SIMBAD references

We report the observations of the clear-sky fraction at the Concordia station during winter 2006 and derive from it the duty cycle for the astronomical observations. The duty cycle and observation duration at Dome C allow for efficient asteroseismic observations. This performance is analyzed and compared to network observations. For network observations, simulations were run using the helioseismic Global Oscillation Network Group as a reference. Observations with one site in Antarctica provide performance similar to or better than that with a six-site network, since the duty cycle limited by meteorology is as high as 92%. On bright targets, a 100 day long time series with a duty cycle of about 87% can be observed, which is not possible for a network observation.