2mass/Hipparcos Extinctions and Distances in the Serpens - Aquila Region.IV. Error Propagation. Individual stars and mean values

Abstract

We estimate errors from the application of the main sequence $(H-K)_0 \ vs. \ (J-H)_0$and$(J-K)_0 \ vs. \ M_J$relations on 2mass photometry to provide stellar extinctions and distances. The error propagation on individual stars in the Serpens -- Aquila star forming region is investigated. Results: errors on the$J-band$extinction$\sigma_{A_J}$are found in the range from 0.05 to 0.20 mag and peak at$\approx$0.1. For the absolute$J-band$magnitudes the$\sigma_{M_J}$range is found from 0.1 to 0.5 mag and the distribution has a pronounced maximum at$\approx$0.3 mag. Individual relative distance errors,$\sigma_{distance}/distance$, are found in the interval from 8$%$to 25$%$and peak at 15$%$. If cloud distances are identified with the location of a local maximum of the$A_J(median)/distance(median)$variation the Serpens -- Aquila cloud may be at 203$\pm$7 pc. We propose that the median absolute deviation from the median of$A_J$ could be used as a cloud distance indicato