Introduction

Why study variable stars?
Research on variable stars is important because it can provide fundamental information about the physical properties, nature, and evolution of stars. Distance, mass, radius, internal and external structure, composition, temperature, and luminosity can be determined using variable star data. Since professional astronomers have neither the time nor the resources needed to gather data on the brightness changes of thousands of variables, amateurs have been making a real and useful contribution to science by observing variable stars and submitting their observations to the AAVSO or similar organizations.

The importance of the contribution of the serious amateur observer was first recognized in the mid-1800’s by Friedrich Wilhelm August Argelander (1799–1875), a German astronomer, famous for his Bonner Durchmusterung (BD) star atlas and catalogue. In 1844 when only 30 variable stars were known, Argelander wrote in an article: “ …I lay these hitherto sorely neglected variables most pressingly on the heart of all lovers of the starry heavens. May you increase your enjoyment by combining the useful and the pleasant while you perform an important part toward the increase of human knowledge.” Argelander’s plea is just as appropriate today.

What is the AAVSO?
The American Association of Variable Star Observers (AAVSO) is a worldwide, nonprofit, scientific and educational organization of amateur and professional astronomers who are interested in variable stars. Founded in 1911 by William Tyler Olcott, an amateur astronomer and lawyer by profession, and Edward C. Pickering, Director of the Harvard College Observatory, the AAVSO was part of the Harvard College Observatory until 1954 when it became an independent, private research organization. Its purpose was—and still is—to coordinate, collect, evaluate, analyze, publish, and archive variable star observations made largely by amateur astronomers, and to make these observations available to professional astronomers, educators, and students. In the year 2004, with over 1200 members in 46 countries, and headquartered in Cambridge, Massachusetts, USA, it is the world’s largest association of variable star observers.

In 2004, the archives of the AAVSO contained nearly 12 million observations on over 7500 stars. Over 700 observers from around the world submit about 450,000 observations every year. At the end of each month, incoming observations are sorted by observer and checked for obvious errors. The observations are then digitized, processed, and added to the data files for each star in the AAVSO International Database. This database is a tribute to the skill, enthusiastic devotion, and dedication of AAVSO observers since 1911.

Services to the Astronomical Community
AAVSO data, both published and unpublished, are disseminated extensively to astronomers around the world, via the AAVSO website (http://www.aavso.org) or upon request of AAVSO Headquarters. AAVSO services are sought by astronomers for the following purposes:

1. Real-time, up-to-date information on unusual stellar activity;
2. Assistance in scheduling and executing of variable star observing programs using earth-based large telescopes and instruments aboard satellites;
3. Assistance in simultaneous optical observations of program stars and immediate notification of their activity during earth-based or satellite observing programs;
4. Correlation of AAVSO optical data with spectroscopic, photometric, and polarimetric multi-wavelength data;
5. Collaborative statistical analysis of stellar behavior using long-term AAVSO data.

Collaboration between the AAVSO and professional astronomers for real-time information or simultaneous optical observations has enabled the successful execution of many observing programs, particularly those using satellites for their research. These collaborative projects include observations by Apollo-Soyuz, HEAO 1 and 2, IUE, EXOSAT, HIPPARCOS, HST, RXTE, EUVE, Chandra, XMM-Newton, Gravity Probe B, CGRO, HETE-2, Swift, and INTEGRAL. A significant number of rare events have been observed with these satellites as a result of timely notification by the AAVSO.

Services to Observers and Educators
The AAVSO enables variable star observers to contribute vitally to astronomy by accepting their observations, incorporating them into the AAVSO data files, publishing them, and making them available to the professional astronomer. Incorporating your observations into the AAVSO International Database means that future researchers will have access to those observations, giving you the opportunity to contribute to the science of the future as well as the present.

Upon request, the AAVSO will help set up an appropriate observing program for an individual, an astronomy club, an elementary school, high school, college, etc. In this way, observers, students, and faculty are able to make the best use of their resources and to do valuable science. The AAVSO can also assist in teaching observing techniques and in suggesting stars to be included in a program.