The principle and the design of a low cost, very stable et luminous instrument devoted to ground based asteroseismic observation will be presented. The principle of the instrument is derived from Fourier transform spectrometry. According to the analysis of the performances already obtained with the FTS based at the CFHT telescope (Mosser et al 1998), we propose now a dedicated instrument. Two major differences distinguish this instrument from a classical FTS : for sake of stability, this dedicated seismometer is without moving parts ; for sake of luminosity, it includes a post-dispersion system that permits to enlarge the acceptable bandpass.
The fundamental velocity noise, limited by the photon noise, has been calculated for synthetic stellar spectra, with spectral types close to solar and moderate rotational velocity (v sin 20 Km s-¹. For quantitative simulations, we consider the instrument to be installed in a network of 2-m class telescopes, such a network being adequate for a long term multi-targets seismic program. Sensitivity about a few cm s-¹ (K2V, v sin =0 km s-¹ : 1 cm s-¹ ; F2V, v sin =20 km s-¹ : 6 cm s-¹ is reached on a 4th magnitude star, after 5 nights observation, with a 2-m class telescope network and a conservative duty cycle of 50%. Such performances make ground based seismic observations competitive, since they allow long term seismic observations of about 80 stellar targets.
The results have been qualitatively and quantitatively compared to the performance of radial velocity measurements obtained with a grating spectrometer (Bouchy et al 2001). Even if the performances remain a factor 1.5 to 2 lower than for a grating spectrometer (depending on the spectral type and on the rotational velocity v sin ), other factors as the total cost, the dimension (50 x 50 x 20 cm³) and the simplicity of use justify to consider it as an efficient solution for a network devoted to asteroseismology. Practically, a network should be composed of both types of instruments.
Mosser B., JP. Maillard, D. Mékarnia, J. Gay 1998. New limit on the p modes oscillation spectrum of Procyon obtained by Fourier transform seismometry. A&A 340, 457-462 Bouchy, F., Pepe, D., Queloz, 2001. Fundamental photon noise limit to radial velocity measurements. A&A 374, 733-739

 
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