of acoustic modes by turbulent convection. Aims: We compare a stochastic excitation model described in Paper I with the asteroseismology data for HD 49933, a star that is rather metal poor and significantly hotter than the Sun. Methods: Using the seismic determinations of the mode linewidths detected by CoRoT for HD 49933 and the theoretical mode excitation rates computed in Paper I for the specific case of HD 49933, 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. Results: Except at rather high frequency, our amplitude calculations are within 1-σ error bars of the mode surface velocity spectrum derived with the HARPS spectrograph. The same is found with respect to the mode amplitudes in intensity derived for HD 49933 from the CoRoT data. On the other hand, at high frequency (? ≳ 1.9 mHz), our calculations depart significantly 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, we present calculations which assume the "new" solar chemical mixture to be in better agreement with the seismic data than those that assumed the "old" solar chemical mixture. Conclusions. These results validate in the case of a star significantly hotter than the Sun and α 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.We also show that it is important to take the surface metal abundance of the solar-like pulsators into account.

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KW - Individual

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