****************************************************** * * * PREFACE TO THE ONLINE VERSION OF THE 6TH EDITION * * * ****************************************************** Seven and a half years after the publication of the previous (5th) edi- tion of the Catalogue of Cataclysmic Binaries, Low-Mass X-Ray Binaries and Related Objects (Ritter 1990, hereafter R90), and almost four years after the deadline of an updated list of cataclysmic binaries published in 1995 (Ritter and Kolb 1995, hereafter RK95), the amount of new lite- rature and the number of new objects to be included have again grown so much that it seems worthwhile to publish an updated edition. The philo- sophy and the purpose of this catalogue (now in its 6th edition) have been outlined in the preface to the 3rd edition (Ritter 1984, hereafter R84) and will not be repeated here. Rather let us briefly recall some of the developments which, over the past seven and a half years, have had (and still have) a major impact on this catalogue: - First, we have seen the successful launch and operation of a num- ber of satellites, e.g. of Rosat, Ginga, ASCA, EUVE, GRO, and XTE, which have led to the detection of many new sources or even new classes of compact binaries (e.g. AM Her stars and supersoft X-ray sources by Rosat or EUVE, X-Ray transients (Black Hole can- didates) by Ginga and GRO), or to new insights concerning previ- ously known sources (e.g. the detection of kHz X-Ray oscillations in low-mass X-ray binaries by RXTE observations). - Second, we have seen the publication of "A Catalog and Atlas of Cataclysmic Variables" by Downes and Shara (1993), and most re- cently of its updated 2nd edition by Downes, Webbink and Shara (1997), both of which are now the primary sources for accurate co- ordinates and finding charts for cataclysmic variables. - Third, since the publication of the 5th edition of this catalogue four new issues of the "Name List of Variable Stars" have appeared (the 70th by Kazarovets and Samus (1990), the 71st by Kazarovets, Samus and Goranskij (1993), the 72nd by Kazarovets and Samus (1995), and finally the 73rd by Kazarovets and Samus (1997)). These lists provide the definitive variable names which are also used as primary names in this catalogue. We note in passing that the catalogue by Downes, Webbink and Shara (1997) does not yet include the designations provided by the 73rd Name List. - Fourth, we note the increasing contribution of amateur astronomers in the field of cataclysmic variables. Equipped with CCD photo- meters, amateur astronomers are now in a position to do photometry of moderate time resolution of rather faint objects, even with te- lescopes of rather small apertures. Such photometry is for example adequate to track down the superhump periods of presumed SU UMa- type stars, or to determine the orbital periods of eclipsing bina- ries. Results of these amateur activities, which can be found on the Web page of the Variable Star Network (VSNET) at http://www. kusastro.kyoto-u.ac.jp/vsnet), have also been incorporated in this compilation. Compared with the 5th edition, the number of objects listed has almost doubled. The current version of this catalogue provides tabulated data and references for 414 objects (318 cataclysmic binaries, 47 low-mass X- ray binaries and 49 related objects). The fact that on the one hand the number of objects, the number of references per object and the length of the "Who's Who?" section are steadily increasing, and that on the other hand the total length of the catalogue must remain within acceptable limits, makes it necessary to drop some of the information given in previous editions. This is done by suppressing essentially all those references already given in the 5th edition (R90). Since the previous three editions (R84, Ritter 1987, hereafter R87, and R90) are published in an easily accessible journal, all the information is still available. Earlier references are only re- peated if they are required for cross-reference (see below). Accordingly the 6th edition provides: - the table sections for all three object classes (cataclysmic bin- aries, low-mass X-ray binaries and related objects) in full; - for each catalogued object a selection of references to the liter- ature, published after 31 December 1989 (the deadline of R90). Earlier references are only included if they are needed for cross- reference, or in cases where there have been few or no new publi- cations of relevance; - a list of selected references to published finding charts. Addi- tional references may be found in previous editions; - the "Who's Who?" section, a cross reference list of alias names of the objects catalogued. Thus the catalogue is complete and self-contained in the table sections and in giving cross-references to alternative object designations. With respect to the bibliography given in the reference sections and to the references to published finding charts it is essentially a supplement to to R90. We should also like to mention three major changes we have introduced with this edition, and which, so we hope, will make the catalogue even more valuable: - First, for better readability we now use upper and lower case cha- racters instead of upper case only as in previous editions. - Second, in order to save space, we have changed the style of re- ferencing. We use shorter abbreviations for the major journals (e.g. ApJ instead of Astrophys. J.) and in case of references with more than five authors we quote only the name of the lead author, followed by et al. and the number of authors in parenthesis. - Third, as we have already done in RK95, we provide now limited in- formation about where the values given in the tables are taken from. How this is done is explained in the Introduction. Every effort has been made to avoid errors and to keep the lists up to date. Nevertheless, the authors are well aware of the fact that also this edition will contain errors and may be incomplete with regard to the criteria stated in the preface to the 3rd edition (R84). It is cer- tainly incomplete with respect to the references quoted. However, it should be stressed that no attempt has been made to provide a complete bibliography. Rather, the aim is to give a selection of references that should allow the user to find his way through the literature addressing mainly the binary properties of the objects in question. For the current version of this catalogue, literature published before 30 June 1997 has, as far as possible, been taken into account. Acknowledgements ---------------- We wish to thank Dr. H.-C. Thomas for keeping us informed about the latest results regarding the optical identification and follow--up obser- vations of new CVs from the ROSAT All Sky Survey. References ---------- Downes, R.A., Shara, M.M. 1993, PASP 105, 127 Downes, R.A., Webbink, R.F., Shara, M.M. 1997, PASP 109, 345 Kazarovets, E.V., Samus, N.N. 1990, IBVS No. 3530 Kazarovets, E.V., Samus, N.N., Goranskij, V.P. 1993, IBVS No. 3840 Kazarovets, E.V., Samus, N.N. 1995, IBVS No. 4140 Kazarovets, E.V., Samus, N.N. 1997, IBVS No. 4471 Ritter, H. 1984, A&AS 57, 385 (3rd edition, R84) Ritter, H. 1987, A&AS 70, 335 (4th edition, R87) Ritter, H. 1990, A&AS 85, 1179 (5th edition, R90) Ritter, H., Kolb, U. 1995, in: X-Ray Binaries, W. H. G. Lewin, J. van Paradijs, and E. P. J. van den Heuvel (eds.), Cambridge University Press, p. 578 (RK 95)