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AAVSO Legacy LPV Program

The list of legacy variables can be downloaded from the files section of this website.

At the beginning of the 20th century, variable stars in general were a mystery.  Many had been discovered, but the mechanism of their light variability and their precise nature was unknown.

In order to obtain regular observations of these stars over a period of months or years, amateur astronomers were enlisted by Harvard College Observatory Director Edward Pickering (left) in 1911 to observe a series of 372 LPVs.  His original list and the names of some of these observers was published as  Harvard College Observatory Circular 166 in that same year.

Many of that original group of observers went on to become the nucleus of the AAVSO.  That group  of 372 variable stars went on, too, forming the bulk of the AAVSO's LPV observing program for nearly a century.  These LPVs have periods in some cases approaching two years; many patient years of gathering data are necessary to properly describe the behavior of these stars. 

Over the years, the list of LPVs observed by AAVSO observers grew in a sometimes haphazard fashion. We are in the process of determining which LPVs out of the thousands of stars in the AAVSO program should be our core, or "Legacy" stars. These would be the stars included in future Bulletins, and those stars whose long term light curves we expect to remain scientifically useful for decades to come.

The initial pass at this list used information on how many observations of each star are in the AAVSO International Database, and how many references to each star were found in the scientific literature. The assumptions being, 1) If we don't have a lot of observations on the star, how can it be a 'legacy' variable, and 2) we should be sure to include stars who astronomers have in the past been, and are currently interested in.

The current list of AAVSO Legacy Stars can be found in our file section.


Why should you observe LPV Legacy Program stars?

We collect data on variable stars in order to understand their physical behavior.  The light curves of these Legacy stars are valuable for several reasons.  First, these are primarily long-period variables, and having long light curves improves our ability to understand exactly how they vary.  When studying periodic behavior in any object, you should make observations over many, many repetitions of the cycle shown by the object.  Since many LPVs take a year or more to complete a cycle, it takes a long, long time to collect a lot of cycles!

Second, nearly all of the stars classified as Long-Period Variables are "old" stars, meaning that they've exhausted most of the nuclear fuel in their cores, and are evolving toward the ends of their lives as stars.  When stars are burning hydrogen in their cores, changes may take millions of years to be measurable, but in later stages of a star's life, these changes may take as little as a few decades.  So by observing stars over a long period of time, you can not only track the variability that makes them so prominent, you may also be able to see evolution in that behavior caused by evolution in the star.  Two good examples of stars undergoing internal changes of some kind in recent years are the Mira variable T Ursae Minoris and the semiregular variable RU Vulpeculae.

Finally, the reason why we've chosen these particular stars is that we already have a lot of data for them.  You might think that if we have a lot of data we don't need to observe them anymore, but the opposite is true.  If they're already well-observed, then continued observations have a better chance of yielding useful physical information.  The logic is as simple as this: if you have a hundred years of data, two hundred years would be even better!  More eloquently, a century of data may allow you to investigate changes that occur on timescales of several decades.  The more data we collect, the longer are the timescales we can study.  If (big if) we could collect data for several centuries -- or even a millenium -- astronomers of the future will be better able to understand changes that occur.  But they can only do that with observational data -- hopefully your observational data!

The data you take will certainly be useful to researchers studying these stars today.  They may also be useful to researchers in the future.  It is our plan -- not just our hope -- that our data will long outlive us, and our work will contribute to future astronomical studies that we can only guess at now.

TYPE C Semiregulars: Waiting for the Spectacular by David Turner

The Type C semiregular variables, or SRCs, are, like many fascinating objects in astronomy, relatively unstudied. But not unobserved, given that many AAVSO members, and especially the more experienced observers, have been observing them for years.
Their basic properties are easy enough to summarize, although the descriptions given for them in many textbooks are, quite simply, wrong.  Read more>
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