The GEOS Association of Variable Star Observers (Abstract)

Volume 40 number 1 (2012)

Franz-Josef Hambsch

address correspondence to J. Hambsch, Oude Bleken 12, Mol 2400, Belgium; hambsch@telenet.be

Jean-François Le Borgne

address correspondence to J. Hambsch, Oude Bleken 12, Mol 2400, Belgium; hambsch@telenet.be

E. Poretti

address correspondence to J. Hambsch, Oude Bleken 12, Mol 2400, Belgium; hambsch@telenet.be

GEOS Association

address correspondence to J. Hambsch, Oude Bleken 12, Mol 2400, Belgium; hambsch@telenet.be

Abstract

(Abstract only) Groupe Européen d’Observation Stellaire (GEOS) is an astronomical association created in the 1970s to promote research among amateurs in Europe. We started in Belgium, France, and Italy, later extended to Spain, Switzerland, and Germany, and more recently, added U.S. amateurs. The basic idea was that amateurs should themselves extract scientific information from their observations (visually at first and later electronically) and publish their results. Some GEOS members have become professional astronomers and the amateur-professional collaboration has strengthened over the years. From the beginning, it has been clear that the study of variable stars is a privileged topic where such projects can develop. Since the 1980s GEOS members have published a number of scientific papers, even in refereed professional journals. Presently, observations are mainly done using CCD cameras though visual measurements still exist. In the past decade our main development has been the creation of a public RR Lyr star maxima database. This is a unique tool for the study of RR Lyr stars, as it enables the user to follow period variations since a star’s discovery, some over 100 years ago. In parallel to the database, a project called “GEOS RR Lyr survey” was designed. Its aims include: first, add significantly more maxima timings of the brightest RR Lyr stars essentially using robotic telescopes; second, study fainter understudied stars to refine their period and find new stars which exhibit the so-called Blazhko effect; third, characterize the Blazhko effect, one of our main research topics. Other variable stars are also studied: eclipsing binaries, d Scuti stars, and so on. GEOS has a good cooperation with other variable star associations, mainly BAV and AAVSO.