The names and catalogues of variable stars


Amateur astronomers know that the brightest stars bear a name, generally of Arabic origin which it is still customary to use : Sirius, Vega, Aldebaran are well-known names. They know the simple and rational system of naming the stars visible to the naked eye introduced by Bayer in 1603 and based on the Greek and Latin alphabets : he named alpha the brightest star of a constellation, beta the second brightest and so on until omega ; then he used the lower-case letters of the Latin alphabet and if necessary the upper-case letters until letter Q in the constellation of the Swan (curiously enough, Q Cygni is catalogued as a nova that exploded in 1876... and accordingly should be considered a recurrent nova). Amateurs also know the more recent system of nomenclature introduced by Flamsteed in 1725 in his "Historia Coelestis Britannica, assigning to each star of a constellation a number running eastward. They also know that variable stars are designated by the name of the constellation in which they are located, preceded by letters or numbers.

The present paper aims at making a short historical survey of variable star designation and of their different catalogues. This work was made possible thanks to the kind permission granted by Mr. Lacroute (then the Director of the Strasbourg Observatory) to peruse the numerous books and documents of the Library of this Institution.

Variable star designation

Although as early as 1596, Fabricius had noticed the curious appearances and disappearances of the star "omicron" in the Whale and although from 1669 on, Montanari had observed the regular falls in brightness of Algol, it was not before the beginning of the XIXth century that astronomers started to undertake a systematic study of the variations of the light of some stars. The variable stars known in those days were scarce and it was sufficient to refer to "the variable in the Lion" or the one in Andromeda for every astronomer to know what star was talked of. So, a well-known astronomer could write in a reputed journal that he was very happpy to learn that "his star" was studied by one of his colleagues.

The first proposal came from a German astronomer who devoted a great part of his career to the study "stars changing brightness". This astronomer was Argelander, the author of the famous Bonn catalogue (Bonner Durchmusterung or BD) and of the method for the visual observation of variable stars that bears his name. In an article of May 3rd, 1855 he wrote :

" I name R the star in the Virgin whose periodic variability was discovered in 1809 by Harding... I hope I will be forgiven for taking the liberty of designating by a letter a star which does not appear in the Bayer catalogue but it seems to me that owing to their originality, variable stars are entitled to claim such a distinction. To my mind, a particular name seems to be almost unavoidable to allow an easy identification of stars that are frequently mentioned. But in order to avoid confusion with the alphabetic designation of Bayer, I chose to use the last letters of the alphabet only and to write them in capitals... "
This statement made by the author himself puts an end to the legend according to which a capital R may have been used by Argelander because most of the variable stars discovered on those days were "red" (Rot in German, Rouge in French).

In its session of 1867 August 23, the General Assembly of the Astronomische Gesellschaft - the German astronomical association that had been created 4 years before - agreed that the way of designating variable stars recommended by Argelander would be adopted, with the exception of bright stars which already had a name or appeared in Bayer's catalogue but not those which had received a number in Flamsteed's catalogue. Each variable star would be designated by a capital letter followed by the Latin name of the constellation in the genitive form. The succession of the letters in the alphabet would follow the chronological order of the discoveries in a given constellation. Thus, the first variable discovered in a constellation would be designated R, the second S, the third T and so on until letter Z. When the series of 9 lettres from R to Z was complete, it was agreed that the letters would be doubled, the 10th variable being designated by RR, then RS until letter RZ, that would be followed by SS (but not SR), ST, etc. until ZZ.

When in 1907, a 54th variable was discovered in the constellation of the Swan (ZZ Cygni), the Commission of Variable Stars - which had been created in 1900 inside the Astronomische Gesellschaft - thought of trebling the letters thus naming RRR Cygni the next variable to be discovered. Finally, after a proposal made by the astronomer Ristenpart, AA Cygni was the adopted solution. The series would be followed by AB, AC, etc. It was believed that the list would stop at AQ so as not to use letters R and Z again even in a different order. Finally, it was decided to proceed until AZ, to be followed by BB (not BA), BC,... BZ until QZ which allowed 334 combinations available. One of the members of this commission estimated that the end of the series would "probably never be reached". However, it was reached in 1929 with the discovery of QZ Sagittarii.

