CoRoT sounds the stars: p-mode parameters of Sun-like oscillations on HD 49933

Abstract

Context. The first asteroseismology results from CoRoT are presented, on a star showing Sun-like oscillations. We have analyzed a 60 day lightcurve of high-quality photometric data collected by CoRoT on the F5 V star HD 49933. The data reveal a rich spectrum of overtones of low-degree p modes. Aims. Our aim was to extract robust estimates of the key parameters of the p modes observed in the power spectrum of the lightcurve. Methods. Estimation of the mode parameters was performed using maximum likelihood estimation of the power spectrum. A global fitting strategy was adopted whereby 15 mode orders of the mode spectrum (45 modes) were fitted simultaneously. Results. The parameter estimates that we list include mode frequencies, peak linewidths, mode amplitudes, and a mean rotational frequency splitting. We find that the average large frequency (overtone) spacing derived from the fitted mode frequencies is 85.9 ± 0.15 μHz. The frequency of maximum amplitude of the radial modes is at 1760 μHz, where the observed rms mode amplitude is 3.75 ± 0.23 ppm. The mean rotational splitting of the non-radial modes appears to be in the range ≈2.7 μHz to ≈3.4 μHz. The angle of inclination offered by the star, as determined by fits to the amplitude ratios of the modes, appears to be in the range ≈50 degrees to ≈62 degrees.

Narrow frequency-windowed autocorrelations as a diagnostic of solar-like stars

“…The rapid decrease in the height of successive peaks in Fig. 3a indicates the short life time of the modes; this is to be expected since the line widths in the power spectrum are broad (Appourchaux et al 2008). Figures 3b-d show the autocorrelation power for three independent narrower windows of 400 μHz.…”

“…It is therefore not necessary to transform back to the time domain but simply to take the Fourier transform of the filtered power spectrum. Figure 1 shows the autocorrelation and the amplitude envelope of the photometric time series of the F5V star HD 49933 observed for 60 days in the initial run of CoRoT (see below and Appourchaux et al 2008), which has been filtered (using a sin 2 filter) in the frequency interval ν = 1200−2400 μHz. The amplitude envelope A e (t) removes the rapidly oscillating component in the autocorrelation due to the frequencies.…”

“…The F5V (m v = 5.77) star HD 49933 was observed for 60 days in the initial run of CoRoT (see Appourchaux et al 2008). After applying several corrections, details of which are given in Samadi et al (2006), the light curves are sampled at a cadence of 32 s, the duty cycle is ∼90% and the gaps, mainly due to the passages of the satellite through the South Atlantic anomaly, are filled by interpolation.…”

Detection of Jovian seismic waves: a new probe of its interior structure

“…l = 1 and l = 2). Oscillating stars also display similar signatures (Appourchaux et al 2008;García et al 2009). However, other effects could a priori cause the measured signal: temperature fluctuations in the interferometer, telescope pointing errors, albedo features on Jupiter, and solar p-modes reflected by Jupiter's atmosphere.…”

Differential Rotation in Sun-like Stars from Surface Variability and Asteroseismology

“…Therefore, for a slowly rotating Sun-like star we may make the approximation that 4) where Ω/2π is equivalent to the rotational splitting which is often denoted by δν. In most studies this is what is used when fitting oscillation spectra in order to measure the mean rotation of stars (Bazot et al 2007, Appourchaux et al 2008, Lund et al 2014a). …”