Structure and activities. Membership.

GEOS structure and activity


1. Introduction

The GEOS is an international organization mainly specialized in the observation and scientific study of variable stars. Founded in 1973 by Alain Figer and some French amateur astronomers, it presently counts nearly eighty active members, amateurs or professionals, disseminated over France, Italy, Belgium, Switzerland, and Spain. Ten of them are professionals whose functions at GEOS are to help amateurs in the interpretation of their observations and also to propose cooperative programs.

The GEOS acronym, in the most represented languages, stands for

European Group of Variable Stars Observation (ENG)
Gruppo Europeo di Osservazione Stellare (I)
Groupe Européen d'Observation Stellaire (FRA)
Grupo Europeo de Observaciones Estelares (ESP)

meaning: European Group for the Observation of Variable Stars.

In more than thirty five years of activity, the GEOS has repeatedly demonstrated the utility of observing variable stars, proving that if these observations are prepared, made and coordinated adequately, it is possible to obtain significant results in the computation of orbital elements for eclipsing variables, search of periods and type of variability for some stars, and the determination and possible correction of ephemeris for many others. These preliminaries show that the group does not stop its efforts once a light curve has been obtained, since by itself a light curve alone does not constitute a result of special scientific interest.

Because of the complexity and diversification of its activities (program management, observations, publications), the group does not refer to a single coordinator. On the contrary, the responsibility for each activity (e.g. determining a class of variability or dealing with a certain type of observation, and even studying isolated stars) is entrusted to individual members, who are thus given an opportunity to develop their personal skills, and escape the risk of ending up as mere data collectors. From the very moment he starts observing, the observer is stimulated into dedicating time to the reduction and interpretation of his data.

Though the observational techniques are still centered around visual estimates, workgroups have been set up to get acquainted with the new technologies and progressively integrate them into a coherent and homogeneous methodological program. Starting from now well-mastered techniques as photography and photoelectric photometry, the first steps have also been taken in the field of CCD photometry. For example, an amateur station has recently been opened in Switzerland in order to perform CCD measurements. However, in spite of these important efforts, the majority of the observations are still carried out visually, and it may be worth noting that starting from 1973, our members have logged a total of more than 2 millions visual estimates.

In spite of the many different ways of approaching the problem of determining the absolute brighteness of a star, it is possible to recognize a common trend in the group's efforts. Aa a matter of fact, we do not consider it much interesting to devote ourselves to the study of irregular and semi-regular variables, or of the most targetted Mirae, or again of some very special classes such as the U Gem, SS Cyg, Z Cam, R CrB types as they are the most widely observed by amateur groups in most regions of the world. On the contrary The GEOS has always favoured the study of rapidly varying stars (short period) and/or with small amplitudes. Even if clear-cut results are harder to obtain, their scientific interest is correspondingly enhanced. Our experience demonstrates the possibility, even for amateur astronomers, to contribute significantly to the study of eclipsing variables and RR Lyr stars.


2. Learning The Job

As mentioned in the previous section, our group's organization differs much from what is commonly found in other associations of variable star observers. In particular, its decentralized structure gives an increased responsibility to each of the members. It is their responsibility to make new members acquainted with our structure, our programs and activities, as well as with the observational techniques.
At the GEOS yearly symposium (see below), professional astronomers open discussions on the correct use of the programs and of the observational techniques presented the year before in the GEOS internal bulletin. In this regard, new members have the possibility of updating their knowledge upon how to carry out observing programs and visual estimates in an optimal way.
Knowing how information is exchanged, and how the data are collected and processed, is of vital importance for a thorough and efficient collaboration between interdependent members since, in most cases and specifically for the visual observers, mutual contribution is imperative to attain objective results.


3. The Research Program

Once every year the GEOS organizes a symposium in which each member is invited to participate. During the symposium, the "PRIORITY OBSERVATION PROGRAM" is defined after discussing the "new" stars proposed for a study. Basically, our policy is to concentrate on projects, where we expect to obtain publishable results rapidly. The only restrictions imposed are that the star must be observable with small telescopes (mag. up to 13.5 in V) and its amplitude at least 0.3 mag. Short period stars are strongly favoured.

The observations, open to any object of some scientific interest, concern mostly the following classes:


Eclipsing Variables

RR Lyr Variable Stars

RV Tau Variable Stars

Other type of Variables

EA (Algol)
EB (ß Lyr)
EW (W UMa)



del Sct,ß Cep,alp CVn,Cepheids


(*) This case refers to stars included in the New Catalogue of Suspected Variable Stars (NSV), and checked for possible variability.

In addition, the group also supports studies that develop new numerical tools profitable for our purposes, that analyse and quantify the factors, both objective and subjective, that affect the quality of the observations, etc...

Each star is catalogued in one of the following categories, according to the importance attributed to its observation or the stage of the studies already accomplished:

RP (Recherche Prioritaire) [Priority Research] As mentioned above, this category includes stars (of primary importance), for which we expect rapid results.
Publications on these stars are usually made very shortly after the end of a campaign.
C (Campagnes) [Observing Campaigns] These are stars are observed very intesively during a short period by as many observers as possible. This type of program is limited to a few stars (four Be stars are currently being studied) and aims at collecting data that cover extensively a time lapse during which the star is believed to behave in an interesting manner.
P (Prospection) [Prospection] The program includes stars whose elements are totally unknown, or which are suspected to behave differently from what is reported in the literature (typical examples are objects listed in the CSV and NSC catalogues and therefore suspected to be variable before a comprehensive study). If the observation of a star included in the prospection program confirms its interest, it may be included in the priority program.
r (Routine) [Routine] This class is rather heterogeneous class lists well-known stars retained for a continued survey (e.g. semi-regular) or for their methodological interest (as, for instance, the Cepheids). It also includes worldwide, super-observed stars, that our members may wish to monitor mostly because of a personal, legitimate interest.

