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Written by Joseph Remis

Category: Uncategorised

Published: 09 September 2016

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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:

(*) 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
JOSEPH REMIS
IBAN: FR78 2004 1010 1002 7122 2J03 101
BIC: PSSTFRPPNCY

 
8. 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

Details

Written by Administrator

Category: Uncategorised

Published: 24 April 2007

Hits: 2723

Once every year the GEOS organizes a symposium in which each group member  is invited to participate. During the symposium, the "PRIORITY OBSERVATION PROGRAM" is defined after discussing the "new" stars proposed 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 (magn. up to 13.5 in V) and that 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 to the following classes:

    (*) 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]

C (Campagnes) [Observing Campaigns]

P (Prospection) [Prospection]

 

The programme include stars whose elements totally unknown, or which are suspected to behave differently from what is rported in the literature (typical examples are objects listed in the CSV and NSC catalogues and therefore suspected to be variable before a comprehensive study is made). If the observation of a star included in the prospection programme confirms its interest, it may be included in the priority program.

r (Routine) [Routine]

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 study in the literature.

(Published in FICHE TECHNIQUE GEOS FT 17 Rév. 18  May 2009)

The prioritary research program has been updated during the last GEOS meeting held at Ca del Monte from May 1st to May 3rd 2009.

Le programme prioritaire a été complètement réorienté lors de la réunion du GEOS qui s’est tenue à Ca’del Monte du 1^er au 3 mai 2009.  Il a été tenu compte du grand intérêt actuel du groupe pour l’observation et l’étude des étoiles variables du type RR Lyrae.  Trois éclipsantes de l’ancien programme ont toutefois été conservées, ainsi que l’éclipse exceptionnelle de Epsilon Aur.

V437 Aur (BNN) : 5h 49m 03s ; 54° 01’ 57" (2000)

C’est une variable Hipparcos de spectre B9, type EA, mag. 8.42 à 8.98, période 3.3638 j.  En fait, plusieurs autres périodes sont possibles.  BNN va rassembler les estimations de DMT et les mesures ccd, notamment celles d’APS, et chercher la solution.

Epsilon  Aur  ( KCH ) : 5h 01m 58s ; 43° 49’ 24 ”   ( 2000 )

Cette étoile bien connue est au programme prioritaire pendant toute la durée de son éclipse. C’est une étoile du type EA/GS  dont la période est de  27 ans. Elle varie de 2.9 à  3.9.  La  NC 1080 rédigée par KCH décrit les conditions du phénomène et donne une carte. On notera que l’éclipse de z Aur est déjà terminée et cette étoile peut donc servir d’étoile de comparaison.

AE Boo (VBR) : 14h 47m 35.3s ; 16° 50’ 44" (2000)

Il s’agit d’une RRc de mag. 10.44 à 10.88 (V), la montée d’éclat = 45% pér. et le spectre est F2.  Sa période a été constante pendant 65 ans et l’éphéméride obtenue avec tous les maxima disponibles est : JJh 2430388.200 + 0.31489332 j.  L’étoile n’a plus été observée depuis 2007 ; l’observation de quelques nouveaux maxima est donc souhaitée.  Elle montre un effet Blazhko, dont il faudrait déterminer la période et l’amplitude.  Une courbe de lumière ccd devrait être publiée.

VW CVn (VBR) : 13h 29m 43s ; 28° 52.9’ (2000)

C’est une RRc cataloguée EW dans le GCVS (voir IBVS 4134 et GEOS Circular RR18).  Sa magnitude va de 11.61 à 12.07 (V) et la montée d’éclat est de 41 à 46 % pér.  Les éléments de sa période sont JJh 2419486.271 + 0.4249860 j.

La période de VW CVn s’est avérée irrégulière au cours des 105 ans pour lesquels nous disposons d’instants de maximum.  L’étoile n’a plus été observée depuis 2003.  De nouveaux maxima sont souhaités.  La forme de sa courbe de lumière est changeante, mais il n’a pas encore été possible de déterminer si c’était dû à un effet Blazhko ou à une multipériodicité.  Il faudrait obtenir de nombreuses mesures ccd précises sur toute la courbe de lumière et faire une nouvelle étude des composants de la période.

TV Lyn (VBR) : 7h 33m 31.7s ; 47° 48’ 10" (2000)

Il s’agit d’une RRc de mag. 11.24 à 11.66 (V), la montée d’éclat = 42 % pér., le spectre est A6.  Sa période a été constante pendant 85 ans et l’éphéméride obtenue avec tous les maxima disponibles est : JJh 40950.9302 + 0.24065140 j.  Comme nous ne disposons plus d’observations depuis 2007, l’obtention de quelques nouveaux instants de maximum est souhaitable.  Il ne semble pas y avoir d’effet Blazhko, mais cela pourrait être vérifié et une courbe de lumière ccd publiée.

