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 \degr –70 \degr .
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 \pm 0.013 mas has been established .
This has led to improved values for the emergent flux = ( 3.43 \pm 0.10 ) \times 10 ^ { 8 } Wm ^ { -2 } , effective temperature = 8819 \pm 67 K and radius = ( 1.213 \pm 0.011 ) \times 10 ^ { 9 } m ( R/R _ { \sun } = 1.744 \pm 0.016 ) .
The luminosity has been found to be ( 6.34 \pm 0.20 ) \times 10 ^ { 27 } W ( L/L _ { \sun } = 16.5 \pm 0.5 ) .