2018A&A...611A...9S

Interstellar extinction is investigated in a 2°x 2° area containing the dust and molecular clouds LDN 183 (MBM 37) and LDN 169, which are located at RA=15^h54^m,Dec=-3°. The study is based on a photometric classification in spectral and luminosity classes of 782 stars selected from the catalogs of 1299 stars down to V=20mag observed in the Vilnius seven-color system. For control, the MK types for the 18 brightest stars with V between 8.5 and 12.8mag were determined spectroscopically. For 14 stars, located closer than 200pc, distances were calculated from trigonometric parallaxes taken from the Gaia Data Release 1. For about 70% of the observed stars, two-dimensional spectral types, interstellar extinctions A_V, and distances were determined. Using 57 stars closer than 200pc, we estimate that the front edge of the clouds begins at 105±8pc. The extinction layer in the vicinities of the clouds can be about 20pc thick. In the outer parts of the clouds and between the clouds, the extinction is 0.5-2.0mag. Behind the Serpens/Libra clouds, the extinction range does not increase; this means that the dust layer at 105pc is a single extinction source.