Asteroseismology of solar–type stars with SARG@TNG

Since 1995, the extra-solar planet search has driven the high resolution spectroscopy community to build more and more stable spectrographs in order to reach the photon statistics limit in radial velocity measurements. This situation opened the possibility of asteroseismic observations of stellar p mode pulsations in solar-like stars. In this contribution we summarize the high precision radial velocity measurements of two solar type stars (α CMi and μ Her) using the SARG spectrograph at TNG equipped with an iodine cell. The analyzed spectra show individual measurement errors of about 1.0 m/s (very close to the theoretical photon noise limit). Further we discuss the synergy between high precision radial velocity asteroseismology campaigns and the search for Super Earths. Individual Objects: Procyon, μ Her Radial velocity uncertainties with SARG SARG (Spettrografo Alta Risoluzione Galileo) is the high resolution optical spectrograph of the Italian Telescopio Nazionale Galileo (TNG). Instrument characteristics include a high spectral resolution (maximum about 160 000), high efficiency (peak at about 13%), rather large spectral coverage in a single shot. SARG was designed as a multipurpose instrument. The instrument, which mounts an iodine absorbing cell, is particularly suited for precise radial velocity programs, such as planet search and asteroseismology (Gratton et al. 2001). Radial velocities are obtained by means of the AUSTRAL code (Endl et al. 2000). We evaluate radial velocity uncertainties for SARG using the appropriate quality factor (see Bouchy et al. 2001) for spectrograph resolution, spectral type and rotational broadening. For stars brighter than 3.5 magnitude the resulting RV uncertainties range between 0.9 to 3 m/s depending on magnitude and spectral type of the star. This result affects also the efficiency of the instrument in detecting oscillations maintaining the number of spectra confined inside a reasonable number necessary to detect oscillation of amplitude νosc over a 4 σ threshold. We are aware that the limits of RV measurements are also set by spectrograph instabilities, but analyzing the results obtained with the subgiant star Procyon and μ Her we can limit the instrumental contribution to RV uncertainty lower than 1 m/s. 22 Asteroseismology of solar–type stars with SARG@TNG