RR Stars - Observing Procedures/Objectives

1. Examine the chart carefully. At the telescope identify the variable and verify the relative brightness of all comparison stars.
2. Current AAVSO objectives call for observation of the star at anytime. This enables the construction of a mean light curve to compare changes from one year to the next. Observations over most of the light curve may be spaced at 20 to 40 minute intervals.
3. During the star's rise to maximum the observations should be spaced at about 10 minute intervals; even less for RR stars of extremely short period. The short observing intervals should begin while the star is still at minimum brightness and continue for an hour or more beyond maximum. If reduction for time of maximum by the Pogson method is anticipated the star should be observed for about two hours beyond maximum. During the last hour observing intervals may be extended to 15 or 20 minutes.
4. At least 200 observations should be obtained each observing season if a mean light curve is to be constructed for comparison from year to year. Depending upon the nature of the light curve and its changes it may be possible to establish measurements of times of maxima via fitting individual light curves to the mean curve.
5. A few things which RR data of sufficient quality may be examined for are:
   1. Measurement of times of maxima for long term changes in period.
   2. Measurement of times of maxima for short term phase shifts in the time of maxima. In some stars it may be cyclic.
   3. Changes in brightness of the star at maximum from cycle to cycle, week to week, or year to year.
   4. Unspecified general changes in the light curve between various points in time.
6. The brightness range for most RR stars is very small for visual work. Therefore, these stars are very unforgiving of sloppy observational work. The observer must be accurate and consistent. Comparison stars cannot be changed at midstream. Some systematic error or bias may be tolerated, but this too must be consistent. Obviously, combining two observers data would be a risky business.
7. Computer reduction to mean light curve appears feasible for some stars. Some work was done in 1968 with considerable success and a computer program may be still available.