The task of assigning a star to one of the preceeding classes belongs to the International Symposium, and should not be considered as definitive. Periodic revisions are planned annually, and stars previously classified as "RP" may occasionally be included into the "r" category because of the publication of a conclusive paper in the literature.


4. The Work of the Observers

The observer devotes his primary interests and efforts on those stars included in the program, favouring objecs classified as "RP" whenever possible.

Within the GEOS, and contrary to what is customary in other organizations, the forwarding of the measurements does not respect any fixed deadline. The data are instead kept by each individual observer and sent on request to the person responsible for the coordination of the study of a specific star. Such requests for measurements (known as "Appels de mesures") are announced in the group's internal circulars. Meanwhile, any member wishing to know how many measurements and/or estimates are avilable for a given object, can find the information in the monthly reports.

At the end of each month, indeed, each observer is expected to report about his activity during the elapsed month. in this monthly report, each observer gives a detailed account of his observations (number and instrument used) for each observed star. The report is sent to the central coordinator of the group who can therefore know at any given time the number of available estimates and communicate the information to those interested (specifications for compiling both monthly reports and annual reports appeared in FT 01, 1992). Every year, each member receives a comprehensive compilation of the estimates available for every star in the program.


5. The GEOS Publications

Every year the GEOS publishes about 30 papers. The Notes Circulaires act as an internal bulletin. more important studies (called GEOS Circulars), as well as some other studies believed interesting for the astronomical community are sent to CDS, Centre de Données Astronomiques de Strasbourg and to the Astronomy and Astrophysics abstracts. Occasionally, papers are submitted to other bulletins such as the "International Bulletin of Variable Stars" IBVS and the "group of eclipsing binary observers of the Swiss Astronomical Society" BBSAG. From time to time, the GEOS internal bulletin also publishes "Fiches Techniques" (Technical Documents), which report on such technical matters as observational techniques, observation programs, cartography, software developed by members of the group. The working languages of the bulletin are English or French, but sometimes Italian and Spanish are used as well.


5.1 Internal Publications

They are distributed within the group for the own exclusive use of its members. They are also posted on this website. Download is reserved for members.

They include :

  • NC (Note Circulaire). They do not exceed 20-25 per year in number and contain the member's monthly reports, request for estimates, preliminary results demanding confirmation, the state of current studies or campaigns and general comments.
  • FT (Fiches Techniques). They offer explanations on such technical details as how to make a report, how to forward estimates or use ephemerides. They also give updates on star classifications and lists of the publications and charts that are available.
  • C (Cartes). There are the finding charts for the stars of the program.


The NCs are the only regularly published material, whilst the FTs and Cs only appear as need arises.


NCOA: Some Notes Circulaires, generally devoted to studies on specific stars but not arbitrated and/or not written in English, are in Open Access.


5.2 External Publications


They are mainly the GEOS Circulars, distributed to each member as well as to institutions and individual professional astronomers directly involved in our work or interested in special areas of research. There are also dedicated GEOS Circulars for each type of variable, i.e. (At the date of writing):


  • GEOS RR (GEOS Circulars on RR Lyr)
  • GEOS EB (on eclipsing binaries)
  • GEOS SR (on semiregulars)
  • GEOS Cep (on Cepheids)


The GEOS Circulars are edited in English only, but with abstracts in French, Italian and Spanish.



A second kind of publications, grouping both direct and indirect contributions of GEOS to specialized publications of international renown, are labelled PE (Publications à l'Extérieur).

All publications are sent through email and posted on this website. Ordinary mail is possible on special request only for NOTES CIRCULAIRES. The distribution of GEOS CIRCULARS to a list of interested people and institutions is done through priority mail.


6. Other Activities

Once a year the GEOS holds a symposium in which all members are invited to participate. The observational programs are discussed; new campaigns are proposed while older ones are closed after the final results have been reported and discussed. Professional astronomers are also invited to these meetings for brief updating seminars, or with the aim of proposing new collaborations. information relative to these meetings appears in the NCs.


7. Membership Fee

The GEOS covers its management expenses through a minimum self-financing fee (not a "subscription"). The amount of this minimum fee is 10.00 € /year.
Payments should be made by wire transfer to
IBAN: FR78 2004 1010 1002 7122 2J03 101

Geos "Nomenklatura"

Chairman :
Jean-François Le Borgne (France).

National coordinators :
Roland Boninsegna (central coordinator for Benelux)
Michel Dumont, (central coordinator for France)
Juan Fabregat (central coordinator for Spain)
Ennio Poretti (central coordinator for Italy)

Treasurer :
Joseph Remis

Secretary Publication Editor :
Stéphane Ferrand

Secretary Photocopies mailing and e-mailing :
Joseph Remis

Board of Editors:
Juan Fabregat, Alain Klotz, Jean-François Le Borgne, Ennio Poretti

Translations : Jacques Vialle, Michel Dumont, Luis Rivas, Ennio Poretti

Website hosted at Valencia Polytechnical University, Spain.
Jaime Busquets : Super Administrator
Juan Fabregat : Administrator
Joseph Remis : Administrator