Eclipsing Binaries Observing tips

The goal of this observing program is to catch more eclipses of these systems and thus be able to determine their periods.

CHARTS: There are still no charts for all the stars. Pavol Duvobsky has made available charts for the Northern eclipsers and I will keep working on some more for the South. When working on a star with no chart, observations should be made using comparison stars previously checked for variability against ASAS-3 or NSVS (Ask for a guide line if you need it). When you report your observations, identify the comparison stars used with their HD or GSC numbers.

Most of the stars in the plan are EA-type eclipsers and show small amplitudes. This version of the plan includes ALL stars that have not been solved including those with amplitudes not suited for visual observations. The suggested lower amplitude limit for telescopic stars is 0.2 mag. and 0.15 mag. for bright binocular variables. This implies that observations MUST be accurate and the observer needs to have experience in variable star estimates. Small observation errors could be interpreted as eclipses giving misleading results. The following tips might be of help to the observer of these small amplitude Algol-type eclipsers:

*Get used to the normal look of the star so a quick look will be enough to see if the star is eclipsed or not. No estimate will be needed if the star is observed as "normal" (= at maximum) since these EAs show almost no variability at maximum.

*Report the normal state of the star as its known V magnitude and with 2 decimal places. Rounding off at these amplitudes is not useful. A 6.25 is not the same as a 6.34 (both would be 6.3) since the latter might be an eclipse for a small amplitude variable with V= 6.25 at maximum. If the star causes the impression of being slightly brighter or fainter , reflect this as 0.02-0.03 mag. differences but no more than that if you don't think an eclipse is happening (see the other tips above and below). Reporting results brighter than the V mag. would be completely useless, and will only mean you' ve made a mistake.

*Try to make your eyes see the star as if it were at maximum so when you see the star is fainter than that, you'll know for sure there is an eclipse ongoing.

*When an eclipse is detected, start making estimates every 30 minutes or so to see if you have caught a descending or ascending branch. It might take several observations till you know for sure what it is. The second observation might be made after a longer time to avoid bias caused by the small amplitudes. If you observe too soon after the initial observation the changes that may have taken place in the star will be smaller than the error of your observation. When you make sure the star is brightening or fading, discard the spurious observations.

*Remember to be patient. It may take months or even years until you observe an eclipse. But also remember that every negative observation is useful to constrain the period.