A method to determine distances to molecular clouds using near-IR photometry

Aims: We aim to develop a method to determine distances to molecular clouds using JHK near-infrared photometry.
Methods: The method is based on a technique that aids spectral classification of stars lying towards the fields containing the clouds into main sequence and giants. In this technique, the observed (J-H) and (H-K_s) colours are dereddened simultaneously using trial values of A _V and a normal interstellar extinction law. The best fit of the dereddened colours to the intrinsic colours giving a minimum value of χ² then yields the corresponding spectral type and A _V for the star. The main sequence stars, thus classified, are then utilized in an A _V versus distance plot to bracket the cloud distances.
Results: We applied the method to four clouds, L1517, Chamaeleon I, Lupus 3 and NGC 7023 and estimated their distances as 167±30, 151±28, 157±29 and 408±76 pc respectively, which are in good agreement with the previous distance estimations available in the literature.