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Astron. Astrophys. 327, 1023-1038 (1997)

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2. Data acquisition and calibration

The observations were performed with the multi-channel multi-colour photometer (MCCP) attached to the 0.8 m telescope at Mt. Wendelstein in the Bavarian Alps. This instrument measures the object, a nearby comparison star, and the sky background simultaneously in 5 colours (UBVRI) with high time resolution. The simultaneous measurements allow a nearly complete compensation for changing atmospheric extinction effects and varying background contributions. High precision differential photometric measurements of IP Peg relative to a nearby comparison star were obtained on 4 nights during the decline from an outburst. Data reduction followed the so-called "standard reduction procedure" (Barwig et al. 1987). A journal of the IP Peg observations is given in Table 1. In all nights an integration time of 2 seconds has been used. Fig. 1 shows the UBVRI light curves.


Table 1. Journal of observations. (IT: integration time, [FORMULA] -flux: V magnitude at phase 0.25)

[FIGURE] Fig. 1. UBVRI light curves of IP Peg in the four successive nights on decline from an outburst. U to I from bottom to top. The vertical lines mark the ingress and egress positions of the hot spot and the white dwarf.
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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998