Solar-like oscillations in HD 181420: data analysis of 156 days of CoRoT data

Abstract

Context. The estimate of solar-like oscillation properties, such as their frequencies, amplitudes and lifetimes, is challenging because of their low amplitudes and will benefit from long and uninterrupted observing runs. The space telescope CoRoT allows us to obtain high-performance photometric data over a long and quasi continuous period. Among its main targets are stars for which we expect solar-like oscillations. Aims. HD 181420, an F2 main sequence star, has been observed by CoRoT during its first long run covering about 156 days. With this unprecedently high-quality set of data, our aim is to derive the p-mode parameters that can be used to probe the stellar interior. Methods. The CoRoT data obtained on HD 181420 is analysed using a classical Fourier approach for the search for the p mode signature. The p-mode parameters are then derived using global fitting of the power spectrum by a Lorentzian model, as used widely in the solar case. Results. From the p-mode frequencies, the mean value of the large spacing is estimated to be 75 μHz. The p-mode amplitudes are slightly less than 4 ppm with a line width of about 8 μHz at the maximum of the p modes. The inclination angle is estimated to be around 45 • . The large mode line-width combined with the observed mode spacing make it difficult to identify the = 2 modes and to estimate the rotational splitting. We explore two scenarios for the identification of the modes.

Short-lived spots in solar-like stars as observed by CoRoT

“…We chose to focus this analysis on the main targets of the CoRoT seismology field already observed: HD 49933 (Appourchaux et al 2008), HD 175726 (Mosser et al 2009), HD 181420 (Barban et al 2009) and HD 181906 (García et al 2009). The list of the stars and their characteristics are presented in Table 1.…”

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

“…HD 181420 is an F2 (m v = 6.57) star observed by CoRoT in a 156 day run , Barban et al 2009). Details of the data reduction are given in Barban et al (2009), but are essentially the same as described above for HD 49933.…”

“…Details of the data reduction are given in Barban et al (2009), but are essentially the same as described above for HD 49933. The power spectrum is given in Fig.…”

“…The power spectrum is given in Fig. 12a and a boxcar spectrum in Barban et al (2009) but as with HD 49933 it is difficult to discriminate between peaks corresponding to modes = 0, 2 and those corresponding to = 1; Barban et al (2009) give frequency sets for both (Scenarios 1 and 2). I here give the results of applying narrow frequency windowed autocorrelations to the time series and see if one can differentiate between them.…”

The underlying physical meaning of theνmax − νcrelation

“…The first question is quite difficult to answer because it is expected to strongly depend on the model used for the description of the pulsation-convection interaction. Nevertheless, CoRoT observations begin to answer this and the data of several stars (HD 49933, HD 180420, HD 49385, and HD 52265) suggest that ν max correponds to the plateau of the damping rates (see Benomar et al 2009;Barban et al 2009;Deheuvels et al 2010;Ballot et al 2011, for details). The second step consists in determining the main physical causes responsible for the plateau of the damping rates and its mean frequency (ν Γ ).…”