Gaia DR1 Tycho–Gaia Astrometric Solution parallaxes , Tycho-2 photometry and reddening/extinction estimates from nine data sources for 38074 giants within 415 pc from the Sun are used to compare their position in the Hertzsprung–Russell diagram with theoretical estimates , which are based on the PARSEC and MIST isochrones and the TRILEGAL model of the Galaxy with its parameters being widely varied .
We conclude that ( 1 ) some systematic errors of the reddening/extinction estimates are the main uncertainty in this study ; ( 2 ) any emission-based 2D reddening map can not give reliable estimates of reddening within 415 pc due to a complex distribution of dust ; ( 3 ) if a TRILEGAL ’ s set of the parameters of the Galaxy is reliable and if the solar metallicity is Z < 0.021 , then the reddening at high Galactic latitudes behind the dust layer is underestimated by all 2D reddening maps based on the dust emission observations of IRAS , COBE , and Planck and by their 3D followers ( we also discuss some explanations of this underestimation ) ; 4 ) the reddening/extinction estimates from recent 3D reddening map by Gontcharov , including the median reddening E ( B - V ) = 0.06 mag at |b| > 50 \degr , give the best fit of the empirical and theoretical data with each other .