Observations and reductions

The photometric data have been gathered during three campaigns at La Silla, Chile. For the A-component HD 220392, 7 nights of measurements were made in June 1990, 11 nights were obtained in September 1991 and 3 in October 1992. For the B-component HD 220391, only observations made in September 1991 and October 1992 are available. The June 1990 and September 1991 campaigns have been performed by P. Lampens with the Swiss 0.7m telescope of the Geneva Observatory while the October 1992 data were obtained with the ESO 0.5m telescope by D.  Sinachopoulos. We dispose of 396 data for the brightest component HD 220392 and 245 data for HD 220391. The characteristics of these data are mentioned in Table 1. Standard as well as additional programme stars have also been observed during these nights. All Geneva measurements are absolute measurements in the filters UBVB₁B₂V₁G obtained through a centralized reduction scheme at the Geneva observatory. This centralized Swiss processing has not been applied to the ESO data taken in the UBV photometric system. The reduction of the October data implied using a check-star HD 220729 whose measurements were interpolated between the two other ones. We have verified the constancy of this star ( $\sigma _{H_{p}}=0.0005\,$mag) in the Hipparcos catalogue and we have fitted a 5th degree polynomial for each night separately. Then we have subtracted this polynomial from the data of both programme stars in order to suppress as well as possible common variations. The ESO data are thus being interpreted as differential data only.

Figure 5: Phase diagrams for the HD 220392-data against the frequencies of 4.67439 cpd (left) (after removal for the 5.52 cpd variation) and 5.52234 cpd (right) (after removal for the 4.67 cpd variation).

Table 1: Photometric data for HD 220392 and HD 220391

Identifier	Instrument	Epoch	Number	Time base
			of data	(days)
HD 220392	Geneva	June 90-Sept. 91	124	464
HD 220392	Geneva+ESO	June 90-Oct. 92	396	866
HD 220392	Hipparcos	Nov. 89-Mar. 93	176	41 months
HD 220391	Geneva	Sept. 1991	98	19.1
HD 220391	Geneva+ESO	Sept. 91-Oct. 92	245	416
HD 220391	Hipparcos	Nov. 89-Mar. 93	172	41 months