1999A&A...351.1041K

A new, efficient method of deriving stellar number density distribution along a line of sight from star count data by using a Linear Programming technique is presented. The derived stellar number density distribution is further used to find a distance to a dark globule. In order to validate the algorithm, we select a dark globule Barnard 361 with known stellar number density distribution and distance. Our estimates of stellar density distribution and distance to the globule are in close agreement with previous results. The effects of the choice of the luminosity function and of the general extinction law on the resulting stellar density function are discussed. The algorithm is applied to star count data for a dark globule, LDN 400, whose distance is unknown. For this purpose, CCD observations were made toward LDN 400 in V band. The stellar number density distribution toward LDN 400 shows two prominent peaks at distances of 1.2 and 2.5kpc. The density peaks roughly coincide with the Sagittarius arm and stellar density enhancement of OB stars. The stellar number density distribution is further used to derive the distance to LDN 400. When using the luminosity function of Gilmore & Reid (1983MNRAS.202.1025G) and the Galaxy model of Bahcall & Soneira (1980ApJS...44...73B), we found a distance to LDN 400 of 450±50pc and an extinction caused by the cloud of 2.4±0.5 magnitudes in the V band.