AAVSO Legacy CVs

Mike Simonsen

There are many stars for which the AAVSO has visual data going back many decades, some 100 years or more. The AAVSO openly encourages the continued observation of these stars by visual observers into the foreseeable future. We call these stars "Legacy Program" stars.

This long time line of observations of these Legacy Stars makes this data particularly useful and scientifically interesting for many reasons. Matthew Templeton, AAVSO Science Director, explains-

"As an example, for any variable with a long-term well observed light curve the scientific values of visual observing come from (a) the long time span, (b) the statistical similarity of errors from visual observers, and (c) the bandpass similarity of human vision across a wide population of observers.

For point (a), long time spans can do at least three valuable things: build up signal-to-noise in the signal domain where there are weak signals less than 0.5 magnitudes; increase frequency precision where periods are stable over the long-term; and uncover long-term changes in behavior.

For point (b), signal processing in the presence of noise is something researchers deal with all the time, so the fact that binned visual observations may have an rms scatter of 0.1-0.3 is not a big deal.

What is much more important is that for a large population of observers, the errors are normally distributed. So when we have a light curve with dozens or hundreds of observers, that's actually a plus, because it makes it more likely that analysis techniques designed for data with normally distributed errors are going to be appropriate.

For point (c), this is really important, because with visual observers, the bandpass under observation may be somewhat fuzzy, but at least it's nearly *the same bandpass* across a sizable population of observers."

The AAVSO Legacy CVs were selected from all the cataclysmic variables in the AAVSO International Database based on the number of observations in the DB (minimum 2500), and the years of observations (minimum 20 years).