Lunar occultation of the double star ZC 2997 (mag 7.2, component mags 7.94 and 8.04, PA 128.5°, separation 0.28")

Limovie analysis of the video recording gave estimated mags of 7.8 and 8.2 for the pair and a step duration of 0.459s. It suggests that the fainter companion disappeared first, contrary to the prediction in Occult software.

Assuming that component A is the fainter star and component B is the brighter, reducing the timings in Occult gave very small O-Cs of 0.04" and 0.00", respectively.

A report was submitted to Brian Loader (NZ), IOTA's double star coordinator, who collates and analyses worldwide observations. Timings of ZC 2997 had been submitted by two observers in the USA. (One had also observed star B as the brighter component).Multi-station timings are combined to estimate the PA and sub-arcsecond separation of a double star. Observations can be taken weeks apart if the binary has a long orbital period.

The solution gave the same separation as derived from the Washington Double Star Catalogue (WDS), but there was a difference of almost 180° in PA. This is because interferometric measurements can have this discrepancy, and star A in the WDS isn't necessarily the brighter component of a double star, as in this case. Lunar occultation observations can resolve these issues.