Seismology of Procyon A: Determination of mode frequencies, amplitudes, lifetimes, and granulation noise

Abstract

The F5 IV-V star Procyon A (α-CMi) was observed in January 2001 by means of the high-resolution spectrograph SARG operating with the TNG 3.5 m Italian telescope (Telescopic Nazionale Galileo) in the Canary Islands, exploiting the iodine cell technique. The time series of about 950 spectra carried out during 6 observation nights and a preliminary data analysis (Claudi et al. 2005) showed a significant power excess between 0.5 and 1.5 mHz, with ≃ 1 ms-1 peak amplitude. Here we present a more detailed analysis of the time series, based on both radial velocity and line equivalent width analyses. From the power spectrum we found a typical p-mode frequency comb-like structure, identified 11 frequencies with a good margin of certainty in the interval 500-1400μHz of modes with l = 0, 1, 2 and 7 ≤ n ≤ 22, and determined large and small frequency separations, Δν = 55.90 ±0.08 μHz and δν02 = 7.1 ± 1.3 μHz, respectively. The mean amplitude per mode (l = 0, 1) at peak power is 0.45 ± 0.07 m s-1, twice larger than the solar one, and the mode lifetime is 2 ± 0.4 d, which indicates a non-coherent, stochastic source of mode excitation. Line equivalent width measurements do not show a significant excess in power in the examined spectral region but allowed us to infer an upper limit to the granulation noise. © ESO 2007.