Some time after Argelander, the French astronomer André , proposed to designate each variable "by the letter V plus a number according the chronological order of the observation of its variability" (Traité , d'astronomie stellaire I, page 103). He was approved by the American Chambers and by the Dane Nijland who, by proposing in 1929 the use of this system of nomenclature, gave it its name. The next variable was therefore V335 Sgr. This type of designation was used successively for Ophiuchus, in 1929 also, for the Swan in 1933, the Centaur and the Scorpion in 1936 and the Eagle in 1937. Let us observe that originally our charts used the two nomenclatures, for example V1 = R Andromedae. To this date (2005-01-25), the constellation of the Archer (Sagittarius) has the greatest number of variable stars, the most recent being V5114 Sgr (i.e. nova 2004-2), whilst the smallest number is found in the Chisel (Caelum) in the southern sky with only 22 known variable stars.

As variable stars were being discovered at an accelerating pace, the Harvard Observatory had proposed to designate them with a 6-digit number, the first four representing the Right Ascension of the star expressed in hours and minutes, the last two representing the declination in degrees for the equinox 1900. When the declination of the star is negative, the last two digits are either underlined or written in italics. Thus, variable R And whose position is 00h 18m 45s and +38ø01'4 is designated 001838 whilst southern variable S Lib whose declination is -22ø33'3 is designated 151822 or 151822. However, it is nowadays customary to insert a "+" or a "-" sign. When the seconds of Right Ascension are superior to 57, the number of minute is increased by 1 : this is why, for example, R Tri whose position for the equinox 1900 is 2h 30m 58s is designated 0231+33... and nobody could give a plausible explanation for that. The Harvard designation, still in use in our association concurrently with the Argelander designation, allows an easy sorting of variable stars in order of Right Ascension but its drawback is the necessity of using indices (a, b, c, etc.) when several variables have the same Right Ascension to the nearest minute of time and the same declination to the nearest degree. This system is improperly named "AAVSO designation" as our sister association uses it, just as we do.

Lastly, Chandler, an American astronomer, designated each variable, concurrently with the Argelander nomenclature, by a number consisting in its Right Ascension for the equinox 1900 expressed in seconds and divided by ten. This number had therefore between one and four digits ranging from 0 to 8640. Thus X And, whose Right Ascension is 00h 10m 50s (1900.0) or 650s was assigned number 65 and Y Cas was designated 8629, or one-tenth of the 86290 seconds corresponding to its position in Right Ascension for 1900.0 (23h 58m 10s).

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While waiting for a definitive designation and in order to allow a rapid and unambiguous identification, a star reported to be variable is generally given a provisional designation. As early as the beginning of the study and search for variable stars, every observatory specialized in the field used to give each newly discovered star a number in chronological order preceded by initials particular to the observatory. Thus, initials HV, in use as early as the end of the XIXth century, mean "Harvard Variables" and designate the stars discovered at the Harvard Observatory (more than 10000!). Initial S is attributed to the variable stars discovered at the Sonnneberg Observatory in Thuringia (Germany) - also over 10000, mostly discovered by the famous variable star observer Cuno Hoffmeister who started his career as an amateur. Letters HBV are used by the Hamburg-Bergedorf Observatory, VV by the Vatican Observatory, TV by the Tokyo Observatory, BV by the Bamberg Observatory whereas all the variable stars discovered by the Russian observatories have the provisional designation SVS meaning Soviet Variable Star, the English translation for Sovietskii Peremenesti Zvezd (SPZ).

There also exist catalogues and name-lists of provisional designations made out by amateurs. Thus, letters Wr identify the variable stars discovered by the Fren ch amateur Roger Weber, GR those discovered by the Italian amateur G. Romano. Lastly, let us not omit the long name-list of the stars suspected of variabiltiy in the Orion cloud established by Antoine Brun, the founder of the AFOEV. Technical progress, first with the advent of photography then of CCD's, has allowed many amateurs to discover several variable stars and to make out long lists of putative variables of which several have received definitive designations : such is the case for the Englishman Collins, the Swede Lennart Dahlmark, the Austrian Klaus Bernhard and the Japanese Haseda, Takamisawa or Yoshida and his "Project MISAO".

o o o o

Up to 1943, in the days when the Commission of Variable stars of the Astronomische Gesellschaft was still at work, the variable stars whose discovery had just been reported were also given an additional provisional designation consisting of a number in chronological order of the discovery followed by the year of discovery and the name of the constellation. For example, variable RY Dra, discovered at Harvard Observatory by Miss Fleming in 1907, was not only originally named HV 1310 (i.e. the 1310th variable discovered at this observatory) but received also the provisional identification number 10.1907 Dra (i.e. the 10th variable discovered in 1907 and located in the Dragon).

