Vc. Duforesto et al., DERIVING OBJECT VISIBILITIES FROM INTERFEROGRAMS OBTAINED WITH A FIBER STELLAR INTERFEROMETER, Astronomy & Astrophysics. Supplement series, 121(2), 1997, pp. 379-392
A method is given for extracting object visibilities from data provide
d by a long baseline interferometer, where the beams are spatially fil
tered by single-mode fibers and interferograms are obtained as scans a
round the zero optical pathlength difference. It is shown how the sign
als can be corrected from the wavefront perturbations caused by atmosp
heric turbulence. If the piston perturbations are also removed, then t
he corrected data contain both spatial and spectral information on the
source (double Fourier interferometry). When the piston cannot be rem
oved, object phase and spectral information are lost, and the observab
le (free of detector noise bias) is the squared modulus of the coheren
ce factor, integrated over the optical bandpass. In a fiber interferom
eter this quantity leads to very accurate object visibility measuremen
ts because the transfer function does not involve an atmospheric term.
The analysis also holds for a more classical pupil plane interferomet
er which does not take advantage of the spatial filtering capability o
f single-mode fibers. In that case however, the transfer function incl
udes a turbulence term that needs to be calibrated by statistical meth
ods.