The VAC contains two files. Both include crossmatches with 2MASS, PanSTARRS-1, Simbad. The two tables differ in which version of Gaia data are included, DR2 or EDR3. Both files are organized in the same way as the mastarall file, which includes 4 extensions named GOODSTARS, GOODVISITS, ALLSTARS, and ALLVISITS. See the MaStar Catalogs page for an explanation of the 4 extensions. Key photometry properties for each star from the GOODSTARS and ALLSTARS tables are propagated to individual visits of the star in the GOODVISITS and ALLVISITS tables.
The data models for the two files can be found here.
The GOODSTARS tables of the two files are also available on the SkyServer with the names, mastar_goodstars_xmatch_gaiadr2 and mastar_goodstars_xmatch_gaiaedr3, respectively. One needs to change to the DR17 context to access the tables. They can be accessed either using the SQL Search tool or using the CASJOBS data access tool.
The crossmatch with 2MASS is done indirectly through Gaia since Gaia Archive provides the crossmatch with 2MASS.
The PanSTARRS1 photometry we use is calibrated by Edward Schlafly from Lawrence Berkeley National Laboratory.
The reddening value provided in the catalog is based on the 3D dust map produced by Green et al. (2020). And the value is taken at the distance according to the Bailer-Jones distance estimates. In the case of Gaia EDR3, we adopt the photogeometric distance estimates.
The extinction correction is done by inverting the formula provided by Danielski et al. (2018). Then the extinction-corrected absolute magnitude and color is derived using the Bailer-Jones distance estimates again.