Edited by Mati Morel
Version 1: In 1994 the first tentative attempt was made to compile a list of comparison stars for variable stars, as reported in certain issues of the IBVS (Morel 1994). In many reports on variable stars where UBV photometry been performed the authors have specified which comparison and check stars were used, and their adopted magnitudes, usually tied to the standard Johnson-Morgan UBV system. To facilitate access to this useful data I compiled a Directory of Comparison Stars Cited in IBVS, commencing with IBVS No. 2081, the earliest one in my set at that time.
The first version tended to concentrate on fainter stars, below 6.00V, for which the IBVS data was likely to be new. Data was compiled by examining each issue of IBVS, initially numbers 2081-4039. V and B-V values were retrieved, and matched with standard catalogue identifiers (HD, SAO, DM etc). Positions were provided for each comparison star, for B1950. In some instances, where IBVS published a sequence of many stars, or a sequence with faint stars below the limit of the Guide Star Catalogue, positions were not readily available, and the table entry merely refers to the entire sequence. Number of records: 520. Version 1 was made available to the astronomical community in two formats: ASCII text file, and spreadsheet (Lotus 1-2-3), on diskette upon request.
Version 2: In 2001, at the suggestion of Dr. Andras Holl, the Directory was expanded to cover many missed issues of IBVS, especially numbers 1-2080. The table format was retained, but the number of records was now almost double, and covered IBVS issues 1 – 4209. The complete table of comparison stars can be found on IBVS CD-ROM II as a text file (auxiliary table 4067-t1.txt, to IBVS 4067). Number of records: 1025.
Version 3 (IBVS4): In Jan. 2003, upon request, it was agreed to update the Directory again. Firstly, all of the numbers of IBVS 4210-5000 were searched for data. Secondly it was decided to check and amend all positions from epoch B1950 to J2000. This was done using Guide 8 (TM) software. The retrieval of higher precision coordinates was greatly facilitated, as well as retrieving other catalogue numbers. This process also allowed easy checking of IBVS data against data from the Hipparcos/Tycho mission. Any discrepancies found were investigated closely and resolved satisfactorily, in most cases. The working name for Version 3 is IBVS4. Number of records: 1322.