VizieR Online Data Catalog: All-sky Compiled Catalogue of 2.5 million stars (Kharchenko 2001)

The All-Sky Compiled Catalogue of 2501968 stars (ASCC-2.5) with the limiting magnitude V=12-14 is a result of a merging of star lists from present day large high-precision catalogues from space (Hipparcos- Tycho family catalogues: Hipparcos main catalogue including Multiple System Annex <I/239>, Tycho-1 <I/239>, Tycho-2 <I/259>, ACT-RC <I/246>, TRC <I/250>) and ground-based (PPM-N <I/146>, PPM-S <I/193>, PPM-add <I/208>, CMC11 <I/256>) observations and reduction to standard systems of corresponding stellar data. Main stellar data presented in the ASCC-2.5 are the equatorial coordinates (J2000, epoch 1991.25), proper motions in the Hipparcos system, B and/or V stellar magnitudes in the Johnson system. Additionally for some stars are given trigonometric parallaxes, spectral classes in the MK or HD system, multiplicity and variability flags, Hipparcos, Tycho-2, HD, DM designations. Equatorial coordinates and their standard errors were taken from the source catalogues in accordance with the priority: Hipparcos (I/239/hip_{main), Tycho-2 (I/259), Tycho-1 (I/239/tyc}main), CMC11 (I/256), PPM (I/146, I/193, I/208). Proper motions from the source catalogues were compared with Hipparcos data. The compiled proper motions in the Hipparcos system and their standard errors were computed as the weighted means. The weights were set in accordance with the proper motion errors listed for individual stars in the source catalogues. Trigonometric parallaxes are taken from Hipparcos and Tycho-1 catalogues. Stellar B, V magnitudes were determined on the basis of the ground-based photometric data taken from CMC11, Hipparcos, and space B_T, V_T from Tycho-1, Tycho-2. Magnitudes from PPM catalogue were used if no other photometric data were available. Tycho data were transformed to the Johnson system with: V = V_T - 0.09 (B-V)_T + d_V, (B-V) = 0.850 (B-V)_T + d_(B-V), i.e. using recommendations from the Introduction to the Tycho catalogue and including additional corrections d_V and d_(B-V). These additional corrections were determined by comparison with ground-based data in the Johnson system. These corrections depend nonlineary on colour and reach 0.02 and 0.04 mag, respectively. Spectral classes in MK or HD systems were taken from Hipparcos, CMC11, and PPM catalogues. Multiplicity and variability flags were taken from Tycho-1, Tycho-2, Hipparcos, CMC11, and PPM catalogues. Stars in the ASCC-2.5 are divided into 30 files in accordance with declination (North and South polar caps and 28 bands with a width of 5 degrees), then sorted in right ascension order within each file. (30 data files).