3D map of reddening and interstellar extinction

As in the previous 2010 and 2012 versions of the map, photometry with an accuracy better than 0.05 mag in the J and Ks bands for more than 70 million stars from the 2MASS catalogue is used in the new version. However, the data reduction technique is considerably more complicated.

As before, an analysis of the distribution of stars near the main-sequence turnoff on the (J-Ks)-Ks diagram, where they form a distribution maximum, provides a basis for the method. The shift of this maximum, i.e., the mode (J-Ks), along (J-Ks) and Ks, given the spatial variations of the mean dereddened color (J-Ks)_0_ of these stars, is interpreted as a growth of the reddening with increasing distance. The main distinction of the new method is that instead of the fixed mean absolute magnitude, dereddened color, distance, and reddening for each cell, the individual values of these quantities are calculated for each star by iterations when solving the system of equations relating them.