Catalogues of variable stars

In 1786, Pigott made out the list of the 12 variables known to that date :

omi Ceti
chi Cyg
R Hya
R Per
eta Aql
eta Lyr
R Leo
delta Cep
alpha Her
R Sct
R Vir

In 1844, Argelander published a list of 18 variables in the Schumacher's Jahrbuch. Then in 1854, Pogson published a list of 53 variables in the Radcliffe Observations. However, the first real catalogue was the one published in 1864 by George W. Chambers in the Astronomische Nachrichten which listed 123 variable stars.

In those days, however, an astronomer discovering a variable immediately gave it a "definitive" designation. It could thus happen that the same letter was used to designate two different variables or that the same variable star, discovered independently by two different observers, would be given two different names. It was quickly realized that the confusion that reigned in nomenclature should be put to an end. Therefore, the General Assembly of the Astronomische Gesellschaft held in 1867, August 23 recommended the adoption of the Argelander system of nomenclature and decided to "admit only those designations of variable stars established by the association in a list that would be published on a three-monthly basis ". The first list was published in 1868 by E. Sch''nfeld and A. Winnecke and included 119 stars, i.e. 4 times less than the Chambers list. The second list, including 143 variables, was published in 1875 only. It did not include the variables of the Orion nebula whose study had just started and whose definitive designations were postponed "until, in this particular case which could arise again in the future, the differing opinions of several astronomers come to an agreement on the nature of these particular star".

In 1883, 1884, 1885 and 1886, several lists were published by the Harvard Observatory in the Proceedings of the American Academy. They were meant as supplements to the 2nd catalogue of Sch''nfeld and Winnecke and included a total of 125 variables which brought the number of known variable stars to 268.

The following catalogues were compiled by the American S.C. Chandler : the first, published in 1888 in the Astronomical Journal, listed 225 variable stars only and the second, published in 1893, 260 ; finally the third published in 1896 included 386 variables. That same year, in the same journal, Roberts published a list of 94 southern variables with declinations lower than -30°.

To replace Chandler who wished to retire owing to a declining health, the Astronomische Gesellschaft created in 1900 a special commission whose duty it was to establish the definitive designations of variable stars whose number was increasing with the advent of photography. This commission, which succeeded the Sch''nfeld-Winnecke team and foreshadowed Commission 27 of the International Astronomical Union, decided that a definitive designation would be given only to "any star whose variability will have been observed by at least two observers working independently from each other, and exceptionnally when results reported by one observer only will have been convincing enough for a confirmation by a second observer to appear unnecessary". Finally, a variability discovered by stellar photography was held as established when "the plates will have been measured by several persons" and when moreover "the amplitude of the variation in brightness will have been superior to at least one magnitude.

Originally, this commisssion included astronomers Duner, Hartwig, Muller and Oudemans. They were joined later by Kempf, Guthnick, Prager and finally Schneller. Between 1900 and 1942, this commission published in the Astronomische Nachtrichten 40 lists of definitive designations also giving for each star its coordinates, its maximum and minimum brightness, its elements and probable type of variation, the reference of the journal which had reported the discovery and finally some more or less detailed notes on the star as well as its designation, if any, in other catalogues.

Meanwhile, the Harvard Observatory had published in 1903 a Provisional Catalog of Variable Stars including 1227 stars and in 1907 Miss Cannon had publihsed her catalogue of 1957 variables.

In addition to its name-lists totalling 8889 variable stars, the Astronomische Gesellschaft's commission published yearly between 1927 and 1943 a Catalogue and Ephemerides of Variable Stars. In 1927, it gave the elements of 2906 objects while the one in 1943 listed 9476 objects.

