HIPPARCOS data

The Hipparcos Epoch Photometry contains 182 measurements of HD 220391 (HIP 115506). As in the first case, all quality flags have bit 4 or higher on. The effective width of the aperture (called Instantaneous-Field-of-View) is 38 arcsec, so companions at angular separations between 10 and 30 arcsec may interfere significantly during the measurement. We selected 172 data with a value of the quality flag not worse than 18, with a transit error on the (dc) magnitude not larger than 0.020 mag (6 data have not) and with good agreement between the (ac) and the (dc) magnitudes (3 data have not). The mean of these is 7.227 mag with a standard deviation equal to 0.026 mag. Fourier analysis between 0. and 23. cpd displays a peak at $\sim$ 11 cpd, which is an artefact frequency of order 2hr^-1 (with an associated amplitude of 0.013 mag), introduced by the rotation period of the satellite and very conspicuous in the spectral window Fouriergrams.