Calibration Observations of Fomalhaut with the VLTI

An investigation of the stability of the transfer function of the European Southern Observatory’s Very Large Telescope Interferometer has been carried out through observations of Fomalhaut, which was observed over a range in hour angle from 21:50–05:24 on 20 October 2002. No significant variation in the transfer function was found for the zenith angle range 5◦–70◦. The projected baseline varied between 139.7 m and 49.8 m during the observations and, as an integral part of the determination of the transfer function, a new accurate limb-darkened angular diameter for Fomalhaut of 2.109 ± 0.013 mas has been established. This has led to improved values for the emergent flux = (3.43 ± 0.10)×10 Wm, effective temperature = 8819 ± 67 K and radius = (1.213 ± 0.011)×10 m (R/R⊙ = 1.744 ± 0.016). The luminosity has been found to be (6.34 ± 0.20)×10 W (L/L⊙ = 16.5 ± 0.5).