However, the Astronomische Gesellschaft's commission of variable stars quickly came to realize that designations lists were not sufficient. It estimated that the notes accompanying these lists should form the core of a new type of catalogue that would aim at "giving, if posssible, an overview of our knowledge on the changes of brightness of the different variables with a complete bibliography of the documents and articles published on these stars". Following this guideline, Muller and Hartwig published their famous work entitled Geschichte und Literatur des Lichtwechsels der bis Ende 1915 als sicher vernderlich anerkannten Sterne ("History and bibliography of the change of brightnes for stars recognized as variables at the end of 1915"). This 2-volume work, GuL in abbreviation, was published between 1918 and 1922. As soon as 1921, this compilation was continued by a renewed commission of the Astronomische Gesellschaft including in succession (and in alphabetical order) the following members : Esch, Graff, Guthnick, Hagen, Hartwig, Hellerich, Hertzsprung, Hoffmeister, Ludendorff, Nijland, Prager, Shapley, Str''mgren, Wolf and Zinner. The second edition, completing the first and including stars discovered between 1916 and 1933, was published in 1934. Lastly, after the Second World War, a new 5-volume edition was undertaken, completing and continuing the first two editions.

After 1945, the publication of Name-Lists 41 to 46 was the responsibility of the Dutch observatory of Utrecht whilst the attributions of the special commission of the Astronomische Gesellschaft were transferred to Commission 27 of the International Astronomical Union.

An exhaustive catalogue of all the variable stars known to that date was published in 1948. This was the work of the Astronomy departement of the Academy of Sciences of the USSR, under the editorship of B.V. Kukarkin and P.P. Parenago. This catalogue is known in the astronomical literature under the abbreviation OKPZ (Objtjyk Katalog Peremennyk Zvezd) or GCVS (General Catalogue of Variable Stars) in English. Between 1948 and 1956, this catalogue was completed by 8 supplements, then replaced by a new general catalogue in 1958. It was again completed by 2 supplements then superseded in 1968 by a third edition which contained 20448 variables. Finally, a 4th edition was published in 3 volumes between 1985 and 1987, containing 28435 variable stars - of which 158 were not variable however. This edition was completed by a fourth volume (1990) giving different tables (lists of variable stars sorted by increasing Right Ascension, identifications with other catalogues). Finally, a fifth and last volume (1995) acts as a catalogue of extragalactic variables and supernovae. After Kukarkin and Parenago, larger and larger teams have been directed by P. N. Kholopov and N.N. Samus. Since the publication of this edition, ten lists of designations have been published, the last one being Name-List Nø 77 (dated 2003-03-27), which brings the number of known variables to a total of 38528. The complete catalogue is now available in electronic form and may be downloaded The electronic version gives the following information for each variable star :

number of the constellation (And = 1, Vul = 88) and of the variable (R = 0001, etc.)
Right Ascension and declination for the equinox 1950
Right Ascension and declination for the equinox 2000
Type of variation
Magnitude at maximum
Magnitude at minimum
Photometric type
Epoch of the elements (and year for the novae)
M-m value or duration of eclipse
Bibliography (article, charts)

During its General Assembly at Berkeley in 1961, the International Astronomical Union accepted a recommendation of its Commission 27 that suggested the creation of a liaison bulletin for variabilists which would announce recent discoveries and give information for the observations. Prof. Detr,, then Director of the Konkoly Observatory at Budapest, was entrusted with the responsibility of publishing what is now known as the International Bulletin on Variable Stars (IBVS). The first issue appeared on October 4, 1961 and the number of issues published to this date is well over 5000.

Catalogues of suspected variables

It then appeared rapidly that some announcements of variability were dubious, not to say wrong. Several astronomers started searching for this kind of data and published catalogues of "stars suspected of variability". One of the first such catalogues was the one published by Zinner in 1929 which contained 2191 suspected variables. Several of them were in fact stars that appeared in the Bonn catalogue (BD) but could not be found at the indicated position. Prager published two catalogues in 1934 and another in 1937, containing respectively 2428 and 3401 stars suspected of variability. The variability of several of these stars was confirmed later.

In 1951, the team in charge of the GCVS published the first catalogue of stars suspected of variabliity. This Catalogue of Suspected Variables (CSV in short) was based on the catalogues of Zinner and Prager with the addition of some stars and it included a total of 8134 objects. A second edition was published in 1965 with 3901 stars.

A New Catalogue of Suspected Variable Stars (NSV in short) was published in 1981 containing 14811 objects. A second edition completing the first, was published in 1999, containing 11206 stars. Both catalogues can also be downloaded at the address mentioned above.

article written by Emile Schweitzer
english translation by Jacques Vialle

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