HIPPARCOS data

The Hipparcos Epoch Photometry contains 183 measurements of HD 220392 (HIP 115510). The note in the Main Catalogue however mentions that the "data are inadequate for confirmation of the period from Ref. 94.191" (ESA, 1997). The reason for this are the quality flags that all have bit 4 on, meaning "possibly interfering object in either field of view", or higher. We selected 177 data with a value of the quality flag not worse than 18, with a transit error on the (dc) magnitude not larger than 0.015 mag (2 data have not) and with good agreement between the (ac) and the (dc) magnitudes (1 datum has not). In addition, we had to eliminate one more datum, the brightest one. The mean then is 6.204 mag with a standard deviation of 0.024 mag. Fourier analysis between 0. and 23. cpd shows a peak at 4.6743 $\pm$ 0.0001 cpd, i.e. the same first frequency as found in all former datasets. The corresponding phase diagram is illustrated in Figure 6: the amplitude associated with f₁ is 0.013 mag large. The second frequency of 5.52 cpd is below detection: prewhitening for the main frequency still leaves a (large) dispersion of 0.021 mag. A double-frequency simultaneous fit attributes an amplitude of 0.013 mag to f₁ but as little as 0.003 mag to f₂.

Table 3: Results of two successive frequency analyses for HD 220392 (program PERIOD98).

Frequency (cpd)	Sept. 1991	June 1990	Oct. 1992	Sept. 1991	Total
		+ Sept. 1991		+ Oct. 1992
	11 nights	18 nights	3 nights	14 nights	21 nights
Resolution (cpd)	0.0523	0.0022	0.1082	0.0024	0.0012
f1	4.674	4.679	4.661	4.664	4.674
(f2)	(6.520)	(6.520)	(6.398)	(6.383)	5.522
f2	5.523	5.520	5.536	5.523	5.522