Distribution of stars in the USNO-A2.0 catalog (Source: USNO)
The positions in the Gaia catalog are very accurate, with a positional uncertainty of about 1 milli arc seconds (mas) for stars of 20mag. Uncertainties in proper motion is expected to be less than 0.04 mas/year for stars brighter than about 15mag and around 0,6 mas/year for very faint stars of 20mag.
Gaia DR3 includes photometry in a three color bands: A broad "white light" color band, called G-band, as well as in red (GRP) and blue (GBP) light. The uncertainties in the magnitudes is estimated between 0.001mag for brighter stars in the G band to about 0.05mag for stars of 20mag in the red and 0.1mag in the blue band.
Astrometrica will query VizieR to download reference star data from Gaia DR3.
ATLAS REFCAT provides high quality photometry in the Sloan g, r, i and z color bands, collected by the Pan-STARRS and ATLAS telescopes, with a precision of about 0.01mag. In addition, ATLAS REFCAT includes broadband G, red GRP and blue GBP magnitudes from Gaia DR2.
Astrometrica will query VizieR to download reference star data from ATLAS REFCAT.
The catalog includes astrometrc positions with an accuracy (at epoch J2000.0) 0.08" to 0.12" where 2MASS astrometry was available (that is, for 410 million objects), and 0.15" to 0.30" where no data from 2MASS could be used. Proper motions are absolute in the ICRS reference frame (not relative, as in the USNO-B1.0). Magnitudes in the PPMXL were taken from USNO-B1.0, so there is no improvement in the photometric calibration compared to the USNO catalog.
Astrometrica can access a local copy of the PPMXL or will query VizieR to download reference star data.
The UCAC 4 includes positions, proper motions and magnitudes for 113,780,093 objects. Reference star positions in UCAC 4 are accurate to about 0.02" for brighter stars (10mag to 14mag), and a precision better than 0.1" is expected at the limiting magnitude of 16mag. Native magnitudes have been measured in one single, non-standard color, but the catalog includes five-band photometry (B,V,g,r,i) from the APASS (AAVSO Photometric All-Sky Survey) for over 50 million stars.
Astrometrica can access a local copy of the UCAC 4, or query VizieR to download reference star data.
Astrometric positions in CMC-15 are precise to 0.05" for bright stars (13mag or brighter) and to 0.1" for stars at the limiting magnitude of 16mag. There are no proper motions, but as the catalog positions were derived from recent CCD observations (1999-2011), the positions are still very precise at current epochs. The catalog includes red magnitudes, with errors from only 0.025mag for bright stars (13mag or brighter) to 0.17mag at the limiting magnitude of 16mag. The photometric data is therefore much better then that of most other astrometric catalogs.
Astrometrica can access a local copy of the CMC-15, or query VizieR to download reference star data.