V1027 Ori (VBR) : 6h 12m 00s ; 11° 55.1’ (2000)

D’après le GCVS, c’est une EA de spectre G5 et de mag. 10.5 à 11 (p).  Grâce à 49 mesures photoélectriques B et V et à de nombreuses estimations visuelles du groupe (voir NC 958), on a pu établir que V1027 Ori est de magnitude 10.49 à 10.59 V hors éclipses avec un min I de mag. 11.19 et un min II situé à la phase 0.55.

Min I = JJh 2425238.684 + 10.393773 E

Min II = JJh 2425239.294 + 10.39376 (E + 0.5)

FUM a promis d’en observer 2 minima ccd afin qu’on puisse écrire une GEOS Circular, mais d’autres membres peuvent aussi essayer.  Je mentionnerai les nuits où cela devrait être possible en « tribune libre ».

RU Psc (VBR) : 1h 14m 26s ; 24° 24’ 56" (2000)

C’est une RRc de mag. 9.93 à 10.40 V avec montée d’éclat = 48 % pér. et spectre A7 – F3.  L’éphéméride du GCVS est : JJh 2440143.4027 + 0.390385 j.  Sur 82 ans, on dispose de 100 maxima qui semblent montrer que la période est croissante.  Toutefois, la parabole a un très faible taux de corrélation et de nombreux maxima sont très peu précis.  Aucun effet Blazhko n’est signalé, mais la courbe de lumière est très aplatie au maximum ; ce dernier pourrait être double, ce qui expliquerait la dispersion des O-C.

De nouveaux instants de maximum sont nécessaires et, si le phénomène du double maximum apparaît, il est impératif d’indiquer si l’instant se rapporte au premier ou au second.  Une bonne courbe de lumière ccd précise devrait être publiée.

GSC 1310 1940 Tau (DMT) : 5h 42m 15s ; 22° 22’ 17" (2000)

Cette étoile de spectre A0 varie grosso modo de 8.0 à 9.0 d’après les mesures Tycho.  Il faudrait analyser les estimations déjà faites avec les mesures disponibles hors du groupe.

Note : L’évolution de la période des RRc sera étudiée par VBR, mais cela ne doit en aucun cas empêcher un autre membre du GEOS d’étudier une de ces étoiles en particulier.

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Written by Joseph Remis

Category: Uncategorised

Published: 28 March 2016

Hits: 2400

The next GEOS meeting (Strasbourg, May 14-16) is approaching.
The meeting will be kindly hosted by the Strasbourg Observatory.

I suggest to met on Saturday May 14 at 14.30 in front of the
Observatory. The meeting will start at 15.00 and will close
around 12.00 on Monday May 16.

Here some preliminary details provided by Michel Dumont:

- L'Observatoire nous a réservé un petit amphithéâtre d'environ 40 à 50 places.
Il est très pentu ! Il est équipé d'un vidéo projecteur et j'ai les coordonnées
de la personne à joindre pour avoir la wifi. Cet amphi est juste à côté du hall
d'entrée où se trouve une grande table ronde où nous prendrons les collations
(samedi en milieu d'après-midi, dimanche matin, dimanche après-midi et lundi matin).
La clé sera confiée à Alexandre COIRIER quelques jours avant et il me la
remettra à notre arrivée.

- L'hôtel IBIS Budget est situé juste en face de la gare. Le trajet (à pied)
Hôtel-Observatoire prend 25 min. Un plan de Strasbourg sera envoyé à chaque
participant ayant réservé une chambre. Il est possible d'effectuer ce trajet en tramway.

- Le repas de dimanche midi aura lieu dans un restaurant alsacien typique
très proche de la cathédrale; le trajet Observatoire- Restaurant est aussi
voisin de 25 min. Il y aura deux menus possibles.

The announced participants are:
Roland Boninsegna, Jacqueline Vandenbroere, Ennio Poretti, Stephane Ferrand,
Michel Dumont, Merce Correa, R. Marcos, Reinhold Auer, Anton Paschke,
Josep Vilalta, Jean-Francois Le Borgne, Juan Fabregat, Francesco Fumagalli.

***   Other participants are welcome !!!  ***
***   Please contact Michel Dumont as soon as possible ***

Details about the payment of the stay at the hotel (2 nights) and the
coffee-breaks will be given soon.

Only a few talks have been submitted so far:

Ennio Poretti - The GEOS observational insights into the Blazhko effect
Josch Hambsch - Recent studies of several RR Lyr stars with Blazhko effect
Josch Hambsch - 5 years Remote Observatory Atacama Desert (ROAD)
Jacqueline Vandenbroere - Les correlations entre les caracteristiques des RRab
Michel Dumont - Variations a faible amplitudes dans les courbes visuelles

*** I kindly ask you to provide other contributions ***

We have to discuss about the GEOS participation to the BAV meeting
(Hamburg, Sep. 17-18).

The programme will be refined and updated in the next weeks.