Interstellar extinction towards open clusters and Galactic structure

We study the distribution of interstellar matter near the Galactic plane on the basis of open star clusters and review the correlation of extinction with different physical parameters of the clusters to understand the Galactic structure. It is seen from the extinction towards open clusters that ∼90 per cent of the absorbing material lies within −5°≤b≤ 5° of the Galactic plane. The mean thickness of the absorbing material, which is determined in terms of the half-width value β, is estimated to be ∼125 ± 21 pc. We show that the interstellar absorption follows a sinusoidal variation with Galactic longitude and maximum and minimum absorptions occur at l∼ 48°± 4° and l∼ 228°± 4°, respectively. It is found that the Galactic plane defined by the reddening material is inclined by an angle of to the formal Galactic plane and inclination is maximum at l∼ 54°± 6°. The reddening analysis has been used to constrain the solar offset which is found to be ∼22.8 ± 3.3 pc above the reddening plane. We obtained a scaleheight of 53 ± 5 pc for the distribution of open clusters while it is 186 ± 25 pc for the distribution of reddening material from the reddening plane.