The Work of the BAV
An Overview of the technical work of the Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne e. V. (BAV)
History of the BAV
The "Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne" was founded  1950 by amateur astronomers at the Archenhold Observatory in Berlin-Treptow. The  intention was - and still is - to support amateurs in the systematic observation  of variable stars. The observations are published and therefore may give professionals additional  information for their work. The observation programs of the BAV are composed in  cooperation with professionals in regard to their research foci.
Observation of Variable Stars
Observation Goals
Especially long-term observations are highly valuable and enable us to deduce  the physical characteristics of variable stars. From measurements of brightness  variations the times of maximum or minimum are derived. Moreover, the elements  of brightness variations of specific stars are derived and new variables are  systematically sought and classified.
Observation Techniques
Until the 1980s visual observations dominated. Later the light-electric  photometry was established, while nowadays the CCD-technology prevails. Today  more than 2,000 maxima and mimima are observed per year.
The Observation Programs of the BAV
The following variable types are systematically observed: Eclipsing binaries,  short-period pulsating stars (RR Lyrae, delta Scuti and delta Cephei stars),  long-period pulsating stars (Mira stars, RV-Tauri and semi-regular stars),  eruptive and cataclysmic stars.
The Publication of Observation Results in the BAV Mitteilungen
The observation results are communicated in the BAV Mitteilungen. Between 1950  and 1981 these were mainly published in the Astronomische Nachrichten, since  then primarily in the Information Bulletin on Variable Stars (IBVS) of the  commissions 27 and 42 of the IAU. Until 2010 more than 200 BAV Mitteilungen were  published with more than 43,000 observed maxima and minima.
Collaboration with Professional Astronomers
The professionals are interested in the collaboration with amateurs as long as  they can rely on high quality CCD-results which are typical for the BAV  observations. At the biennial BAV conventions professionals do not only present  their work, but also express wishes for support by amateurs.
The Lichtenknecker-Database of the BAV
Collection of more than 160,000 times of minima about 2,000 eclipsing binaries
In 2004 this data collection – to honor its creator now called "Lichtenknecker- Database of the BAV" – was opened to the experts. It is available through  this BAV- webpage. The BAV does not have any rights on the recorded observation results;  these are still with the authors and observers. But particularly with regard to  the enormous efforts we expect the citation of the official title  "Lichtenknecker-Database of the BAV" whenever using its data.
The observations were collected from many worldwide available literature  sources. In our understanding they are nearly complete, especially with regard  to historic observations. The search covered more than 200 publications and  periodicals. The criteria for including stars in the database are a brightness  of more than 13 mag in normal light and a declination north of -20 degree. There  is no limit for the amplitude or period.

A comprehensive description of the work of the BAV is available through one  of the following links available. english version german version

Berlin, September 21st, 2010; Joachim Hübscher